Unusual seasonal patterns and inferred processes of nitrogen retention in forested headwater catchments of the Upper Susquehanna basin

NASA Astrophysics Data System (ADS)

Goodale, C. L.; Thomas, S. A.; Fredriksen, G.; Elliott, E. M.; Flinn, K. M.; Butler, T. J.

2008-12-01

The Susquehanna River provides two-thirds of the annual nitrogen (N) load to the Chesapeake Bay, and atmospheric deposition is a major contributor to the basin's N inputs. Yet, there are few measurements of the retention of atmospheric N in the Upper Susquehanna's forested headwaters. We characterized the amount, form (nitrate, ammonium, and dissolved organic nitrogen), isotopic composition (del18O- and del15N-nitrate), and seasonality of stream N over two years from 8-15 small forested headwater catchments of the Susquehanna Basin. We expected high rates of N retention and seasonal nitrate patterns typical of other seasonally snow-covered catchments: dormant season peaks and growing season minima. Annual nitrate exports were approximately 0.1-0.7 kg N ha-1 y-1, and correlated positively with the percent of catchment free from historical agriculture. DON export averaged 0.6 +/- 0.1 kg N ha-1 y-1. All catchments had high rates of N retention but with atypical seasonal nitrate patterns, consisting of summer peaks, fall crashes, and modest rebounds during the dormant season. The fall nitrate crash coincided with carbon inputs at leaffall, indicating in-stream heterotrophic uptake. Stream del18O-nitrate values indicated microbial nitrification as the dominant source of stream nitrate, with modest contributions directly from precipitation in early stages of snowmelt. Three hypothesized sources of summer nitrate peaks include: delayed release of nitrate flushed to groundwater at snowmelt, weathering of geologic N, and increased net nitrate production. Measurements of shale del15N as well as soil, well-, and springwater nitrate within one catchment point toward a summer increase in net nitrification in surface soils. Rather than plant demand, processes governing the production, retention, and hydrologic transport of nitrate in surface mineral soils may drive the unusual nitrate seasonality in this and other systems, and provide insights on N retention in general.

The role of climate on inter-annual variation in stream nitrate fluxes and concentrations.

PubMed

Gascuel-Odoux, Chantal; Aurousseau, Pierre; Durand, Patrick; Ruiz, Laurent; Molenat, Jérôme

2010-11-01

In recent decades, temporal variations in nitrate fluxes and concentrations in temperate rivers have resulted from the interaction of anthropogenic and climatic factors. The effect of climatic drivers remains unclear, while the relative importance of the drivers seems to be highly site dependent. This paper focuses on 2-6 year variations called meso-scale variations, and analyses the climatic drivers of these variations in a study site characterized by high N inputs from intensive animal farming systems and shallow aquifers with impervious bedrock in a temperate climate. Three approaches are developed: 1) an analysis of long-term records of nitrate fluxes and nitrate concentrations in 30 coastal rivers of Western France, which were well-marked by meso-scale cycles in the fluxes and concentration with a slight hysteresis; 2) a test of the climatic control using a lumped two-box model, which demonstrates that hydrological assumptions are sufficient to explain these meso-scale cycles; and 3) a model of nitrate fluxes and concentrations in two contrasted catchments subjected to recent mitigation measures, which analyses nitrate fluxes and concentrations in relation to N stored in groundwater. In coastal rivers, hydrological drivers (i.e., effective rainfall), and particularly the dynamics of the water table and rather stable nitrate concentration, explain the meso-scale cyclic patterns. In the headwater catchment, agricultural and hydrological drivers can interact according to their settings. The requirements to better distinguish the effect of climate and human changes in integrated water management are addressed: long-term monitoring, coupling the analysis and the modelling of large sets of catchments incorporating different sizes, land uses and environmental factors. Copyright © 2009 Elsevier B.V. All rights reserved.

Interannual climate variability and spatially heterogeneous improvement of agricultural management impede detection of a decreasing trend in nitrate pollution in an agricultural catchment

NASA Astrophysics Data System (ADS)

Fovet, Ophélie; Dupas, Rémi; Durand, Patrick; Gascuel-Odoux, Chantal; Gruau, Gérard; Hamon, Yannick; Petitjean, Patrice

2016-04-01

Despite widespread implementation of the nitrate directive in the European Union since the 1990s, the impact on nitrate concentration in rivers is limited (Bouraoui and Grizzetti, 2011). To assess whether this lack of response is due to the long time lags of nitrate transfer or to inadequate programs of measure, long term river and groundwater monitoring data are necessary. This study analyses 15 years of daily nitrate concentration data at the outlet of an intensively farmed catchment in Western France (Kervidy-Naizin, 5 km²) and quarterly nitrate concentration data in the groundwater of two hillslopes equipped with piezometers (Kerroland and Gueriniec) within the same catchment. In this catchment groundwater contribution to annual stream flow is dominant. The objectives of this study were to i) disentangle the influence of interannual climate variability and improvement of agricultural practices (i.e. reduction in N surplus) in the stream chemistry and ii) discuss the reasons for slow catchment recovery from nitrate pollution by comparing trends in groundwater and stream concentrations. Analysis of stream data showed that flow-weighted mean annual concentration at the outlet of the Kervidy-Naizin catchment has decreased by 1.2 mg NO3- l-1 yr-1 from 1999 to 2015. This decrease was slow but significant (p value < 0.01) even though interannual climate variability (i.e. annual cumulated runoff) added noise to the signal: i) deviation in the linear model of nitrate decrease with time was negatively correlated with annual runoff (r = -0.54, p < 0.01) and ii) local minimums in the nitrate time series were coincident with local maximums in the annual runoff. Thus high runoff during wet years led to dilution of the nitrate originating from groundwater, which added variability to the signal of linear decrease in stream concentration. Analysis of groundwater data showed a significant and sharp decrease in nitrate concentration in the Kerroland piezometer transect (4.0 mg NO3- l-1 yr-1) and no significant evolution in the Gueriniec piezometer transect, from 1999 to 2015. This contrasting evolution of groundwater nitrate concentration between the two transects was consistent with data on soil surface nitrogen surplus, with a balanced fertilisation in the Kerroland transect (N surplus close to 0 kg N ha-1 yr-1) and excessive fertilisation in the Gueriniec transect (N surplus > 100 kg N ha-1 yr-1). We conclude that, despite the lags due to pluri annual nitrate transfer through the unsaturated and satured zones in catchments of Western France, significant decrease in nitrate concentration in groundwater and streams should be visible within less than 10 years after implementation of an efficient program of measures. Spatial heterogeneity in the implementation of programs of measures (i.e. reduction of N surplus) is a likely cause of slow, sometimes undetectable, reduction in nitrate concentration. Bouraoui, F., and Grizzetti, B.: Long term change of nutrient concentrations of rivers discharging in European seas, The Science of the total environment, 409, 4899-4916, 10.1016/j.scitotenv.2011.08.015, 2011.

Effects of Atmospheric Nitrate on an Upland Stream of the Northeastern USA

NASA Astrophysics Data System (ADS)

Sebestyen, S. D.; Shanley, J. B.; Boyer, E. W.; Kendall, C.

2009-05-01

Excess nitrogen cascades through terrestrial biogeochemical cycles and affects stream nitrate concentrations in upland forests where atmospheric deposition is an important source of anthropogenic nitrogen. We will discuss approaches including high-frequency sampling, isotopic tracers, and end-member mixing analysis that can be used to decipher the sources, transformations, and hydrological processes that affect nitrate transport through forested upland catchments to streams. We present results of studies at the Sleepers River Research Watershed in Vermont, USA, a site where we have intensively measured stream nitrate concentrations during baseflow and stormflow. Stream nitrate concentrations are typically low and nearly 75% of annual inorganic N inputs from atmospheric deposition are retained within the catchment. However, high concentrations and stream loadings of nitrate occur during storm events due to source variation and hydrological flushing of nitrate from catchment soils. Using isotopic tracers and end-member mixing analysis, we have quantified source inputs of unprocessed atmospheric nitrate and show that this stream is directly affected by nitrogen pollution. Using a long-term record of stream hydrochemistry and our findings on event- scale nitrate flushing dynamics, we then explore how stream nitrate loading may respond to anthropogenic climate forcing during the next century. Results suggest that stream runoff and nitrate loadings will change during future emission scenarios (i.e. longer growing seasons and higher winter precipitation rates). Understanding the timing and magnitude of hydrological and hydrochemical responses is important because climate change effects on catchment hydrology may alter how nitrate is retained, produced, and hydrologically flushed in headwater ecosystems with implications for aquatic metabolism, nutrient export from catchments, and downstream eutrophication.

An approach to predict water quality in data-sparse catchments using hydrological catchment similarity

NASA Astrophysics Data System (ADS)

Pohle, Ina; Glendell, Miriam; Stutter, Marc I.; Helliwell, Rachel C.

2017-04-01

An understanding of catchment response to climate and land use change at a regional scale is necessary for the assessment of mitigation and adaptation options addressing diffuse nutrient pollution. It is well documented that the physicochemical properties of a river ecosystem respond to change in a non-linear fashion. This is particularly important when threshold water concentrations, relevant to national and EU legislation, are exceeded. Large scale (regional) model assessments required for regulatory purposes must represent the key processes and mechanisms that are more readily understood in catchments with water quantity and water quality data monitored at high spatial and temporal resolution. While daily discharge data are available for most catchments in Scotland, nitrate and phosphorus are mostly available on a monthly basis only, as typified by regulatory monitoring. However, high resolution (hourly to daily) water quantity and water quality data exist for a limited number of research catchments. To successfully implement adaptation measures across Scotland, an upscaling from data-rich to data-sparse catchments is required. In addition, the widespread availability of spatial datasets affecting hydrological and biogeochemical responses (e.g. soils, topography/geomorphology, land use, vegetation etc.) provide an opportunity to transfer predictions between data-rich and data-sparse areas by linking processes and responses to catchment attributes. Here, we develop a framework of catchment typologies as a prerequisite for transferring information from data-rich to data-sparse catchments by focusing on how hydrological catchment similarity can be used as an indicator of grouped behaviours in water quality response. As indicators of hydrological catchment similarity we use flow indices derived from observed discharge data across Scotland as well as hydrological model parameters. For the latter, we calibrated the lumped rainfall-runoff model TUWModel using multiple objective functions. The relationships between indicators of hydrological catchment similarity, physical catchment characteristics and nitrate and phosphorus concentrations in rivers are then investigated using multivariate statistics. This understanding of the relationship between catchment characteristics, hydrological processes and water quality will allow us to implement more efficient regulatory water quality monitoring strategies, to improve existing water quality models and to model mitigation and adaptation scenarios to global change in data-sparse catchments.

Hydrological controls on DOC  :  nitrate resource stoichiometry in a lowland, agricultural catchment, southern UK

NASA Astrophysics Data System (ADS)

Heppell, Catherine M.; Binley, Andrew; Trimmer, Mark; Darch, Tegan; Jones, Ashley; Malone, Ed; Collins, Adrian L.; Johnes, Penny J.; Freer, Jim E.; Lloyd, Charlotte E. M.

2017-09-01

The role that hydrology plays in governing the interactions between dissolved organic carbon (DOC) and nitrogen in rivers draining lowland, agricultural landscapes is currently poorly understood. In light of the potential changes to the production and delivery of DOC and nitrate to rivers arising from climate change and land use management, there is a pressing need to improve our understanding of hydrological controls on DOC and nitrate dynamics in such catchments. We measured DOC and nitrate concentrations in river water of six reaches of the lowland river Hampshire Avon (Wiltshire, southern UK) in order to quantify the relationship between BFI (BFI) and DOC : nitrate molar ratios across contrasting geologies (Chalk, Greensand, and clay). We found a significant positive relationship between nitrate and BFI (p < 0. 0001), and a significant negative relationship between DOC and BFI (p < 0. 0001), resulting in a non-linear negative correlation between DOC : nitrate molar ratio and BFI. In the Hampshire Avon, headwater reaches which are underlain by clay and characterized by a more flashy hydrological regime are associated with DOC : nitrate ratios > 5 throughout the year, whilst groundwater-dominated reaches underlain by Chalk, with a high BFI have DOC : nitrate ratios in surface waters that are an order of magnitude lower (< 0.5). Our analysis also reveals significant seasonal variations in DOC : nitrate transport and highlights critical periods of nitrate export (e.g. winter in sub-catchments underlain by Chalk and Greensand, and autumn in drained, clay sub-catchments) when DOC : nitrate molar ratios are low, suggesting low potential for in-stream uptake of inorganic forms of nitrogen. Consequently, our study emphasizes the tight relationship between DOC and nitrate availability in agricultural catchments, and further reveals that this relationship is controlled to a great extent by the hydrological setting.

Assessing the impacts of Best Management Practices on nitrate pollution in an agricultural dominated lowland catchment considering environmental protection versus economic development.

PubMed

Haas, Marcelo B; Guse, Björn; Fohrer, Nicola

2017-07-01

Water quality is strongly affected by nitrate inputs in agricultural catchments. Best Management Practices (BMPs) are alternative practices aiming to mitigate the impacts derived from agricultural activities and to improve water quality. Management activities are influenced by different governmental policies like the Water Framework Directive (WFD) and the Renewable Energy Sources Act (EEG). Their distinct goals can be contrasting and hamper an integrated sustainable development. Both need to be addressed in the actual conjuncture in rural areas. Ecohydrological models like the SWAT model are important tools for land cover and land use changes investigation and the assessment of BMPs implementation effects on water quality. Thus, in this study, buffer strip, fertilization reduction and alternative crops were considered as BMPs and were implemented in the SWAT model for the Treene catchment. Their efficiency in terms of nitrate loads reduction related to implementation costs at the catchment scale was investigated. The practices correspond to the catchment conditions and are based on small and mid areal changes. Furthermore, the BMPs were evaluated from the perspective of ecologic and economic policies. The results evidenced different responses of the BMPs. The critical periods in winter were addressed by most of the BMPs. However, some practices like pasture land increase need to be implemented in greater area for better results in comparison to current activities. Furthermore, there is a greater nitrate reduction potential by combining BMPs containing fertilization reduction, buffer strips and soil coverage in winter. The discussion about efficiency showed the complexity of costs stipulation and the relation with arable land and yield losses. Furthermore, as the government policies can be divergent an integrated approach considering all the involved actors is important and seeks a sustainable development. Copyright © 2017 Elsevier Ltd. All rights reserved.

River-groundwater connectivity and nutrient dynamics in a mesoscale catchment

NASA Astrophysics Data System (ADS)

Fleckenstein, Jan H.; Musolff, Andreas; Gilfedder, Benjamin; Frei, Sven; Wankmüller, Fabian; Trauth, Nico

2017-04-01

Diffuse solute exports from catchments are governed by many interrelated factors such as land use, climate, geological-/ hydrogeological setup and morphology. Those factors create spatial variations in solute concentrations and turnover rates in the subsurface as well as in the stream network. River-groundwater connectivity is a crucial control in this context: On the one hand groundwater is a main pathway for nitrate inputs to the stream. On the other hand, groundwater connectivity with the stream affects the magnitude of hyporheic exchange of stream water with the stream bed. We present results of a longitudinal sampling campaign along the Selke river, a 67 km long third-order stream in the Harz mountains in central Germany. Water quality at the catchment outlet is strongly impacted by agriculture with high concentrations of nitrate and a chemostatic nitrate export regime. However, the specific nitrate pathways to the stream are not fully understood as there is arable land distributed throughout the catchment. While the sparsely distributed arable land in the mountainous upper catchment receives much higher amounts of precipitation, the downstream alluvial plains are drier, but more intensively used. The three-day campaign was conducted in June 2016 under constant low flow conditions. Stream water samples were taken every 2 km along the main stem of the river and at its major tributaries. Samples were analyzed for field parameters, major cations and anions, N-O isotopes, nutrients and Radon-222 (Rn) concentrations. Additionally, at each sampling location, river discharge was manually measured using current meters. Groundwater influxes to each sampled river section were quantified from the Rn measurements using the code FINIFLUX, (Frei and Gilfedder 2015). Rn and ion concentrations showed an increase from the spring to the mouth, indicating a growing impact of groundwater flux to the river. However, increases in groundwater gains were not gradual. The strongest gains were observed downstream of where the Selke River leaves the Harz Mountains and enters the alluvial plains. At this location, land use, hydrogeological setup and river slope as well as average slope of the contributing catchment area change significantly. Downstream of this point 15N isotope values were also significantly higher, suggesting higher denitrification activity in the deeper aquifers of lower catchment. While specific discharge (discharge per catchment area) was 3 times higher in the upper catchment, nitrate mass flux per area was more than 3 times higher in lower catchment compared to the respective other part of the catchment. We conclude that catchment morphology, (hydro)geology and hydrology control river-groundwater connectivity while the interplay with land use controls in stream nitrate concentrations. Repeated sampling campaigns will allow assessing seasonal changes in solute inputs and turnover. References Frei, S. & Gilfedder, B.S. (2015): FINIFLUX: An implicit finite element model for quantification of groundwater fluxes and hyporheic exchange in streams and rivers using radon. Water Resources Research, DOI: 10.1002/2015WR017212.

Drivers of atmospheric nitrate processing and export in forested catchments

Treesearch

Lucy A. Rose; Stephen D. Sebestyen; Emily M. Elliott; Keisuke Koba

2015-01-01

Increased deposition of reactive atmospheric N has resulted in the nitrogen saturation of many forested catchments worldwide. Isotope-based studies from multiple forest sites report low proportions (mean = ~10%) of unprocessed atmospheric nitrate in streams during baseflow, regardless of N deposition or nitrate export rates. Given similar proportions of...

Estimating nitrate emissions to surface water at regional and national scale: comparison of models using detailed regional and national-wide databases (France)

NASA Astrophysics Data System (ADS)

Dupas, R.; Gascuel-Odoux, C.; Durand, P.; Parnaudeau, V.

2012-04-01

The European Union (EU) Water Framework Directive (WFD) requires River Basin District managers to carry out an analysis of nutrient pressures and impacts, in order to evaluate the risk of water bodies failing to reach "good ecological status" and to identify those catchments where prioritized nonpoint-source control measures should be implemented. A model has been developed to estimate nitrate nonpoint-source emissions to surface water, using readily available data in France. It was inspired from US model SPARROW (Smith al., 1997) and European model GREEN (Grizzetti et al., 2008), i.e. statistical approaches consisting of linking nitrogen sources and catchments' land and rivers characteristics. The N-nitrate load (L) at the outlet of a catchment is expressed as: L= R*(B*Lsgw+Ldgw+PS)-denitlake Where denitlake is a denitrification factor for lakes and reservoirs, Lsgw is the shallow groundwater discharge to streams (derived from the base flow index and N surplus in kgN.ha-1.yr-1), Ldgw is the deep groundwater discharge to streams (derived from total runoff, the base flow index and deep groundwater N concentration), PS is point sources from domestic and industrial origin (kgN.ha-1.yr-1) and R and B are the river system and basin reduction factor, respectively. Besides calibrating and evaluating the model at a national scale, its predictive quality was compared with those of regionalized models in Brittany (Western France) and in the Seine river basin (Paris basin), where detailed regional databases are available. The national-scale model proved to provide robust predictions in most conditions encountered in France, as it fitted observed N-nitrate load with an efficiency of 0.69. Regionalization of the model reduced the standard error in the prediction of N-nitrate loads by about 19 Hence, the development of regionalized models should be advocated only after the trade-off between improvement of fit and degradation of parameters' estimation has come under scrutiny.

Improving catchment discharge predictions by inferring flow route contributions from a nested-scale monitoring and model setup

NASA Astrophysics Data System (ADS)

van der Velde, Y.; Rozemeijer, J. C.; de Rooij, G. H.; van Geer, F. C.; Torfs, P. J. J. F.; de Louw, P. G. B.

2011-03-01

Identifying effective measures to reduce nutrient loads of headwaters in lowland catchments requires a thorough understanding of flow routes of water and nutrients. In this paper we assess the value of nested-scale discharge and groundwater level measurements for the estimation of flow route volumes and for predictions of catchment discharge. In order to relate field-site measurements to the catchment-scale an upscaling approach is introduced that assumes that scale differences in flow route fluxes originate from differences in the relationship between groundwater storage and the spatial structure of the groundwater table. This relationship is characterized by the Groundwater Depth Distribution (GDD) curve that relates spatial variation in groundwater depths to the average groundwater depth. The GDD-curve was measured for a single field site (0.009 km2) and simple process descriptions were applied to relate groundwater levels to flow route discharges. This parsimonious model could accurately describe observed storage, tube drain discharge, overland flow and groundwater flow simultaneously with Nash-Sutcliff coefficients exceeding 0.8. A probabilistic Monte Carlo approach was applied to upscale field-site measurements to catchment scales by inferring scale-specific GDD-curves from the hydrographs of two nested catchments (0.4 and 6.5 km2). The estimated contribution of tube drain effluent (a dominant source for nitrates) decreased with increasing scale from 76-79% at the field-site to 34-61% and 25-50% for both catchment scales. These results were validated by demonstrating that a model conditioned on nested-scale measurements improves simulations of nitrate loads and predictions of extreme discharges during validation periods compared to a model that was conditioned on catchment discharge only.

Nachlassender Nitratabbau im Grundwasser und deren Folgen - abgestufte modellgestützte Bewertungsansätze

NASA Astrophysics Data System (ADS)

Wilde, Siegfried; Hansen, Carsten; Bergmann, Axel

2017-11-01

In many water catchment areas, denitrification processes in aquifers ensure lower nitrate contamination in groundwater. The denitrification capacity of aquifers mainly depends on organic carbon and iron disulfide which, being finite resources, are susceptible to depletion. This will generally result in increasing nitrate concentrations in groundwater. Within the scope of a DVGW-supported research project, consequences of a decreasing denitrification capacity in aquifers have been investigated and evaluated in 38 water catchment areas. A scaled four-stage evaluation procedure enables adapting to specific regional settings and assessment requirements. Based on measured and predicted nitrate concentrations in raw water, the "sustainability" of groundwater resources management has been assessed. Hydrogeochemical models and methods of varying complexity were applied. Thus, consequences and risks of nitrate pollution in raw water can be identified and assessed, and effects of groundwater protection measures can be shown.

Identification of nitrate sources in groundwater and potential impact on drinking water reservoir (Goczałkowice reservoir, Poland)

NASA Astrophysics Data System (ADS)

Czekaj, Joanna; Jakóbczyk-Karpierz, Sabina; Rubin, Hanna; Sitek, Sławomir; Witkowski, Andrzej J.

2016-08-01

Goczałkowice dammed reservoir (area - 26 km2) is a strategic object for flood control in the Upper Vistula River catchment and one of the most important source of drinking water in the Upper Silesian Industrial Region (Southern Poland). Main aims of the investigation were identification of sources of nitrate and assessment of their significance in potential risk to groundwater quality. In the catchment area monitoring network of 22 piezometers, included 14 nested, have been installed. The significant spatial and seasonal differences in chemical composition between northern and southern part of the catchment were indicated based on the groundwater sampling conducted twice - in autumn 2011 and spring 2012. Maximum observed concentrations of nitrate were identified in northern part of the study area 255 mg/L as a results of inappropriate sewage management and agriculture activity. Results, based on the combines multi-scale hydrogeological and hydrochemical field studies, groundwater flow and transport modelling, dual stable isotope approach and geochemical modelling indicate mainly agriculture and inappropriate sewage water management as a sources of NO3- contamination of groundwater which moreover is affected by geochemical processes. In general, contaminated groundwater does not impact surface water quality. However, due to high concentration of nitrate in northern part a continues measurements of nitrogen compounds should be continued and used for reducing uncertainty of the predictive scenarios of the mass transport modelling in the study area.

Spatial and temporal dynamics of nitrate fluxes in a mesoscale catchment

NASA Astrophysics Data System (ADS)

Muller, C.; Musolff, A.; Strachauer, U.; Brauns, M.; Tarasova, L.; Merz, R.; Knoeller, K.

2017-12-01

Spatially and temporally variable and often superimposing processes like mobilization and turnover of N-species strongly affect nitrate fluxes at catchment outlets. It remains thus challenging to determine dominant nitrate sources to derive an effective river management. Here, we combine data sets from two spatially highly resolved key-date monitoring campaigns of nitrate fluxes along a mesoscale catchment in Germany with four years of monitoring data from two representative sites within the catchment. The study area is characterized by a strong land use gradient from pristine headwaters to lowland sub-catchments with intense agricultural land use and wastewater sources. Flow conditions were assessed by a hydrograph separation showing the clear dominance of base flow during both investigations. However, the absolute amounts of discharge differed significantly from each other (outlet: 1.42 m³ s-1 versus 0.43 m³ s-1). Nitrate concentration and flux in the headwater was found to be low. In contrast, nitrate loads further downstream originate from anthropogenic sources such as effluents from wastewater treatment plants (WWTP) and agricultural land use. The agricultural contribution did not vary in terms of nitrate concentration and isotopic signature between the years but in terms of flux. The contrasting amounts of discharge between the years led to a strongly increased relative wastewater contribution with decreasing discharge. This was mainly manifested in elevated δ18O-NO3- values downstream from the wastewater discharge. The four-year monitoring at two sides clearly indicates the chemostatic character of the agricultural N-source and its distinct, yet stable isotopic fingerprint. Denitrification was found to play no dominant role only for controlling nitrate loads in the river. The spatially highly resolved monitoring approach helped to accurately define hot spots of nitrate inputs into the stream while the long-term information allowed a classification of the results with respect to the seasonal N-dynamics in the catchment.

Hybrid modeling of nitrate fate in large catchments using fuzzy-rules

NASA Astrophysics Data System (ADS)

van der Heijden, Sven; Haberlandt, Uwe

2010-05-01

Especially for nutrient balance simulations, physically based ecohydrological modeling needs an abundance of measured data and model parameters, which for large catchments all too often are not available in sufficient spatial or temporal resolution or are simply unknown. For efficient large-scale studies it is thus beneficial to have methods at one's disposal which are parsimonious concerning the number of model parameters and the necessary input data. One such method is fuzzy-rule based modeling, which compared to other machine-learning techniques has the advantages to produce models (the fuzzy-rules) which are physically interpretable to a certain extent, and to allow the explicit introduction of expert knowledge through pre-defined rules. The study focuses on the application of fuzzy-rule based modeling for nitrate simulation in large catchments, in particular concerning decision support. Fuzzy-rule based modeling enables the generation of simple, efficient, easily understandable models with nevertheless satisfactory accuracy for problems of decision support. The chosen approach encompasses a hybrid metamodeling, which includes the generation of fuzzy-rules with data originating from physically based models as well as a coupling with a physically based water balance model. For the generation of the needed training data and also as coupled water balance model the ecohydrological model SWAT is employed. The conceptual model divides the nitrate pathway into three parts. The first fuzzy-module calculates nitrate leaching with the percolating water from soil surface to groundwater, the second module simulates groundwater passage, and the final module replaces the in-stream processes. The aim of this modularization is to create flexibility for using each of the modules on its own, for changing or completely replacing it. For fuzzy-rule based modeling this can explicitly mean that the re-training of one of the modules with newly available data will be possible without problem, while the module assembly does not have to be modified. Apart from the concept of hybrid metamodeling first results are presented for the fuzzy-module for nitrate passage through the unsaturated zone.

Process Based Modelling of Climate Change Impacts on River Water Quality: Case studies from the England, Wales and Scotland

NASA Astrophysics Data System (ADS)

Whitehead, P. G.; Jin, L.; Futter, M.; Crossman, J.

2011-12-01

A modelling study has been undertaken as part of a UK Water Industry Research Project to study and assess the likely impacts of climate change on river water quality across the UK. A range of climate scenarios (http://ukclimateprojections.defra.gov.uk/ ) have been used to generate future precipitation, evaporation and temperature time series at a range of catchments across the UK. These time series have then been used to drive the Integrated Catchment Model (INCA) suite to simulate flow, nitrate, ammonia, total and soluble reactive phosphorus, sediments, dissolved organic carbon (DOC) in the Rivers Tamar, Lugg, Tame, Kennet, Tweed and Lambourn. A wide range of responses have been obtained with impacts varying depending on river character, catchment location, flow regime, type of scenario and the time into the future. For example, The INCA-DOC model has been applied to the Hore catchment of the upper Severn catchment at Plynlimon, Wales. DOC is becoming an issue in the UK uplands due to rising trends in recent years. The trends are thought to be due primarily to reducing sulphur deposition but the climate variability certainly has an effect. This is because when peats dry out the oxidation processes enhance the production of DOC. The INCA-DOC model has been used to assess potential changes in DOC under the 2020s and 2050s climate. These results show quite large rises in October and September months when the soils become saturated and flush DOC. The INCA-N results for the Rivers Tweed (Scotland) and Kennet (England) suggest that nitrate and ammonia concentrations will be slightly higher in the winter months under the climate change scenarios, perhaps reflecting the higher flushing of nitrogen load from the catchment soils. However, in summer month nitrates fall significantly which reflects enhanced denitrification processes in the rivers. However, lower down the rivers where major point sources from effluents affect the river, nitrates and ammonia may increase because of lower flows in summer and hence less dilution. Modelling phosphorus and sediments in the Rivers Lugg, Tame and the Wensum (England) suggest phosphorus concentrations will decrease in summer due to lower flows in rural areas and the reduced flushing of diffuse sources of P from agricultural areas. However, in catchments with significant effluent discharges, the P concentrations will increase due to the reduced dilution of effluents. Sediments will increase with intense rainfall during winter months, although the increased frequency of storms, especially in summer months, will generate higher concentrations as sediments are flushed from the catchments. However, mean summer sediment concentrations will be lower due to the reduced diffuse runoff from agricultural areas. Finally it is worth pointing out that adaptation measures are possible with mitigation measures to control N deposition, fertiliser application rates, reintroducing wetlands and land management control.

Stream Nitrate Concentrations in a Small Catchment in South West England over a Period of 35 Years (1970-2005)

NASA Astrophysics Data System (ADS)

Burt, T.; Worrall, F.

2008-12-01

A 35-year record of nitrate concentration for the Slapton Wood stream, a small agricultural catchment in south west England, is presented. The study reconsiders earlier work in order to assess whether upward trends have been maintained and how controls on catchment nitrate processes have altered. The study has shown that: (i) the catchment has reached a new position of equilibrium and increases in nitrate concentration have levelled off; (ii) the occurrence of severe droughts means that records of less than a decade are misleading and only longer records can illustrate changes of system state; (iii) the change of state observed in the catchment is illustrated in the switching of long-term memory effects from a negative to a positive annual memory; (iv) a significant long-term impulsivity relationship with rainfall becomes insignificant over the course of the study period. The study shows the importance of long records in exposing changes in state in catchment systems and understanding the time constants of a range of driving processes. The study by its very nature also demonstrates the importance of maintaining long-term monitoring programmes.

Nitrate dynamics in agricultural catchments deduced from groundwater dating and long-term nitrate monitoring in surface- and groundwaters.

PubMed

Aquilina, L; Vergnaud-Ayraud, V; Labasque, T; Bour, O; Molénat, J; Ruiz, L; de Montety, V; De Ridder, J; Roques, C; Longuevergne, L

2012-10-01

Although nitrate export in agricultural catchments has been simulated using various types of models, the role of groundwater in nitrate dynamics has rarely been fully taken into account. We used groundwater dating methods (CFC analyses) to reconstruct the original nitrate concentrations in the groundwater recharge in Brittany (Western France) from 1950 to 2009. This revealed a sharp increase in nitrate concentrations from 1977 to 1990 followed by a slight decrease. The recharge concentration curve was then compared with past chronicles of groundwater concentration. Groundwater can be interpreted as resulting from the annual dilution of recharge water in an uncontaminated aquifer. Two aquifers were considered: the weathered aquifer and the deeper fractured aquifer. The nitrate concentrations observed in the upper part of the weathered aquifer implied an annual renewal rate of 27 to 33% of the reservoir volume while those in the lower part indicated an annual renewal rate of 2-3%. The concentrations in the deep fractured aquifer showed an annual renewal rate of 0.1%. The river concentration can be simulated by combining these various groundwater reservoirs with the recharge. Winter and summer waters contain i) recharge water, or water from the variably saturated zone with rapid transfer and high nitrate concentrations, and ii) a large contribution (from 35 to 80% in winter and summer, respectively) from the lower part of the aquifer (lower weathered aquifer and deep fractured aquifer). This induces not only a relatively rapid response of the catchment to variations in agricultural pressure, but also a potential inertia which has to be taken into account. Copyright © 2012 Elsevier B.V. All rights reserved.

Modelling the effect of wildfire on forested catchment water quality using the SWAT model

NASA Astrophysics Data System (ADS)

Yu, M.; Bishop, T.; van Ogtrop, F. F.; Bell, T.

2016-12-01

Wildfire removes the surface vegetation, releases ash, increase erosion and runoff, and therefore effects the hydrological cycle of a forested water catchment. It is important to understand chnage and how the catchment recovers. These processes are spatially sensitive and effected by interactions between fire severity and hillslope, soil type and surface vegetation conditions. Thus, a distributed hydrological modelling approach is required. In this study, the Soil and Water Analysis Tool (SWAT) is used to predict the effect of 2001/02 Sydney wild fire on catchment water quality. 10 years pre-fire data is used to create and calibrate the SWAT model. The calibrated model was then used to simulate the water quality for the 10 years post-fire period without fire effect. The simulated water quality data are compared with recorded water quality data provided by Sydney catchment authority. The mean change of flow, total suspended solid, total nitrate and total phosphate are compare on monthly, three month, six month and annual basis. Two control catchment and three burn catchment were analysed.

Modelling the impacts of agricultural management practices on river water quality in Eastern England.

PubMed

Taylor, Sam D; He, Yi; Hiscock, Kevin M

2016-09-15

Agricultural diffuse water pollution remains a notable global pressure on water quality, posing risks to aquatic ecosystems, human health and water resources and as a result legislation has been introduced in many parts of the world to protect water bodies. Due to their efficiency and cost-effectiveness, water quality models have been increasingly applied to catchments as Decision Support Tools (DSTs) to identify mitigation options that can be introduced to reduce agricultural diffuse water pollution and improve water quality. In this study, the Soil and Water Assessment Tool (SWAT) was applied to the River Wensum catchment in eastern England with the aim of quantifying the long-term impacts of potential changes to agricultural management practices on river water quality. Calibration and validation were successfully performed at a daily time-step against observations of discharge, nitrate and total phosphorus obtained from high-frequency water quality monitoring within the Blackwater sub-catchment, covering an area of 19.6 km(2). A variety of mitigation options were identified and modelled, both singly and in combination, and their long-term effects on nitrate and total phosphorus losses were quantified together with the 95% uncertainty range of model predictions. Results showed that introducing a red clover cover crop to the crop rotation scheme applied within the catchment reduced nitrate losses by 19.6%. Buffer strips of 2 m and 6 m width represented the most effective options to reduce total phosphorus losses, achieving reductions of 12.2% and 16.9%, respectively. This is one of the first studies to quantify the impacts of agricultural mitigation options on long-term water quality for nitrate and total phosphorus at a daily resolution, in addition to providing an estimate of the uncertainties of those impacts. The results highlighted the need to consider multiple pollutants, the degree of uncertainty associated with model predictions and the risk of unintended pollutant impacts when evaluating the effectiveness of mitigation options, and showed that high-frequency water quality datasets can be applied to robustly calibrate water quality models, creating DSTs that are more effective and reliable. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Simulating nitrogen budgets in complex farming systems using INCA: calibration and scenario analyses for the Kervidy catchment (W. France)

NASA Astrophysics Data System (ADS)

Durand, P.

The integrated nitrogen model INCA (Integrated Nitrogen in Catchments) was used to analyse the nitrogen dynamics in a small rural catchment in Western France. The agrosystem studied is very complex, with: extensive use of different organic fertilisers, a variety of crop rotations, a structural excess of nitrogen (i.e. more animal N produced by the intensive farming than the N requirements of the crops and pastures), and nitrate retention in both hydrological stores and riparian zones. The original model features were adapted here to describe this complexity. The calibration results are satisfactory, although the daily variations in stream nitrate are not simulated in detail. Different climate scenarios, based on observed climate records, were tested; all produced a worsening of the pollution in the short term. Scenarios of alternative agricultural practices (reduced fertilisation and catch crops) were also analysed, suggesting that a reduction by 40% of the fertilisation combined with the introduction of catch crops would be necessary to stop the degradation of water quality.

Land-use effects on fluxes of suspended sediment, nitrogen and phosphorus from a river catchment of the Great Barrier Reef, Australia

NASA Astrophysics Data System (ADS)

Hunter, Heather M.; Walton, Richard S.

2008-07-01

SummaryA 6-year study was conducted in the Johnstone River system in the wet tropics of north-eastern Australia, to address concerns that the Great Barrier Reef is at risk from elevated levels of suspended sediment (SS) and nutrients discharged from its river catchments. Aims were to quantify: (i) fluxes of SS, phosphorus (P) and nitrogen (N) exported annually from the catchment and (ii) the influence of rural land uses on these fluxes. Around 55% of the 1602 km2 catchment was native rainforest, with the reminder developed mainly for livestock and crop production. Water quality and stream flow were monitored at 16 sites, with the emphasis on sampling major runoff events. Monitoring data were used to calibrate a water quality model for the catchment (HSPF), which was run with 39 years of historical precipitation and evaporation data. Modelled specific fluxes from the catchment of 1.2 ± 1.1 t SS ha-1 y-1, 2.2 ± 1.8 kg P ha-1 y-1 and 11.4 ± 7.3 kg N ha-1y-1 were highly variable between and within years. Fluxes of SS and P were strongly dominated by major events, with 91% of SS and 84% of P exported during the highest 10% of daily flows. On average, sediment P comprised 81% of the total P flux. The N flux was less strongly dominated by major events and sediment N comprised 46% of total N exports. Specific fluxes of SS, N and P from areas receiving precipitation of 3545 mm y-1 were around 3-4 times those from areas receiving 1673 mm y-1. For a given mean annual precipitation, specific fluxes of SS and P from beef pastures, dairy pastures and unsewered residential areas were similar to those from rainforest, while fluxes from areas of sugar cane and bananas were 3-4 times higher. Specific fluxes of N from areas with an annual precipitation of 3545 mm ranged from 8.9 ± 6.5 kg N ha-1 y-1 (rainforest) to 72 ± 50 kg N ha-1 y-1 (unsewered residential). Aggregated across the entire catchment, disproportionately large fluxes of SS, total P and total N were derived from areas of sugar cane and banana production. Fluxes of nitrate N comprised 32% of mean annual total N flux and were disproportionately high from unsewered residential areas and from areas used for sugar cane and banana production. Notably, 60% of the total catchment flux of nitrate came from areas of sugar cane, which comprised only 12% of the total land area. Modelled scenarios suggest contemporary nitrate fluxes were nearly six times those under natural conditions (pre-development), a much greater increase than estimated for SS, total P and total N. These elevated nitrate fluxes are of particular concern for the protection of aquatic ecosystems, since nitrate is a readily bio-available form of N. Results of the study suggest management practices associated with certain land uses may need further investigation and improvement. To reduce nitrate fluxes, this includes a need to address fertiliser management in the sugar cane and banana industries and wastewater disposal practices in unsewered residential areas.

What impact might mitigation of diffuse nitrate pollution have on river water quality in a rural catchment?

PubMed

Hutchins, Michael G

2012-10-30

Observations of river flow, river quality and solar radiation were collated to assess the degree to which light and nutrients may be limiting phytoplankton growth at seven sites in the River Ouse catchment in NE England under average conditions. Hydraulic information derived from river network model applications was then used to determine where river water has sufficient residence time above the tidal limit to facilitate bloom development. A nitrate model (NALTRACES) was developed to estimate the impact of land management change on mean river nitrate concentrations. Applications of this model showed that although agricultural activity contributes substantially to nitrate loads in the Ouse it is likely to have little impact on phytoplankton growth, which could still occur extensively in its absence given favourable sunny and dry conditions. As an example of a means of controlling light availability, establishing full riparian tree cover would appear to be a considerably more effective management scenario than suppressing inputs to the river of nitrate or phosphorus. Any actions should be prioritised in headwater areas such as the upper reaches of the Swale and Ure tributaries. These conclusions are in broad agreement with those arising from more detailed simulations at daily resolution using the QUESTOR river quality model. The combination of simple modelling approaches applied here allows an initial identification of suitable spatially-targeted options for mitigating against phytoplankton blooms which can be applied more widely at a regional or national level. Copyright © 2012 Elsevier Ltd. All rights reserved.

Changes in stream nitrate concentrations due to land management practices, ecological succession, and climate: Developing a system approach to integrated catchment response

Treesearch

F. Worrall; Wayne T. Swank; T. P. Burt

2003-01-01

This study uses time series analysis to examine long-term stream water nitrate concentration records from a pair of forested catchments at the Coweeta Hydrologic Laboratory, North Carolina, USA. Monthly average concentrations were available from 1970 through 1997 for two forested catchments, one of which was clear-felled in 1977 and the other maintained as a control....

INCA Modelling of the Lee System: strategies for the reduction of nitrogen loads

NASA Astrophysics Data System (ADS)

Flynn, N. J.; Paddison, T.; Whitehead, P. G.

The Integrated Nitrogen Catchment model (INCA) was applied successfully to simulate nitrogen concentrations in the River Lee, a northern tributary of the River Thames for 1995-1999. Leaching from urban and agricultural areas was found to control nitrogen dynamics in reaches unaffected by effluent discharges and abstractions; the occurrence of minimal flows resulted in an upward trend in nitrate concentration. Sewage treatment works (STW) discharging into the River Lee raised nitrate concentrations substantially, a problem which was compounded by abstractions in the Lower Lee. The average concentration of nitrate (NO3) for the simulation period 1995-96 was 7.87 mg N l-1. Ammonium (NH4) concentrations were simulated less successfully. However, concentrations of ammonium rarely rose to levels which would be of environmental concern. Scenarios were run through INCA to assess strategies for the reduction of nitrate concentrations in the catchment. The conversion of arable land to ungrazed vegetation or to woodland would reduce nitrate concentrations substantially, whilst inclusion of riparian buffer strips would be unsuccessful in reducing nitrate loading. A 50% reduction in nitrate loading from Luton STW would result in a fall of up to 5 mg N l-1 in the reach directly affected (concentrations fell from maxima of 13 to 8 mg N l-1 , nearly a 40 % reduction), whilst a 20% reduction in abstractions would reduce maximum peaks in concentration in the lower Lee by up to 4 mg l-1 (from 17 to 13 mg N l-1, nearly a 25 % reduction),.

Modelling of catchment nitrogen concentrations response to observed varying fertilizer application intensities

NASA Astrophysics Data System (ADS)

Jomaa, Seifeddine; Jiang, Sanyuan; Yang, Xiaoqiang; Rode, Michael

2016-04-01

Eutrophication is a serious environmental problem. Despite numerous experimental and modelling efforts, understanding of the effect of land use and agriculture practices on in-stream nitrogen fluxes is still not fully achieved. This study combined intensive field monitoring and numerical modelling using 30 years of surface water quality data of a drinking water reservoir catchment in central Germany. The Weida catchment (99.5 km2) is part of the Elbe river basin and has a share of 67% of agricultural land use with significant changes in agricultural practices within the investigation period. The geology of the Weida catchment is characterized by clay schists and eruptive rocks, where rocks have low permeability. The semi-distributed hydrological water quality HYPE (Hydrological Predictions for the Environment) model was used to reproduce the measured data. First, the model was calibrated for discharge and nitrate-N concentrations (NO3-N) during the period 1997-2000. Then, the HYPE model was validated successfully for three different periods 1983-1987, 1989-1996 and 2000-2003, which are charaterized by different fertilizer application rates (with lowest discharge prediction performance of NSE = 0.78 and PBIAS = 3.74%, considering calibration and validation periods). Results showed that the measured as well as simulated in-stream nitrate-N concentration respond quickly to fertilizer application changes (increase/decrease). This rapid response can be explained with short residence times of interflow and baseflow runoff components due to the hardrock geological properties of the catchment. Results revealed that the surface runoff and interflow are the most dominant runoff components. HYPE model could reproduce reasonably well the NO3-N daily loads for varying fertilizer application, when detailed input data in terms of crop management (field-specific survey) are considered.

Pollution indicators in groundwater of two agricultural catchments in Lower Silesia (Poland)

NASA Astrophysics Data System (ADS)

Kasperczyk, Lidia; Modelska, Magdalena; Staśko, Stanisław

2016-12-01

The article discusses the content and source of mineral nitrogen compounds in groundwater, based on the data collected in two river catchments in two series (spring and autumn 2014). The study area comprises two catchments located in Lower Silesia, Poland - Cicha Woda and Sąsiecznica. Both catchments are characterised agricultural character of development. In the both researched areas, the points of State Environmental Monitoring (SEM) are located but only the Cicha Woda area is classified as nitrate vulnerable zone (NVZ). To analyse and compare the contamination of Quaternary and Neogene aquifers, the concentration of nitrates, nitrites, ammonium and potassium ions was measured primarily. Results showed the exceedance of nitrogen mineral forms of shallow groundwater Quaternary aquifer in both basins. The concentration of nitrates range from 0.08 to 142.12 mgNO3 -/dm3 (Cicha Woda) and from 2.6 to 137.65 mg NO3 -/dm3 (Sąsiecznica). The major source of pollution is probably the intensive agriculture activity. It causes a degradation of the shallow groundwater because of nitrate, nitrite, potassium, phosphates and ammonium contents. There was no observed contamination of anthropogenic origin in the deeper Neogene aquifer of Cicha Woda catchment.

Synchronicity of long-term nitrate patterns in forested catchments across the northeastern U.S.

EPA Science Inventory

Nitrogen movement through minimally-disturbed catchments can be affected by a variety of biogeochemical processes, climatic effects, hydrology and in-stream or in-lake processes. These combine to create dizzying complexity in long-term and seasonal nitrate patterns, with adjacen...

Simulation of quantity and quality of storm runoff for urban catchments in Fresno, California

USGS Publications Warehouse

Guay, J.R.; Smith, P.E.

1988-01-01

Rainfall-runoff models were developed for a multiple-dwelling residential catchment (2 applications), a single-dwelling residential catchment, and a commercial catchment in Fresno, California, using the U.S. Geological Survey Distributed Routing Rainfall-Runoff Model (DR3M-II). A runoff-quality model also was developed at the commercial catchment using the Survey 's Multiple-Event Urban Runoff Quality model (DR3M-qual). The purpose of this study was: (1) to demonstrate the capabilites of the two models for use in designing storm drains, estimating the frequency of storm runoff loads, and evaluating the effectiveness of street sweeping on an urban drainage catchment; and (2) to determine the simulation accuracies of these models. Simulation errors of the two models were summarized as the median absolute deviation in percent (mad) between measured and simulated values. Calibration and verification mad errors for runoff volumes and peak discharges ranged from 14 to 20%. The estimated annual storm-runoff loads, in pounds/acre of effective impervious area, that could occur once every hundred years at the commercial catchment was 95 for dissolved solids, 1.6 for the dissolved nitrite plus nitrate, 0.31 for total recoverable lead, and 120 for suspended sediment. Calibration and verification mad errors for the above constituents ranged from 11 to 54%. (USGS)

Cost-Effective Mitigation of Diffuse Pollution: Setting Criteria for River Basin Management at Multiple Locations

NASA Astrophysics Data System (ADS)

Hutchins, Mike; Fezzi, Carlo; Bateman, Ian; Posen, Paulette; Deflandre-Vlandas, Amelie

2009-08-01

A case study of the Yorkshire Derwent (UK) catchment is used to illustrate an integrated approach for assessing the viability of policy options for reducing diffuse nitrate losses to waterbodies. For a range of options, modeling methods for simulating river nitrate levels are combined with techniques for estimating the economic costs to agriculture of modifying those levels. By incorporating spatially explicit data and information on catchment residence times (which may span many decades particularly in areas of groundwater discharge) a method is developed for efficient spatial targeting of measures, for example, to the most at-risk freshwater environments. Combining hydrological and economic findings, the analysis reveals that, in terms of cost-effectiveness, the ranking of options is highly sensitive to both (i) whether or not specific stretches of river within a catchment are regarded as a priority for protection, and (ii) the criterion of nitrate concentration deemed most appropriate as an indicator of the health of the environment. Therefore, given the focus under European legislation upon ecological status of freshwaters, these conclusions highlight the need to improve understanding of mechanistic linkages between the chemical and biological dynamics of aquatic systems.

Of microbes and men: Determining sources of nitrate in a high alpine catchment in the Front Range of Colorado and science outreach on alpine hydrology

NASA Astrophysics Data System (ADS)

Hafich, Katya A.

High elevation ecosystems throughout the Colorado Front Range are undergoing changes in biogeochemical cycling due to an increase in nitrogen deposition in precipitation and a changing climate. While nitrate concentrations continue to rise in surface water of the Green Lakes Valley (GLV) by 0.27 umol L-1 per year, atmospheric deposition of inorganic nitrogen has recently curtailed due to drought, leaving a gap in our understanding of the source of the increased export of nitrate. Here, we employ a novel triple isotope method, using Delta 17O-NO3- for the first time in an alpine catchment to quantify the terrestrial and atmospheric contribution of nitrate to numerous water types in GLV. Results show that nitrate in surface waters, including talus, soil water and rock glacier melt, is more than 75% terrestrial, with the strongest atmospheric signals present during snowmelt. Results suggest that alpine catchment biogeochemistry in GLV has transitioned to a net nitrification system.

Catchment-scale variation in the nitrate concentrations of groundwater seeps in the Catskill Mountains, New York, U.S.A.

USGS Publications Warehouse

West, A.J.; Findlay, S.E.G.; Burns, Douglas A.; Weathers, K.C.; Lovett, Gary M.

2001-01-01

Forested headwater streams in the Catskill Mountains of New York show significant among-catchment variability in mean annual nitrate (NO3-) concentrations. Large contributions from deep groundwater with high NO3- concentrations have been invoked to explain high NO3- concentrations in stream water during the growing season. To determine whether variable contributions of groundwater could explain among-catchment differences in streamwater, we measured NO3- concentrations in 58 groundwater seeps distributed across six catchments known to have different annual average streamwater concentrations. Seeps were identified based on release from bedrock fractures and bedding planes and had consistently lower temperatures than adjacent streamwaters. Nitrate concentrations in seeps ranged from near detection limits (0.005 mg NO3--N/L) to 0.75 mg NO3--N/L. Within individual catchments, groundwater residence time does not seem to strongly affect NO3- concentrations because in three out of four catchments there were non-significant correlations between seep silica (SiO2) concentrations, a proxy for residence time, and seep NO3- concentrations. Across catchments, there was a significant but weak negative relationship between NO3- and SiO2 concentrations. The large range in NO3- concentrations of seeps across catchments suggests: 1) the principal process generating among-catchment differences in streamwater NO3- concentrations must influence water before it enters the groundwater flow system and 2) this process must act at large spatial scales because among-catchment variability is much greater than intra-catchment variability. Differences in the quantity of groundwater contribution to stream baseflow are not sufficient to account for differences in streamwater NO3- concentrations among catchments in the Catskill Mountains.

Tropical montane forest conversion affects spatial and temporal nitrogen dynamics in Kenyan headwater catchment

NASA Astrophysics Data System (ADS)

Jacobs, Suzanne; Weeser, Björn; Breuer, Lutz; Butterbach-Bahl, Klaus; Guzha, Alphonce; Rufino, Mariana

2017-04-01

Deforestation and land use change (LUC) are often stated as major contributors to changes in water quality, although other catchment characteristics such as topography, geology and climate can also play a role. Understanding how stream water chemistry is affected by LUC is essential for sustainable water management and land use planning. However, there is often a lack of reliable data, especially in less studied regions such as East Africa. This study focuses on three sub-catchments (27-36 km2) with different land use types (natural forest, smallholder agriculture and tea/tree plantations) nested in a 1023 km2 headwater catchment in the Mau Forest Complex, Kenya's largest closed-canopy indigenous tropical montane forest. In the past decades approx. 25% of the natural forest was lost due to land use change. We studied seasonal, diurnal and spatial patterns of total dissolved nitrogen (TDN), nitrate (NO3-N) and dissolved organic nitrogen (DON) using a combination of high-resolution in-situ measurements, bi-weekly stream water samples and spatial sampling campaigns. Multiple linear regression analysis of the spatial data indicates that land use shows a strong influence on TDN and nitrate, while DON is more influenced by precipitation. Highest TDN and nitrate concentrations are found in tea plantations, followed by smallholder agriculture and natural forest. This ranking does not change throughout the year, though concentrations of TDN and nitrate are respectively 27.6 and 25.4% lower in all catchments during the dry season. Maximum Overlap Discrete Wavelet Transform (MODWT) analysis of the high resolution nitrate data revealed a seasonal effect on diurnal patterns in the natural forest catchment, where the daily peak shifts from early morning in the wet season to mid-afternoon in the dry season. The smallholder and tea catchment do not exhibit clear diurnal patterns. The results suggest that land use affects dissolved nitrogen concentrations, leading to higher N export in catchments under managed land use. Furthermore, the changes in diurnal patterns in the forest catchment and absence of similar patterns in the other catchments are an indication that biogeochemical processes such as nitrification and denitrification in areas under different land use are affected as well. This could have implications for regional N-cycling.

Nitrate pollution in intensively farmed regions: What are the prospects for sustaining high-quality groundwater?

NASA Astrophysics Data System (ADS)

Howden, Nicholas J. K.; Burt, Tim P.; Worrall, Fred; Mathias, Simon; Whelan, Mick J.

2011-06-01

Widespread pollution of groundwater by nutrients due to 20th century agricultural intensification has been of major concern in the developed world for several decades. This paper considers the River Thames catchment (UK), where water-quality monitoring at Hampton (just upstream of London) has produced continuous records for nitrate for the last 140 years, the longest continuous record of water chemistry anywhere in the world. For the same period, data are available to characterize changes in both land use and land management at an annual scale. A modeling approach is used that combines two elements: an estimate of nitrate available for leaching due to land use and land management; and, an algorithm to route this leachable nitrate through to surface or groundwaters. Prior to agricultural intensification at the start of World War II, annual average inputs were around 50 kg ha-1, and river concentrations were stable at 1 to 2 mg l-1, suggesting in-stream denitrification capable of removing 35 (±15) kt N yr-1. Postintensification data suggest an accumulation of 100 (±40) kt N yr-1 in the catchment, most of which is stored in the aquifer. This build up of reactive N species within the catchments means that restoration of surface nitrate concentrations typical of the preintensification period would require massive basin-wide changes in land use and management that would compromise food security and take decades to be effective. Policy solutions need to embrace long-term management strategies as an urgent priority.

Isotopic signals from precipitation and denitrification in nitrate in a northern hardwood forest

NASA Astrophysics Data System (ADS)

Goodale, C. L.; Wexller, S.

2012-12-01

Denitrification can represent an important term in the nitrogen budget of small catchments; however, this process varies greatly over space and time and is notoriously difficult to quantify. Measurements of the natural abundance of stable isotopes of nitrogen and oxygen in dissolved nitrate in stream- and river water can sometimes provide evidence of denitrification, particularly in large river basins or agriculturally impacted catchments. To date, however, this approach has provided little to no evidence of denitrification in catchments in temperate forests. Here, we examined d15N and d18O of nitrate in water samples collected during summer 2011 not only from streams and precipitation, but also from groundwater from the hydrologic reference watershed (W3) drained by Paradise Brook, at the Hubbard Brook Experimental Forest, in the White Mountains, New Hampshire. Despite low nitrate concentrations (< 0.5 to 8.8 uM nitrate) dual-isotopic signals of nitrate sources and nitrogen cycle processes were clearly distinguishable, including sources from atmospheric deposition, and from nitrification of atmospheric ammonium and from or soil organic nitrogen, as well as nitrate affected by soil denitrification. An atmospheric signal from nitrate in precipitation (enriched with 18O) was observed immediately following a precipitation event in mid-July contributing roughly 22% of stream nitrate export on this date. Stream samples the day following this and other storms showed this export of event nitrate to be short-lived. Hillslope piezometers showed low nitrate concentrations and high d15N- and d18O-nitrate values (averaging 12 and 18 per mil, repectively) indicating denitrification, which preferentially removes isotopically light N and O in N gases and leaves isotopically heavy nitrate behind. These samples showed a positive relationship between nitrogen and oxygen isotopic composition with a regression line slope of 0.76 (R2 = 0.68), and an isotope enrichment factor -12.7 per mil for denitrification removal of nitrate in these hillslope soils. The isotopic composition of a time series of samples from three riparian piezometers crossing Paradise Brook shows strong connections between the riparian soil water and the stream, as well as a different dominant source of nitrate in each piezometer. Repeated surveys of stream nitrate show modest positive enrichment in N and O isotopes with a slope between 18O and 15N of 0.96, indicating either in- or near-stream denitrification or mixing between stream and hillslope water bearing a stronger denitrification signal. The dual isotope approach provides detailed information on nitrogen cycling dynamics during the summer in a northern hardwood forested catchment. Together, these observations provide strong isotopic evidence for rapid rates of denitrification during summer in the soils of this small forested catchment.

Nutrient Losses from Non-Point Sources or from Unidentified Point Sources? Application Examples of the Smartphone Based Nitrate App.

NASA Astrophysics Data System (ADS)

Rozemeijer, J.; Ekkelenkamp, R.; van der Zaan, B.

2017-12-01

In 2016 Deltares launched the free to use Nitrate App which accurately reads and interprets nitrate test strips. The app directly displays the measured concentration and gives the option to share the result. Shared results are visualised in map functionality within the app and online. Since its introduction we've been seeing an increasing number of nitrate app applications. In this presentation we show some unanticipated types of application. The Nitrate App was originally intended to enable farmers to measure nitrate concentrations on their own farms. This may encourage farmers to talk to specialists about the right nutrient best management practices (BMP's) for their farm. Several groups of farmers have recently started to apply the Nitrate App and to discuss their results with each other and with the authorities. Nitrate concentration routings in catchments have proven to be another useful application. Within a day a person can generate a catchment scale nitrate concentration map identifying nitrate loss hotspots. In several routings in agricultural catchments clear point sources were found, for example at small scale manure processing plants. These routings proved that the Nitrate App can help water managers to target conservation practices more accurately to areas with the highest nitrate concentrations and loads. Other current applications are the screening of domestic water wells in California, the collection of extra measurements (also pH and NH4) in the National Monitoring Network for the Evaluation of the Manure Policy in the Netherlands, and several educational initiatives in cooperation with schools and universities.

Spatial and temporal changes in the structure of groundwater nitrate concentration time series (1935 1999) as demonstrated by autoregressive modelling

NASA Astrophysics Data System (ADS)

Jones, A. L.; Smart, P. L.

2005-08-01

Autoregressive modelling is used to investigate the internal structure of long-term (1935-1999) records of nitrate concentration for five karst springs in the Mendip Hills. There is a significant short term (1-2 months) positive autocorrelation at three of the five springs due to the availability of sufficient nitrate within the soil store to maintain concentrations in winter recharge for several months. The absence of short term (1-2 months) positive autocorrelation in the other two springs is due to the marked contrast in land use between the limestone and swallet parts of the catchment, rapid concentrated recharge from the latter causing short term switching in the dominant water source at the spring and thus fluctuating nitrate concentrations. Significant negative autocorrelation is evident at lags varying from 4 to 7 months through to 14-22 months for individual springs, with positive autocorrelation at 19-20 months at one site. This variable timing is explained by moderation of the exhaustion effect in the soil by groundwater storage, which gives longer residence times in large catchments and those with a dominance of diffuse flow. The lags derived from autoregressive modelling may therefore provide an indication of average groundwater residence times. Significant differences in the structure of the autocorrelation function for successive 10-year periods are evident at Cheddar Spring, and are explained by the effect the ploughing up of grasslands during the Second World War and increased fertiliser usage on available nitrogen in the soil store. This effect is moderated by the influence of summer temperatures on rates of mineralization, and of both summer and winter rainfall on the timing and magnitude of nitrate leaching. The pattern of nitrate leaching also appears to have been perturbed by the 1976 drought.

Dissolved organic nitrogen (DON) losses from nested artificially drained lowland catchments with contrasting soil types

NASA Astrophysics Data System (ADS)

Tiemeyer, Bärbel; Kahle, Petra; Lennartz, Bernd

2010-05-01

Artificial drainage is a common practice to improve moisture and aeration conditions of agricultural land. It shortens the residence time of water in the soil and may therefore contribute to the degradation of peatlands as well as to the still elevated level of diffuse pollution of surface water bodies, particularly if flow anomalies like preferential flow cause a further acceleration of water and solute fluxes. Especially in the case of nitrate, artificially drained sub-catchments are found to control the catchment-scale nitrate losses. However, it is frequently found that nitrate losses and nitrogen field balances do not match. At the same time, organic fertilizers are commonly applied and, especially in lowland catchments, organic soils have been drained for agricultural use. Thus, the question arises whether dissolved organic nitrogen (DON) forms an important component of the nitrogen losses from artificially drained catchments. However, in contrast to nitrate and even to dissolved organic carbon (DOC), this component is frequently overlooked, especially in nested catchment studies with different soil types and variable land use. Here, we will present data from a hierarchical water quantity and quality measurement programme in the federal state Mecklenburg-Vorpommern (North-Eastern Germany). The monitoring programme in the pleistocene lowland catchment comprises automatic sampling stations at a collector drain outlet (4.2 ha catchment), at a ditch draining arable land on mineral soils (179 ha), at a ditch mainly draining grassland on organic soils (85 ha) and at a brook with a small rural catchment (15.5 km²) of mixed land use and soil types. At all sampling stations, daily to weekly composite samples were taken, while the discharge and the meteorological data were recorded continuously. Water samples were analyzed for nitrate-nitrogen, ammonium-nitrogen and total nitrogen. We will compare two years: 2006/07 was a very wet year (P = 934 mm) with a high summer precipitation, while 2007/08 was considerably drier than average (P = 554 mm). We will present concentrations and losses of all nitrogen fractions and their relationship to the dominating soil type, precipitation characteristics, discharge, and fertilization practice. Furthermore, we will assess whether the determination of DON helps to improve the correlation between nitrogen input and nitrogen losses.

Evaluating the source of streamwater nitrate using δ15N and δ18O in nitrate in two watersheds in New Hampshire, USA

USGS Publications Warehouse

Pardo, Linda H.; Kendall, Carol; Pett-Ridge, Jennifer; Chang, Cecily C.Y.

2004-01-01

The natural abundance of nitrogen and oxygen isotopes in nitrate can be a powerful tool for identifying the source of nitrate in streamwater in forested watersheds, because the two main sources of nitrate, atmospheric deposition and microbial nitrification, have distinct δ18O values. Using a simple mixing model, we estimated the relative fractions in streamwater derived from these sources for two forested watersheds with markedly different streamwater nitrate outputs. In this study, we monitored δ15N and δ18O of nitrate biweekly in atmospheric deposition and in streamwater for 20 months at the Hubbard Brook Experimental Forest, New Hampshire, USA (moderate nitrogen export), and monthly in streamwater at the Bowl Research Natural Area, New Hampshire, USA (high nitrogen export). For rain, δ18O values ranged from +47 to +77‰ (mean: +58‰) and δ15N from −5 to +1‰ (mean: −3‰); for snow, δ18O values ranged from +52 to +75‰ (mean: +67‰) and δ15N from −3 to +2‰ (mean: −1‰). Streamwater nitrate, in contrast to deposition, had δ18O values between +12 and +33‰ (mean: +18‰) and δ15N between −3 and +6‰ (mean: 0‰). Since nitrate produced by nitrification typically has δ18O values ranging from −5 to +15‰, our field data suggest that most of the nitrate lost from the watersheds in streamflow was nitrified within the catchment. Our results confirm the importance of microbial nitrogen transformations in regulating nitrogen losses from forested ecosystems and suggest that hydrologic storage may be a factor in controlling catchment nitrate losses.

An approach to derive groundwater and stream threshold values for total nitrogen and ensure good ecological status of associated aquatic ecosystems - example from a coastal catchment to a vulnerable Danish estuary.

NASA Astrophysics Data System (ADS)

Hinsby, Klaus; Markager, Stiig; Kronvang, Brian; Windolf, Jørgen; Sonnenborg, Torben; Sørensen, Lærke

2015-04-01

Nitrate, which typically makes up the major part (~>90%) of dissolved inorganic nitrogen in groundwater and surface water, is the most frequent pollutant responsible for European groundwater bodies failing to meet the good status objectives of the European Water Framework Directive generally when comparing groundwater monitoring data with the nitrate quality standard of the Groundwater Directive (50 mg/l = the WHO drinking water standard). Still, while more than 50 % of the European surface water bodies do not meet the objective of good ecological status "only" 25 % of groundwater bodies do not meet the objective of good chemical status according to the river basin management plans reported by the EU member states. However, based on a study on interactions between groundwater, streams and a Danish estuary we argue that nitrate threshold values for aerobic groundwater often need to be significantly below the nitrate quality standard to ensure good ecological status of associated surface water bodies, and hence that the chemical status of European groundwater is worse than indicated by the present assessments. Here we suggest a methodology for derivation of groundwater and stream threshold values for total nitrogen ("nitrate") in a coastal catchment based on assessment of maximum acceptable nitrogen loadings (thresholds) to the associated vulnerable estuary. The applied method use existing information on agricultural practices and point source emissions in the catchment, groundwater, stream quantity and quality monitoring data that all feed data to an integrated groundwater and surface water modelling tool enabling us to conduct an assessment of total nitrogen loads and threshold concentrations derived to ensure/restore good ecological status of the investigated estuary. For the catchment to the Horsens estuary in Denmark we estimate the stream and groundwater thresholds for total nitrogen to be about 13 and 27 mg/l (~ 12 and 25 mg/l of nitrate). The shown example of deriving nitrogen threshold concentrations is for groundwater and streams in a coastal catchment discharging to a vulnerable estuary in Denmark, but the principles may be applied to large river basins with sub-catchments in several countries such as e.g. the Danube or the Rhine. In this case the relevant countries need to collaborate on derivation of nitrogen thresholds based on e.g. maximum acceptable nitrogen loadings to the Black Sea / the North Sea, and finally agree on thresholds for different parts of the river basin. Phosphorus is another nutrient which frequently results in or contributes to the eutrophication of surface waters. The transport and retention processes of total phosphorus (TP) is more complex than for nitrate (or alternatively total N), and presently we are able to establish TP thresholds for streams but not for groundwater. Derivation of TP thresholds is covered in an accompanying paper by Kronvang et al.

Responses of stream nitrate and DOC loadings to hydrological forcing and climate change in an upland forest of the northeastern United States

NASA Astrophysics Data System (ADS)

Sebestyen, Stephen D.; Boyer, Elizabeth W.; Shanley, James B.

2009-06-01

In coming decades, higher annual temperatures, increased growing season length, and increased dormant season precipitation are expected across the northeastern United States in response to anthropogenic forcing of global climate. We synthesized long-term stream hydrochemical data from the Sleepers River Research Watershed in Vermont, United States, to explore the relationship of catchment wetness to stream nitrate and DOC loadings. We modeled changes in growing season length and precipitation patterns to simulate future climate scenarios and to assess how stream nutrient loadings respond to climate change. Model results for the 2070-2099 time period suggest that stream nutrient loadings during both the dormant and growing seasons will respond to climate change. During a warmer climate, growing season stream fluxes (runoff +20%, nitrate +57%, and DOC +58%) increase as more precipitation (+28%) and quick flow (+39%) occur during a longer growing season (+43 days). During the dormant season, stream water and nutrient loadings decrease. Net annual stream runoff (+8%) and DOC loading (+9%) increases are commensurate with the magnitude of the average increase of net annual precipitation (+7%). Net annual stream water and DOC loadings are primarily affected by increased dormant season precipitation. In contrast, decreased annual loading of stream nitrate (-2%) reflects a larger effect of growing season controls on stream nitrate and the effects of lengthened growing seasons in a warmer climate. Our findings suggest that leaching of nitrate and DOC from catchment soils will be affected by anthropogenic climate forcing, thereby affecting the timing and magnitude of annual stream loadings in the northeastern United States.

User-inspired Research Quantifies How Floodplain Restoration Paired With Cover Crops Reduces Nutrient Export From an Agricultural Catchment Translating to Conservation Success in the Midwestern Cornbelt.

NASA Astrophysics Data System (ADS)

Tank, J. L.; Hanrahan, B.; Christopher, S. F.; Mahl, U. H.; Royer, T. V.

2017-12-01

The Midwestern US has undergone extensive land use change as forest, wetlands, and prairies have been converted to agroecosystems. Today, excess fertilizer nutrients from farm fields enter agricultural streams, which degrades both local and downstream water quality. We are quantifying the nutrient reduction benefits of two conservation practices implemented at the catchment scale. In partnership with The Nature Conservancy, in a small Indiana catchment, we have quantified how 600m of floodplain restoration (i.e., a two-stage ditch) increased nitrate-N removal via denitrification and reduced sediment export, but impacts on stream nutrient concentrations were negligible due to very high catchment loading relative to the short implementation reach. Requests from state and federal partners led to development and parameterization of a new two-stage ditch module in the SWAT model to determine the potential catchment-scale benefits when implementation lengths were extended. More recently, in partnership with state SWCD managers, we have added a landscape practice to quantify how winter cover crops reduce nutrient loss from fields, sampling year-round nutrient fluxes from multiple subsurface tile drains and longitudinally along the stream channel. Nitrate-N and dissolved P fluxes were significantly lower in tiles draining fields with cover crops compared to those without. At the urging of farmers and federal NRCS partners, we also linked tile drain nutrient reductions to changes in soil chemistry. Both soil nitrate-N and dissolved P were lower in cover cropped fields, and we found significant correlations between soil and tile drain nutrients, which may encourage future adoption of the conservation practice as soil health benefits appeal to farmers. As biogeochemists, this research has provided valuable insights on how floodplains and land cover change can alter patterns of catchment-scale nutrient export. The translation of successful soil and water quality outcomes through this significant regional demonstration project make it a potentially powerful agent of change for advancing conservation success.

Modelling the impacts of altered management practices, land use and climate changes on the water quality of the Millbrook catchment-reservoir system in South Australia.

PubMed

Nguyen, Hong Hanh; Recknagel, Friedrich; Meyer, Wayne; Frizenschaf, Jacqueline; Shrestha, Manoj Kumar

2017-11-01

Sustainable management of drinking water reservoirs requires taking into account the potential effects of their catchments' development. This study is an attempt to estimate the daily patterns of nutrients transport in the catchment - reservoir systems through the application of the ensemble of complementary models SWAT-SALMO. SWAT quantifies flow, nitrate and phosphate loadings originating in catchments before entering downstream reservoirs meanwhile SALMO determines phosphate, nitrate, and chlorophyll-a concentrations within the reservoirs. The study applies to the semi-arid Millbrook catchment-reservoir system that supplies drinking water to north-eastern suburbs of Adelaide, South Australia. The catchment hosts viti- and horticultural land uses. The warm-monomictic, mesotrophic reservoir is artificially aerated in summer. After validating the simulation results for both Millbrook catchment and reservoir, a comprehensive scenario analysis has been conducted to reveal cascading effects of altered management practices, land uses and climate conditions on water quality in the reservoir. Results suggest that the effect on reservoir condition in summer would be severe, most likely resulting in chlorophyll-a concentrations of greater than 40 μg/l if the artificial destratification was not applied from early summer. A 50% curbing of water diversion from an external pipeline to the catchment will slightly limit chlorophyll-a concentrations by 1.22% as an effect of reduced inflow phosphate loads. The simulation of prospective land use scenarios converting 50% of present pasture in the Millbrook catchment into residential and orchards areas indicates an increase of summer chlorophyll-a concentrations by 9.5-107.9%, respectively in the reservoir. Global warming scenarios based on the high emission simulated by SWAT-SALMO did result in earlier growth of chlorophyll-a but overall the effects on water quality in the Millbrook reservoir was not significant. However scenarios combining global warming and land use changes resulted in significant eutrophication effects in the reservoir, especially in the unmanaged condition with stratification in summer. This study has demonstrated that complementary model ensembles like SWAT-SALMO allow to comprehend more realistically cascading effects of distinct catchment processes on internal reservoir's processes, and facilitate integrated management scenarios. Copyright © 2017 Elsevier Ltd. All rights reserved.

Assessing the spatial and temporal variations of water quality in lowland areas, Northern Germany

NASA Astrophysics Data System (ADS)

Lam, Q. D.; Schmalz, B.; Fohrer, N.

2012-05-01

SummaryThe pollution of rivers and streams with agro-chemical contaminants has become one of the most crucial environmental problems in the world. The assessment of spatial and temporal variations of water quality influenced by point and diffuse source pollution is necessary to manage the environment sustainably in various watershed scales. The overall objectives of this study were to assess the transferability of parameter sets between lowland catchments on different scales using the ecohydrological model SWAT (Soil and Water Assessment Tool) and to evaluate the temporal and spatial patterns of water quality in the whole catchments before and after implementation of best management practices (BMPs). The study area Kielstau catchment is located in Northern Germany as typical example of lowland - flood plain landscape. Sandy, loamy and peat soils are characteristic for this area. Land use is dominated by arable land and pasture. In this study we examined two catchment areas including Kielstau catchment 50 km2 and its subcatchment, namely Moorau, with the area of 7.6 km2. The water quality of these catchments is not only influenced by diffuse sources from agricultural areas but also by point sources from municipal wastewater treatment plants (WWTPs). Diffuse sources as well as punctual entries from the WWTPs are considered in the model set-up. For this study, the calibration and validation of the model were carried out in a daily time step for flow and nutrients. The results indicate that the parameter sets could be transferred in lowland catchments with similar environmental conditions. Shallow groundwater is the major contributor to total nitrate load in the stream accounting for about 93% of the total nitrate load, while only about 7% originates in surface runoff and lateral flow. The study also indicates that applying a spatially distributed modeling approach was an appropriate method to generate source maps showing the spatial distribution of TN load from hydrologic response units (HRUs) as well as from subbasins and to identify the crucial pollution areas within a watershed whose management practices can be improved to control more effectively nitrogen loading to water bodies.

Identification of nitrate sources and discharge-depending nitrate dynamics in a mesoscale catchment

NASA Astrophysics Data System (ADS)

Mueller, Christin; Strachauer, Ulrike; Brauns, Mario; Musolff, Andreas; Kunz, Julia Vanessa; Brase, Lisa; Tarasova, Larisa; Merz, Ralf; Knöller, Kay

2017-04-01

During the last decades, nitrate concentrations in surface and groundwater have increased due to land use change and accompanying application of fertilizer in agriculture as well as increased atmospheric deposition. To mitigate nutrient impacts on downstream aquatic ecosystems, it is important to quantify potential nitrate sources, instream nitrate processing and its controls in a river system. The objective of this project is to characterize and quantify (regional) scale dynamics and trends in water and nitrogen fluxes of the entire Holtemme river catchment in central Germany making use of isotopic fingerprinting methods. Here we compare two key date sampling campaigns in 2014 and 2015, with spatially highly resolved measurements of discharge at 23 sampling locations including 11 major tributaries and 12 locations at the main river. Additionally, we have data from continuous runoff measurements at 10 locations operated by the local water authorities. Two waste water treatment plants contribute nitrogen to the Holtemme stream. This contribution impacts nitrate loads and nitrate isotopic signatures depending on the prevailing hydrological conditions. Nitrogen isotopic signatures in the catchment are mainly controlled by different sources (nitrified soil nitrogen in the headwater and manure/ effluents from WWTPs in the lowlands) and increase with raising nitrate concentrations along the main river. Nitrate loads at the outlet of the catchment are extremely different between both sampling campaigns (2014: NO3- = 97 t a-1, 2015: NO3- = 5 t a-1) which is associated with various runoff (2014: 0.8 m3 s-1, 2015: 0.2 m3 s-1). In 2015, the inflow from WWTP's raises the NO3- loads and enriches δ18O-NO3 values. Generally, oxygen isotope signatures from nitrate are more variable and are controlled by biogeochemical processes in concert with the oxygen isotopic composition of the ambient water. Elevated δ18O-NO3 in 2015 are most likely due to higher temperatures and lower discharge resulting in a higher impact of evaporation on water isotopes and a higher/different level of biological activity (esp. in the WWTP). Enriched isotope values for nitrogen and oxygen are not indicative of a significant impact of bacterial denitrification, because they are accompanied by increased nitrate concentrations (1 to 16 mg L-1). Based on the presented study, 50 % of the nitrate export from the Holtemme river catchment can be attributed to WWTP effluent. The remaining amount is related to agricultural land use. Consequently, nitrate load reduction in the river system cannot rely on internal processing but needs to be regulated by preventive measures especially by an improved wastewater treatment and land use management.

Long-term trends in dissolved iron and DOC concentration linked to nitrate depletion in riparian soils

NASA Astrophysics Data System (ADS)

Musolff, Andreas; Selle, Benny; Fleckenstein, Jan H.; Oosterwoud, Marieke R.; Tittel, Jörg

2016-04-01

The instream concentrations of dissolved organic carbon (DOC) are rising in many catchments of the northern hemisphere. Elevated concentrations of DOC, mainly in the form of colored humic components, increase efforts and costs of drinking water purification. In this study, we evaluated a long-term dataset of 110 catchments draining into German drinking water reservoirs in order to assess sources of DOC and drivers of a potential long-term change. The average DOC concentrations across the wide range of different catchments were found to be well explained by the catchment's topographic wetness index. Higher wetness indices were connected to higher average DOC concentrations, which implies that catchments with shallow topography and pronounced riparian wetlands mobilize more DOC. Overall, 37% of the investigated catchments showed a significant long-term increase in DOC concentrations, while 22% exhibited significant negative trends. Moreover, we found that increasing trends in DOC were positively correlated to trends in dissolved iron concentrations at pH≤6 due to remobilization of DOC previously sorbed to iron minerals. Both, increasing trends in DOC and dissolve iron were found to be connected to decreasing trends and low concentrations of nitrate (below ~6 mg/L). This was especially observed in forested catchments where atmospheric N-depositions were the major source for nitrate availability. In these catchments, we also found long-term increases of phosphate concentrations. Therefore, we argue that dissolved iron, DOC and phosphate were jointly released under iron-reducing conditions when nitrate as a competing electron acceptor was too low in concentrations to prevent the microbial iron reduction. In contrast, we could not explain the observed increasing trends in DOC, iron and phosphate concentrations by the long-term trends of pH, sulfate or precipitation. Altogether this study gives strong evidence that both, source and long-term increases in DOC are primarily controlled by riparian wetland soils within the catchments. Here, the achievement of a long-term reduction in nitrogen deposition may in turn lead to a more pronounced iron reduction and a subsequent release of DOC and other iron-bound substances such as phosphate.

One Year of Monthly N and O Isotope Measurements in Nitrate from 18 Streamwater Monitoring Stations Within the Predominantly Pastoral Upper Manawatu Catchment, New Zealand

NASA Astrophysics Data System (ADS)

Baisden, W. T.; Douence, C.

2010-12-01

New Zealand's intensive pastoral agricultural systems have a significant impact on water quality due to nitrogen loading in rivers. A research programme has been designed to develop indicators of the sources and denitrification losses of nitrate in streamwater. This work describes the results of one year of monthly measurements at ~18 monitoring locations in the 1260 square km upper Manawatu River catchment. The catchment was chosen for study because it is among the most pastoral catchments in New Zealand, with little non-pastoral agriculture and limited forest area outside of the Tararua mountain range on the west side of the catchment. The use of N and O isotope ratios in nitrate has considerable potential to elucidate the sources and fate of nitrate with greater precision than in most other nations due to the lack of nitrate in atmospheric deposition and the lack of nitrates used as fertilizer. We measured N and O isotope ratios in nitrate plus nitrite using cadmium and azide chemical denitrification method, and refer to the results as nitrate for brevity due to low nitrite concentrations. When examined as annual averages at each monitoring site, we found the lowest N and O isotope ratios in our only site draining native forest. All agricultural monitoring sites sit approximately on a 1:1 line, enriched in N-15 and O-18 by 2-6 per mil relative to the native forest subcatchment. The three main effluent point sources in the catchment demonstrated unexpected variability in isotope ratios. Two modern sewage treatment ponds had N and O isotope ratios close to those found in agricultural catchments, while a closed meat freezing factory effluent pond had isotope ratios strongly enriched in N-15 and O-18. The lack of summer low flows during monitoring period, combined with the variability in isotope ratios from point source, appeared to be responsible for our inability to clearly detect the effect of point sources in the isotope data from stations upstream and downstream of the point source inputs. Month-to-month variation in some catchments sat near the 1:1 line expected for denitrification as the primary driver of variability in isotope ratios, but the data from many stations including river's main stem was more complex. Overall, we are hopeful about the potential for the development of isotope indicators as planned. Specifically, our results tentatively support the use of the O isotope composition of soil water as a function of elevation and irrigation, and N isotope composition of soil N as a function of agricultural intensity driving the use of N and O isotopes to identify sources. While diffusion processes appear to suppress the isotope effect associated with denitrification, it may be observable and consistent in smaller and more uniform subcatchments. These smaller subcatchments will therefore become an increasing focus of our study. If successful, the indicators we intend to develop have the potential to work within a nitrogen cap and trade scheme for the catchment, providing an important efficiency tool to enable agriculture intensification in areas of effective N removal while targeting areas of poor nitrogen removal for decreased agricultural intensity or alternate land uses.

Determination of dominant sources of nitrate contamination in transboundary (Russian Federation/Ukraine) catchment with heterogeneous land use.

PubMed

Vystavna, Y; Diadin, D; Grynenko, V; Yakovlev, V; Vergeles, Y; Huneau, F; Rossi, P M; Hejzlar, J; Knöller, K

2017-09-18

Nitrate contamination of surface water and shallow groundwater was studied in transboundary (Russia/Ukraine) catchment with heterogeneous land use. Dominant sources of nitrate contamination were determined by applying a dual δ 15 N-NO 3 and δ 18 O-NO 3 isotope approach, multivariate statistics, and land use analysis. Nitrate concentration was highly variable from 0.25 to 22 mg L -1 in surface water and from 0.5 to 100 mg L -1 in groundwater. The applied method indicated that sewage to surface water and sewage and manure to groundwater were dominant sources of nitrate contamination. Nitrate/chloride molar ratio was added to support the dual isotope signature and indicated the contribution of fertilizers to the nitrate content in groundwater. Groundwater temperature was found to be an additional indicator of manure and sewerage leaks in the shallow aquifer which has limited protection and is vulnerable to groundwater pollution.

Responses of stream nitrate and dissolved organic carbon loadings to hydrological forcing and climate change in an upland forest of the northeast USA

USGS Publications Warehouse

Sebestyen, Stephen D.; Boyer, Elizabeth W.; Shanley, James B.

2009-01-01

[1] In coming decades, higher annual temperatures, increased growing season length, and increased dormant season precipitation are expected across the northeastern United States in response to anthropogenic forcing of global climate. We synthesized long-term stream hydrochemical data from the Sleepers River Research Watershed in Vermont, United States, to explore the relationship of catchment wetness to stream nitrate and DOC loadings. We modeled changes in growing season length and precipitation patterns to simulate future climate scenarios and to assess how stream nutrient loadings respond to climate change. Model results for the 2070–2099 time period suggest that stream nutrient loadings during both the dormant and growing seasons will respond to climate change. During a warmer climate, growing season stream fluxes (runoff +20%, nitrate +57%, and DOC +58%) increase as more precipitation (+28%) and quick flow (+39%) occur during a longer growing season (+43 days). During the dormant season, stream water and nutrient loadings decrease. Net annual stream runoff (+8%) and DOC loading (+9%) increases are commensurate with the magnitude of the average increase of net annual precipitation (+7%). Net annual stream water and DOC loadings are primarily affected by increased dormant season precipitation. In contrast, decreased annual loading of stream nitrate (−2%) reflects a larger effect of growing season controls on stream nitrate and the effects of lengthened growing seasons in a warmer climate. Our findings suggest that leaching of nitrate and DOC from catchment soils will be affected by anthropogenic climate forcing, thereby affecting the timing and magnitude of annual stream loadings in the northeastern United States.

Responses of stream nitrate and DOC loadings to hydrological forcing and climate change in an upland forest of the northeastern United States

USGS Publications Warehouse

Sebestyen, S.D.; Boyer, E.W.; Shanley, J.B.

2009-01-01

In coming decades, higher annual temperatures, increased growing season length, and increased dormant season precipitation are expected across the northeastern United States in response to anthropogenic forcing of global climate. We synthesized long-term stream hydrochemical data from the Sleepers River Research Watershed in Vermont, United States, to explore the relationship of catchment wetness to stream nitrate and DOC loadings. We modeled changes in growing season length and precipitation patterns to simulate future climate scenarios and to assess how stream nutrient loadings respond to climate change. Model results for the 2070-2099 time period suggest that stream nutrient loadings during both the dormant and growing seasons will respond to climate change. During a warmer climate, growing season stream fluxes (runoff+20%, nitrate +57%, and DOC +58%) increase as more precipitation (+28%) and quick flow (+39%) occur during a longer growing season (+43 days). During the dormant season, stream water and nutrient loadings decrease. Net annual stream runoff (+8%) and DOC loading (+9%) increases are commensurate with the magnitude of the average increase of net annual precipitation (+7%). Net annual stream water and DOC loadings are primarily affected by increased dormant season precipitation. In contrast, decreased annual loading of stream nitrate (-2%) reflects a larger effect of growing season controls on stream nitrate and the effects of lengthened growing seasons in a warmer climate. Our findings suggest that leaching of nitrate and DOC from catchment soils will be affected by anthropogenic climate forcing, thereby affecting the timing and magnitude of annual stream loadings in the northeastern United States. Copyright 2009 by the American Geophysical Union.

Denitrification constitutes an import N sink in subtropical N-saturated forests - a nitrate dual isotope study

NASA Astrophysics Data System (ADS)

Yu, Lonfei; Zhu, Jing; Mulder, Jan; Dörsch, Peter

2016-04-01

Forests in China receive variable but increasing amounts of nitrogen from the atmosphere causing N saturation and nitrate runoff. Surprisingly high N-retention has been reported from subtropical forests, suggesting active mechanisms of N removal. Here we report a multi-site study of 15N and 18O abundances in soil nitrate (NO3-) across seven forested catchments spanning from temperate to subtropical China. In each catchment, samples were taken on one date during one or two summer along the hydrological continuum comprising hillslope positions and riparian zones. We had found previously in an intensive multi-year study at one of the sites, that the spatial pattern of summertime 15N and 18O in soil nitrate was remarkably stable across climatically distinct years, suggesting persistent N removal by denitrification at the foot of hill slopes and in groundwater discharge zones (Yu et al., submitted). In the present study, we extended the scope to five subtropical Chinese catchments and compared them with two temperate forests. Our data confirm the general pattern of efficient nitrification on hillslopes and strong denitrification in riparian zones in the subtropical catchments but not in the temperate ones. This is likely because high summer rainfalls at the monsoonal sites connect N mineralization and oxidation in upland positions with NO3- reduction in ground water discharge zones via NO3- runoff, rendering subtropical forests an efficient sink for reactive N with implications for regional N budgets. The impact of N deposition level, hydrology and edaphic factors on the predictive power of nitrate isotope signatures for N removal processes will be discussed. Yu L, Zhu J, Mulder J, Dörsch P: Spatiotemporal patterns in dual nitrate isotopes reveal efficient N transformation and denitrification along a hydrological continuum in N-saturated, subtropical forest. Submitted

Preferential Flow Paths In A Karstified Spring Catchment: A Study Of Fault Zones As Conduits To Rapid Groundwater Flow

NASA Astrophysics Data System (ADS)

Kordilla, J.; Terrell, A. N.; Veltri, M.; Sauter, M.; Schmidt, S.

2017-12-01

In this study we model saturated and unsaturated flow in the karstified Weendespring catchment, located within the Leinetal graben in Goettingen, Germany. We employ the finite element COMSOL Multiphysics modeling software to model variably saturated flow using the Richards equation with a van Genuchten type parameterization. As part of the graben structure, the Weende spring catchment is intersected by seven fault zones along the main flow path of the 7400 m cross section of the catchment. As the Weende spring is part of the drinking water supply in Goettingen, it is particularly important to understand the vulnerability of the catchment and effect of fault zones on rapid transport of contaminants. Nitrate signals have been observed at the spring only a few days after the application of fertilizers within the catchment at a distance of approximately 2km. As the underlying layers are known to be highly impermeable, fault zones within the area are likely to create rapid flow paths to the water table and the spring. The model conceptualizes the catchment as containing three hydrogeological limestone units with varying degrees of karstification: the lower Muschelkalk limestone as a highly conductive layer, the middle Muschelkalk as an aquitard, and the upper Muschelkalk as another conductive layer. The fault zones are parameterized based on a combination of field data from quarries, remote sensing and literary data. The fault zone is modeled considering the fracture core as well as the surrounding damage zone with separate, specific hydraulic properties. The 2D conceptual model was implemented in COMSOL to study unsaturated flow at the catchment scale using van Genuchten parameters. The study demonstrates the importance of fault zones for preferential flow within the catchment and its effect on the spatial distribution of vulnerability.

The effectiveness of agricultural stewardship for improving water quality at the catchment scale: Experiences from an NVZ and ECSFDI watershed

NASA Astrophysics Data System (ADS)

Kay, Paul; Grayson, Richard; Phillips, Martin; Stanley, Karen; Dodsworth, Alan; Hanson, Ann; Walker, Andrew; Foulger, Miles; McDonnell, Iain; Taylor, Simon

2012-02-01

SummaryAgriculture is estimated to be responsible for 70% of nitrate and 30-50% of phosphorus pollution, contributing to ecological and water treatment problems. Despite the fact that significant gaps remain in our understanding, it is known that agricultural stewardship can be highly effective in controlling water pollution at the plot and field scales. Knowledge at the catchment scale is, to a large extent, entirely lacking though and this is of paramount concern given that the catchment is the management unit used by regulatory authorities. The few studies that have examined the impact of agricultural stewardship at the catchment scale have found that Nitrate Vulnerable Zones (NVZs) in the UK have resulted in little improvement in water quality which concurs with the current catchment study. In addition to NVZs, there was little evidence to suggest that the England Catchment Sensitive Farming Delivery Initiative had impacted water quality and suggestions have been made for improvements, such as ensuring that stewardship measures are used in key pollution source areas and their implementation and impacts are monitored more closely. This will be essential if agricultural catchment management schemes are going to provide the benefits expected of them. Nevertheless, more intensive monitoring than that carried out by regulators showed a significant trend in decreasing winter nitrate peaks in some streams which is hypothesised to be due to recent reduced inorganic fertiliser application as a result of increasing prices. It was concluded that, collectively, these findings indicate that agricultural stewardship measures have the potential to improve water quality at the catchment scale but that voluntary schemes with insufficient financial reward or regulatory pressure are unlikely to be successful.

Identification of groundwater nitrate sources in pre-alpine catchments: a multi-tracer approach

NASA Astrophysics Data System (ADS)

Stoewer, Myriam; Stumpp, Christine

2014-05-01

Porous aquifers in pre-alpine areas are often used as drinking water resources due to their good water quality status and water yield. Maintaining these resources requires knowledge about possible sources of pollutants and a sustainable management practice in groundwater catchment areas. Of particular interest in agricultural areas, like in pre-alpine regions, is limiting nitrate input as main groundwater pollutant. Therefore, the objective of the presented study is i) to identify main nitrate sources in a pre-alpine groundwater catchment with current low nitrate concentration using stable isotopes of nitrate (d18O and d15N) and ii) to investigate seasonal dynamics of nitrogen compounds. The groundwater catchment areas of four porous aquifers are located in Southern Germany. Most of the land use is organic grassland farming as well as forestry and residential area. Thus, potential sources of nitrate mainly are mineral fertilizer, manure/slurry, leaking sewage system and atmospheric deposition of nitrogen compounds. Monthly freshwater samples (precipitation, river water and groundwater) are analysed for stable isotope of water (d2H, d18O), the concentration of major anions and cations, electrical conductivity, water temperature, pH and oxygen. In addition, isotopic analysis of d18O-NO3- and d15N-NO3- for selected samples is carried out using the denitrifier method. In general, all groundwater samples were oxic (10.0±2.6mg/L) and nitrate concentrations were low (0.2 - 14.6mg/L). The observed nitrate isotope values in the observation area compared to values from local precipitation, sewage, manure and mineral fertilizer as well as to data from literature shows that the nitrate in freshwater samples is of microbial origin. Nitrate derived from ammonium in fertilizers and precipitation as well as from soil nitrogen. It is suggested that a major potential threat to the groundwater quality is ammonia and ammonium at a constant level mainly from agriculture activities as well as continuously release of nitrogen stored in agricultural soils due to mineralization processes. In all groundwater and river water samples a seasonal variation of nitrate sources and concentration is absent but nitrate in precipitation shows a clear seasonal variation with peaks in spring and fall according to agricultural activity. This points to dilution effects of high nitrate inputs due to the large groundwater volume and mean residence time and highlights the function of soil as initial sink for nitrogen compounds delivered by fertilizer. Even though nitrate contamination was low in the study area, the results emphasize the importance of reducing additional nitrate sources in pre-alpine oxic aquifers. This will maintain the good water quality status of the aquifers and enable its use for drinking water supply.

Memory of the Lake Rotorua catchment - time lag of the water in the catchment and delayed arrival of contaminants from past land use activities

NASA Astrophysics Data System (ADS)

Morgenstern, Uwe; Daughney, Christopher J.; Stewart, Michael K.; McDonnell, Jeffrey J.

2013-04-01

The transit time distribution of streamflow is a fundamental descriptor of the flowpaths of water through a catchment and the storage of water within it, controlling its response to landuse change, pollution, ecological degradation, and climate change. Significant time lags (catchment memory) in the responses of streams to these stressors and their amelioration or restoration have been observed. Lag time can be quantified via water transit time of the catchment discharge. Mean transit times can be in the order of years and decades (Stewart et al 2012, Morgenstern et al., 2010). If the water passes through large groundwater reservoirs, it is difficult to quantify and predict the lag time. A pulse shaped tracer that moves with the water can allow quantification of the mean transit time. Environmental tritium is the ideal tracer of the water cycle. Tritium is part of the water molecule, is not affected by chemical reactions in the aquifer, and the bomb tritium from the atmospheric nuclear weapons testing represents a pulse shaped tracer input that allows for very accurate measurement of the age distribution parameters of the water in the catchment discharge. Tritium time series data from all catchment discharges (streams and springs) into Lake Rotorua, New Zealand, allow for accurate determination of the age distribution parameters. The Lake Rotorua catchment tritium data from streams and springs are unique, with high-quality tritium data available over more than four decades, encompassing the time when the bomb-tritium moved through the groundwater system, and from a very high number of streams and springs. Together with the well-defined tritium input into the Rotorua catchment, this data set allows for the best understanding of the water dynamics through a large scale catchment, including validation of complicated water mixing models. Mean transit times of the main streams into the lake range between 27 and 170 years. With such old water discharging into the lake, most of the water inflows into the lake are not yet fully representing the nitrate loading in their sub-catchments from current land use practises. These water inflows are still 'diluted' by pristine old water, but over time, the full amount of nitrate load will arrive at the lake. With the age distribution parameters, it is possible to predict the increase in nitrate load to the lake via the groundwater discharges. All sub-catchments have different mean transit times. The mean transit times are not necessarily correlated with observable hydrogeologic properties like hydraulic conductivity and catchment size. Without such age tracer data, it is therefore difficult to predict mean transit times (lag times, memory) of water transfer through catchments. References: Stewart, M.K., Morgenstern, U., McDonnell, J.J., Pfister, L. (2012). The 'hidden streamflow' challenge in catchment hydrology: A call to action for streamwater transit time analysis. Hydrol. Process. 26,2061-2066, Invited commentary. DOI: 10.1002/hyp.9262 Morgenstern, U., Stewart, M.K., and Stenger, R. (2010) Dating of streamwater using tritium in a post nuclear bomb pulse world: continuous variation of mean transit time with streamflow, Hydrol. Earth Syst. Sci, 14, 2289-2301

Are groundwater nitrate concentrations reaching a turning point in some chalk aquifers?

PubMed

Smith, J T; Clarke, R T; Bowes, M J

2010-09-15

In past decades, there has been much scientific effort dedicated to the development of models for simulation and prediction of nitrate concentrations in groundwaters, but producing truly predictive models remains a major challenge. A time-series model, based on long-term variations in nitrate fertiliser applications and average rainfall, was calibrated against measured concentrations from five boreholes in the River Frome catchment of Southern England for the period spanning from the mid-1970s to 2003. The model was then used to "blind" predict nitrate concentrations for the period 2003-2008. To our knowledge, this represents the first "blind" test of a model for predicting nitrate concentrations in aquifers. It was found that relatively simple time-series models could explain and predict a significant proportion of the variation in nitrate concentrations in these groundwater abstraction points (R(2)=0.6-0.9 and mean absolute prediction errors 4.2-8.0%). The study highlighted some important limitations and uncertainties in this, and other modelling approaches, in particular regarding long-term nitrate fertiliser application data. In three of the five groundwater abstraction points (Hooke, Empool and Eagle Lodge), once seasonal variations were accounted for, there was a recent change in the generally upward historical trend in nitrate concentrations. This may be an early indication of a response to levelling-off (and declining) fertiliser application rates since the 1980s. There was no clear indication of trend change at the Forston and Winterbourne Abbas sites nor in the trend of nitrate concentration in the River Frome itself from 1965 to 2008. Copyright 2010 Elsevier B.V. All rights reserved.

Persistent Influences of the 2002 Hayman Fire on Stream Nitrate and Dissolved Organic Carbon

NASA Astrophysics Data System (ADS)

Rhoades, C.; Pierson, D. N.; Fegel, T. S., II; Chow, A. T.; Covino, T. P.

2016-12-01

Large, high severity wildfires alter the physical and biological conditions that determine how watersheds retain and release nutrients and regulate stream water quality. For five years after the 2002 Hayman Fire burned in Colorado conifer forests, stream nitrate concentrations and export increased steadily in watersheds with extensive high-severity burning. Stream temperature and turbidity also increased in relation to the extent of high-severity burning and remained elevated above background levels throughout the initial five year post-fire period. Our recent sampling documents that 14 years after the Hayman Fire stream nitrate remains an order of magnitude higher in extensively-burned (35-90%) compared to unburned watersheds (0.2 vs 2.8 mg L-1). Nitrate represents 83% of the total dissolved N in extensively-burned watersheds compared to 29% in unburned watersheds. In contrast, dissolved organic carbon (DOC), was highest in watersheds that burned to a moderate extent (10-20%) and lowest in those with extensive burning. Catchments with a moderate extent burned had DOC concentrations 2.5 and 1.7 times more than those with extensive burning and unburned catchments, respectively. Peak concentrations of DOC and nitrate track the rising limb of the streamflow hydrograph and reach a maximum in May, but patterns among burn extent categories were seasonally consistent. Current riparian conditions are linked to stream nitrate in burned watersheds. For example, stream nitrate increases proportionally to the extent of riparian zones with low shrub cover (R2 = 0.76). We found signs of watershed recovery compared to the initial post-fire period; stream temperature and turbidity remained elevated in extensively burned catchments, but increases were only significant during the spring season. The persistent stream nitrate concentrations as well as the relation between riparian cover and post-fire stream nitrate may help prioritize restoration planting efforts and mitigate chronic, elevated nitrate export from burned watersheds.

European nitrogen policies, nitrate in rivers and the use of the INCA model

NASA Astrophysics Data System (ADS)

Skeffington, R.

This paper is concerned with nitrogen inputs to European catchments, how they are likely to change in future, and the implications for the INCA model. National N budgets show that the fifteen countries currently in the European Union (the EU-15 countries) probably have positive N balances - that is, N inputs exceed outputs. The major sources are atmospheric deposition, fertilisers and animal feed, the relative importance of which varies between countries. The magnitude of the fluxes which determine the transport and retention of N in catchments is also very variable in both space and time. The most important of these fluxes are parameterised directly or indirectly in the INCA Model, though it is doubtful whether the present version of the model is flexible enough to encompass short-term (daily) variations in inputs or longer-term (decadal) changes in soil parameters. As an aid to predicting future changes in deposition, international legislation relating to atmospheric N inputs and nitrate in rivers is reviewed briefly. Atmospheric N deposition and fertiliser use are likely to decrease over the next 10 years, but probably not sufficiently to balance national N budgets.

Streamwater nitrate concentrations in six agricultural catchments in Scotland.

PubMed

Hooda, P S; Moynagh, M; Svoboda, I F; Thurlow, M; Stewart, M; Thomson, M; Anderson, H A

1997-08-01

The concentrations of nitrate-N (NO3-N) in catchment inputs and outputs have been compared and contrasted between 6 farm catchments in Scotland, 3 in the West and 3 in the North-East. Forms of intensive animal farming ranging between beef and dairy cattle, sheep and poultry give different sources for potential NO3-N leakage from the systems. While stream reaches bordered by intensive cereal production give rise to the largest inputs to surface waters, climatic influences result in the more-efficient use of fertilizer- and farm waste-N in the West, and an enhanced potential for N-loss to waters in the cooler North-East, regardless of the N-inputs being considerably lower in the latter region. Although the EC Nitrate Directive limit of 11.3 mg NO3-N 1(-1) was not exceeded, peak values occurring during summer baseflows and autumn soil rewetting were commonly larger than the 'target' maximum concentration of 5.65 mg NO3-N 1-1.

Understanding the relationship between DOC and nitrate export and dominant rainfall-runoff processes through long-term high frequency measurements

NASA Astrophysics Data System (ADS)

Schwab, Michael; Klaus, Julian; Pfister, Laurent; Weiler, Markus

2016-04-01

Over the past decades, stream sampling protocols for hydro-geochemical parameters were often limited by logistical and technological constraints. While long-term monitoring protocols were typically based on weekly sampling intervals, high frequency sampling was commonly limited to a few single events. In our study, we combined high frequency and long-term measurements to understand the DOC and nitrate behaviour and dynamics for different runoff events and seasons. Our study area is the forested Weierbach catchment (0.47 km2) in Luxembourg. The fractured schist bedrock is covered by cambisol soils. The runoff response of the catchment is characterized by a double peak behaviour. A first discharge peak occurs during or right after a rainfall event (triggered by fast near surface runoff generation processes), while a second delayed peak lasts several days (generated by subsurface flow/ shallow groundwater flow). Peaks in DOC concentrations are closely linked to the first discharge peak, whereas nitrate concentrations follow the second peak. Our observations were carried out with the field deployable instrument spectro::lyser (scan Messtechnik GmbH). This instrument relies on the principles of UV-Vis spectrometry and measures DOC and nitrate concentrations. The measurements were carried out at a high frequency of 15 minutes in situ in the Weierbach creek for more than two years. In addition, a long-term validation was carried out with data obtained from the analysis of water collected with automatic samplers. The long-term, high-frequency measurements allowed us to calculate a complete and detailed balance of DOC and nitrate export over two years. Transport behaviour of the DOC and nitrate showed different dynamics between the first and second hydrograph peaks. DOC is mainly exported during first peaks, while nitrate is mostly exported during the delayed second peaks. In combination with other measurements in the catchment, the long and detailed observations have enabled us to derive relationships between DOC and nitrate export and different catchment states: soil wetness and groundwater levels, precipitation and seasonality. Altogether, the long-term and high-frequency time series provides the opportunity to study DOC and nitrate export without having to just rely only on either a few single event measurements or coarse measurement protocols.

Estimates of nitrate loads and yields from groundwater to streams in the Chesapeake Bay watershed based on land use and geology

USGS Publications Warehouse

Terziotti, Silvia; Capel, Paul D.; Tesoriero, Anthony J.; Hopple, Jessica A.; Kronholm, Scott C.

2018-03-07

The water quality of the Chesapeake Bay may be adversely affected by dissolved nitrate carried in groundwater discharge to streams. To estimate the concentrations, loads, and yields of nitrate from groundwater to streams for the Chesapeake Bay watershed, a regression model was developed based on measured nitrate concentrations from 156 small streams with watersheds less than 500 square miles (mi2 ) at baseflow. The regression model has three predictive variables: geologic unit, percent developed land, and percent agricultural land. Comparisons of estimated and actual values within geologic units were closely matched. The coefficient of determination (R2 ) for the model was 0.6906. The model was used to calculate baseflow nitrate concentrations at over 83,000 National Hydrography Dataset Plus Version 2 catchments and aggregated to 1,966 total 12-digit hydrologic units in the Chesapeake Bay watershed. The modeled output geospatial data layers provided estimated annual loads and yields of nitrate from groundwater into streams. The spatial distribution of annual nitrate yields from groundwater estimated by this method was compared to the total watershed yields of all sources estimated from a Chesapeake Bay SPAtially Referenced Regressions On Watershed attributes (SPARROW) water-quality model. The comparison showed similar spatial patterns. The regression model for groundwater contribution had similar but lower yields, suggesting that groundwater is an important source of nitrogen for streams in the Chesapeake Bay watershed.

Sources and mechanisms of nitrate and orthophosphate transport in urban stormwater runoff from residential catchments.

PubMed

Yang, Yun-Ya; Toor, Gurpal S

2017-04-01

Nutrients export from residential catchments contributes to water quality impairment in urban water bodies. We investigated the concentrations, transport mechanisms, and sources of nitrate-nitrogen (NO 3 -N) and orthophosphate-phosphorus (PO 4 -P) in urban stormwater runoff generated in residential catchments in Tampa Bay, Florida, United States. Street runoff samples, collected over 21 storm events, were supplemented with rainfall and roof runoff samples from six representative residential catchments. Samples were analyzed for N and P forms, N and oxygen (O) isotopes of nitrate (δ 18 O-NO 3 - and δ 15 N-NO 3 - ), and δ 18 O and hydrogen (δD) isotopes of water (H 2 O). We found that the main NO 3 -N source in street runoff was atmospheric deposition (range: 35-64%), followed by chemical N fertilizers (range: 1-39%), and soil and organic N (range: 7-33%), whereas PO 4 -P in the street runoff likely originated from erosion of soil particles and mineralization from organic materials (leaves, grass clippings). The variability in the sources and concentrations of NO 3 -N and PO 4 -P across catchments is attributed to different development designs and patterns, use of various fill materials during land development, and landscaping practices. This data can be useful to develop strategies to offset the impacts of urban development (e.g., designs and patterns resulting in variable impervious areas) and management (e.g., fertilizer use, landscaping practices) on NO 3 -N and PO 4 -P transport in urban residential catchments. Copyright © 2017 Elsevier Ltd. All rights reserved.

Nitrogen budgets on Appalachian forest catchments

Treesearch

David R. DeWalle

1997-01-01

Variations in nitrogen losses in streamflow on catchments in the Appalachians suggests that the level of nitrogen retention in hardwood forests varies widely. Stream losses of dissolved nitrate-N on several small experimental forested catchments range from about 0.2 to 8.5 kg ha-1 y-1. This wide range of losses is equivalent to less than 10% to nearly 100% of measured...

Two tales of legacy effects on stream nutrient behaviour

NASA Astrophysics Data System (ADS)

Bieroza, M.; Heathwaite, A. L.

2017-12-01

Intensive agriculture has led to large-scale land use conversion, shortening of flow pathways and increased loads of nutrients in streams. This legacy results in gradual build-up of nutrients in agricultural catchments: in soil for phosphorus (biogeochemical legacy) and in the unsaturated zone for nitrate (hydrologic legacy), controlling the water quality in the long-term. Here we investigate these effects on phosphorus and nitrate stream concentrations using high-frequency (10-5 - 100 Hz) sampling with in situ wet-chemistry analysers and optical sensors. Based on our 5 year study, we observe that storm flow responses differ for both nutrients: phosphorus shows rapid increases (up to 3 orders of magnitude) in concentrations with stream flow, whereas nitrate shows both dilution and concentration effects with increasing flow. However, the range of nitrate concentrations change is narrow (up to 2 times the mean) and reflects chemostatic behaviour. We link these nutrient responses with their dominant sources and flow pathways in the catchment. Nitrate from agriculture (with the peak loading in 1983) is stored in the unsaturated zone of the Penrith Sandstone, which can reach up to 70 m depth. Thus nitrate legacy is related to a hydrologic time lag with long travel times in the unsaturated zone. Phosphorus is mainly sorbed to soil particles, therefore it is mobilised rapidly during rainfall events (biogeochemical legacy). The phosphorus stream response will however depend on how well connected is the stream to the catchment sources (driven by soil moisture distribution) and biogeochemical activity (driven by temperature), leading to both chemostatic and non-chemostatic responses, alternating on a storm-to-storm and seasonal basis. Our results also show that transient within-channel storage is playing an important role in delivery of phosphorus, providing an additional time lag component. These results show, that consistent agricultural legacy in the catchment (high historical loads of nutrients) has different effects on nutrients stream responses, depending on their dominant sources and pathways. Both types of time lags, biogeochemical for phosphorus and hydrologic for nitrate, need to be taken into account when designing and evaluating the effectiveness of the agri-environmental mitigation measures.

Using StorAge Selection Functions to Improve Simulation of Groundwater Nitrate Lag Times in the SWAT Modeling Framework.

NASA Astrophysics Data System (ADS)

Wilusz, D. C.; Fuka, D.; Cho, C.; Ball, W. P.; Easton, Z. M.; Harman, C. J.

2017-12-01

Intensive agriculture and atmospheric deposition have dramatically increased the input of reactive nitrogen into many watersheds worldwide. Reactive nitrogen can leach as nitrate into groundwater, which is stored and eventually released over years to decades into surface waters, potentially degrading water quality. To simulate the fate and transport of groundwater nitrate, many researchers and practitioners use the Soil and Water Assessment Tool (SWAT) or an enhanced version of SWAT that accounts for topographically-driven variable source areas (TopoSWAT). Both SWAT and TopoSWAT effectively assume that nitrate in the groundwater reservoir is well-mixed, which is known to be a poor assumption at many sites. In this study, we describe modifications to TopoSWAT that (1) relax the assumption of groundwater well-mixedness, (2) more flexibly parameterize groundwater transport as a time-varying distribution of travel times using the recently developed theory of rank StorAge Selection (rSAS) functions, and (3) allow for groundwater age to be represented by position on the hillslope or hydrological distance from the stream. The approach conceptualizes the groundwater aquifer as a population of water parcels entering as recharge with a particular nitrate concentration, aging as they move through storage, and eventually exiting as baseflow. The rSAS function selects the distribution of parcel ages that exit as baseflow based on a parameterized probability distribution; this distribution can be adjusted to preferentially select different distributions of young and old parcels in storage so as to reproduce (in principle) any form of transport. The modified TopoSWAT model (TopoSWAT+rSAS) is tested at a small agricultural catchment in the Eastern Shore, MD with an extensive hydrologic and hydrochemical data record for calibration and evaluation. The results examine (1) the sensitivity of TopoSWAT+rSAS modeling of nitrate transport to assumptions about the distribution of travel times of the groundwater aquifer, (2) which travel times are most likely at our study site based on available data, and (3) how TopoSWAT+rSAS performs and can be applied to other catchments.

Hydrological and water quality impact assessment of a Mediterranean limno-reservoir under climate change and land use management scenarios

NASA Astrophysics Data System (ADS)

Molina-Navarro, Eugenio; Trolle, Dennis; Martínez-Pérez, Silvia; Sastre-Merlín, Antonio; Jeppesen, Erik

2014-02-01

Water scarcity and water pollution constitute a big challenge for water managers in the Mediterranean region today and will exacerbate in a projected future warmer world, making a holistic approach for water resources management at the catchment scale essential. We expanded the Soil and Water Assessment Tool (SWAT) model developed for a small Mediterranean catchment to quantify the potential effects of various climate and land use change scenarios on catchment hydrology as well as the trophic state of a new kind of waterbody, a limno-reservoir (Pareja Limno-reservoir), created for environmental and recreational purposes. We also checked for the possible synergistic effects of changes in climate and land use on water flow and nutrient exports from the catchment. Simulations showed a noticeable impact of climate change in the river flow regime and consequently the water level of the limno-reservoir, especially during summer, complicating the fulfillment of its purposes. Most of the scenarios also predicted a deterioration of trophic conditions in the limno-reservoir. Fertilization and soil erosion were the main factors affecting nitrate and total phosphorus concentrations. Combined climate and land use change scenarios showed noticeable synergistic effects on nutrients exports, relative to running the scenarios individually. While the impact of fertilization on nitrate export is projected to be reduced with warming in most cases, an additional 13% increase in the total phosphorus export is expected in the worst-case combined scenario compared to the sum of individual scenarios. Our model framework may help water managers to assess and manage how these multiple environmental stressors interact and ultimately affect aquatic ecosystems.

Attributes for MRB_E2RF1 Catchments by Major River Basins in the Conterminous United States: Normalized Atmospheric Deposition for 2002, Nitrate (NO3)

USGS Publications Warehouse

Wieczorek, Michael; LaMotte, Andrew E.

2010-01-01

This tabular data set represents the average normalized (wet) deposition, in kilograms per square kilometer multiplied by 100, of Nitrate (NO3) for the year 2002 compiled for every MRB_E2RF1 catchment of the Major River Basins (MRBs, Crawford and others, 2006). Estimates of NO3 deposition are based on National Atmospheric Deposition Program (NADP) measurements (B. Larsen, U.S. Geological Survey, written. commun., 2007). De-trending methods applied to the year 2002 are described in Alexander and others, 2001. NADP site selection met the following criteria: stations must have records from 1995 to 2002 and have a minimum of 30 observations. The MRB_E2RF1 catchments are based on a modified version of the U.S. Environmental Protection Agency's (USEPA) ERF1_2 and include enhancements to support national and regional-scale surface-water quality modeling (Nolan and others, 2002; Brakebill and others, 2011). Data were compiled for every MRB_E2RF1 catchment for the conterminous United States covering New England and Mid-Atlantic (MRB1), South Atlantic-Gulf and Tennessee (MRB2), the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy (MRB3), the Missouri (MRB4), the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf (MRB5), the Rio Grande, Colorado, and the Great basin (MRB6), the Pacific Northwest (MRB7) river basins, and California (MRB8).

Hydrogeology of a Danish Riparian Lowland: the Importance of Groundwater Upwelling on Nitrate Removal

NASA Astrophysics Data System (ADS)

Steiness, M.; van't Veen, S. G. W.; Jessen, S.; Engesgaard, P. K.

2016-12-01

Riparian zones are critical interfaces between streams and uplands with many of the characteristics for being key areas for nitrate removal. The hydrogeology is a controlling factor for the source, flow paths, magnitude of groundwater discharge to the stream, nitrate loading, and therefore the occurrence of "hot spots" with increased denitrification. A riparian lowland was investigated through field studies (geophysics, hydrogeology), water quality assessment, and flow and reactive transport modelling. One of the objectives was to understand the role of the landscape and hydrogeology on diffusive versus focused groundwater discharge and also nitrate removal. The investigated riparian zone is characterized by diffusive flow of groundwater to the stream from the northern bank (from a maize field) and groundwater upwelling in several places with overland flow to the stream from south (wetland area). Nitrate is effectively removed by pyrite oxidation (as shown by the reactive transport model high sulphate concentrations) on the northern side, whereas the groundwater-fed springs carry up to 74 mg/L nitrate. Groundwater flow modeling shows that upwelling may account for almost 25 % of the flow to the stream. Two other riparian zones were subsequently included and, on the catchment scale, the occurrence of diffusive and focused discharge is found to be common suggesting that riparian zones in this area are only partly effective in removing nitrate.

Processes controlling the episodic streamwater transport of atrazine and other agrichemicals in an agricultural watershed

USGS Publications Warehouse

Hyer, Kenneth; Hornberger, George M.; Herman, Janet S.

2001-01-01

Episodic streamwater transport of atrazine (a common agricultural herbicide) and nutrients has been observed throughout agricultural watersheds in the United States and poses a serious threat to the quality of its water resources. Catchment-scale atrazine and nutrient transport processes after agricultural application are still poorly understood, and predicting episodic streamwater composition remains an elusive goal. We instrumented a 1.2-km2 agricultural catchment near Harrisonburg, Virginia, and examined streamwater, overland flow, soil water, groundwater, and rainfall during the summer of 1998. Storm chemographs demonstrated different patterns for constituents derived primarily from weathering (silica and calcium), compared to constituents derived primarily from early spring land applications (nitrate, atrazine, DOC, potassium, chloride, and sulfate). During storms, the concentrations of silica and calcium decreased, the atrazine response was variable, and the concentrations of nitrate, DOC, potassium, chloride, and sulfate increased; the elevated nitrate signal lagged several hours behind the other elevated constituents. Graphical and statistical analyses indicated a relatively stable spring-fed baseflow was modified by a mixture of overland flow and soil water. A rapid, short-duration overland-flow pulse dominated the streamflow early in the event and contributed most of the potassium, DOC, chloride, suspended sediment, and atrazine. A longer-duration soil–water pulse dominated the streamflow later in the event and contributed the nitrate as well as additional potassium, DOC, sulfate, and atrazine. The contributions to the episodic streamflow were quantified using a flushing model in which overland-flow and soil–water concentrations decreased exponentially with time during an episode. Flushing time constants for the overland-flow and soil–water reservoirs were calculated on a storm-by-storm basis using separate tracers for each time-variable reservoir. Initial component concentrations were estimated through regression analyses. Mass-balance calculations were used for flow separations and to predict the observed streamwater composition. Model forecasts indicated that reduced fertilizer and pesticide application (rather than elimination of overland-flow or soil–water contributions) was necessary to improve the episodic streamwater composition. This study provides important additional understanding of the catchment-scale processes by which land-applied pesticides and nutrients can move through agricultural systems.

The Catchment Runoff Attenuation Flux Tool, a minimum information requirement nutrient pollution model

NASA Astrophysics Data System (ADS)

Adams, R.; Quinn, P. F.; Bowes, M. J.

2015-04-01

A model for simulating runoff pathways and water quality fluxes has been developed using the minimum information requirement (MIR) approach. The model, the Catchment Runoff Attenuation Flux Tool (CRAFT), is applicable to mesoscale catchments and focusses primarily on hydrological pathways that mobilise nutrients. Hence CRAFT can be used to investigate the impact of flow pathway management intervention strategies designed to reduce the loads of nutrients into receiving watercourses. The model can help policy makers meet water quality targets and consider methods to obtain "good" ecological status. A case study of the 414 km2 Frome catchment, Dorset, UK, has been described here as an application of CRAFT in order to highlight the above issues at the mesoscale. The model was primarily calibrated on 10-year records of weekly data to reproduce the observed flows and nutrient (nitrate nitrogen - N; phosphorus - P) concentrations. Data from 2 years with sub-daily monitoring at the same site were also analysed. These data highlighted some additional signals in the nutrient flux, particularly of soluble reactive phosphorus, which were not observable in the weekly data. This analysis has prompted the choice of using a daily time step as the minimum information requirement to simulate the processes observed at the mesoscale, including the impact of uncertainty. A management intervention scenario was also run to demonstrate how the model can support catchment managers investigating how reducing the concentrations of N and P in the various flow pathways. This mesoscale modelling tool can help policy makers consider a range of strategies to meet the European Union (EU) water quality targets for this type of catchment.

Developing a nutrient pollution model to assist policy makers by using a meso-scale Minimum Information Requirement (MIR) approach

NASA Astrophysics Data System (ADS)

Adams, R.; Quinn, P. F.; Bowes, M. J.

2014-09-01

A model for simulating runoff pathways and water quality fluxes has been developed using the Minimum Information (MIR) approach. The model, the Catchment Runoff Attenuation Tool (CRAFT) is applicable to meso-scale catchments which focusses primarily on hydrological pathways that mobilise nutrients. Hence CRAFT can be used investigate the impact of management intervention strategies designed to reduce the loads of nutrients into receiving watercourses. The model can help policy makers, for example in Europe, meet water quality targets and consider methods to obtain "good" ecological status. A case study of the 414 km2 Frome catchment, Dorset UK, has been described here as an application of the CRAFT model. The model was primarily calibrated on ten years of weekly data to reproduce the observed flows and nutrient (nitrate nitrogen - N - and phosphorus - P) concentrations. Also data from two years of sub-daily high resolution monitoring at the same site were also analysed. These data highlighted some additional signals in the nutrient flux, particularly of soluble reactive phosphorus, which were not observable in the weekly data. This analysis has prompted the choice of using a daily timestep for this meso-scale modelling study as the minimum information requirement. A management intervention scenario was also run to show how the model can support catchment managers to investigate how reducing the concentrations of N and P in the various flow pathways. This scale appropriate modelling tool can help policy makers consider a range of strategies to to meet the European Union (EU) water quality targets for this type of catchment.

Legacy of contaminant N sources to the NO3- signature in rivers: a combined isotopic (δ15N-NO3-, δ18O-NO3-, δ11B) and microbiological investigation

NASA Astrophysics Data System (ADS)

Briand, Cyrielle; Sebilo, Mathieu; Louvat, Pascale; Chesnot, Thierry; Vaury, Véronique; Schneider, Maude; Plagnes, Valérie

2017-02-01

Nitrate content of surface waters results from complex mixing of multiple sources, whose signatures can be modified through N reactions occurring within the different compartments of the whole catchment. Despite this complexity, the determination of nitrate origin is the first and crucial step for water resource preservation. Here, for the first time, we combined at the catchment scale stable isotopic tracers (δ15N and δ18O of nitrate and δ11B) and fecal indicators to trace nitrate sources and pathways to the stream. We tested this approach on two rivers in an agricultural region of SW France. Boron isotopic ratios evidenced inflow from anthropogenic waters, microbiological markers revealed organic contaminations from both human and animal wastes. Nitrate δ15N and δ18O traced inputs from the surface leaching during high flow events and from the subsurface drainage in base flow regime. They also showed that denitrification occurred within the soils before reaching the rivers. Furthermore, this study highlighted the determinant role of the soil compartment in nitrate formation and recycling with important spatial heterogeneity and temporal variability.

δ(15)N and δ(18)O Reveal the Sources of Nitrate-Nitrogen in Urban Residential Stormwater Runoff.

PubMed

Yang, Yun-Ya; Toor, Gurpal S

2016-03-15

Nitrogen (N) sources are widely distributed in the complex urban environment. High-resolution data elucidating N sources in the residential catchments are not available. We used stable isotopes of N and oxygen (O) of nitrate (δ(18)O-NO3(-) and δ(15)N-NO3(-)) along with δ(18)O and hydrogen (δD) of water (H2O) to understand the sources and transformations of N in residential stormwater runoff. Stormwater runoff samples were collected over 25 stormwater events at 5 min intervals using an autosampler installed at the residential catchment outlet pipe that drained 31 low-density homes with a total drainage area of 0.11 km(2). Bayesian mixing model results indicated that atmospheric deposition (range 43-71%) and chemical N fertilizers (range <1-49%) were the dominant NO3-N sources in the stormwater runoff and that there was a continuum of source changes during the stormwater events. Further, the NO3-N transport in the stormwater runoff from the residential catchment was driven by mixing of multiple sources and biotic (i.e., nitrification) processes. This work suggests that a better understanding of N transport and sources is needed to reduce N export and improve water quality in urban water systems.

Integrated modelling of nitrate loads to coastal waters and land rent applied to catchment-scale water management.

PubMed

Refsgaard, A; Jacobsen, T; Jacobsen, B; Ørum, J-E

2007-01-01

The EU Water Framework Directive (WFD) requires an integrated approach to river basin management in order to meet environmental and ecological objectives. This paper presents concepts and full-scale application of an integrated modelling framework. The Ringkoebing Fjord basin is characterized by intensive agricultural production and leakage of nitrate constitute a major pollution problem with respect groundwater aquifers (drinking water), fresh surface water systems (water quality of lakes) and coastal receiving waters (eutrophication). The case study presented illustrates an advanced modelling approach applied in river basin management. Point sources (e.g. sewage treatment plant discharges) and distributed diffuse sources (nitrate leakage) are included to provide a modelling tool capable of simulating pollution transport from source to recipient to analyse the effects of specific, localized basin water management plans. The paper also includes a land rent modelling approach which can be used to choose the most cost-effective measures and the location of these measures. As a forerunner to the use of basin-scale models in WFD basin water management plans this project demonstrates the potential and limitations of comprehensive, integrated modelling tools.

Vulnerability of boreal zone for increased nitrogen loading due to climate change

NASA Astrophysics Data System (ADS)

Rankinen, Katri; Holmberg, Maria

2016-04-01

The observed rapid warming of the boreal zone that has been observed in Finland (0.14 °C by decade) is expected to continue (http://www.ipcc.ch/report/ar5/wg1/). Also precipitation is assumed to increase in future. These changes may increase nitrogen (N) loading from terrestrial environments to water bodies by accelerating soil organic matter decay and by increasing runoff. Nitrogen is limiting nutrient in the Baltic Sea but also in some lakes, so increased loading may increase eutrophication. Further, high nitrate levels in drinking water may cause methaemoglobin anemia for humans, and nitrate is also connected to increased risk of diabetes and cancer. Thus EU has set upper limits to nitrate concentration in drinking water. MONIMET (LIFE12 ENV/FI/000409) is a project about Climate Change Indicators and Vulnerability of Boreal Zone. We simulated N loading from two boreal catchments to the receiving waters by the dynamic, catchment scale model INCA in different climate change and land use change scenarios. We calculated land use specific N loading values for these two well monitored catchments that belong to the LTER (The Long Term Ecological Research) monitoring network. We upscaled the results to the larger river basin, combining them with the information on drinking water supply to assess the vulnerability. Specific emphasis was paid on nitrate concentrations in soil water and groundwater. In general, land use change has higher influence on N loading than increase in precipitation and temperature alone. Peak runoff will sift from snow melting peak in April to late autumn and winter. Growing season will become longer allowing more efficient vegetation uptake of nutrients. Small groundwater aquifers and private wells in the middle of agricultural fields will be in the risk of increased N concentrations, if agricultural N loading increases due to changes in agricultural patterns and land use change.

Climatic and physiographic controls on catchment-scale nitrate loss at different spatial scales: insights from a top-down model development approach

NASA Astrophysics Data System (ADS)

Shafii, Mahyar; Basu, Nandita; Schiff, Sherry; Van Cappellen, Philippe

2017-04-01

Dramatic increase in nitrogen circulating in the biosphere due to anthropogenic activities has resulted in impairment of water quality in groundwater and surface water causing eutrophication in coastal regions. Understanding the fate and transport of nitrogen from landscape to coastal areas requires exploring the drivers of nitrogen processes in both time and space, as well as the identification of appropriate flow pathways. Conceptual models can be used as diagnostic tools to provide insights into such controls. However, diagnostic evaluation of coupled hydrological-biogeochemical models is challenging. This research proposes a top-down methodology utilizing hydrochemical signatures to develop conceptual models for simulating the integrated streamflow and nitrate responses while taking into account dominant controls on nitrate variability (e.g., climate, soil water content, etc.). Our main objective is to seek appropriate model complexity that sufficiently reproduces multiple hydrological and nitrate signatures. Having developed a suitable conceptual model for a given watershed, we employ it in sensitivity studies to demonstrate the dominant process controls that contribute to the nitrate response at scales of interest. We apply the proposed approach to nitrate simulation in a range of small to large sub-watersheds in the Grand River Watershed (GRW) located in Ontario. Such multi-basin modeling experiment will enable us to address process scaling and investigate the consequences of lumping processes in terms of models' predictive capability. The proposed methodology can be applied to the development of large-scale models that can help decision-making associated with nutrients management at regional scale.

Identifying the impacts of land use on water and nutrient cycling in the South-West Mau, Kenya

NASA Astrophysics Data System (ADS)

Jacobs, Suzanne; Weeser, Björn; Breuer, Lutz; Butterbach-Bahl, Klaus; Rufino, Mariana

2016-04-01

The Mau Forest is the largest closed canopy forest system and indigenous montane forest in Kenya, covering approximately 400,000 ha. It is the source of twelve major rivers in the Rift Valley and Western Kenya and one of Kenya's five 'water towers' that provide around 10 million people with fresh water. Significant areas have been affected by deforestation and land use changes in the past decades, resulting in a loss of approx. 25% of the forest area. Recent changes in downstream water supply are discussed to be attributed to land use change, though compelling scientific evidence is still lacking. The study area is located in the South-West Mau as a part of the Sondu River basin that drains into Lake Victoria. This area has suffered a forest loss of 25% through conversion of natural forest to smallholder agriculture and tea/tree plantations. A nested catchment approach has been applied, whereby automatic measurement equipment for monitoring discharge, turbidity, nitrate, total and dissolved organic carbon, electrical conductivity and water temperature at a 10 minute interval has been set up at the outlets of three sub-catchments of 27 - 36 km² and the outlet of the 1023 km² major catchment. The dominant land use in the sub-catchments is either natural forest, tea/tree plantation or smallholder agriculture. The river data is complemented by six precipitation gauging stations and three climate stations, that all measure at the same interval. Installed during October 2014, the systems have collected high resolution data for one and a half year now. The high resolution dataset is being analysed for patterns in stream flow and water quality during dry and wet seasons as well as diurnal cycling of nitrate. The results of the different sub-catchments are compared to identify the role of land use in water and nutrient cycling. First results of the high temporal resolution data already indicate that the different types of land use affect the stream nitrate concentration. In addition to that the high resolution allows to investigate diurnal patterns, showing a shift in nitrate concentrations between wet and dry seasons. Additional spatial stream water snapshot sampling campaigns within the major catchment, as well as sampling for End Member Mixing Analysis (EMMA) and analysis of stable isotopes of precipitation, throughfall, stream water and soil and ground water is ongoing and will provide further information to increase our understanding of hydrological and biogeochemical processes and how these are affected by land use in the Mau Forest. We will report results from six snapshot sampling campaigns that depict the impact of tea/tree plantations on nitrate concentrations and an influence of land use on catchment specific discharge.

Nutrient Flux from Mediterranean Coastal Streams: Carpinteria Valley, California

NASA Astrophysics Data System (ADS)

Robinson, T. H.; Leydecker, A.; Melack, J. M.; Keller, A. A.

2003-12-01

Along the southern California coast, near Santa Barbara, California, we are measuring nutrient export from specific land uses and developing a model to predict nutrient export at a watershed scale. The area is characterized by a Mediterranean-like climate and short steep catchments producing flashy runoff. The six land uses include chaparral, avocado orchards, greenhouse agriculture, open-field nurseries, and residential and commercial development. Sampling sites are located on defined drainages or storm drains that collect runoff from relatively homogeneous areas representing each land use. Stream water samples are taken once a week during the rainy season, every two weeks during the dry season and every one to four hours during storms. Samples are analyzed for ammonium, nitrate, phosphate, total dissolved nitrogen and particulate nitrogen and phosphorus. Intensive sampling at the thirteen sites of the study was conducted throughout Water Year (WY) 2002 and 2003. We determine discharge from measurements of stage derived from pressure transducers at all sampling sites. This information is then converted to flux at a high temporal resolution. Wet and dry season sampling has shown that nitrate baseflow concentrations vary over three orders of magnitude, from a few micromoles per liter in undeveloped catchments, to a few 100 æmol/L in agricultural and urban watersheds, to 1000 æmol/L where intensive "greenhouse" agriculture dominates. Nitrate loading ranged from a few moles per hectare per storm at undeveloped and residential sites to hundreds at the greenhouse site. Phosphate concentrations show a similar, but smaller, variation from 1 to 100 æmol/L, although the loading is comparable at 1-100 moles/ha-storm. Stormflow concentrations fluctuate with the storm hydrograph: phosphate increases with flow, while nitrate typically decreases due to dilution from runoff probably from impervious surfaces. Nitrate export patterns indicate a marked difference between land use type (1, 10, 100 g ha-1mm-1 for undisturbed, urban, and greenhouse sites respectively) and show little variance storm to storm during WY2002 and WY2003. The phosphate export pattern with successive storms is not as clear. Cumulative rainfall and/or runoff/rainfall ratios for nitrate and phosphate show promise as variables to simulate the magnitude of nutrient export for individual storms in non-monitored catchments.

Quantifying nutrient sources in an upland catchment using multiple chemical and isotopic tracers

NASA Astrophysics Data System (ADS)

Sebestyen, S. D.; Boyer, E. W.; Shanley, J. B.; Doctor, D. H.; Kendall, C.; Aiken, G. R.

2006-12-01

To explore processes that control the temporal variation of nutrients in surface waters, we measured multiple environmental tracers at the Sleepers River Research Watershed, an upland catchment in northeastern Vermont, USA. Using a set of high-frequency stream water samples, we quantified the variation of nutrients over a range of stream flow conditions with chemical and isotopic tracers of water, nitrate, and dissolved organic carbon (DOC). Stream water concentrations of nitrogen (predominantly in the forms of nitrate and dissolved organic nitrogen) and DOC reflected mixing of water contributed from distinct sources in the forested landscape. Water isotopic signatures and end-member mixing analysis revealed when solutes entered the stream from these sources and that the sources were linked to the stream by preferential shallow subsurface and overland flow paths. Results from the tracers indicated that freshly-leached, terrestrial organic matter was the overwhelming source of high DOC concentrations in stream water. In contrast, in this region where atmospheric nitrogen deposition is chronically elevated, the highest concentrations of stream nitrate were attributable to atmospheric sources that were transported via melting snow and rain fall. These findings are consistent with a conceptual model of the landscape in which coupled hydrological and biogeochemical processes interact to control stream solute variability over time.

Modeling the fate of nitrogen on the catchment scale using a spatially explicit hydro-biogeochemical simulation system

NASA Astrophysics Data System (ADS)

Klatt, S.; Butterbach-Bahl, K.; Kiese, R.; Haas, E.; Kraus, D.; Molina-Herrera, S. W.; Kraft, P.

2015-12-01

The continuous growth of the human population demands an equally growing supply for fresh water and food. As a result, available land for efficient agriculture is constantly diminishing which forces farmers to cultivate inferior croplands and intensify agricultural practices, e.g., increase the use of synthetic fertilizers. This intensification of marginal areas in particular will cause a dangerous rise in nitrate discharge into open waters or even drinking water resources. In order to reduce the amount of nitrate lost by surface runoff or lateral subsurface transport, bufferstrips have proved to be a valuable means. Current laws, however, promote rather static designs (i.e., width and usage) even though a multitude of factors, e.g., soil type, slope, vegetation and the nearby agricultural management, determines its effectiveness. We propose a spatially explicit modeling approach enabling to assess the effects of those factors on nitrate discharge from arable lands using the fully distributed hydrology model CMF coupled to the complex biogeochemical model LandscapeDNDC. Such a modeling scheme allows to observe the displacement of dissolved nutrients in both vertical and horizontal directions and serves to estimate both their uptake by the vegetated bufferstrip and loss to the environment. First results indicate a significant reduction of nitrate loss in the presence of a bufferstrip (2.5 m). We show effects induced by various buffer strip widths and plant cover on the nitrate retention.

Distributed nitrate transport and reaction routines (NTR) inside the mesoscale Hydrological Model (mHM) framework: Development and Application in the Selke catchment

NASA Astrophysics Data System (ADS)

Sinha, Sumit; Rode, Michael; Kumar, Rohini; Yang, Xiaoqiang; Samaniego, Luis; Borchardt, Dietrich

2016-04-01

Precise measurements of where, when and how much denitrification occurs on the basis of measurements alone persist to be vexing and intractable research problem at all spatial and temporal scales. As a result, models have become essential and vital tools for furthering our current understanding of the processes that control denitrification on catchment scale. Emplacement of Water Framework Directive (WFD) and continued efforts in improving water treatment facilities has resulted in alleviating the problems associated with point sources of pollution. However, the problem of eutrophication still persists and is primarily associated with the diffused sources of pollution originating from agricultural area. In this study, the nitrate transport and reaction (NTR) routines are developed inside the distributed mesoscale Hydrological Model (mHM www.ufz.de/mhm) which is a fully distributed hydrological model with a novel parameter regionalization scheme (Samaniego et al. 2010; Kumar et al. 2013) and has been applied to whole Europe (Rakovec et al. 2016) and numerous catchments worldwide. The aforementioned NTR model is applied to a mesoscale river basin, Selke (463 km2) located in central Germany. The NTR model takes in account the critical and pertinent processes like transformation in vadose zone, atmospheric deposition, plant uptake, instream denitrification and also simulates the process of manure and fertilizer application. Both streamflow routines and the NTR model are run on daily time steps. The split-sample approach was used for model calibration (1994-1999) and validation (2000-2004). Flow dynamics at three gauging stations located inside this catchment are successfully captured by the model with consistently high Nash-Sutcliffe Efficiency (NSE) of at least 0.8. Regarding nitrate estimates, the NSE values are greater than 0.7 for both validation and calibration periods. Finally, the NTR model is used for identifying the critical source areas (CSAs) that contribute significantly to nutrient pollution due to different local hydrological and topographical conditions. Postulations for a comprehensive sensitivity analysis and further regionalization of key parameters of the NTR model are also investigated. References: Kumar, R., L. Samaniego, and S. Attinger (2013a), Implications of distributed hydrologic model parameterization on water fluxes at multiple scales and locations, Water Resour. Res., 49, 360-379, doi:10.1029/2012WR012195. Samaniego, L., R. Kumar, and S. Attinger (2010), Multiscale parameter regionalization of a grid-based hydrologic model at the mesoscale, Water Resour. Res., 46, W05523, doi:10.1029/2008WR007327. Rakovec, O., Kumar, R., Mai, J., Cuntz, M., Thober, S., Zink, M., Attinger, S., Schäfer, D., Schrön, M., Samaniego, L. (2016): Multiscale and multivariate evaluation of water fluxes and states over European river basins, J. Hydrometeorol., 17, 287-307, doi: 10.1175/JHM-D-15-0054.1.

Groundwater nitrate reduction versus dissolved gas production: A tale of two catchments.

PubMed

McAleer, E B; Coxon, C E; Richards, K G; Jahangir, M M R; Grant, J; Mellander, Per E

2017-05-15

At the catchment scale, a complex mosaic of environmental, hydrogeological and physicochemical characteristics combine to regulate the distribution of groundwater and stream nitrate (NO 3 - ). The efficiency of NO 3 - removal (via denitrification) versus the ratio of accumulated reaction products, dinitrogen (excess N 2 ) & nitrous oxide (N 2 O), remains poorly understood. Groundwater was investigated in two well drained agricultural catchments (10km 2 ) in Ireland with contrasting subsurface lithologies (sandstone vs. slate) and landuse. Denitrification capacity was assessed by measuring concentration and distribution patterns of nitrogen (N) species, aquifer hydrogeochemistry, stable isotope signatures and aquifer hydraulic properties. A hierarchy of scale whereby physical factors including agronomy, water table elevation and permeability determined the hydrogeochemical signature of the aquifers was observed. This hydrogeochemical signature acted as the dominant control on denitrification reaction progress. High permeability, aerobic conditions and a lack of bacterial energy sources in the slate catchment resulted in low denitrification reaction progress (0-32%), high NO 3 - and comparatively low N 2 O emission factors (EF 5g 1). In the sandstone catchment denitrification progress ranged from 4 to 94% and was highly dependent on permeability, water table elevation, dissolved oxygen concentration solid phase bacterial energy sources. Denitrification of NO 3 - to N 2 occurred in anaerobic conditions, while at intermediate dissolved oxygen; N 2 O was the dominant reaction product. EF 5g 1 (mean: 0.0018) in the denitrifying sandstone catchment was 32% less than the IPCC default. The denitrification observations across catchments were supported by stable isotope signatures. Stream NO 3 - occurrence was 32% lower in the sandstone catchment even though N loading was substantially higher than the slate catchment. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Using rates of oxygen and nitrate reduction to map the subsurface distribution of groundwater denitrification

NASA Astrophysics Data System (ADS)

Kolbe, T.; De Dreuzy, J. R.; Abbott, B. W.; Aquilina, L.; Babey, T.; Green, C. T.; Fleckenstein, J. H.; Labasque, T.; Laverman, A.; Marçais, J.; Peiffer, S.; Thomas, Z.; Pinay, G.

2017-12-01

Widespread fertilizer application over the last 70 years has caused serious ecological and socioeconomic problems in aquatic and estuarine ecosystems. When surplus nitrogen leaches as nitrate (a major groundwater pollutant) to the aquifer, complex flow dynamics and naturally occurring degradation processes control its transport. Under the conditions of depleted oxygen and abundant electron donors, microorganisms reduce NO3- to N2 (denitrification). Denitrification rates vary over orders of magnitude among sites within the same aquifer, complicating estimation of denitrification capacity at the catchment scale. Because it is impractical or impossible to access the subsurface to directly quantify denitrification rates, reactivity is often assumed to occur continuous along flowlines, potentially resulting in substantial over- or underestimation of denitrification. Here we investigated denitrification in an unconfined crystalline aquifer in western France using a combination of common tracers (chlorofluorocarbons, O2, NO3-, and N2) measured in 16 wells to inform a time-based modeling approach. We found that spatially variable denitrification rates arise from the intersection of nitrate rich water with reactive zones defined by the abundance of electron donors (primarily pyrite). Furthermore, based on observed reaction rates of the sequential reduction of oxygen and nitrate, we present a general framework to estimate the location and intensity of the reactive zone in aquifers. Accounting for the vertical distribution of reaction rates results in large differences in estimations of net denitrification rates that assume homogeneous reactivity. This new framework provides a tractable approach for quantifying catchment and regional groundwater denitrification rates that could be used to improve estimation of groundwater resilience to nitrate pollution and develop more realistic management strategies.

Improved Environmental Life Cycle Assessment of Crop Production at the Catchment Scale via a Process-Based Nitrogen Simulation Model.

PubMed

Liao, Wenjie; van der Werf, Hayo M G; Salmon-Monviola, Jordy

2015-09-15

One of the major challenges in environmental life cycle assessment (LCA) of crop production is the nonlinearity between nitrogen (N) fertilizer inputs and on-site N emissions resulting from complex biogeochemical processes. A few studies have addressed this nonlinearity by combining process-based N simulation models with LCA, but none accounted for nitrate (NO3(-)) flows across fields. In this study, we present a new method, TNT2-LCA, that couples the topography-based simulation of nitrogen transfer and transformation (TNT2) model with LCA, and compare the new method with a current LCA method based on a French life cycle inventory database. Application of the two methods to a case study of crop production in a catchment in France showed that, compared to the current method, TNT2-LCA allows delineation of more appropriate temporal limits when developing data for on-site N emissions associated with specific crops in this catchment. It also improves estimates of NO3(-) emissions by better consideration of agricultural practices, soil-climatic conditions, and spatial interactions of NO3(-) flows across fields, and by providing predicted crop yield. The new method presented in this study provides improved LCA of crop production at the catchment scale.

Legacy of contaminant N sources to the NO3− signature in rivers: a combined isotopic (δ15N-NO3−, δ18O-NO3−, δ11B) and microbiological investigation

PubMed Central

Briand, Cyrielle; Sebilo, Mathieu; Louvat, Pascale; Chesnot, Thierry; Vaury, Véronique; Schneider, Maude; Plagnes, Valérie

2017-01-01

Nitrate content of surface waters results from complex mixing of multiple sources, whose signatures can be modified through N reactions occurring within the different compartments of the whole catchment. Despite this complexity, the determination of nitrate origin is the first and crucial step for water resource preservation. Here, for the first time, we combined at the catchment scale stable isotopic tracers (δ15N and δ18O of nitrate and δ11B) and fecal indicators to trace nitrate sources and pathways to the stream. We tested this approach on two rivers in an agricultural region of SW France. Boron isotopic ratios evidenced inflow from anthropogenic waters, microbiological markers revealed organic contaminations from both human and animal wastes. Nitrate δ15N and δ18O traced inputs from the surface leaching during high flow events and from the subsurface drainage in base flow regime. They also showed that denitrification occurred within the soils before reaching the rivers. Furthermore, this study highlighted the determinant role of the soil compartment in nitrate formation and recycling with important spatial heterogeneity and temporal variability. PMID:28150819

Legacy effects of nitrogen and phosphorus in a eutrophic lake catchment: Slapton Ley, SW England

NASA Astrophysics Data System (ADS)

Burt, T. P.; Worrall, F.; Howden, N. J. K.

2017-12-01

Slapton Ley is a freshwater coastal lagoon in SW England. The Ley is part of a National Nature Reserve, which is divided into two basins: the Higher Ley (39 ha) is mainly reed swamp; the Lower Ley (77 ha) is a shallow lake (maximum depth 2.9 m). In the 1960s it became apparent that the Lower Ley was becoming increasingly eutrophic. In order to gauge water, sediment and nutrient inputs into the lake, measurements began on the main catchments in 1969. Continuous monitoring of discharge and a weekly water-sampling programme have been maintained by the Slapton Ley Field Centre ever since. The monitoring programme has been supplemented by a number of research projects which have sought to identify the salient hydrological processes operating within the Slapton catchments and to relate these to the delivery of sediment and solute to the stream system. Long-term monitoring data are also available for the catchment area including the lake from the Environment Agency.The nitrate issue has been of particular interest at Slapton; although many longer series exist for large river basins like the Thames, the long record of nitrate data for the Slapton catchments is unique in Britain for a small rural basin. Recent declines in nitrate concentration may reflect less intensive agricultural activity, lower fertiliser inputs in particular, but there may also be a legacy effect in the shallow groundwater system. Phosphorus concentrations in stream and lake water have also shown declining concentrations but a phosphorus legacy in the surficial lake sediments means that algal blooms continue to develop in most summers, as indicated by a continued rise in summer pH levels. Further field observation at the sediment-water interface is needed to better understand the biogeochemical drivers and the balance between N and P limitation in the lake. Successful management of the Nature Reserve requires better understanding of the links between hydrological and biogeochemical processes operating within the catchment area.

The nitrate time bomb: a numerical way to investigate nitrate storage and lag time in the unsaturated zone.

PubMed

Wang, L; Butcher, A S; Stuart, M E; Gooddy, D C; Bloomfield, J P

2013-10-01

Nitrate pollution in groundwater, which is mainly from agricultural activities, remains an international problem. It threatens the environment, economics and human health. There is a rising trend in nitrate concentrations in many UK groundwater bodies. Research has shown it can take decades for leached nitrate from the soil to discharge into groundwater and surface water due to the 'store' of nitrate and its potentially long travel time in the unsaturated and saturated zones. However, this time lag is rarely considered in current water nitrate management and policy development. The aim of this study was to develop a catchment-scale integrated numerical method to investigate the nitrate lag time in the groundwater system, and the Eden Valley, UK, was selected as a case study area. The method involves three models, namely the nitrate time bomb-a process-based model to simulate the nitrate transport in the unsaturated zone (USZ), GISGroundwater--a GISGroundwater flow model, and N-FM--a model to simulate the nitrate transport in the saturated zone. This study answers the scientific questions of when the nitrate currently in the groundwater was loaded into the unsaturated zones and eventually reached the water table; is the rising groundwater nitrate concentration in the study area caused by historic nitrate load; what caused the uneven distribution of groundwater nitrate concentration in the study area; and whether the historic peak nitrate loading has reached the water table in the area. The groundwater nitrate in the area was mainly from the 1980s to 2000s, whilst the groundwater nitrate in most of the source protection zones leached into the system during 1940s-1970s; the large and spatially variable thickness of the USZ is one of the major reasons for unevenly distributed groundwater nitrate concentrations in the study area; the peak nitrate loading around 1983 has affected most of the study area. For areas around the Bowscar, Beacon Edge, Low Plains, Nord Vue, Dale Springs, Gamblesby, Bankwood Springs, and Cliburn, the peak nitrate loading will arrive at the water table in the next 34 years; statistical analysis shows that 8.7 % of the Penrith Sandstone and 7.3 % of the St Bees Sandstone have not been affected by peak nitrate. This research can improve the scientific understanding of nitrate processes in the groundwater system and support the effective management of groundwater nitrate pollution for the study area. With a limited number of parameters, the method and models developed in this study are readily transferable to other areas.

DOC and nitrate export linked to dominant rainfall-runoff processes, end-members and seasonality - a long-term high frequency measurement campaign

NASA Astrophysics Data System (ADS)

Schwab, M. P.; Klaus, J.; Pfister, L.; Weiler, M.

2016-12-01

Over the past decades, stream sampling protocols for hydro-geochemical parameters were often limited by logistical and technological constraints. While long-term monitoring protocols were typically based on weekly sampling intervals, high frequency sampling was commonly limited to a few single events. In this contribution, we combined high frequency and long-term measurements to understand DOC and nitrate dynamics in a forest headwater for different runoff events and seasons. Our study area is the forested Weierbach catchment (0.47 km2) in Luxembourg, where the fractured schist bedrock is covered by cambisol soils. The runoff response is characterized by a double peak behaviour. The first peak occurs during or right after a rainfall event triggered by fast near surface runoff generation processes, while a second delayed peak lasts several days and is generated by subsurface flow. This second peak occurs only if a distinct storage threshold of the catchment is exceeded. Our observations were carried out with a field deployable UV-Vis spectrometer measuring DOC and nitrate concentrations in-situ at 15 min intervals for more than two years. In addition, a long-term validation was carried out with data obtained from the analysis of water collected with grab samples. The long-term, high-frequency measurements allowed us to calculate a complete and detailed balance of DOC and nitrate export over two years. Transport behaviour of the DOC and nitrate showed different dynamics between the first and second hydrograph peaks. DOC is mainly exported during the first peaks, while nitrate is mostly exported during the delayed second peaks. Biweekly end-member measurement of soil and groundwater over several years enables us to link the behaviour of DOC and nitrate export to various end-members in the catchment. Altogether, the long-term and high-frequency time series provides the opportunity to study DOC and nitrate export processes without having to just rely only on either a few single event measurements or coarse measurement protocols.

Tracing Nitrogen Sources in Forested Catchments Under Varying Flow Conditions: Seasonal and Event Scale Patterns

NASA Astrophysics Data System (ADS)

Sebestyen, S. D.; Shanley, J. B.; Boyer, E. W.; Kendall, C.

2004-12-01

Our ability to assess how stream nutrient concentrations respond to biogeochemical transformations and stream flow dynamics is often limited by datasets that do not include all flow conditions that occur over event, monthly, seasonal, and yearly time scales. At the Sleepers River Research Watershed in northeastern Vermont, USA, nitrate, DOC (dissolved organic carbon), and major ion concentrations were measured on samples collected over a wide range of flow conditions from summer 2002 through summer 2004. Nutrient flushing occurred at the W-9 catchment and high-frequency sampling revealed critical insights into seasonal and event-scale controls on nutrient concentrations. In this seasonally snow-covered catchment, the earliest stage of snowmelt introduced nitrogen directly to the stream from the snowpack. As snowmelt progressed, the source of stream nitrate shifted to flushing of soil nitrate along shallow subsurface flow paths. In the growing season, nitrogen flushing to streams varied with antecedent moisture conditions. More nitrogen was available to flush to streams when antecedent moisture was lowest, and mobile nitrogen stores in the landscape regenerated under baseflow conditions on times scales as short as 7 days. Leaf fall was another critical time when coupled hydrological and biogeochemical processes controlled nutrient fluxes. With the input of labile organic carbon from freshly decomposing leaves, nitrate concentrations declined sharply in response to in-stream immobilization or denitrification. These high-resolution hydrochemical data from multiple flow regimes are identifying "hot spots" and "hot moments" of biogeochemical and hydrological processes that control nutrient fluxes in streams.

Tracing freshwater nitrate sources in pre-alpine groundwater catchments using environmental tracers

NASA Astrophysics Data System (ADS)

Stoewer, M. M.; Knöller, K.; Stumpp, C.

2015-05-01

Groundwater is one of the main resources for drinking water. Its quality is still threatened by the widespread contaminant nitrate (NO3-). In order to manage groundwater resources in a sustainable manner, we need to find options of lowering nitrate input. Particularly, a comprehensive knowledge of nitrate sources is required in areas which are important current and future drinking water reservoirs such as pre-alpine aquifers covered with permanent grassland. The objective of the present study was to identify major sources of nitrate in groundwater with low mean nitrate concentrations (8 ± 2 mg/L). To achieve the objective, we used environmental tracer approaches in four pre-alpine groundwater catchments. The stable isotope composition and tritium content of water were used to study the hydrogeology and transit times. Furthermore, nitrate stable isotope methods were applied to trace nitrogen from its sources to groundwater. The results of the nitrate isotope analysis showed that groundwater nitrate was derived from nitrification of a variety of ammonium sources such as atmospheric deposition, mineral and organic fertilizers and soil organic matter. A direct influence of mineral fertilizer, atmospheric deposition and sewage was excluded. Since temporal variation in stable isotopes of nitrate were detected only in surface water and locally at one groundwater monitoring well, aquifers appeared to be well mixed and influenced by a continuous nitrate input mainly from soil derived nitrogen. Hydrogeological analysis supported that the investigated aquifers were less vulnerable to rapid impacts due to long average transit times, ranging from 5 to 21 years. Our study revealed the importance of combining environmental tracer approaches and a comprehensive sampling campaign (local sources of nitrate, soil water, river water, and groundwater) to identify the nitrate sources in groundwater and its vulnerability. In future, the achieved results will help develop targeted strategies for a sustainable groundwater management focusing more on soil nitrogen storage.

Isotopic signals of denitrification in a northern hardwood forested catchment

NASA Astrophysics Data System (ADS)

Wexler, Sarah; Goodale, Christine

2013-04-01

Water samples from streams, groundwater and precipitation were collected during summer from the hydrologic reference watershed (W3) at Hubbard Brook Experimental Forest in the White Mountains, New Hampshire, and analysed for d15N-NO3 and d18O-NO3. Despite very low nitrate concentrations (<0.5 to 8.8 uM NO3-) dual-isotopic signals of sources and processes were clearly distinguishable. The isotopic composition of nitrate from shallow groundwater showed evidence of dual isotopic fractionation in line with denitrification, with a positive relationship between nitrogen and oxygen isotopic composition, a regression line slope of 0.76 (r2 = 0.68), and an empirical isotope enrichment factor of ɛP-S 15N-NO3 -12.7%. The isotopic composition of riparian groundwater nitrate from time-series samples showed variation in processes over a small spatial scale. The expected isotopic composition of nitrate sources in the watershed was used to distinguish nitrate in rain and nitrate from nitrification of both rainfall ammonium and ammonium from mineralised soil organic nitrogen. Evidence of oxygen exchange with water during nitrification was seen in the isotopic composition of stream and shallow groundwater nitrate. The isotopic composition of streamwater nitrate following a period of storms indicated that 25% of nitrate in the streamwater was of atmospheric origin. This suggests rapid infiltration of rainfall via vertical bypass flow to the saturated zone, enabling transport of atmospheric nitrate to the stream channels. Across the Hubbard Brook basin, the isotopic composition of nitrate from paired samples from watersheds 4-7 indicated a switch between a nitrification and assimilation dominated system, to a system influenced by rainfall nitrogen inputs and denitrification. The dual isotope approach has revealed evidence of denitrification of nitrate from different sources at low concentrations at Hubbard Brook during summer. This isotopic evidence deepens our understanding of the significance and spatial variability of denitrification in environments with low levels of nitrate, represented by this northern hardwood forested catchment.

Agriculture and groundwater nitrate contamination in the Seine basin. The STICS-MODCOU modelling chain.

PubMed

Ledoux, E; Gomez, E; Monget, J M; Viavattene, C; Viennot, P; Ducharne, A; Benoit, M; Mignolet, C; Schott, C; Mary, B

2007-04-01

A software package is presented here to predict the fate of nitrogen fertilizers and the transport of nitrate from the rooting zone of agricultural areas to surface water and groundwater in the Seine basin, taking into account the long residence times of water and nitrate in the unsaturated and aquifer systems. Information on pedological characteristics, land use and farming practices is used to determine the spatial units to be considered. These data are converted into input data for the crop model STICS which simulates the water and nitrogen balances in the soil-plant system with a daily time-step. A spatial application of STICS has been derived at the catchment scale which computes the water and nitrate fluxes at the bottom of the rooting zone. These fluxes are integrated into a surface and groundwater coupled model MODCOU which calculates the daily water balance in the hydrological system, the flow in the rivers and the piezometric variations in the aquifers, using standard climatic data (rainfall, PET). The transport of nitrate and the evolution of nitrate contamination in groundwater and to rivers is computed by the model NEWSAM. This modelling chain is a valuable tool to predict the evolution of crop productivity and nitrate contamination according to various scenarios modifying farming practices and/or climatic changes. Data for the period 1970-2000 are used to simulate the past evolution of nitrogen contamination. The method has been validated using available data bases of nitrate concentrations in the three main aquifers of the Paris basin (Oligocene, Eocene and chalk). The approach has then been used to predict the future evolution of nitrogen contamination up to 2015. A statistical approach allowed estimating the probability of transgression of different concentration thresholds in various areas in the basin. The model is also used to evaluate the cost of the damage resulting of the treatment of drinking water at the scale of a groundwater management unit in the Seine river basin.

Hydrological versus biogeochemical controls on catchment nitrate export: a test of the flushing mechanism

NASA Astrophysics Data System (ADS)

Ocampo, Carlos J.; Oldham, Carolyn E.; Sivapalan, Murugesu; Turner, Jeffrey V.

2006-12-01

Deciphering the connection between streamflows and nitrate (NO-3) discharge requires identification of the various water flow pathways within a catchment, and the different time-scales at which hydrological and biogeochemical processes occur. Despite the complexity of the processes involved, many catchments around the world present a characteristic flushing response of NO-3 export. Yet the controls on the flushing response, and how they vary across space and time, are still not clearly understood. In this paper, the flushing response of NO-3 export from a rural catchment in Western Australia was investigated using isotopic (deuterium), chemical (chloride, NO-3), and hydrometric data across different antecedent conditions and time-scales. The catchment streamflow was at all time-scales dominated by a pre-event water source, and the NO-3 discharge was correlated with the magnitude of areas contributing to saturation overland flow. The NO-3 discharge also appeared related to the shallow groundwater dynamics. Thus, the antecedent moisture condition of the catchment at seasonal and interannual time-scales had a major impact on the NO-3 flushing response. In particular, the dynamics of the shallow ephemeral perched aquifer drove a shift from hydrological controls on NO-3 discharge during the early flushing stage to an apparent biogeochemical control on NO-3 discharge during the steady decline stage of the flushing response. This temporally variable control hypothesis provides a new and alternative description of the mechanisms behind the commonly seen flushing response. Copyright

Understanding hydrological and nitrogen interactions by sensitivity analysis of a catchment-scale nitrogen model

NASA Astrophysics Data System (ADS)

Medici, Chiara; Wade, Andrew; Frances, Felix

2010-05-01

Nitrogen is present in both terrestrial and aquatic ecosystems and research is needed to understand its storage, transportation and transformations in river catchments world-wide because of its importance in controlling plant growth and freshwater trophic status (Vitousek et al. 2009; Chu et al. 2008; Schlesinger et al 2006; Ocampo et al. 2006; Green et al., 2004; Arheimer et al., 1996). Numerous mathematical models have been developed to describe the nitrogen dynamics, but there is a substantial gap between the outputs now expected from these models and what modellers are able to provide with scientific justification (McIntyre et al., 2005). In fact, models will always necessarily be simplification of reality; hence simplifying assumptions are sources of uncertainty that must be well understood for an accurate model results interpretation. Therefore, estimating prediction uncertainties in water quality modelling is becoming increasingly appreciated (Dean et al., 2009, Kruger et al., 2007, Rode et al., 2007). In this work the lumped LU4-N model (Medici et al., 2008; Medici et al., EGU2009-7497) is subjected to an extensive regionalised sensitivity analysis (GSA, based on Monte Carlo simulations) in application to the Fuirosos catchment, Catalonia. The main results are: 1) the hydrological model is greatly affected by the maximum static storage water content (Hu_max), which defines the amount of water held in soil that can leave the catchment only by evapotranspiration. Thus, it defines also the amount of water not retained that is free to move and supplies the other model tanks; 2) the use of several objective functions in order to take into account different hydrograph characteristic helped to constrain parameter values; 3) concerning nitrogen, to obtain a sufficient level of behavioural parameter sets for the statistical analysis, not very severe criteria could be adopted; 4) stream water concentrations are sensitive to the shallow aquifer parameters, especially the nitrification constant (Knitr-aquif) and also to the certain soil parameters, like the mineralization constant (Kmin), the annual maximum ammonium uptake (MaxUPNH4) and the mineralization, nitrification and immobilisation thresholds (Umin, Unitr and Uimmob). Moreover the results give a clear indication that the hydrological model greatly affects the streamwater nitrate and ammonium concentrations; 5) result shows that the LU4-N model succeeded in achieving near-optimum fits simultaneously to flow and nitrate, but not ammonium; 6) however, the optimum flow model has not produced a near-optimum nitrate model. The analysis of this result indicated that calibrating the flow-related parameters first, then calibrating the remaining parameters instead of calibrating all parameters together, may not be the best strategy as pointed out for another study by McIntyre et al., 2005 ; 7) a final analysis seems also to support the idea that to obtain a satisfactory nitrogen simulation necessarily the flow should be acceptably represented, which lead to the conclusion that observed stream concentrations may indirectly help to calibrated the rainfall-runoff model, or at least the parameters to which they are sensitive.

Beaver Ponds: Resurgent Nitrogen Sinks for Rural Watersheds in the Northeastern United States.

PubMed

Lazar, Julia G; Addy, Kelly; Gold, Arthur J; Groffman, Peter M; McKinney, Richard A; Kellogg, Dorothy Q

2015-09-01

Beaver-created ponds and dams, on the rise in the northeastern United States, reshape headwater stream networks from extensive, free-flowing reaches to complexes of ponds, wetlands, and connecting streams. We examined seasonal and annual rates of nitrate transformations in three beaver ponds in Rhode Island under enriched nitrate-nitrogen (N) conditions through the use of N mass balance techniques on soil core mesocosm incubations. We recovered approximately 93% of the nitrate N from our mesocosm incubations. Of the added nitrate N, 22 to 39% was transformed during the course of the incubation. Denitrification had the highest rates of transformation (97-236 mg N m d), followed by assimilation into the organic soil N pool (41-93 mg N m d) and ammonium generation (11-14 mg N m d). Our denitrification rates exceeded those in several studies of freshwater ponds and wetlands; however, rates in those ecosystems may have been limited by low concentrations of nitrate. Assuming a density of 0.7 beaver ponds km of catchment area, we estimated that in nitrate-enriched watersheds, beaver pond denitrification can remove approximately 50 to 450 kg nitrate N km catchment area. In rural watersheds of southern New England with high N loading (i.e., 1000 kg km), denitrification from beaver ponds may remove 5 to 45% of watershed nitrate N loading. Beaver ponds represent a relatively new and substantial sink for watershed N if current beaver populations persist. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Assessment of variables controlling nitrate dynamics in groundwater: is it a threat to surface aquatic ecosystems?

PubMed

Rasiah, V; Armour, J D; Cogle, A L

2005-01-01

The impact of fertilised cropping on nitrate-N dynamics in groundwater (GW) was assessed in a catchment from piezometers installed: (i) to different depths, (ii) in different soil types, (iii) on different positions on landscape, and (iv) compared with the Australian and New Zealand Environmental and Conservation Council guideline values provided for different aquatic ecosystems. The GW and NO(3)-N concentration dynamics were monitored in 39 piezometer wells, installed to 5-90 m depth, under fertilized sugarcane (Saccharum officinarum-S) in the Johnstone River Catchment, Australia, from 1999 January through September 2002. The median nitrate-N concentration ranged from 14 to 1511 microg L(-1), and the 80th percentile from 0 to 1341 microg L(-1). In 34 out of the 39 piezometer wells the 80th percentile or 80% of the nitrate-N values were higher than 30 microg L(-1), which is the maximum trigger value provided in the ANZECC table for sustainable health of different aquatic ecosystems. Nitrate-N concentration decreased with increasing well depth, increasing depth of water in wells, and with decreasing relief on landscape. Nitrate-N was higher in alluvial soil profiles than on those formed in-situ. Nitrate-N increased with increasing rainfall at the beginning of the rainy season, fluctuated during the peak rainy period, and then decreased when the rain ceased. The rapid decrease in GW after the rains ceased suggested potential existed for nitrate-N to be discharged as lateral-flow into streams. This may contribute towards the deterioration in the health of down-stream aquatic ecosystems.

Application of a water quality model in the White Cart water catchment, Glasgow, UK.

PubMed

Liu, S; Tucker, P; Mansell, M; Hursthouse, A

2003-03-01

Water quality models of urban systems have previously focused on point source (sewerage system) inputs. Little attention has been given to diffuse inputs and research into diffuse pollution has been largely confined to agriculture sources. This paper reports on new research that is aimed at integrating diffuse inputs into an urban water quality model. An integrated model is introduced that is made up of four modules: hydrology, contaminant point sources, nutrient cycling and leaching. The hydrology module, T&T consists of a TOPMODEL (a TOPography-based hydrological MODEL), which simulates runoff from pervious areas and a two-tank model, which simulates runoff from impervious urban areas. Linked into the two-tank model, the contaminant point source module simulates the overflow from the sewerage system in heavy rain. The widely known SOILN (SOIL Nitrate model) is the basis of nitrogen cycle module. Finally, the leaching module consists of two functions: the production function and the transfer function. The production function is based on SLIM (Solute Leaching Intermediate Model) while the transfer function is based on the 'flushing hypothesis' which postulates a relationship between contaminant concentrations in the receiving water course and the extent to which the catchment is saturated. This paper outlines the modelling methodology and the model structures that have been developed. An application of this model in the White Cart catchment (Glasgow) is also included.

Dynamics of nitrate and chloride during storm events in agricultural catchments with different subsurface drainage intensity (Indiana, USA)

USDA-ARS?s Scientific Manuscript database

Grids of perforated pipe buried beneath many poorly drained agricultural fields in the Midwestern U.S. are believed to “short circuit” pools of nitrate-laden soil water and shallow groundwater directly into streams that eventually discharge to the Mississippi River. Although much is known about the ...

Downstream changes of water quality in a lowland river due to groundwater inflows.

NASA Astrophysics Data System (ADS)

Zieba, Damian; Bar-Michalczyk, Dominika; Kania, Jarosław; Malina, Grzegorz; Michalczyk, Tomasz; Rozanski, Kazimierz; Witczak, Stanislaw; Wachniew, Przemyslaw; Zurek, Anna J.

2016-04-01

The Kocinka catchment (ca. 250 km2) in southern Poland receives substantial inflows of groundwater from a major fissured-carbonate aquifer polluted with nitrates originating from agriculture and domestic sewage. The 40 km long Kocinka river reveals large spatial variations in physical and chemical water properties with large downstream changes of nitrate concentrations. Detailed longitudinal surveys of such water characteristics as nitrate concentration, water temperature, pH, electric conductivity, stable isotopic composition, tritium concentration were performed in order to identify and quantify groundwater inflows. The river gains groundwater down to the 25 km from the source and a looses water further downstream. The subsequent increase and decrease of nitrate concentration in the upper and middle reaches of the river are caused by inflows of the, respectively, polluted and non-polluted groundwaters. The range of such changes can be even five-fold while the drop of nitrate concentration along the semi natural, 18 km long, lower reach where the river is well connected to its riparian and hyporheic zones nitrate loss is of the order of 10%. More significant nitrate losses were observed in the dammed reaches and in a small reservoir in the upper part of the river. Results of the study have implications for identification of measures that can be undertaken to reduce nitrate export from the catchment. Because of the role of groundwater in river runoff reduction of nitrate loads to the aquifer should be primary objective. Acknowledgements. The work was carried out as part of the BONUS Soils2Sea project on groundwater system (http:/www.soils2sea.eu) financed by the European Commission 7 FP contract 226536 and the statutory funds of the AGH University of Science and Technology (project No.11.11.140.026 and 11.11.220.01).

Recent trends in water quality in an agricultural catchment in Eastern Scotland: elucidating the roles of hydrology and land use.

PubMed

Dunn, S M; Sample, J; Potts, J; Abel, C; Cook, Y; Taylor, C; Vinten, A J A

2014-07-01

Across the EU, programmes of measures have been introduced as part of river basin management planning as a means of tackling problems of diffuse pollution from agriculture. Evidence is required to demonstrate the effectiveness of these measures and with this overarching objective, monitoring of an agricultural catchment in Eastern Scotland was initiated in 2007. As a precursor to evaluating the effect of new management measures it is essential to understand how other factors, including hydrology and land use changes, could have influenced water quality. This study undertook an analysis of the trends in concentrations and loads of nitrate, soluble reactive phosphorus (SRP), suspended solids (SS) and turbidity measured at six points in the catchment over a six year period. The results identified both differing trends between determinands and differing trends occurring over varying spatial scales. The only direct relationships between land use and water quality that could be identified based on annual data was a positive link between arable cropping and nitrate concentrations. At the sub-catchment scale some temporal changes in land use and management explained short-term trends in nitrate but not in SRP. Lags in the system were identified due to soil adsorption, in-stream/loch processing and groundwater transport making the identification of cause and effect problematic. The results have implications for the demonstration of effectiveness of measures over the shorter term and the timescales of recovery from diffuse pollution. Longer term monitoring at small scales will be important in this regard.

Evaluation of Nitrate Fluxes to Groundwater under Agriculture Land Uses across the Loess Plateau - A Catchment Scale Investigation

NASA Astrophysics Data System (ADS)

Turkeltaub, T.; Jia, X.; Binley, A. M.

2016-12-01

Nitrate management is required for fulfilling the objective of high agriculture productivity and concurrently reduced groundwater contamination to minimum. Yet, nitrate is considered as a non-point contaminant. Therefore, understanding the temporal and spatial processes controls of nitrate transport in the vadose zone are imperative for protection of groundwater. This study is conducted in the Loess Plateau which located in the north-central of mainland China and characterized with a semi-arid climate. Moreover, it accounts for about 6.6% of the Chinese territory and supports over 8.5% of the Chinese population. This area undergoes high pressure from human activities and requiring optimal management interventions. Integrated modelling frameworks, which include unsaturated and saturated processes, are able to simulate nitrate transport under various scenarios, and provide reasonable prediction for the decision-makers. We used data obtained from soil samples collected across a region of 41 × 104 km2 (243 samples, to 5 m depth) to derive unsaturated flow and transport properties. Particle size distributions, saturated hydraulic conductivity, water content at field capacity (0.33 atm) and saturated water content were also obtained for the shallower layers (0-40 cm). The van Genuchten - Mualem soil parameters describing the retention and the unsaturated hydraulic conductivity curves were estimated with the Rosetta code. The analysis of the soil samples indicated that the silt loam soil type is dominant. Hence, a scaling approach was chosen as an adequate method for estimation of representative retention and hydraulic conductivity curves. Water flow and nitrate leaching were simulated with mechanistic based 1-D model for each agriculture land use within the area. The simulated nitrate losses were compared with results of root zone model simulations. Subsequently, the calculated fluxes were input as upper boundary conditions in the Modflow model to examine the regional groundwater nitrate concentration levels. Ultimately, this integrated model framework is flexible and therefore allows testing various land-use scenarios.

Modeling greenhouse gas emissions (CO2, N2O, CH4) from managed arable soils with a fully coupled hydrology-biogeochemical modeling system simulating water and nutrient transport and associated carbon and nitrogen cycling at catchment scale

NASA Astrophysics Data System (ADS)

Klatt, Steffen; Haas, Edwin; Kraus, David; Kiese, Ralf; Butterbach-Bahl, Klaus; Kraft, Philipp; Plesca, Ina; Breuer, Lutz; Zhu, Bo; Zhou, Minghua; Zhang, Wei; Zheng, Xunhua; Wlotzka, Martin; Heuveline, Vincent

2014-05-01

The use of mineral nitrogen fertilizer sustains the global food production and therefore the livelihood of human kind. The rise in world population will put pressure on the global agricultural system to increase its productivity leading most likely to an intensification of mineral nitrogen fertilizer use. The fate of excess nitrogen and its distribution within landscapes is manifold. Process knowledge on the site scale has rapidly grown in recent years and models have been developed to simulate carbon and nitrogen cycling in managed ecosystems on the site scale. Despite first regional studies, the carbon and nitrogen cycling on the landscape or catchment scale is not fully understood. In this study we present a newly developed modelling approach by coupling the fully distributed hydrology model CMF (catchment modelling framework) to the process based regional ecosystem model LandscapeDNDC for the investigation of hydrological processes and carbon and nitrogen transport and cycling, with a focus on nutrient displacement and resulting greenhouse gas emissions in a small catchment at the Yanting Agro-ecological Experimental Station of Purple Soil, Sichuan province, China. The catchment hosts cypress forests on the outer regions, arable fields on the sloping croplands cultivated with wheat-maize rotations and paddy rice fields in the lowland. The catchment consists of 300 polygons vertically stratified into 10 soil layers. Ecosystem states (soil water content and nutrients) and fluxes (evapotranspiration) are exchanged between the models at high temporal scales (hourly to daily) forming a 3-dimensional model application. The water flux and nutrients transport in the soil is modelled using a 3D Richards/Darcy approach for subsurface fluxes with a kinematic wave approach for surface water runoff and the evapotranspiration is based on Penman-Monteith. Biogeochemical processes are modelled by LandscapeDNDC, including soil microclimate, plant growth and biomass allocation, organic matter mineralisation, nitrification, denitrification, chemodenitrification and methanogenesis producing and consuming soil based greenhouse gases. The model application will present first validation results of the coupled model to simulate soil based greenhouse gas emissions as well as nitrate discharge from the Yanting catchment. The model application will also present the effects of different management practices (fertilization rates and timings, tilling, residues management) on the redistribution of N surplus within the catchment causing biomass productivity gradients and different levels of indirect N2O emissions along topographical gradients.

Catchment influence on nitrate and dissolved organic matter in Alaskan streams across a latitudinal gradient

DOE PAGES

Harms, Tamara K.; Edmonds, Jennifer W.; Genet, Hélène; ...

2016-01-10

Spatial patterns in carbon (C) and nitrogen (N) cycles of high-latitude catchments have been linked to climate and permafrost and used to infer potential changes in biogeochemical cycles under climate warming. However, inconsistent spatial patterns across regions indicate that factors in addition to permafrost and regional climate may shape responses of C and N cycles to climate change. In this paper, we hypothesized that physical attributes of catchments modify responses of C and N cycles to climate and permafrost. We measured dissolved organic C (DOC) and nitrate (NO 3 ¯) concentrations, and composition of dissolved organic matter (DOM) in 21more » streams spanning boreal to arctic Alaska, and assessed permafrost, topography, and attributes of soils and vegetation as predictors of stream chemistry. Multiple regression analyses indicated that catchment slope is a primary driver, with lower DOC and higher NO 3 ¯ concentration in streams draining steeper catchments, respectively. Depth of the active layer explained additional variation in concentration of DOC and NO 3 ¯. Vegetation type explained regional variation in concentration and composition of DOM, which was characterized by optical methods. Composition of DOM was further correlated with attributes of soils, including moisture, temperature, and thickness of the organic layer. Finally, regional patterns of DOC and NO 3 ¯ concentrations in boreal to arctic Alaska were driven primarily by catchment topography and modified by permafrost, whereas composition of DOM was driven by attributes of soils and vegetation, suggesting that predicting changes to C and N cycling from permafrost-influenced regions should consider catchment setting in addition to dynamics of climate and permafrost.« less

Towards hydrochemical PUB - stable vs. heterogeneous NO3 and COD signatures across hydrographic structure and size

NASA Astrophysics Data System (ADS)

Ecrepont, Stephane; Cudennec, Christophe; Jaffrezic, Anne; de Lavenne, Alban

2017-04-01

Towards hydrochemical PUB - stable vs. heterogeneous NO3 and DOC signatures across hydrographic structure and size Ecrepont, S.1Cudennec, C.1 Jaffrézic, A.1 de Lavenne, A.2 1UMR SAS, Agrocampus Ouest, Rennes, France 2 HBAN, Irstea, Antony, France Intensive agriculture is a major disturbing factor for water quality in Brittany, France. Observations of chemical data from 350 catchments over a 15 year period show that the high variability of hydrochemical dynamics between catchments in relation to geographic characteristics and farming practices, decreases with an increase in the catchment size. A stable signature of nitrate and DOC dynamics does emerge for bigger catchments, and was evidenced statistically. We adapted a modified version of the standard deviation formula to calculate an index on mean inter-annual winter nitrate and dissolved organic carbon concentrations to characterize each catchment. The method was applied to the whole sample of catchments, some of them nested, to investigate variation of our new index across scales and regions. Results show an increasing and non-linear relationship between the criterion and the surface, with threshold effects. The stability of the thresholds across river basins in Brittany, and across seasons and years is explored. This emergence relates to the progressive connection of streams with heterogeneous characteristic chemical signatures into a mixing dominant effect. The better assessment of this relationship opens two major perspectives: i) to define a geomorphology-based PUB (Prediction in Ungauged Basins) approach for hydrochemistry; ii) to identify the most critical sub-catchments for mitigating actions in terms of farming and landscape practices towards water quality recovery.

New insights into biogeochemical processing gained from sub-daily river monitoring

NASA Astrophysics Data System (ADS)

Halliday, S. J.; Wade, A. J.; Skeffington, R. A.; Bowes, M.; Palmer-Felgate, E.; Loewenthal, M.; Jarvie, H.; Neal, C.; Reynolds, B.; Gozzard, E.; Newman, J.

2012-12-01

This talk will focus on the insights obtained from sub-daily hydrochemical monitoring for a sustained time periods (> 1 year), at multiple sites within a catchment and across different catchment types. Sub-daily instream hydrochemical dynamics were investigated, using non-stationary time-series analysis techniques, for two catchments representative of upland and lowland UK. The River Hafren at Plynlimon, mid-Wales drains an upland catchment where half the land cover is unmanaged moorland and the other half is first generation plantation forestry. The Hafren was monitored at two sites on a 7-hourly basis, between March 2007 and January 2009, using a Xian automatic sampler. The River Enborne, Berkshire, southeast England, is a rural lowland catchment, impacted by agricultural runoff, and septic tank and sewage treatment works discharges. The Enborne was monitored on an hourly basis between November 2009 and February 2012, using in situ field deployable analytical equipment to measure: Total Reactive Phosphorus (TRP: Systea Micromac C), Nitrate (Hach-Lange Nitratax), pH, dissolved oxygen, conductivity and water temperature (YSI 6600 Multi-parameter sonde). The results reveal complex diurnal patterns which exhibit seasonal changes in phase and amplitude, and are influenced by both flow conditions and nutrient sources. The comparison of the upland and lowland nitrate time series highlights how the different nitrogen sources within each system results in marked differences in the seasonal and diurnal dynamics, with a seasonal maximum in winter and a single peak diurnal cycle in the upland system, compared to a summer maximum and a two peak diurnal cycle in the lowland system. The analysis of TRP and nitrate concentrations in the Enborne catchment, in combination with flow, pH, dissolved oxygen, conductivity and water temperature, allowed the main processes controlling the observed sub-daily nutrient dynamics to be investigated. The different monitoring approaches adopted revealed the complexities involved in the accurate extraction of diurnal dynamics under lower frequency sampling, and the inherent issues of aliasing. Monitoring for 2 years also allowed an initial assessment of the inter-annual variability in the observed dynamics.

Test of a simplified modeling approach for nitrogen transfer in agricultural subsurface-drained catchments

NASA Astrophysics Data System (ADS)

Henine, Hocine; Julien, Tournebize; Jaan, Pärn; Ülo, Mander

2017-04-01

In agricultural areas, nitrogen (N) pollution load to surface waters depends on land use, agricultural practices, harvested N output, as well as the hydrology and climate of the catchment. Most of N transfer models need to use large complex data sets, which are generally difficult to collect at larger scale (>km2). The main objective of this study is to carry out a hydrological and a geochemistry modeling by using a simplified data set (land use/crop, fertilizer input, N losses from plots). The modelling approach was tested in the subsurface-drained Orgeval catchment (Paris Basin, France) based on following assumptions: Subsurface tile drains are considered as a giant lysimeter system. N concentration in drain outlets is representative for agricultural practices upstream. Analysis of observed N load (90% of total N) shows 62% of export during the winter. We considered prewinter nitrate (NO3) pool (PWNP) in soils at the beginning of hydrological drainage season as a driving factor for N losses. PWNP results from the part of NO3 not used by crops or the mineralization part of organic matter during the preceding summer and autumn. Considering these assumptions, we used PWNP as simplified input data for the modelling of N transport. Thus, NO3 losses are mainly influenced by the denitrification capacity of soils and stream water. The well-known HYPE model was used to perform water and N losses modelling. The hydrological simulation was calibrated with the observation data at different sub-catchments. We performed a hydrograph separation validated on the thermal and isotopic tracer studies and the general knowledge of the behavior of Orgeval catchment. Our results show a good correlation between the model and the observations (a Nash-Sutcliffe coefficient of 0.75 for water discharge and 0.7 for N flux). Likewise, comparison of calibrated PWNP values with the results from a field survey (annual PWNP campaign) showed significant positive correlation. One can conclude that the simplified modeling approach using PWNP as a driving factor for the evaluation of N losses from drained agricultural catchments gave satisfactory results and we can propose this approach for a wider use.

Spatial Connectivity and Temporal Response of Variable Source Areas (VSAs): Implications for Catchment Scale Water and Solute Mixing

NASA Astrophysics Data System (ADS)

Inamdar, S.; Mitchell, M.; McDonnell, J.; McGlynn, B.; Shanley, J.

2001-05-01

The significance of variable source areas (VSAs) in storm runoff generation and as loci for mixing of event and pre-event waters has long been recognized. Recent research suggests that VSAs may also play an important role in regulating the export of C and N solutes from catchments. We hypothesize that the spatial distribution of VSAs in the catchment and their connectedness with the stream network is a first order control on the temporal dynamics and expression of water and solutes from the catchment. We examined two contrasting scenarios of VSA distribution: (1) VSAs located lower in the catchment and well connected to the stream network, versus, (2) discrete VSAs located in the upper portions of the catchment and disconnected from the stream network. We evaluated the potential impact of these scenarios on: (a) the timing and peak of event water contributions, and (b) the timing and peak of solute signatures. We hypothesized that if VSAs are well connected to the stream network (Scenario 1), then event water contributions would be distinct and would predominate early on during the rising limb of the hydrograph of stream discharge. In contrast, if VSAs are isolated and disconnected (Scenario 2), then event water contributions would be damped and delayed and possibly continue to be observed through hydrograph recession. We believe solutes such as dissolved organic carbon (DOC), which are primarily flushed from near surface soil horizons, will follow an event water trajectory. We tested these hypotheses for a 135 ha forested headwater catchment in the Adirondack Mountains of New York. Detailed storm runoff and solute data for the catchment are available since 1994. A two-component separation model using base cations (Na, Mg, Ca, and K) was used to partition stormflow discharge into pre-event and event components. Event water contributions were small on the rising limb of the hydrograph, reached their maximum just after the discharge peak, and continued through the recession limb, hours after cessation of rainfall. DOC concentrations followed a temporal pattern very similar to the event water contributions, with a peak at or just after peak discharge. In contrast, the timing of the nitrate peak appeared to vary seasonally, indicating availability of nitrate in the soil profile as a controlling mechanism. Nitrate peaks appeared to match DOC and event water peaks for spring events, but occurred much earlier on the rising limb of the discharge hydrograph during fall events. Results from this study appear to confirm our hypothesis for scenario 2, where the disconnected nature of VSAs is displayed by the delayed expression of event water and DOC. These results also confirm our hypothesis that the spatial distribution of VSAs will have a greater impact on the temporal expression of solutes that are available in near surface soil horizons, as opposed to solutes whose availability in the near surface soil varies with seasons. These hypotheses are also being evaluated for a forested subcatchment of the Sleepers River watershed in Vermont.

USE OF TRACER INJECTION EXPERIMENTS TO QUANTIFY NITRATE LOSS IN TWO ADJACENT WETLAND STREAMS DRAINING AN AGRICULTURAL FIELD IN THE GEORGIA PIEDMONT

EPA Science Inventory

This study investigated the extent to which nitrate was removed from and/or stored in a small wetland depression downgradient of a 10-ha cattle rotational grazing pasture and a 2.5-ha cropped catchment at the USDA-ARS J. Phil Campbell Sr. Natural Resource Conservation Center in W...

A Monte Carlo approach to the inverse problem of diffuse pollution risk in agricultural catchments

NASA Astrophysics Data System (ADS)

Milledge, D.; Lane, S. N.; Heathwaite, A. L.; Reaney, S.

2012-04-01

The hydrological and biogeochemical processes that operate in catchments influence the ecological quality of freshwater systems through delivery of fine sediment, nutrients and organic matter. As an alternative to the, often complex, reductionist models we outline a - data-driven - approach based on 'inverse modelling'. We invert SCIMAP, a parsimonious risk based model that has an explicit treatment of hydrological connectivity, and use a Bayesian approach to determine the risk that must be assigned to different land uses in a catchment in order to explain the spatial patterns of measured in-stream nutrient concentrations. First, we apply the model to a set of eleven UK catchments to show that: 1) some land use generates a consistently high or low risk of diffuse nitrate (N) and Phosphate (P) pollution; but 2) the risks associated with different land uses vary both between catchments and between P and N delivery; and 3) that the dominant sources of P and N risk in the catchment are often a function of the spatial configuration of land uses. These results suggest that on a case by case basis, inverse modelling may be used to help prioritise the focus of interventions to reduce diffuse pollution risk for freshwater ecosystems. However, a key uncertainty in this approach is the extent to which it can recover the 'true' risks associated with a land cover given error in both the input parameters and equifinality in model outcomes. We test this using a set of synthetic scenarios in which the true risks can be pre-assigned then compared with those recovered from the inverse model. We use these scenarios to identify the number of simulations and observations required to optimize recovery of the true weights, then explore the conditions under which the inverse model becomes equifinal (hampering recovery of the true weights) We find that this is strongly dependent on the covariance in land covers between subcatchments, introducing the possibility that instream sampling could be designed or subsampled to maximize identifiability of the risks associated with a given land cover.

Constructed wetland attenuation of nitrogen exported in subsurface drainage from irrigated and rain-fed dairy pastures.

PubMed

Tanner, C C; Nguyen, M L; Sukias, J P S

2005-01-01

Nitrogen removal performance is reported for constructed wetlands treating subsurface drainage from irrigated and rain-fed dairy pastures in North Island, New Zealand. Flow-proportional sampling of inflow and outflow concentrations were combined with continuous flow records to calculate mass balances for the wetlands. Drainage flows from the irrigated catchment were 2.5-4 fold higher and N exports up to 5 fold higher per unit area than for the rain-fed catchment. Hydraulic and associated N loadings to the wetlands were highly pulsed, associated with rainfall, soil water status, and irrigation events. Transient pulses of organic nitrogen were an important form of N loss from the rain-fed landscape in the first year, and were very effectively removed in the wetland (> 90%). Median nitrate concentrations of approximately 10 g m(-3) in the drainage inflows were reduced by 15-67% during passage through the wetlands and annual nitrate-N loads by 16-61% (38-31 7 g N m(-2)y(-1)). Generation in the wetlands of net ammoniacal-N and organic-N (irrigated site) partially negated reduction in nitrate-N loads. The results show that constructed wetlands comprising 1-2% of catchment area can provide moderate reductions in TN export via pastoral drainage, but performance is markedly influenced by variations in seasonal loading and establishment/maturation factors.

Hydrochemical responses among nested catchments of the Sleepers River Research Watershed.

NASA Astrophysics Data System (ADS)

Sebestyen, S. D.; Boyer, E. W.; Shanley, J. B.; Kendall, C.

2005-12-01

We are probing chemical and isotopic tracers of dissolved organic carbon (DOC) and nitrate over both space and time to determine how stream nutrient dynamics change with increasing basin size and differ with flow conditions. At the Sleepers River Research Watershed in northeastern Vermont, USA, 20 to 30 nested sub-basins that ranged in size from 3 to 11,000 ha were sampled repeatedly under baseflow conditions. These synoptic surveys showed a pattern of heterogeneity in headwaters that converged to a consistent response at larger basin sizes and is consistent with findings of other studies. In addition to characterizing spatial patterns under baseflow, we sampled rainfall and snowmelt events over a gradient of basin sizes to investigate scaling responses under different flow conditions. During high flow events, DOC and nitrate flushing responses varied among different basins where high-frequency event samples were collected. While the DOC and nitrate concentration patterns were similar at four headwater basins, the concentration responses of larger basins were markedly different in that the concentration patterns, flushing duration, and maximum concentrations were attenuated from headwaters to the largest basin. We are using these data to explore how flow paths and solute mixing aggregate. Overall, these results highlight the complexities of understanding spatial scaling issues in catchments and underscore the need to consider event responses of hydrology and chemistry among catchments.

High-frequency DOC and nitrate measurements provide new insights into their export and their relationships to rainfall-runoff processes

NASA Astrophysics Data System (ADS)

Schwab, Michael; Klaus, Julian; Pfister, Laurent; Weiler, Markus

2015-04-01

Over the past decades, stream sampling protocols for environmental tracers were often limited by logistical and technological constraints. Long-term sampling programs would typically rely on weekly sampling campaigns, while high-frequency sampling would remain restricted to a few days or hours at best. We stipulate that the currently predominant sampling protocols are too coarse to capture and understand the full amplitude of rainfall-runoff processes and its relation to water quality fluctuations. Weekly sampling protocols are not suited to get insights into the hydrological system during high flow conditions. Likewise, high frequency measurements of a few isolated events do not allow grasping inter-event variability in contributions and processes. Our working hypothesis is based on the potential of a new generation of field-deployable instruments for measuring environmental tracers at high temporal frequencies over an extended period. With this new generation of instruments we expect to gain new insights into rainfall-runoff dynamics, both at intra- and inter-event scales. Here, we present the results of one year of DOC and nitrate measurements with the field deployable UV-Vis spectrometer spectro::lyser (scan Messtechnik GmbH). The instrument measures the absorption spectrum from 220 to 720 nm in situ and at high frequencies and derives DOC and nitrate concentrations. The measurements were carried out at 15 minutes intervals in the Weierbach catchment (0.47 km2) in Luxemburg. This fully forested catchment is characterized by cambisol soils and fractured schist as underlying bedrock. The time series of DOC and nitrate give insights into the high frequency dynamics of stream water. Peaks in DOC concentrations are closely linked to discharge peaks that occur during or right after a rainfall event. Those first discharge peaks can be linked to fast near surface runoff processes and are responsible for a remarkable amount of DOC export. A special characterisation of the Weierbach catchment are the delayed second peaks a few days after the rainfall event. Nitrate concentrations are following this second peak. We assume that this delayed response is going back to subsurface or upper groundwater flows, with nitrate enriched water. On an inter-event scale during low flow / base flow conditions, we observe interesting diurnal patterns of both DOC and nitrate concentrations. Overall, the long-term high-frequency measurements of DOC and nitrate provide us the opportunity to separate different rainfall-runoff processes and link the amount of DOC and nitrate export to them to quantify the overall relevance of the different processes.

Stochastic Controls on Nitrate Transport and Cycling

NASA Astrophysics Data System (ADS)

Botter, G.; Settin, T.; Alessi Celegon, E.; Marani, M.; Rinaldo, A.

2005-12-01

In this paper, the impact of nutrient inputs on basin-scale nitrates losses is investigated in a probabilistic framework by means of a continuous, geomorphologically based, Montecarlo approach, which explicitly tackles the random character of the processes controlling nitrates generation, transformation and transport in river basins. This is obtained by coupling the stochastic generation of climatic and rainfall series with simplified hydrologic and biogeochemical models operating at the hillslope scale. Special attention is devoted to the spatial and temporal variability of nitrogen sources of agricultural origin and to the effect of temporally distributed rainfall fields on the ensuing nitrates leaching. The influence of random climatic variables on bio-geochemical processes affecting the nitrogen cycle in the soil-water system (e.g. plant uptake, nitrification and denitrification, mineralization), is also considered. The approach developed has been applied to a catchment located in North-Eastern Italy and is used to provide probabilistic estimates of the NO_3 load transferred downstream, which is received and accumulated in the Venice lagoon. We found that the nitrogen load introduced by fertilizations significantly affects the pdf of the nitrates content in the soil moisture, leading to prolonged risks of increased nitrates leaching from soil. The model allowed the estimation of the impact of different practices on the probabilistic structure of the basin-scale hydrologic and chemical response. As a result, the return period of the water volumes and of the nitrates loads released into the Venice lagoon has been linked directly to the ongoing climatic, pluviometric and agricultural regimes, with relevant implications for environmental planning activities aimed at achieving sustainable management practices.

Modeling greenhouse gas emissions and nutrient transport in managed arable soils with a fully coupled hydrology-biogeochemical modeling system

NASA Astrophysics Data System (ADS)

Haas, Edwin; Klatt, Steffen; Kiese, Ralf; Butterbach-Bahl, Klaus; Kraft, Philipp; Breuer, Lutz

2015-04-01

The use of mineral nitrogen fertilizer sustains the global food production and therefore the livelihood of human kind. The rise in world population will put pressure on the global agricultural system to increase its productivity leading most likely to an intensification of mineral nitrogen fertilizer use. The fate of excess nitrogen and its distribution within landscapes is manifold. Process knowledge on the site scale has rapidly grown in recent years and models have been developed to simulate carbon and nitrogen cycling in managed ecosystems on the site scale. Despite first regional studies, the carbon and nitrogen cycling on the landscape or catchment scale is not fully understood. In this study we present a newly developed modelling approach by coupling the fully distributed hydrology model CMF (catchment modelling framework) to the process based regional ecosystem model LandscapeDNDC for the investigation of hydrological processes and carbon and nitrogen transport and cycling, with a focus on nutrient displacement and resulting greenhouse gas emissions in various virtual landscapes / catchment to demonstrate the capabilities of the modelling system. The modelling system was applied to simulate water and nutrient transport at the at the Yanting Agro-ecological Experimental Station of Purple Soil, Sichuan province, China. The catchment hosts cypress forests on the outer regions, arable fields on the sloping croplands cultivated with wheat-maize rotations and paddy rice fields in the lowland. The catchment consists of 300 polygons vertically stratified into 10 soil layers. Ecosystem states (soil water content and nutrients) and fluxes (evapotranspiration) are exchanged between the models at high temporal scales (hourly to daily) forming a 3-dimensional model application. The water flux and nutrients transport in the soil is modelled using a 3D Richards/Darcy approach for subsurface fluxes with a kinematic wave approach for surface water runoff and the evapotranspiration is based on Penman-Monteith. Biogeochemical processes are modelled by LandscapeDNDC, including soil microclimate, plant growth and biomass allocation, organic matter mineralisation, nitrification, denitrification, chemodenitrification and methanogenesis producing and consuming soil based greenhouse gases. The model application will present first results of the coupled model to simulate soil based greenhouse gas emissions as well as nitrate discharge from the Yanting catchment. The model application will also present the effects of different management practices (fertilization rates and timings, tilling, residues management) on the redistribution of N surplus within the catchment causing biomass productivity gradients and different levels of indirect N2O emissions along topographical gradients.

Sources, transformations, and hydrological processes that control stream nitrate and dissolved organic matter concentrations during snowmelt in an upland forest

Treesearch

Stephen D. Sebestyen; Elizabeth W. Boyer; James B. Shanley; Carol Kendall; Daniel H. Doctor; George R. Aiken; Nobuhito Ohte

2008-01-01

We explored catchment processes that control stream nutrient concentrations at an upland forest in northeastern Vermont, USA, where inputs of nitrogen via atmospheric deposition are among the highest in the nation and affect ecosystem functioning. We traced sources of water, nitrate, and dissolved organic matter (DOM) using stream water samples collected at high...

Combined investigations on long-term hydrochemical monitoring and high frequency measurements in the Critical Zone from the Auradé catchment (SW, France)

NASA Astrophysics Data System (ADS)

Ponnou-Delaffon, Vivien; Probst, Anne; Payre-Suc, Virginie; Ferrant, Sylvain; Probst, Jean-Luc

2017-04-01

The Critical Zone (CZ) is now well identified as the land-atmosphere interface under the influence of many human pressures rendering up vulnerable for future generations. Although many investigations have been undergone over the last 30 years in the different compartments of the CZ, it remains important to understand the overall functioning of this area in a context of global change. A long-term hydrological and chemical monitoring was performed since 30 years for nitrates and discharge, and for 10 years for major elements at the stream outlet of a small agricultural carbonated catchment (Auradé site). This catchment is part of the observatories network OZCAR infrastructure and since 1992 it was a pilot for improving agricultural practices. Two time scales were investigated based on a discrete sampling during low water flow and hydrological events, and since 2006 on high frequency datas (every 10mn) for pH, conductivity, nitrate, temperature…using a multiparameter probe. The long-term trends indicated mostly a decreasing in nitrate, Ca and Mg concentrations namely and an increase in DOC, which can be related to the influence of the environmental practices (fertilizers inputs, vegetative filter strip etc..), but more recently to the changes in temperature and hydrological patterns (decreasing discharge and occurrence of rare but intensive events). The high frequency measurements on short-term events allowed: (i) to highlight the mechanisms involved in flux exportations (nycthemeral cycle for nitrates as ex.), (ii) to reconstruct the chemical patterns by correlating the parameters to major elements, and finally (iii) to have a better and more precise approach of the contribution of weathering and land use on the hydrochemical functioning of the CZ, particularly on the disturbance of carbon cycle by anthropogenic fingerprints.

Sensitivity of stream water age to climatic variability and land use change: implications for water quality

NASA Astrophysics Data System (ADS)

Soulsby, Chris; Birkel, Christian; Geris, Josie; Tetzlaff, Doerthe

2016-04-01

Advances in the use of hydrological tracers and their integration into rainfall runoff models is facilitating improved quantification of stream water age distributions. This is of fundamental importance to understanding water quality dynamics over both short- and long-time scales, particularly as water quality parameters are often associated with water sources of markedly different ages. For example, legacy nitrate pollution may reflect deeper waters that have resided in catchments for decades, whilst more dynamics parameters from anthropogenic sources (e.g. P, pathogens etc) are mobilised by very young (<1 day) near-surface water sources. It is increasingly recognised that water age distributions of stream water is non-stationary in both the short (i.e. event dynamics) and longer-term (i.e. in relation to hydroclimatic variability). This provides a crucial context for interpreting water quality time series. Here, we will use longer-term (>5 year), high resolution (daily) isotope time series in modelling studies for different catchments to show how variable stream water age distributions can be a result of hydroclimatic variability and the implications for understanding water quality. We will also use examples from catchments undergoing rapid urbanisation, how the resulting age distributions of stream water change in a predictable way as a result of modified flow paths. The implication for the management of water quality in urban catchments will be discussed.

Multiple stressor effects on biological quality elements in the Ebro River: Present diagnosis and predicted responses.

PubMed

Herrero, Albert; Gutiérrez-Cánovas, Cayetano; Vigiak, Olga; Lutz, Stefanie; Kumar, Rohini; Gampe, David; Huber-García, Verena; Ludwig, Ralf; Batalla, Ramon; Sabater, Sergi

2018-07-15

Multiple abiotic stressors affect the ecological status of water bodies. The status of waterbodies in the Ebro catchment (NE Spain) is evaluated using the biological quality elements (BQEs) of diatoms, invertebrates and macrophytes. The multi-stressor influence on the three BQEs was evaluated using the monitoring dataset available from the catchment water authority. Nutrient concentrations, especially total phosphorus (TP), affected most of the analyzed BQEs, while changes in mean discharge, water temperature, or river morphology did not show significant influences. Linear statistical models were used to evaluate the change of water bodies' ecological status under different combinations of future socioeconomic and climate scenarios. Changes in land use, rainfall, water temperature, mean discharge, TP and nitrate concentrations were modeled according to the future scenarios. These revealed an evolution of the abiotic stressors that could lead to a general decrease in the ecosystem quality of water bodies within the Ebro catchment. This deterioration was especially evidenced on the diatoms and invertebrate biological indices, mainly because of the foreseen increase in TP concentrations. Water bodies located in the headwaters were seen as the most sensitive to future changes. Copyright © 2018 The Author(s). Published by Elsevier B.V. All rights reserved.

Delimitation of areas under the real pressure from agricultural activities due to nitrate water pollution in Poland

NASA Astrophysics Data System (ADS)

Wozniak, E.; Nasilowska, S.; Jarocinska, A.; Igras, J.; Stolarska, M.; Bernoussi, A. S.; Karaczun, Z.

2012-04-01

The aim of the performed research was to determine catchments under the nitrogen pressure in Poland in period of 2007-2010. National Water Management Authority in Poland uses the elaborated methodology to fulfil requirements of Nitrate Directive and Water Framework Directive. Multicriteria GIS analysis was conducted on the base on various types of environmental data, maps and remote sensing products. Final model of real agricultural pressure was made using two components: (i) potential pressure connected with agriculture (ii) the vulnerability of the area. The agricultural pressure was calculated using the amount of nitrogen in fertilizers and the amount of nitrogen produced by animal breeding. The animal pressure was based on the information about the number of bred animals of each species for communes in Poland. The spatial distribution of vegetation pressure was calculated using kriging for the whole country base on the information about 5000 points with the amount of nitrogen dose in fertilizers. The vulnerability model was elaborated only for arable lands. It was based on the probability of the precipitation penetration to the ground water and runoff to surface waters. Catchment, Hydrogeological, Soil, Relief or Land Cover maps allowed taking into account constant environmental conditions. Additionally information about precipitation for each day of analysis and evapotranspiration for every 16-day period (calculated from satellite images) were used to present influence of meteorological condition on vulnerability of the terrain. The risk model is the sum of the vulnerability model and the agricultural pressure model. In order to check the accuracy of the elaborated model, the authors compared the results with the eutrophication measurements. The model accuracy is from 85,3% to 91,3%.

Storm runoff quality and pollutant loading from commercial, residential, and industrial catchments in the tropic.

PubMed

Chow, M F; Yusop, Z; Shirazi, S M

2013-10-01

Information on the pollution level and the influence of hydrologic regime on the stormwater pollutant loading in tropical urban areas are still scarce. More local data are still required because rainfall and runoff generation processes in tropical environment are very different from the temperate regions. This study investigated the extent of urban runoff pollution in residential, commercial, and industrial catchments in the south of Peninsular Malaysia. Stormwater samples and flow rate data were collected from 51 storm events. Samples were analyzed for total suspended solids, 5-day biochemical oxygen demand, chemical oxygen demand, oil and grease (O&G), nitrate nitrogen (NO3-N), nitrite nitrogen, ammonia nitrogen, soluble reactive phosphorus, total phosphorus (TP), and zinc (Zn). It was found that the event mean concentrations (EMCs) of pollutants varied greatly between storm characteristics and land uses. The results revealed that site EMCs for residential catchment were lower than the published data but higher for the commercial and industrial catchments. All rainfall variables were negatively correlated with EMCs of most pollutants except for antecedent dry days (ADD). This study reinforced the earlier findings on the importance of ADD for causing greater EMC values with exceptions for O&G, NO3-N, TP, and Zn. In contrast, the pollutant loadings are influenced primarily by rainfall depth, mean intensity, and max 5-min intensity in all the three catchments. Overall, ADD is an important variable in multiple linear regression models for predicting the EMC values in the tropical urban catchments.

Inverse coupling of DOC and nitrate export from soils and streams

NASA Astrophysics Data System (ADS)

Goodale, Christine

2013-04-01

Over the last two decades, nitrate concentrations in surface waters have decreased across the Northeastern United States and parts of northern Europe. Many hypotheses have been proposed to explain this decrease, but the cause remains unclear. One control may be associated with increasing abundance of dissolved organic carbon (DOC), which in turn may be a result of soil recovery from acidification. Compared across catchments, surface water NO3- decreases sharply with increasing DOC concentration. Here, we used measurements of soil and solution nitrate, DOC, and their isotopic composition (13C-DOC, 15N- and 18O-NO3) to test several related hypotheses that changing acidification affects the release of DOC and bio-available DOC (bDOC) from soil, and that variation in stocks of soil C and release of bDOC partly control NO3- export from forested catchments in New York State, USA. We examined whether DOC and NO3- are both driven by soil C processes that produce inverse coupling at the scale of soil cores as well as across catchments, through comparison of soil and surface water chemistry across nine catchments selected from long-term monitoring networks in the Catskill and Adirondack Mountains. In addition, we conducted a series of soil core leaching experiments to examine the role of acidification and recovery in driving the net production of DOC and NO3- from soils. Over 8 months, soil cores were leached biweekly with simulated rainfall solutions of varying pH (3.6 to 7.0) from additions of H2SO4, CaCO3 and NaOH. These experiments did not yield a pH-induced change in DOC quantity, but did show a change in DOC quality, in that acidified cores released more bio-available DOC with less depleted 13C-DOC than cores with experimentally increased pH. All cores leached substantial amounts of nitrate. Together, these lab- and field comparisons are being used to identify the role of soil production and consumption processes in driving cross-watershed differences in DOC and NO3- loss, or whether other factors (e.g., riparian, in-stream or hydrologic processes) likely explain this relationship.

DIN retention-transport through four hydrologically connected zones in a headwater catchment of the Upper Mississippi River

USGS Publications Warehouse

Triska, F.J.; Duff, J.H.; Sheibley, R.W.; Jackman, A.P.; Avanzino, R.J.

2007-01-01

Dissolved inorganic nitrogen (DIN) retention-transport through a headwater catchment was synthesized from studies encompassing four distinct hydrologic zones of the Shingobee River Headwaters near the origin of the Mississippi River. The hydrologic zones included: (1) hillslope ground water (ridge to bankside riparian); (2) alluvial riparian ground water; (3) ground water discharged through subchannel sediments (hyporheic zone); and (4) channel surface water. During subsurface hillslope transport through Zone 1, DIN, primarily nitrate, decreased from ???3 mg-N/l to <0.1 mg-N/l. Ambient seasonal nitrate:chloride ratios in hillslope flow paths indicated both dilution and biotic processing caused nitrate loss. Biologically available organic carbon controlled biotic nitrate retention during hillslope transport. In the alluvial riparian zone (Zone 2) biologically available organic carbon controlled nitrate depletion although processing of both ambient and amended nitrate was faster during the summer than winter. In the hyporheic zone (Zone 3) and stream surface water (Zone 4) DIN retention was primarily controlled by temperature. Perfusion core studies using hyporheic sediment indicated sufficient organic carbon in bed sediments to retain ground water DIN via coupled nitrification-denitrification. Numerical simulations of seasonal hyporheic sediment nitrification-denitrification rates from perfusion cores adequately predicted surface water ammonium but not nitrate when compared to 5 years of monthly field data (1989-93). Mass balance studies in stream surface water indicated proportionally higher summer than winter N retention. Watershed DIN retention was effective during summer under the current land use of intermittently grazed pasture. However, more intensive land use such as row crop agriculture would decrease nitrate retention efficiency and increase loads to surface water. Understanding DIN retention capacity throughout the system, including special channel features such as sloughs, wetlands and floodplains that provide surface water-ground water connectivity, will be required to develop effective nitrate management strategies. ?? 2007 American Water Resources Association.

Role of antecedent conditions on nitrogen and phosphorus mobilisation observed in a lowland arable catchment in eastern England: insights from high-frequency monitoring

NASA Astrophysics Data System (ADS)

Outram, Faye; Hiscock, Kevin; Dugdale, Stephen; Lovett, Andrew

2015-04-01

In order to reduce annual riverine loadings of nutrients which are responsible for degradation of ecosystems downstream and in near coastal areas, it is important to first understand the mobilisation and pathways responsible for transporting them from source to river and how these pathways vary in space and time. The Blackwater tributary of the River Wensum in Norfolk, England, has been equipped with a sensor network as part of the Demonstration Test Catchments project, which has the aim of reducing pollution from agriculture to river systems whilst maintaining food security by the trial of mitigation measures on working farms at the sub-catchment level. The River Wensum is a lowland chalk catchment with intensive arable agriculture and high occurrence of tile drainage on heavier soils. Three hydrological years of high-frequency data have been gathered in the Blackwater since October 2011, including rainfall, half hourly measurements of discharge and groundwater level coupled with hydrochemical parameters including nitrate, total phosphorus (TP) and total reactive phosphorus (TRP). In the three years of data collection, there were distinct departures from long-term rainfall averages as the winter of 2011-12 was extremely dry following a drought from the previous hydrological year, followed by a summer which was unseasonably wet, which continued into the following winter. The relationship between rainfall, storage and discharge was found to be complex, which in turn had an impact on the dominant controls transporting nutrients from the landscape to the river network. Thirty three storms occurred throughout the three year period which have been analysed in the context of the range of hydrometeorological conditions observed throughout the dataset. Discharge-concentration hysteretic responses of nitrogen, TP and TRP have been used alongside statistical analysis of storm characteristics including antecedent hydrological conditions. The nitrate storm response showed distinct seasonal patterns which were greatly impacted by the activation of tile drain flow throughout the winter period and during the fertiliser application window between March-May, with the dry winter in 2011-12 standing apart from the more 'typical' years. Four different storm response categories were identified for nitrate according to dominant flow pathways. The phosphorus response was far less uniform throughout the study period, showing patterns of exhaustion with successive events. Both nitrate and phosphorus loads were disproportionate to flow volume in storm events which occurred after significant dry periods. The data show the importance of antecedent conditions in the storage, mobilisation and transport of nitrogen and phosphorus in agricultural catchments which has important implications for the conceptual understanding of catchment functioning and environmental management.

Using groundwater age to understand sources and dynamics of nutrient contamination through the catchment into Lake Rotorua, New Zealand

NASA Astrophysics Data System (ADS)

Morgenstern, U.; Daughney, C. J.; Leonard, G.; Gordon, D.; Donath, F. M.; Reeves, R.

2014-08-01

The water quality of Lake Rotorua has declined continuously over the past 50 yr despite mitigation efforts over recent decades. Delayed response of the groundwater discharges to historic land-use intensification 50 yr ago was the reason suggested by early tritium measurements, which indicated large transit times through the groundwater system. We use the isotopic and chemistry signature of the groundwater for detailed understanding of the origin, fate, flow pathways, lag times, and future loads of contaminants. A unique set of high-quality tritium data over more than four decades, encompassing the time when the tritium spike from nuclear weapons testing moved through the groundwater system, allows us to determine detailed age distribution parameters of the water discharging into Lake Rotorua. The Rotorua volcanic groundwater system is complicated due to the highly complex geology that has evolved through volcanic activity. Vertical and steeply-inclined geological contacts preclude a simple flow model. The extent of the Lake Rotorua groundwater catchment is difficult to establish due to the deep water table in large areas, combined with inhomogeneous groundwater flow patterns. Hierarchical cluster analysis of the water chemistry parameters provided evidence of the recharge source of the large springs near the lake shore, with discharge from the Mamaku ignimbrite through lake sediment layers. Groundwater chemistry and age data show clearly the source of nutrients that cause lake eutrophication, nitrate from agricultural activities and phosphate from geologic sources. With a naturally high phosphate load reaching the lake continuously via all streams, the only effective way to limit algae blooms and improve lake water quality in such environments is by limiting the nitrate load. The groundwater in the Rotorua catchment, once it has passed through the soil zone, shows no further decrease in dissolved oxygen, indicating absence of electron donors in the aquifer that could facilitate microbial denitrification reactions. Nitrate from land-use activities that leaches out of the root zone of agricultural land into the deeper part of the groundwater system must be expected to travel with the groundwater to the lake. The old age and the highly mixed nature of the water discharges imply a very slow and lagged response of the streams and the lake to anthropogenic contaminants in the catchment, such as nitrate. Using the age distribution as deduced from tritium time series data measured in the stream discharges into the lake allows prediction of future nutrient loads from historic land-use activities 50 yr ago. For Hamurana Stream, the largest stream to Lake Rotorua, it takes more than a hundred years for the groundwater-dominated stream discharge to adjust to changes in land-use activities. These time scales apply to activities that cause contamination, but also to remediation action.

Distributed modelling of hydrologic regime at three subcatchments of Kopaninský tok catchment

NASA Astrophysics Data System (ADS)

Žlábek, Pavel; Tachecí, Pavel; Kaplická, Markéta; Bystřický, Václav

2010-05-01

Kopaninský tok catchment is situated in crystalline area of Bohemo-Moravian highland hilly region, with cambisol cover and prevailing agricultural land use. It is a subject of long term (since 1980's) observation. Time series (discharge, precipitation, climatic parameters...) are nowadays available in 10 min. time step, water quality average daily composit samples plus samples during events are available. Soil survey resulting in reference soil hydraulic properties for horizons and vegetation cover survey incl. LAI measurement has been done. All parameters were analysed and used for establishing of distributed mathematical models of P6, P52 and P53 subcatchments, using MIKE SHE 2009 WM deterministic hydrologic modelling system. The aim is to simulate long-term hydrologic regime as well as rainfall-runoff events, serving the base for modelling of nitrate regime and agricultural management influence in the next step. Mentioned subcatchments differs in ratio of artificial drainage area, soil types, land use and slope angle. The models are set-up in a regular computational grid of 2 m size. Basic time step was set to 2 hrs, total simulated period covers 3 years. Runoff response and moisture regime is compared using spatially distributed simulation results. Sensitivity analysis revealed most important parameters influencing model response. Importance of spatial distribution of initial conditions was underlined. Further on, different runoff components in terms of their origin, flow paths and travel time were separated using a combination of two runoff separation techniques (a digital filter and a simple conceptual model GROUND) in 12 subcatchments of Kopaninský tok catchment. These two methods were chosen based on a number of methods testing. Ordinations diagrams performed with Canoco software were used to evaluate influence of different catchment parameters on different runoff components. A canonical ordination method analyses (RDA) was used to explain one data set (runoff components - either volumes of each runoff component or occurence of baseflow) with another data set (catchment parameters - proportion of arable land, proportion of forest, proportion of vulnerable zones with high infiltration capacity, average slope, topographic index and runoff coefficient). The influence was analysed both for long-term runoff balance and selected rainfall-runoff events. Keywords: small catchment, water balance modelling, rainfall-runoff modelling, distributed deterministic model, runoff separation, sensitivity analysis

Filling Gaps in Biogeochemical Understanding of Wildfire Effects on Watersheds and Water Quality

NASA Astrophysics Data System (ADS)

Rhoades, Charles; Covino, Timothy; Chow, Alex

2017-04-01

Large, high-severity wildfires alter the biogeochemical conditions that determine how watersheds retain and release nutrients and influence stream water quality. These effects are commonly expected to abate within a few years, but recent studies show that post-fire watershed changes can have persistent, but poorly-understood biogeochemical consequences. Owing to the increased frequency and extent of high-severity wildfires predicted for western North America, and the growing awareness of the links between wildfire and clean water supply, there is a need to address these knowledge gaps. For the past 15 years we have tracked stream nutrients, chemistry, temperature, and sediment after the 2002 Hayman Fire, the largest wildfire in Colorado history. Our earlier work showed that headwater catchments that experienced extensive, high-severity forest fires had elevated stream nitrate, temperature, and turbidity for five post-fire years. Recent sampling, conducted 13 and 14 years after the fire, found that turbidity had largely returned to pretreatment levels, but that stream nitrate remained an order of magnitude above pre-fire levels in catchments with extensive high-severity wildfire. Stream temperature and total dissolved nitrogen concentration also remained higher in those catchments compared to unburned streams. Decreased plant demand is the mechanism commonly credited for post-fire nutrient losses, though our current work is evaluating the implications of soil and stream nutrient uptake and supply on persistent nitrogen (N) export from severely-burned catchments. For example, we have measured higher total soil N and higher net N mineralization in severely-burned portions of the Hayman Fire compared to moderately or unburned areas, indicating that higher soil N supply may contribute to N losses from upland soils. Conversely, using a nutrient tracer approach we found reduced N uptake in burned streams, which suggests a switch from the N-limited conditions typical of pristine catchments. Low stream dissolved organic carbon (DOC) in severely-burned catchments suggests greater carbon limitation on in-stream biological activity. This is the likely result of organic matter losses during the wildfire compounded by low allochthonous inputs from uplands or riparian zones. We also find that catchments with severely-burned headwater reaches and sparse riparian vegetation have high stream nitrate. Our findings regarding soil N supply and in-stream N retention coupled with the persistent N losses from burned headwaters and exposed riparian zones help prioritize restoration efforts aimed at mitigating long-term water quality effects of severe wildfires.

An analysis of the chemical and microbiological quality of ground water from boreholes and shallow wells in Zimbabwe

NASA Astrophysics Data System (ADS)

Moyo, N. A. G.

Groundwater from boreholes and shallow wells is a major source of drinking water in most rural areas of Zimbabwe. The quality of groundwater has been taken for granted and the status and the potential threats to groundwater quality have not been investigated on a large scale in Zimbabwe. A borehole and shallow well water quality survey was undertaken between January, 2009 and February, 2010 to determine the chemical and microbial aspects of drinking water in three catchment areas. Groundwater quality physico-chemical indicators used in this study were nitrates, chloride, water hardness, conductivity, alkalinity, total dissolved solids, iron, magnesium, manganese, potassium, calcium, fluoride, sulphates, sodium and pH. The microbiological indicators were total coliforms, faecal coliforms and heterotrophs. Principal component analysis (PCA) showed that most of the variation in ground water quality in all catchment areas is accounted for by Total Dissolved Solids (TDS), electrical conductivity (EC), sodium, bicarbonate and magnesium. The principal dissolved constituents in ground water are in the form of electrically charged ions. Nitrate is a significant problem as the World Health Organization recommended levels were exceeded in 36%, 37% and 22% of the boreholes in the Manyame, Mazowe and Gwayi catchment areas respectively. The nitrate levels were particularly high in commercial farming areas. Iron and manganese also exceeded the recommended levels. The probable source of high iron levels is the underlying geology of the area which is dominated by dolerites. Dolerites weather to give soils rich in iron and other mafic minerals. The high level of manganese is probably due to the lithology of the rock as well as mining activity in some areas. Water hardness is a problem in all catchment areas, particularly in the Gwayi catchment area where a value of 2550 mg/l was recorded in one borehole. The problems with hard water use are discussed. Chloride levels exceeded the recommended levels in a few areas under irrigation. Most of the chloride is probably from agricultural activity particularly the application of potassium chloride. Fluoride levels were particularly elevated in the Gwayi catchment area and this is because of the geology of the area. There was no evidence of microbial contamination in all the boreholes sampled as the total coliform, faecal coliforms, heterotrophs count was nil. However, severe microbial contamination was found in the wells especially those in clay areas.

Turbidity and nitrate transfer in karstic aquifers in rural areas: the Brionne Basin case-study.

PubMed

Nebbache, S; Feeny, V; Poudevigne, I; Alard, D

2001-08-01

The degradation of water quality in many groundwaters of Europe is a major source of concern. Rises in turbidity and nitrate concentrations represent present or potential threats for the quality of drinking water in rural areas. They are for the most part a consequence of agricultural intensification which has considerably affected land cover and land use in recent decades. In our case-study (a karstic catchment) the mechanisms which explain changes in water quality, as far as turbidity and nitrate are concerned, result from a strong continuity between surface and underground waters. The karstic system of the Brionne Basin can be considered as both the focus of rapid horizontal flows (runoff, a rapid process in which rainwater reaches the spring directly through sinkholes) and slow vertical flows (leaching, in which rainwater filters through the soil to the spring). A hierarchical approach to the water pollution problem of the basin suggests that turbidity or nitrate concentrations peak during heavy rain episodes and are short-term events. In terms of management, this implies that the solution to water pollution caused by such events is also short-term and can therefore be addressed at a local scale. The rise of nitrate concentrations during the past twenty years is the main concern. The solution can only be found at a global scale (all the catchment area must be taken in account: land plots and their spatial configuration), and by taking a long-term approach.

The water quality of the River Enborne, UK: insights from high-frequency monitoring

NASA Astrophysics Data System (ADS)

Halliday, Sarah; Skeffington, Richard; Wade, Andrew; Bowes, Mike; Gozzard, Emma; Palmer-Felgate, Elizabeth; Newman, Johnathan; Jarvie, Helen; Loewenthal, Matt

2014-05-01

The River Enborne is a rural lowland catchment, impacted by agricultural runoff, and septic tank and sewage treatment works (STWs) discharges. Between November 2009 and February 2012, the river was instrumented with in situ analytical equipment to take hourly measurements of total reactive phosphorus (TRP), using a Systea Micromac C; nitrate, using a Hach Lange Nitratax; and pH, chlorophyll, dissolved oxygen, conductivity, turbidity and water temperature, using a YSI 6600 Multi-parameter sonde. In addition, weekly 'grab samples' were also collected and analysed for a wide range of chemical determinands including major ions, nutrients, and trace elements. The catchment land use is largely agricultural, with wheat the dominant crop, and the average population density is 123 persons per sq. km. The river water is largely derived from calcareous groundwater, with a mean calcium concentration of 68.5 mg/l, and high nitrogen and phosphorus concentrations, with mean nitrate and TRP concentrations of 3.96 mg/l-N and 0.17 mg/l-P respectively. A mass-balance for the catchment demonstrated that agricultural fertiliser is the dominant source of annual loads of both nitrogen and phosphorus, accounting for 77 % and 84 % respectively. However, the concentration data show that sewage effluent discharges have a disproportionate effect on the river nitrogen and phosphorus dynamics, with the diurnal STW discharge signal discernable in the high-frequency nutrient dynamics. The nutrient dynamics and correlation structure of the data indicate a substantial contribution of groundwater and agricultural runoff to stream nitrate concentrations, whereas discharges from septic tank systems and sewage treatment works are a more important source of phosphorus. The high-frequency turbidity and conductivity dynamics reveal key information about the seasonal changes controlling the system dynamics, with marked differences in diurnal conductivity dynamics at the onset of riparian shading linked to the decreased importance of the photosynthetically-driven cycle of bicarbonate concentration. Only 4 % of the phosphorus input and 9 % of the nitrogen input is exported from the catchment by the river, highlighting the importance of catchment process understanding in predicting nutrient concentrations. High-frequency monitoring will be a key to developing this vital process understanding.

Relative importance of time, land use and lithology on determining aquifer-scale denitrification

NASA Astrophysics Data System (ADS)

Kolbe, Tamara; de Dreuzy, Jean-Raynald; Abbott, Benjamin W.; Marçais, Jean; Babey, Tristan; Thomas, Zahra; Peiffer, Stefan; Aquilina, Luc; Labasque, Thierry; Laverman, Anniet; Fleckenstein, Jan; Boulvais, Philippe; Pinay, Gilles

2017-04-01

Unconfined shallow aquifers are commonly contaminated by nitrate in agricultural regions, because of excess fertilizer application over the last decades. Watershed studies have indicated that 1) changes in agricultural practices have caused changes in nitrate input over time, 2) denitrification occurs in localized hotspots within the aquifer, and 3) heterogeneous groundwater flow circulation has led to strong nitrate gradients in aquifers that are not yet well understood. In this study we investigated the respective influence of land use, groundwater transit time distribution, and hotspot distribution on groundwater denitrification with a particular interest on how a detailed understanding of transit time distributions could be used to upscale the point denitrification measurements to the aquifer-scale. We measured CFC-based groundwater age, oxygen, nitrate, and dinitrogen gas excess in 16 agricultural wells of an unconfined crystalline aquifer in Brittany, France. Groundwater age data was used to calibrate a mechanistic groundwater flow model of the study site. Historical nitrate inputs were reconstructed by using measured nitrate concentrations, dinitrogen gas excess and transit time distributions of the wells. Field data showed large differences in denitrification activity among wells, strongly associated with differences in transit time distribution. This suggests that knowing groundwater flow dynamics and consequent transit time distributions at the catchment-scale could be used to estimate the overall denitrification capacity of agricultural aquifers.

Using Spring Water Nitrate to Monitor Spatiotemporal Trends in Nitrogen Deposition for the Santa Clara Valley Habitat Plan

NASA Astrophysics Data System (ADS)

Weiss, S. B.; Hastings, M. G.

2016-12-01

Atmospheric nitrogen deposition is a major acute threat to biodiversity, but has rarely been addressed in regulatory conservation plans. The Santa Clara Valley Habitat Plan is a Habitat Conservation Plan/Natural Communities Conservation Plan (HCP/NCCP) that addresses development impacts on 19 covered species, most of which inhabit nutrient-poor serpentine grasslands that are highly sensitive to N-deposition with a critical load of 6 kg-N ha-1 year-1. Increased N-deposition from highway improvements and development was a major regulatory nexus, and a novel nitrogen fee based on car trips generated is one of the funding mechanisms, driving a need for cost-effective and robust monitoring of N-deposition trends over the 50-year plan and beyond. In the high deposition zone (10-20 kg-N ha-1 year-1), spring water nitrate levels up to 25 ppm (as NO3-) were measured in baseflow, levels higher than any reported for non-agricultural sites in California. Nitrate measurements follow measured and modeled deposition gradients, and are affected by catchment soils, geomorphology, and vegetation. Existing knowledge of local nitrogen deposition using passive samplers, CMAQ models, N-cycling measurements, and emissions inventories/projections are used to generate hypotheses that can be tested with a combination of spring water nitrate sampled through the year and across deposition gradients, N and O isotopic analysis including 17O to trace atmospheric nitrate, modeled recharge rates, and groundwater dating. A set of sentinel springs for long-term monitoring will be identified and sampled on an interval commensurate with shallow groundwater residence times. The unique characteristics of serpentine grasslands (low productivity, shallow soils, highly fractured bedrock, and numerous springs) provide a model system for tracing N-deposition and its effects on protected species.

Environmental land use conflicts in catchments: A major cause of amplified nitrate in river water.

PubMed

Pacheco, F A L; Sanches Fernandes, L F

2016-04-01

Environmental land use conflicts are uses of the land that ignore soil capability. In this study, environmental land use conflicts were investigated in mainland Portugal, using Partial Least Squares (PLS) regression combined with GIS modeling and a group of 85 agricultural watersheds (with >50% occupation by agriculture) as work sample. The results indicate a dominance of conflicts in a region where vineyards systematically invaded steep hillsides (the River Douro basin), where forests would be the most appropriate use. As a consequence of the conflicts, nitrate concentrations in rivers and lakes from these areas have increased, sometimes beyond the legal limit of 50mg/L imposed by the European and Portuguese laws. Excessive nitrate concentrations were also observed along the Atlantic coast of continental Portugal, but associated to a combination of other factors: large population densities, and incomplete coverage by sewage systems and inadequate functioning of wastewater treatment plants. Before this study, environmental land use conflicts were never recognized as possible boost of nitrate concentrations in surface water. Bearing in mind the consequences of drinking water nitrate for human health, a number of land use change scenarios were investigated to forecast their impact on freshwater nitrate concentrations. It was seen that an aggravation of the conflicts would duplicate the number of watersheds with maximum nitrate concentrations above 50mg/L (from 11 to 20 watersheds), while the elimination of the conflicts would greatly reduce that number (to 3 watersheds). Copyright © 2016 Elsevier B.V. All rights reserved.

Evaluating Ecosystem Services for Reducing Groundwater Nitrate Contamination: Nitrate Attenuation in the Unsaturated and Saturated Zones

NASA Astrophysics Data System (ADS)

Wang, J.

2013-12-01

Nitrates are the most common type of groundwater contamination in agricultural regions. Environmental policies targeting nitrates have focused on input control (e.g., restricted fertilizer application), intermediate loads control (e.g., reduce nitrate leached from crop fields), and final loads control (e.g., reduce catchment nitrate loads). Nitrate loads can be affected by hydrological processes in both unsaturated and saturated zones. Although many of these processes have been extensively investigated in literature, they are commonly modeled as exogenous to farm management. A couple of recent studies by scientists from the Lawrence Livermore National Laboratory show that in some situations nitrate attenuation processes in the unsaturated/saturated zone, particularly denitrification, can be intensified by certain management practices to mitigate nitrate loads. Therefore, these nitrate attenuation processes can be regarded as a set of ecosystem services that farmers can take advantage of to reduce their cost of complying with environmental policies. In this paper, a representative California dairy farm is used as a case study to show how such ecosystem attenuation services can be framed within the farm owner's decision-making framework as an option for reducing groundwater nitrate contamination. I develop an integrated dynamic model, where the farmer maximizes discounted net farm profit over multiple periods subject to environmental regulations. The model consists of three submodels: animal-waste-crop, hydrologic, and economic model. In addition to common choice variables such as irrigation, fertilization, and waste disposal options, the farmer can also endogenously choose from three water sources: surface water, deep groundwater (old groundwater in the deep aquifer that is not affected by farm effluent in the short term), and shallow groundwater (drainage water that can be recycled via capture wells at the downstream end of the farm). The capture wells not only recycle wastewater, but can also increase the likelihood of denitrification. Thus the farmer essentially can choose whether, and to which extent, to install capture wells and take advantage of the ecosystem attenuation services. Decision rules from the dynamic optimization model demonstrate best management practices for the farm to improve its economic and environmental performance. I further use an economic valuation technique to value these services. Under the Millennium Ecosystem Assessment framework, nitrate attenuation in the unsaturated and saturated zone provides regulatory ecosystem services to humans, mainly nutrient regulation and waste treatment. With the integrated farm model, the production function approach is adopted to get the economic value of these regulatory services. The results highlight the significant role the environment can play in nitrate pollution control and potential benefits from designing policies that acknowledge this role. The most desirable policies are those that create incentive for farmers to use potential ecosystem services, which significantly reduce environmental compliance costs and increase social welfare.

Spatial and temporal trends in nitrate concentrations in the River Derwent, North Yorkshire, and its need for NVZ status.

PubMed

Mian, Ishaq A; Begum, Shaheen; Riaz, Muhammad; Ridealgh, Mike; McClean, Colin J; Cresser, Malcolm S

2010-01-15

Long-term spatial and temporal variations in nitrate-N concentrations along the River Derwent have been examined using Environment Agency data to investigate the relative importance of impacts of atmospheric N deposition, land use, and changes in management. Where moorland and rough grazing dominate upstream of Forge Valley and Malton, over the 20 years since 1988 mean nitrate-N concentrations were initially increasing significantly, but are now levelling off, with peaks at ca. 4.5 mg Nl(-1). As expected in a catchment in a nitrate vulnerable zone (NVZ), more agricultural land use increases mean nitrate concentrations and the occurrence of distinct winter maxima, though the latter have become markedly less pronounced since 2001. It is suggested that this improvement is a combined effect of imposition of NVZ designation in the lower reaches in 2002, animal number declines associated with the Foot & Mouth outbreak in the region in 2001, and the impact of farmers' responses to increasing fertilizer prices and to beneficial pollutant mineral N inputs from the atmosphere. Minima in nitrate-N concentrations in summer have become much less pronounced over the past decade and are typically ca. 60% higher in concentration than a decade earlier. This probably is attributable to the effects of pollutant-N leaching to depths in soil below the rooting zone when near surface biotic uptake is low in winter. The resultant N mineralization in summer enhances summer nitrate leaching. The Derwent is a relatively clean river; however, its entire catchment was designated justifiably as a NVZ in January 2009, apparently based upon a projected 95 percentile nitrate-N concentration >11.29 mg l(-1) for 2010 based upon forward projection of data from 1990 to 2004 for Derwent Bridge. A survey of water quality in March 2009 showed that some agricultural areas are still making a significant contribution to the total nitrate level well downstream, at the point responsible for implementation of NVZ status. At 3 of the 29 sites sampled, nitrate concentration exceeded 60 mg l(-1). Copyright 2009 Elsevier B.V. All rights reserved.

Coupled hydrological and biogeochemical processes controlling variability of nitrogen species in streamflow during autumn in an upland forest

USGS Publications Warehouse

Sebestyen, Stephen D.; Shanley, James B.; Boyer, Elizabeth W.; Kendall, Carol; Doctor, Daniel H.

2014-01-01

Autumn is a season of dynamic change in forest streams of the northeastern United States due to effects of leaf fall on both hydrology and biogeochemistry. Few studies have explored how interactions of biogeochemical transformations, various nitrogen sources, and catchment flow paths affect stream nitrogen variation during autumn. To provide more information on this critical period, we studied (1) the timing, duration, and magnitude of changes to stream nitrate, dissolved organic nitrogen (DON), and ammonium concentrations; (2) changes in nitrate sources and cycling; and (3) source areas of the landscape that most influence stream nitrogen. We collected samples at higher temporal resolution for a longer duration than typical studies of stream nitrogen during autumn. This sampling scheme encompassed the patterns and extremes that occurred during base flow and stormflow events of autumn. Base flow nitrate concentrations decreased by an order of magnitude from 5.4 to 0.7 µmol L−1 during the week when most leaves fell from deciduous trees. Changes to rates of biogeochemical transformations during autumn base flow explained the low nitrate concentrations; in-stream transformations retained up to 72% of the nitrate that entered a stream reach. A decrease of in-stream nitrification coupled with heterotrophic nitrate cycling were primary factors in the seasonal nitrate decline. The period of low nitrate concentrations ended with a storm event in which stream nitrate concentrations increased by 25-fold. In the ensuing weeks, peak stormflow nitrate concentrations progressively decreased over closely spaced, yet similarly sized events. Most stormflow nitrate originated from nitrification in near-stream areas with occasional, large inputs of unprocessed atmospheric nitrate, which has rarely been reported for nonsnowmelt events. A maximum input of 33% unprocessed atmospheric nitrate to the stream occurred during one event. Large inputs of unprocessed atmospheric nitrate show direct and rapid effects on forest streams that may be widespread, although undocumented, throughout nitrogen-polluted temperate forests. In contrast to a week-long nitrate decline during peak autumn litterfall, base flow DON concentrations increased after leaf fall and remained high for 2 months. Dissolved organic nitrogen was hydrologically flushed to the stream from riparian soils during stormflow. In contrast to distinct seasonal changes in base flow nitrate and DON concentrations, ammonium concentrations were typically at or below the detection limit, similar to the rest of the year. Our findings reveal couplings among catchment flow paths, nutrient sources, and transformations that control seasonal extremes of stream nitrogen in forested landscapes.

Simulation of Nitrogen and Phosphorus Losses in Loess Landforms of Northern Iran

NASA Astrophysics Data System (ADS)

Kiani, F.; Behtarinejad, B.; Najafinejad, A.; Kaboli, R.

2018-02-01

Population growth, urban expansion and intensive agriculture and thus increased use of fertilizers aimed at increasing the production capacity cause extensive loss of nutrients such as nitrogen and phosphorus and lead to reduced quality of soil and water. Therefore, identification of nutrients in the soil and their potential are essential. The aim of this study was to evaluate the capability of the SWAT model in simulating runoff, sediment, and nitrogen and phosphorus losses in Tamer catchment. Runoff and sediment measured at Tamar gauging station were used to calibrate and validate the model. Simulated values were generally consistent with the data observed during calibration and validation period (0.6 < R 2 and 0.5 < NS). In the case of nitrogen loss, the model performed an almost good simulation (0.6 < R 2 and 0.47 < NS), but phosphorus simulation yielded better results (0.76 < R 2 and 0.66 < NS). The results showed that cultivated lands had higher loss of nitrogen and phosphorus than other types of land use. Among the various forms of nitrogen and phosphorus, the loss of organic nitrogen and nitrate and soluble phosphorus and mineral phosphorus attached to the sediments showed the greatest sensitivity to the type of land use. Results also showed that the average nutrient loss caused by erosion in this catchment, was 6.99 kg/ha for nitrogen, 0.35 kg/ha for nitrate, 1.3 kg/ha for organic phosphorus, 0.015 kg/ha for soluble phosphorus, and 0.45 kg/ha for mineral phosphorus.

Understanding solute transport at catchment scales by using a synthesis of bottom-up and top-down modelling approaches

NASA Astrophysics Data System (ADS)

Selle, Benny; Schwientek, Marc; Osenbrück, Karsten

2013-04-01

The understanding of flow paths and travel times of water and solutes in catchments can be substantially improved by a combination of bottom-up and top-down modelling approaches. This hypothesis was tested for the 180 km² Ammer catchment in south-western Germany in which the landuse is dominated by agricultural and urban areas. The Ammer River with a mean discharge of 1 m³/s is mainly fed by springs from karstified and fractured aquifers. A limestone aquifer is extensively used for groundwater production. As a first step, we analysed measured concentrations of major ions, selected organic micro-pollutants and environmental tracers for surface water, springs and deep groundwater from wells using typical top-down approaches such as principal component analysis and lumped parameter models. From these approaches, we gained an initial understanding of water and solute fluxes in the catchment. The initial hypotheses on subsurface flow paths and travel times were subsequently tested using a numerical, 3-D groundwater model as a typical bottom-up approach. Our synthesis of top-down and bottom-up approaches provided us with a reliable picture of the dominant processes governing water and solute fluxes in the Ammer catchment. Several spring waters indicated mixing with wastewater. These contaminations were indentified to be caused by either recharge of surface water or leaky sewer systems. Deep percolation below the plant root zone polluted with agrochemicals was found to affect most springs and surface waters resulting in nitrate concentrations of approximately 30 mg/l. This process also influenced some of the drinking-water wells, although water quality for most of these wells is still relatively high due to some attenuation of pollutants but - above all - due to a significant proportion of groundwater with ages > 50 years. However, water quality will likely decrease if contaminants break through and/or conditions for microbiological attenuation process will deteriorate, for example due to depletion of suitable electron donors.

Forecasting the effects of EU policy measures on the nitrate pollution of groundwater based on a coupled agroeconomic - hydro(geo)logic model (Invited)

NASA Astrophysics Data System (ADS)

Wendland, F.

2010-12-01

The fundamental objectives of the European Union-Water Framework Directive and the EU Groundwater Directive are to attain a good status of water and groundwater resources in the member states of the EU by 2015. For river basins, whose good status cannot be guaranteed by 2015, catchment wide operational plans and measurement programs have to be drafted and implemented until 2009. In the river basin district Weser, Germany, which comprises a catchment area of ca. 49.000 km2, the achievement of the good status is unclear, or rather unlikely for 63% of the groundwater bodies. Inputs from diffuse sources and most of all nitrate losses from agriculturally used land have been identified as the main reasons for exceeding the groundwater threshold value for nitrate (50 mg/l) and for failing the good qualitative status of groundwater. The achievement of good qualitative status of groundwater bodies entails a particular challenge as the complex ecological, hydrological, hydrogeological and agro-economic relationships have to be considered simultaneously. We used an interdisciplinary model network to predict the nitrogen intakes into groundwater at the regional scale using an area differentiated approach. The model system combines the agro-economic model RAUMIS for estimating nitrogen surpluses from agriculture and the hydrological models GROWA/DENUZ/WEKU for describing the reactive nitrate transport in the soil-groundwater system. In a first step the model is used to analyze the present situation using N surpluses from agriculture for the year 2003. In many region of the Weser basin, particularly in the northwestern part which is characterized by high livestock densities, predicted nitrate concentrations in percolation water exceed the EU groundwater quality standard of 50 mg/L by far. In a second step the temporal and spatial impacts of the common agricultural policy (CAP) of the EU, already implemented agri-environmental measures of the Federal States and the expected developments of agriculture were assessed with regard to both, groundwater quality in 2015 and the regional agricultural income. On average for the whole Weser basin, the reduction of nitrogen surpluses for agricultural areas leads to a decrease of nitrate concentrations in the leachate by about 10 mg NO3/L. In the agricultural intensive used regions much higher reductions in the order of 40 mg NO3/L may be expected. Using the environmental target value for groundwater, i.e. a concentration of 50 mg NO3/L in the leachate as a target for groundwater protection, the model results were used directly to identify those regions where additional agro-environmental reduction measures are required. There, a backward calculation allows the quantification of maximal permissible nitrogen surplus levels, which was used as a reference for the derivation of additional nitrogen reduction measures. It could be shown that a further reduction by ca. 20.000 t N/a (19%) is necessary to reach a nitrate concentration in groundwater of 50 mg/l. The related costs sum up to ca. 75 Mio €/a. The research work was carried out in the framework of the AGRUM Weser project which was funded on behalf of the German Federal Ministry of Food, Agriculture and Consumer protection (BMELV) and the River Basin Commission Weser (FGG).

Patterns and processes of nutrient transfers from land to water: a catchment approach to evaluate Good Agricultural Practice in Ireland

NASA Astrophysics Data System (ADS)

Mellander, P.-E.; Melland, A. R.; Shortle, G.; Wall, D.; Mechan, S.; Buckley, C.; Fealy, R.; Jordan, P.

2009-04-01

Eutrophication of fresh, transitional and coastal waters by excessive nutrient inputs is one of the most widespread water quality problems in developed countries. Sources of nutrient nitrogen (N) and phosphorus (P) can come from a multiplicity of sources and be dependent on numerous hydrological controls from catchments with both urban and agricultural landuses. Aquatic impacts are widely reported as a result of excessive nutrient transfers from land to water and include changes in ecological integrity and loss of amenity. In the European Union, the Water Framework Directive (WFD) and associated Directives are the key structures with which member states must develop national and often trans-national polices to deal with issues of water resources management. The linked Nitrates Directive is particularly concerned with integrating sustainable agriculture and good water quality objectives and is written into national polices. In Ireland this policy is the Nitrates Directive National Action Programme (NAP), Statutory Instruction 378, Good Agricultural Practise regulation, and amongst other things, sets targets and limits on the use of organic and inorganic fertilisers, soil fertility and slurry/fertiliser spreading and cultivation times. To evaluate the effectiveness of this policy, Teagasc, the Irish Agriculture and Food Development Authority, is undertaking a catchment scale audit on sources, sinks, and changes in nutrient use and export over several years. The Agricultural Catchments Programme is based on a science-stakeholder-management partnership to generate knowledge and specifically to protect water quality from nitrogen and phosphorus transfers within the constraints of the requirements of modern Irish agricultural practises. Eight catchments of 5-12 km2 have been selected for the programme to represent a range of agricultural intensities and vulnerabilities to nitrogen and phosphorus loss including catchments that are situated on permeable and impermeable grassland soils; areas where arable production represents a significant landuse; and catchments on productive and unproductive aquifers. The catchments were identified using a GIS-based multicriteria decision analysis with objective criteria that included landuse data (including agricultural and settlement statistics) combined with soils and geology data to evaluate the risk of P and N loss. Shortlisted catchments were then finalised using practical criteria based on the potential for hydrometry and hydrochemistry research. In each catchment, a conceptual model approach is being used to hypothesize the sources, seasonal mobilisation and pathways of nutrients and water through the soil/subsoil system and transfer into surface and ground water systems to stratify each catchment experimental design. Knowledge of the nutrient management of each catchment farm and resulting soil fertility will be used to monitor the sources of agricultural N and P. Environmental soil nutrient tests will provide baselines and checks on the potential for mobilisation. Areas of high soil fertility that are coincident with high surface or sub-surface hydrological connectivity will be monitored for subsequent nutrient transfer. Other potential nutrient source loads within the catchments, such as rural waste-water treatment plants and domestic septic systems, will be factored in as non-agricultural sources. Similarly, the potential for farmyard transfers will also be assessed. The net balance of nutrient transfer at the catchment outlets will be monitored using a high resolution method that is coincident with hydrometric measurements to ensure that there is a full understanding of the inter-dependence between point and diffuse nutrient transfers and hydrodynamics. This source to transfer approach is highly appropriate and a move towards inductive understanding of nutrient use and export in river catchments - the scale at which policies for water resources management will be assessed under the WFD. The data are also highly conducive to constraining catchment scale, distributed models for predicting chemical transfers in runoff. As the Programme is aiming to integrate the often perceived contentious objectives of water quality management with those of sustainable agriculture, farm economics will also be monitored at the same time and an assessment made of farmer attitudes. An advisory programme is also a major component and dedicated farm advisors will ensure that farmers are fully appraised of obligations and opportunities in the National Action Programme.

Groundwater resource vulnerability and spatial variability of nitrate contamination: Insights from high density tubewell monitoring in a hard rock aquifer.

PubMed

Buvaneshwari, Sriramulu; Riotte, Jean; Sekhar, M; Mohan Kumar, M S; Sharma, Amit Kumar; Duprey, Jean Louis; Audry, Stephane; Giriraja, P R; Praveenkumarreddy, Yerabham; Moger, Hemanth; Durand, Patrick; Braun, Jean-Jacques; Ruiz, Laurent

2017-02-01

Agriculture has been increasingly relying on groundwater irrigation for the last decades, leading to severe groundwater depletion and/or nitrate contamination. Understanding the links between nitrate concentration and groundwater resource is a prerequisite for assessing the sustainability of irrigated systems. The Berambadi catchment (ORE-BVET/Kabini Critical Zone Observatory) in Southern India is a typical example of intensive irrigated agriculture and then an ideal site to study the relative influences of land use, management practices and aquifer properties on NO 3 spatial distribution in groundwater. The monitoring of >200 tube wells revealed nitrate concentrations from 1 to 360mg/L. Three configurations of groundwater level and elevation gradient were identified: i) NO 3 hot spots associated to deep groundwater levels (30-60m) and low groundwater elevation gradient suggest small groundwater reserve with absence of lateral flow, then degradation of groundwater quality due to recycling through pumping and return flow; ii) high groundwater elevation gradient, moderate NO 3 concentrations suggest that significant lateral flow prevented NO 3 enrichment; iii) low NO 3 concentrations, low groundwater elevation gradient and shallow groundwater indicate a large reserve. We propose that mapping groundwater level and gradient could be used to delineate zones vulnerable to agriculture intensification in catchments where groundwater from low-yielding aquifers is the only source of irrigation. Then, wells located in low groundwater elevation gradient zones are likely to be suitable for assessing the impacts of local agricultural systems, while wells located in zones with high elevation gradient would reflect the average groundwater quality of the catchment, and hence should be used for regional mapping of groundwater quality. Irrigation with NO 3 concentrated groundwater induces a "hidden" input of nitrogen to the crop which can reach 200kgN/ha/yr in hotspot areas, enhancing groundwater contamination. Such fluxes, once taken into account in fertilizer management, would allow optimizing fertilizer consumption and mitigate high nitrate concentrations in groundwater. Copyright © 2016 Elsevier B.V. All rights reserved.

Stream nitrate responses to hydrological forcing and climate change in northern forests of the USA (Invited)

NASA Astrophysics Data System (ADS)

Sebestyen, S. D.; Campbell, J. L.; Shanley, J. B.; Pourmokhtarian, A.; Driscoll, C. T.; Boyer, E. W.

2009-12-01

There is a need to understand how climate variability and change affect nutrient delivery to surface waters. We analyzed long-term records of hydrochemical data to explore how the forms, concentrations, and loadings of nitrogen in forest streams throughout the northern USA vary with catchment wetness. We considered projected changes in growing season length and precipitation patterns to simulate future climate scenarios and to assess how stream nitrate loading responds to hydrological forcing under different climate change scenarios. At the Sleepers River Research Watershed in northeastern Vermont, model results suggest that stream nutrient loadings over the next century will respond to hydrological forcing during climate change that affects the amount of water that flows through the landscape. For example, growing season stream water yield (+20%) and nitrate loadings (+57%) increase in response to greater amounts of precipitation (+28%) during a warmer climate with a longer growing season (+43 days). We further explore these findings by presenting model results from a biogeochemical process model (PnET-BGC) to separate changes that are due to biogeochemical cycling and the effects of hydrological forcing. Our findings suggest that nitrogen cycling and transport will intensify during anthropogenic climate forcing, thereby affecting the timing and magnitude of annual stream nutrient loadings in northern forests of the USA.

Relationships between stream nitrate concentration and spatially distributed snowmelt in high-elevation catchments of the western U.S.

NASA Astrophysics Data System (ADS)

Perrot, Danielle; Molotch, Noah P.; Williams, Mark W.; Jepsen, Steven M.; Sickman, James O.

2014-11-01

This study compares stream nitrate (NO3-) concentrations to spatially distributed snowmelt in two alpine catchments, the Green Lakes Valley, Colorado (GLV4) and Tokopah Basin, California (TOK). A snow water equivalent reconstruction model and Landsat 5 and 7 snow cover data were used to estimate daily snowmelt at 30 m spatial resolution in order to derive indices of new snowmelt areas (NSAs). Estimates of NSA were then used to explain the NO3- flushing behavior for each basin over a 12 year period (1996-2007). To identify the optimal method for defining NSAs and elucidate mechanisms underlying catchment NO3- flushing, we conducted a series of regression analyses using multiple thresholds of snowmelt based on temporal and volumetric metrics. NSA indices defined by volume of snowmelt (e.g., snowmelt ≤ 30 cm) rather than snowmelt duration (e.g., snowmelt ≤ 9 days) were the best predictors of stream NO3- concentrations. The NSA indices were better correlated with stream NO3- concentration in TOK (average R2= 0.68) versus GLV4 (average R2= 0.44). Positive relationships between NSA and stream NO3- concentration were observed in TOK with peak stream NO3- concentration occurring on the rising limb of snowmelt. Positive and negative relationships between NSA and stream NO3- concentration were found in GLV4 with peak stream NO3- concentration occurring as NSA expands. Consistent with previous works, the contrasting NO3- flushing behavior suggests that streamflow in TOK was primarily influenced by overland flow and shallow subsurface flow, whereas GLV4 appeared to be more strongly influenced by deeper subsurface flow paths.

Impact of European Union Legislation On The Wash Catchment, U.k.

NASA Astrophysics Data System (ADS)

Daldorph, P.; Wheater, H.; Saunders, A.

A case study is presented which shows the impact of existing European Legislation (Urban Waste Water Directive, Nitrate Directive, Bathing Waters Directive, Habitats Directive) on aquatic nutrient concentrations in the 16112 km2 catchment area of The Wash in eastern England , including both the inland and coastal zones. Information is provided on the implementation process (administrative and economic) and the observed impacts of measures to reduce environmental nutrient levels. Impacts are compared with simulations of nutrients in the inland and coastal zones, and the modeling tools are further used to predict impacts of future management change, e.g. to meet possible requirements of the Water Framework Directive. The issues in setting future environmental targets and research needs to underpin this process are discussed in the context of developing river basin management plans to support the Common Implementation Strategy for the Water Framework Directive.

Sources, transformations, and hydrological processes that control stream nitrate and dissolved organic matter concentrations during snowmelt in an upland forest

USGS Publications Warehouse

Sebestyen, Stephen D.; Boyer, Elizabeth W.; Shanley, James B.; Kendall, Carol; Doctor, Daniel H.; Aiken, George R.; Ohte, Nobuhito

2008-01-01

We explored catchment processes that control stream nutrient concentrations at an upland forest in northeastern Vermont, USA, where inputs of nitrogen via atmospheric deposition are among the highest in the nation and affect ecosystem functioning. We traced sources of water, nitrate, and dissolved organic matter (DOM) using stream water samples collected at high frequency during spring snowmelt. Hydrochemistry, isotopic tracers, and end‐member mixing analyses suggested the timing, sources, and source areas from which water and nutrients entered the stream. Although stream‐dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) both originated from leaching of soluble organic matter, flushing responses between these two DOM components varied because of dynamic shifts of hydrological flow paths and sources that supply the highest concentrations of DOC and DON. High concentrations of stream water nitrate originated from atmospheric sources as well as nitrified sources from catchment soils. We detected nitrification in surficial soils during late snowmelt which affected the nitrate supply that was available to be transported to streams. However, isotopic tracers showed that the majority of nitrate in upslope surficial soil waters after the onset of snowmelt originated from atmospheric sources. A fraction of the atmospheric nitrogen was directly delivered to the stream, and this finding highlights the importance of quick flow pathways during snowmelt events. These findings indicate that interactions among sources, transformations, and hydrologic transport processes must be deciphered to understand why concentrations vary over time and over space as well as to elucidate the direct effects of human activities on nutrient dynamics in upland forest streams.

Simulation of nitrate reduction in groundwater - An upscaling approach from small catchments to the Baltic Sea basin

NASA Astrophysics Data System (ADS)

Hansen, A. L.; Donnelly, C.; Refsgaard, J. C.; Karlsson, I. B.

2018-01-01

This paper describes a modeling approach proposed to simulate the impact of local-scale, spatially targeted N-mitigation measures for the Baltic Sea Basin. Spatially targeted N-regulations aim at exploiting the considerable spatial differences in the natural N-reduction taking place in groundwater and surface water. While such measures can be simulated using local-scale physically-based catchment models, use of such detailed models for the 1.8 million km2 Baltic Sea basin is not feasible due to constraints on input data and computing power. Large-scale models that are able to simulate the Baltic Sea basin, on the other hand, do not have adequate spatial resolution to simulate some of the field-scale measures. Our methodology combines knowledge and results from two local-scale physically-based MIKE SHE catchment models, the large-scale and more conceptual E-HYPE model, and auxiliary data in order to enable E-HYPE to simulate how spatially targeted regulation of agricultural practices may affect N-loads to the Baltic Sea. We conclude that the use of E-HYPE with this upscaling methodology enables the simulation of the impact on N-loads of applying a spatially targeted regulation at the Baltic Sea basin scale to the correct order-of-magnitude. The E-HYPE model together with the upscaling methodology therefore provides a sound basis for large-scale policy analysis; however, we do not expect it to be sufficiently accurate to be useful for the detailed design of local-scale measures.

Quantifying the combined effects of land use and climate changes on stream flow and nutrient loads: A modelling approach in the Odense Fjord catchment (Denmark).

PubMed

Molina-Navarro, Eugenio; Andersen, Hans E; Nielsen, Anders; Thodsen, Hans; Trolle, Dennis

2018-04-15

Water pollution and water scarcity are among the main environmental challenges faced by the European Union, and multiple stressors compromise the integrity of water resources and ecosystems. Particularly in lowland areas of northern Europe, high population density, flood protection and, especially, intensive agriculture, are important drivers of water quality degradation. In addition, future climate and land use changes may interact, with uncertain consequences for water resources. Modelling approaches have become essential to address water issues and to evaluate ecosystem management. In this work, three multi-stressor future storylines combining climatic and socio-economic changes, defined at European level, have been downscaled for the Odense Fjord catchment (Denmark), giving three scenarios: High-Tech agriculture (HT), Agriculture for Nature (AN) and Market-Driven agriculture (MD). The impacts of these scenarios on water discharge and inorganic and organic nutrient loads to the streams have been simulated using the Soil and Water Assessment Tool (SWAT). The results revealed that the scenario-specific climate inputs were most important when simulating hydrology, increasing river discharge in the HT and MD scenarios (which followed the high emission 8.5 representative concentration pathway, RCP), while remaining stable in the AN scenario (RCP 4.5). Moreover, discharge was the main driver of changes in organic nutrients and inorganic phosphorus loads that consequently increased in a high emission scenario. Nevertheless, both land use (via inputs of fertilizer) and climate changes affected the nitrate transport. Different levels of fertilization yielded a decrease in the nitrate load in AN and an increase in MD. In HT, however, nitrate losses remained stable because the fertilization decrease was counteracted by a flow increase. Thus, our results suggest that N loads will ultimately depend on future land use and management in an interaction with climate changes, and this knowledge is of utmost importance for the achievement of European environmental policy goals. Copyright © 2017 Elsevier B.V. All rights reserved.

In situ high-frequency UV-Vis spectrometer probes for investigating runoff processes and end member stability.

NASA Astrophysics Data System (ADS)

Schwab, Michael; Weiler, Markus; Pfister, Laurent; Klaus, Julian

2014-05-01

In recent years, several limitations as to the application of end member mixing analysis with isotope and geochemical tracers have been revealed: unstable end member solutions, inputs varying in space and time, and unrealistic mixing assumptions. In addition, the necessary high-frequency sampling using conventional methods is time and resources consuming, and hence most sampling rates are not suitable for capturing the response times of the majority of observed headwater catchments. However, high-frequency observations are considered fundamental for gaining new insights into hydrological systems. In our study, we have used two portable, in situ, high-frequency UV-Vis spectrometers (spectro::lyser; scan Messtechnik GmbH) to investigate the variability of several signatures in streamflow and end member stability. The spectro::lyser measures TOC, DOC, nitrate and the light absorption spectrum from 220 to 720 nm with 2.5 nm increment. The Weierbach catchment (0.45 km2) in the Attert basin (297 km2) in Luxemburg is a small headwater research catchment (operated by the CRP Gabriel Lippmann), which is completely forested and underlain by schist bedrock. The catchment is equipped with a dense network of hydrological instruments and for this study, the outlet of the Weierbach catchment was equipped with one spectro::lyser, permanently sensing stream water at a 15 minutes time step over several months. Hydrometric and meteorologic data was compared with the high-frequency spectro::lyser time series of TOC, DOC, nitrate and the light absorption spectrum, to get a first insight into the behaviour of the catchment under different environmental conditions. As a preliminary step for a successful end member mixing analysis, the stability of rainfall, soil water, and groundwater was tested with one spectro::lyser, both temporally and spatially. Thereby, we focused on the investigation of changes and patterns of the light absorption spectrum of the different end members and the stream water. Besides using DOC and nitrate for characterizing the end members, our idea is to use the light absorption spectrum as a fingerprint of various constituents of the water. To get a better understanding on how to handle the in situ spectro::lyser, the instrument was compared to conventionally analysed water samples with a special focus on fundamental technical issues: Is there a general difference between in situ and lab measurements and does it make a difference whether the samples are analysed immediately in the field or after days and weeks in the lab and/or again with the spectro::lyser? First results indicate the value of using in situ spectrometers to capture high-frequency variations of hydro-chemistry and end member mixing during runoff events in a small headwater catchment.

Land-use controls on sources and processing of nitrate in small watersheds: Insights from dual isotopic analysis

USGS Publications Warehouse

Barnes, R.T.; Raymond, P.A.

2010-01-01

Studies have repeatedly shown that agricultural and urban areas export considerably more nitrogen to streams than forested counterparts, yet it is difficult to identify and quantify nitrogen sources to streams due to complications associated with terrestrial and in-stream biogeochemical processes. In this study, we used the isotopic composition of nitrate (??15N-NO3- and ??18O- NO3-) in conjunction with a simple numerical model to examine the spatial and temporal variability of nitrate (NO3-) export across a land-use gradient and how agricultural and urban development affects net removal mechanisms. In an effort to isolate the effects of land use, we chose small headwater systems in close proximity to each other, limiting the variation in geology, surficial materials, and climate between sites. The ??15N and ??18Oof stream NO 3- varied significantly between urban, agricultural, and forested watersheds, indicating that nitrogen sources are the primary determinant of the ??15N-NO3-, while the ??18O-NO3- was found to reflect biogeochemical processes. The greatest NO3- concentrations corresponded with the highest stream ??15N-NO3- values due to the enriched nature of two dominant anthropogenic sources, septic and manure, within the urban and agricultural watersheds, respectively. On average, net removal of the available NO3- pool within urban and agricultural catchments was estimated at 45%. The variation in the estimated net removal of NO3- from developed watersheds was related to both drainage area and the availability of organic carbon. The determination of differentiated isotopic land-use signatures and dominant seasonal mechanisms illustrates the usefulness of this approach in examining the sources and processing of excess nitrogen within headwater catchments. ?? 2010 by the Ecological Society of America.

Using a physically-based water flow model to explore the dynamics of transit times and mixing in a small agricultural catchment

NASA Astrophysics Data System (ADS)

Yang, Jie; Heidbüchel, Ingo; Musolff, Andreas; Fleckenstein, Jan H.

2017-04-01

Catchment-scale transit time distributions (TTDs) for discharge and residence time distributions of the water in storage (RTDs) are promising tools to characterize the discharge and mixing behavior of a catchment and can help to interpret the associated solute loads to the stream in a spatially implicit way. TTDs and RTDs are dynamic in time, influenced by dynamic rainfall and evapotranspiration forcing, and changing groundwater storage in the catchment. In order to understand the links between the dynamics of TTDs and groundwater mixing in the small agricultural catchment Schäfertal, in central Germany, a 3D hydrological model was set up for the catchment using the fully coupled surface-subsurface numerical model HydroGeoSphere (HGS). The model is calibrated using discharge and groundwater level measurements, and runs transiently for a period of 10 years from 1997 to 2007. A particle tracking tool was implemented in HGS to track the movement of water parcels in the subsurface, outputting TTDs of channel discharge and RTDs of groundwater storage at daily intervals. Results show that the mean age of the discharge water is significantly younger than that of the water in storage, indicating a poorly mixed subsurface. Discharge preferentially samples faster flowing younger water originating from the more conductive top parts of the aquifer. Spatial variations of the age of water in storage are observed, highly influenced by aquifer heterogeneity. Computed StorAge Selection (SAS) functions [Rinaldo et al. 2015] show clear shifts in the discharge sampling preferences between wet and dry states: during wet states in winter and spring, discharge has a preference for younger water because the shallow flow paths are active due to high groundwater levels and low evapotranspiration. Conversely, during dry states in summer and autumn, discharge has a preference for older water because the shallow flow paths are inactive due to low groundwater levels and stronger evapotranspiration. Measured nitrate (NO3) loads in discharge, mainly originating from fertilizer in shallow soils, decrease significantly with decreasing wetness of the catchment. This trend confirms the shifts of discharge sampling preferences between wet and dry states. Reference: Rinaldo, A., P. Benettin, C. J. Harman, M. Hrachowitz, K. J. McGuire, Y. van der Velde, E. Bertuzzo, and G. Botter (2015), Storage selection functions: A coherent framework for quantifying how catchments store and release water and solutes, Water Resour. Res., 51, 4840-4847, doi:10.1002/2015WR017273.

Nitratreduktion in einem quartären Grundwasserleiter in Ostwestfalen, NRW

NASA Astrophysics Data System (ADS)

Wisotzky, Frank; Wohnlich, Stefan; Böddeker, Martin

2018-06-01

Groundwater chemistry and sediment chemistry are characterized in a catchment of a water works in the lower terrace of the river Ems, in east-Westphalia (Germany). In spite of strong nitrate input in the shallow groundwater, the nitrate concentration in the wells is very low, suggesting strong nitrate reduction. The aims of this study were to determine the type of nitrate reduction and to determine the depth of these reactions. As part of the groundwater investigation, soil samples were also used. All soil samples have low sulfide-sulfur contents but high organic-carbon contents. The shallow groundwater has nitrate concentrations up to 185 mg/l. Enhanced carbon-dioxide concentrations in the deeper part of the aquifer indicate a dominant organotrophic nitrate reduction. Data from a multi-level observation well show a 25% lithotrophic and 75% organotrophic nitrate reduction. Investigations of nitrate isotopes (δ15N-NO3-values and δ18O-NO3-values) and sulfate isotopes (δ34S-SO4-values and δ18O-SO4-values) support the findings.

Tracing Nitrate Contributions to Streams During Varying Flow Regimes at the Sleepers River Research Watershed, Vermont, USA

NASA Astrophysics Data System (ADS)

Sebestyen, S. D.; Shanley, J. B.; Boyer, E. W.; Ohte, N.; Doctor, D. H.; Kendall, C.

2003-12-01

Quantifying sources and transformations of nitrate in headwater catchments is fundamental to understanding the movement of nitrogen to streams. At the Sleepers River Research Watershed in northeastern Vermont (USA), we are using multiple chemical tracer and mixing model approaches to quantify sources and transport of nitrate to streams under varying flow regimes. We sampled streams, lysimeters, and wells at nested locations from the headwaters to the outlet of the 41 ha W-9 watershed under the entire range of flow regimes observed throughout 2002-2003, including baseflow and multiple events (stormflow and snowmelt). Our results suggest that nitrogen sources, and consequently stream nitrate concentrations, are rapidly regenerated during several weeks of baseflow and nitrogen is flushed from the watershed by stormflow events that follow baseflow periods. Both basic chemistry data (anions, cations, & dissolved organic carbon) and isotopic data (nitrate, dissolved organic carbon, and dissolved inorganic carbon) indicate that nitrogen source contributions vary depending upon the extent of saturation in the watershed, the initiation of shallow subsurface water inputs, and other hydrological processes. Stream nitrate concentrations typically peak with discharge and are higher on the falling than the rising limb of the hydrograph. Our data also indicate the importance of terrestrial and aquatic biogeochemical processes, in addition to hydrological connectivity in controlling how nitrate moves from the terrestrial landscape to streams. Our detailed sampling data from multiple flow regimes are helping to identify and quantify the "hot spots" and "hot moments" of biogeochemical and hydrological processes that control nitrogen fluxes in streams.

Modelling of in-stream nitrogen and phosphorus concentrations using different sampling strategies for calibration data

NASA Astrophysics Data System (ADS)

Jomaa, Seifeddine; Jiang, Sanyuan; Yang, Xiaoqiang; Rode, Michael

2016-04-01

It is known that a good evaluation and prediction of surface water pollution is mainly limited by the monitoring strategy and the capability of the hydrological water quality model to reproduce the internal processes. To this end, a compromise sampling frequency, which can reflect the dynamical behaviour of leached nutrient fluxes responding to changes in land use, agriculture practices and point sources, and appropriate process-based water quality model are required. The objective of this study was to test the identification of hydrological water quality model parameters (nitrogen and phosphorus) under two different monitoring strategies: (1) regular grab-sampling approach and (2) regular grab-sampling with additional monitoring during the hydrological events using automatic samplers. First, the semi-distributed hydrological water quality HYPE (Hydrological Predictions for the Environment) model was successfully calibrated (1994-1998) for discharge (NSE = 0.86), nitrate-N (lowest NSE for nitrate-N load = 0.69), particulate phosphorus and soluble phosphorus in the Selke catchment (463 km2, central Germany) for the period 1994-1998 using regular grab-sampling approach (biweekly to monthly for nitrogen and phosphorus concentrations). Second, the model was successfully validated during the period 1999-2010 for discharge, nitrate-N, particulate-phosphorus and soluble-phosphorus (lowest NSE for soluble phosphorus load = 0.54). Results, showed that when additional sampling during the events with random grab-sampling approach was used (period 2011-2013), the hydrological model could reproduce only the nitrate-N and soluble phosphorus concentrations reasonably well. However, when additional sampling during the hydrological events was considered, the HYPE model could not represent the measured particulate phosphorus. This reflects the importance of suspended sediment during the hydrological events increasing the concentrations of particulate phosphorus. The HYPE model could reproduce the total phosphorus during the period 2011-2013 only when the sediment transport-related model parameters was re-identified again considering the automatic sampling during the high-flow conditions.

Morphology, geology and water quality assessment of former tin mining catchment.

PubMed

Ashraf, Muhammad Aqeel; Maah, Mohd Jamil; Yusoff, Ismail

2012-01-01

Bestari Jaya, former tin mining catchment covers an area of 2656.31 hectares comprised of four hundred and forty-two different-size lakes and ponds. The present study area comprise of 92 hectares of the catchment that include four large size lakes. Arc GIS version 9.2 used to develop bathymetric map, Global Positioning System (GPS) for hydrographical survey and flow meter was utilized for water discharge analysis (flow routing) of the catchment. The water quality parameters (pH, temperature, electric conductivity, dissolved oxygen DO, total dissolved solids TDS, chlorides, ammonium, nitrates) were analyzed by using Hydrolab. Quality assurance (QA) and quality control (QC) procedures were strictly followed throughout the field work and data analysis. Different procedures were employed to evaluate the analytical data and to check for possible transcription or dilution errors, changes during analysis, or unusual or unlikely values. The results obtained are compared with interim national water quality standards for Malaysia indicates that water quality of area is highly degraded. It is concluded that Bestri Jaya ex-mining catchment has a high pollution potential due to mining activities and River Ayer Hitam, recipient of catchment water, is a highly polluted river.

Morphology, Geology and Water Quality Assessment of Former Tin Mining Catchment

PubMed Central

Ashraf, Muhammad Aqeel; Maah, Mohd. Jamil; Yusoff, Ismail

2012-01-01

Bestari Jaya, former tin mining catchment covers an area of 2656.31 hectares comprised of four hundred and forty-two different-size lakes and ponds. The present study area comprise of 92 hectares of the catchment that include four large size lakes. Arc GIS version 9.2 used to develop bathymetric map, Global Positioning System (GPS) for hydrographical survey and flow meter was utilized for water discharge analysis (flow routing) of the catchment. The water quality parameters (pH, temperature, electric conductivity, dissolved oxygen DO, total dissolved solids TDS, chlorides, ammonium, nitrates) were analyzed by using Hydrolab. Quality assurance (QA) and quality control (QC) procedures were strictly followed throughout the field work and data analysis. Different procedures were employed to evaluate the analytical data and to check for possible transcription or dilution errors, changes during analysis, or unusual or unlikely values. The results obtained are compared with interim national water quality standards for Malaysia indicates that water quality of area is highly degraded. It is concluded that Bestri Jaya ex-mining catchment has a high pollution potential due to mining activities and River Ayer Hitam, recipient of catchment water, is a highly polluted river. PMID:22761549

Characterization and source identification of stormwater runoff in tropical urban catchments.

PubMed

Chow, M F; Yusop, Z

2014-01-01

The characteristics of urban stormwater pollution in the tropics are still poorly understood. This issue is crucial to the tropical environment because its rainfall and runoff generation processes are so different from temperate regions. In this regard, a stormwater monitoring program was carried out at three urban catchments (e.g. residential, commercial and industrial) in the southern part of Peninsular Malaysia. A total of 51 storm events were collected at these three catchments. Samples were analyzed for total suspended solids, 5-day biochemical oxygen demand, chemical oxygen demand (COD), oil and grease, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen (NH3-N), soluble reactive phosphorus and total phosphorus. Principal component analysis (PCA) and hierarchical cluster analysis were used to interpret the stormwater quality data for pattern recognition and identification of possible sources. The most likely sources of stormwater pollutants at the residential catchment were from surface soil and leachate of fertilizer from domestic lawns and gardens, whereas the most likely sources for the commercial catchment were from discharges of food waste and washing detergent. In the industrial catchment, the major sources of pollutants were discharges from workshops and factories. The PCA factors further revealed that COD and NH3-N were the major pollutants influencing the runoff quality in all three catchments.

Baseline Q-values for streams in intensive agricultural catchments in Ireland

NASA Astrophysics Data System (ADS)

Melland, Alice; Jordan, Phil; Wall, David; Mellander, Per-Erik; Mechan, Sarah; Shortle, Ger

2010-05-01

The effectiveness of regulations introduced in Ireland in 2006 in response to the European Union Nitrates Directives for minimising nutrient loss to waterways from farms is being studied by Teagasc, the Irish Agriculture and Food Development Authority as part of an Agricultural Catchments Programme from 2008 - 2011. The regulations in Ireland require that during winter, green cover is established and maintained on arable farms, manure is stored and not spread, ploughing is not conducted and that chemical fertiliser is not spread. The regulations also require buffer zones between fields and water courses when applying organic or chemical fertilisers and that nutrient application rates and timing match crop requirements. An upper limit for livestock manure loading of 170 kg ha-1 organic N each year is also set. The biophysical research component of the Agricultural Catchments Programme is focussed on quantifying nutrient source availability, surface and subsurface transport pathways and stream chemical water quality. A baseline description of stream ecological quality was also sought. Stream ecology was measured in autumn 2009 at 3-5 locations within four surface water catchments and at the spring emergence of a catchment underlain by karst limestone. Landuse in each catchment is dominated by medium to high intensity grassland or cereal farming and annual average rainfall ranges from 900 - 1200 mm. Surveys were conducted in 1st to 3rd order streams throughout each catchment at locations which had minimal observed point source inputs for 100m upstream, incomplete shade, a hard streambed substrate and riffle conditions suitable for the sampling methods. Benthic macroinvertebrates were identified and quantified and used to calculate the biological indices Small Stream Risk Score, Q-value, Biological Monitoring Working Party (BMWP), Average Score Per Taxa (ASPT) and EQR (Observed Q-value/Reference Q-value). Diatom community assemblages were identified from samples collected by scraping submerged cobbles and a Trophic Diatom Index and EQR were calculated. Hydromorphology of each sample location was assessed using the River Hydromorphology Assessment Technique (RHAT). Stream water chemistry (nitrate-N, total N, total phosphorus, reactive phosphorus, electrical conductivity, suspended sediments, major cations, pH) was measured at monthly intervals near each ecological survey location. The ecology measurements will be repeated in summer and autumn 2010 to provide a baseline indication of Q-values in the catchments. A fish survey will also be conducted in 2010. The ecological surveys were conducted by the Aquatic Services Unit at University College Cork, Ireland. This paper describes the major farming and stream chemical characteristics of the five catchments and reports on results of the 2009 ecological surveys.

Scaling properties of rainfall-runoff generation processes and nutrient flushing mechanisms in the Oregon Cascade Mountain

NASA Astrophysics Data System (ADS)

Segura, C.; Nickolas, L. B.; Leshchinsky, B. A.

2015-12-01

Even though it is widely recognized that water quality and availability are crucial to society and wildlife sustainability, we are still not able to predict how much water is moved through a given catchment after a storm event nor what nutrients, solutes, and contaminates are mobilized. We will present preliminary results of a study incorporating of hydrometric information, water stable isotopes (δ18O), and concentrations of total nitrogen (TN), ammonia (NH3), and nitrate (NO3) within 4 sites in a nested framework at the HJ Andrews Experimental Forest (HJA), OR. Preliminary analysis of 2 storms (54mm and 145mm) indicate highly variable responses across space along with a positive relation between transit time of event water and storm magnitude in all catchments. In addition there appears to be a moisture threshold after which transit time scales with drainage area across the landscape likely related to higher degree of connectivity. We also found a strong correlation between transit times computed based on temporal variability of δ18O and electrical connectivity (EC). This lead to the analysis of over 50 storm across 10 catchments in the HJA during the last 3 years. In-stream NO3- during storm response are highest within the smaller catchments (1-5 km2) and tend to remain elevated throughout the response period. The larger catchments (15-64 km2) demonstrate smaller increases in NO3-, the response time lags behind that of the smaller catchments, and the concentration returns rapidly to baseflow conditions rather than remaining elevated. In contrast, in-stream NH3 show a higher degree of similarity between sites in terms of magnitude and timing of increases in concentration over the duration of the response period. Ultimately we found that fractions of inorganic nitrogen correlate with transit time and drainage area, opening the possibility of a catchment wide model of nutrient export prediction.

Threshold values and management options for nutrients in a catchment of a temperate estuary with poor ecological status

NASA Astrophysics Data System (ADS)

Hinsby, K.; Markager, S.; Kronvang, B.; Windolf, J.; Sonnenborg, T. O.; Thorling, L.

2012-08-01

Intensive farming has severe impacts on the chemical status of groundwater and streams and consequently on the ecological status of dependent ecosystems. Eutrophication is a widespread problem in lakes and marine waters. Common problems are hypoxia, algal blooms, fish kills, and loss of water clarity, underwater vegetation, biodiversity and recreational value. In this paper we evaluate the nitrogen (N) and phosphorus (P) concentrations of groundwater and surface water in a coastal catchment, the loadings and sources of N and P, and their effect on the ecological status of an estuary. We calculate the necessary reductions in N and P loadings to the estuary for obtaining a good ecological status, which we define based on the number of days with N and P limitation, and the corresponding stream and groundwater threshold values assuming two different management options. The calculations are performed by the combined use of empirical models and a physically based 3-D integrated hydrological model of the whole catchment. The assessment of the ecological status indicates that the N and P loads to the investigated estuary should be reduced to levels corresponding to 52 and 56% of the current loads, respectively, to restore good ecological status. Model estimates show that threshold total N (TN) concentrations should be in the range of 2.9 to 3.1 mg l-1 in inlet freshwater (streams) to Horsens estuary and 6.0 to 9.3 mg l-1 in shallow aerobic groundwater (∼ 27-41 mg l-1 of nitrate), depending on the management measures implemented in the catchment. The situation for total P (TP) is more complex, but data indicate that groundwater threshold values are not needed. The stream threshold value for TP to Horsens estuary for the selected management options is 0.084 mg l-1. Regional climate models project increasing winter precipitation and runoff in the investigated region resulting in increasing runoff and nutrient loads to the Horsens estuary and many other coastal waters if present land use and farming practices continue. Hence, lower threshold values are required in many coastal catchments in the future to ensure good status of water bodies and ecosystems.

High-resolution monitoring of catchment nutrient response to the end of the 2011-2012 drought in England, captured by the demonstration test catchments

NASA Astrophysics Data System (ADS)

Outram, F. N.; Lloyd, C.; Jonczyk, J.; Benskin, C. McW. H.; Grant, F.; Dorling, S. R.; Steele, C. J.; Collins, A. L.; Freer, J.; Haygarth, P. M.; Hiscock, K. M.; Johnes, P. J.; Lovett, A. L.

2013-12-01

The Demonstration Test Catchments (DTC) project is a UK Government funded initiative to test the effectiveness of on-farm mitigation measures designed to reduce agricultural pollution without compromising farm productivity. Three distinct catchments in England have been chosen to test the efficacy of mitigation measures on working farms in small tributary sub-catchments equipped with continuous water quality monitoring stations. The Hampshire Avon in the south is a mixed livestock and arable farming catchment, the River Wensum in the east is a lowland catchment with predominantly arable farming and land use in the River Eden catchment in the north-west is predominantly livestock farming. One of the many strengths of the DTC as a national research platform is that it provides the ability to investigate catchment hydrology and biogeochemical response across different landscapes and geoclimatic characteristics, with a range of differing flow behaviours, geochemistries and nutrient chemistries. Although numerous authors present studies of individual catchment responses to storms, no studies exist of multiple catchment responses to the same rainfall event captured with in situ high-resolution nutrient monitoring at a national scale. This paper brings together findings from all three DTC research groups to compare the response of the catchments to a major storm event in April 2012. This was one of the first weather fronts to track across the country following a prolonged drought period affecting much of the UK through 2011-2012, marking an unusual meteorological transition when a rapid shift from drought to flood risk occurred. The effects of the weather front on discharge and water chemistry parameters, including nitrogen species (NO3-N and NH4-N) and phosphorus fractions (total P (TP) and total reactive P (TRP)), measured at a half-hourly time step are examined. When considered in the context of one hydrological year, flow and concentration duration curves reveal that the weather fronts resulted in extreme flow, nitrate and TP concentrations in all three catchments but with distinct differences in both hydrographs and chemographs. Hysteresis loops constructed from high resolution data are used to highlight an array of potential pollutant sources and delivery pathways. In the Hampshire Avon DTC, transport was dominated by sub-surface processes, where phosphorus, largely in the soluble form, was found to be transport-limited. In the Wensum DTC, transport was largely dominated by rapid sub-surface movement due to the presence of under-drainage, which mobilised large quantities of nitrate during the storm. In the Eden DTC, transport was found to be initially dominated by surface runoff, which switched to subsurface delivery on the falling limb of the hydrograph, with the surface delivery transporting large amounts of particulate phosphorus to the river, with a transport-limited response. The lack of exhaustion of nutrient delivery in response to such extreme flow generation indicates the size of the nutrient pools stored in these catchments, and highlights the scale of the challenges faced by environmental managers when designing mitigation measures to reduce the flux of nutrients to UK river systems from diffuse agricultural sources.

Tracing the source and fate of nitrate in contemporary mixed land-use surface water systems

NASA Astrophysics Data System (ADS)

Stewart, S. D.; Young, M. B.; Horton, T. W.; Harding, J. S.

2011-12-01

Nitrogenous fertilizers increase agricultural productivity, ultimately feeding the planet. Yet, it is possible to have too much of a good thing, and nitrogen is no exception. When in excess nitrogen has been shown to accelerate eutrophication of water bodies, and act as a chronic toxin (e.g. methemoglobinemia). As land-use intensity continues to rise in response to increases in agricultural productivity, the risk of adverse effects of nitrogen loading on surface water bodies will also increase. Stable isotope proxies are potential tracers of nitrate, the most common nitrogenous phase in surface waters. Applying stable isotope proxies therefore presents an opportunity to identify and manage sources of excess nitrogen before aquatic systems are severely degraded. However, the heterogeneous nature of potential pollution sources themselves, and their distribution with a modified catchment network, make understanding this issue highly complex. The Banks Peninsula, an eroded late tertiary volcanic complex located on the east coast of the South Island New Zealand, presents a unique opportunity to study and understand the sources and fates of nitrate within streams in a contemporary mixed land-use setting. Within this small geographic area there a variety of agricultural activities are practiced, including: heavily fertilized golf courses; stands of regenerating native forest; and areas of fallow gorse (Ulex europaeus; a invasive N-fixing shrub). Each of these landuse classes has its own unique nitrogen budget. Multivariate analysis was used on stream nitrate concentrations to reveal that stream reaches dominated by gorse had significantly higher nitrate concentrations than other land-use classes. Nitrate δ15N & δ18O data from these sites show strong covariance, plotting along a distinct fractionation line (r2 = 0.96). This finding facilitates interpretation of what processes are controlling nitrate concentration within these systems. Further, complementary aquatic foodweb δ15N δ13C analyses of multiple species in various trophic positions allow for a unique, holistic insight in to the fate of gorse-derived nitrate at an ecosystem level. We present here physicochemical and stable isotopic data from a variety of aqueous and aquatic foodweb components. Data is generated using emerging and established analytical techniques, in order to explore links between foodweb ecology, ecosystem function, and fate and transport of excess nitrate along longitudinal gradients of mixed land-use catchments.

Mean transit times in headwater catchments: insights from the Otway Ranges, Australia

NASA Astrophysics Data System (ADS)

Howcroft, William; Cartwright, Ian; Morgenstern, Uwe

2018-01-01

Understanding the timescales of water flow through catchments and the sources of stream water at different flow conditions is critical for understanding catchment behaviour and managing water resources. Here, tritium (3H) activities, major ion geochemistry and streamflow data were used in conjunction with lumped parameter models (LPMs) to investigate mean transit times (MTTs) and the stores of water in six headwater catchments in the Otway Ranges of southeastern Australia. 3H activities of stream water ranged from 0.20 to 2.14 TU, which are significantly lower than the annual average 3H activity of modern local rainfall, which is between 2.4 and 3.2 TU. The 3H activities of the stream water are lowest during low summer flows and increase with increasing streamflow. The concentrations of most major ions vary little with streamflow, which together with the low 3H activities imply that there is no significant direct input of recent rainfall at the streamflows sampled in this study. Instead, shallow younger water stores in the soils and regolith are most likely mobilised during the wetter months. MTTs vary from approximately 7 to 230 years. Despite uncertainties of several years in the MTTs that arise from having to assume an appropriate LPM, macroscopic mixing, and uncertainties in the 3H activities of rainfall, the conclusion that they range from years to decades is robust. Additionally, the relative differences in MTTs at different streamflows in the same catchment are estimated with more certainty. The MTTs in these and similar headwater catchments in southeastern Australia are longer than in many catchments globally. These differences may reflect the relatively low rainfall and high evapotranspiration rates in southeastern Australia compared with headwater catchments elsewhere. The long MTTs imply that there is a long-lived store of water in these catchments that can sustain the streams over drought periods lasting several years. However, the catchments are likely to be vulnerable to decadal changes in land use or climate. Additionally, there may be considerable delay in contaminants reaching the stream. An increase in nitrate and sulfate concentrations in several catchments at high streamflows may represent the input of contaminants through the shallow groundwater that contributes to streamflow during the wetter months. Poor correlations between 3H activities and catchment area, drainage density, land use, and average slope imply that the MTTs are not controlled by a single parameter but a variety of factors, including catchment geomorphology and the hydraulic properties of the soils and aquifers.

The dark side of the hyporheic zone: Depth profiles of nitrogen and its processing in stream sediments

USGS Publications Warehouse

Stelzer, R.S.; Bartsch, L.A.; Richardson, W.B.; Strauss, E.A.

2011-01-01

1.Although it is well known that sediments can be hot spots for nitrogen transformation in streams, many previous studies have confined measurements of denitrification and nitrate retention to shallow sediments (<5cm deep). We determined the extent of nitrate processing in deeper sediments of a sand plains stream (Emmons Creek) by measuring denitrification in core sections to a depth of 25cm and by assessing vertical nitrate profiles, with peepers and piezometers, to a depth of 70cm. 2.Denitrification rates of sediment slurries based on acetylene block were higher in shallower core sections. However, core sections deeper than 5cm accounted for 68% of the mean depth-integrated denitrification rate. 3.Vertical hydraulic gradient and vertical profiles of pore water chloride concentration suggested that deep ground water upwelled through shallow sediments before discharging to the stream channel. The results of a two-source mixing model based on chloride concentrations suggested that the hyporheic zone was very shallow (<5cm) in Emmons Creek. 4.Vertical profiles showed that nitrate concentration in shallow ground water was about 10-60% of the nitrate concentration of deep ground water. The mean nitrate concentrations of deep and shallow ground water were 2.17 and 0.73mgNO3-NL-1, respectively. 5.Deep ground water tended to be oxic (6.9mgO2L-1) but approached anoxia (0.8mgO2L-1) after passing through shallow, organic carbon-rich sediments, which suggests that the decline in the nitrate concentrations of upwelling ground water was because of denitrification. 6.Collectively, our results suggest that there is substantial nitrate removal occurring in deep sediments, below the hyporheic zone, in Emmons Creek. Our findings suggest that not accounting for nitrate removal in deep sediments could lead to underestimates of nitrogen processing in streams and catchments. ?? 2011 Blackwell Publishing Ltd.

Catchment Models and Management Tools for diffuse Contaminants (Sediment, Phosphorus and Pesticides): DIFFUSE Project

NASA Astrophysics Data System (ADS)

Mockler, Eva; Reaney, Simeon; Mellander, Per-Erik; Wade, Andrew; Collins, Adrian; Arheimer, Berit; Bruen, Michael

2017-04-01

The agricultural sector is the most common suspected source of nutrient pollution in Irish rivers. However, it is also often the most difficult source to characterise due to its predominantly diffuse nature. Particulate phosphorus in surface water and dissolved phosphorus in groundwater are of particular concern in Irish water bodies. Hence the further development of models and indices to assess diffuse sources of contaminants are required for use by the Irish Environmental Protection Agency (EPA) to provide support for river basin planning. Understanding connectivity in the landscape is a vital component of characterising the source-pathway-receptor relationships for water-borne contaminants, and hence is a priority in this research. The DIFFUSE Project will focus on connectivity modelling and incorporation of connectivity into sediment, nutrient and pesticide risk mapping. The Irish approach to understanding and managing natural water bodies has developed substantially in recent years assisted by outputs from multiple research projects, including modelling and analysis tools developed during the Pathways and CatchmentTools projects. These include the Pollution Impact Potential (PIP) maps, which are an example of research output that is used by the EPA to support catchment management. The PIP maps integrate an understanding of the pollution pressures and mobilisation pathways and, using the source-pathways-receptor model, provide a scientific basis for evaluation of mitigation measures. These maps indicate the potential risk posed by nitrate and phosphate from diffuse agricultural sources to surface and groundwater receptors and delineate critical source areas (CSAs) as a means of facilitating the targeting of mitigation measures. Building on this previous research, the DIFFUSE Project will develop revised and new catchment managements tools focused on connectivity, sediment, phosphorus and pesticides. The DIFFUSE project will strive to identify the state-of-the-art methods and models that are most applicable to Irish conditions and management challenges. All styles of modelling considered useful for water resources management are relevant to this project and a balance of technical sophistication, data availability and operational practicalities is the ultimate goal. Achievement of this objective will be measured by comparing the performance of the new models developed in the project with models used in other countries. The models and tools developed in the course of the project will be evaluated by comparison with Irish catchment data and with other state-of-the-art models in a model-inter-comparison workshop which will be open to other models and the wider research community.

Using groundwater age and hydrochemistry to understand sources and dynamics of nutrient contamination through the catchment into Lake Rotorua, New Zealand

NASA Astrophysics Data System (ADS)

Morgenstern, U.; Daughney, C. J.; Leonard, G.; Gordon, D.; Donath, F. M.; Reeves, R.

2015-02-01

The water quality of Lake Rotorua has steadily declined over the past 50 years despite mitigation efforts over recent decades. Delayed response of the groundwater discharges to historic land-use intensification 50 years ago was the reason suggested by early tritium measurements, which indicated large transit times through the groundwater system. We use the isotopic and chemistry signature of the groundwater for detailed understanding of the origin, fate, flow pathways, lag times and future loads of contaminants. A unique set of high-quality tritium data over more than four decades, encompassing the time when the tritium spike from nuclear weapons testing moved through the groundwater system, allows us to determine detailed age distribution parameters of the water discharging into Lake Rotorua. The Rotorua volcanic groundwater system is complicated due to the highly complex geology that has evolved through volcanic activity. Vertical and steeply inclined geological contacts preclude a simple flow model. The extent of the Lake Rotorua groundwater catchment is difficult to establish due to the deep water table in large areas, combined with inhomogeneous groundwater flow patterns. Hierarchical cluster analysis of the water chemistry parameters provided evidence of the recharge source of the large springs near the lake shore, with discharge from the Mamaku ignimbrite through lake sediment layers. Groundwater chemistry and age data show clearly the source of nutrients that cause lake eutrophication, nitrate from agricultural activities and phosphate from geologic sources. With a naturally high phosphate load reaching the lake continuously via all streams, the only effective way to limit algae blooms and improve lake water quality in such environments is by limiting the nitrate load. The groundwater in the Rotorua catchment, once it has passed through the soil zone, shows no further decrease in dissolved oxygen, indicating an absence of bioavailable electron donors along flow paths that could facilitate microbial denitrification reactions. Nitrate from land-use activities that leaches out of the root zone of agricultural land into the deeper part of the groundwater system must be expected to travel with the groundwater to the lake. The old age and the highly mixed nature of the water discharges imply a very slow and lagged response of the streams and the lake to anthropogenic contaminants in the catchment, such as nitrate. Using the age distribution as deduced from tritium time series data measured in the stream discharges into the lake allows prediction of future nutrient loads from historic land-use activities 50 years ago. For Hamurana Stream, the largest stream to Lake Rotorua, it takes more than a hundred years for the groundwater-dominated stream discharge to adjust to changes in land-use activities. About half of the currently discharging water is still pristine old water, and after this old water is completely displaced by water affected by land use, the nitrogen load of Hamurana Stream will approximately double. These timescales apply to activities that cause contamination, but also to remediation action.

An Open Source Framework for Coupled Hydro-Hydrogeo-Chemical Systems in Catchment Research

NASA Astrophysics Data System (ADS)

Delfs, J.; Sachse, A.; Gayler, S.; Grathwohl, P.; He, W.; Jang, E.; Kalbacher, T.; Klein, C.; Kolditz, O.; Maier, U.; Priesack, E.; Rink, K.; Selle, B.; Shao, H.; Singh, A. K.; Streck, T.; Sun, Y.; Wang, W.; Walther, M.

2013-12-01

This poster presents an open-source framework designed to assist water scientists in the study of catchment hydraulic functions with associated chemical processes, e.g. contaminant degradation, plant nutrient turnover. The model successfully calculates the feedbacks between surface water, subsurface water and air in standard benchmarks. In specific model applications to heterogeneous catchments, subsurface water is driven by density variations and runs through double porous media. Software codes of water science are tightly coupled by iteration, namely the Storm Water Management Model (SWMM) for urban runoff, Expert-N for simulating water fluxes and nutrient turnover in agricultural and forested soils, and OpenGeoSys (OGS) for groundwater. The coupled model calculates flow of hydrostatic shallow water over the land surface with finite volume and difference methods. The flow equations for water in the porous subsurface are discretized in space with finite elements. Chemical components are transferred through 1D, 2D or 3D watershed representations with advection-dispersion solvers or, as an alternative, random walk particle tracking. A transport solver can be in sequence with a chemical solver, e.g. PHREEQ-C, BRNS, additionally. Besides coupled partial differential equations, the concept of hydrological response units is employed in simulations at regional scale with scarce data availability. In this case, a conceptual hydrological model, specifically the Jena Adaptable Modeling System (JAMS), passes groundwater recharge through a software interface into OGS, which solves the partial differential equations of groundwater flow. Most components of the modeling framework are open source and can be modified for individual purposes. Applications range from temperate climate regions in Germany (Ammer catchment and Hessian Ried) to arid regions in the Middle East (Oman and Dead See). Some of the presented examples originate from intensively monitored research sites of the WESS research centre and the monitoring initiative TERENO. Other examples originate from the IWAS project on integrated water resources management. The model applications are primarily concerned with groundwater resources, which are endangered by overexploitation, intrusion of saltwater, and nitrate loads.

Potential pollutant sources in a Choptank River (USA) subwatershed and the influence of land use and watershed characteristics

USGS Publications Warehouse

Nino de Guzman, Gabriela T.; Hapeman, Cathleen J.; Prabhakara, Kusuma; Codling, Eton E.; Shelton, Daniel R.; Rice, Clifford P.; Hively, W. Dean; McCarty, Gregory W.; Lang, Megan W.; Torrents, Alba

2012-01-01

Row-crop and poultry production have been implicated as sources of water pollution along the Choptank River, an estuary and tributary of the Chesapeake Bay. This study examined the effects of land use, subwatershed characteristics, and climatic conditions on the water quality parameters of a subwatershed in the Choptank River watershed. The catchments within the subwatershed were defined using advanced remotely-sensed data and current geographic information system processing techniques. Water and sediment samples were collected in May–October 2009 and April–June 2010 under mostly baseflow conditions and analyzed for select bacteria, nitrate-N, ammonium-N, total arsenic, total phosphorus (TP), orthophosphate (ortho-P), and particle-phase phosphorus (PP); n = 96 for all analytes except for arsenic, n = 136, and for bacteria, n = 89 (aqueous) and 62 (sediment). Detections of Enterococci and Escherichia coli concentrations were ubiquitous in this subwatershed and showed no correlation to location or land use, however larger bacterial counts were observed shortly after precipitation. Nitrate-N concentrations were not correlated with agricultural lands, which may reflect the small change in percent agriculture and/or the similarity of agronomic practices and crops produced between catchments. Concentration data suggested that ammonia emission and possible deposition to surface waters occurred and that these processes may be influenced by local agronomic practices and climatic conditions. The negative correlation of PP and arsenic concentrations with percent forest was explained by the stronger signal of the head waters and overland flow of particulate phase analytes versus dissolved phase inputs from groundwater. Service roadways at some poultry production facilities were found to redirect runoff from the facilities to neighboring catchment areas, which affected water quality parameters. Results suggest that in this subwatershed, catchments with poultry production facilities are possible sources for arsenic and PP as compared to catchment areas where these facilities were not present.

Effectiveness of conservation practices within watersheds: Case study in tile-drained systems

USDA-ARS?s Scientific Manuscript database

The effectiveness of conservation practices are governed in part by the spatial and temporal patterns of water flow as runoff and subsurface (tile) drainage. The variability in patterns of nitrate loss were examined using data from different sized catchments with four CEAP watersheds located in cent...

Fluoride, boron and nitrate toxicity in ground water of northwest Rajasthan, India.

PubMed

Chaudhary, Veena; Kumar, Mukesh; Sharma, Mukesh; Yadav, B S

2010-02-01

The study was carried out to access the fluoride, boron, and nitrate concentrations in ground water samples of different villages in Indira Gandhi, Bhakra, and Gang canal catchment area of northwest Rajasthan, India. Rural population, in the study site, is using groundwater for drinking and irrigation purposes, without any quality test of water. All water samples (including canal water) were contaminated with fluoride. Fluoride, boron, and nitrate were observed in the ranges of 0.50-8.50, 0.0-7.73, and 0.0-278.68 mg/l, respectively. Most of the water samples were in the categories of fluoride 1.50 mg/l, of boron 2.0-4.0 mg/l, and of nitrate < 45 mg/l. There was no industrial pollution in the study site; hence, availability of these compounds in groundwater was due to natural reasons and by the use of chemical fertilizers.

Transposing Concentration-Discharge Curves onto Unmonitored Catchments to Estimate Seasonal Nutrient Loads

NASA Astrophysics Data System (ADS)

Minaudo, C.; Moatar, F.; Abbott, B. W.; Dupas, R.; Gascuel-Odoux, C.; Pinay, G.; Roubeix, V.; Danis, P. A.

2017-12-01

Many lakes and reservoirs in Europe suffer from severe eutrophication. Accurate quantification of nutrient loads are critical for effective mitigation measures, but this information is often unknown. For example, in France, only 50 out of 481 lakes and reservoirs have national monitoring allowing estimation of interannual nitrogen and phosphorus loads, and even these loads are computed from low-frequency data. To address this lack of data, we developed a straightforward method to predict seasonal loads in lake tributaries. First, we analyzed concentration-discharge (C-Q) curves in monitored catchments and identified slopes, intercepts, and coefficient of variation of the log(C)-log(Q) regressions determined for both low and high flows, separated by the median daily flow [Moatar et al., 2017]. Then, we used stepwise multiple linear regression models to empirically link the characteristics of C-Q curves with a set of catchment descriptors such as land use, lithology, morphology indices, climate, and hydrological indicators. Modeled C-Q relationships were then used to estimate annual and seasonal nutrient loads in nearby and similar unmonitored catchments. We implemented this approach on a large dataset from France where stream flow was surveyed daily and water quality (suspended solids, nitrate, total phosphorus, and orthophosphate concentrations) was measured on a monthly basis at 233 stations over the past 20 years in catchments from 10 to 3000 km². The concentration at the median daily flow (seen here as a metric of the general level of contamination in a catchment) was predicted with uncertainty ranging between 30 and 100 %, depending on the variable. C-Q slopes were predicted with large errors, but a sensitivity analysis was conducted to determine the impact of C-Q slopes uncertainties on computed annual and seasonal loads. This approach allows estimation of seasonal and annual nutrient loads and could be potentially implemented to improve protection and restoration of aquatic ecosystems. Moatar, F., B. W. Abbott, C. Minaudo, F. Curie, and G. Pinay. 2017. Elemental properties, hydrology, and biology interact to shape concentration-discharge curves for carbon, nutrients, sediment, and major ions. Water Resources Research 53:1270-1287.

Implementation of agronomical and geochemical modules into a 3D groundwater code for assessing nitrate storage and transport through unconfined Chalk aquifer

NASA Astrophysics Data System (ADS)

Picot-Colbeaux, Géraldine; Devau, Nicolas; Thiéry, Dominique; Pettenati, Marie; Surdyk, Nicolas; Parmentier, Marc; Amraoui, Nadia; Crastes de Paulet, François; André, Laurent

2016-04-01

Chalk aquifer is the main water resource for domestic water supply in many parts in northern France. In same basin, groundwater is frequently affected by quality problems concerning nitrates. Often close to or above the drinking water standards, nitrate concentration in groundwater is mainly due to historical agriculture practices, combined with leakage and aquifer recharge through the vadose zone. The complexity of processes occurring into such an environment leads to take into account a lot of knowledge on agronomy, geochemistry and hydrogeology in order to understand, model and predict the spatiotemporal evolution of nitrate content and provide a decision support tool for the water producers and stakeholders. To succeed in this challenge, conceptual and numerical models representing accurately the Chalk aquifer specificity need to be developed. A multidisciplinary approach is developed to simulate storage and transport from the ground surface until groundwater. This involves a new agronomic module "NITRATE" (NItrogen TRansfer for Arable soil to groundwaTEr), a soil-crop model allowing to calculate nitrogen mass balance in arable soil, and the "PHREEQC" numerical code for geochemical calculations, both coupled with the 3D transient groundwater numerical code "MARTHE". Otherwise, new development achieved on MARTHE code allows the use of dual porosity and permeability calculations needed in the fissured Chalk aquifer context. This method concerning the integration of existing multi-disciplinary tools is a real challenge to reduce the number of parameters by selecting the relevant equations and simplifying the equations without altering the signal. The robustness and the validity of these numerical developments are tested step by step with several simulations constrained by climate forcing, land use and nitrogen inputs over several decades. In the first time, simulations are performed in a 1D vertical unsaturated soil column for representing experimental nitrates vertical soil profiles (0-30m depth experimental measurements in Somme region). In the second time, this approach is used to simulate with a 3D model a drinking water catchment area in order to compared nitrate contents time series calculated and measured in the domestic water pumping well since 1995 (field in northern France - Avre Basin region). This numerical tool will help the decision-making in all activities in relation with water uses.

A view of annual water quality cycle and inter-annual variations in agricultural headwater catchment (Kervidy-Naizin, France)

NASA Astrophysics Data System (ADS)

Aubert, A.; Gascuel-odoux, C.; Merot, P.; Grimaldi, C.; Gruau, G.; Ruiz, L.

2011-12-01

Climatic conditions impact biotransformation and transfer of solutes. Therefore, they modify solute emissions in streams. Studying these modifications requires long term and detailed monitoring of both internal processes and river loads, which are rarely combined. The Kervidy-Naizin catchment, implemented in 1993, is part of the French network of catchment for environmental research (SOERE RBV, focused on the Critical Zone). It is an intensive agricultural catchment located in a temperate climate in Western France (Brittany) (Molenat et al., 2008; Morel et al., 2009). It presents shallow aquifers due to impervious bedrock. Both hydrology and water chemistry are monitored with a daily time step since 2000-01, as well as possible explanatory data (land use, meteorology, etc.). Concentrations in major anions in this catchment are extremely high, which make people call it a "saturated" catchment. We identified annual patterns for chloride, sulphate, dissolved organic and inorganic carbon and nitrate concentration variations. First, we considered the complete set of concentration data as function of the time. From that, we foresaw 3 cyclic temporal patterns. Then, from representing the concentrations as function of meteorological parameters, intra-annual hysteretic variations and their inter-annual variations were clearly identified. Our driving question is to know if and how climatic conditions are responsible for variations of the patterns in and between years. In winter, i.e. rainy and cold period, rainfall is closely linked to discharge because of a direct recharge to the shallow groundwater. Reversely, in transition periods (spring and fall) and hot periods, both rainfall and temperature influences discharge in relation to their range of variations. Moreover, biological processes, driven by temperature and wetness, also act during these periods. On the whole, we can emphasize the specificity of water chemistry patterns for each element. Noticeable differences between hot and cold years and between wet and dry years can mainly be observed during spring and autumn period, i.e. when combining variations of rainfall and temperature. Further jointed statistical analyses between water chemistry and meteorology have to be carried on. References Molenat, J., Gascuel-Odoux, C., Ruiz, L., and Gruau, G. (2008). Role of water table dynamics on stream nitrate export and concentration. in agricultural headwater catchment (France). Journal of Hydrology 348, 363-378. Morel, B., Durand, P., Jaffrezic, A., Gruau, G., and Molenat, J. (2009). Sources of dissolved organic carbon during stormflow in a headwater agricultural catchment. Hydrological Processes 23, 2888-2901.

Future Proofing Water Policy and Catchment Management for a Changing Climate: A Case Study of Competing Demands and Water Scarcity in the River Thames and Catchment

NASA Astrophysics Data System (ADS)

Whitehead, P. G.; Crossman, J.; Jin, L.

2011-12-01

The River Thames Catchment is the major water supply system in Southern England and supplies all of London's water supply from either the River Lee (a tributary of the Thames) or the main river abstraction site at Teddington (see Figure 1) or from groundwater sources in London. There has been a measurable change in rainfall patterns over the past 250 years with reducing summer rainfall and, hence flows, over the past 40 years. In 1976, following 3 dry winters, the London Reservoirs were more or less empty and the river flow direction was reversed to ensure a supply of water for London. Recent climate change studies in the Thames catchments suggest an increasing threat to water supply and also damage to river water quality and ecology. In addition to a changing climate, population levels in London have risen in recent years and the catchment is increasingly vulnerable to land use change. Since the 1920s changes in land use have increased the levels of nitrogen and phosphorus in the catchment and this trend is predicted to be exacerbated as climate change reduces freshwater dilution. Also land use is predicted to change as agriculture becomes more intensive as farmers react to higher grain and food prices. At the same time rising water temperatures has exposed the river to the potential for toxic algal blooms, such as cyanobacteria. This doom and gloom story is being managed however using a range of policy instruments, led by central government and public and private organisations such as Thames Water and the Environment Agency. Measures such as new reservoirs, a water transfer scheme from Wales and water metering to reduce demand are all being actively pursued, as are land management measures to control diffuse pollution. In order to assess the effects of climate change on the Thames catchment a major modelling study has been undertaken. The Integrated Catchment Model (INCA) has been set up for the Thames to model flow, nitrogen, phosphorus and ecology. Climate Change simulations predict reduced flow regimes in the river system and changes to the nitrogen patterns. Nitrate is predicted to reduce in summer, due to the lower flows which generate longer water residence times and hence allow more time for denitrification processes to occur. Phosphorus levels increase, however, due to the reduced dilution of effluents with subsequent detrimental effects on ecology. The model has been used to evaluate alternative water management policies such as a new reservoir for London, the transfer of water from the River Severn into the Thames, the reduction in P discharges from Sewage Treatment Works and the control of diffuse runoff by improved land management. Thus using the models to evaluate alternative strategies is very positive contribution to policy and planning.

Hydrology, nutrient concentrations, and nutrient yields in nearshore areas of four lakes in northern Wisconsin, 1999-2001

USGS Publications Warehouse

Graczyk, David J.; Hunt, Randall J.; Greb, Steven R.; Buchwald, Cheryl A.; Krohelski, James T.

2003-01-01

The effects of shoreline development on water quality and nutrient yields in nearshore areas of four lakes in northern Wisconsin were investigated from October 1999 through September 2001. The study measured surface runoff and ground-water flows from paired developed (sites containing lawn, rooftops, sidewalks, and driveways) and undeveloped (mature and immature woods) catchments adjacent to four lakes in northern Wisconsin. Water samples from surface runoff and ground water were collected and analyzed for nutrients. Coupled with water volumes, loads and subsequent yields of selected constituents were computed for developed and undeveloped catchments. The median runoff from lawn surfaces ranged from 0.0019 to 0.059 inch over the catchment area. Median surface runoff estimates from the wooded catchments were an order of magnitude less than those from the lawn catchments. The increased water volumes from the lawn catchments resulted in greater nutrient loads and subsequent annual nutrient yields from the developed sites. Soil temperature and soil moisture were measured at two sites with mixed lawn and wooded areas. At both of these sites, the area covered with a lawn commonly was warmer than the wooded area. No consistent differences in soil moisture were found. A ground-water model was constructed to simulate the local flow systems at two of the paired catchments. Model simulations showed that much of the ground water delivered to the lake originated from distant areas that did not contribute runoff directly to the lake. Surface runoff and ground-water nutrient concentrations from the lawn and wooded catchments did not have apparent patterns. Some of the median concentrations from lawns were significantly different (at the 0.05 significance level) from those at wooded catchments. Water wells and piezometers were sampled for chemical analyses three times during the study period. Variability in the shallow ground-water chemistry over time in the lawn samples was larger than samples from the wooded areas and upgradient wells. Median nutrient yields in surface runoff from lawns always were greater than those from the wooded catchments. Runoff volumes were the most important factor in determining whether lawns or wooded catchments contribute more nutrients to the lake. The ground-water system had appreciable nutrient concentrations, and are likely an important pathway for nutrient transport to the lake. The nitrate plus nitrite nitrogen and total phosphorus yields to the ground-water system from a lawn catchment were approximately 3 to 4 times greater than those from the wooded catchment. There was no difference in the yields of dissolved inorganic phosphorus to the ground-water system from the lawn and wooded catchments. Study results demonstrate that choosing the appropriate landscape position for locating lawns in sloped areas (specifically, slopes that do not terminate at the lake or areas with intervening flat or buffer zones between lawn and lake) can help reduce the adverse effect of lawns on the shallow ground water and, ultimately, the lake. Additional information would be needed to extrapolate these results to a large drainage area of a lake.

Effect of Agricultural Practices on Hydrology and Water Chemistry in a Small Irrigated Catchment, Yakima River Basin, Washington

USGS Publications Warehouse

McCarthy, Kathleen A.; Johnson, Henry M.

2009-01-01

The role of irrigation and artificial drainage in the hydrologic cycle and the transport of solutes in a small agricultural catchment in central Washington's Yakima Valley were explored using hydrologic, chemical, isotopic, age-dating, and mineralogical data from several environmental compartments, including stream water, ground water, overland flow, and streambed pore water. A conceptual understanding of catchment hydrology and solute transport was developed and an inverse end-member mixing analysis was used to further explore the effects of agriculture in this small catchment. The median concentrations of major solutes and nitrates were similar for the single field site and for the catchment outflow site, indicating that the net effects of transport processes for these constituents were similar at both scales. However, concentrations of nutrients were different at the two sites, suggesting that field-scale variations in agricultural practices as well as nearstream and instream biochemical processes are important components of agricultural chemical transformation and transport in this catchment. This work indicates that irrigation coupled with artificial drainage networks may exacerbate the ecological effects of agricultural runoff by increasing direct connectivity between fields and streams and minimizing potentially mitigating effects (denitrification and dilution, for example) of longer subsurface pathways.

Using hydrochemical tracers to conceptualise hydrological function in a larger scale catchment draining contrasting geologic provinces

NASA Astrophysics Data System (ADS)

Capell, R.; Tetzlaff, D.; Malcolm, I. A.; Hartley, A. J.; Soulsby, C.

2011-09-01

SummaryA year-long multivariate tracer study in the 749 km 2 catchment of the North-Esk in north east Scotland was carried out to infer the dominant runoff generation processes in two markedly different geologic provinces. The upper 60% of the catchment has montane headwaters dominated by impermeable metamorphic rocks, steep topography, peaty soils and a sub-arctic climate with over 1400 mm of precipitation. The lowlands of the catchment are underlain by a major sandstone aquifer, and mainly have freely draining, fertile soils that support intensive arable farming under a drier climate with around 800 mm of precipitation. Storm runoff in the uplands is dominated by near-surface processes in soils and sedimentary layers which generate around 60% of annual stream flows with water of low alkalinity and ionic strength. In contrast, tributaries in the lower parts of the catchment are dominated by groundwater-fed base flows which account for 75% of annual runoff and are characterised by alkaline waters with high concentrations of base cations and high levels of nitrate. Multivariate statistical methods were used to derive a generic typology of catchment source waters, their spatial and temporal dynamics and particularly, how they integrate together at the larger catchment scale. The uplands dominate the winter high flow response of the whole catchment. The influence of lowland groundwater from major aquifers becomes more apparent under low flows. However, groundwater from small upland aquifers plays a critical role for ecosystem service in dry periods providing baseflows which dilute pollutant inputs from lowland areas at the large catchment scale.

Simulation of pesticide dissipation in soil at the catchment scale over 23 years

NASA Astrophysics Data System (ADS)

Queyrel, Wilfried; Florence, Habets; Hélène, Blanchoud; Céline, Schott; Laurine, Nicola

2014-05-01

Pesticide applications lead to contamination risks of environmental compartments causing harmful effects on water resource used for drinking water. Pesticide fate modeling is assumed to be a relevant approach to study pesticide dissipation at the catchment scale. Simulations of five herbicides (atrazine, simazine, isoproturon, chlortoluron, metolachor) and one metabolite (DEA) were carried out with the crop model STICS over a 23-year period (1990-2012). The model application was performed using real agricultural practices over a small rural catchment (104 km²) located at 60km east from Paris (France). Model applications were established for two crops: wheat and maize. The objectives of the study were i) to highlight the main processes implied in pesticide fate and transfer at long-term; ii) to assess the influence of dynamics of the remaining mass of pesticide in soil on transfer; iii) to determine the most sensitive parameters related to pesticide losses by leaching over a 23-year period. The simulated data related to crop yield, water transfer, nitrates and pesticide concentrations were first compared to observations over the 23-year period, when measurements were available at the catchment scale. Then, the evaluation of the main processes related to pesticide fate and transfer was performed using long-term simulations at a yearly time step and monthly average variations. Analyses of the monthly average variations were oriented on the impact of pesticide application, water transfer and pesticide transformation on pesticide leaching. The evolution of the remaining mass of pesticide in soil, including the mobile phase (the liquid phase) and non-mobile (adsorbed at equilibrium and non-equilibrium), was studied to evaluate the impact of pesticide stored in soil on the fraction available for leaching. Finally, a sensitivity test was performed to evaluate the more sensitive parameters regarding the remaining mass of pesticide in soil and leaching. The findings of the study show that the dynamic of the remaining mass of pesticide in soil is a relevant issue to understand pesticide dissipation at long term. Attention must be paid on parameters influencing sorption and availability of the pesticide for leaching. To conclude, the significant discrepancies in the simulated pesticide leaching for the two types of crops (maize and wheat) highlight the interest of using a crop model to simulate the fate of pesticides at the catchment scale.

Water and Nutrient Balances in a Large Tile-Drained Agricultural Catchment: A Distributed Modeling Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Hongyi; Sivapalan, Murugesu; Tian, Fuqiang

This paper presents the development and implementation of a distributed model of coupled water nutrient processes, based on the representative elementary watershed (REW) approach, to the Upper Sangamon River Basin, a large, tile-drained agricultural basin located in central Illinois, mid-west of USA. Comparison of model predictions with the observed hydrological and biogeochemical data, as well as regional estimates from literature studies, shows that the model is capable of capturing the dynamics of water, sediment and nutrient cycles reasonably well. The model is then used as a tool to gain insights into the physical and chemical processes underlying the inter- andmore » intra-annual variability of water and nutrient balances. Model predictions show that about 80% of annual runoff is contributed by tile drainage, while the remainder comes from surface runoff (mainly saturation excess flow) and subsurface runoff. It is also found that, at the annual scale nitrogen storage in the soil is depleted during wet years, and is supplemented during dry years. This carryover of nitrogen storage from dry year to wet year is mainly caused by the lateral loading of nitrate. Phosphorus storage, on the other hand, is not affected much by wet/dry conditions simply because the leaching of it is very minor compared to the other mechanisms taking phosphorous out of the basin, such as crop harvest. The analysis then turned to the movement of nitrate with runoff. Model results suggested that nitrate loading from hillslope into the channel is preferentially carried by tile drainage. Once in the stream it is then subject to in-stream denitrification, the significant spatio-temporal variability of which can be related to the variation of the hydrologic and hydraulic conditions across the river network.« less

REGIONAL ANALYSIS OF INORGANIC NITROGEN YIELD AND RETENTION IN HIGH-ELEVATION ECOSYSTEMS OF THE SIERRA NEVADA AND ROCKY MOUNTAINS

EPA Science Inventory

Yields and retention of inorganic nitrogen (DIN) and nitrate concentrations in surface runoff are summarized for 28 high elevation watersheds in the Sierra Nevada, California and Rocky Mountains of Wyoming and Colorado. Catchments ranged in elevation from 2475 to 3603 m and from...

Using Data Warehouses to extract knowledge from Agro-Hydrological simulations

NASA Astrophysics Data System (ADS)

Bouadi, Tassadit; Gascuel-Odoux, Chantal; Cordier, Marie-Odile; Quiniou, René; Moreau, Pierre

2013-04-01

In recent years, simulation models have been used more and more in hydrology to test the effect of scenarios and help stakeholders in decision making. Agro-hydrological models have oriented agricultural water management, by testing the effect of landscape structure and farming system changes on water and chemical emission in rivers. Such models generate a large amount of data while few of them, such as daily concentrations at the outlet of the catchment, or annual budgets regarding soil, water and atmosphere emissions, are stored and analyzed. Thus, a great amount of information is lost from the simulation process. This is due to the large volumes of simulated data, but also to the difficulties in analyzing and transforming the data in an usable information. In this talk we illustrate a data warehouse which has been built to store and manage simulation data coming from the agro-hydrological model TNT (Topography-based nitrogen transfer and transformations, (Beaujouan et al., 2002)). This model simulates the transfer and transformation of nitrogen in agricultural catchments. TNT was used over 10 years on the Yar catchment (western France), a 50 km2 square area which present a detailed data set and have to facing to environmental issue (coastal eutrophication). 44 output key simulated variables are stored at a daily time step, i.e, 8 GB of storage size, which allows the users to explore the N emission in space and time, to quantify all the processes of transfer and transformation regarding the cropping systems, their location within the catchment, the emission in water and atmosphere, and finally to get new knowledge and help in making specific and detailed decision in space and time. We present the dimensional modeling process of the Nitrogen in catchment data warehouse (i.e. the snowflake model). After identifying the set of multileveled dimensions with complex hierarchical structures and relationships among related dimension levels, we chose the snowflake model to design our agri-environmental data warehouse. The snowflake schema is required for flexible querying complex dimension relationships. We have designed the Nitrogen in catchment data warehouse using the open source Business Intelligence Platform Pentaho Version 3.5. We use the online analytical processing (OLAP) to access and exploit, intuitively and quickly, the multidimensional and aggregated data from the Nitrogen in catchment data warehouse. We illustrate how the data warehouse can be efficiently used to explore spatio-temporal dimensions and to discover new knowledge and enrich the exploitation level of simulations. We show how the OLAP tool can be used to provide the user with the ability to synthesize environmental information and to understand nitrates emission in surface water by using comparative, personalized views on historical data. To perform advanced analyses that aim to find meaningful patterns and relationships in the data, the Nitrogen in catchment data warehouse should be extended with data mining or information retrieval methods as Skyline queries (Bouadi et al., 2012). (Beaujouan et al., 2002) Beaujouan, V., Durand, P., Ruiz, L., Aurousseau, P., and Cotteret, G. (2002). A hydrological model dedicated to topography-based simulation of nitrogen transfer and transformation: rationale and application to the geomorphology denitrification relationship. Hydrological Processes, pages 493-507. (Bouadi et al., 2012) Bouadi, T., Cordier, M., and Quiniou, R. (2012). Incremental computation of skyline queries with dynamic preferences. In DEXA (1), pages 219-233.

Water and chemical recharge in subsurface catchment: observations and consequences for modeling

NASA Astrophysics Data System (ADS)

Gascuel-odoux, C.; Aquilina, L.; Faucheux, M.; Merot, P.; Molenat, J.; de Monteti, V.; Sebilo, M.; Rouxel, M.; Ruiz, L.

2011-12-01

Shallow groundwater that develops on hillslopes is the main compartment in headwater catchments for flow and solute transport to rivers. Although spatial and temporal variations in its chemical composition are reported in the literature, there is no coherent description of the way these variations are organized, nor is there an accepted conceptual model for the recharge mechanisms and flows in the groundwater involved. We instrumented an intensive farming and subsurface dominant catchment located in Oceanic Western Europe (France), included in AgrHyS catchments (for Agro-Hydro-SyStem) and a part of the French network of catchments for environmental research (SOERE RBV dedicated to the Critical Zone). It is strongly constrained by anthropogenic pressures (agriculture) and is characterized by a clear non-equilibrium status. A network of 42 nested piezometers was installed along a 200 m hillslope allowing water sampling in the permanent water table as well as in what we call the fluctuating zone, characterized by seasonal alternance of saturated and unsaturated conditions. Water composition was monitored at high frequency (weekly) over a 3-year period for major anion composition and over a one year period for detailed 15N, CFC, SF6 and other dissolved gases composition. The results demonstrated that (i) the anionic composition in water table fluctuation zone varied significantly compared to deeper portions of the aquifer on the hillslope, confirming that this layer constitutes a main compartment for the mixing of new recharge water and old groundwater, (ii) seasonally, the variations of 15N and CFC are much higher during the recharge period than during the recession period, confirming the preferential flow during early recharge events, iii) variations of nitrate 15N and O18 composition was suggesting any significant denitrification process in the fluctuating zone, confirming the dominance of the mixing processes in the fluctuating zone, iv) deeper parts of the aquifer exhibited seasonal variations with structured hysteretic patterns, suggesting that mixing process also occurred at greater depths and v) these hysteretic patterns were dampered from upslope to downslope, indicating an increased influence of lateral flow downslope. These results indicate that we have to change the way we model subsurface dominant catchment, taken into account the degree of saturation of the catchment, the mixing processes varying from the surface to depth, and upslope to downslope. As of now, we can deduce from these results that the residence times estimated from end member approaches considering the groundwater as homogeneous lumped reservoir are likely to be underestimated. Instrumented observatories are required to understand the anthropogenic and environmental processes and their interactions, to model and predict the effect and the response time of these systems under different constraints. Rouxel, M., Molenat, J., Ruiz, L., Legout C., Faucheux, M., Gascuel-Odoux C., 2011. Seasonal and spatial variation in groundwater quality at the hillslope scale: study in an agricultural headwater catchment in Brittany (France). Hydrological Processes, 25, 831-841.

Synergetic Use of Sentinel-1 and 2 to Improve Agro-Hydrological Modeling

NASA Astrophysics Data System (ADS)

Ferrant, Sylvain; Kerr, Yann; Al-Bitar, Ahmad; Le Page, Michel; Selles, Adrien; Mermoz, Stephane; Bouvet, Alexandre; Marechal, Jean-Christophe; Tomer, Sat; Sekhar, Muddu; Dedieu, Gerard; Le Toan, Thuy; Bustillo, Vincent

2016-08-01

In the context of global changes and population growth, agricultural activities are a growing factor influencing water resources availability in term of quantity and quality. Water management strategies have to be analyzed at a regional catchment scales. Yet, agricultural practices, crop water and nutrient consumption that drive the main water and nutrient fluxes at the catchment scale have to be monitored at a high spatial (crop extension) and temporal resolution (crop growth period). This proceeding describes some advances in the framework of a co-funded ESA Living Planet Fellowship project, called ―agro-hydrology from space‖, which aims at demonstrating the improvement brought by synergetic observations of Sentinel-1 (S1) and Sentinel-2 (S2) satellite mission in agro- hydrological studies. Geo-information time-series of vegetation and water index with multi-spectral optical detection S2 together with surface roughness time series with C-band radar detection S1 are used to re-set soil water holding capacity parameters (depth, porosity) and agricultural practices (sowing date, irrigated area extent) of a crop model coupled with a hydrological model in two contrasted water management issues: stream water nitrate pollution in Gascogne region in south-west of France and groundwater depletion and shortages for irrigation in Deccan Plateau, in south-India.

Isotopic signals of summer denitrification in a northern hardwood forested catchment.

PubMed

Wexler, Sarah K; Goodale, Christine L; McGuire, Kevin J; Bailey, Scott W; Groffman, Peter M

2014-11-18

Despite decades of measurements, the nitrogen balance of temperate forest catchments remains poorly understood. Atmospheric nitrogen deposition often greatly exceeds streamwater nitrogen losses; the fate of the remaining nitrogen is highly uncertain. Gaseous losses of nitrogen to denitrification are especially poorly documented and are often ignored. Here, we provide isotopic evidence (δ(15)NNO3 and δ(18)ONO3) from shallow groundwater at the Hubbard Brook Experimental Forest indicating extensive denitrification during midsummer, when transient, perched patches of saturation developed in hillslopes, with poor hydrological connectivity to the stream, while streamwater showed no isotopic evidence of denitrification. During small rain events, precipitation directly contributed up to 34% of streamwater nitrate, which was otherwise produced by nitrification. Together, these measurements reveal the importance of denitrification in hydrologically disconnected patches of shallow groundwater during midsummer as largely overlooked control points for nitrogen loss from temperate forest catchments.

Isotopic signals of summer denitrification in a northern hardwood forested catchment

PubMed Central

Wexler, Sarah K.; Goodale, Christine L.; Bailey, Scott W.; Groffman, Peter M.

2014-01-01

Despite decades of measurements, the nitrogen balance of temperate forest catchments remains poorly understood. Atmospheric nitrogen deposition often greatly exceeds streamwater nitrogen losses; the fate of the remaining nitrogen is highly uncertain. Gaseous losses of nitrogen to denitrification are especially poorly documented and are often ignored. Here, we provide isotopic evidence (δ15NNO3 and δ18ONO3) from shallow groundwater at the Hubbard Brook Experimental Forest indicating extensive denitrification during midsummer, when transient, perched patches of saturation developed in hillslopes, with poor hydrological connectivity to the stream, while streamwater showed no isotopic evidence of denitrification. During small rain events, precipitation directly contributed up to 34% of streamwater nitrate, which was otherwise produced by nitrification. Together, these measurements reveal the importance of denitrification in hydrologically disconnected patches of shallow groundwater during midsummer as largely overlooked control points for nitrogen loss from temperate forest catchments. PMID:25368188

Temporal coherence of two alpine lake basins of the Colorado Front Range, USA

USGS Publications Warehouse

Baron, Jill S.; Caine, N.

2000-01-01

1. Knowledge of synchrony in trends is important to determining regional responses of lakes to disturbances such as atmospheric deposition and climate change. We explored the temporal coherence of physical and chemical characteristics of two series of mostly alpine lakes in nearby basins of the Colorado Rocky Mountains. Using year-to-year variation over a 10-year period, we asked whether lakes more similar in exposure to the atmosphere be-haved more similarly than those with greater influence of catchment or in-lake processes.2. The Green Lakes Valley and Loch Vale Watershed are steeply incised basins with strong altitudinal gradients. There are glaciers at the heads of each catchment. The eight lakes studied are small, shallow and typically ice-covered for more than half the year. Snowmelt is the dominant hydrological event each year, flushing about 70% of the annual discharge from each lake between April and mid-July. The lakes do not thermally stratify during the period of open water. Data from these lakes included surface water temper-ature, sulphate, nitrate, calcium, silica, bicarbonate alkalinity and conductivity.3. Coherence was estimated by Pearson's correlation coefficient between lake pairs for each of the different variables. Despite close geographical proximity, there was not a strong direct signal from climatic or atmospheric conditions across all lakes in the study. Individual lake characteristics overwhelmed regional responses. Temporal coherence was higher for lakes within each basin than between basins and was highest for nearest neighbours.4. Among the Green Lakes, conductivity, alkalinity and temperature were temporally coherent, suggesting that these lakes were sensitive to climate fluctuations. Water tem-perature is indicative of air temperature, and conductivity and alkalinity concentrations are indicative of dilution from the amount of precipitation flushed through by snowmelt.5. In Loch Vale, calcium, conductivity, nitrate, sulphate and alkalinity were temporally coherent, while silica and temperature were not. This suggests that external influences are attenuated by internal catchment and lake processes in Loch Vale lakes. Calcium and sulphate are primarily weathering products, but sulphate derives both from deposition and from mineral weathering. Different proportions of snowmelt versus groundwater in different years could influence summer lake concentrations. Nitrate is elevated in lake waters from atmospheric deposition, but the internal dynamics of nitrate and silica may be controlled by lake food webs. Temperature is attenuated by inconsistently different climates across altitude and glacial meltwaters.6. It appears that, while the lakes in the two basins are topographically close, geologically and morphologically similar, and often connected by streams, only some attributes are temporally coherent. Catchment and in-lake processes influenced temporal patterns, especially for temperature, alkalinity and silica. Montane lakes with high altitudinal gradients may be particularly prone to local controls compared to systems where coherence is more obvious.

C, N, P export regimes from headwater catchments to downstream reaches

NASA Astrophysics Data System (ADS)

Dupas, R.; Musolff, A.; Jawitz, J. W.; Rao, P. S.; Jaeger, C. G.; Fleckenstein, J. H.; Rode, M.; Borchardt, D.

2017-12-01

Excessive amounts of nutrients and dissolved organic matter in freshwater bodies affect aquatic ecosystems. In this study, the spatial and temporal variability in nitrate (NO3), dissolved organic carbon (DOC) and soluble reactive phosphorus (SRP) was analyzed in the Selke river continuum from headwaters draining 1 - 3 km² catchments to downstream reaches representing spatially integrated signals from 184 - 456 km² catchments (part of TERENO - Terrestrial Environmental Observatories, in Germany). Three headwater catchments were selected as archetypes of the main landscape units (land use x lithology) present in the Selke catchment. Export regimes in headwater catchments were interpreted in terms of NO3, DOC and SRP land-to-stream transfer processes. Headwater signals were subtracted from downstream signals, with the differences interpreted in terms of in-stream processes and contribution of point-source emissions. The seasonal dynamics for NO3 were opposite those of DOC and SRP in all three headwater catchments, and spatial differences also showed NO3 contrasting with DOC and SRP. These dynamics were interpreted as the result of the interplay of hydrological and biogeochemical processes, for which riparian zones were hypothesized to play a determining role. In the two downstream reaches, NO3 was transported almost conservatively, whereas DOC was consumed and produced in the upper and lower river sections, respectively. The natural export regime of SRP in the three headwater catchments mimicked a point-source signal, which may lead to overestimation of domestic contributions in the downstream reaches. Monitoring the river continuum from headwaters to downstream reaches proved effective to investigate jointly land-to-stream and in-stream transport and transformation processes.

The Influence of temporal sampling regime on the WFD classification of catchments within the Eden Demonstration Test Catchment Project

NASA Astrophysics Data System (ADS)

Jonczyk, Jennine; Haygarth, Phil; Quinn, Paul; Reaney, Sim

2014-05-01

A high temporal resolution data set from the Eden Demonstration Test Catchment (DTC) project is used to investigate the processes causing pollution and the influence of temporal sampling regime on the WFD classification of three catchments. This data highlights WFD standards may not be fit for purpose. The Eden DTC project is part of a UK government-funded project designed to provide robust evidence regarding how diffuse pollution can be cost-effectively controlled to improve and maintain water quality in rural river catchments. The impact of multiple water quality parameters on ecosystems and sustainable food production are being studied at the catchment scale. Three focus catchments approximately 10 km2 each, have been selected to represent the different farming practices and geophysical characteristics across the Eden catchment, Northern England. A field experimental programme has been designed to monitor the dynamics of agricultural diffuse pollution at multiple scales using state of the art sensors providing continuous real time data. The data set, which includes Total Phosphorus and Total Reactive Phosphorus, Nitrate, Ammonium, pH, Conductivity, Turbidity and Chlorophyll a reveals the frequency and duration of nutrient concentration target exceedance which arises from the prevalence of storm events of increasing magnitude. This data set is sub-sampled at different time intervals to explore how different sampling regimes affects our understanding of nutrient dynamics and the ramification of the different regimes to WFD chemical status. This presentation seeks to identify an optimum temporal resolution of data for effective catchment management and to question the usefulness of the WFD status metric for determining health of a system. Criteria based on high frequency short duration events needs to be accounted for.

Nitrogen attenuation along delivery pathways in agricultural catchments

NASA Astrophysics Data System (ADS)

McAleer, Eoin; Mellander, Per-Erik; Coxon, Catherine; Richards, Karl G.

2014-05-01

Hillslope hydrologic systems and in particular near-stream saturated zones are active sites of nitrogen (N) biogeochemical dynamics. The efficiency of N removal and the ratio of reaction products (nitrous oxide and dinitrogen) in groundwater is highly variable and depends upon aquifer hydrology, mineralogy, dissolved oxygen, energy sources and redox chemistry. There are large uncertainties in the closing of N budgets in agricultural catchments. Spatial and temporal variability in groundwater physico-chemistry, catchment hydrology and land-use gives rise to hotspots and hot moments of N attenuation. In addition the production, consumption and movement of denitrification products remains poorly understood. The focus of this study is to develop a holistic understanding of N dynamics in groundwater as it moves from the top of the hillslope to the stream. This includes saturated groundwater flow, exchange at the groundwater-surface water interface and hyporheic zone flow. This project is being undertaken in two ca. 10km2 Irish catchments, characterised by permeable soils. One catchment is dominated by arable land overlying slate bedrock and the other by grassland overlying sandstone. Multi-level monitoring wells have been installed at the upslope, midslope and bottom of each hillslope. The piezometers are screened to intercept the subsoil, weathered bedrock and competent bedrock zones. Groundwater samples for nitrate (NO3-N) nitrite (NO2-N), ammonium (NH4-N) and total nitrogen are collected on a monthly basis while dissolved gas concentrations are collected seasonally. Groundwater NO3-N profiles from monitoring data to date in both catchments differ markedly. Although the two catchments had similar 3 year mean concentrations of 6.89 mg/L (arable) and 6.24 mg/L (grassland), the grassland catchment had higher spatial and temporal variation. The arable catchment showed relatively homogenous NO3-N concentrations in all layers and zones (range: 1.2 - 12.13 mg/L, SD = 1.60 mg/L). Whereas in the grassland catchment NO3-N concentrations ranged from 0.001 - 23.9 mg/L (SD = 4.40 mg/L) with elevated concentrations in the midslope and upslope zones and groundwater at the hillslope bottom which were consistently close to the limits of detection, indicating a potential denitrifying zone. Using a combination of groundwater flow modelling (Visual Modflow-Flex), high density spatial and temporal sampling and push pull tracer techniques; it is aimed to contribute to the wider understanding of N dynamics in terms of the individual environmental parameters affecting N attenuation, spatial and temporal variability in denitrification rates and gaseous emissions along the hillslope flow path.

Local recharge processes in glacial and alluvial deposits of a temperate catchment

NASA Astrophysics Data System (ADS)

Fragalà, Federico A.; Parkin, Geoff

2010-07-01

SummaryThis study demonstrates that the composition and structure of Quaternary deposits and topography significantly influence rates of recharge and distribution of diffuse agricultural pollution at the hillslope scale. Analyses were made of vertical profiles of naturally-occurring chloride and nitrate, and artificially introduced bromide, in unsaturated and saturated sections of borehole cores of glacial till and alluvium under different land uses in the Upper Eden valley (UK). Estimates of local potential recharge were made based on chloride mass balance and nitrate peak methods. Persistent chloride bulges below the root zone were observed, and are interpreted to result from filtration processes at lithological boundaries. Changes in the shape of chloride profiles downslope, corroborated by nitrate profiles, indicate the roles of surface or near-surface runoff and runon, and the existence of lateral subsurface flows at depth. These findings have implications for estimation of recharge rates through unsaturated zones in Quaternary deposits, and the interpretation of potential 'hot-spots' of diffuse agrochemicals, particularly nitrates, moving through Quaternary deposits into groundwater.

Identifying source and formation altitudes of nitrates in drinking water from Réunion Island, France, using a multi-isotopic approach.

PubMed

Rogers, Karyne M; Nicolini, Eric; Gauthier, Virginie

2012-09-01

Nitrate concentrations, water isotopes (δ(2)H and δ(18)O(water)) and associated nitrate isotopes (δ(15)N(nitrate) and δ(18)O(nitrate)) from 10 drinking water wells, 5 fresh water springs and the discharge from 3 wastewater treatment stations in Réunion Island, located in the Indian Ocean, were analysed. We used a multi isotopic approach to investigate the extent of nitrate contamination, nitrate formation altitude and source of nitrates in Réunion Island's principal aquifer. Water from these study sites contained between 0.1 and 85.3 mg/L nitrate. δ(15)N(nitrate) values between +6 and +14‰ suggested the main sources of contamination were animal and/or human waste, rather than inorganic (synthetic) fertilisers, infiltrating through the subsurface into the saturated zone, due to rainfall leaching of the unsaturated zone at various altitudes of precipitation. Based on δ(15)N(nitrate) values alone, it was not possible to distinguish between animal and human activities responsible for the contamination of each specific catchment. However, using a multi isotope approach (δ(18)O(water) and δ(15)N(nitrate)), it was possible to relate the average altitude of rainfall infiltration (δ(18)O(water)) associated with the nitrate contamination (δ(18)O(nitrate)). This relationship between land use, rainfall recharge altitude and isotopic composition (δ(15)N(nitrate) and δ(18)O(water)) discriminated between the influences of human waste at lower (below 600 m elevation) or animal derived contamination (at elevations between 600 and 1300 m). By further comparing the theoretical altitude of nitrate formation calculated by the δ(18)O(nitrate), it was possible to determine that only 5 out of 15 fresh water wells and springs followed the conservative nitrate formation mechanism of 2/3δ(18)O(water)+1/3δ(18)O(air), to give nitrate formation altitudes which corresponded to land use activities. Copyright © 2012 Elsevier B.V. All rights reserved.

A framework for managing runoff and pollution in the rural landscape using a Catchment Systems Engineering approach.

PubMed

Wilkinson, M E; Quinn, P F; Barber, N J; Jonczyk, J

2014-01-15

Intense farming plays a key role in increasing local scale runoff and erosion rates, resulting in water quality issues and flooding problems. There is potential for agricultural management to become a major part of improved strategies for controlling runoff. Here, a Catchment Systems Engineering (CSE) approach has been explored to solve the above problem. CSE is an interventionist approach to altering the catchment scale runoff regime through the manipulation of hydrological flow pathways throughout the catchment. By targeting hydrological flow pathways at source, such as overland flow, field drain and ditch function, a significant component of the runoff generation can be managed in turn reducing soil nutrient losses. The Belford catchment (5.7 km(2)) is a catchment scale study for which a CSE approach has been used to tackle a number of environmental issues. A variety of Runoff Attenuation Features (RAFs) have been implemented throughout the catchment to address diffuse pollution and flooding issues. The RAFs include bunds disconnecting flow pathways, diversion structures in ditches to spill and store high flows, large wood debris structure within the channel, and riparian zone management. Here a framework for applying a CSE approach to the catchment is shown in a step by step guide to implementing mitigation measures in the Belford Burn catchment. The framework is based around engagement with catchment stakeholders and uses evidence arising from field science. Using the framework, the flooding issue has been addressed at the catchment scale by altering the runoff regime. Initial findings suggest that RAFs have functioned as designed to reduce/attenuate runoff locally. However, evidence suggested that some RAFs needed modification and new RAFs be created to address diffuse pollution issues during storm events. Initial findings from these modified RAFs are showing improvements in sediment trapping capacities and reductions in phosphorus, nitrate and suspended sediment losses during storm events. © 2013.

Groundwater denitrification in two agricultural river catchments: influence of hydro-geological setting and aquifer geochemistry

NASA Astrophysics Data System (ADS)

McAleer, Eoin; Mellander, Per-Erik; Coxon, Catherine; Richards, Karl G.; Jahangir, Mohammad M. R.

2015-04-01

Identifying subsurface environments with a natural capacity for denitrification is important for improving agricultural management. At the catchment scale, a complex hierarchy of landscape, hydro-geological and physico-chemical characteristics combine to affect the distribution of groundwater nitrate (NO3-). This study was conducted along four instrumented hillslopes in two ca. 10km2 agricultural river catchments in Ireland, one dominated by arable and one by grassland agriculture. Both catchments are characterised by well drained soils, but have differing aquifer characteristics. The arable catchment is underlain by weathered Ordovician slate bedrock which is extensively fractured with depth. The grassland catchment is characterised by Devonian sandstone bedrock, exhibiting both lateral (from upslope to near stream) and vertical variations in permeability along each hillslope. The capacity for groundwater denitrification was assessed by examining the concentration and distribution patterns of N species (total nitrogen, nitrate, nitrite, ammonium), dissolved organic carbon (DOC), dissolved oxygen (DO) and redox potential (Eh) in monthly samples from shallow and deep groundwater piezometers (n=37). Additionally, the gaseous products of denitrification: nitrous oxide (N2O) and excess dinitrogen (excess N2) were measured seasonally using gas chromatography and membrane inlet mass spectroscopy, respectively. The slate catchment was characterised by uniformity, both laterally and vertically, in aquifer geochemistry and gaseous denitrification products. The four year spatial mean groundwater NO3--N concentration was 6.89 mg/l and exhibited low spatial and temporal variability (temporal SD: 1.19 mg/l, spatial SD: 1.185 mg/l). Elevated DO concentrations (mean: 9.75 mg/l) and positive Eh (mean: +176.5mV) at all sample horizons indicated a setting with little denitrification potential. This non-reducing environment was reflected in a low accumulation of denitrification products (excess N2 mean: 1.57 mg/l, N2O mean: 1.61µg/l). Groundwater in the sandstone catchment had a comparable mean NO3--N concentration to that of the slate site (6.24mg/l) and while temporal variation was low (SD: 0.9 mg/l), spatial variation was substantially greater (SD: 3.63 mg/l). The accumulation of denitrification products in the sandstone catchment showed a large contrast to that of the slate with excess N2 ranging from 0.16-8.77 mg/l and N2O from 0.07-66.42 µg/l. Mean dissolved oxygen concentration and redox potential were 5.6mg/l and 67.5mV respectively. The near stream zones in particular were marked by favourable denitrifying conditions: hydraulic conductivity (<2m/day), Eh (<50mV) and DO (<5mg/l). Winter recharge had a diluting effect, increasing the concentration of DO and Eh with a concurrent decrease in excess N2 and N2O. The evolution of groundwater geochemistry along a subsurface flow path is a function of residence time. While both catchments are characterised as permeable, the slate catchment exhibits greater hydraulic conductivity values, particularly at depth, with groundwater geochemistry in all horizons reflective of recently recharged water. The deeper groundwater pathways and near stream zones in the sandstone catchment have a lower hydraulic conductivity. As such, dissolved oxygen and redox gradients occur with depth, causing the development of NO3- reducing zones.

Long-Term Water Quality Studies in a Eutrophic Lake Catchment: Slapton Ley, SW England

NASA Astrophysics Data System (ADS)

Burt, T. P.; Worrall, F.; Howden, N. J. K.

2014-12-01

Monitoring is the process by which we keep the behaviour of the environment in view, an essential way of discovering whether there are significant undesirable changes taking place. Long-term datasets reveal important patterns for scientists to explain and are essential for testing hypotheses undreamt of at the time monitoring scheme was set up. Many environmental processes take place over relatively long periods of time; very often, subtle processes are embedded within highly variable systems so that their weak signal cannot be extracted without a long record. Slapton Ley is a freshwater coastal lagoon in SW England. The Ley is part of a National Nature Reserve, wetland 116 ha in area which is divided into two basins: the Higher Ley (39 ha) is mainly reed swamp; the Lower Ley (77 ha) is open water. In the 1960s it became apparent that the Ley was becoming increasingly eutrophic. In order to gauge water, sediment and nutrient inputs into the lake, measurements began on the main catchments in late 1969. Continuous monitoring of discharge and a weekly water-sampling programme have been maintained by the Slapton Ley Field Centre ever since. The monitoring programme has been supplemented by a number of research projects which have sought to identify the salient hydrological processes operating within the Slapton catchments and to relate these to the delivery of sediment and solute to the stream system. The nitrate issue has been of particular interest at Slapton; although many longer series exist for large rivers like the Thames, the long record of nitrate data for the Slapton catchments is unique in Britain for small rural basins. Other issues to be explored will be the phosphorus legacy in lake sediments and a long-term decline in lake pH. The Slapton water quality record has confirmed that undesirable changes are taking place, revealed evidence of important patterns to be explained, allowed testing of new hypotheses (e.g. links with land-use change) and helped provide strategies for more successful management of the catchment area.

Chemical pollution assessment and prioritisation model for the Upper and Middle Vaal water management areas of South Africa.

PubMed

Dzwairo, B; Otieno, F A O

2014-12-01

A chemical pollution assessment and prioritisation model was developed for the Upper and Middle Vaal water management areas of South Africa in order to provide a simple and practical Pollution Index to assist with mitigation and rehabilitation activities. Historical data for 2003 to 2008 from 21 river sites were cubic-interpolated to daily values. Nine parameters were considered for this purpose, that is, ammonium, chloride, electrical conductivity, dissolved oxygen, pH, fluoride, nitrate, phosphate and sulphate. Parameter selection was based on sub-catchment pollution characteristics and availability of a consistent data range, against a harmonised guideline which provided five classes. Classes 1, 2, 3 and 4 used ideal catchment background values for Vaal Dam, Vaal Barrage, Blesbokspruit/Suikerbosrant and Klip Rivers, respectively. Class 5 represented values which fell above those for Klip River. The Pollution Index, as provided by the model, identified pollution prioritisation monitoring points on Rietspruit-W:K2, Natalspruit:K12, Blesbokspruit:B1, Rietspruit-L:R1/R2, Taaibosspruit:T1 and Leeuspruit:L1. Pre-classification indicated that pollution sources were domestic, industrial and mine effluent. It was concluded that rehabilitation and mitigation measures should prioritise points with high classes. Ability of the model to perform simple scenario building and analysis was considered to be an effective tool for acid mine drainage pollution assessment.

Atmospheric nitrate export in streams along a montane to urban gradient.

PubMed

Bourgeois, Ilann; Savarino, Joel; Némery, Julien; Caillon, Nicolas; Albertin, Sarah; Delbart, Franck; Voisin, Didier; Clément, Jean-Christophe

2018-08-15

Nitrogen (N) emissions associated with urbanization exacerbate the atmospheric N influx to remote ecosystems - like mountains -, leading to well-documented detrimental effects on ecosystems (e.g., soil acidification, pollution of freshwaters). Here, the importance and fate of N deposition in a watershed was evaluated along a montane to urban gradient, using a multi-isotopic tracers approach (Δ 17 O, δ 15 N, δ 18 O of nitrate, δ 2 H and δ 18 O of water). In this setting, the montane streams had higher proportions of atmospheric nitrate compared to urban streams, and exported more atmospheric nitrate on a yearly basis (0.35 vs 0.10 kg-Nha -1 yr -1 ). In urban areas, nitrate exports were driven by groundwater, whereas in the catchment head nitrate exports were dominated by surface runoff. The main sources of nitrate to the montane streams were microbial nitrification and atmospheric deposition, whereas microbial nitrification and sewage leakage contributed most to urban streams. Based on the measurement of δ 15 N and δ 18 O-NO 3 - , biological processes such as denitrification or N assimilation were not predominant in any streams in this study. The observed low δ 15 N and δ 18 O range of terrestrial nitrate (i.e., nitrate not coming from atmospheric deposition) in surface water compared to literature suggests that atmospheric deposition may be underestimated as a direct source of N. Copyright © 2018 Elsevier B.V. All rights reserved.

Threshold values and management options for nutrients in a catchment of a temperate estuary with poor ecological status

NASA Astrophysics Data System (ADS)

Hinsby, K.; Markager, S.; Kronvang, B.; Windolf, J.; Sonnenborg, T. O.; Thorling, L.

2012-02-01

Intensive farming has severe impacts on the chemical status of groundwater and streams and consequently on the ecological status of dependent ecosystems. Eutrophication is a widespread problem in lakes and marine waters. Common problems are hypoxia, algal blooms and fish kills, and loss of water clarity, underwater vegetation, biodiversity, and recreational value. In this paper we evaluate the nitrogen (N) and phosphorus (P) chemistry of groundwater and surface water in a coastal catchment, the loadings and sources of N and P and their effect on the ecological status of an estuary. We calculate the necessary reductions in N and P loadings to the estuary for obtaining a good ecological status, which we define based on the number of days with N and P limitation, and the equivalent stream and groundwater threshold values assuming two different management options. The calculations are performed by the combined use of empirical models and a physically based 3-D integrated hydrological model of the whole catchment. The assessment of the ecological status indicates that the N and P loads to the investigated estuary should be reduced by a factor of 0.52 and 0.56, respectively, to restore good ecological status. Model estimates show that threshold total N concentrations should be in the range of 2.9 to 3.1 mg l-1 in inlet freshwater to Horsens Estuary and 6.0 to 9.3 mg l-1 in shallow aerobic groundwater (∼27-41 mg l-1 of nitrate), depending on the management measures implemented in the catchment. The situation for total P is more complex but data indicate that groundwater threshold values are not needed. The inlet freshwater threshold value for total P to Horsens Estuary for the selected management options is 0.084 mg l-1. Regional climate models project increasing winter precipitation and runoff in the investigated region resulting in increasing runoff and nutrient loads to coastal waters if present land use and farming practices continue. Hence, lower threshold values are required in the future to ensure good status of all water bodies and ecosystems.

Nitrogen and salt loads in the irrigation return flows of the Ebro River Basin (Spain)

NASA Astrophysics Data System (ADS)

Isidoro, Daniel; Balcells, Maria; Clavería, Ignacio; Dechmi, Farida; Quílez, Dolores; Aragüés, Ramón

2013-04-01

The conservation of the quality of surface waters demanded by the European Water Framework Directive requires, among others, an assessment of the irrigation-induced pollution. The contribution of the irrigation return flows (IRF) to the pollution of the receiving water bodies is given by its pollutant load, since this load determines the quality status or pollutant concentration in these water bodies. The aim of this work was to quantify the annual nitrogen and salt loads in the IRF of four irrigated catchments within the Ebro River Basin: Violada (2006-10), Alcanadre (2008-10), Valcuerna (2010), and Clamor Amarga (2010). The daily flow (Q), salt (EC) and nitrate concentration (NO3) were measured in the drainage outlets of each basin. The net irrigation-induced salt and nitrogen loads were obtained from these measurements after discounting the salt and nitrogen inputs from outside the catchments and the non-irrigated areas. The N-fertilizer applications were obtained from farmer surveys and animal farming statistical sources. Irrigation water salinity was very low in all catchments (EC < 0.4 dS/m), but IRF salinity was very high in Valcuerna (7.9 dS/m) with underlain saline lutites, high to moderate in Clamor (2.6 dS/m) and Violada (2.1 dS/m) with gypsum-rich soils, and low in Alcanadre (1.0 dS/m) due to dilution in the inefficient traditional flood-irrigation system. Annual salt loads were highest in Valcuerna (11.9 Mg/ha) and lowest in Alcanadre (3.6 Mg/ha) and Clamor (3.3 Mg/ha). Salt load was also high in flood-irrigated Violada (10.3 Mg/ha), but dropped to 2.6 Mg/ha after its modernization to sprinkler irrigation (in 2008-09). N-fertilizer applications ranged from 221 kg/ha in the corn-dominated Valcuerna in 2010 to 63 kg/ha in 2008 in Violada, when farmers barely applied fertilizers due to the irrigation modernization works in progress that year. The highest N applications derived from pig slurry applications by farmers that used their lands as disposal sites for their farm residues. The highest NO3 concentrations (mean of 113 mg/L) and annual N loads (mean of 38 kg/ha) were found in Valcuerna, the most intense corn sprinkler-irrigated catchment. The lowest NO3 concentrations (21 mg/L; 5 times lower than Valcuerna) were measured in the Alcanadre flood-irrigated catchment. In contrast, Alcanadre N loads (21 kg/ha) were only about two times lower than in Valcuerna, due to the higher IRF volumes in Alcanadre (353 mm versus 132 mm in Valcuerna). Irrigation modernization in Violada decreased N loads from 20 to 5 kg N/ha (four times lower) due to the sharp reduction of IRF while maintaining NO3 concentration around 20 mg/L. The only significant contribution of ammonium (17% to the total N load of 13 hg/ha) was found in Clamor, the catchment with highest agro-industrial development. Overall, IRF salt and nitrate concentrations tended to increase and salt and nitrate loads tended to decrease in modernized sprinkler irrigation catchments, but the presence of soluble minerals, the applied inorganic and especially organic N, and the cropping patterns also played a significant role in this behaviour.

A biogeochemical comparison of two well-buffered catchments with contrasting histories of acid deposition

USGS Publications Warehouse

Shanley, J.B.; Kram, P.; Hruska, J.; Bullen, T.D.

2004-01-01

Much of the biogeochemical cycling research in catchments in the past 25 years has been driven by acid deposition research funding. This research has focused on vulnerable base-poor systems; catchments on alkaline lithologies have received little attention. In regions of high acid loadings, however, even well-buffered catchments are susceptible to forest decline and episodes of low alkalinity in streamwater. As part of a collaboration between the Czech and U.S. Geological Surveys, we compared biogeochemical patterns in two well-studied, well-buffered catchments: Pluhuv Bor in the western Czech Republic, which has received high loading of atmospheric acidity, and Sleepers River Research Watershed in Vermont, U.S.A., where acid loading has been considerably less. Despite differences in lithology, wetness, forest type, and glacial history, the catchments displayed similar patterns of solute concentrations and flow. At both catchments, base cation and alkalinity diluted with increasing flow, whereas nitrate and dissolved organic carbon increased with increasing flow. Sulfate diluted with increasing flow at Sleepers River, while at Pluhuv Bor the sulfate-flow relation shifted from positive to negative as atmospheric sulfur (S) loadings decreased and soil S pools were depleted during the 1990s. At high flow, alkalinity decreased to near 100 ??eq L-1 at Pluhuv Bor compared to 400 ??eq L-1 at Sleepers River. Despite the large amounts of S flushed from Pluhuv Bor soils, these alkalinity declines were caused solely by dilution, which was greater at Pluhuv Bor relative to Sleepers River due to greater contributions from shallow flow paths at high flow. Although the historical high S loading at Pluhuv Bor has caused soil acidification and possible forest damage, it has had little effect on the acid/base status of streamwater in this well-buffered catchment. ?? 2004 Kluwer Academic Publishers.

Modelling Common Agricultural Policy-Water Framework Directive interactions and cost-effectiveness of measures to reduce nitrogen pollution.

PubMed

Mouratiadou, Ioanna; Russell, Graham; Topp, Cairistiona; Louhichi, Kamel; Moran, Dominic

2010-01-01

Selecting cost-effective measures to regulate agricultural water pollution to conform to the Water Framework Directive presents multiple challenges. A bio-economic modelling approach is presented that has been used to explore the water quality and economic effects of the 2003 Common Agricultural Policy Reform and to assess the cost-effectiveness of input quotas and emission standards against nitrate leaching, in a representative case study catchment in Scotland. The approach combines a biophysical model (NDICEA) with a mathematical programming model (FSSIM-MP). The results indicate only small changes due to the Reform, with the main changes in farmers' decision making and the associated economic and water quality indicators depending on crop price changes, and suggest the use of target fertilisation in relation to crop and soil requirements, as opposed to measures targeting farm total or average nitrogen use.

Aquatic Nitrate Retention at River Network Scales Across Flow Conditions Determined Using Nested In Situ Sensors

NASA Astrophysics Data System (ADS)

Wollheim, W. M.; Mulukutla, G. K.; Cook, C.; Carey, R. O.

2017-11-01

Nonpoint pollution sources are strongly influenced by hydrology and are therefore sensitive to climate variability. Some pollutants entering aquatic ecosystems, e.g., nitrate, can be mitigated by in-stream processes during transport through river networks. Whole river network nitrate retention is difficult to quantify with observations. High frequency, in situ nitrate sensors, deployed in nested locations within a single watershed, can improve estimates of both nonpoint inputs and aquatic retention at river network scales. We deployed a nested sensor network and associated sampling in the urbanizing Oyster River watershed in coastal New Hampshire, USA, to quantify storm event-scale loading and retention at network scales. An end member analysis used the relative behavior of reactive nitrate and conservative chloride to infer river network fate of nitrate. In the headwater catchments, nitrate and chloride concentrations are both increasingly diluted with increasing storm size. At the mouth of the watershed, chloride is also diluted, but nitrate tended to increase. The end member analysis suggests that this pattern is the result of high retention during small storms (51-78%) that declines to zero during large storms. Although high frequency nitrate sensors did not alter estimates of fluxes over seasonal time periods compared to less frequent grab sampling, they provide the ability to estimate nitrate flux versus storm size at event scales that is critical for such analyses. Nested sensor networks can improve understanding of the controls of both loading and network scale retention, and therefore also improve management of nonpoint source pollution.

Spatial patterns of soil nitrification and nitrate export from forested headwaters in the northeastern United States

Treesearch

Donald S. Ross; James B. Shanley; John L. Campbell; Gregory B. Lawrence; Scott W. Bailey; Gene E. Likens; Beverley C. Wemple; I.F. Creed; F. Courchesne

2012-01-01

Nitrogen export from small forested watersheds is known to be affected by N deposition but with high regional variability. We studied 10 headwater catchments in the northeastern United States across a gradient of N deposition (5.4 − 9.4 kg ha−1 yr−1) to determine if soil nitrification rates...

Managing the drinking water catchment areas: the French agricultural cooperatives feed back.

PubMed

Charrière, Séverine; Aumond, Claire

2016-06-01

The quality of raw water is problematic in France, largely polluted by nitrates and pesticides (Mueller and Helsel, Nutrients in the nation's waters-too much of a good thing? Geological Survey (U.S.), 1996; European Environment Agency, European waters-assessment of status and pressures, 2012).This type of pollution, even though not always due to agriculture (example of the catchment of Ambleville, county 95, France where the nitrate pollution is mainly due to sewers (2012)), has been largely related to the agricultural practices (Sci Total Environ 407:6034-6043, 2009).Taking note of this observation, and instead of letting it paralyze their actions, the agricultural cooperatives decided with Agrosolutions to act directly on the field with their subscribers to change the agricultural practices impacting the water and the environment.This article shows how the French agricultural cooperatives transformed the awareness of the raw water quality problem into an opportunity for the development and implementation of more precise and responsible practices, to protect their environment. They measure in order to pilot, co-construct and build the best action plans possible according to the three pillars of environment, economy and agronomy.

From microbes to water districts: Linking observations across scales to uncover the implications of riparian and channel management on water quality in an irrigated agricultural landscape

NASA Astrophysics Data System (ADS)

Webster, A.; Cadenasso, M. L.

2016-12-01

Interactions among runoff, riparian and stream ecosystems, and water quality remain uncertain in many settings, particularly those heavily impacted by human activities. For example, waterways in the irrigated agricultural landscape of California's Central Valley are seasonally disconnected from groundwater tables and are extensively modified by infrastructure and management. These conditions make the impact of riparian and channel management difficult to predict across scales, which hinders efforts to promote best management practices to improve water quality. We seek to link observations across catchment, reach, and patch scales to understand patterns of nitrate and turbidity in waterways draining irrigated cropland. Data was collected on 80 reaches spanning two water management districts. At the catchment scale, water districts implemented waterway and riparian management differently: one water district had a decentralized approach, allowing individual land owners to manage their waterway channels and banks, while the other had a centralized approach, in which land owners defer management to a district-run program. At the reach scale, riparian and waterway vegetation, geomorphic complexity, and flow conditions were quantified. Reach-scale management such as riparian planting projects and channel dredging frequency were also considered. At the patch scale, denitrification potential and organic matter were measured in riparian toe-slope soils and channel sediments, along with associated vegetation and geomorphic features. All factors were tested for their ability to predict water quality using generalized linear mixed effects models and the consistency of predictors within and across scales was evaluated. A hierarchy of predictors emerges: catchment-scale management regimes predict reach-scale geomorphic and vegetation complexity, which in turn predicts sediment denitrification potential - the patch-scale factor most associated with low nitrate. Similarly, turbidity conveyance was most associated with reach-scale factors. These findings suggest that, in the absence of other regulations, a decentralized management approach to riparian zones and waterways allows reach-scale complexity to arise, which in turn promotes ecosystem function and improved water quality.

Influences of upland and riparian land use patterns on stream biotic integrity

USGS Publications Warehouse

Snyder, C.D.; Young, J.A.; Villella, R.; Lemarie, D.P.

2003-01-01

We explored land use, fish assemblage structure, and stream habitat associations in 20 catchments in Opequon Creek watershed, West Virginia. The purpose was to determine the relative importance of urban and agriculture land use on stream biotic integrity, and to evaluate the spatial scale (i.e., whole-catchment vs riparian buffer) at which land use effects were most pronounced. We found that index of biological integrity (IBI) scores were strongly associated with extent of urban land use in individual catchments. Sites that received ratings of poor or very poor based on IBI scores had > 7% of urban land use in their respective catchments. Habitat correlations suggested that urban land use disrupted flow regime, reduced water quality, and altered stream channels. In contrast, we found no meaningful relationship between agricultural land use and IBI at either whole-catchment or riparian scales despite strong correlations between percent agriculture and several important stream habitat measures, including nitrate concentrations, proportion of fine sediments in riffles, and the abundance of fish cover. We also found that variation in gradient (channel slope) influenced responses of fish assemblages to land use. Urban land use was more disruptive to biological integrity in catchments with steeper channel slopes. Based on comparisons of our results in the topographically diverse Opequon Creek watershed with results from watersheds in flatter terrains, we hypothesize that the potential for riparian forests to mitigate effects of deleterious land uses in upland portions of the watershed is inversely related to gradient.

Using high-frequency sensors to identify hydroclimatological controls on storm-event variability in catchment nutrient fluxes and source zone activation

NASA Astrophysics Data System (ADS)

Blaen, Phillip; Khamis, Kieran; Lloyd, Charlotte; Krause, Stefan

2017-04-01

At the river catchment scale, storm events can drive highly variable behaviour in nutrient and water fluxes, yet short-term dynamics are frequently missed by low resolution sampling regimes. In addition, nutrient source contributions can vary significantly within and between storm events. Our inability to identify and characterise time dynamic source zone contributions severely hampers the adequate design of land use management practices in order to control nutrient exports from agricultural landscapes. Here, we utilise an 8-month high-frequency (hourly) time series of streamflow, nitrate concentration (NO3) and fluorescent dissolved organic matter concentration (FDOM) derived from optical in-situ sensors located in a headwater agricultural catchment. We characterised variability in flow and nutrient dynamics across 29 storm events. Storm events represented 31% of the time series and contributed disproportionately to nutrient loads (43% of NO3 and 36% of CDOM) relative to their duration. Principal components analysis of potential hydroclimatological controls on nutrient fluxes demonstrated that a small number of components, representing >90% of variance in the dataset, were highly significant model predictors of inter-event variability in catchment nutrient export. Hysteresis analysis of nutrient concentration-discharge relationships suggested spatially discrete source zones existed for NO3 and FDOM, and that activation of these zones varied on an event-specific basis. Our results highlight the benefits of high-frequency in-situ monitoring for characterising complex short-term nutrient dynamics and unravelling connections between hydroclimatological variability and river nutrient export and source zone activation under extreme flow conditions. These new process-based insights are fundamental to underpinning the development of targeted management measures to reduce nutrient loading of surface waters.

Where did all the Nitrogen go? Use of Watershed-Scale Budgets to Quantify Nitrogen Inputs, Storages, and Losses.

NASA Astrophysics Data System (ADS)

Boyer, E. W.; Goodale, C. L.; Howarth, R. W.; VanBreemen, N.

2001-12-01

Inputs of nitrogen (N) to aquatic and terrestrial ecosystems have increased during recent decades, primarily from the production and use of fertilizers, the planting of N-fixing crops, and the combustion of fossil fuels. We present mass-balanced budgets of N for 16 catchments along a latitudinal profile from Maine to Virginia, which encompass a range of climatic variability and are major drainages to the coast of the North Atlantic Ocean. We quantify inputs of N to each catchment from atmospheric deposition, application of nitrogenous fertilizers, biological nitrogen fixation by crops and trees, and import of N in agricultural products (food and feed). We relate these input terms to losses of N (total, organic, and nitrate) in streamflow. The importance of the relative N sources to N exports varies widely by watershed and is related to land use. Atmospheric deposition was the largest source of N to the forested catchments of northern New England (e.g., Penobscot and Kennebec); import of N in food was the largest source of N to the more populated regions of southern New England (e.g., Charles and Blackstone); and agricultural inputs were the dominant N sources in the Mid-Atlantic region (e.g., Schuylkill and Potomac). In all catchments, N inputs greatly exceed outputs, implying additional loss terms (e.g., denitrification or volatilization and transport of animal wastes), or changes in internal N stores (e.g, accumulation of N in vegetation, soil, or groundwater). We use our N budgets and several modeling approaches to constrain estimates about the fate of this excess N, including estimates of N storage in accumulating woody biomass, N losses due to in-stream denitrification, and more. This work is an effort of the SCOPE Nitrogen Project.

Integrated cost-effectiveness analysis of agri-environmental measures for water quality.

PubMed

Balana, Bedru B; Jackson-Blake, Leah; Martin-Ortega, Julia; Dunn, Sarah

2015-09-15

This paper presents an application of integrated methodological approach for identifying cost-effective combinations of agri-environmental measures to achieve water quality targets. The methodological approach involves linking hydro-chemical modelling with economic costs of mitigation measures. The utility of the approach was explored for the River Dee catchment in North East Scotland, examining the cost-effectiveness of mitigation measures for nitrogen (N) and phosphorus (P) pollutants. In-stream nitrate concentration was modelled using the STREAM-N and phosphorus using INCA-P model. Both models were first run for baseline conditions and then their effectiveness for changes in land management was simulated. Costs were based on farm income foregone, capital and operational expenditures. The costs and effects data were integrated using 'Risk Solver Platform' optimization in excel to produce the most cost-effective combination of measures by which target nutrient reductions could be attained at a minimum economic cost. The analysis identified different combination of measures as most cost-effective for the two pollutants. An important aspect of this paper is integration of model-based effectiveness estimates with economic cost of measures for cost-effectiveness analysis of land and water management options. The methodological approach developed is not limited to the two pollutants and the selected agri-environmental measures considered in the paper; the approach can be adapted to the cost-effectiveness analysis of any catchment-scale environmental management options. Copyright © 2015 Elsevier Ltd. All rights reserved.

Integrated climate-chemical indicators of diffuse pollution from land to water.

PubMed

Mellander, Per-Erik; Jordan, Phil; Bechmann, Marianne; Fovet, Ophélie; Shore, Mairead M; McDonald, Noeleen T; Gascuel-Odoux, Chantal

2018-01-17

Management of agricultural diffuse pollution to water remains a challenge and is influenced by the complex interactions of rainfall-runoff pathways, soil and nutrient management, agricultural landscape heterogeneity and biogeochemical cycling in receiving water bodies. Amplified cycles of weather can also influence nutrient loss to water although they are less considered in policy reviews. Here, we present the development of climate-chemical indicators of diffuse pollution in highly monitored catchments in Western Europe. Specifically, we investigated the influences and relationships between weather processes amplified by the North Atlantic Oscillation during a sharp upward trend (2010-2016) and the patterns of diffuse nitrate and phosphorus pollution in rivers. On an annual scale, we found correlations between local catchment-scale nutrient concentrations in rivers and the influence of larger, oceanic-scale climate patterns defined by the intensity of the North Atlantic Oscillation. These influences were catchment-specific showing positive, negative or no correlation according to a typology. Upward trends in these decadal oscillations may override positive benefits of local management in some years or indicate greater benefits in other years. Developing integrated climate-chemical indicators into catchment monitoring indicators will provide a new and important contribution to water quality management objectives.

Hydrogeomorphological and water quality impacts of oil palm conversion and logging in Sabah, Malaysian Borneo: a multi-catchment approach

NASA Astrophysics Data System (ADS)

Walsh, Rory; Nainar, Anand; Bidin, Kawi; Higton, Sam; Annammala, Kogilavani; Blake, William; Luke, Sarah; Murphy, Laura; Perryman, Emily; Wall, Katy; Hanapi, Jamil

2016-04-01

The last three decades have seen a combination of logging and land-use change across most of the rainforest tropics. This has involved conversion to oil palm across large parts of SE Asia. Although much is now known about the hydrological and sediment transport impacts of logging, relatively little is known about how impacts of oil palm conversion compare with those of logging. Furthermore little is known about the impacts of both on river morphology and water quality. This paper reports some findings of the first phase of a ten-year large-scale manipulative multi-catchment experiment (part of the SAFE - Stability of Altered Forest Ecosystems - Project), based in the upper part of the Brantian Catchment in Sabah, Malaysian Borneo; the project is designed to assess the degree to which adverse impacts of oil palm conversion (on erosion, downstream channel change, water quality and river ecology) might be reduced by retaining buffer zones of riparian forest of varying width from zero to 120 metres. Ten 2 km2 catchments of contrasting land use history have been instrumented since 2011 to record discharge, turbidity, conductivity and water temperature at 5-minute intervals. These comprise 6 repeat-logged catchments being subjected in 2015-16 to conversion to oil palm with varying riparian forest widths; a repeat-logged 'control' catchment; an old regrowth catchment; an oil palm catchment; and a primary forest catchment. In addition, (1) monthly water samples from the catchments have been analysed for nitrates and phosphates, (2) channel cross-sectional change along each stream has been monitored at six-monthly intervals and (3) supplementary surveys have been made of downstream bankfull channel cross-sectional size and water chemistry at a wider range of catchment sites, and (4) sediment cores have been taken and contemporary deposition monitored at a hierarchical network of sites in the large Brantian catchment for geochemical analysis and dating to establish the history of sedimentation and inferred changes in upstream sediment sources. Effects on river ecology were also assessed. This paper summarises the key findings to date, focussing on differences in suspended sediment dynamics, downstream bankfull channel size and shape, and pollution between oil palm catchments, and catchments under post-logging and primary rainforest.

The Demonstration Test Catchment Approach to Land and Water Management in the river Eden Watershed, UK. (Invited)

NASA Astrophysics Data System (ADS)

Jonczyk, J.; Quinn, P. F.; Haygarth, P.; Reaney, S.; Wilkinson, M.; Burke, S.; McGonigle, D.; Harris, B.

2010-12-01

The Demonstration Test Catchment (DTC) initiative is a five year project to address pollution issues in catchments. The initiative will study the wider environmental problems suffered by catchments which are under intense farming pressures and potential climate change impacts. The UK Department for Food, Agriculture and Rural Affairs (Defra) in partnership with the Environment Agency for England and Wales (EA) have funded this initiative to answer key policy concerns in catchments. The first key step has been the establishment of a ‘research platform’ at three catchments in the UK (The Eden, Wensum and Hampshire Avon) whereby funding of 9.3 million dollars has gone into funding new equipment and pollution sampling regimes have been established. Within each catchment between three and four, 8-10km2 sub-catchments have been established. The experimental design and thinking for DTCs will be explained fully in this paper. The next phase of the project will install an extensive suite of land management and pollution mitigation interventions. In parallel to this monitoring work, a full knowledge exchange package will seek to engage with farmers, the rural community and understand the governance regime at the broader catchment scale. There is also a need for a modelling component to upscale the findings to the whole of the UK. Whilst this is an ambitious goal, there is a very basic commitment of working with rural communities to come up with real solutions that will help underpin effective policy making for the future. The research platform covers a multi-scale approach to the monitoring strategy that will allow local grouping of mitigation measures to be studied local in terms of impact and propagated to the catchment scale. Even with high level of funding, the DTC can only fully instrument a catchment of 8-10km2. Beyond this scale, the EA and the standard catchment monitoring will continue as normal. The focus here is to prove that mitigation can be achieved within smaller land units that have a clear catchment scale benefit. This will provide the evidence base for future policy which is of use to all location in the UK. Hence, the need to have suite of parameters that can be evaluated has given rise to specific experimental design. Fundamental to this is to use continuous telemetered sampling at as many location as possible, including field laboratories capable of measuring, Nitrate, Ammonia, Total Phosphorus, dissolved phosphorus, suspended sediment and chlorophyll a. Standard hydro-metrological equipment is also fully telemetered. The goal is to allow all the data to be freely available to all end users via an internet data portal. The long term goal is to invite experts from many environmental and social sciences to work at the established research platform and ultimately give a better understanding of what a healthy catchment should be like. Being able to communicate this point to both local and national audiences will also be made and will link closely to the UK Virtual Observatory project funded by the NERC.

Vulnerability of groundwater resources to nitrate pollution: A simple and effective procedure for delimiting Nitrate Vulnerable Zones.

PubMed

Arauzo, Mercedes

2017-01-01

This research was undertaken to further our understanding of the factors involved in nonpoint-source nitrate pollution of groundwater. The shortcomings of some of the most commonly used methods for assessing groundwater vulnerability have been analysed and a new procedure that incorporates key improvements has been proposed. The new approach (LU-IV procedure) allows us to assess and map groundwater vulnerability to nitrate pollution and to accurately delimit the Nitrate Vulnerable Zones. The LU-IV procedure proved more accurate than the most widely used methods to assess groundwater vulnerability (DRASTIC, GOD), when compared with nitrate distribution in the groundwater of 46 aquifers included in the study (using the drainage basin as the unit of analysis). The proposed procedure stands out by meeting the following requirements: (1) it uses readily available parameters that provide enough data to feed the model, (2) it excludes redundant parameters, (3) it avoids the need to assign insufficiently contrasted weights to parameters, (4) it assess the whole catchment area that potentially drains N-polluted waters into the receptor aquifer, (5) it can be implemented within a GIS, and (6) it provides a multi-scale representation. As the LU-IV procedure has been demonstrated to be a reliable tool for delimiting NVZ, it could be particularly interesting to use it in countries where certain types of environmental data are either not available or have only limited availability. Based on this study (and according to the LU-IV procedure), it was concluded that an area of at least 1728km 2 should be considered as NVZ. This sharply contrasts with the current 328km 2 officially designated in the study area by the Spain's regional administrations. These results highlight the need to redefine the current NVZ designation, which is essential for an appropriate implementation of action programmes designed to restore water quality in line with Directive 91/676/EEC. Copyright © 2016 Elsevier B.V. All rights reserved.

Regional meteorological drivers and long term trends of winter-spring nitrate dynamics across watersheds in northeastern North America

USGS Publications Warehouse

Crossman, Jill; Eimers, M Catherine; Casson, Nora J.; Burns, Douglas A.; Campbell, John L.; Likens, Gene E; Mitchell, Myron J; Nelson, Sarah J.; Shanley, James B.; Watmough, Shaun A.; Webster, Kara L

2016-01-01

This study evaluated the contribution of winter rain-on-snow (ROS) events to annual and seasonal nitrate (N-NO3) export and identified the regional meteorological drivers of inter-annual variability in ROS N-NO3 export (ROS-N) at 9 headwater streams located across Ontario, Canada and the northeastern United States. Although on average only 3.3 % of annual precipitation fell as ROS during winter over the study period, these events contributed a significant proportion of annual and winter N-NO3 export at the majority of sites (average of 12 and 42 %, respectively); with the exception of the most northern catchment, where total winter precipitation was exceptionally low (average 77 mm). In years with a greater magnitude of ROS events, the timing of the peak N-NO3 export period (during spring melt) was redistributed to earlier in the year. Variability in ROS frequency and magnitude amongst sites was high and a generalised linear model demonstrated that this spatial variability could be explained by interactive effects between regional and site-specific drivers. Snowpack coverage was particularly important for explaining the site-specific ROS response. Specifically, ROS events were less common when higher temperatures eliminated snow cover despite increasing the proportion of winter rainfall, whereas ROS event frequency was greater at sites where sufficient snow cover remained. This research suggests that catchment response to changes in N deposition is sensitive to climate change; a vulnerability which appears to vary in intensity throughout the seasonally snow-covered temperate region. Furthermore, the sensitivity of stream N-NO3 export to ROS events and potential shifts (earlier) in the timing of N-NO3 export relative to other nutrients affect downstream nutrient stoichiometry and the community composition of phytoplankton and other algae.

Agro-hydrology and multi-temporal high-resolution remote sensing: toward an explicit spatial processes calibration

NASA Astrophysics Data System (ADS)

Ferrant, S.; Gascoin, S.; Veloso, A.; Salmon-Monviola, J.; Claverie, M.; Rivalland, V.; Dedieu, G.; Demarez, V.; Ceschia, E.; Probst, J.-L.; Durand, P.; Bustillo, V.

2014-12-01

The growing availability of high-resolution satellite image series offers new opportunities in agro-hydrological research and modeling. We investigated the possibilities offered for improving crop-growth dynamic simulation with the distributed agro-hydrological model: topography-based nitrogen transfer and transformation (TNT2). We used a leaf area index (LAI) map series derived from 105 Formosat-2 (F2) images covering the period 2006-2010. The TNT2 model (Beaujouan et al., 2002), calibrated against discharge and in-stream nitrate fluxes for the period 1985-2001, was tested on the 2005-2010 data set (climate, land use, agricultural practices, and discharge and nitrate fluxes at the outlet). Data from the first year (2005) were used to initialize the hydrological model. A priori agricultural practices obtained from an extensive field survey, such as seeding date, crop cultivar, and amount of fertilizer, were used as input variables. Continuous values of LAI as a function of cumulative daily temperature were obtained at the crop-field level by fitting a double logistic equation against discrete satellite-derived LAI. Model predictions of LAI dynamics using the a priori input parameters displayed temporal shifts from those observed LAI profiles that are irregularly distributed in space (between field crops) and time (between years). By resetting the seeding date at the crop-field level, we have developed an optimization method designed to efficiently minimize this temporal shift and better fit the crop growth against both the spatial observations and crop production. This optimization of simulated LAI has a negligible impact on water budgets at the catchment scale (1 mm yr-1 on average) but a noticeable impact on in-stream nitrogen fluxes (around 12%), which is of interest when considering nitrate stream contamination issues and the objectives of TNT2 modeling. This study demonstrates the potential contribution of the forthcoming high spatial and temporal resolution products from the Sentinel-2 satellite mission for improving agro-hydrological modeling by constraining the spatial representation of crop productivity.

Can spatial statistical river temperature models be transferred between catchments?

NASA Astrophysics Data System (ADS)

Jackson, Faye L.; Fryer, Robert J.; Hannah, David M.; Malcolm, Iain A.

2017-09-01

There has been increasing use of spatial statistical models to understand and predict river temperature (Tw) from landscape covariates. However, it is not financially or logistically feasible to monitor all rivers and the transferability of such models has not been explored. This paper uses Tw data from four river catchments collected in August 2015 to assess how well spatial regression models predict the maximum 7-day rolling mean of daily maximum Tw (Twmax) within and between catchments. Models were fitted for each catchment separately using (1) landscape covariates only (LS models) and (2) landscape covariates and an air temperature (Ta) metric (LS_Ta models). All the LS models included upstream catchment area and three included a river network smoother (RNS) that accounted for unexplained spatial structure. The LS models transferred reasonably to other catchments, at least when predicting relative levels of Twmax. However, the predictions were biased when mean Twmax differed between catchments. The RNS was needed to characterise and predict finer-scale spatially correlated variation. Because the RNS was unique to each catchment and thus non-transferable, predictions were better within catchments than between catchments. A single model fitted to all catchments found no interactions between the landscape covariates and catchment, suggesting that the landscape relationships were transferable. The LS_Ta models transferred less well, with particularly poor performance when the relationship with the Ta metric was physically implausible or required extrapolation outside the range of the data. A single model fitted to all catchments found catchment-specific relationships between Twmax and the Ta metric, indicating that the Ta metric was not transferable. These findings improve our understanding of the transferability of spatial statistical river temperature models and provide a foundation for developing new approaches for predicting Tw at unmonitored locations across multiple catchments and larger spatial scales.

Collaborative Catchment-Scale Water Quality Management using Integrated Wireless Sensor Networks

NASA Astrophysics Data System (ADS)

Zia, Huma; Harris, Nick; Merrett, Geoff

2013-04-01

Electronics and Computer Science, University of Southampton, United Kingdom Summary The challenge of improving water quality (WQ) is a growing global concern [1]. Poor WQ is mainly attributed to poor water management and outdated agricultural activities. We propose that collaborative sensor networks spread across an entire catchment can allow cooperation among individual activities for integrated WQ monitoring and management. We show that sharing information on critical parameters among networks of water bodies and farms can enable identification and quantification of the contaminant sources, enabling better decision making for agricultural practices and thereby reducing contaminants fluxes. Motivation and results Nutrient losses from land to water have accelerated due to agricultural and urban pursuits [2]. In many cases, the application of fertiliser can be reduced by 30-50% without any loss of yield [3]. Thus information about nutrient levels and trends around the farm can improve agricultural practices and thereby reduce water contamination. The use of sensor networks for monitoring WQ in a catchment is in its infancy, but more applications are being tested [4]. However, these are focussed on local requirements and are mostly limited to water bodies. They have yet to explore the use of this technology for catchment-scale monitoring and management decisions, in an autonomous and dynamic manner. For effective and integrated WQ management, we propose a system that utilises local monitoring networks across a catchment, with provision for collaborative information sharing. This system of networks shares information about critical events, such as rain or flooding. Higher-level applications make use of this information to inform decisions about nutrient management, improving the quality of monitoring through the provision of richer datasets of catchment information to local networks. In the full paper, we present example scenarios and analyse how the benefits of collaborative information sharing can have a direct influence on agricultural practice. We apply a nutrient management scheme to a model of an example catchment with several individual networks. The networks are able to correlate catchment events to events within their zone of influence, allowing them to adapt their monitoring and control strategy in light of wider changes across the catchment. Results indicate that this can lead to significant reductions in nutrient losses (up to 50%) and better reutilization of nutrients amongst farms, having a positive impact on catchment scale water quality and fertilizer costs. 1. EC, E.C., Directive 2000/60/EC establishing a framework for Community action in the field of water policy, 2000. 2. Rivers, M., K. Smettem, and P. Davies. Estimating future scenarios for farm-watershed nutrient fluxes using dynamic simulation modelling-Can on-farm BMPs really do the job at the watershed scale? in Proc.29th Int.Conf System Dynamics Society, 2011. 2010. Washington 3. Liu, C., et al., On-farm evaluation of winter wheat yield response to residual soil nitrate-N in North China Plain. Agronomy Journal, 2008. 100(6): p. 1527-1534. 4. Kotamäki, N., et al., Wireless in-situ sensor network for agriculture and water monitoring on a river basin scale in Southern Finland: Evaluation from a data user's perspective. Sensors, 2009. 9(4): p. 2862-2883.

The effects of catchment and riparian forest quality on stream environmental conditions across a tropical rainforest and oil palm landscape in Malaysian Borneo.

PubMed

Luke, Sarah H; Barclay, Holly; Bidin, Kawi; Chey, Vun Khen; Ewers, Robert M; Foster, William A; Nainar, Anand; Pfeifer, Marion; Reynolds, Glen; Turner, Edgar C; Walsh, Rory P D; Aldridge, David C

2017-06-01

Freshwaters provide valuable habitat and important ecosystem services but are threatened worldwide by habitat loss and degradation. In Southeast Asia, rainforest streams are particularly threatened by logging and conversion to oil palm, but we lack information on the impacts of this on freshwater environmental conditions, and the relative importance of catchment versus riparian-scale disturbance. We studied 16 streams in Sabah, Borneo, including old-growth forest, logged forest, and oil palm sites. We assessed forest quality in riparian zones and across the whole catchment and compared it with stream environmental conditions including water quality, structural complexity, and organic inputs. We found that streams with the highest riparian forest quality were nearly 4 °C cooler, over 20 cm deeper, had over 40% less sand, greater canopy cover, more stored leaf litter, and wider channels than oil palm streams with the lowest riparian forest quality. Other variables were significantly related to catchment-scale forest quality, with streams in the highest quality forest catchments having 40% more bedrock and 20 times more dead wood, along with higher phosphorus, and lower nitrate-N levels compared to streams with the lowest catchment-scale forest quality. Although riparian buffer strips went some way to protecting waterways, they did not maintain fully forest-like stream conditions. In addition, logged forest streams still showed signs of disturbance 10-15 years after selective logging. Our results suggest that maintenance and restoration of buffer strips can help to protect healthy freshwater ecosystems but logging practices and catchment-scale forest management also need to be considered.

Effect of climate, intra and inter-annual variability, on nutrients emission (C,N, P) in stream water: lessons from an agricultural long term observatory of the temperate zone

NASA Astrophysics Data System (ADS)

Gascuel-Odoux, Chantal; Remi, Dupas; Patrick, Durand; Ophélie, Fovet; Gerard, Gruau; Anne, Jaffrezic; Guillaume, Humbert; Philippe, Merot; Gu, Sen

2016-04-01

Agriculture greatly contributes to modify C, N and P cycles, particularly in animal breeding regions due to high inputs. Climatic conditions, intra and inter-annual variabilities, modify nutrient stream water emissions, acting in time on transfer and transformation, accumulation and mobilization processes, connecting and disconnecting in time different compartments (soil, riparian areas, groundwater). In agricultural catchments, nutrient perturbations are dominated by agricultural land use, and decoupling human activities and climate effects is far from easy. Climate change generally appears as a secondary driver compared to land use. If studied, generally only one nutrient is considered. Only long term, high frequency and multiple element data series can decouple these two drivers. The Kervidy-Naizin watershed belongs to the AgrHyS environmental research observatory (http://www6.inra.fr/ore_agrhys_eng), itself included in RBV (French catchment network of the CZO). On this catchment, 6 years of daily data on DOC, NO3, SRP, TP concentrations allow us to analyze the effect of seasonal and inter-annual climatic variabilities on water quality (C, N, P). Different papers have been published on the effect of climate on nitrate (Molenat et al, 2008), SRP and TP (Dupas et al, 2015) and DOC (Humbert et al, 2015). We will present first results comparing the effect of climate on these three major solute forms of C, N and P. While C and P dynamics are very close and controlled by fluctuation of water table downslope, i.e. in riparian areas, mobilizing C and P in time, nitrate dynamics is controlled by GW dynamics upslope acting as the major N reservoir. As example, the dryness conditions in summer appears a key factor of the C and P emissions in autumn. All the three solute forms interact when anoxic conditions are observed in riparian zones. These basic processes explain how climatic variability can influence and explain interactions between C, N and P emissions in stream water. These results underline three major lack in most of our observatories: high frequency data as flood event are important for C and P emissions; multiple element approach, as very few observatories have currently C, N and P, their solute and particulate forms; climate but also soil wetness, GW fluctuations explaining biotransformation and connection between reservoirs on catchments, so that linking hydrological and biogeochimical condition is necessary to explain export. These lacks of observations is a barrier to develop process based models assessing and predicting the effect of climate on water quality. References Dupas R., Gruau G., Sen Gu, Humbert G., Jaffrezic A., Gascuel-Odoux C., 2015. Groundwater control of biogeochemical processes causing phosphorus release from riparian wetlands. Water Research 84, 307-314 Humbert G., Jaffrezic A., Fovet O., Gruau G., Durand P., 2015. Dry-season length and runoff control annual variability in stream DOC dynamics in a small, shallow groundwater-dominated agricultural watershed. Water Resources Research. Molenat J., Gascuel-Odoux C., Ruiz L., Gruau G., 2008. Role of water table dynamics on stream nitrate export and concentration in agricultural headwater. Journal of Hydrology 348, 363- 378.

Predicting long-term catchment nutrient export: the use of nonlinear time series models

NASA Astrophysics Data System (ADS)

Valent, Peter; Howden, Nicholas J. K.; Szolgay, Jan; Komornikova, Magda

2010-05-01

After the Second World War the nitrate concentrations in European water bodies changed significantly as the result of increased nitrogen fertilizer use and changes in land use. However, in the last decades, as a consequence of the implementation of nitrate-reducing measures in Europe, the nitrate concentrations in water bodies slowly decrease. This causes that the mean and variance of the observed time series also changes with time (nonstationarity and heteroscedascity). In order to detect changes and properly describe the behaviour of such time series by time series analysis, linear models (such as autoregressive (AR), moving average (MA) and autoregressive moving average models (ARMA)), are no more suitable. Time series with sudden changes in statistical characteristics can cause various problems in the calibration of traditional water quality models and thus give biased predictions. Proper statistical analysis of these non-stationary and heteroscedastic time series with the aim of detecting and subsequently explaining the variations in their statistical characteristics requires the use of nonlinear time series models. This information can be then used to improve the model building and calibration of conceptual water quality model or to select right calibration periods in order to produce reliable predictions. The objective of this contribution is to analyze two long time series of nitrate concentrations of the rivers Ouse and Stour with advanced nonlinear statistical modelling techniques and compare their performance with traditional linear models of the ARMA class in order to identify changes in the time series characteristics. The time series were analysed with nonlinear models with multiple regimes represented by self-exciting threshold autoregressive (SETAR) and Markov-switching models (MSW). The analysis showed that, based on the value of residual sum of squares (RSS) in both datasets, SETAR and MSW models described the time-series better than models of the ARMA class. In most cases the relative improvement of SETAR models against AR models of first order was low ranging between 1% and 4% with the exception of the three-regime model for the River Stour time-series where the improvement was 48.9%. In comparison, the relative improvement of MSW models was between 44.6% and 52.5 for two-regime and from 60.4% to 75% for three-regime models. However, the visual assessment of models plotted against original datasets showed that despite a high value of RSS, some ARMA models could describe the analyzed time-series better than AR, MA and SETAR models with lower values of RSS. In both datasets MSW models provided a very good visual fit describing most of the extreme values.

Catchment virtual observatory for sharing flow and transport models outputs: using residence time distribution to compare contrasting catchments

NASA Astrophysics Data System (ADS)

Thomas, Zahra; Rousseau-Gueutin, Pauline; Kolbe, Tamara; Abbott, Ben; Marcais, Jean; Peiffer, Stefan; Frei, Sven; Bishop, Kevin; Le Henaff, Geneviève; Squividant, Hervé; Pichelin, Pascal; Pinay, Gilles; de Dreuzy, Jean-Raynald

2017-04-01

The distribution of groundwater residence time in a catchment provides synoptic information about catchment functioning (e.g. nutrient retention and removal, hydrograph flashiness). In contrast with interpreted model results, which are often not directly comparable between studies, residence time distribution is a general output that could be used to compare catchment behaviors and test hypotheses about landscape controls on catchment functioning. In this goal, we created a virtual observatory platform called Catchment Virtual Observatory for Sharing Flow and Transport Model Outputs (COnSOrT). The main goal of COnSOrT is to collect outputs from calibrated groundwater models from a wide range of environments. By comparing a wide variety of catchments from different climatic, topographic and hydrogeological contexts, we expect to enhance understanding of catchment connectivity, resilience to anthropogenic disturbance, and overall functioning. The web-based observatory will also provide software tools to analyze model outputs. The observatory will enable modelers to test their models in a wide range of catchment environments to evaluate the generality of their findings and robustness of their post-processing methods. Researchers with calibrated numerical models can benefit from observatory by using the post-processing methods to implement a new approach to analyzing their data. Field scientists interested in contributing data could invite modelers associated with the observatory to test their models against observed catchment behavior. COnSOrT will allow meta-analyses with community contributions to generate new understanding and identify promising pathways forward to moving beyond single catchment ecohydrology. Keywords: Residence time distribution, Models outputs, Catchment hydrology, Inter-catchment comparison

Agro-hydrology and multi temporal high resolution remote sensing: toward an explicit spatial processes calibration

NASA Astrophysics Data System (ADS)

Ferrant, S.; Gascoin, S.; Veloso, A.; Salmon-Monviola, J.; Claverie, M.; Rivalland, V.; Dedieu, G.; Demarez, V.; Ceschia, E.; Probst, J.-L.; Durand, P.; Bustillo, V.

2014-07-01

The recent and forthcoming availability of high resolution satellite image series offers new opportunities in agro-hydrological research and modeling. We investigated the perspective offered by improving the crop growth dynamic simulation using the distributed agro-hydrological model, Topography based Nitrogen transfer and Transformation (TNT2), using LAI map series derived from 105 Formosat-2 (F2) images during the period 2006-2010. The TNT2 model (Beaujouan et al., 2002), calibrated with discharge and in-stream nitrate fluxes for the period 1985-2001, was tested on the 2006-2010 dataset (climate, land use, agricultural practices, discharge and nitrate fluxes at the outlet). A priori agricultural practices obtained from an extensive field survey such as seeding date, crop cultivar, and fertilizer amount were used as input variables. Continuous values of LAI as a function of cumulative daily temperature were obtained at the crop field level by fitting a double logistic equation against discrete satellite-derived LAI. Model predictions of LAI dynamics with a priori input parameters showed an temporal shift with observed LAI profiles irregularly distributed in space (between field crops) and time (between years). By re-setting seeding date at the crop field level, we proposed an optimization method to minimize efficiently this temporal shift and better fit the crop growth against the spatial observations as well as crop production. This optimization of simulated LAI has a negligible impact on water budget at the catchment scale (1 mm yr-1 in average) but a noticeable impact on in-stream nitrogen fluxes (around 12%) which is of interest considering nitrate stream contamination issues and TNT2 model objectives. This study demonstrates the contribution of forthcoming high spatial and temporal resolution products of Sentinel-2 satellite mission in improving agro-hydrological modeling by constraining the spatial representation of crop productivity.

Acceleration of chemical weathering related to intensive agriculture: evidence from groundwater dating

NASA Astrophysics Data System (ADS)

Aquilina, Luc; Marçais, Jean; de Dreuzy, Jean-Raynald; Labasque, Thierry; Abbott, Ben; Vergnaud, Virginie; Walter, Christian; Viville, Daniel; Chabaux, François; Pinay, Gilles

2017-04-01

Agricultural pollution is a matter of political and scientific concern throughout the world. Intensive agriculture can cause nutrient contamination of groundwater and surface water. Nutrient pollution causes eutrophication in freshwater and estuarine ecosystems. A secondary effect of agricultural intensification is river acidification. Oxidation of chemical fertilizers such as ammonium (NH4+) to nitrate (NO3-) produces H+ ions that cause leaching of cations from soil and deeper material to maintain charge balance. Monitoring of various rivers in Brittany (western France) revealed that agriculture intensification has led to increased cation export starting in the 1980s. From the cation ratios, we deduced that cation increase comes approximately equally from dissolution of carbonate added to soil (liming practices) and silicate dissolution. Cation export represented about 30% of the soil cation exchange potential. If compensated by liming, it may constitute a non-negligible source to atmospheric CO2 (Aquilina et al., 2012). We further investigated the potential for silicate dissolution through the use of groundwater dating in various sites of Brittany. Coupling chemical analyses to groundwater ages in a large range of aquifers and a large range of depths (down to 110m) allowed us to reconstruct a chronicle for the last 50 yrs of the cation concentrations of groundwater. It clearly shows a contemporaneous increase in sodium and nitrate and a decrease in calcium, with the most dramatic changes occurring during the 70s and 80s. Using groundwater dating, we were also able to determine a silica production geochronometer. A tight and linear relationship between silica concentration and groundwater age (Figure) was observed and allowed a production rate in groundwater to be determined. Except for short residence-times (Kerrien), the silica production rate for different granitic catchments was consistent, ranging from 0.3 to 0.4 mg.L-1.yr-1. To assess the role of anthropogenic activity in silica production rate, we compared production rates from Brittany with catchments in the Vosges Mountains, a relatively pristine area. Dissolution rates were much higher in the Brittany catchments, indicating the effect of human activities on chemical weathering and cation export at the catchment scale. Aquilina L. et al., 2012 - Long-term effects of high nitrogen loads on cation and carbon riverine export in agricultural catchments. Env. Sci & Technology 46-17, 9447-9455..

Deconstructing the Effects of Flow on DOC, Nitrate, and Major Ion Interactions Using a High-Frequency Aquatic Sensor Network

NASA Astrophysics Data System (ADS)

Koenig, L. E.; Shattuck, M. D.; Snyder, L. E.; Potter, J. D.; McDowell, W. H.

2017-12-01

Streams provide a physical linkage between land and downstream river networks, delivering solutes derived from multiple catchment sources. We analyzed high-frequency time series of stream solutes to characterize the timing and magnitude of major ion, nutrient, and organic matter transport over event, seasonal, and annual timescales as well as to assess whether nitrate (NO3-) and dissolved organic carbon (DOC) transport are coupled in catchments, which would be expected if they are subject to similar biogeochemical controls throughout the watershed. Our data set includes in situ observations of NO3-, fluorescent dissolved organic matter (DOC proxy), and specific conductance spanning 2-4 years in 10 streams and rivers across New Hampshire, including observations of nearly 700 individual hydrologic events. We found a positive response of NO3- and DOC to flow in forested streams, but watershed development led to a negative relationship between NO3- and discharge, and thus a decoupling of the overall NO3- and DOC responses to flow. On event and seasonal timescales, NO3- and DOC consistently displayed different behaviors. For example, in several streams, FDOM yield was greatest during summer storms while NO3- yield was greatest during winter storms. Most streams had generalizable storm NO3- and DOC responses, but differences in the timing of NO3- and DOC transport suggest different catchment sources. Further, certain events, including rain-on-snow and summer storms following dry antecedent conditions, yielded disproportionate NO3- responses. High-frequency data allow for increased understanding of the processes controlling solute variability and will help reveal their responses to changing climatic regimes.

Potential benefits of farm scale measures versus landscape measures for reducing nitrate loads in a Danish catchment.

PubMed

Hashemi, Fatemeh; Olesen, Jørgen E; Børgesen, Christen D; Tornbjerg, Henrik; Thodsen, Hans; Dalgaard, Tommy

2018-05-08

To comply with the EU Water Framework Directive, Denmark must further reduce the nitrate (N)-load to marine ecosystems from agricultural areas. Under the anticipated future spatially targeted regulation, the required N-load reductions will differ between catchments, and these are expected to be mitigated by a combination of land and water management measures. Here, we explored how the expected N-load reduction target of 38% for a Danish catchment (River Odense) could be achieved through a combination of farm and landscape measures. These include: (a) N-leaching reduction through changing the crop rotation and applying cover crops, (b) enhancing N-reduction through (re)establishment of wetlands, and (c) reducing N-leaching through spatially targeting of set-aside to high N-load areas. Changes in crop rotations were effective in reducing N-leaching by growing crops with a longer growing season and by allowing a higher use of cover crops. A combination of wetlands and changes in crop rotations were needed for reaching the N-load reduction target without use of set-aside. However, not all combinations of wetlands and crop rotation changes achieved the required N-load reduction, resulting in a need for targeted set-aside, implying a need for balancing measures at farm and landscape scale to maximize N load reduction while minimizing loss of productive land. The effectiveness of farm scale measures is affected by farm and soil types as well as by N-reduction in groundwater, while the possibilities for using wetlands for decreasing the N-load depends on landscape features, allowing the establishment of wetlands connected to streams and rivers. Copyright © 2018 Elsevier B.V. All rights reserved.

Nitrate contamination of water resources in a small catchment with intensive livestock facilities in Korea

NASA Astrophysics Data System (ADS)

Kim, Y.; Woo, N.

2003-04-01

The study area is a small catchment developed along a stream, Hwabong-chun, running toward north, with a length of about 4 km. Because of gentle slopes of the area, land is utilized for various agricultural activities in different scales including paddy fields, grape vineyards, and intensive livestock facilities of swine, cow and poultry. In this area, groundwater is the main source of domestic and agricultural water-supply, and appears to be under severe risk of contamination from various potential sources. Therefore, this study was initiated to identify the extent and sources of groundwater contamination by nitrate. A total of 49 groundwater and surface-water samples were collected in February and April 2002, and concentrations of dissolved constituents and nitrogen-isotope ratio of nitrate were analyzed. Little change of concentrations of dissolved ions in samples of Feb. and Apr. implies that spring discharge of groundwater might not occur yet. About 77% of groundwater samples have NO3-N concentrations of greater than 3 mg/L, indicating their origins from anthropogenic sources at surface. About 37% of samples detected NO3-N levels higher than 10 mg/L, Korean Drinking Water Guidelines. Although groundwater is being used for domestic uses during the winter season, nitrate levels show no significant changes between February and April. This implies that the sources would be large enough to continuously discharge nitrate into the groundwater system. Correlation matrix shows Na, Ca, Cl, NO3-N, SO4 moving together in the groundwater system. Results of Principal Component Analysis(PCA) indicate these constituents are the most dominant factor controlling groundwater quality in the area. Seepages from a swine farm and a poultry farm were analyzed and show significantly elevated concentrations of K, Na, Ca, Cl, NH4, PO4, SO4. Considering low mobility of K and PO4 and transformation of NH4 to NO3 in the shallow subsurface environments, those water-quality controlling constituents are supposed to be originated from seepages of the livestock facilities. About 59% of total groundwater samples have (del)15N-NO3 values greater than 8 ‰, indicating the influence of seepage from manures and septic tanks. Countours of (del)15N-NO3 match well with the distribution of nitrate concentrations in groundwater. However, a part of southern area without the livestock facilities also shows high concentrations of nitrate and high values of (del)15N in groundwater. Based on the landuse history of the area, we interpreted that the elevated nitrate concentrations were due to the abondoned facilities, which had been operated until 5-years ago. This further implies two important facts: 1) records of landuse history should be examined to identify contamination sources properly, and 2) nitrate contamination from seepages of livestock facilities could last for a while even after disclosure of facilities.

Evidence for nutrient enrichment of high-elevation lakes in the Sierra Nevada, California

USGS Publications Warehouse

Sickman, James O.; Melack, John M.; Clow, David W.

2003-01-01

Long-term measurements (1983-2001) of nutrients and seston in Emerald Lake (Sierra Nevada, California) have revealed ecologically significant patterns. Nitrate, both during spring runoff and during growing seasons, declined from 1983 through 1995. Declining snowmelt nitrate was caused primarily by changes in snow regime induced by the 1987-1992 drought: years with shallow, early melting snowpacks had lower snowmelt nitrate concentrations owing to less labile N production in catchment soils and longer plant growing seasons. However, nitrate declines during growing seasons carried through the wetter years of 1993-2000 and are likely the result of increased P loading to the lake and the release of phytoplankton from P limitation. Contemporaneous with these changes was an increase in algal biomass and a shift from P limitation toward more frequent N limitation of phytoplankton abundance. Particulate carbon concentrations in the late 1990s were two- to threefold greater than in the early 1980s. These trends were reflected in a larger set of Sierra Nevada lakes sampled as part of synoptic surveys (n = 28). Between 1985 and 1999, nitrate decreased and total P increased in >70% of the lakes sampled. Our data suggest that lakes throughout the Sierra Nevada are experiencing measurable eutrophication in response to the atmospheric deposition of nutrients.

Tracing the Fate of Atmospheric Nitrate in a Subalpine Watershed Using Δ17O.

PubMed

Bourgeois, Ilann; Savarino, Joël; Caillon, Nicolas; Angot, Hélène; Barbero, Albane; Delbart, Franck; Voisin, Didier; Clément, Jean-Christophe

2018-05-15

Nitrogen is an essential nutrient for life on Earth, but in excess, it can lead to environmental issues (e.g., N saturation, loss of biodiversity, acidification of lakes, etc.). Understanding the nitrogen budget (i.e., inputs and outputs) is essential to evaluate the prospective decay of the ecosystem services (e.g., freshwater quality, erosion control, loss of high patrimonial-value plant species, etc.) that subalpine headwater catchments provide, especially as these ecosystems experience high atmospheric nitrogen deposition. Here, we use a multi-isotopic tracer (Δ 17 O, δ 15 N and δ 18 O) of nitrate in aerosols, snow, and streams to assess the fate of atmospherically deposited nitrate in the subalpine watershed of the Lautaret Pass (French Alps). We show that atmospheric N deposition contributes significantly to stream nitrate pool year-round, either by direct inputs (up to 35%) or by in situ nitrification of atmospheric ammonium (up to 35%). Snowmelt in particular leads to high exports of atmospheric nitrate, most likely fast enough to impede assimilation by surrounding ecosystems. Yet, in a context of climate change, with shorter snow seasons, and increasing nitrogen emissions, our results hint at possibly stronger ecological consequences of nitrogen atmospheric deposition in the close future.

Preferential flow and mixing process in the chemical recharge in subsurface catchments: observations and modeling

NASA Astrophysics Data System (ADS)

Gascuel-Odoux, C.; Rouxel, M.; Molenat, J.; Ruiz, L.; Aquilina, L.; Faucheux, M.; Labasque, T.; Sebilo, M.

2012-04-01

Shallow groundwater that develops on hillslopes is the main compartment in headwater catchments for flow and solute transport to rivers. Although spatial and temporal variations in its chemical composition are reported in the literature, there is no coherent description of the way these variations are organized, nor is there an accepted conceptual model for the recharge mechanisms and flows in the groundwater involved. We instrumented an intensive farming and subsurface dominant catchment located in Oceanic Western Europe (Kerbernez, Brittany, France), a headwater catchment included in the Observatory for Research on Environment AgrHyS (Agro-Hydro-System) and a part of the French Network of catchments for environmental research (SOERE RBV focused on the Critical Zone). These systems are strongly constrained by anthropogenic pressures (agriculture) and are characterized by a clear non-equilibrium status. A network of 42 nested piezometers was installed along a 200 m hillslope allowing water sampling along two transects in the permanent water table as well as in what we call the "fluctuating zone", characterized by seasonal alternance of saturated and unsaturated conditions. Water composition was monitored at high frequency (weekly) over a 3-year period for major anion composition and over a one year period for detailed 15N, CFC, SF6 and other dissolved gases. The results demonstrated that (i) the anionic composition in water table fluctuation zone varied significantly compared to deeper portions of the aquifer on the hillslope, confirming that this layer constitutes a main compartment for the mixing of new recharge water and old groundwater, (ii) seasonally, the variations of 15N and CFC are much higher during the recharge period than during the recession period, confirming the preferential flow during early recharge events, iii) variations of nitrate 15N and O18 composition was suggesting any significant denitrification process in the fluctuating zone, confirming the dominance of the mixing processes in the fluctuating zone, iv) deeper parts of the aquifer exhibited seasonal variations with structured hysteretic patterns, suggesting that mixing process also occurred at greater depths and v) these hysteretic patterns were dampered from upslope to downslope, indicating an increased influence of lateral flow downslope. A first modeling approach has been tested adding to a convection-dispersion model a mobile-immobile model, representing a mixing process between the pre-recharge water and the recharge water, and therefore taken into account the mixing processes varying from the surface to depth.As of now, we can deduce from these results that the residence times calculated from end member approaches considering the groundwater as homogeneous lumped reservoir are likely to be highly underestimated. We can also dedude that the water sampled in the shallow groundwater during the first part of the recharge period is chemically different from the water sampled after. Instrumented observatories including spatial and temporal monitoring of the hillslope groundwater are required to understand the anthropogenic and environmental processes and their interactions, to model and predict the effect and the response time of such systems under different constraints. This work is funded by AN-08-STRA-01 (National research Agency). Legout, C.; Molenat, J.; Aquilina, L.; Gascuel-Odoux, C.; Faucheux, M.; Fauvel, Y.; Bariac, T. 2007. Solute transfer in the unsaturated zone-groundwater continuum of a headwater catchment. Journal of Hydrology. 332 (2-4), 427-441. Rouxel, M., Molenat, J., Ruiz, L., Legout C., Faucheux, M., Gascuel-Odoux C., 2011. Seasonal and spatial variation in groundwater quality at the hillslope scale: study in an agricultural headwater catchment in Brittany (France). Hydrological Processes, 25, 831-841.

Water and salt balance modelling to predict the effects of land-use changes in forested catchments. 1. Small catchment water balance model

NASA Astrophysics Data System (ADS)

Sivapalan, Murugesu; Ruprecht, John K.; Viney, Neil R.

1996-03-01

A long-term water balance model has been developed to predict the hydrological effects of land-use change (especially forest clearing) in small experimental catchments in the south-west of Western Australia. This small catchment model has been used as the building block for the development of a large catchment-scale model, and has also formed the basis for a coupled water and salt balance model, developed to predict the changes in stream salinity resulting from land-use and climate change. The application of the coupled salt and water balance model to predict stream salinities in two small experimental catchments, and the application of the large catchment-scale model to predict changes in water yield in a medium-sized catchment that is being mined for bauxite, are presented in Parts 2 and 3, respectively, of this series of papers.The small catchment model has been designed as a simple, robust, conceptually based model of the basic daily water balance fluxes in forested catchments. The responses of the catchment to rainfall and pan evaporation are conceptualized in terms of three interdependent subsurface stores A, B and F. Store A depicts a near-stream perched aquifer system; B represents a deeper, permanent groundwater system; and F is an intermediate, unsaturated infiltration store. The responses of these stores are characterized by a set of constitutive relations which involves a number of conceptual parameters. These parameters are estimated by calibration by comparing observed and predicted runoff. The model has performed very well in simulations carried out on Salmon and Wights, two small experimental catchments in the Collie River basin in south-west Western Australia. The results from the application of the model to these small catchments are presented in this paper.

Nitrate removal in stream ecosystems measured by 15N addition experiments: Total uptake

USGS Publications Warehouse

Hall, R.O.; Tank, J.L.; Sobota, D.J.; Mulholland, P.J.; O'Brien, J. M.; Dodds, W.K.; Webster, J.R.; Valett, H.M.; Poole, G.C.; Peterson, B.J.; Meyer, J.L.; McDowell, W.H.; Johnson, S.L.; Hamilton, S.K.; Grimm, N. B.; Gregory, S.V.; Dahm, Clifford N.; Cooper, L.W.; Ashkenas, L.R.; Thomas, S.M.; Sheibley, R.W.; Potter, J.D.; Niederlehner, B.R.; Johnson, L.T.; Helton, A.M.; Crenshaw, C.M.; Burgin, A.J.; Bernot, M.J.; Beaulieu, J.J.; Arangob, C.P.

2009-01-01

We measured uptake length of 15NO-3 in 72 streams in eight regions across the United States and Puerto Rico to develop quantitative predictive models on controls of NO-3 uptake length. As part of the Lotic Intersite Nitrogen eXperiment II project, we chose nine streams in each region corresponding to natural (reference), suburban-urban, and agricultural land uses. Study streams spanned a range of human land use to maximize variation in NO-3 concentration, geomorphology, and metabolism. We tested a causal model predicting controls on NO-3 uptake length using structural equation modeling. The model included concomitant measurements of ecosystem metabolism, hydraulic parameters, and nitrogen concentration. We compared this structural equation model to multiple regression models which included additional biotic, catchment, and riparian variables. The structural equation model explained 79% of the variation in log uptake length (S Wtot). Uptake length increased with specific discharge (Q/w) and increasing NO-3 concentrations, showing a loss in removal efficiency in streams with high NO-3 concentration. Uptake lengths shortened with increasing gross primary production, suggesting autotrophic assimilation dominated NO-3 removal. The fraction of catchment area as agriculture and suburban-urban land use weakly predicted NO-3 uptake in bivariate regression, and did improve prediction in a set of multiple regression models. Adding land use to the structural equation model showed that land use indirectly affected NO-3 uptake lengths via directly increasing both gross primary production and NO-3 concentration. Gross primary production shortened SWtot, while increasing NO-3 lengthened SWtot resulting in no net effect of land use on NO- 3 removal. ?? 2009.

Dissolved and Particulate Organic Carbon Transport, Loads and Relationships from Catchments in the Dryland Agricultural Region of the Inland Pacific Northwest

NASA Astrophysics Data System (ADS)

Boylan, R. D.; Brooks, E. S.

2012-12-01

It has long been understood that soil organic matter (SOM) plays important role in the chemistry of agricultural soils. Promoting both cation exchange capacity and water retention, SOM also has the ability to sequester atmospheric carbon adding to a soils organic carbon content. Increasing soil organic carbon in the dryland agricultural region of the Inland Pacific Northwest is not only good for soil health, but also has the potential to mitigate greenhouse gas emissions. Implementing strategies that minimizing the loss of soil carbon thus promoting carbon sequestration require a fundamental understanding of the dominant hydrologic flow paths and runoff generating processes in this landscape. Global fluxes of organic carbon from catchments range from 0.4-73,979 kg C km-2 year-1 for particulate organic carbon and 1.2-56,946 kg C km-2 year-1 for dissolved organic carbon (Alvarez-Cobelas, 2010). This small component of the global carbon cycle has been relatively well studied but there have yet to be any studies that focus on the dryland agricultural region of the Inland Pacific Northwest. In this study event based samples were taken at 5 sites across the Palouse Basin varying in land use and management type as well as catchment size, ranging from 1km2 to 7000 km2. Data collection includes streamflow, suspended sediment, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), particulate organic carbon (POC), dissolved organic nitrogen (TN), and nitrate concentrations as well as soil organic carbon (SOC) from distributed source areas. It is predicted that management type and streamflow will be the main drivers for DOC and POC concentrations. Relationships generated and historic data will then be used in conjunction with the Water Erosion Prediction Project (WEPP) to simulate field scale variability in the soil moisture, temperature, surface saturation, and soil erosion. Model assessment will be based on both surface runoff and sediment load measured at the outlet of these field catchments and distributed measurements capturing spatial variability within the catchments. We demonstrate how the accurate representation of the field scale variability in hydrology is an essential first step in the development of full scale cropping models capable of evaluating precision-based mitigation strategies.

Seasonal variability of stream water quality response to storm events captured using high-frequency and multi-parameter data

NASA Astrophysics Data System (ADS)

Fovet, O.; Humbert, G.; Dupas, R.; Gascuel-Odoux, C.; Gruau, G.; Jaffrezic, A.; Thelusma, G.; Faucheux, M.; Gilliet, N.; Hamon, Y.; Grimaldi, C.

2018-04-01

The response of stream chemistry to storm is of major interest for understanding the export of dissolved and particulate species from catchments. The related challenge is the identification of active hydrological flow paths during these events and of the sources of chemical elements for which these events are hot moments of exports. An original four-year data set that combines high frequency records of stream flow, turbidity, nitrate and dissolved organic carbon concentrations, and piezometric levels was used to characterize storm responses in a headwater agricultural catchment. The data set was used to test to which extend the shallow groundwater was impacting the variability of storm responses. A total of 177 events were described using a set of quantitative and functional descriptors related to precipitation, stream and groundwater pre-event status and event dynamics, and to the relative dynamics between water quality parameters and flow via hysteresis indices. This approach led to identify different types of response for each water quality parameter which occurrence can be quantified and related to the seasonal functioning of the catchment. This study demonstrates that high-frequency records of water quality are precious tools to study/unique in their ability to emphasize the variability of catchment storm responses.

Quantifying shallow and deep groundwater inputs to rivers with groundwater dating in hydrological observatories.

NASA Astrophysics Data System (ADS)

Aquilina, Luc; Marçais, Jean; Gauvain, Alexandre; Kolbe, Tamara; de Dreuzy, Jean-Raynald; Labasque, Thierry; Abbott, Benjamin W.; Vergnaud, Virginie; Chatton, Eliot; Thomas, Zahra; Ruiz, Laurent; Bour, Olivier; Pinay, Gilles

2017-04-01

River water derives in part from groundwater—water that has spent some time in the subsurface (e.g. soil, unsaturated zone, saturated zone). However, because groundwater residence times vary from months to millennia, determining the proportion of shallow and deep groundwater contribution can be challenging. Groundwater dating with anthropogenic gases and natural geochemical tracers can decipher the origin of groundwater contribution to rivers, particularly when repeat samplings are carried out in different hydrological conditions. Here, we present two different applications of this approach from three hydrological observatories (H+ hydrogeological network; Aghrys and Armorique observatories) in western France, all these observatories belonging to the OZCAR national network. We carried out a regional investigation of mean groundwater ages in hard rock aquifers in Brittany, using long-term chronicles from hydrological observatories and regional monitoring sites. We determined the mean residence-time (RT) and annual renewal rate (RR) of four compartments of these aquifers: the direct contribution of a very young water component (i.e. RT less than 1-2 yr), the upper variably saturated zone (RR 27-33%), the weathered layer (RR 1.8-2.1%) and the fractured zone (RR 0.1%). From these values and a nitrate chronicle, we were able to determine the respective contributions of each compartment to the largest river in Brittany, the Vilaine, which drains 30% of the region. We found that the deep fractured compartment with very slow renewal times contributed to 25-45% of river water in winter and 30-60% in summer. The very young water which includes direct precipitation and soil fluxes constituted 40-65% of the winter river water (Aquilina et al., 2012). To complement these estimates, we investigated the relationship between dissolved silica and groundwater age in the Armorique hydrological observatory in northern Brittany. We computed the silica concentration expected along the river from the groundwater age deduced from a deterministic model of the aquifer (Kolbe et al., 2016). The relationship between silica concentration determined with anthropogenic gases and observed silica concentration was strong (R2= 0.54-0.92), indicating that silica was a reliable geochemical chronometer, though it systematically underestimated anthropogenic gas age estimates. The difference could be accounted for by the very young water contribution : approximately 20 - 40% of overall discharge. Both approaches indicated that very young water is particularly important during winter and that deep groundwater contributes at least a third of the river discharge throughout the year. This last result has implications for river nitrate dynamics and understanding the potential limits of catchment management interventions which only reduce nitrate dynamics in shallow groundwater on decadal timescales. Aquilina L. et al., 2012 - Nitrate dynamics in agricultural catchments deduced from groundwater dating and long-term nitrate monitoring in surface- and groundwaters. Sci of the total Environment 435, 167-178. Kolbe et al., 2016 - Coupling 3D groundwater modeling with CFC-based age dating to classify local groundwater circulation in an unconfined crystalline aquifer. J. of Hydrology DOI: 10.1016/j.jhydrol.2016.05.020

Characterization of major-ion chemistry and nutrients in headwater streams along the Appalachian National Scenic Trail and within adjacent watersheds, Maine to Georgia

USGS Publications Warehouse

Argue, Denise M.; Pope, Jason P.; Dieffenbach, Fred

2012-01-01

An inventory of water-quality data on field parameters, major ions, and nutrients provided a summary of water quality in headwater (first- and second-order) streams within watersheds along the Appalachian National Scenic Trail (Appalachian Trail). Data from 1,817 sampling sites in 831 catchments were used for the water-quality summary. Catchment delineations from NHDPlus were used as the fundamental geographic units for this project. Criteria used to evaluate sampling sites for inclusion were based on selected physical attributes of the catchments adjacent to the Appalachian Trail, including stream elevation, percentage of developed land cover, and percentage of agricultural land cover. The headwater streams of the Appalachian Trail are generally dilute waters, with low pH, low acid neutralizing capacity (ANC), and low concentrations of nutrients. The median pH value was slightly acidic at 6.7; the median specific conductance value was 23.6 microsiemens per centimeter, and the median ANC value was 98.7 milliequivalents per liter (μeq/L). Median concentrations of cations (calcium, magnesium, sodium, and potassium) were each less than 1.5 milligrams per liter (mg/L), and median concentrations of anions (bicarbonate, chloride, fluoride, sulfate, and nitrate) were less than 10 mg/L. Differences in water-quality constituent levels along the Appalachian Trail may be related to elevation, atmospheric deposition, geology, and land cover. Spatial variations were summarized by ecological sections (ecosections) developed by the U.S. Forest Service. Specific conductance, pH, ANC, and concentrations of major ions (calcium, chloride, magnesium, sodium, and sulfate) were all negatively correlated with elevation. The highest elevation ecosections (White Mountains, Blue Ridge Mountains, and Allegheny Mountains) had the lowest pH, ANC, and concentrations of major ions. The lowest elevation ecosections (Lower New England and Hudson Valley) generally had the highest pH, ANC, and concentrations of major ions. The geology in discrete portions of these two ecosections was classified as containing carbonate minerals which has likely influenced the chemical character of the streamwater. Specific conductance, pH, ANC, and concentrations of major ions (calcium, chloride, magnesium, sodium, and sulfate) were all positively correlated with percentages of developed and agricultural land uses at the lower elevations of the central region of the Appalachian Trail (including the Green-Taconic-Berkshire Mountains, Lower New England, Hudson Valley, and Northern Ridge and Valley ecosections). The distinctly different chemical character of the streams in the central sections of the Appalachian Trail is likely related to the lower elevations, the presence of carbonate minerals in the geology, higher percentages of developed and agricultural land uses, and possibly the higher inputs of sulfate and nitrate from atmospheric deposition. Acid deposition of sulfate and nitrate are important influences on the acid-base chemistry of the surface waters of the Appalachian Trail. Atmospheric deposition estimates are consistently high (more than 18 kilograms per hectare (kg/ha) for sulfate, and more than 16 kg/ha for nitrate) at both the highest and lowest elevations. However, the lowest elevation (Green-Taconic-Berkshire Mountains, Lower New England, Hudson Valley, Northern Glaciated Allegheny Plateau, and Northern Ridge and Valley ecosections) included the largest spatial area of sustained high estimates of atmospheric deposition. Calcium-bicarbonate was the most frequently calculated water type in the Lower New England and Hudson Valley ecosections. In the northern and southern sections of the Appalachian Trail mix-cation water types were most prevalent and sulfate was the predominate anion. The predominance of the sulfate anion in the surface waters of the northern and southern ecosections likely reflects the influence of sulfate deposition. Although the central portion of the Appalachian Trail has the largest spatial area of high atmospheric acid deposition, the lower ionic strength waters in the northern and southern ecosections of the Appalachian Trail may have been more adversely affected by acid deposition. The low ionic strength of the streams in the White Mountains, Blue Ridge Mountains, and Allegheny Mountains ecosections makes parts of these regions susceptible to seasonal or event-driven episodic acidification, which can be detrimental to health of aquatic and terrestrial ecosystems. Median catchment ANC values were classified into three groups - acidic, sensitive, and insensitive. The White Mountains, Blue Ridge Mountains, and Allegheny Mountains ecosections included the highest frequency of catchments classified as acidic or sensitive. More than 56 percent of the catchments from the White Mountains ecosection were classified as sensitive to acidic inputs. In the Blue Ridge ecosection, 1.6 percent of the catchments were classified as acidic, and 38.2 percent of the catchments were classified as sensitive to acidic inputs. In the Allegheny Mountains ecosection, 17.6 percent of the catchments were classified as acidic, and 29.4 percent of the catchments were classified as sensitive to acidic inputs. Median concentrations of nitrogen species were less than 0.4 mg/L, and median concentrations of total phosphorus were less than 0.02 mg/L along the Appalachian Trail. A comparison of median catchment concentrations of nutrients to estimated national background concentrations demonstrated that concentrations along the Appalachian Trail are generally lower. A comparison of median concentrations of total nitrogen and total phosphorus to the U.S. Environmental Protection Agency's (USEPA) nutrient criteria for the Eastern U.S. ecoregions showed that the concentrations of total nitrogen in the northern section of the Appalachian Trail were generally higher than the USEPA criterion. Similarly, median concentrations of total phosphorus in the southern regions of the Appalachian Trail were approximately twice as high as USEPA criteria. Sections of the Appalachian Trail are adjacent to modest amounts of agricultural and developed land areas. These nonforested land areas may be contributing to the percentage of catchments in which concentrations of total nitrogen and total phosphorus are higher than USEPA nutrient ecoregion criteria.

Nitrate dynamics within a stream-lake network through time and space

NASA Astrophysics Data System (ADS)

Loken, L. C.; Crawford, J. T.; Childress, E. S.; Casson, N. J.; Stanley, E. H.

2014-12-01

Nitrate dynamics in streams are governed by biology, hydrology, and geomorphology, and the ability to parse these drivers apart has improved with the development of accurate high-frequency sensors. By combining a stationary Eulerian and a quasi-Lagrangian sensor platform, we investigated the timing of nitrate flushing and identified locations of elevated biogeochemical cycling along a stream-lake network in Northern Wisconsin, USA. Two years of continuous oxygen, carbon dioxide, and discharge measurements were used to compute gross primary production (GPP) and ecosystem respiration (ER) downstream of a wetland reach of Allequash Creek. Metabolic rates and flow patterns were compared with nitrate concentrations measured every 30 minutes using an optical sensor. Additionally, we floated a sensor array from the headwater spring ponds through a heterogeneous stream reach consisting of wetlands, beaver ponds, forested segments, and two lakes. Two distinct temporal patterns of stream nitrate concentrations were observed. During high flow events such as spring snowmelt and summer rain events, nitrate concentrations increased from ~5 μM (baseflow) to 12 μM, suggesting flushing from catchment sources. During baseflow conditions, nitrate followed a diel cycle with a 0.3-1.0 μM daytime draw down. Daily nitrate reduction was positively correlated with GPP calculated from oxygen and carbon dioxide records. Lastly, spatial analyses revealed lowest nitrate concentrations in the wetland reach, approximately 2-3 μM lower than the upstream spring ponds, and downstream lakes and forested reaches. This snapshot implies greater nitrate removal potential in the wetland reach likely driven by denitrification in organic rich sediments and macrophyte uptake in the open canopy stream segment. Taken together the temporal and spatial results show the dynamics of hydrology, geomorphology, and biology to influence nitrate delivery and variability in ecosystem processing through a stream-lake system. Future ecosystem studies could benefit by including multiple reference frameworks to better assess processes not captured by a single station approach.

Relationship between land-use and sources and fate of nitrate in groundwater in a typical recharge area of the North China Plain.

PubMed

Wang, Shiqin; Zheng, Wenbo; Currell, Matthew; Yang, Yonghui; Zhao, Huan; Lv, Mengyu

2017-12-31

Identification of different nitrate sources in groundwater is challenging in areas with diverse land use and multiple potential inputs. An area with mixed land-uses, typical of the piedmont-plain recharge area of the North China Plain, was selected to investigate different nitrate sources and the impact of land use on nitrate distribution in groundwater. Multiple environmental tracers were examined, including major ions, stable isotopes of water (δ 2 H-H 2 O, δ 18 O-H 2 O) and nitrate (δ 15 N-NO 3 - and δ 18 O-NO 3 - ). Groundwater was sampled from four land-use types; natural vegetation (NV), farmland (FL), economic forestland (EF) and residential areas (RA). A mixing model using δ 18 O and Cl - concentrations showed that groundwater recharge predominantly comprises precipitation and lateral groundwater flow from areas of natural vegetation in the upper catchment, while irrigation return water and wastewater from septic tanks were major inputs in farmland and residential areas, respectively. Land use variation is the major contributing factor to different nitrate concentrations. In total, 80%, 49% and 86% of samples from RA, FL and EF, respectively exceeded the WHO standard (50mg/L NO 3 - ), compared to 6.9% of samples from NV. Isotopes of δ 15 N-NO 3 - and δ 18 O-NO 3 - verified that nitrate in groundwater of the NV (with δ 15 N ranging from 1.7‰ to 4.7‰) was sourced from soil and precipitation. Examination of δ 15 N-NO 3 - vs δ 18 O-NO 3 - values along with multivariate statistical analysis (principle component and cluster analysis) helped identify sources with overlapping isotopic values in other land-use areas (where δ 15 N values range from 2.5‰ to 10.2‰). Manure and septic waste were dominant sources for most groundwater with high NO 3 - and Cl - concentrations in both farmland and residential areas. The lack of de-nitrification and fact that the area is a recharge zone for the North China Plain highlight the importance of controlling nitrate sources through careful application of manure and fertilizers, and control of septic leakage. Copyright © 2017 Elsevier B.V. All rights reserved.

DOC quantity and quality in northeastern USA catchments

NASA Astrophysics Data System (ADS)

Shanley, J. B.; Sebestyen, S. D.; Aiken, G.; Pellerin, B. A.

2011-12-01

At the Sleepers River Research Watershed in Vermont we have studied interactions of dissolved organic carbon (DOC) cycling and hydrological processes for nearly 20 years to determine how and when DOC is transported through the landscape. Stream DOC concentration in this cool temperate forested catchment varies from ~1 to ~15 mg L-1 and is transport-limited; concentrations increase with increasing flow, even under the wettest conditions, suggesting shifting but non-depletable sources. Specific UV absorbance (SUVA) also increases consistently with flow. Source strength does vary seasonally, however, evidenced by higher DOC for a given flow during autumn leaf fall relative to spring snowmelt. Recent high-frequency optical sensor measurements have revealed fine-scale structure in the temporal DOC pattern not possible from discrete sampling. We observe a consistent counterclockwise hysteresis and diurnal cycles with seasonally variable amplitude. In this presentation we infer DOC sources and processes through analysis of antecedent moisture conditions and concurrent variations in nitrate, dissolved organic nitrogen, and SUVA. With sensors and sampling in place at several other research catchments, we are investigating the similarity of patterns across the northeastern USA.

Water and salt balance modelling to predict the effects of land-use changes in forested catchments. 3. The large catchment model

NASA Astrophysics Data System (ADS)

Sivapalan, Murugesu; Viney, Neil R.; Jeevaraj, Charles G.

1996-03-01

This paper presents an application of a long-term, large catchment-scale, water balance model developed to predict the effects of forest clearing in the south-west of Western Australia. The conceptual model simulates the basic daily water balance fluxes in forested catchments before and after clearing. The large catchment is divided into a number of sub-catchments (1-5 km2 in area), which are taken as the fundamental building blocks of the large catchment model. The responses of the individual subcatchments to rainfall and pan evaporation are conceptualized in terms of three inter-dependent subsurface stores A, B and F, which are considered to represent the moisture states of the subcatchments. Details of the subcatchment-scale water balance model have been presented earlier in Part 1 of this series of papers. The response of any subcatchment is a function of its local moisture state, as measured by the local values of the stores. The variations of the initial values of the stores among the subcatchments are described in the large catchment model through simple, linear equations involving a number of similarity indices representing topography, mean annual rainfall and level of forest clearing.The model is applied to the Conjurunup catchment, a medium-sized (39·6 km2) catchment in the south-west of Western Australia. The catchment has been heterogeneously (in space and time) cleared for bauxite mining and subsequently rehabilitated. For this application, the catchment is divided into 11 subcatchments. The model parameters are estimated by calibration, by comparing observed and predicted runoff values, over a 18 year period, for the large catchment and two of the subcatchments. Excellent fits are obtained.

Using high resolution water quality monitoring across three English catchments to capture a storm event during a transition from dry to wet conditions

NASA Astrophysics Data System (ADS)

Outram, F.; Lloyd, C.; Jonczyk, J.; Benskin, C.; Grant, F.

2013-12-01

The Demonstration Test Catchment (DTC) project is a UK government funded initiative to test the effectiveness of on-farm mitigation measures designed to reduce agricultural pollution without compromising farm productivity. Three distinct catchments in England have been chosen to test mitigation measures on working farms in small tributary catchments equipped with continuous water quality monitoring stations. The River Avon in the south is a chalk and sandstone catchment with livestock and arable farming, the River Wensum in the east is a lowland chalk catchment with predominantly arable farming and the River Eden in the North has a limestone and sandstone geology with predominantly livestock farming. One of the many strengths of the DTC as a national programme is that it provides the ability to investigate catchment hydrology and biogeochemical response across three different English landscapes. This is a collaborative paper involving members of all three DTC consortia, which aims to compare the responses of each of the catchments to a single storm event from April 2012, which was as a result of one of the first weather fronts to track across the country following a drought period affecting much of the UK, producing heavy rainfall in all three catchments. This was an unusual meteorological period, with subsequent hydrological implications when a rapid shift from drought to flood risk occurred across parts of the country. The effects of the weather front on discharge and water chemistry parameters, including N (NO3- and NH4), P (Total P (TP) and Total Reactive P (TRP)), dissolved oxygen (DO), chlorophyll and turbidity, measured at a half-hourly time step, are examined. When considered in the context of one hydrological year, flow and concentration duration curves reveal that the weather fronts resulted in extreme flow, nitrate and TP concentrations in all three catchments but with distinct differences in hydrograph and nutrient response. Hysteresis loops constructed from high resolution data are used to highlight an array of pollutant sources and delivery pathways. Phosphorus delivery to the stream was source-limited in the River Wensum but transport-limited in the Avon and Eden rivers. Load calculations show that nitrogen losses were an order of magnitude higher per hectare in the Wensum catchment than in the Avon catchment. These data demonstrate the consequences during such times of transition and the importance of understanding the relationship between water quality and meteorological conditions, with each catchment highlighting pressures from different pollutants.

The impact of surface water - groundwater interactions on nitrate cycling assessed by means of hydrogeologic and isotopic techniques in the Alento river basin (Italy)

NASA Astrophysics Data System (ADS)

Stellato, Luisa; Di Rienzo, Brunella; Di Fusco, Egidio; Rubino, Mauro; Marzaioli, Fabio; Terrasi, Filippo; D'Onofrio, Antonio; De Vita, Pantaleone; Allocca, Vincenzo; Salluzzo, Antonio; Rimauro, Juri; Romano, Nunzio; Celico, Fulvio

2017-04-01

Currently a major concern of water resources managers is to understand the fate and dynamics of nutrients in riverine ecosystems because of their potential impacts on both river quality and human health (e.g., European Council Directive 91/676/EEC). Nutrients are released within a catchment (or river basin) mainly by agricultural practices and urban/industrial activities, in addition to natural sources such as soils and organic matter. They are discharged into surface water bodies by means of nutrient-rich groundwater inflows and/or overland flow pathways, which can be important controls on hot moment/hot spot type biogeochemical behaviors. Groundwater has been recognized to have a major role in controlling stream ecosystem health since it influences stream ecology when surface and subsurface water are hydraulically connected. In particular, processes occurring at the reach or sub-reach scale more directly influence nutrient transport to rivers than larger scale processes. In this general context, the main scope of this study, within the framework of the IAEA Coordinated Research Project (CRP) "Environmental Isotopes and Age Dating Methods to Assess Nitrogen Pollution and Other Quality Issues in Rivers", was to spatially and temporally quantify groundwater inflows to the Alento river (Southern Italy) to characterize sw-gw interactions in the catchment in order to finally assess nitrates contamination of a groundwater dependent river ecosystem. Four sampling campaigns have been carried out in July and October 2014, in April 2015 and in June 2016 during which 1 spring, rain water, 17 surface water and 27 groundwater points were sampled all over the plain. The piezometric reconstruction has been realized by means of the monitoring of groundwater levels in 43 domestic and agricultural wells (10-15 m deep). The preliminary hydrogeological (water table morphology and stream discharge measurements), physico-chemical (T and EC), hydrochemical and isotopic (222Rn, δD and δ18O) data evidence a gaining river in the northern part of the plain. Moreover, δD and δ18O data evidence a fast recharge from seasonal precipitations originating from evaporated and re-evaporated air masses. Finally, even though chemical data evidence no groundwater nitrate pollution (< 50 mg L-1) in the study area, δ15N and δ18O of dissolved nitrates have been used to infer possible nitrate sources in the study area.

Validation of catchment models for predicting land-use and climate change impacts. 2. Case study for a Mediterranean catchment

NASA Astrophysics Data System (ADS)

Parkin, G.; O'Donnell, G.; Ewen, J.; Bathurst, J. C.; O'Connell, P. E.; Lavabre, J.

1996-02-01

Validation methods commonly used to test catchment models are not capable of demonstrating a model's fitness for making predictions for catchments where the catchment response is not known (including hypothetical catchments, and future conditions of existing catchments which are subject to land-use or climate change). This paper describes the first use of a new method of validation (Ewen and Parkin, 1996. J. Hydrol., 175: 583-594) designed to address these types of application; the method involves making 'blind' predictions of selected hydrological responses which are considered important for a particular application. SHETRAN (a physically based, distributed catchment modelling system) is tested on a small Mediterranean catchment. The test involves quantification of the uncertainty in four predicted features of the catchment response (continuous hydrograph, peak discharge rates, monthly runoff, and total runoff), and comparison of observations with the predicted ranges for these features. The results of this test are considered encouraging.

Effects of model structure and catchment discretization on discharge simulation in a small forest catchment

NASA Astrophysics Data System (ADS)

Spieler, Diana; Schwarze, Robert; Schütze, Niels

2017-04-01

In the past a variety of different modeling approaches has been developed in catchment hydrology. Even though there is no argument on the relevant processes taking place, there is no unified theory on how best to represent them computationally. Thus a vast number of models has been developed, varying from lumped models to physically based models. Most of them have a more or less fixed model structure and follow the "one fits all" paradigm. However, a more flexible approach could improve model realism by designing catchment specific model structures based on data availability. This study focuses on applying the flexible hydrological modelling framework RAVEN (Craig et al., 2013), to systematically test several conceptual model structures on the 19 km2 Große Ohe Catchment in the Bavarian Forest (Germany). By combining RAVEN with the DREAM algorithm (Vrugt et al., 2009), the relationship between catchment characteristics, model structure, parameter uncertainty and data availability are analyzed. The model structure is progressively developed based on the available data of the well observed forested catchment area. In a second step, the impact of the catchment discretization is analyzed by testing different spatial resolutions of topographic input data.

Effects of temporal and spatial resolution of calibration data on integrated hydrologic water quality model identification

NASA Astrophysics Data System (ADS)

Jiang, Sanyuan; Jomaa, Seifeddine; Büttner, Olaf; Rode, Michael

2014-05-01

Hydrological water quality modeling is increasingly used for investigating runoff and nutrient transport processes as well as watershed management but it is mostly unclear how data availablity determins model identification. In this study, the HYPE (HYdrological Predictions for the Environment) model, which is a process-based, semi-distributed hydrological water quality model, was applied in two different mesoscale catchments (Selke (463 km2) and Weida (99 km2)) located in central Germany to simulate discharge and inorganic nitrogen (IN) transport. PEST and DREAM(ZS) were combined with the HYPE model to conduct parameter calibration and uncertainty analysis. Split-sample test was used for model calibration (1994-1999) and validation (1999-2004). IN concentration and daily IN load were found to be highly correlated with discharge, indicating that IN leaching is mainly controlled by runoff. Both dynamics and balances of water and IN load were well captured with NSE greater than 0.83 during validation period. Multi-objective calibration (calibrating hydrological and water quality parameters simultaneously) was found to outperform step-wise calibration in terms of model robustness. Multi-site calibration was able to improve model performance at internal sites, decrease parameter posterior uncertainty and prediction uncertainty. Nitrogen-process parameters calibrated using continuous daily averages of nitrate-N concentration observations produced better and more robust simulations of IN concentration and load, lower posterior parameter uncertainty and IN concentration prediction uncertainty compared to the calibration against uncontinuous biweekly nitrate-N concentration measurements. Both PEST and DREAM(ZS) are efficient in parameter calibration. However, DREAM(ZS) is more sound in terms of parameter identification and uncertainty analysis than PEST because of its capability to evolve parameter posterior distributions and estimate prediction uncertainty based on global search and Bayesian inference schemes.

Attributes for NHDPlus Catchments (Version 1.1) for the Conterminous United States: Normalized Atmospheric Deposition for 2002, Nitrate (NO3)

USGS Publications Warehouse

Wieczorek, Michael; LaMotte, Andrew E.

2010-01-01

This data set represents the average normalized atmospheric (wet) deposition, in kilograms, of Nitrate (NO3) for the year 2002 compiled for every catchment of NHDPlus for the conterminous United States. Estimates of NO3 deposition are based on National Atmospheric Deposition Program (NADP) measurements (B. Larsen, U.S. Geological Survey, written commun., 2007). De-trending methods applied to the year 2002 are described in Alexander and others, 2001. NADP site selection met the following criteria: stations must have records from 1995 to 2002 and have a minimum of 30 observations. The NHDPlus Version 1.1 is an integrated suite of application-ready geospatial datasets that incorporates many of the best features of the National Hydrography Dataset (NHD) and the National Elevation Dataset (NED). The NHDPlus includes a stream network (based on the 1:100,00-scale NHD), improved networking, naming, and value-added attributes (VAAs). NHDPlus also includes elevation-derived catchments (drainage areas) produced using a drainage enforcement technique first widely used in New England, and thus referred to as "the New England Method." This technique involves "burning in" the 1:100,000-scale NHD and when available building "walls" using the National Watershed Boundary Dataset (WBD). The resulting modified digital elevation model (HydroDEM) is used to produce hydrologic derivatives that agree with the NHD and WBD. Over the past two years, an interdisciplinary team from the U.S. Geological Survey (USGS), and the U.S. Environmental Protection Agency (USEPA), and contractors, found that this method produces the best quality NHD catchments using an automated process (USEPA, 2007). The NHDPlus dataset is organized by 18 Production Units that cover the conterminous United States. The NHDPlus version 1.1 data are grouped by the U.S. Geologic Survey's Major River Basins (MRBs, Crawford and others, 2006). MRB1, covering the New England and Mid-Atlantic River basins, contains NHDPlus Production Units 1 and 2. MRB2, covering the South Atlantic-Gulf and Tennessee River basins, contains NHDPlus Production Units 3 and 6. MRB3, covering the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy River basins, contains NHDPlus Production Units 4, 5, 7 and 9. MRB4, covering the Missouri River basins, contains NHDPlus Production Units 10-lower and 10-upper. MRB5, covering the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf River basins, contains NHDPlus Production Units 8, 11 and 12. MRB6, covering the Rio Grande, Colorado and Great Basin River basins, contains NHDPlus Production Units 13, 14, 15 and 16. MRB7, covering the Pacific Northwest River basins, contains NHDPlus Production Unit 17. MRB8, covering California River basins, contains NHDPlus Production Unit 18.

A simple model of variable residence time flow and nutrient transport in the chalk

NASA Astrophysics Data System (ADS)

Jackson, Bethanna M.; Wheater, Howard S.; Mathias, Simon A.; McIntyre, Neil; Butler, Adrian P.

2006-10-01

SummaryA basic problem of modelling flow and transport in Chalk catchments arises from the existence of a deep unsaturated zone, with complex interactions between flow in fractures and water held in the fine pores of the rock matrix. The response of the water table to major infiltration episodes is rapid (of the order of days). However, chemical signals are strongly damped, suggesting that this water is of varying age, with a corresponding mixed history of nutrient loading. Clearly this effect should be represented in any model of nutrients in Chalk systems. The applicability of simplified physically-based model formulations to represent the dual response in an integrated way has been investigated by a variety of researchers, but it has been shown that these approximations break down in application to the Chalk. Mathias et al. [Mathias, S., Butler, A.P., Jackson, B.M., Wheater, H.S., this issue. Characterising flow in the Chalk unsaturated zone. In: Wheater, H.S., Peach, D., Neal, C, editors, Hydrology on LOCAR in the Pang/Lambourn, special issue of J. Hydrol, doi:10.1016/j.jhydrol.2006.04.010] present a dual permeability model that explains the observed response, but such complex formulations are not readily incorporated in catchment-scale nutrient models. This paper reviews previous approaches to modelling the Chalk and then presents a pragmatic approach, with transport of solute and water through the unsaturated zone treated separately, and combined at the water table. Varying residence times are included through considering the distance between the water table and the soil surface, and the history of nutrient application at the surface. If an average rate of downwards migration of the nutrients is assumed, it is possible to derive a travel time distribution of nitrate transport to the water table using a DTM (digital terrain model) map of elevation and information on groundwater levels. This distribution can then be implemented through difference equations. The rationale behind the model and the resulting algorithm is described, and the algorithm then applied to a hypothetical case study of nutrient loading located in the Lambourn, a groundwater-dominated Chalk catchment in Southern England. Simulated groundwater concentrations are very similar in magnitude and variability to observed Chalk groundwater series, suggesting that this simple conceptual model may well be able to capture the dominant responses of nutrient transport through the Chalk.

Scaling Dissolved Nutrient Removal in River Networks: A Comparative Modeling Investigation

NASA Astrophysics Data System (ADS)

Ye, Sheng; Reisinger, Alexander J.; Tank, Jennifer L.; Baker, Michelle A.; Hall, Robert O.; Rosi, Emma J.; Sivapalan, Murugesu

2017-11-01

Along the river network, water, sediment, and nutrients are transported, cycled, and altered by coupled hydrological and biogeochemical processes. Our current understanding of the rates and processes controlling the cycling and removal of dissolved inorganic nutrients in river networks is limited due to a lack of empirical measurements in large, (nonwadeable), rivers. The goal of this paper was to develop a coupled hydrological and biogeochemical process model to simulate nutrient uptake at the network scale during summer base flow conditions. The model was parameterized with literature values from headwater streams, and empirical measurements made in 15 rivers with varying hydrological, biological, and topographic characteristics, to simulate nutrient uptake at the network scale. We applied the coupled model to 15 catchments describing patterns in uptake for three different solutes to determine the role of rivers in network-scale nutrient cycling. Model simulation results, constrained by empirical data, suggested that rivers contributed proportionally more to nutrient removal than headwater streams given the fraction of their length represented in a network. In addition, variability of nutrient removal patterns among catchments was varied among solutes, and as expected, was influenced by nutrient concentration and discharge. Net ammonium uptake was not significantly correlated with any environmental descriptor. In contrast, net daily nitrate removal was linked to suspended chlorophyll a (an indicator of primary producers) and land use characteristics. Finally, suspended sediment characteristics and agricultural land use were correlated with net daily removal of soluble reactive phosphorus, likely reflecting abiotic sorption dynamics. Rivers are understudied relative to streams, and our model suggests that rivers can contribute more to network-scale nutrient removal than would be expected based upon their representative fraction of network channel length.

Assessing the response of Emerald Lake, an alpine watershed in Sequoia National Park, California, to acidification during snowmelt by using a simple hydrochemical model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hooper, R.P.; West, C.T.; Peters, N.E.

1990-01-01

A sparsely parameterized hydrochemical model has been developed by using data from Emerald Lake watershed, which is a 120-ha alpine catchment in Sequoia National Park, California. Greater than 90% of the precipitation to this watershed is snow; hence, snowmelt is the dominant hydrologic event. A model which uses a single alkalinity-generating mechanism, primary mineral weathering, was able to capture the pattern of solute concentrations in surface waters during snowmelt. An empirical representation of the weathering reaction, which is based on rock weathering stoichiometry and which uses discharge as a measure of residence time, was included in the model. Results ofmore » the model indicate that current deposition levels would have to be increased between three-fold and eight-fold to exhaust the alkalinity of the lake during snowmelt if their is a mild acidic pulse in the stream at the beginning of snowmelt as was observed during the study period. The acidic pulse in the inflow stream at the onset of snowmelt was less pronounced than acidic pulses observed in the meltwater draining the snowpack at a point using snow lysimeters or in the laboratory. Sulfate concentrations in the stream water were the most constant; chloride and nitrate concentrations increased slightly at the beginning of snowmelt. Additional field work is required to resolve whether an acidic meltwater pulse occurs over a large area as well as at a point or whether, due to physical and chemical processes within the snowpack, the acidic meltwater pulse is attenuated at the catchment scale. The modest data requirements of the model permit its applications to other alpine watersheds that are much less intensively studied than Emerald Lake watershed.« less

Representing macropore flow at the catchment scale: a comparative modeling study

NASA Astrophysics Data System (ADS)

Liu, D.; Li, H. Y.; Tian, F.; Leung, L. R.

2017-12-01

Macropore flow is an important hydrological process that generally enhances the soil infiltration capacity and velocity of subsurface water. Up till now, macropore flow is mostly simulated with high-resolution models. One possible drawback of this modeling approach is the difficulty to effectively represent the overall typology and connectivity of the macropore networks. We hypothesize that modeling macropore flow directly at the catchment scale may be complementary to the existing modeling strategy and offer some new insights. Tsinghua Representative Elementary Watershed model (THREW model) is a semi-distributed hydrology model, where the fundamental building blocks are representative elementary watersheds (REW) linked by the river channel network. In THREW, all the hydrological processes are described with constitutive relationships established directly at the REW level, i.e., catchment scale. In this study, the constitutive relationship of macropore flow drainage is established as part of THREW. The enhanced THREW model is then applied at two catchments with deep soils but distinct climates, the humid Asu catchment in the Amazon River basin, and the arid Wei catchment in the Yellow River basin. The Asu catchment has an area of 12.43km2 with mean annual precipitation of 2442mm. The larger Wei catchment has an area of 24800km2 but with mean annual precipitation of only 512mm. The rainfall-runoff processes are simulated at a hourly time step from 2002 to 2005 in the Asu catchment and from 2001 to 2012 in the Wei catchment. The role of macropore flow on the catchment hydrology will be analyzed comparatively over the Asu and Wei catchments against the observed streamflow, evapotranspiration and other auxiliary data.

Assessment of surface water resources availability using catchment modelling and the results of tracer studies in the mesoscale Migina Catchment, Rwanda

NASA Astrophysics Data System (ADS)

Munyaneza, O.; Mukubwa, A.; Maskey, S.; Uhlenbrook, S.; Wenninger, J.

2014-12-01

In the present study, we developed a catchment hydrological model which can be used to inform water resources planning and decision making for better management of the Migina Catchment (257.4 km2). The semi-distributed hydrological model HEC-HMS (Hydrologic Engineering Center - the Hydrologic Modelling System) (version 3.5) was used with its soil moisture accounting, unit hydrograph, liner reservoir (for baseflow) and Muskingum-Cunge (river routing) methods. We used rainfall data from 12 stations and streamflow data from 5 stations, which were collected as part of this study over a period of 2 years (May 2009 and June 2011). The catchment was divided into five sub-catchments. The model parameters were calibrated separately for each sub-catchment using the observed streamflow data. Calibration results obtained were found acceptable at four stations with a Nash-Sutcliffe model efficiency index (NS) of 0.65 on daily runoff at the catchment outlet. Due to the lack of sufficient and reliable data for longer periods, a model validation was not undertaken. However, we used results from tracer-based hydrograph separation from a previous study to compare our model results in terms of the runoff components. The model performed reasonably well in simulating the total flow volume, peak flow and timing as well as the portion of direct runoff and baseflow. We observed considerable disparities in the parameters (e.g. groundwater storage) and runoff components across the five sub-catchments, which provided insights into the different hydrological processes on a sub-catchment scale. We conclude that such disparities justify the need to consider catchment subdivisions if such parameters and components of the water cycle are to form the base for decision making in water resources planning in the catchment.

Integrated modelling of nitrogen transport and turnover in lowland catchements of northern Germany

NASA Astrophysics Data System (ADS)

Wriedt, G.

2003-04-01

Nitrogen loads in surface water often do not reflect the actual input situation. This retention of nitrogen can be explained by chemical transformations in the soil and groundwater (e.g. denitrification) and hydrological factors (e.g. transition time, mixing) in soil and groundwater and depends strongly on the geological and chemical patterns within the catchment areas (e.g. reactive substances, conductivities). In order to facilitate modelling studies on the relation between nitrogen transport and catchment characteristics we developed a modelling approach, that allows simulation of the complete nitrogen transport path from the soil input until the exfiltration into the surface water system. This approach is based on the loose coupling of a soil water model and an analytical soil nitrogen model (mRISK-N) with a groundwater flow model (MODFLOW) and a multi-species reactive transport model (RT3D). Groundwater nitrogen turnover is represented by a closed reaction scheme that explicitly includes oxidation of organic matter and pyrite oxidation by several electron acceptors as the main reactive pathways, in order to link nitrogen turnover directly to the availability of the substances involved in the chemical reactions. This reaction module has been implemented into the modelling system as a user defined reaction module within the RT3D-environment. The soil submodel was tested against lysimeter data. It was found, that soil water balance was represented quite well. Nitrogen leaching rates however, can only be interpreted for larger time scales, whereas considerable deviations from measured values do occur in single years. Nevertheless, model performance is comparable to other, more complex soil water and nitrogen models currently available. It was found, that the high uncertainty of model parameters and input data as well as limited knowledge on processes limit the accuracy of soil nitrogen models in general. The next step of the project is the model application in the study area “Schaugraben catchment”. The study area is located near Osterburg/Altmark in the north of Sachsen-Anhalt, its size is about 25 km2. The geology is determined by pleistocene deposits, mainly glacial till in the plateau areas and glaciofluvial sandy deposits in the valleys. A dense drainage network, a high groundwater table and intensive agricultural use provide a high risk for both, groundwater and surface water quality. Model application focuses on the analysis of the interactions between catchment characteristics (hydrological and geological), spatial input patterns and the fate of nitrogen within the catchment. This is done by applying sensitivity analysis, uncertainty analysis and scenario simulation. A three dimensional groundwater flow model for the Schaugraben area has been set up and calibrated in order to analyse the regional flow paths, transition times and groundwater catchments. More detailed modelling studies including the reactive groundwater transport are performed on selected cutouts and transects, defining specific hydrogeological settings, e.g. riparian areas, buffer stripes, hydrological windows etc. Under special consideration is also the influence of spatial input patterns of nitrate and organic matter leaching to the groundwater. Results of the modelling studies are expect until March ‘03. The modelling approach developed here is a tool for the assessment of transport-turnover interaction and may help to improve experimental studies and measurement strategies and to provide useful information for managing purposes.

In-Situ Denitrification and N2O Emission from Natural and Semi-natural Land Use Types in two UK Catchments

NASA Astrophysics Data System (ADS)

Sgouridis, F.; Ullah, S.

2014-12-01

Whilst data and understanding of the controls of denitrification process and the subsequent emission of N2O at microbial and plot scale exist, quantification of in situ annual denitrification rates at catchment scales is scarce due to methodological constraints in measuring in situ denitrification in large temporal and spatial scales. In situ denitrification (DNT) was measured monthly (April 2013 - October 2014) in organic (peat bog, heathland, acid grassland), forest (mixed and deciduous), and grassland (improved and semi-improved) land use types in the Ribble-Wyre and Conwy River catchments in the UK. A static chamber technique according to the 15N-Gas Flux method1 was employed for quantifying the fluxes of 15N-N2 and 15N-N2O gases after labelling the soil with 98 at% K15NO3- at tracer level amounts (10% of the ambient nitrate concentration) and sampling the chamber headspace at 0, 1, 2 and 20 hour intervals. The DNT rates ranged between 0 and 2.3 mg N m-2 h-1 and were significantly influenced by land use type (p<0.05). The annual denitrification rate of organic and forest soils (4 kg N ha-1 y-1) was 3 and 6 times less than that of semi-improved (12 kg N ha-1 y-1) and improved (23 kg N ha-1 y-1) grassland soils, respectively. The N2O emission, due to denitrification, followed a similar trend with lower fluxes from organic and higher from improved grassland soils (range: 0 - 0.04 mg N m-2 h-1), whilst the N2O:N2 ratio ranged between 0.2 and 4%. The relative contribution of denitrification to net N2O flux varied temporally and across the different land use types and ranged from 0.2 to 75%. The 15N-Gas Flux method can be successfully applied in a variety of land use types for relatively high temporal and spatial resolution measurement of in situ denitrification and the simultaneous quantification of N2 and N2O fluxes due to denitrification. Therefore the ratio of N2O:N2 and also the source apportionment for N2O can be estimated more accurately. The results suggested a difference in DNT rates between unmanaged/ low nitrate content versus managed/ high nitrate content land use types, which was further supported by the significant positive correlation between DNT and soil nitrate content. 1R. Stevens and R. Laughlin, Nutr. Cycling Agroecosyst., 1998, 52, 131-139.

Fate of Upstream Anthropogenic Nitrogen Inputs in a Tropical Catchment, Athi-Galana-Sabaki River, Kenya.

NASA Astrophysics Data System (ADS)

Marwick, Trent R.

2013-04-01

As part of a broader study on the riverine biogeochemistry in the Athi-Galana-Sabaki (A-G-S) River basin (Kenya), we present data collected during three climatic seasons to constrain the sources, transformations and transit of multiple N species as they flow through the A-G-S basin (~47,000 km2), stretching from downstream of heavily polluted Nairobi and surrounds to the outlet at the Indian Ocean. Total dissolved inorganic nitrogen (DIN) concentrations entering the study area were highest during the dry season (1195 µmol/L), almost completely in the form of ammonium (99.8%), whilst total DIN was an order of magnitude lower during the short and long rain seasons (212 and 193 µmol/L, respectively). Nitrate was the dominant form of DIN entering the study area during the short and long rain seasons (97.9% and 85.6% of total DIN respectively), with the increased flow conditions resulting in minimal instream N-cycling prior to discharge to the ocean. Conversely, longer water residence time and intense cycling and removal of N in the upper- to mid-catchment during the dry season creates two polarities comparative to wet season conditions, where (1) significantly less DIN is exported to the ocean during the dry season, and (2) dry season particulate N export is significantly enriched in δ15N, strongly reflecting the dominance of organic wastes as the source of riverine nitrogen. The rapid removal of ammonium in the upper study area during the dry season was followed by a quantitatively similar production of nitrate and nitrous oxide downstream, pointing towards strong nitrification over this reach during the dry season. The nitrous oxide was rapidly degassed downstream, while the elevated nitrate concentrations steadily decreased to levels observed elsewhere in African river networks. Low pelagic primary production rates over the same reach suggest benthic denitrification was the dominant process controlling the removal of these nitrates, although large cyanobacterial blooms downstream highlight the significant role of primary producers assimilating DIN lower in the drainage network. The intense upstream N-cycling leads to a significantly enriched δ15NPN during the dry season (mean: 16.5 ± 8.2‰) comparative to the short (7.3 ± 2.6‰) and long (7.6 ± 5.9‰) rain seasons. The strong correlation found between seasonal δ15NPN and δ18OH2O (δ18OH2O as a proxy of discharge; p = 0.0258, n = 26) presents the possibility of employing a combination of proxies such as δ15NPN of sediments, corals and bivalves, to build the foundation of how historical land-use changes have influenced nitrogen cycling within the catchment whilst potentially providing foresight for future land management decisions.

Gained insights from combined high-frequency and long-term water quality monitoring in agricultural catchments

NASA Astrophysics Data System (ADS)

Jomaa, Seifeddine; Dupas, Rémi; Musolff, Andreas; Rozemeijer, Joachim; Borchardt, Dietrich; Rode, Michael

2017-04-01

Despite extensive efforts to reduce nitrate (NO3) transfer in agricultural areas, the NO3 concentration in rivers often changes little. To investigate the reasons for this limited response, NO3 dynamics in a 100 km2 agricultural catchment in eastern Germany was analysed from decadal to infra-hourly time scales. First, Dynamic Harmonic Regression (DHR) analysis of a 32-year (1982-2014) record of NO3 and discharge revealed that i) the long-term trend in NO3 concentration was closely related to that in discharge, suggesting that large-scale weather and climate patterns were masking the effect of improved nitrogen management on NO3 trends; ii) maximum winter and minimum summer concentrations had a persistent seasonal pattern, which was interpreted as a dynamic NO3 concentration from the soil and subsoil columns; and iii) the catchment progressively changed from chemodynamic to more chemostatic behaviour over the three decades of study, which is a sign of long-term homogenisation of NO3 concentrations in the profile. Second, infra-hourly (15 min time interval) analysis of storm-event dynamics during a typical hydrological year (2005-2006) was performed to identify periods of the year with high leaching risk and to link the latter to agricultural management practices in the catchment. Also, intra-hourly data was used to improve NO3 load estimation during storm events. An Event Response Reconstruction (ERR) model was built using NO3 concentration response descriptor variables and predictor variables deduced from discharge and precipitation records. The ERR approach significantly improved NO3 load estimates compared to linear interpolation of grab-sampling data (error was reduced from 10 to 1%). Finally, this study shows that detailed physical understanding of NO3 dynamics across time scales can be obtained only through combined analysis of long-term records and high-resolution sensor data. Hence, a joint effort is advocated between environmental authorities, who usually perform long-term monitoring, and scientific programmes, which usually perform high-resolution monitoring.

Identifying Hydrogeological Controls of Catchment Low-Flow Dynamics Using Physically Based Modelling

NASA Astrophysics Data System (ADS)

Cochand, F.; Carlier, C.; Staudinger, M.; Seibert, J.; Hunkeler, D.; Brunner, P.

2017-12-01

Identifying key catchment characteristics and processes which control the hydrological response under low-flow conditions is important to assess the catchments' vulnerability to dry periods. In the context of a Swiss Federal Office for the Environment (FOEN) project, the low-flow behaviours of two mountainous catchments were investigated. These neighboring catchments are characterized by the same meteorological conditions, but feature completely different river flow dynamics. The Roethenbach is characterized by high peak flows and low mean flows. Conversely, the Langete is characterized by relatively low peak flows and high mean flow rates. To understand the fundamentally different behaviour of the two catchments, a physically-based surface-subsurface flow HydroGeoSphere (HGS) model for each catchment was developed. The main advantage of a physically-based model is its ability to realistically reproduce processes which play a key role during low-flow periods such as surface-subsurface interactions or evapotranspiration. Both models were calibrated to reproduce measured groundwater heads and the surface flow dynamics. Subsequently, the calibrated models were used to explore the fundamental physics that control hydrological processes during low-flow periods. To achieve this, a comparative sensitivity analysis of model parameters of both catchments was carried out. Results show that the hydraulic conductivity of the bedrock (and weathered bedrock) controls the catchment water dynamics in both models. Conversely, the properties of other geological formations such as alluvial aquifer or soil layer hydraulic conductivity or porosity play a less important role. These results change significantly our perception of the streamflow catchment dynamics and more specifically the way to assess catchment vulnerability to dry period. This study suggests that by analysing catchment scale bedrock properties, the catchment dynamics and the vulnerability to dry period may be assessed.

Influences of historical and projected changes in climate and land management practices on nutrient fluxes in the Mississippi River Basin, 1948-2100

NASA Astrophysics Data System (ADS)

Spak, S.; Ward, A. S.; Li, Y.; Dalrymple, K. E.

2016-12-01

Nitrogen fertilization is central to contemporary row crop production in the U.S., but resultant nitrate transport leads to eutrophication, hypoxia, and algal blooms throughout the Mississippi River Basin and in coastal waters of the Gulf of Mexico. Effective basin-scale nutrient management requires a comprehensive understanding of the dynamics of nitrate transport in this large river catchment and the roles of individual management practices, that must then be operationalized to optimize management for both local geophysical and agricultural conditions and in response to decadal and inter-annual variations in local and regional climate. Here, we apply ensemble simulations with Agro-IBIS and THMB using spatially and temporally specific land cover, soil, agricultural, topographic, and climate data to simulate the individual and combined effects of land management and climate on historical (1948-2007) nitrate concentrations and transport in the Mississippi River Basin. We further identify sensitivities of in-stream nitrate dynamics to local and regional applications of Best Management Practices. The ensemble resolves the effects of techniques recommended in the Iowa Nutrient Reduction Strategy, including crop rotations, fertilizer management, tillage and residue management, and cover crops. Analysis of the nitrate transport response surfaces identifies non-linear effects of combined nutrient management tactics, and quantifies the stationarity of the relative and absolute influences of land management and climate during the 60-year study period.

Using high-frequency nitrogen and carbon measurements to decouple temporal dynamics of catchment and in-stream transport and reaction processes in a headwater stream

NASA Astrophysics Data System (ADS)

Blaen, P.; Riml, J.; Khamis, K.; Krause, S.

2017-12-01

Within river catchments across the world, headwater streams represent important sites of nutrient transformation and uptake due to their high rates of microbial community processing and relative abundance in the landscape. However, separating the combined influence of in-stream transport and reaction processes from the overall catchment response can be difficult due to spatio-temporal variability in nutrient and organic matter inputs, flow regimes, and reaction rates. Recent developments in optical sensor technologies enable high-frequency, in situ nutrient measurements, and thus provide opportunities for greater insights into in-stream processes. Here, we use in-stream observations of hourly nitrate (NO3-N), dissolved organic carbon (DOC) and dissolved oxygen (DO) measurements from paired in situ sensors that bound a 1 km headwater stream reach in a mixed-use catchment in central England. We employ a spectral approach to decompose (1) variances in solute loading from the surrounding landscape, and (2) variances in reach-scale in-stream nutrient transport and reaction processes. In addition, we estimate continuous rates of reach-scale NO3-N and DOC assimilation/dissimilation, ecosystem respiration and primary production. Comparison of these results over a range of hydrological conditions (baseflow, variable storm events) and timescales (event-based, diel, seasonal) facilitates new insights into the physical and biogeochemical processes that drive in-stream nutrient dynamics in headwater streams.

Hydrologic controls on the transport and cycling of carbon and nitrogen in a boreal catchment underlain by continuous permafrost

NASA Astrophysics Data System (ADS)

Koch, J. C.; Runkel, R. L.; Striegl, R.; McKnight, D. M.

2013-06-01

ecosystems represent a large carbon (C) reservoir and a substantial source of greenhouse gases. Hydrologic conditions dictate whether C leached from boreal soils is processed in catchments or flushed to less productive environments via the stream. This study quantified hydrologic and biogeochemical C loss from a boreal catchment underlain by frozen silt, where flowpaths may deepen as the active layer thaws over the summer. We hypothesized a decrease in the magnitude of C mineralization over the summer associated with changing flowpaths and decreasing hydrologic connectivity, organic matter lability, and nitrogen (N) availability. Conservative tracers were used to partition C and N loss between catchment export and biogeochemical processing. Coupling tracers with tributary and porewater chemistry indicated C and N cycling in soil flowpaths, with an exponential decrease over the summer. Nitrate was primarily reduced in hillslope flowpaths and the lack of N reaching the stream appeared to limit C mineralization. Stream export accounted for the greatest loss of C, removing 247 and 113 mol hr-1 in the early and late summer, respectively. Reactivity was related to hydrologic connectivity between the soils and stream, which was greatest early in the summer and following a large flood. While a warming climate may increase storage potential in thawed soils, the early-season flush of labile material and late-season runoff through mineral flowpaths may maintain high C export rates. Therefore, we highlight physical export as a dominant cause of aqueous C loss from silty catchments as the Arctic continues to thaw.

Catchment-scale evaluation of environmental regulations in the agricultural sector in Ireland (Invited)

NASA Astrophysics Data System (ADS)

Melland, A. R.; Jordan, P.; Mellander, P.; Wall, D. J.; Buckley, C.; Mechan, S.; Shortle, G.

2010-12-01

The European Union (EU) Nitrates Directive regulations in Ireland limits the use of agricultural fertilisers to agronomic optima and aims to minimise surplus phosphorus (P) and nitrogen (N) losses to the aquatic environment. The legislated measures include limits on nutrient application according to soil P status, crop type and livestock intensity and restricts chemical and organic fertiliser spreading and ploughing to periods of the year with typically lower exposure of nutrients to runoff and leaching. These agricultural policies are being evaluated in an Agricultural Catchments Programme in six representative catchments dominated by moderate to high intensity grassland and arable enterprises across Ireland (Fealy et al., 2010). An experimental programme has been established to provide a baseline of farm nutrient management and water body quality during the early years of the measures and to provide estimates of trajectories towards (or otherwise) water quality targets. A ‘nutrient transfer continuum’ from source, through pathways, to delivery and impact in a water body receptor describes the different phases of diffuse pollution and is being used as a framework for evaluation. Compliance with Irish standards at different levels of the continuum is being evaluated and demonstrative studies are being conducted to provide evidence of linkages between source and delivery to validate conceptual models of P and N transfers in time and space in each catchment. Source compliance is being evaluated through census soil testing and a survey of nutrient management practice and farmyard infrastructure. Mobilisation and pathways of nutrient transfers do not have chemical standards except where a groundwater body acts as both a receptor and a pathway. To demonstrate these linkages, however, representative groundwater pathways are being monitored through piezometer, chemical end-member and tracer studies, and surface water pathways are being evaluated through subcatchment storm sampling and terrain analysis modelling. Delivery and impact compliance are being assessed against EU and Irish chemical and biological standards for water body receptors. Trajectories of change will be considered. For example the time for current policies to have an impact on biological water quality may be dependant on soil P status decline rates, mobilisation rates for P stores in waterways and rates of ecological response to change in the trophic status of water body receptors. The attitudes of farmer stakeholders towards the measures and the economic impacts of investment in infrastructure and changed management are also being evaluated. Some preliminary data are presented including scenarios that suggest a lack of connectivity between farm source and water quality compliance standards. Fealy, R.M., Buckley, C., Mechan, S., Melland, A., Mellander, P.-E., Shortle, G., Wall, D. and Jordan, P. 2010. The Irish Agricultural Catchments Programme: catchment selection using spatial multi-criteria decision analysis. Soil Use and Management.23:225-236

Response of current phosphorus mitigation measures across the nutrient transfer continuum in two hydrological contrasting agricultural catchments

NASA Astrophysics Data System (ADS)

McDonald, Noeleen; Shore, Mairead; Mellander, Per-Erik; Shortle, Ger; Jordan, Phil

2015-04-01

Effective assessment of National Action Programme (NAP) measures introduced under the EU Nitrates Directive (ND), to manage nutrient use and risk of loss to waters from agriculture, is best achieved when examined across the nutrient transfer continuum at catchment scale. The Irish NAP measures are implemented on a whole-territory basis for both nitrogen (N) and phosphorus (P), with P being the key trophic pressure. The aim of this research was to observe the efficacy of P regulation measures and P source management across the transfer continuum and resultant water quality status (i.e. source to impact), in two contrasting agricultural catchments over a four year period. The catchments are ca. 11 km2 and are located in the south-east of Ireland. One is well-drained and arable dominated, while the other is mostly poorly-drained and grassland dominated. In 2009 and 2013 soil surveys for plant-available P were carried out (<2 ha sample areas) in both catchments. Concurrently, high temporal resolution monitoring of water discharge and P concentration was conducted at each catchment outlet across four hydrological years (April to March). Ecological impact surveys were carried out at four sites within each catchment in May and September across the observed four year period (2009-2013). Importantly, the proportion of farmland with excessive soil P concentrations decreased in both the arable (20% to 11.8%) and grassland catchments (5.9 to 3.6%). However, soil P concentrations also declined critically in both catchments, as proportional areas below the national crop agronomic optimum thresholds (grassland; <5 mg P l-1, arable; <6 mg P l-1) increased from 57% to 68% in the arable catchment and 75% to 87% in the grassland catchment. This decline in plant available P strongly indicates a reduced or sustained level of P inputs in both catchments. Indications of responses to soil P change in the surface waters of these catchments appeared to be highly influenced by their hydrological differences and the impact that annual and inter-annual climate and hydrological processes have on nutrient delivery. In the arable catchment total reactive P (TRP) concentrations in interpreted pathways declined across the quickflow, interflow and shallow groundwater of the slowflow, while TRP concentrations in the deeper groundwater, mostly contributing to baseflow, remained the same. However, the complexity of the flow pathways in the grassland catchment made it difficult to determine any trends in P concentrations as a result of changes in P source pressures. Additionally, although there were some inter annual trends, there was no clear indication of improvement in the ecological quality status in either catchment. Overall, a positive response to NAP measures (high soil P declines) was more clearly observable in the source component of the P transfer continuum for both catchments over the study period. This highlights the careful balance required for consideration between lag-time (policy implementation and water quality response) and agronomic sustainability (soil P fertility) in agricultural catchments.

Benchmarking hydrological model predictive capability for UK River flows and flood peaks.

NASA Astrophysics Data System (ADS)

Lane, Rosanna; Coxon, Gemma; Freer, Jim; Wagener, Thorsten

2017-04-01

Data and hydrological models are now available for national hydrological analyses. However, hydrological model performance varies between catchments, and lumped, conceptual models are not able to produce adequate simulations everywhere. This study aims to benchmark hydrological model performance for catchments across the United Kingdom within an uncertainty analysis framework. We have applied four hydrological models from the FUSE framework to 1128 catchments across the UK. These models are all lumped models and run at a daily timestep, but differ in the model structural architecture and process parameterisations, therefore producing different but equally plausible simulations. We apply FUSE over a 20 year period from 1988-2008, within a GLUE Monte Carlo uncertainty analyses framework. Model performance was evaluated for each catchment, model structure and parameter set using standard performance metrics. These were calculated both for the whole time series and to assess seasonal differences in model performance. The GLUE uncertainty analysis framework was then applied to produce simulated 5th and 95th percentile uncertainty bounds for the daily flow time-series and additionally the annual maximum prediction bounds for each catchment. The results show that the model performance varies significantly in space and time depending on catchment characteristics including climate, geology and human impact. We identify regions where models are systematically failing to produce good results, and present reasons why this could be the case. We also identify regions or catchment characteristics where one model performs better than others, and have explored what structural component or parameterisation enables certain models to produce better simulations in these catchments. Model predictive capability was assessed for each catchment, through looking at the ability of the models to produce discharge prediction bounds which successfully bound the observed discharge. These results improve our understanding of the predictive capability of simple conceptual hydrological models across the UK and help us to identify where further effort is needed to develop modelling approaches to better represent different catchment and climate typologies.

Rice agriculture impacts catchment hydrographic patterns and nitrogen export characteristics in subtropical central China: a paired-catchment study.

PubMed

Wang, Yi; Liu, Xinliang; Wang, Hua; Li, Yong; Li, Yuyuan; Liu, Feng; Xiao, Runlin; Shen, Jianlin; Wu, Jinshui

2017-06-01

Increased nitrogen (N) concentrations in water bodies have highlighted issues regarding nutrient pollution in agricultural catchments. In this study, the ammonium-N (NH 4 + -N), nitrate-N (NO 3 - -N), and total N (TN) concentrations were observed in the stream water and groundwater of two contrasting catchments (named Tuojia and Jianshan) in subtropical central China from 2010 to 2014, to determine the rice agriculture impacts on the hydrographic patterns, and N export characteristics of the catchments. The results suggested that greater amounts of stream flow (523.0 vs. 434.7 mm year -1 ) and base flow (237.6 vs. 142.8 mm year -1 ) were produced in Tuojia than in Jianshan, and a greater base flow contribution to stream flow and higher frequencies of high-base flow days were observed during the fallow season than during the rice-growing season, indicating that intensive rice agriculture strongly influences the catchment hydrographic pattern. Rice agriculture resulted in moderate N pollution in the stream water and groundwater, particularly in Tuojia. Primarily, rice agriculture increased the NH 4 + -N concentration in the stream water; however, it increased the NO 3 - -N concentrations in the groundwater, suggesting that the different N species in the paddy fields migrated out of the catchments through distinct hydrological pathways. The average TN loading via stream flow and base flow was greater in Tuojia than in Jianshan (1.72 and 0.58 vs. 0.72 and 0.15 kg N ha -1  month -1 , respectively). Greater TN loading via stream flow was observed during the fallow season in Tuojia and during the rice-growing season in Jianshan, and these different results were most likely a result of the higher base flow contribution to TN loading (33.5 vs. 21.3%) and greater base flow enrichment ratio (1.062 vs. 0.876) in Tuojia than in Jianshan. Therefore, the impact of rice agriculture on catchment eco-hydrological processes should be considered when performing water quality protection and treatment in subtropical central China.

Eco-hydrologic model cascades: Simulating land use and climate change impacts on hydrology, hydraulics and habitats for fish and macroinvertebrates.

PubMed

Guse, Björn; Kail, Jochem; Radinger, Johannes; Schröder, Maria; Kiesel, Jens; Hering, Daniel; Wolter, Christian; Fohrer, Nicola

2015-11-15

Climate and land use changes affect the hydro- and biosphere at different spatial scales. These changes alter hydrological processes at the catchment scale, which impact hydrodynamics and habitat conditions for biota at the river reach scale. In order to investigate the impact of large-scale changes on biota, a cascade of models at different scales is required. Using scenario simulations, the impact of climate and land use change can be compared along the model cascade. Such a cascade of consecutively coupled models was applied in this study. Discharge and water quality are predicted with a hydrological model at the catchment scale. The hydraulic flow conditions are predicted by hydrodynamic models. The habitat suitability under these hydraulic and water quality conditions is assessed based on habitat models for fish and macroinvertebrates. This modelling cascade was applied to predict and compare the impacts of climate- and land use changes at different scales to finally assess their effects on fish and macroinvertebrates. Model simulations revealed that magnitude and direction of change differed along the modelling cascade. Whilst the hydrological model predicted a relevant decrease of discharge due to climate change, the hydraulic conditions changed less. Generally, the habitat suitability for fish decreased but this was strongly species-specific and suitability even increased for some species. In contrast to climate change, the effect of land use change on discharge was negligible. However, land use change had a stronger impact on the modelled nitrate concentrations affecting the abundances of macroinvertebrates. The scenario simulations for the two organism groups illustrated that direction and intensity of changes in habitat suitability are highly species-dependent. Thus, a joined model analysis of different organism groups combined with the results of hydrological and hydrodynamic models is recommended to assess the impact of climate and land use changes on river ecosystems. Copyright © 2015 Elsevier B.V. All rights reserved.

Typecasting catchments: Classification, directionality, and the pursuit of universality

NASA Astrophysics Data System (ADS)

Smith, Tyler; Marshall, Lucy; McGlynn, Brian

2018-02-01

Catchment classification poses a significant challenge to hydrology and hydrologic modeling, restricting widespread transfer of knowledge from well-studied sites. The identification of important physical, climatological, or hydrologic attributes (to varying degrees depending on application/data availability) has traditionally been the focus for catchment classification. Classification approaches are regularly assessed with regard to their ability to provide suitable hydrologic predictions - commonly by transferring fitted hydrologic parameters at a data-rich catchment to a data-poor catchment deemed similar by the classification. While such approaches to hydrology's grand challenges are intuitive, they often ignore the most uncertain aspect of the process - the model itself. We explore catchment classification and parameter transferability and the concept of universal donor/acceptor catchments. We identify the implications of the assumption that the transfer of parameters between "similar" catchments is reciprocal (i.e., non-directional). These concepts are considered through three case studies situated across multiple gradients that include model complexity, process description, and site characteristics. Case study results highlight that some catchments are more successfully used as donor catchments and others are better suited as acceptor catchments. These results were observed for both black-box and process consistent hydrologic models, as well as for differing levels of catchment similarity. Therefore, we suggest that similarity does not adequately satisfy the underlying assumptions being made in parameter regionalization approaches regardless of model appropriateness. Furthermore, we suggest that the directionality of parameter transfer is an important factor in determining the success of parameter regionalization approaches.

Modeller's attitude in catchment modelling: a comparative study

NASA Astrophysics Data System (ADS)

Battista Chirico, Giovanni

2010-05-01

Ten modellers have been invited to predict, independently from each other, the discharge of the artificial Chicken Creek catchment in North-East Germany for simulation period of three years, providing them only soil texture, terrain and meteorological data. No data concerning the discharge or other sources of state variables and fluxes within the catchment have been provided. Modellers had however the opportunity to visit the experimental catchment and inspect areal photos of the catchments since its initial development stage. This study has been a unique comparative study focussing on how different modellers deal with the key issues in predicting the discharge in ungauged catchments: 1) choice of the model structure; 2) identification of model parameters; 3) identification of model initial and boundary conditions. The first general lesson learned during this study was that the modeller is just part of the entire modelling process and has a major bearing on the model results, particularly in ungauged catchments where there are more degrees of freedom in making modelling decisions. Modellers' attitudes during the stages of the model implementation and parameterisation have been deeply influenced by their own experience from previous modelling studies. A common outcome was that modellers have been mainly oriented to apply process-based models able to exploit the available data concerning the physical properties of the catchment and therefore could be more suitable to cope with the lack of data concerning state variables or fluxes. The second general lesson learned during this study was the role of dominant processes. We believed that the modelling task would have been much easier in an artificial catchment, where heterogeneity were expected to be negligible and processes simpler, than in catchments that have evolved over a longer time period. The results of the models were expected to converge, and this would have been a good starting point to proceed for a model comparison in natural, more challenging catchments. This model comparison showed instead that even a small artificial catchment exhibits heterogeneities which lead to similar modelling problems as in natural catchments. We also verified that qualitative knowledge of the potential surface processes, such as that could be gained by visual inspection of the catchment (erosion marks, canopy features, soil crusting, ect.), have been vastly employed by the modellers to guess the dominant processes to be modelled and therefore to make choices on model structure and guesses of model parameters. The two lessons learned from this intercomparison study are closely linked. The experience of a modeller is crucial in the (subjective) process of deciding upon the dominant processes that seem to be sufficiently important to be incorporated into the model. On the other hand, the cumulated experience will also play an important role in how different pieces of evidence from, for example, field inspections, will modify the initial conceptual understanding.

Assessment of surface water resources availability using catchment modeling and the results of tracer studies in the meso-scale Migina Catchment, Rwanda

NASA Astrophysics Data System (ADS)

Munyaneza, O.; Mukubwa, A.; Maskey, S.; Wenninger, J.; Uhlenbrook, S.

2013-12-01

In the last couple of years, different hydrological research projects were undertaken in the Migina catchment (243.2 km2), a tributary of the Kagera river in Southern Rwanda. These projects were aimed to understand hydrological processes of the catchment using analytical and experimental approaches and to build a pilot case whose experience can be extended to other catchments in Rwanda. In the present study, we developed a hydrological model of the catchment, which can be used to inform water resources planning and decision making. The semi-distributed hydrological model HEC-HMS (version 3.5) was used with its soil moisture accounting, unit hydrograph, liner reservoir (for base flow) and Muskingum-Cunge (river routing) methods. We used rainfall data from 12 stations and streamflow data from 5 stations, which were collected as part of this study over a period of two years (May 2009 and June 2011). The catchment was divided into five sub-catchments each represented by one of the five observed streamflow gauges. The model parameters were calibrated separately for each sub-catchment using the observed streamflow data. Calibration results obtained were found acceptable at four stations with a Nash-Sutcliffe Model Efficiency of 0.65 on daily runoff at the catchment outlet. Due to the lack of sufficient and reliable data for longer periods, a model validation (split sample test) was not undertaken. However, we used results from tracer based hydrograph separation from a previous study to compare our model results in terms of the runoff components. It was shown that the model performed well in simulating the total flow volume, peak flow and timing as well as the portion of direct runoff and base flow. We observed considerable disparities in the parameters (e.g. groundwater storage) and runoff components across the five sub-catchments, that provided insights into the different hydrological processes at sub-catchment scale. We conclude that such disparities justify the need to consider catchment subdivisions, if such parameters and components of the water cycle are to form the base for decision making in water resources planning in the Migina catchment.

Stormflow influence on nutrient dynamics in micro-catchments under contrasting land use in the Cerrado and Amazon Biomes, Brazil

NASA Astrophysics Data System (ADS)

Edelmann, Katharina; Nóbrega, Rodolfo L. B.; Gerold, Gerhard

2017-04-01

The Amazon and Cerrado biomes in Brazil have been under intense land-use change during the past few decades. The conversion of native vegetation to pastures and croplands has caused impacts on hydrological processes in these biomes, resulting in increased streamflow and nutrient fluxes. Our aim was to compare the nutrient dynamics during stormflow events in two pairs of adjacent micro-catchments with similar physical characteristics under contrasting land use, i.e. native vegetation (rainforest or cerrado) and pasture. One pair of catchments was located in the Amazon and the other in the Cerrado, both on the Amazon Agricultural Frontier in the Brazilian states of Mato Grosso and Pará. We collected hydrological and hydrochemical data on 50 stormflow events on a sub-hourly resolution during the wet seasons of 2013 and 2014. We compared the dynamics of total inorganic carbon (TIC), total organic carbon (TOC), dissolved organic carbon (DOC), nitrate (NO3), calcium (Ca), potassium (K), and magnesium (Mg) in different hydrograph parts, i.e. rising limb, peak and recession limb, between the catchments within the same biome. For the Cerrado biome, our findings show that the nutrient concentrations in the stormflows were higher in the pasture catchment than in the cerrado catchment. In the Amazon biome, we found an inverse relationship with higher concentrations in the forest catchment than in the pasture catchment, except for TIC and K. Most nutrients in the cerrado catchment had the highest concentrations in the rising limb. Mg, however, reached highest concentrations during peak discharge, and lowest in the recession limb. In the adjacent pasture catchment, in contrast, the highest nutrient concentrations were observed during the peak discharge (TIC, TOC, Ca) or the recession limb (DOC, NO3, K, Mg) with lowest in the rising limb, except for NO3, which showed the lowest concentrations during peak discharge. In the Amazon forest catchment, the peak discharge showed the highest nutrient concentrations, while concentrations in the recession limb were higher than in the rising limb. We also found that in this catchment K concentrations were lower in the recession limb than in the rising limb. In the Amazonian pasture catchment, the peak discharge showed the greatest concentrations for TIC, TOC, and Ca, and the rising limb the lowest. DOC and NO3 concentrations in this catchment were the highest in the rising and were lowest in peak discharge, while K increased over time. Based on that, we conclude that stormflow is an important driver of nutrients fluxes due to land-use change on the Amazon Agricultural Frontier, with significant increases and distinguished dynamics during the storm events, and higher nutrient concentrations in the catchments with pastures than in the ones with native vegetation, especially for TIC and K.

Changes in catchment hydrology in relation to vegetation recovery: a comparative modelling experiment

NASA Astrophysics Data System (ADS)

Lana-Renault, Noemí; Karssenberg, Derek; Latron, Jérôme; Serrano, Mā Pilar; Regüés, David; Bierkens, Marc F. P.

2010-05-01

Mediterranean mountains have been largely affected by land abandonment and subsequent vegetation recovery, with a general expansion of shrubs and forests. Such a large scale land-cover change has modified the hydrological behavior of these areas, with significant impact on runoff production. Forecasting the trend of water resources under future re-vegetation scenarios is of paramount importance in Mediterranean basins, where water management relies on runoff generated in these areas. With this purpose, a modelling experiment was designed based on the information collected in two neighbouring research catchments with a different history of land use in the central Spanish Pyrenees. One (2.84 km2) is an abandoned agricultural catchment subjected to plant colonization and at present mainly covered by shrubs. The other (0.92 km2) is a catchment covered by dense natural forest, representative of undisturbed environments. Here we present the results of the analysis of the hydrological differences between the two catchments, and a description of the approach and results of the modelling experiment. In a statistical analysis of the field data, significant differences were observed in the streamflow response of the two catchments. The forested catchment recorded fewer floods per year compared to the old agricultural catchment, and its hydrological response was characterised by a marked seasonality, with autumn and spring as the only high flow periods. Stormflow was generally higher in the old agricultural catchment, especially for low to intermediate size events; only for large events the stormflow in the forested catchment was sometimes greater. Under drier conditions, the relative differences in the stormflow between the two catchments tended to increase whereas under wet conditions they tended to be similar. The forested catchment always reacted more slowly to rainfall, with lower peakflows (generally one order of magnitude lower) and longer recession limbs. The modelling experiment aims at separating the effect of land cover from other differences (e.g. catchment area, morphology) between the two catchments. This approach allows us to make general statements on effects of land cover, required for future predictions for larger areas. In our modelling experiment, a process-based distributed hydrological model is used for the two catchments. First, we calibrate the model using data from the two catchments until a single set of parameters valid for both is found. With this set of parameters and considering a given meteorological driver (due to their proximity, it can be considered the same for both catchments), runoff at the outlet of each catchment is simulated. Land cover is then swapped between catchments and a new runoff simulation is performed for each "swapped" catchment, using the same set of parameters and the same meteorological driver. The effects of the land cover change are determined by analysing the differences between the first and the "swapped" simulations. This study is based on an analysis of the hydrological differences of two catchments with different history of land use, and a comparative modelling experiment applied to them. Following this approach, we attempt to advance our understanding of the effects of land-use/land-cover changes in catchment hydrology and, ultimately, anticipate their hydrological consequences under a future re-vegetation scenario.

Carbon-nitrogen-water interactions: is model parsimony fruitful?

NASA Astrophysics Data System (ADS)

Puertes, Cristina; González-Sanchis, María; Lidón, Antonio; Bautista, Inmaculada; Lull, Cristina; Francés, Félix

2017-04-01

It is well known that carbon and nitrogen cycles are highly intertwined and both should be explained through the water balance. In fact, in water-controlled ecosystems nutrient deficit is related to this water scarcity. For this reason, the present study compares the capability of three models in reproducing the interaction between the carbon and nitrogen cycles and the water cycle. The models are BIOME-BGCMuSo, LEACHM and a simple carbon-nitrogen model coupled to the hydrological model TETIS. Biome-BGCMuSo and LEACHM are two widely used models that reproduce the carbon and nitrogen cycles adequately. However, their main limitation is that these models are quite complex and can be too detailed for watershed studies. On the contrary, the TETIS nutrient sub-model is a conceptual model with a vertical tank distribution over the active soil depth, dividing it in two layers. Only the input of the added litter and the losses due to soil respiration, denitrification, leaching and plant uptake are considered as external fluxes. Other fluxes have been neglected. The three models have been implemented in an experimental plot of a semi-arid catchment (La Hunde, East of Spain), mostly covered by holm oak (Quercus ilex). Plant transpiration, soil moisture and runoff have been monitored daily during nearly two years (26/10/2012 to 30/09/2014). For the same period, soil samples were collected every two months and taken to the lab in order to obtain the concentrations of dissolved organic carbon, microbial biomass carbon, ammonium and nitrate. In addition, between field trips soil samples were placed in PVC tubes with resin traps and were left incubating (in situ buried cores). Thus, mineralization and nitrification accumulated fluxes for two months, were obtained. The ammonium and nitrate leaching accumulated for two months were measured using ion-exchange resin cores. Soil respiration was also measured every field trip. Finally, water samples deriving from runoff, were collected to obtain the concentrations of dissolved organic carbon, dissolved organic nitrogen, ammonium and nitrate. The comparison shows a better performance of the complex models reproducing carbon and nitrogen cycles. However, the TETIS nutrient sub-model, even simpler than BIOME-BGCMuSo and LEACHM, reproduces the water balance adequately and it obtains a suitable representation of the carbon and nitrogen cycles.

Using High-Resolution Data to Assess Land Use Impact on Nitrate Dynamics in East African Tropical Montane Catchments

NASA Astrophysics Data System (ADS)

Jacobs, Suzanne R.; Weeser, Björn; Guzha, Alphonce C.; Rufino, Mariana C.; Butterbach-Bahl, Klaus; Windhorst, David; Breuer, Lutz

2018-03-01

Land use change alters nitrate (NO3-N) dynamics in stream water by changing nitrogen cycling, nutrient inputs, uptake and hydrological flow paths. There is little empirical evidence of these processes for East Africa. We collected a unique 2 year high-resolution data set to assess the effects of land use (i.e., natural forest, smallholder agriculture and commercial tea plantations) on NO3-N dynamics in three subcatchments within a headwater catchment in the Mau Forest Complex, Kenya's largest tropical montane forest. The natural forest subcatchment had the lowest NO3-N concentrations (0.44 ± 0.043 mg N L-1) with no seasonal variation. NO3-N concentrations in the smallholder agriculture (1.09 ± 0.11 mg N L-1) and tea plantation (2.13 ± 0.19 mg N L-1) subcatchments closely followed discharge patterns, indicating mobilization of NO3-N during the rainy seasons. Hysteresis patterns of rainfall events indicate a shift from subsurface flow in the natural forest to surface runoff in agricultural subcatchments. Distinct peaks in NO3-N concentrations were observed during rainfall events after a longer dry period in the forest and tea subcatchments. The high-resolution data set enabled us to identify differences in NO3-N transport of catchments under different land use, such as enhanced NO3-N inputs to the stream during the rainy season and higher annual export in agricultural subcatchments (4.9 ± 0.3 to 12.0 ± 0.8 kg N ha-1 yr-1) than in natural forest (2.6 ± 0.2 kg N ha-1 yr-1). This emphasizes the usefulness of our monitoring approach to improve the understanding of land use effects on riverine N exports in tropical landscapes, but also the need to apply such methods in other regions.

Extended principle component analysis - a useful tool to understand processes governing water quality at catchment scales

NASA Astrophysics Data System (ADS)

Selle, B.; Schwientek, M.

2012-04-01

Water quality of ground and surface waters in catchments is typically driven by many complex and interacting processes. While small scale processes are often studied in great detail, their relevance and interplay at catchment scales remain often poorly understood. For many catchments, extensive monitoring data on water quality have been collected for different purposes. These heterogeneous data sets contain valuable information on catchment scale processes but are rarely analysed using integrated methods. Principle component analysis (PCA) has previously been applied to this kind of data sets. However, a detailed analysis of scores, which are an important result of a PCA, is often missing. Mathematically, PCA expresses measured variables on water quality, e.g. nitrate concentrations, as linear combination of independent, not directly observable key processes. These computed key processes are represented by principle components. Their scores are interpretable as process intensities which vary in space and time. Subsequently, scores can be correlated with other key variables and catchment characteristics, such as water travel times and land use that were not considered in PCA. This detailed analysis of scores represents an extension of the commonly applied PCA which could considerably improve the understanding of processes governing water quality at catchment scales. In this study, we investigated the 170 km2 Ammer catchment in SW Germany which is characterised by an above average proportion of agricultural (71%) and urban (17%) areas. The Ammer River is mainly fed by karstic springs. For PCA, we separately analysed concentrations from (a) surface waters of the Ammer River and its tributaries, (b) spring waters from the main aquifers and (c) deep groundwater from production wells. This analysis was extended by a detailed analysis of scores. We analysed measured concentrations on major ions and selected organic micropollutants. Additionally, redox-sensitive variables and environmental tracers indicating groundwater age were analysed for deep groundwater from production wells. For deep groundwater, we found that microbial turnover was stronger influenced by local availability of energy sources than by travel times of groundwater to the wells. Groundwater quality primarily reflected the input of pollutants determined by landuse, e.g. agrochemicals. We concluded that for water quality in the Ammer catchment, conservative mixing of waters with different origin is more important than reactive transport processes along the flow path.

Development of a process-based model to predict pathogen budgets for the Sydney drinking water catchment.

PubMed

Ferguson, Christobel M; Croke, Barry F W; Beatson, Peter J; Ashbolt, Nicholas J; Deere, Daniel A

2007-06-01

In drinking water catchments, reduction of pathogen loads delivered to reservoirs is an important priority for the management of raw source water quality. To assist with the evaluation of management options, a process-based mathematical model (pathogen catchment budgets - PCB) is developed to predict Cryptosporidium, Giardia and E. coli loads generated within and exported from drinking water catchments. The model quantifies the key processes affecting the generation and transport of microorganisms from humans and animals using land use and flow data, and catchment specific information including point sources such as sewage treatment plants and on-site systems. The resultant pathogen catchment budgets (PCB) can be used to prioritize the implementation of control measures for the reduction of pathogen risks to drinking water. The model is applied in the Wingecarribee catchment and used to rank those sub-catchments that would contribute the highest pathogen loads in dry weather, and in intermediate and large wet weather events. A sensitivity analysis of the model identifies that pathogen excretion rates from animals and humans, and manure mobilization rates are significant factors determining the output of the model and thus warrant further investigation.

Process-based interpretation of conceptual hydrological model performance using a multinational catchment set

NASA Astrophysics Data System (ADS)

Poncelet, Carine; Merz, Ralf; Merz, Bruno; Parajka, Juraj; Oudin, Ludovic; Andréassian, Vazken; Perrin, Charles

2017-08-01

Most of previous assessments of hydrologic model performance are fragmented, based on small number of catchments, different methods or time periods and do not link the results to landscape or climate characteristics. This study uses large-sample hydrology to identify major catchment controls on daily runoff simulations. It is based on a conceptual lumped hydrological model (GR6J), a collection of 29 catchment characteristics, a multinational set of 1103 catchments located in Austria, France, and Germany and four runoff model efficiency criteria. Two analyses are conducted to assess how features and criteria are linked: (i) a one-dimensional analysis based on the Kruskal-Wallis test and (ii) a multidimensional analysis based on regression trees and investigating the interplay between features. The catchment features most affecting model performance are the flashiness of precipitation and streamflow (computed as the ratio of absolute day-to-day fluctuations by the total amount in a year), the seasonality of evaporation, the catchment area, and the catchment aridity. Nonflashy, nonseasonal, large, and nonarid catchments show the best performance for all the tested criteria. We argue that this higher performance is due to fewer nonlinear responses (higher correlation between precipitation and streamflow) and lower input and output variability for such catchments. Finally, we show that, compared to national sets, multinational sets increase results transferability because they explore a wider range of hydroclimatic conditions.

Stationarity and Inequality from the Mississippi to the Kissimmee: Climatic Control of Temporal Patterns in Catchment Discharge and Solute Export

NASA Astrophysics Data System (ADS)

Jawitz, J. W.

2011-12-01

What are the relative contributions of climatic variability, land management, and local geomorphology in determining the temporal dynamics of streamflow and the export of solutes from watersheds to receiving water bodies? A simple analytical framework is introduced for characterizing the temporal inequality of stream discharge and solute export from catchments using Lorenz diagrams and the associated Gini coefficient. These descriptors are used to illustrate a broad range of observed flow variability with a synthesis of multi-decadal flow data from 22 rivers in Florida. The analytical framework is extended to comprehensively link variability in flows and loads to climatically-driven inputs in terms of these inequality-based metrics. Further, based on a synthesis of data from the basins of the Baltic Sea, the Mississippi River, the Kissimmee River and other tributaries to Lake Okeechobee, FL, it is shown that inter-annual variations in exported loads for geogenic constituents, and for total N and total P, are dominantly controlled by discharge. Emergence of this consistent pattern across diverse managed catchments is attributed to the anthropogenic legacy of accumulated nutrient sources generating memory, similar to ubiquitously present sources for geogenic constituents. Multi-decadal phosphorus load data from 4 of the primary tributaries to Lake Okeechobee and sodium and nitrate load data from 9 of the Hubbard Brook, NH long-term study site catchments are used to examine the relation between inequality of climatic inputs, river flows and catchment loads. The intra-annual loads to Lake Okeechobee are shown to be highly unequal, such that 90% of annual load is delivered in as little as 15% of the time. Analytic expressions are developed for measures of inequality in terms of parameters of the lognormal distribution under general conditions that include intermittency. In cases where climatic variability is high compared to that of concentrations (chemostatic conditions), such as for P in the Lake Okeechobee basin and Na in Hubbard Brook, the temporal inequality of rainfall and flow are strong surrogates for load inequality. However, in cases where variability of concentrations is high compared to that of flows (chemodynamic conditions), such as for nitrate in the Hubbard Brook catchments, load inequality is greater than rainfall or flow inequality. The measured degree of correspondence between climatic, flow, and load inequality for these data sets are shown to be well described using the general inequality framework introduced here. Important implications are that (1) variations in hydro-climatic or anthropogenic forcing can be used to robustly predict inter-annual variations in flows and loads, (2) water quality problems in receiving inland and coastal waters may persist until the accumulated storages of nutrients have been substantially depleted, and (3) remedial measures designed to intercept or capture exported flows and loads must be designed with consideration of the intra-annual inequality.

Runoff forecasting using a Takagi-Sugeno neuro-fuzzy model with online learning

NASA Astrophysics Data System (ADS)

Talei, Amin; Chua, Lloyd Hock Chye; Quek, Chai; Jansson, Per-Erik

2013-04-01

SummaryA study using local learning Neuro-Fuzzy System (NFS) was undertaken for a rainfall-runoff modeling application. The local learning model was first tested on three different catchments: an outdoor experimental catchment measuring 25 m2 (Catchment 1), a small urban catchment 5.6 km2 in size (Catchment 2), and a large rural watershed with area of 241.3 km2 (Catchment 3). The results obtained from the local learning model were comparable or better than results obtained from physically-based, i.e. Kinematic Wave Model (KWM), Storm Water Management Model (SWMM), and Hydrologiska Byråns Vattenbalansavdelning (HBV) model. The local learning algorithm also required a shorter training time compared to a global learning NFS model. The local learning model was next tested in real-time mode, where the model was continuously adapted when presented with current information in real time. The real-time implementation of the local learning model gave better results, without the need for retraining, when compared to a batch NFS model, where it was found that the batch model had to be retrained periodically in order to achieve similar results.

The value of oxygen-isotope data and multiple discharge records in calibrating a fully-distributed, physically-based rainfall-runoff model (CRUM3) to improve predictive capability

NASA Astrophysics Data System (ADS)

Neill, Aaron; Reaney, Sim

2015-04-01

Fully-distributed, physically-based rainfall-runoff models attempt to capture some of the complexity of the runoff processes that operate within a catchment, and have been used to address a variety of issues including water quality and the effect of climate change on flood frequency. Two key issues are prevalent, however, which call into question the predictive capability of such models. The first is the issue of parameter equifinality which can be responsible for large amounts of uncertainty. The second is whether such models make the right predictions for the right reasons - are the processes operating within a catchment correctly represented, or do the predictive abilities of these models result only from the calibration process? The use of additional data sources, such as environmental tracers, has been shown to help address both of these issues, by allowing for multi-criteria model calibration to be undertaken, and by permitting a greater understanding of the processes operating in a catchment and hence a more thorough evaluation of how well catchment processes are represented in a model. Using discharge and oxygen-18 data sets, the ability of the fully-distributed, physically-based CRUM3 model to represent the runoff processes in three sub-catchments in Cumbria, NW England has been evaluated. These catchments (Morland, Dacre and Pow) are part of the of the River Eden demonstration test catchment project. The oxygen-18 data set was firstly used to derive transit-time distributions and mean residence times of water for each of the catchments to gain an integrated overview of the types of processes that were operating. A generalised likelihood uncertainty estimation procedure was then used to calibrate the CRUM3 model for each catchment based on a single discharge data set from each catchment. Transit-time distributions and mean residence times of water obtained from the model using the top 100 behavioural parameter sets for each catchment were then compared to those derived from the oxygen-18 data to see how well the model captured catchment dynamics. The value of incorporating the oxygen-18 data set, as well as discharge data sets from multiple as opposed to single gauging stations in each catchment, in the calibration process to improve the predictive capability of the model was then investigated. This was achieved by assessing by how much the identifiability of the model parameters and the ability of the model to represent the runoff processes operating in each catchment improved with the inclusion of the additional data sets with respect to the likely costs that would be incurred in obtaining the data sets themselves.

Connecting Soil Water to Groundwater to Streams: Understanding Controls of Nitrate Losses from a Dryland Agricultural Landscape in the Upper Missouri River Watershed

NASA Astrophysics Data System (ADS)

Sigler, W. A.; Ewing, S. A.; Payn, R. A.; Jones, C. A.; Brookshire, J.; Klassen, J. K.; Jackson-Smith, D.; Weissmann, G. S.

2016-12-01

Shallow aquifers impaired by nitrate from agriculture are widespread and remediation or prevention of this problem requires understanding of N leaching rates at a variety of spatial scales. Characterization of the drivers of nitrate leaching at an intermediate scale (103 to 105 ha) is needed to bridge from field scale observations to the landscape-scale context, allowing informed water resource management decisions. Here we explore patterns in nitrate leaching rates across a depositional landform with a predominant land use of non-irrigated small grain production in the Northern Great Plains within the Upper Missouri Basin. The shallow Moccasin terrace (260,000 ha) aquifer is bounded in vertical extent by underlying shale and is isolated from mountain front stream recharge, such that aquifer recharge is dominated by infiltration of precipitation through agricultural soils. We leverage this simplified landform scale water balance to estimate leaching rates using groundwater nitrate concentrations and surface water discharge, and quantify uncertainty using a Monte Carlo approach based on spatial variation in groundwater nitrate concentrations. Landform-scale nitrate-N leaching rates ranged between 10 and 24 kg ha-1 yr-1 during 2012-2014 across two terrace catchments. These rates represent 11 to 27% of fertilizer application rates but are likely derived from a combination of soil organic N mineralization and direct fertilizer loss. While groundwater apparent age is relatively young (0-5 y) based on tritium-helium analysis, whole-aquifer turnover time calculations are an order of magnitude longer (20-23 y), suggesting aquifer heterogeneity and thus a longer potential response time to management changes than suggested by tracer-based aging. We collaborated with local producers to undertake this work, and discussed our results with community members throughout the study. Based on a follow-up survey, producers are now more likely to consider nitrate leaching when making management decisions, suggesting that location-specific producer engagement can facilitate practical solutions to non-point source water quality issues.

Mining nitrate concentration patterns from high-frequency in situ monitoring: a step towards more detailed understanding of hydrological processes?

NASA Astrophysics Data System (ADS)

Aubert, Alice; Houska, Tobias; Plesca, Ina; Kraft, Philipp; Breuer, Lutz

2015-04-01

Recently developed sensing technics allow collecting a considerable amount of high-frequency data; not only for hydrologic parameters (water levels, rainfall, etc.) but also for water chemistry. With devices such as in situ spectrophotometer, nitrate concentration can be monitored down to sub-hourly intervals. Thus, opening the way to new questions: what about daily or sub-daily instream nitrate concentration variations? What do these newly observed variations tell us about hydrological processes? In the Vollnkirchener Bach catchment, a headwater creek flows through a human impacted landscape dominated by agricultural and forest use and including a small settlement. Since March 2013, a Pro-PS device has been installed at the gauging station (monitored since 2011). Nitrate concentration is measured every 15 minutes, discharge and water temperature every 5 minutes. Data mining, more precisely motif discovery, is performed on these time series to identify high-resolution patterns. Spectral analysis highlighted that, in data measured at sub-hourly sampling frequency, variations up to a few hours are more likely to be dominated by measurement noise rather than real-world fluctuations. Therefore, we focus on daily motifs and flood patterns (given the fact that hydrological conditions are changing during flood events, we assume that nitrate concentration changes are depicting real processes). Various flood motifs were extracted: (1) nitrate can either be diluted or (2) concentrated, or (3) both (dilution followed by a bumpy recession curve indicating nitrate enrichment at the end of the flood). In addition to these classical nutrient-discharge behaviors, a variety of other interesting motifs were highlighted. (4) A daily nitrate cycle is clearly observed, but only during a specific year period. (5) Lag to peak time between parameters differentiate flood patterns: sometimes nitrate peaks first, sometimes discharge peaks first. (6) Furthermore, we are able to pinpoint the contributions of a combined sewer overflow, as it creates a different motif from diffuse nitrate inflows from adjacent agricultural fields. We look into the other hydrological parameters to explain this variety of patterns and their occurrence time.

Effects of land use and seasonality on stream water quality in a small tropical catchment: The headwater of Córrego Água Limpa, São Paulo (Brazil).

PubMed

Rodrigues, Valdemir; Estrany, Joan; Ranzini, Mauricio; de Cicco, Valdir; Martín-Benito, José Mª Tarjuelo; Hedo, Javier; Lucas-Borja, Manuel E

2018-05-01

Stream water quality is controlled by the interaction of natural and anthropogenic factors over a range of temporal and spatial scales. Among these anthropogenic factors, land cover changes at catchment scale can affect stream water quality. This work aims to evaluate the influence of land use and seasonality on stream water quality in a representative tropical headwater catchment named as Córrego Água Limpa (Sao Paulo, Brasil), which is highly influenced by intensive agricultural activities and urban areas. Two systematic sampling approach campaigns were implemented with six sampling points along the stream of the headwater catchment to evaluate water quality during the rainy and dry seasons. Three replicates were collected at each sampling point in 2011. Electrical conductivity, nitrates, nitrites, sodium superoxide, Chemical Oxygen Demand (DQO), colour, turbidity, suspended solids, soluble solids and total solids were measured. Water quality parameters differed among sampling points, being lower at the headwater sampling point (0m above sea level), and then progressively higher until the last downstream sampling point (2500m above sea level). For the dry season, the mean discharge was 39.5ls -1 (from April to September) whereas 113.0ls -1 were averaged during the rainy season (from October to March). In addition, significant temporal and spatial differences were observed (P<0.05) for the fourteen parameters during the rainy and dry period. The study enhance significant relationships among land use and water quality and its temporal effect, showing seasonal differences between the land use and water quality connection, highlighting the importance of multiple spatial and temporal scales for understanding the impacts of human activities on catchment ecosystem services. Copyright © 2017 Elsevier B.V. All rights reserved.

Climate Variability over India and Bangladesh from the Perturbed UK Met Office Hadley Model: Impacts on Flow and Nutrient Fluxes in the Ganges Delta System

NASA Astrophysics Data System (ADS)

Whitehead, P. G.; Caesar, J.; Crossman, J.; Barbour, E.; Ledesma, J.; Futter, M. N.

2015-12-01

A semi-distributed flow and water quality model (INCA- Integrated Catchments Model) has been set up for the whole of the Ganges- Brahmaputra- Meghna (GBM) River system in India and Bangladesh. These massive rivers transport large fluxes of water and nutrients into the Bay of Bengal via the GBM Delta system in Bangladesh. Future climate change will impact these fluxes with changing rainfall, temperature, evapotranspiration and soil moisture deficits being altered in the catchment systems. In this study the INCA model has been used to assess potential impacts of climate change using the UK Met Office Hadley Centre GCM model linked to a regionally coupled model of South East Asia, covering India and Bangladesh. The Hadley Centre model has been pururbed by varying the parameters in the model to generate 17 realisations of future climates. Some of these reflect expected change but others capture the more extreme potential behaviour of future climate conditions. The 17 realisations have been used to drive the INCA Flow and Nitrogen model inorder to generate downstream times series of hydrology and nitrate- nitrogen. The variability of the climates on these fluxes are investigated and and their likley impact on the Bay of Begal Delta considered. Results indicate a slight shift in the monsoon season with increased wet season flows and increased temperatures which alter nutrient fluxes. Societal Importance to Stakeholders The GBM Delta supports one of the most densely populated regions of people living in poverty, who rely on ecosystem services provided by the Delta for survival. These ecosystem services are dependent upon fluxes of water and nutrients. Freshwater for urban, agriculture, and aquaculture requirements are essential to livelihoods. Nutrient loads stimulate estuarine ecosystems, supporting fishing stocks, which contribute significantly the economy of Bangladesh. Thus the societal importance of upstream climate driven change change in Bangladesh are very significant to many stakeholders in Bangladesh at the local, regional and national levels.

The role of recharge zones, discharge zones, springs and tile drainage systems in peneplains of Central European highlands with regard to water quality generation processes

NASA Astrophysics Data System (ADS)

Doležal, František; Kvítek, Tomáš

The hydrogeology, runoff generation and water quality generation in old peneplains of Central Europe built by acid crystalline rocks (such as the Bohemo-Moravian Highland) are described and interpreted in terms of a three-zone concept. The recharge zones are located on flat tops of hills and their soils are mostly permeable. It is mainly through them that the shallow groundwater-bearing formations are loaded with nitrate. The groundwater exfiltrates on the lower parts of slopes (in the so-called transient zone) and in narrow valleys (in the discharge zone), creating dispersed springs and waterlogged areas. In addition, the rapid and shallow flow of perched groundwater down the slope, which takes place during wet periods in the recharge zone and, mainly, in the transient zone, leaches the nitrate from the soil directly to the stream, without necessarily being in contact with the permanent groundwater table of the recharge and the transient zones. Discharge and water quality measurements in the Kopaninský tok experimental catchment (6.7 km 2) were analysed, using a combination of two runoff separation techniques (a digital filter and a simple conceptual model GROUND). Three runoff components were distinguished (direct runoff, interflow and baseflow). There is a weak but significant positive correlation between the stream nitrate concentration on the one hand and either the interflow or the baseflow on the other hand. There is also a weak but significant negative correlation between the stream nitrate concentration on the one hand and either the ratio of direct runoff to total stream flow or the logarithm of this ratio on the other hand, provided that the cases of zero direct runoff are disregarded. A simple mixing model was used to estimate the characteristic nitrate concentrations of individual runoff components. The interflow has the highest characteristic nitrate concentration and is probably the main stream water polluter with nitrate. The baseflow is identified as the likely second main polluter. The differences in water quality between a drainage outlet and a forest spring indicate the importance of a proper nitrogen management in the recharge zones. It is also concluded that the tile drainage and tillage of formerly waterlogged sites, mainly located in transient zones, reduce the opportunity for denitrification of both baseflow and interflow. The ploughed lands in the recharge zones represent an established basis for local agriculture and cannot be easily set aside. Many such lands have been declared as vulnerable to nitrate pollution in order to protect waters against impacts of risky agricultural practices. It is proposed that some waterlogged and drained sites in the transient and discharge zones are set aside rather than the flat ploughed lands on the hill tops. To increase the denitrification, tile drainage runoff from the transient and the discharge zones should be retarded.

Water resources in Central Asia - status quo and future conflicts in transboundary river catchments - the example of the Zarafshan River (Tajikistan-Uzbekistan)

NASA Astrophysics Data System (ADS)

Groll, Michael; Opp, Christian; Kulmatov, Rashid; Normatov, Inom; Stulina, Galina; Shermatov, Nurmakhmad

2014-05-01

Water is the most valuable resource in Central Asia and due to its uneven distribution and usage among the countries of the region it is also the main source of tension between upstream and downstream water users. Due to the rapidly shrinking glaciers in the Pamir, Tien-Shan and Alai mountains, the available water resources will, by 2030, be 30% lower than today while the water demand of the growing economies will increase by 30%. This will further aggravate the pressure on the water resources and increase the water deficit caused by an unsustainable water use and political agendas. These challenges can only be overcome by an integrated water resource management for the important transboundary river catchments. The basis for such an IWRM approach however needs to be a solid data base about the status quo of the water resources. To that end the research presented here provides a detailed overview of the transboundary Zarafshan River (Tajikistan-Uzbekistan), the lifeline for more than 6 mln people. The Zarafshan River is well suited for this as it is not only one of the most important rivers in Central Asia but because the public availability of hydrological and ecological data is very limited, Furthermore the catchment is characterized by the same imbalances in the Water-Energy-Food-Nexus as most river systems in that region, which makes the Zarafshan a perfect model river for Central Asia as a whole. The findings presented here are based on field measurements, existing data from the national hydrometeorological services and an extensive literature analysis and cover the status quo of the meteorological and hydrological characteristics of the Zarafshan as well as the most important water quality parameters (pH, conductivity, nitrate, phosphate, arsenic, chromate, copper, zinc, fluoride, petroleum products, phenols and the aquatic invertebrate fauna). The hydrology of the Zarafshan is characterized by a high natural discharge dynamic in the mountainous upper parts of the catchment and by sizeable anthropogenic water extractions in the lower parts of the catchment, where on average 60.6% of the available water is diverted for irrigation purposes in the Samarkand and Navoi provinces. The water quality is heavily affected by the unsustainable land use and inadequate/missing water purification techniques. The reduced discharge and the return flow of untreated agricultural drainage water lead to a critical pollution of the river in the lower parts of the catchment. Additional sources of pollutants where identified in the upstream (the Anzob ore mining and processing complex) and downstream (the Navoi special economic area) parts of the catchment. The impact of the different water uses on the availability and the quality of the water resources are discussed in detail and outlook for the expected development during the next decades is given. These results form the basis for future investigations and for the conception of an IWRM plan for the Zarafshan River catchment.

High resolution stream water quality assessment in the Vancouver, British Columbia region: a citizen science study.

PubMed

Shupe, Scott M

2017-12-15

Changing land cover and climate regimes modify water quantity and quality in natural stream systems. In regions undergoing rapid change, it is difficult to effectively monitor and quantify these impacts at local to regional scales. In Vancouver, British Columbia, one of the most rapidly urbanizing areas in Canada, 750 measurements were taken from a total of 81 unique sampling sites representing 49 streams located in urban, forest, and agricultural-dominant watersheds at a frequency of up to 12 times per year between 2013 and 2016. Dissolved nitrate (NO 3 -N) and phosphate (PO 4 -P) concentrations, turbidity, water temperature, pH and conductivity were measured by citizen scientists in addition to observations of hydrology, vegetation, land use, and visible stream impacts. Land cover was mapped at a 15-m resolution using Landsat 8 OLI imagery and used to determine dominant land cover for each watershed in which a sample was recorded. Regional, seasonal, and catchment-type trends in measurements were determined using statistical analyses. The relationships of nutrients to land cover varied seasonally and on a catchment-type basis. Nitrate showed seasonal highs in winter and lows in summer, though phosphate had less seasonal variation. Overall, nitrate concentrations were positively associated to agriculture and deciduous forest and negatively associated with coniferous forest. In contrast, phosphate concentrations were positively associated with agricultural, deciduous forest, and disturbed land cover and negatively associated with urban land cover. Both urban and agricultural land cover were significantly associated with an increase in water conductivity. Increased forest land cover was associated with better water quality, including lower turbidity, conductivity, and water temperature. This study showed the importance of high resolution sampling in understanding seasonal and spatial dynamics of stream water quality, made possible with the large number of measurements taken with the help of trained volunteers. The results underscore the value of citizen science in freshwater research. Copyright © 2017 Elsevier B.V. All rights reserved.

Streamflow characteristics from modelled runoff time series: Importance of calibration criteria selection

USGS Publications Warehouse

Poole, Sandra; Vis, Marc; Knight, Rodney; Seibert, Jan

2017-01-01

Ecologically relevant streamflow characteristics (SFCs) of ungauged catchments are often estimated from simulated runoff of hydrologic models that were originally calibrated on gauged catchments. However, SFC estimates of the gauged donor catchments and subsequently the ungauged catchments can be substantially uncertain when models are calibrated using traditional approaches based on optimization of statistical performance metrics (e.g., Nash–Sutcliffe model efficiency). An improved calibration strategy for gauged catchments is therefore crucial to help reduce the uncertainties of estimated SFCs for ungauged catchments. The aim of this study was to improve SFC estimates from modeled runoff time series in gauged catchments by explicitly including one or several SFCs in the calibration process. Different types of objective functions were defined consisting of the Nash–Sutcliffe model efficiency, single SFCs, or combinations thereof. We calibrated a bucket-type runoff model (HBV – Hydrologiska Byråns Vattenavdelning – model) for 25 catchments in the Tennessee River basin and evaluated the proposed calibration approach on 13 ecologically relevant SFCs representing major flow regime components and different flow conditions. While the model generally tended to underestimate the tested SFCs related to mean and high-flow conditions, SFCs related to low flow were generally overestimated. The highest estimation accuracies were achieved by a SFC-specific model calibration. Estimates of SFCs not included in the calibration process were of similar quality when comparing a multi-SFC calibration approach to a traditional model efficiency calibration. For practical applications, this implies that SFCs should preferably be estimated from targeted runoff model calibration, and modeled estimates need to be carefully interpreted.

Discharge controls on the sediment and dissolved nutrient transport flux of the lowermost Mississippi River: Implications for export to the ocean and for delta restoration

NASA Astrophysics Data System (ADS)

Allison, Mead A.; Pratt, Thad C.

2017-12-01

Lagrangian longitudinal surveys and fixed station data are utilized from the lowermost Mississippi River reach in Louisiana at high and low discharge in 2012-2013 to examine the changing stream power, sediment transport capacity, and nitrate conveyance in this backwater reach of the river. Nitrate appears to remain conservative through the backwater reach at higher discharges (>15,000 m3/s), thus, nitrate levels supplied from the catchment are those exported to the Gulf of Mexico, fueling coastal hypoxia. At lower discharges, interaction with fine sediments and organic matter stored on the bed due to estuarine and tidal processes, likely elevates nitrate levels prior to entering the Gulf: a further 1-2 week long spike in nitrate concentrations is associated with the remobilization of this sediments during the rising discharge phase of the Mississippi. Backwater characteristics are clearly observed in the study reach starting at river kilometer 703 (Vicksburg) in both longitudinal study periods. Stream power at the lowermost station is only 16% of that at Vicksburg in the high discharge survey, and 0.6% at low flow. The high-to-low discharge study differential in unit stream power at a station increases between Vicksburg and the lowermost station from a factor of 3 to 47-50 times. At high discharge, ∼30% of this energy loss can be ascribed to the removal of water to the Atchafalaya at Old River Control. Suspended sediment flux decreases downstream in the studied reach in both studies: the lowermost station has 75% of the flux at Vicksburg in the high discharge study, and 0.9% in the low discharge study. The high discharge values, given that this study was conducted during the highest rising hydrograph of the water year, are augmented by sediment resuspended from the bed that was deposited in the previous low discharge phase. Examination of this first detailed field observation studies of the backwater phenomenon in a major river, shows that observed suspended particle sizes and calculated shear velocities compare favorably with suspension coefficients derived by previous investigators using flume experiments and modeling.

Alpine Warming induced Nitrogen Export from Green Lakes Valley, Colorado Front Range, USA

NASA Astrophysics Data System (ADS)

Barnes, R. T.; Williams, M. W.; Parman, J.

2012-12-01

Alpine ecosystems are particularly susceptible to disturbance due to their short growing seasons, sparse vegetation and thin soils. Atmospheric nitrogen deposition and warming temperatures currently affect Green Lakes Valley (GLV) within the Colorado Front Range. Research conducted within the alpine links chronic nitrogen inputs to a suite of ecological impacts, resulting in increased nitrate export. According to NADP records at the site, the atmospheric flux of nitrogen has decreased by 0.56 kg ha-1 yr-1 since 2000, due to a decrease in precipitation. Concurrent with this decrease, alpine nitrate yields have continued to increase; by 32% relative to the previous decade (1990-1999). In order to determine the source(s) of the sustained nitrate increases we utilized long term datasets to construct a mass balance model for four stream segments (glacier to subalpine) for nitrogen and weathering product constituents. We also compared geochemical fingerprints of various solute sources (glacial meltwater, thawing permafrost, snow, and stream water) to alpine stream water to determine if sources had changed over time. Long term trends indicate that in addition to increases in nitrate; sulfate, calcium, and silica have also increased over the same period. The geochemical composition of thawing permafrost (as indicated by rock glacial meltwater) suggests it is the source of these weathering products. Mass balance results indicate the high ammonium loads within glacial meltwater are rapidly nitrified, contributing approximately 0.45 kg yr-1 to the NO3- flux within the upper reaches of the watershed. The sustained export of these solutes during dry, summer months is likely facilitated by thawing cryosphere providing hydraulic connectivity late into the growing season. In a neighboring catchment, lacking permafrost and glacial features, there were no long term weathering or nitrogen solute trends; providing further evidence that the changes in alpine chemistry in GLV are likely due to cryospheric thaw exposing soils to biological and geochemical processes. These findings suggest that efforts to reduce nitrogen deposition loads may not improve water quality, as thawing cryosphere associated with climate change may affect alpine nitrate concentrations as much, or more than atmospheric deposition trends.

Influence of Hydrological Flow Paths on Rates and Forms of Nitrogen Losses from Mediterranean Watersheds

NASA Astrophysics Data System (ADS)

Lohse, K. A.; Sanderman, J.; Amundson, R. G.

2005-12-01

Patterns of precipitation and runoff in California are changing and likely to influence the structure and functioning of watersheds. Studies have demonstrated that hydrologic flushing during seasonal transitions in Mediterranean ecosystems can exert a strong control on nitrogen (N) export, yet few studies have examined the influence of different hydrological flow paths on rates and forms of nitrogen (N) losses. Here we illuminate the influence of variations in precipitation and hydrological pathways on the rate and form of N export along a toposequence of a well-characterized Mediterranean catchment in northern California. As a part of a larger study examining particulate and dissolved carbon loss, we analyzed seasonal patterns of dissolved organic nitrogen (DON), nitrate and ammonium concentrations in rainfall, throughfall, matrix and preferential flow, and stream samples over the course of one water year. We also analyzed seasonal soil N dynamics along this toposequence. During the transition to the winter rain season, but prior to any soil water displacement to the stream, DON and nitrate moved through near-surface soils as preferential flow. Once hillslope soils became saturated, saturated subsurface flow flushed nitrate from the hollow resulting in high stream nitrate/DON concentrations. Between storms, stream nitrate/DON concentrations were lower and appeared to reflect deep subsurface water flow chemistry. During the transition to the wet season, rates of soil nitrate production were high in the hollow relative to the hillslope soils. In the spring, these rates systematically declined as soil moisture decreased. Results from our study suggest seasonal fluctuations in soil moisture control soil N cycling and seasonal changes in the hydrological connection between hillslope soils and streams control the seasonal production and export of hydrologic N.

Principal locations of major-ion, trace-element, nitrate, and Escherichia coli loading to Emigration Creek, Salt Lake County, Utah, October 2005

USGS Publications Warehouse

Kimball, Briant A.; Runkel, Robert L.; Walton-Day, Katherine

2008-01-01

Housing development and recreational activity in Emigration Canyon have increased substantially since 1980, perhaps causing an observed decrease in water quality of this northern Utah stream located near Salt Lake City. To identify reaches of the stream that contribute to water-quality degradation, a tracer-injection and synoptic-sampling study was done to quantify mass loading of major ions, trace elements, nitrate, and Escherichia coli (E. coli) to the stream. The resulting mass-loading profiles for major ions and trace elements indicate both geologic and anthropogenic inputs to the stream, principally from tributary and spring inflows to the stream at Brigham Fork, Burr Fork, Wagner Spring, Emigration Tunnel Spring, Blacksmith Hollow, and Killyon Canyon. The pattern of nitrate loading does not correspond to the major-ion and trace-element loading patterns. Nitrate levels in the stream did not exceed water-quality standards at the time of synoptic sampling. The majority of nitrate mass loading can be considered related to anthropogenic input, based on the field settings and trends in stable isotope ratios of nitrogen. The pattern of E. coli loading does not correspond to the major-ion, trace-element, or nitrate loading patterns. The majority of E. coli loading was related to anthropogenic sources based on field setting, but a considerable part of the loading also comes from possible animal sources in Killyon Canyon, in Perkins Flat, and in Rotary Park. In this late summer sampling, E. coli concentrations only exceeded water-quality standards in limited sections of the study reach. The mass-loading approach used in this study provides a means to design future studies and to evaluate the loading on a catchment scale.

Reducing calibration parameters to increase insight in catchment organization and similarity

NASA Astrophysics Data System (ADS)

Skaugen, Thomas; Onof, Christian

2013-04-01

Ideally, hydrological models should be built from equations parameterised from observed catchment characteristics and data. This state of affairs may never be reached, but a governing principle in hydrological modelling should be to keep the number of calibration parameters to a minimum. A reduced number of parameters to be calibrated, while maintaining the accuracy and detail required by modern hydrological models, will reduce parameter and model structure uncertainty and improve model diagnostics. The dynamics of runoff for small catchments are derived from the distribution of distances from points in the catchments to the nearest stream in a catchment. This distribution is unique for each catchment and can be determined from a geographical information system (GIS). The distribution of distances, will, when a celerity of (subsurface) flow is introduced, provide a distribution of travel times, or a unit hydrograph (UH). For spatially varying levels of saturation deficit we have different celerities and, hence, different UHs. Runoff is derived from the super-positioning of the different UHs. This study shows how celerities can be estimated if we assume that recession events represent the superpositioned UH for different levels of saturation deficit. The performance of the DDD (Distance Distribution Dynamics) model is compared to that of the Swedish HBV model and is found to perform equally well for eight Norwegian catchments although the number of parameters to be calibrated in the module concerning soil moisture and runoff dynamics is reduced from 7 in the HBV model to 1 in the DDD model. It is also shown that the DDD model has a more realistic representation of the subsurface hydrology. The transparency of the DDD model makes model diagnostics more easy and experience with DDD shows that differences in model performance may be related to differences in catchment characteristics. More specifically, it appears that the hydrological dynamics of bogs have to be taken especially into account when modelling Norwegian catchments.

A catchment scale water balance model for FIFE

NASA Technical Reports Server (NTRS)

Famiglietti, J. S.; Wood, E. F.; Sivapalan, M.; Thongs, D. J.

1992-01-01

A catchment scale water balance model is presented and used to predict evaporation from the King's Creek catchment at the First ISLSCP Field Experiment site on the Konza Prairie, Kansas. The model incorporates spatial variability in topography, soils, and precipitation to compute the land surface hydrologic fluxes. A network of 20 rain gages was employed to measure rainfall across the catchment in the summer of 1987. These data were spatially interpolated and used to drive the model during storm periods. During interstorm periods the model was driven by the estimated potential evaporation, which was calculated using net radiation data collected at site 2. Model-computed evaporation is compared to that observed, both at site 2 (grid location 1916-BRS) and the catchment scale, for the simulation period from June 1 to October 9, 1987.

Pesticide fate on catchment scale: conceptual modelling of stream CSIA data

NASA Astrophysics Data System (ADS)

Lutz, Stefanie R.; van der Velde, Ype; Elsayed, Omniea F.; Imfeld, Gwenaël; Lefrancq, Marie; Payraudeau, Sylvain; van Breukelen, Boris M.

2017-10-01

Compound-specific stable isotope analysis (CSIA) has proven beneficial in the characterization of contaminant degradation in groundwater, but it has never been used to assess pesticide transformation on catchment scale. This study presents concentration and carbon CSIA data of the herbicides S-metolachlor and acetochlor from three locations (plot, drain, and catchment outlets) in a 47 ha agricultural catchment (Bas-Rhin, France). Herbicide concentrations at the catchment outlet were highest (62 µg L-1) in response to an intense rainfall event following herbicide application. Increasing δ13C values of S-metolachlor and acetochlor by more than 2 ‰ during the study period indicated herbicide degradation. To assist the interpretation of these data, discharge, concentrations, and δ13C values of S-metolachlor were modelled with a conceptual mathematical model using the transport formulation by travel-time distributions. Testing of different model setups supported the assumption that degradation half-lives (DT50) increase with increasing soil depth, which can be straightforwardly implemented in conceptual models using travel-time distributions. Moreover, model calibration yielded an estimate of a field-integrated isotopic enrichment factor as opposed to laboratory-based assessments of enrichment factors in closed systems. Thirdly, the Rayleigh equation commonly applied in groundwater studies was tested by our model for its potential to quantify degradation on catchment scale. It provided conservative estimates on the extent of degradation as occurred in stream samples. However, largely exceeding the simulated degradation within the entire catchment, these estimates were not representative of overall degradation on catchment scale. The conceptual modelling approach thus enabled us to upscale sample-based CSIA information on degradation to the catchment scale. Overall, this study demonstrates the benefit of combining monitoring and conceptual modelling of concentration and CSIA data and advocates the use of travel-time distributions for assessing pesticide fate and transport on catchment scale.

Operational validation of a multi-period and multi-criteria model conditioning approach for the prediction of rainfall-runoff processes in small forest catchments

NASA Astrophysics Data System (ADS)

Choi, H.; Kim, S.

2012-12-01

Most of hydrologic models have generally been used to describe and represent the spatio-temporal variability of hydrological processes in the watershed scale. Though it is an obvious fact that hydrological responses have the time varying nature, optimal values of model parameters were normally considered as time invariants or constants in most cases. The recent paper of Choi and Beven (2007) presents a multi-period and multi-criteria model conditioning approach. The approach is based on the equifinality thesis within the Generalised Likelihood Uncertainty Estimation (GLUE) framework. In their application, the behavioural TOPMODEL parameter sets are determined by several performance measures for global (annual) and short (30-days) periods, clustered using a Fuzzy C-means algorithm, into 15 types representing different hydrological conditions. Their study shows a good performance on the calibration of a rainfall-runoff model in a forest catchment, and also gives strong indications that it is uncommon to find model realizations that were behavioural over all multi-periods and all performance measures, and multi-period model conditioning approach may become new effective tool for predictions of hydrological processes in ungauged catchments. This study is a follow-up study on the Choi and Beven's (2007) model conditioning approach to test how the approach is effective for the prediction of rainfall-runoff responses in ungauged catchments. To achieve this purpose, 6 small forest catchments are selected among the several hydrological experimental catchments operated by Korea Forest Research Institute. In each catchment, long-term hydrological time series data varying from 10 to 30 years were available. The areas of the selected catchments range from 13.6 to 37.8 ha, and all areas are covered by coniferous or broad-leaves forests. The selected catchments locate in the southern coastal area to the northern part of South Korea. The bed rocks are Granite gneiss, Granite or Limestone. The study is progressed based on the followings. Firstly, hydrological time series of each catchment are sampled and clustered into multi-period having distinctly different temporal characteristics, and secondly, behavioural parameter distributions are determined in each multi-period based on the specification of multi-criteria model performance measures. Finally, behavioural parameter sets of each multi-period of single catchment are applied on the corresponding period of other catchments, and the cross-validations are conducted in this manner for all catchments The multi-period model conditioning approach is clearly effective to reduce the width of prediction limits, giving better model performance against the temporal variability of hydrological characteristics, and has enough potential to be the effective prediction tool for ungauged catchments. However, more advanced and continuous studies are needed to expand the application of this approach in prediction of hydrological responses in ungauged catchments,

Is fractal 1/f scaling in stream chemistry universal?

NASA Astrophysics Data System (ADS)

Hrachowitz, Markus

2016-04-01

Stream water chemistry data from catchments worldwide suggest that catchments act as filters that transform white noise, i.e. random, input signals such as in precipitation, into 1/f^α noise whose slope in a power spectrum typically ranges between -0.5>α>-1.5. This previously lead to the hypothesis that catchments act as fractal filters. In other words, it was posed that considering uncertainty, a slope of α=-1 may be a universal and intrinsic property of catchments. Such fractal scaling characteristics would have considerable implications on the predictability of stream water chemistry, as both, temporal short- and long-range interdependence and memory control the system response. While short memories and thus flatter slopes with α closer to 0 indicate poor short term but good long-term predictability, steeper slopes with values of α <<-1 indicate the opposite. In fractal systems, i.e. where α=-1, this therefore leads to inherent problems of robustly predicting both, short and long-term response patterns. The hypothesis of catchments acting as fractal filters (α=-1), however, remains to be tested more profoundly. It is, for example, not yet clear, if the observed inter-catchment variations in α indeed need to be interpreted as uncertainty and noise in the signal or if the variations underlie a systematic pattern and can be explained by some characteristic of catchment function, as was recently suggested in a modelling study based two experimental catchments (Hrachowitz et al., 2015). Here we will therefore further test the hypothesis that the spectral slope of stream water chemistry is not necessarily α=-1 and that catchments therefore do not inherently act as fractal filters. Further, it will be tested if closer links between the variations in spectral slope and hydrological function of catchments can be identified. The combined data-analysis and modelling study uses hydrochemical data (i.e. Cl- and O-18) from a wide range of catchments worldwide to allow a robust inter-comparison of response characteristics. The high number of study catchments is chosen to represent physically contrasting catchments in distinct climate zones, distinct landscape types and with distinct vegetation patterns. To identify potential patterns in the variations of α, firstly the power spectra of the observed stream chemistry in the study catchments are compared with physical catchment characteristics using statistical methods such as cluster analysis. In a subsequent step, the stream water dynamics of the study catchments are modeled using integrated catchment-scale conceptual models. Catchments for which the observed spectral signature can be meaningfully reproduced by the model, are used for further analysis, relating the model-internal flux and state dynamics to variations in α, to explore if systematic links between different flow processes and a can be established.

Evaluation of a semi-distributed model through an assessment of the spatial coherence of Intercatchment Groundwater Flows

NASA Astrophysics Data System (ADS)

de Lavenne, Alban; Thirel, Guillaume; Andréassian, Vazken; Perrin, Charles; Ramos, Maria-Helena

2016-04-01

Semi-distributed hydrological models aim to provide useful information to understand and manage the spatial distribution of water resources. However, their evaluation is often limited to independent and single evaluations at each sub-catchment within larger catchments. This enables to qualify model performance at different points, but does not provide a coherent assessment of the overall spatial consistency of the model. To cope with these methodological deficiencies, we propose a two-step strategy. First, we apply a sequential spatial calibration procedure to define spatially consistent model parameters. Secondly, we evaluate the hydrological simulations using variables that involve some dependency between sub-catchments to evaluate the overall coherence of model outputs. In this study, we particularly choose to look at the simulated Intercatchment Groundwater Flows (IGF). The idea is that the water that is lost in one place should be recovered somewhere else within the catchment to guarantee a spatially coherent water balance in time. The model used is a recently developed daily semi-distributed model, which is based on a spatial distribution of the lumped GR5J model. The model has five parameters for each sub-catchments and a streamflow velocity parameter for flow routing between them. It implements two reservoirs, one for production and one for routing, and estimates IGF according to the level of the second in a way that catchment can release water to IGF during high flows and receive water through IGF during low flows. The calibration of the model is performed from upstream to downstream, making an efficient use of spatially distributed streamflow measurements. To take model uncertainty into account, we implemented three variants of the original model structure, each one computing in a different way the IGF in each sub-catchment. The study is applied on over 1000 catchments in France. By exploring a wide area and a variability of hydrometeorological conditions, we aim to detect IGF even between catchments which can be quite distant from one another.

Global-scale regionalization of hydrological model parameters using streamflow data from many small catchments

NASA Astrophysics Data System (ADS)

Beck, Hylke; de Roo, Ad; van Dijk, Albert; McVicar, Tim; Miralles, Diego; Schellekens, Jaap; Bruijnzeel, Sampurno; de Jeu, Richard

2015-04-01

Motivated by the lack of large-scale model parameter regionalization studies, a large set of 3328 small catchments (< 10000 km2) around the globe was used to set up and evaluate five model parameterization schemes at global scale. The HBV-light model was chosen because of its parsimony and flexibility to test the schemes. The catchments were calibrated against observed streamflow (Q) using an objective function incorporating both behavioral and goodness-of-fit measures, after which the catchment set was split into subsets of 1215 donor and 2113 evaluation catchments based on the calibration performance. The donor catchments were subsequently used to derive parameter sets that were transferred to similar grid cells based on a similarity measure incorporating climatic and physiographic characteristics, thereby producing parameter maps with global coverage. Overall, there was a lack of suitable donor catchments for mountainous and tropical environments. The schemes with spatially-uniform parameter sets (EXP2 and EXP3) achieved the worst Q estimation performance in the evaluation catchments, emphasizing the importance of parameter regionalization. The direct transfer of calibrated parameter sets from donor catchments to similar grid cells (scheme EXP1) performed best, although there was still a large performance gap between EXP1 and HBV-light calibrated against observed Q. The schemes with parameter sets obtained by simultaneously calibrating clusters of similar donor catchments (NC10 and NC58) performed worse than EXP1. The relatively poor Q estimation performance achieved by two (uncalibrated) macro-scale hydrological models suggests there is considerable merit in regionalizing the parameters of such models. The global HBV-light parameter maps and ancillary data are freely available via http://water.jrc.ec.europa.eu.

Modeling flash floods in ungauged mountain catchments of China: A decision tree learning approach for parameter regionalization

NASA Astrophysics Data System (ADS)

Ragettli, S.; Zhou, J.; Wang, H.; Liu, C.

2017-12-01

Flash floods in small mountain catchments are one of the most frequent causes of loss of life and property from natural hazards in China. Hydrological models can be a useful tool for the anticipation of these events and the issuing of timely warnings. Since sub-daily streamflow information is unavailable for most small basins in China, one of the main challenges is finding appropriate parameter values for simulating flash floods in ungauged catchments. In this study, we use decision tree learning to explore parameter set transferability between different catchments. For this purpose, the physically-based, semi-distributed rainfall-runoff model PRMS-OMS is set up for 35 catchments in ten Chinese provinces. Hourly data from more than 800 storm runoff events are used to calibrate the model and evaluate the performance of parameter set transfers between catchments. For each catchment, 58 catchment attributes are extracted from several data sets available for whole China. We then use a data mining technique (decision tree learning) to identify catchment similarities that can be related to good transfer performance. Finally, we use the splitting rules of decision trees for finding suitable donor catchments for ungauged target catchments. We show that decision tree learning allows to optimally utilize the information content of available catchment descriptors and outperforms regionalization based on a conventional measure of physiographic-climatic similarity by 15%-20%. Similar performance can be achieved with a regionalization method based on spatial proximity, but decision trees offer flexible rules for selecting suitable donor catchments, not relying on the vicinity of gauged catchments. This flexibility makes the method particularly suitable for implementation in sparsely gauged environments. We evaluate the probability to detect flood events exceeding a given return period, considering measured discharge and PRMS-OMS simulated flows with regionalized parameters. Overall, the probability of detection of an event with a return period of 10 years is 62%. 44% of all 10-year flood peaks can be detected with a timing error of 2 hours or less. These results indicate that the modeling system can provide useful information about the timing and magnitude of flood events at ungauged sites.

Nitrate transport and transformation processes in unsaturated porous media

USGS Publications Warehouse

Tindall, James A.; Petrusak, Robin L.; McMahon, Peter B.

1995-01-01

A series of experiments was conducted on two contrasting agricultural soils to observe the influence of soil texture, preferential flow, and plants on nitrate transport and denitrification under unsaturated conditions. Calcium nitrate fertilizer was applied to the surface of four large undisturbed soil cores (30 cm diameter by 40 cm height). Two of the cores were a structured clay obtained from central Missouri and two were an unstructured fine sand obtained from central Florida. The cores were irrigated daily and maintained at a matric potential of -20 kPa, representative of soil tension in the rooting zone of irrigated agricultural fields. Volumetric water content (θ), concentration of nitrate-N in the soil solution, and nitrous oxide flux at the surface, 10, 20, and 30 cm were monitored daily. Leaching loss of surface-applied N03− -N was significant in both the sand and the clay. In unplanted sand cores, almost all of the applied nitrate was leached below 30 cm within 10 days. Gaseous N loss owing to denitrification was no greater than 2% of the nitrate-N applied to the unplanted sand cores and, in general, was less than 1 %. Although leaching was somewhat retarded in the clay cores, about 60% of the applied nitrate-N was leached from the unplanted clay soil in 5–6 weeks. Under unsaturated conditions, the clay had little to no tendency to denitrify despite the greater moisture content of the clay and retarded leaching of nitrate in the clay. The planted sand cores had surprisingly large gaseous N loss owing to denitrification, as much as 17% of the nitrate-N. Results from both the clay and sand experiments show that the dynamics of nitrate transport and transformation in unsaturated soils are affected by small, localized variations in the soil moisture content profile, the gaseous diffusion coefficient of the soil, the rate at which the nitrate pulse passes through the soil, the solubility of N2O and N2 and the diffusion of the gasses through the soil solution, and development of a water content profile in the soil. Limited dentrification in the clay soil was due to a limited volume of soil available for infiltration after internal catchment and the development of denitrifying conditions resulting from the presence of an extensive macropore system.

Modeling of storm runoff and pollutant wash off processes during storm event in rapidly urbanizing catchment

NASA Astrophysics Data System (ADS)

Qin, H. P.; Yu, X. Y.; Khu, S. T.

2009-04-01

Many urban catchments in developing countries are undergoing fast economic growth, population expansion and land use/cover change. Due to the mixture of agricultural/industrial/residential land use or different urbanization level as well as lack of historical monitoring data in the developing area, storm-water runoff pollution modeling is faced with challenges of considerable spatial variations and data insufficiency. Shiyan Reservoir catchment is located in the rapidly urbanizing coastal region of Southeast China. It has six sub-catchments with largely different land use patterns and urbanization levels. A simple semi-distributed model was used to simulate the storm-water runoff pollution process during storm event in the catchment. The model adopted modified IHACRES model and exponential wash-off functions to describe storm-runoff and pollutant wash-off processes, respectively, in each of six sub-catchments. Temporary hydrological and water quality monitoring sites were set at the downstream section of each sub-catchment in Feb-May 2007, spanning non-rain and rain seasons. And the model was calibrated for storm-runoff and water quality data during two typical storm events with rainfall amount of 10mm/4hr and 73mm/5hr, respectively. The results indicated that the Nash-Sutcliffe (NS) coefficients are greater than 0.65 and 0.55 respectively for storm-runoff model calibration and validation. However although NS coefficients can reach 0.7~0.9 for pollutant wash-off model calibration based on measured data in each storm event, the simulation data can not fit well with the measured data in model validation. According to field survey observation, many litters and residuals were found to distribute in disorder in some sub-catchments or their drainage systems and to instantaneously wash off into the surface water when the rainfall amount and intensity are large enough. In order to improve storm-water runoff pollution simulation in the catchment, the variations of pollutant source and wash off processes in different storm intensity should be consider in future monitoring and model development. Keywords: storm runoff; wash off; urbanization; catchment modeling; litter; residual

Identifying fine sediment sources to alleviate flood risk caused by fine sediments through catchment connectivity analysis

NASA Astrophysics Data System (ADS)

Twohig, Sarah; Pattison, Ian; Sander, Graham

2017-04-01

Fine sediment poses a significant threat to UK river systems in terms of vegetation, aquatic habitats and morphology. Deposition of fine sediment onto the river bed reduces channel capacity resulting in decreased volume to contain high flow events. Once the in channel problem has been identified managers are under pressure to sustainably mitigate flood risk. With climate change and land use adaptations increasing future pressures on river catchments it is important to consider the connectivity of fine sediment throughout the river catchment and its influence on channel capacity, particularly in systems experiencing long term aggradation. Fine sediment erosion is a continuing concern in the River Eye, Leicestershire. The predominately rural catchment has a history of flooding within the town of Melton Mowbray. Fine sediment from agricultural fields has been identified as a major contributor of sediment delivery into the channel. Current mitigation measures are not sustainable or successful in preventing the continuum of sediment throughout the catchment. Identifying the potential sources and connections of fine sediment would provide insight into targeted catchment management. 'Sensitive Catchment Integrated Modelling Analysis Platforms' (SCIMAP) is a tool often used by UK catchment managers to identify potential sources and routes of sediment within a catchment. SCIMAP is a risk based model that combines hydrological (rainfall) and geomorphic controls (slope, land cover) to identify the risk of fine sediment being transported from source into the channel. A desktop version of SCIMAP was run for the River Eye at a catchment scale using 5m terrain, rainfall and land cover data. A series of SCIMAP model runs were conducted changing individual parameters to determine the sensitivity of the model. Climate Change prediction data for the catchment was used to identify potential areas of future connectivity and erosion risk for catchment managers. The results have been subjected to field validation as part of a wider research project which provides an indication of the robustness of widespread models as effective management tools.

The significance of spatial variability of rainfall on streamflow: A synthetic analysis at the Upper Lee catchment, UK

NASA Astrophysics Data System (ADS)

Pechlivanidis, Ilias; McIntyre, Neil; Wheater, Howard

2017-04-01

Rainfall, one of the main inputs in hydrological modeling, is a highly heterogeneous process over a wide range of scales in space, and hence the ignorance of the spatial rainfall information could affect the simulated streamflow. Calibration of hydrological model parameters is rarely a straightforward task due to parameter equifinality and parameters' 'nature' to compensate for other uncertainties, i.e. structural and forcing input. In here, we analyse the significance of spatial variability of rainfall on streamflow as a function of catchment scale and type, and antecedent conditions using the continuous time, semi-distributed PDM hydrological model at the Upper Lee catchment, UK. The impact of catchment scale and type is assessed using 11 nested catchments ranging in scale from 25 to 1040 km2, and further assessed by artificially changing the catchment characteristics and translating these to model parameters with uncertainty using model regionalisation. Synthetic rainfall events are introduced to directly relate the change in simulated streamflow to the spatial variability of rainfall. Overall, we conclude that the antecedent catchment wetness and catchment type play an important role in controlling the significance of the spatial distribution of rainfall on streamflow. Results show a relationship between hydrograph characteristics (streamflow peak and volume) and the degree of spatial variability of rainfall for the impermeable catchments under dry antecedent conditions, although this decreases at larger scales; however this sensitivity is significantly undermined under wet antecedent conditions. Although there is indication that the impact of spatial rainfall on streamflow varies as a function of catchment scale, the variability of antecedent conditions between the synthetic catchments seems to mask this significance. Finally, hydrograph responses to different spatial patterns in rainfall depend on assumptions used for model parameter estimation and also the spatial variation in parameters indicating the need of an uncertainty framework in such investigation.

Modeling flash floods in ungauged mountain catchments of China: A decision tree learning approach for parameter regionalization

NASA Astrophysics Data System (ADS)

Ragettli, S.; Zhou, J.; Wang, H.; Liu, C.; Guo, L.

2017-12-01

Flash floods in small mountain catchments are one of the most frequent causes of loss of life and property from natural hazards in China. Hydrological models can be a useful tool for the anticipation of these events and the issuing of timely warnings. One of the main challenges of setting up such a system is finding appropriate model parameter values for ungauged catchments. Previous studies have shown that the transfer of parameter sets from hydrologically similar gauged catchments is one of the best performing regionalization methods. However, a remaining key issue is the identification of suitable descriptors of similarity. In this study, we use decision tree learning to explore parameter set transferability in the full space of catchment descriptors. For this purpose, a semi-distributed rainfall-runoff model is set up for 35 catchments in ten Chinese provinces. Hourly runoff data from in total 858 storm events are used to calibrate the model and to evaluate the performance of parameter set transfers between catchments. We then present a novel technique that uses the splitting rules of classification and regression trees (CART) for finding suitable donor catchments for ungauged target catchments. The ability of the model to detect flood events in assumed ungauged catchments is evaluated in series of leave-one-out tests. We show that CART analysis increases the probability of detection of 10-year flood events in comparison to a conventional measure of physiographic-climatic similarity by up to 20%. Decision tree learning can outperform other regionalization approaches because it generates rules that optimally consider spatial proximity and physical similarity. Spatial proximity can be used as a selection criteria but is skipped in the case where no similar gauged catchments are in the vicinity. We conclude that the CART regionalization concept is particularly suitable for implementation in sparsely gauged and topographically complex environments where a proximity-based regionalization concept is not applicable.

Improving flood forecasting capability of physically based distributed hydrological models by parameter optimization

NASA Astrophysics Data System (ADS)

Chen, Y.; Li, J.; Xu, H.

2016-01-01

Physically based distributed hydrological models (hereafter referred to as PBDHMs) divide the terrain of the whole catchment into a number of grid cells at fine resolution and assimilate different terrain data and precipitation to different cells. They are regarded to have the potential to improve the catchment hydrological process simulation and prediction capability. In the early stage, physically based distributed hydrological models are assumed to derive model parameters from the terrain properties directly, so there is no need to calibrate model parameters. However, unfortunately the uncertainties associated with this model derivation are very high, which impacted their application in flood forecasting, so parameter optimization may also be necessary. There are two main purposes for this study: the first is to propose a parameter optimization method for physically based distributed hydrological models in catchment flood forecasting by using particle swarm optimization (PSO) algorithm and to test its competence and to improve its performances; the second is to explore the possibility of improving physically based distributed hydrological model capability in catchment flood forecasting by parameter optimization. In this paper, based on the scalar concept, a general framework for parameter optimization of the PBDHMs for catchment flood forecasting is first proposed that could be used for all PBDHMs. Then, with the Liuxihe model as the study model, which is a physically based distributed hydrological model proposed for catchment flood forecasting, the improved PSO algorithm is developed for the parameter optimization of the Liuxihe model in catchment flood forecasting. The improvements include adoption of the linearly decreasing inertia weight strategy to change the inertia weight and the arccosine function strategy to adjust the acceleration coefficients. This method has been tested in two catchments in southern China with different sizes, and the results show that the improved PSO algorithm could be used for the Liuxihe model parameter optimization effectively and could improve the model capability largely in catchment flood forecasting, thus proving that parameter optimization is necessary to improve the flood forecasting capability of physically based distributed hydrological models. It also has been found that the appropriate particle number and the maximum evolution number of PSO algorithm used for the Liuxihe model catchment flood forecasting are 20 and 30 respectively.

Parameter Set Cloning Based on Catchment Similarity for Large-scale Hydrologic Modeling

NASA Astrophysics Data System (ADS)

Liu, Z.; Kaheil, Y.; McCollum, J.

2016-12-01

Parameter calibration is a crucial step to ensure the accuracy of hydrological models. However, streamflow gauges are not available everywhere for calibrating a large-scale hydrologic model globally. Thus, assigning parameters appropriately for regions where the calibration cannot be performed directly has been a challenge for large-scale hydrologic modeling. Here we propose a method to estimate the model parameters in ungauged regions based on the values obtained through calibration in areas where gauge observations are available. This parameter set cloning is performed according to a catchment similarity index, a weighted sum index based on four catchment characteristic attributes. These attributes are IPCC Climate Zone, Soil Texture, Land Cover, and Topographic Index. The catchments with calibrated parameter values are donors, while the uncalibrated catchments are candidates. Catchment characteristic analyses are first conducted for both donors and candidates. For each attribute, we compute a characteristic distance between donors and candidates. Next, for each candidate, weights are assigned to the four attributes such that higher weights are given to properties that are more directly linked to the hydrologic dominant processes. This will ensure that the parameter set cloning emphasizes the dominant hydrologic process in the region where the candidate is located. The catchment similarity index for each donor - candidate couple is then created as the sum of the weighted distance of the four properties. Finally, parameters are assigned to each candidate from the donor that is "most similar" (i.e. with the shortest weighted distance sum). For validation, we applied the proposed method to catchments where gauge observations are available, and compared simulated streamflows using the parameters cloned by other catchments to the results obtained by calibrating the hydrologic model directly using gauge data. The comparison shows good agreement between the two models for different river basins as we show here. This method has been applied globally to the Hillslope River Routing (HRR) model using gauge observations obtained from the Global Runoff Data Center (GRDC). As next step, more catchment properties can be taken into account to further improve the representation of catchment similarity.

Probabilistic postprocessing models for flow forecasts for a system of catchments and several lead times

NASA Astrophysics Data System (ADS)

Engeland, Kolbjorn; Steinsland, Ingelin

2014-05-01

This study introduces a methodology for the construction of probabilistic inflow forecasts for multiple catchments and lead times, and investigates criterions for evaluation of multi-variate forecasts. A post-processing approach is used, and a Gaussian model is applied for transformed variables. The post processing model has two main components, the mean model and the dependency model. The mean model is used to estimate the marginal distributions for forecasted inflow for each catchment and lead time, whereas the dependency models was used to estimate the full multivariate distribution of forecasts, i.e. co-variances between catchments and lead times. In operational situations, it is a straightforward task to use the models to sample inflow ensembles which inherit the dependencies between catchments and lead times. The methodology was tested and demonstrated in the river systems linked to the Ulla-Førre hydropower complex in southern Norway, where simultaneous probabilistic forecasts for five catchments and ten lead times were constructed. The methodology exhibits sufficient flexibility to utilize deterministic flow forecasts from a numerical hydrological model as well as statistical forecasts such as persistent forecasts and sliding window climatology forecasts. It also deals with variation in the relative weights of these forecasts with both catchment and lead time. When evaluating predictive performance in original space using cross validation, the case study found that it is important to include the persistent forecast for the initial lead times and the hydrological forecast for medium-term lead times. Sliding window climatology forecasts become more important for the latest lead times. Furthermore, operationally important features in this case study such as heteroscedasticity, lead time varying between lead time dependency and lead time varying between catchment dependency are captured. Two criterions were used for evaluating the added value of the dependency model. The first one was the Energy score (ES) that is a multi-dimensional generalization of continuous rank probability score (CRPS). ES was calculated for all lead-times and catchments together, for each catchment across all lead times and for each lead time across all catchments. The second criterion was to use CRPS for forecasted inflows accumulated over several lead times and catchments. The results showed that ES was not very sensitive to correct covariance structure, whereas CRPS for accumulated flows where more suitable for evaluating the dependency model. This indicates that it is more appropriate to evaluate relevant univariate variables that depends on the dependency structure then to evaluate the multivariate forecast directly.

Modelling the influence of elevation and snow regime on winter stream temperature in the rain-on-snow zone

NASA Astrophysics Data System (ADS)

Leach, J.; Moore, D.

2015-12-01

Winter stream temperature of coastal mountain catchments influences fish growth and development. Transient snow cover and advection associated with lateral throughflow inputs are dominant controls on stream thermal regimes in these regions. Existing stream temperature models lack the ability to properly simulate these processes. Therefore, we developed and evaluated a conceptual-parametric catchment-scale stream temperature model that includes the role of transient snow cover and lateral advection associated with throughflow. The model provided reasonable estimates of observed stream temperature at three test catchments. We used the model to simulate winter stream temperature for virtual catchments located at different elevations within the rain-on-snow zone. The modelling exercise examined stream temperature response associated with interactions between elevation, snow regime, and changes in air temperature. Modelling results highlight that the sensitivity of winter stream temperature response to changes in climate may be dependent on catchment elevation and landscape position.

Modeling nonlinear responses of DOC transport in boreal catchments in Sweden

NASA Astrophysics Data System (ADS)

Kasurinen, Ville; Alfredsen, Knut; Ojala, Anne; Pumpanen, Jukka; Weyhenmeyer, Gesa A.; Futter, Martyn N.; Laudon, Hjalmar; Berninger, Frank

2016-07-01

Stream water dissolved organic carbon (DOC) concentrations display high spatial and temporal variation in boreal catchments. Understanding and predicting these patterns is a challenge with great implications for water quality projections and carbon balance estimates. Although several biogeochemical models have been used to estimate stream water DOC dynamics, model biases common during both rain and snow melt-driven events. The parsimonious DOC-model, K-DOC, with 10 calibrated parameters, uses a nonlinear discharge and catchment water storage relationship including soil temperature dependencies of DOC release and consumption. K-DOC was used to estimate the stream water DOC concentrations over 5 years for eighteen nested boreal catchments having total area of 68 km2 (varying from 0.04 to 67.9 km2). The model successfully simulated DOC concentrations during base flow conditions, as well as, hydrological events in catchments dominated by organic and mineral soils reaching NSEs from 0.46 to 0.76. Our semimechanistic model was parsimonious enough to have all parameters estimated using statistical methods. We did not find any clear differences between forest and mire-dominated catchments that could be explained by soil type or tree species composition. However, parameters controlling slow release and consumption of DOC from soil water behaved differently for small headwater catchments (less than 2 km2) than for those that integrate larger areas of different ecosystem types (10-68 km2). Our results emphasize that it is important to account for nonlinear dependencies of both, soil temperature, and catchment water storage, when simulating DOC dynamics of boreal catchments.

Is Fractal 1/f Scaling in Stream Chemistry Universal?

NASA Astrophysics Data System (ADS)

Hrachowitz, M.

2016-12-01

Stream water chemistry data from catchments worldwide suggest that catchments act as filters that transform white noise, i.e. random input signals such as in precipitation, into 1/fαnoise whose slope in a power spectrum typically ranges between -0.5>α> -1.5. This previously lead to the hypothesis that catchments act as fractal filters, i.e. a slope of α=-1 may be a universal and intrinsic property of catchments. That would have considerable implications on the predictability of stream water chemistry, as both, temporal short- and long-range interdependence control the system response. While short memories and thus flatter slopes with α closer to 0 indicate poor short term but good long-term predictability, steeper slopes (α <<-1) indicate the opposite. In fractal systems, i.e. α=-1, this therefore leads to inherent problems of predicting both, short and long-term response patterns. The hypothesis of catchments acting as fractal filters remains to be tested more profoundly. It is not yet clear, if observed inter-catchment variations in α need to be interpreted as noise in the signal or if the variations underlie a systematic pattern and can be explained by some characteristic of catchment function. Here we will test the hypothesis that the spectral slope of stream water chemistry is not necessarily α=-1 and that catchments therefore do not inherently act as fractal filters. Further, it will be tested if closer links between the variations in spectral slope and hydrological function of catchments can be identified. The combined data-analysis and modelling study uses hydrochemical data (i.e. Cl-) from a wide range of catchments worldwide. The study catchments are physically contrasting, from distinct climate zones, and with distinct landscapes and vegetation. To identify patterns in the variations of α, firstly the power spectra of observed stream chemistry are compared with physical catchment characteristics using methods such as cluster analysis. In a subsequent step, the stream water dynamics of the study catchments are modelled using integrated catchment-scale models. Catchments for which the observed spectral signature can be meaningfully reproduced by the model, are used for further analysis, relating the modelled flux and state dynamics to variations in α, to explore links between flow processes α.

River water infiltration enhances denitrification efficiency in riparian groundwater.

PubMed

Trauth, Nico; Musolff, Andreas; Knöller, Kay; Kaden, Ute S; Keller, Toralf; Werban, Ulrike; Fleckenstein, Jan H

2018-03-01

Nitrate contamination in ground- and surface water is a persistent problem in countries with intense agriculture. The transition zone between rivers and their riparian aquifers, where river water and groundwater interact, may play an important role in mediating nitrate exports, as it can facilitate intensive denitrification, which permanently removes nitrate from the aquatic system. However, the in-situ factors controlling riparian denitrification are not fully understood, as they are often strongly linked and their effects superimpose each other. In this study, we present the evaluation of hydrochemical and isotopic data from a 2-year sampling period of river water and groundwater in the riparian zone along a 3rd order river in Central Germany. Based on bi- and multivariate statistics (Spearman's rank correlation and partial least squares regression) we can show, that highest rates for oxygen consumption and denitrification in the riparian aquifer occur where the fraction of infiltrated river water and at the same time groundwater temperature, are high. River discharge and depth to groundwater are additional explanatory variables for those reaction rates, but of minor importance. Our data and analyses suggest that at locations in the riparian aquifer, which show significant river water infiltration, heterotrophic microbial reactions in the riparian zone may be fueled by bioavailable organic carbon derived from the river water. We conclude that interactions between rivers and riparian groundwater are likely to be a key control of nitrate removal and should be considered as a measure to mitigate high nitrate exports from agricultural catchments. Copyright © 2017 Elsevier Ltd. All rights reserved.

Export of dissolved organic carbon and nitrate from grassland in winter using high temporal resolution, in situ UV sensing.

PubMed

Sandford, Richard C; Hawkins, Jane M B; Bol, Roland; Worsfold, Paul J

2013-07-01

Co-deployment of two reagentless UV sensors for high temporal resolution (15 min) real time determination of wintertime DOC and nitrate-N export from a grassland lysimeter plot (North Wyke, Devon, UK) is reported. They showed rapid, transient but high impact perturbations of DOC (5.3-23 mg CL(-1)) and nitrate-N export after storm/snow melt which discontinuous sampling would not have observed. During a winter freeze/thaw cycle, DOC export (1.25 kg Cha(-1)d(-1)) was significantly higher than typical UK catchment values (maximum 0.25 kg Chad(-1)) and historical North Wyke data (0.7 kg Cha(-1)d(-1)). DOC concentrations were inversely correlated with the key DOC physico-chemical drivers of pH (January r=-0.65), and conductivity (January r=-0.64). Nitrate-N export (0.8-1.5 mg NL(-1)) was strongly correlated with DOC export (r ≥ 0.8). The DOC:NO3-N molar ratios showed that soil microbial N assimilation was not C limited and therefore high N accrual was not promoted in the River Taw, which is classified as a nitrate vulnerable zone (NVZ). The sensor was shown to be an effective sentinel device for identifying critical periods when rapid ecosystem N accumulation could be triggered by a shift in resource stoichiometry. It is therefore a useful tool to help evaluate land management strategies and impacts from climate change and intensive agriculture. Copyright © 2013 Elsevier B.V. All rights reserved.

Improving flood forecasting capability of physically based distributed hydrological model by parameter optimization

NASA Astrophysics Data System (ADS)

Chen, Y.; Li, J.; Xu, H.

2015-10-01

Physically based distributed hydrological models discrete the terrain of the whole catchment into a number of grid cells at fine resolution, and assimilate different terrain data and precipitation to different cells, and are regarded to have the potential to improve the catchment hydrological processes simulation and prediction capability. In the early stage, physically based distributed hydrological models are assumed to derive model parameters from the terrain properties directly, so there is no need to calibrate model parameters, but unfortunately, the uncertanties associated with this model parameter deriving is very high, which impacted their application in flood forecasting, so parameter optimization may also be necessary. There are two main purposes for this study, the first is to propose a parameter optimization method for physically based distributed hydrological models in catchment flood forecasting by using PSO algorithm and to test its competence and to improve its performances, the second is to explore the possibility of improving physically based distributed hydrological models capability in cathcment flood forecasting by parameter optimization. In this paper, based on the scalar concept, a general framework for parameter optimization of the PBDHMs for catchment flood forecasting is first proposed that could be used for all PBDHMs. Then, with Liuxihe model as the study model, which is a physically based distributed hydrological model proposed for catchment flood forecasting, the improverd Particle Swarm Optimization (PSO) algorithm is developed for the parameter optimization of Liuxihe model in catchment flood forecasting, the improvements include to adopt the linear decreasing inertia weight strategy to change the inertia weight, and the arccosine function strategy to adjust the acceleration coefficients. This method has been tested in two catchments in southern China with different sizes, and the results show that the improved PSO algorithm could be used for Liuxihe model parameter optimization effectively, and could improve the model capability largely in catchment flood forecasting, thus proven that parameter optimization is necessary to improve the flood forecasting capability of physically based distributed hydrological model. It also has been found that the appropriate particle number and the maximum evolution number of PSO algorithm used for Liuxihe model catchment flood forcasting is 20 and 30, respectively.

Estimation of groundwater recharge via percolation outputs from a rainfall/runoff model for the Verlorenvlei estuarine system, west coast, South Africa

NASA Astrophysics Data System (ADS)

Watson, Andrew; Miller, Jodie; Fleischer, Melanie; de Clercq, Willem

2018-03-01

Wetlands are conservation priorities worldwide, due to their high biodiversity and productivity, but are under threat from agricultural and climate change stresses. To improve the water management practices and resource allocation in these complex systems, a modelling approach has been developed to estimate potential recharge for data poor catchments using rainfall data and basic assumptions regarding soil and aquifer properties. The Verlorenvlei estuarine lake (RAMSAR #525) on the west coast of South Africa is a data poor catchment where rainfall records have been supplemented with farmer's rainfall records. The catchment has multiple competing users. To determine the ecological reserve for the wetlands, the spatial and temporal distribution of recharge had to be well constrained using the J2000 rainfall/runoff model. The majority of rainfall occurs in the mountains (±650 mm/yr) and considerably less in the valley (±280 mm/yr). Percolation was modelled as ∼3.6% of rainfall in the driest parts of the catchment, ∼10% of rainfall in the moderately wet parts of the catchment and ∼8.4% but up to 28.9% of rainfall in the wettest parts of the catchment. The model results are representative of rainfall and water level measurements in the catchment, and compare well with water table fluctuation technique, although estimates are dissimilar to previous estimates within the catchment. This is most likely due to the daily timestep nature of the model, in comparison to other yearly average methods. These results go some way in understanding the fact that although most semi-arid catchments have very low yearly recharge estimates, they are still capable of sustaining high biodiversity levels. This demonstrates the importance of incorporating shorter term recharge event modeling for improving recharge estimates.

Catchments as non-linear filters: evaluating data-driven approaches for spatio-temporal predictions in ungauged basins

NASA Astrophysics Data System (ADS)

Bellugi, D. G.; Tennant, C.; Larsen, L.

2016-12-01

Catchment and climate heterogeneity complicate prediction of runoff across time and space, and resulting parameter uncertainty can lead to large accumulated errors in hydrologic models, particularly in ungauged basins. Recently, data-driven modeling approaches have been shown to avoid the accumulated uncertainty associated with many physically-based models, providing an appealing alternative for hydrologic prediction. However, the effectiveness of different methods in hydrologically and geomorphically distinct catchments, and the robustness of these methods to changing climate and changing hydrologic processes remain to be tested. Here, we evaluate the use of machine learning techniques to predict daily runoff across time and space using only essential climatic forcing (e.g. precipitation, temperature, and potential evapotranspiration) time series as model input. Model training and testing was done using a high quality dataset of daily runoff and climate forcing data for 25+ years for 600+ minimally-disturbed catchments (drainage area range 5-25,000 km2, median size 336 km2) that cover a wide range of climatic and physical characteristics. Preliminary results using Support Vector Regression (SVR) suggest that in some catchments this nonlinear-based regression technique can accurately predict daily runoff, while the same approach fails in other catchments, indicating that the representation of climate inputs and/or catchment filter characteristics in the model structure need further refinement to increase performance. We bolster this analysis by using Sparse Identification of Nonlinear Dynamics (a sparse symbolic regression technique) to uncover the governing equations that describe runoff processes in catchments where SVR performed well and for ones where it performed poorly, thereby enabling inference about governing processes. This provides a robust means of examining how catchment complexity influences runoff prediction skill, and represents a contribution towards the integration of data-driven inference and physically-based models.

Conceptualisation of Snowpack Isotope Dynamics in Spatially Distributed Tracer-Aided Runoff Models in Snow Influenced Northern Cathments

NASA Astrophysics Data System (ADS)

Ala-aho, P. O. A.; Tetzlaff, D.; Laudon, H.; McNamara, J. P.; Soulsby, C.

2016-12-01

We use the Spatially distributed Tracer-Aided Rainfall-Runoff (STARR) modelling framework to explore non-stationary flow and isotope response in three northern headwater catchments. The model simulates dynamic, spatially variable tracer concentration in different water stores and fluxes within a catchment, which can constrain internal catchment mixing processes, flow paths and associated water ages. To date, a major limitation in using such models in snow-dominated catchments has been the difficulties in paramaterising the isotopic transformations in snowpack accumulation and melt. We use high quality long term datasets for hydrometrics and stable water isotopes collected in three northern study catchments for model calibration and testing. The three catchments exhibit different hydroclimatic conditions, soil and vegetation types, and topographic relief, which brings about variable degree of snow dominance across the catchments. To account for the snow influence we develop novel formulations to estimate the isotope evolution in the snowpack and melt. Algorithms for the isotopic evolution parameterize an isotopic offset between snow evaporation and melt fluxes and the remaining snow storage. The model for each catchment is calibrated to match both streamflow and tracer concentration at the stream outlet to ensure internal consistency of the system behaviour. The model is able to reproduce the streamflow along with the spatio-temporal differences in tracer concentrations across the three studies catchments reasonably well. Incorporating the spatially distributed snowmelt processes and associated isotope transformations proved essential in capturing the stream tracer reponse for strongly snow-influenced cathments. This provides a transferrable tool which can be used to understand spatio-temporal variability of mixing and water ages for different storages and flow paths in other snow influenced, environments.

Groundwater-surface water interactions across scales in a boreal landscape investigated using a numerical modelling approach

NASA Astrophysics Data System (ADS)

Jutebring Sterte, Elin; Johansson, Emma; Sjöberg, Ylva; Huseby Karlsen, Reinert; Laudon, Hjalmar

2018-05-01

Groundwater and surface-water interactions are regulated by catchment characteristics and complex inter- and intra-annual variations in climatic conditions that are not yet fully understood. Our objective was to investigate the influence of catchment characteristics and freeze-thaw processes on surface and groundwater interactions in a boreal landscape, the Krycklan catchment in Sweden. We used a numerical modelling approach and sub-catchment evaluation method to identify and evaluate fundamental catchment characteristics and processes. The model reproduced observed stream discharge patterns of the 14 sub-catchments and the dynamics of the 15 groundwater wells with an average accumulated discharge error of 1% (15% standard deviation) and an average groundwater-level mean error of 0.1 m (0.23 m standard deviation). We show how peatland characteristics dampen the effect of intense rain, and how soil freeze-thaw processes regulate surface and groundwater partitioning during snowmelt. With these results, we demonstrate the importance of defining, understanding and quantifying the role of landscape heterogeneity and sub-catchment characteristics for accurately representing catchment hydrological functioning.

Picturing and modelling catchments by representative hillslopes

NASA Astrophysics Data System (ADS)

Loritz, Ralf; Hassler, Sibylle; Jackisch, Conrad; Zehe, Erwin

2016-04-01

Hydrological modelling studies often start with a qualitative sketch of the hydrological processes of a catchment. These so-called perceptual models are often pictured as hillslopes and are generalizations displaying only the dominant and relevant processes of a catchment or hillslope. The problem with these models is that they are prone to become too much predetermined by the designer's background and experience. Moreover it is difficult to know if that picture is correct and contains enough complexity to represent the system under study. Nevertheless, because of their qualitative form, perceptual models are easy to understand and can be an excellent tool for multidisciplinary exchange between researchers with different backgrounds, helping to identify the dominant structures and processes in a catchment. In our study we explore whether a perceptual model built upon an intensive field campaign may serve as a blueprint for setting up representative hillslopes in a hydrological model to reproduce the functioning of two distinctly different catchments. We use a physically-based 2D hillslope model which has proven capable to be driven by measured soil-hydrological parameters. A key asset of our approach is that the model structure itself remains a picture of the perceptual model, which is benchmarked against a) geo-physical images of the subsurface and b) observed dynamics of discharge, distributed state variables and fluxes (soil moisture, matric potential and sap flow). Within this approach we are able to set up two behavioral model structures which allow the simulation of the most important hydrological fluxes and state variables in good accordance with available observations within the 19.4 km2 large Colpach catchment and the 4.5 km2 large Wollefsbach catchment in Luxembourg without the necessity of calibration. This corroborates, contrary to the widespread opinion, that a) lower mesoscale catchments may be modelled by representative hillslopes and b) physically-based models can be parametrized based on comprehensive field data and a good perceptual model. Our results particularly indicate that the main challenge in understanding and modelling the seasonal water balance of a catchment is a proper representation of the phenological cycle of vegetation, not exclusively the structure of the subsurface and spatial variability of soil hydraulic parameters.

Constraining Distributed Catchment Models by Incorporating Perceptual Understanding of Spatial Hydrologic Behaviour

NASA Astrophysics Data System (ADS)

Hutton, Christopher; Wagener, Thorsten; Freer, Jim; Han, Dawei

2016-04-01

Distributed models offer the potential to resolve catchment systems in more detail, and therefore simulate the hydrological impacts of spatial changes in catchment forcing (e.g. landscape change). Such models tend to contain a large number of poorly defined and spatially varying model parameters which are therefore computationally expensive to calibrate. Insufficient data can result in model parameter and structural equifinality, particularly when calibration is reliant on catchment outlet discharge behaviour alone. Evaluating spatial patterns of internal hydrological behaviour has the potential to reveal simulations that, whilst consistent with measured outlet discharge, are qualitatively dissimilar to our perceptual understanding of how the system should behave. We argue that such understanding, which may be derived from stakeholder knowledge across different catchments for certain process dynamics, is a valuable source of information to help reject non-behavioural models, and therefore identify feasible model structures and parameters. The challenge, however, is to convert different sources of often qualitative and/or semi-qualitative information into robust quantitative constraints of model states and fluxes, and combine these sources of information together to reject models within an efficient calibration framework. Here we present the development of a framework to incorporate different sources of data to efficiently calibrate distributed catchment models. For each source of information, an interval or inequality is used to define the behaviour of the catchment system. These intervals are then combined to produce a hyper-volume in state space, which is used to identify behavioural models. We apply the methodology to calibrate the Penn State Integrated Hydrological Model (PIHM) at the Wye catchment, Plynlimon, UK. Outlet discharge behaviour is successfully simulated when perceptual understanding of relative groundwater levels between lowland peat, upland peat and valley slopes within the catchment are used to identify behavioural models. The process of converting qualitative information into quantitative constraints forces us to evaluate the assumptions behind our perceptual understanding in order to derive robust constraints, and therefore fairly reject models and avoid type II errors. Likewise, consideration needs to be given to the commensurability problem when mapping perceptual understanding to constrain model states.

Application of the MAGIC model to the Glacier Lakes catchments

Treesearch

John O. Reuss

1994-01-01

The MAGIC model (Cosby et al. 1985, 1986) was calibrated for East and West Glacier Lakes, two adjacent high-altitude (3200 m- 3700 m) catchments in the Medicine Bow National Forest of southern Wyoming. This model uses catchment characteristics including weathering rates, soil chemical characteristics, hydrological parameters, and precipitation amounts and composition...

Reducing surface water pollution through the assessment of the cost-effectiveness of BMPs at different spatial scales.

PubMed

Panagopoulos, Y; Makropoulos, C; Mimikou, M

2011-10-01

Two kinds of agricultural Best Management Practices (BMPs) were examined with respect to cost-effectiveness (CE) in reducing sediment, nitrates-nitrogen (NO(3)-N) and total phosphorus (TP) losses to surface waters of the Arachtos catchment in Western Greece. The establishment of filter strips at the edge of fields and a non-structural measure, namely fertilization reduction in alfalfa, combined with contour farming and zero-tillage in corn and reduction of animal numbers in pastureland, were evaluated. The Soil and Water Assessment Tool (SWAT) model was used as the non-point-source (NPS) estimator, while a simple economic component was developed estimating BMP implementation cost as the mean annual expenses needed to undertake and operate the practice for a 5-year period. After each BMP implementation, the ratio of their CE in reducing pollution was calculated for each Hydrologic Response Unit (HRU) separately, for each agricultural land use type entirely and for the whole catchment. The results at the HRU scale are presented comprehensively on a map, demonstrating the spatial differentiation of CE ratios across the catchment that enhances the identification of locations where each BMP is most advisable for implementation. Based on the analysis, a catchment management solution of affordable total cost would include the expensive measure of filter strips in corn and only in a small number of pastureland fields, in combination with the profitable measure of reducing fertilization to alfalfa fields. When examined for its impact on river loads at the outlet, the latter measure led to a 20 tn or 8% annual decrease of TP from the baseline with savings of 15€/kg of pollutant reduction. Filter strips in corn fields reduced annual sediments by 66 Ktn or 5%, NO(3)-N by 71 tn or 9.5% and TP by 27 tn or 10%, with an additional cost of 3.1 €/tn, 3.3 €/kg and 8.1 €/kg of each pollutant respectively. The study concludes that considerable reductions of several pollutant types at the same time can be achieved, even at low total cost, by combining targeted BMP implementation strategies only in small parts of the catchment, also enabling policy makers to take local socio-economic constraints into consideration. The methodology and the results presented aim to facilitate decision making for a cost-effective management of diffuse pollution by enabling modelers and researchers to make rapid and reliable BMP cost estimations and thus being able to calculate their CE at the local level in order to identify the most suitable areas for their implementation. Copyright © 2011 Elsevier Ltd. All rights reserved.

Chapter 16Tracing Nitrogen Sources and Cycling in Catchments

USGS Publications Warehouse

Kendall, Carol

1998-01-01

This chapter focuses on the uses of isotopes to understand water chemistry.I Isotopic compositions generally cannot be interpreted successfully in the absence of other chemical and hydrologic data. The chapter focusses on uses of isotopes in tracing sources and cycling of nitrogen in the water-component of forested catchment, and on dissolved nitrate in shallow waters, nutrient uptake studies in agricultural areas, large-scale tracer experiments, groundwater contamination studies, food-web investigations, and uses of compound-specific stable isotope techniques. Shallow waters moving along a flowpath through a relatively uniform material and reacting with minerals probably do not achieve equilibrium but gradually approach some steady-state composition. The chapter also discusses the use of isotopic techniques to assess impacts of changes in land-management practices and land use on water quality. The analysis of individual molecular components for isotopic composition has much potential as a method for tracing the source, biogeochemistry, and degradation of organic liquids and gases because different materials have characteristic isotope spectrums or biomarkers.

Tracking changing X-ray contrast media application to an urban-influenced karst aquifer in the Wadi Shueib, Jordan.

PubMed

Zemann, Moritz; Wolf, Leif; Grimmeisen, Felix; Tiehm, Andreas; Klinger, Jochen; Hötzl, Heinz; Goldscheider, Nico

2015-03-01

Sewage input into a karst aquifer via leaking sewers and cesspits was investigated over five years in an urbanized catchment. Of 66 samples, analyzed for 25 pharmaceuticals, 91% indicated detectable concentrations. The former standard iodinated X-ray contrast medium (ICM) diatrizoic acid was detected most frequently. Remarkably, it was found more frequently in groundwater (79%, median: 54 ng/l) than in wastewater (21%, 120 ng/l), which is supposed to be the only source in this area. In contrast, iopamidol, a possible substitute, spread over the aquifer during the investigation period whereas concentrations were two orders of magnitude higher in wastewater than in groundwater. Knowledge about changing application of pharmaceuticals thus is essential to assess urban impacts on aquifers, especially when applying mass balances. Since correlated concentrations provide conclusive evidence that, for this catchment, nitrate in groundwater rather comes from urban than from rural sources, ICM are considered useful tracers. Copyright © 2015 Elsevier Ltd. All rights reserved.

Ecological effects of nitrogen deposition in the western United States

USGS Publications Warehouse

Fenn, M.E.; Baron, Jill S.; Allen, E.B.; Rueth, H.M.; Nydick, K.R.; Geiser, L.; Bowman, W.D.; Sickman, J.O.; Meixner, T.; Johnson, D.W.; Neitlich, P.

2003-01-01

In the western United States vast acreages of land are exposed to low levels of atmospheric nitrogen (N) deposition, with interspersed hotspots of elevated N deposition downwind of large, expanding metropolitan centers or large agricultural operations. Biological response studies in western North America demonstrate that some aquatic and terrestrial plant and microbial communities are significantly altered by N deposition. Greater plant productivity is counterbalanced by biotic community changes and deleterious effects on sensitive organisms (lichens and phytoplankton) that respond to low inputs of N (3 to 8 kilograms N per hectare per year). Streamwater nitrate concentrations are elevated in high-elevation catchments in Colorado and are unusually high in southern California and in some chaparral catchments in the southwestern Sierra Nevada. Chronic N deposition in the West is implicated in increased fire frequency in some areas and habitat alteration for threatened species. Between hotspots, N deposition is too low to cause noticeable effects or has not been studied.

Water-quality characteristics indicative of wastewater in selected streams in the upper Neuse River Basin, Durham and Orange Counties, North Carolina, from 2004 to 2013

USGS Publications Warehouse

Ferrell, Gloria M.; Yearout, Matthew S.; Grimes, Barbara H.; Graves, Alexandria K.; Fitzgerald, Sharon A.; Meyer, Michael T.

2014-01-01

During the third phase of data collection, May 2012 to January 2013, data were collected to address the suitability of optical brighteners as tracers of wastewater in small streams during streamflow recession. Samples were collected at five small streams following periods of rainfall and analyzed for optical brighteners, specific conductance nutrients, and selected hormones. Optical brighteners were absent in the undeveloped catchment but were present in the recession period after rainfall events in catchments with centralized though possibly leaky sewage treatment and areas with onsite treatment. Sand filter systems in areas with onsite treatment appear to change the effluent flow and retention characteristics such that optical brighteners were present both before and after rainfall events. Nitrate plus nitrite, as nitrogen concentrations in samples from this last study phase generally were larger than those collected during baseflow conditions in the previous phases of this study.

Modelling metaldehyde in catchments: a River Thames case-study.

PubMed

Lu, Q; Whitehead, P G; Bussi, G; Futter, M N; Nizzetto, L

2017-04-19

The application of metaldehyde to agricultural catchment areas to control slugs and snails has caused severe problems for drinking water supply in recent years. In the River Thames catchment, metaldehyde has been detected at levels well above the EU and UK drinking water standards of 0.1 μg l -1 at many sites across the catchment between 2008 and 2015. Metaldehyde is applied in autumn and winter, leading to its increased concentrations in surface waters. It is shown that a process-based hydro-biogeochemical transport model (INCA-contaminants) can be used to simulate metaldehyde transport in catchments from areas of application to the aquatic environment. Simulations indicate that high concentrations in the river system are a direct consequence of excessive application rates. A simple application control strategy for metaldehyde in the Thames catchment based on model results is presented.

N fluxes in two nitrogen saturated forested catchments in Germany: dynamics and modelling with INCA

NASA Astrophysics Data System (ADS)

Langusch, J.-J.; Matzner, E.

The N cycle in forests of the temperate zone in Europe has been changed substantially by the impact of atmospheric N deposition. Here, the fluxes and concentrations of mineral N in throughfall, soil solution and runoff in two German catchments, receiving high N inputs are investigated to test the applicability of an Integrated Nitrogen Model for European Catchments (INCA) to small forested catchments. The Lehstenbach catchment (419 ha) is located in the German Fichtelgebirge (NO Bavaria, 690-871 m asl.) and is stocked with Norway spruce (Picea abies (L.) Karst.) of different ages. The Steinkreuz catchment (55 ha) with European beech (Fagus sylvatica L.) as the dominant tree species is located in the Steigerwald (NW Bavaria, 400-460 m asl.). The mean annual N fluxes with throughfall were slightly higher at the Lehstenbach (24.6 kg N ha-1) than at the Steinkreuz (20.4 kg N ha-1). In both catchments the N fluxes in the soil are dominated by NO3. At Lehstenbach, the N output with seepage at 90 cm soil depth was similar to the N flux with throughfall. At Steinkreuz more than 50 % of the N deposited was retained in the upper soil horizons. In both catchments, the NO3 fluxes with runoff were lower than those with seepage. The average annual NO3 concentrations in runoff in both catchments were between 0.7 to 1.4 mg NO3-N L-1 and no temporal trend was observed. The N budgets at the catchment scale indicated similar amounts of N retention (Lehstenbach: 19 kg N ha-1yr-1 ; Steinkreuz: 17 kg N ha-1yr-1). The parameter settings of the INCA model were simplified to reduce the model complexity. In both catchments, the NO3 concentrations and fluxes in runoff were matched well by the model. The seasonal patterns with lower NO3 runoff concentrations in summer at the Lehstenbach catchment were replicated. INCA underestimated the increased N3 concentrations during short periods of rewetting in late autumn at the Steinkreuz catchment. The model will be a helpful tool for the calculation of "critical loads"? for the N deposition in Central European forests including different hydrological regimes.

Benefits of incorporating spatial organisation of catchments for a semi-distributed hydrological model

NASA Astrophysics Data System (ADS)

Schumann, Andreas; Oppel, Henning

2017-04-01

To represent the hydrological behaviour of catchments a model should reproduce/reflect the hydrologically most relevant catchment characteristics. These are heterogeneously distributed within a watershed but often interrelated and subject of a certain spatial organisation. Since common models are mostly based on fundamental assumptions about hydrological processes, the reduction of variance of catchment properties as well as the incorporation of the spatial organisation of the catchment is desirable. We have developed a method that combines the idea of the width-function used for determination of the geomorphologic unit hydrograph with information about soil or topography. With this method we are able to assess the spatial organisation of selected catchment characteristics. An algorithm was developed that structures a watershed into sub-basins and other spatial units to minimise its heterogeneity. The outcomes of this algorithm are used for the spatial setup of a semi-distributed model. Since the spatial organisation of a catchment is not bound to a single characteristic, we have to embed information of multiple catchment properties. For this purpose we applied a fuzzy-based method to combine the spatial setup for multiple single characteristics into a union, optimal spatial differentiation. Utilizing this method, we are able to propose a spatial structure for a semi-distributed hydrological model, comprising the definition of sub-basins and a zonal classification within each sub-basin. Besides the improved spatial structuring, the performed analysis ameliorates modelling in another way. The spatial variability of catchment characteristics, which is considered by a minimum of heterogeneity in the zones, can be considered in a parameter constrained calibration scheme in a case study both options were used to explore the benefits of incorporating the spatial organisation and derived parameter constraints for the parametrisation of a HBV-96 model. We use two benchmark model setups (lumped and semi-distributed by common approaches) to address the benefits for different time and spatial scales. Moreover, the benefits for calibration effort, model performance in validation periods and process extrapolation are shown.

Regional estimation of response routine parameters

NASA Astrophysics Data System (ADS)

Tøfte, Lena S.

2015-04-01

Reducing the number of calibration parameters is of a considerable advantage when area distributed hydrological models are to be calibrated, both due to equifinality and over-parameterization of the model in general, and for making the calibration process more efficient. A simple non-threshold response model for drainage in natural catchments based on among others Kirchner's article in WRR 2009 is implemented in the gridded hydrological model in the ENKI framework. This response model takes only the hydrogram into account; it has one state and two parameters, and is adapted to catchments that are dominated by terrain drainage. In former analyses of natural discharge series from a large number of catchments in different regions of Norway, we found that these response model parameters can be calculated from some known catchment characteristics, as catchment area and lake percentage, found in maps or data bases, meaning that the parameters can easily be found also for ungauged catchments. In the presented work from the EU project COMPLEX a large region in Mid-Norway containing 27 simulated catchments of different sizes and characteristics is calibrated. Results from two different calibration strategies are compared: 1) removing the response parameters from the calibration by calculating them in advance, based on the results from our former studies, and 2) including the response parameters in the calibration, both as maps with different values for each catchment, and as a constant number for the total region. The resulting simulation performances are compared and discussed.

Sediment transport in forested head water catchments - Calibration and validation of a soil erosion and landscape evolution model

NASA Astrophysics Data System (ADS)

Hancock, G. R.; Webb, A. A.; Turner, L.

2017-11-01

Sediment transport and soil erosion can be determined by a variety of field and modelling approaches. Computer based soil erosion and landscape evolution models (LEMs) offer the potential to be reliable assessment and prediction tools. An advantage of such models is that they provide both erosion and deposition patterns as well as total catchment sediment output. However, before use, like all models they require calibration and validation. In recent years LEMs have been used for a variety of both natural and disturbed landscape assessment. However, these models have not been evaluated for their reliability in steep forested catchments. Here, the SIBERIA LEM is calibrated and evaluated for its reliability for two steep forested catchments in south-eastern Australia. The model is independently calibrated using two methods. Firstly, hydrology and sediment transport parameters are inferred from catchment geomorphology and soil properties and secondly from catchment sediment transport and discharge data. The results demonstrate that both calibration methods provide similar parameters and reliable modelled sediment transport output. A sensitivity study of the input parameters demonstrates the model's sensitivity to correct parameterisation and also how the model could be used to assess potential timber harvesting as well as the removal of vegetation by fire.

The SMAP Level-4 ECO Project: Linking the Terrestrial Water and Carbon Cycles

NASA Technical Reports Server (NTRS)

Kolassa, J.; Reichle, R. H.; Liu, Qing; Koster, Randal D.

2017-01-01

The SMAP (Soil Moisture Active Passive) Level-4 projects aims to develop a fully coupled hydrology-vegetation data assimilation algorithm to generate improved estimates of modeled hydrological fields and carbon fluxes. This includes using the new NASA Catchment-CN (Catchment-Carbon-Nitrogen) model, which combines the Catchment land surface hydrology model with dynamic vegetation components from the Community Land Model version 4 (CLM4). As such, Catchment-CN allows a more realistic, fully coupled feedback between the land hydrology and the biosphere. The L4 ECO project further aims to inform the model through the assimilation of Soil Moisture Active Passive (SMAP) brightness temperature observations as well as observations of Moderate Resolution Imaging Spectroradiometer (MODIS) fraction of absorbed photosynthetically active radiation (FPAR). Preliminary results show that the assimilation of SMAP observations leads to consistent improvements in the model soil moisture skill. An evaluation of the Catchment-CN modeled vegetation characteristics showed that a calibration of the model's vegetation parameters is required before an assimilation of MODIS FPAR observations is feasible.

Stormflow generation: a meta-analysis of field studies and research catchments

NASA Astrophysics Data System (ADS)

Barthold, Frauke; Elsenbeer, Helmut

2014-05-01

Runoff characteristics are expressions of runoff generation mechanisms. In this study, we want to test the hypothesis if storm hydrographs of catchments with prevailing near-surface flow paths are dominated by new water. We aim to test this hypothesis using published data from the scientific literature. We developed a classification system based on three runoff characteristics: (1) hydrograph response (HR: slowly or quickly), (2) the temporal source of water that dominates the hydrograph (TS: pre-event vs. event water) and (3) the flow paths that the water takes until it is released to the stream (FP: subsurface vs. surface flow paths). We then performed a literature survey to collect information on these runoff characteristics for small, forested headwater catchments that served as study areas in runoff generation studies and assigned each study catchment to one of the 8 classes. For this purpose, we designed a procedure to objectively diagnose the predominant conceptual model of storm flow generation in each catchment and assess its temporal and spatial relevance for the catchment. Finally, we performed an explorative analysis of the classified research catchments and summarized field evidence. Our literature survey yielded a sample of 22 research catchments that fell within our defined criteria (small, naturally forested catchments which served as study areas in stormflow generation studies). We applied our classification procedure to all of these catchments. Among them were 14 catchments for which our meta-analysis yielded a complete set of stormflow characteristics resulting in one of the 8 model concepts and were assigned into our classification scheme. Of the 14 classified research catchments, 10 were dominated by subsurface flow paths while 4 were dominated by overland flow. The data also indicate that the spatial and temporal relevance is high for catchments with subsurface flow paths while often weak for surface flow paths dominated catchments. The catalogue of catchments supports our hypothesis; however, it is afflicted with a relative high degree of uncertainty. Two theories exist that may explain the imbalance between surface and subsurface dominated catchments: (1) the selection of research sites for stormflow generation studies was guided by the leading research question in hydrology, i.e. to address the "old water paradox", and (2) catchments with prevailing subsurface flow paths are much more common in nature. In a next step, the proposed catalogue of research catchments allows correlation of environmental characteristics with runoff characteristics to address questions of catchment organization and similarity. However, the successful application and relevance of such an approach depends on the range of conceptual models for which field support exist. Our results prompt us to highlight future research needs: (1) in order to cover a broader range of combinations of runoff characteristics a careful selection of research sites is necessary and (2) propose guidelines for field studies in order achieve higher comparability of resulting conceptual models of research sites and increase the spatial and temporal relevance of the dominant conceptual model.

A Catchment-Based Approach to Modeling Land Surface Processes in a GCM. Part 1; Model Structure

NASA Technical Reports Server (NTRS)

Koster, Randal D.; Suarez, Max J.; Ducharne, Agnes; Stieglitz, Marc; Kumar, Praveen

2000-01-01

A new strategy for modeling the land surface component of the climate system is described. The strategy is motivated by an arguable deficiency in most state-of-the-art land surface models (LSMs), namely the disproportionately higher emphasis given to the formulation of one-dimensional, vertical physics relative to the treatment of horizontal heterogeneity in surface properties -- particularly subgrid soil moisture variability and its effects on runoff generation. The new strategy calls for the partitioning of the continental surface into a mosaic of hydrologic catchments, delineated through analysis of high-resolution surface elevation data. The effective "grid" used for the land surface is therefore not specified by the overlying atmospheric grid. Within each catchment, the variability of soil moisture is related to characteristics of the topography and to three bulk soil moisture variables through a well-established model of catchment processes. This modeled variability allows the partitioning of the catchment into several areas representing distinct hydrological regimes, wherein distinct (regime-specific) evaporation and runoff parameterizations are applied. Care is taken to ensure that the deficiencies of the catchment model in regions of little to moderate topography are minimized.

Modelling catchment areas for secondary care providers: a case study.

PubMed

Jones, Simon; Wardlaw, Jessica; Crouch, Susan; Carolan, Michelle

2011-09-01

Hospitals need to understand patient flows in an increasingly competitive health economy. New initiatives like Patient Choice and the Darzi Review further increase this demand. Essential to understanding patient flows are demographic and geographic profiles of health care service providers, known as 'catchment areas' and 'catchment populations'. This information helps Primary Care Trusts (PCTs) to review how their populations are accessing services, measure inequalities and commission services; likewise it assists Secondary Care Providers (SCPs) to measure and assess potential gains in market share, redesign services, evaluate admission thresholds and plan financial budgets. Unlike PCTs, SCPs do not operate within fixed geographic boundaries. Traditionally, SCPs have used administrative boundaries or arbitrary drive times to model catchment areas. Neither approach satisfactorily represents current patient flows. Furthermore, these techniques are time-consuming and can be challenging for healthcare managers to exploit. This paper presents three different approaches to define catchment areas, each more detailed than the previous method. The first approach 'First Past the Post' defines catchment areas by allocating a dominant SCP to each Census Output Area (OA). The SCP with the highest proportion of activity within each OA is considered the dominant SCP. The second approach 'Proportional Flow' allocates activity proportionally to each OA. This approach allows for cross-boundary flows to be captured in a catchment area. The third and final approach uses a gravity model to define a catchment area, which incorporates drive or travel time into the analysis. Comparing approaches helps healthcare providers to understand whether using more traditional and simplistic approaches to define catchment areas and populations achieves the same or similar results as complex mathematical modelling. This paper has demonstrated, using a case study of Manchester, that when estimating the catchment area of a planned new hospital, the extra level of detail provided by the gravity model may prove necessary. However, in virtually all other applications, the Proportional Flow method produced the optimal model for catchment populations in Manchester, based on several criteria: it produced the smallest RMS error; it addressed cross-boundary flows; the data used to create the catchment was readily available to SCPs; and it was simpler to reproduce than the gravity model method. Further work is needed to address how the Proportional Flow method can be used to reflect service redesign and handle OAs with zero or low activity. A next step should be the rolling out of the method across England and looking at further drill downs of data such as catchment by Healthcare Resource Group (HRG) rather than specialty level.

Combining abiotic and biotic models - Hydraulical modeling to fill the gap between catchment and hydro-dynamic models

NASA Astrophysics Data System (ADS)

Guse, B.; Sulc, D.; Schmalz, B.; Fohrer, N.

2012-04-01

The European Water Framework Directive (WFD) requires a catchment-based approach, which is assessed in the IMPACT project by combining abiotic and biotic models. The core point of IMPACT is a model chain (catchment model -> 1-D-hydraulic model -> 3-D-hydro-morphodynamic model -> biotic habitat model) with the aim to estimate the occurrence of the target species of the WFD. Firstly, the model chain is developed for the current land use and climate conditions. Secondly, land use and climate change scenarios are developed at the catchment scale. The outputs of the catchment model for the scenarios are used as input for the next models within the model chain to estimate the effect of these changes on the target species. The eco-hydrological catchment model SWAT is applied for the Treene catchment in Northern Germany and delivers discharge and water quality parameters as a spatial explicit output for each subbasin. There is no water level information given by SWAT. However, water level values are needed as lower boundary condition for the hydro-dynamic and habitat models which are applied for the 300 m candidate reference reach. In order to fill the gap between the catchment and the hydro-morphodynamic model, the 1-D hydraulic model HEC-RAS is applied for a 3 km long reach transect from the next upstream hydrological station until the upper bound of the candidate study reach. The channel geometry for HEC-RAS was estimated based on 96 cross-sections which were measured in the IMPACT project. By using available discharge and water level measurements from the hydrological station and own flow velocity measurements, the channel resistence was estimated. HEC-RAS was run with different statistical indices (mean annual drought, mean discharge, …) for steady flow conditions. The rating curve was then constructed for the target cross-section, i.e. the lower bound of the candidate study reach, to fulfill the combining with the hydro- and morphodynamic models. These statistical indices can also be calculated for the discharge series provided by land use and climate scenarios. In this way, the effect of land use and climate change on the catchment and the hydraulic processes can be assessed.

Assessment of Spatial Transferability of Process-Based Hydrological Model Parameters in Two Neighboring Catchments in the Himalayan Region

NASA Astrophysics Data System (ADS)

Nepal, S.

2016-12-01

The spatial transferability of the model parameters of the process-oriented distributed J2000 hydrological model was investigated in two glaciated sub-catchments of the Koshi river basin in eastern Nepal. The basins had a high degree of similarity with respect to their static landscape features. The model was first calibrated (1986-1991) and validated (1992-1997) in the Dudh Koshi sub-catchment. The calibrated and validated model parameters were then transferred to the nearby Tamor catchment (2001-2009). A sensitivity and uncertainty analysis was carried out for both sub-catchments to discover the sensitivity range of the parameters in the two catchments. The model represented the overall hydrograph well in both sub-catchments, including baseflow and medium range flows (rising and recession limbs). The efficiency results according to both Nash-Sutcliffe and the coefficient of determination was above 0.84 in both cases. The sensitivity analysis showed that the same parameter was most sensitive for Nash-Sutcliffe (ENS) and Log Nash-Sutcliffe (LNS) efficiencies in both catchments. However, there were some differences in sensitivity to ENS and LNS for moderate and low sensitive parameters, although the majority (13 out of 16 for ENS and 16 out of 16 for LNS) had a sensitivity response in a similar range. A generalized likelihood uncertainty estimation (GLUE) result suggest that most of the time the observed runoff is within the parameter uncertainty range, although occasionally the values lie outside the uncertainty range, especially during flood peaks and more in the Tamor. This may be due to the limited input data resulting from the small number of precipitation stations and lack of representative stations in high-altitude areas, as well as to model structural uncertainty. The results indicate that transfer of the J2000 parameters to a neighboring catchment in the Himalayan region with similar physiographic landscape characteristics is viable. This indicates the possibility of applying process-based J2000 model be to the ungauged catchments in the Himalayan region, which could provide important insights into the hydrological system dynamics and provide much needed information to support water resources planning and management.

Modeling seasonal water balance based on catchments' hedging strategy on evapotranspiration for climate seasonality

NASA Astrophysics Data System (ADS)

Wu, S.; Zhao, J.; Wang, H.

2017-12-01

This paper develops a seasonal water balance model based on the hypothesis that natural catchments utilize hedging strategy on evapotranspiration for climate seasonality. According to the monthly aridity index, one year is split into wet season and dry season. A seasonal water balance model is developed by analogy to a two-stage reservoir operation model, in which seasonal rainfall infiltration, evapotranspiration and saturation-excess runoff is corresponding to the inflow, release and surplus of the catchment system. Then the optimal hedging between wet season and dry season evapotranspiration is analytically derived with marginal benefit principle. Water budget data sets of 320 catchments in the United States covering the period from 1980 to 2010 are used to evaluate the performance of this model. The Nash-Sutcliffe Efficiency coefficient for evapotranspiration is higher than 0.5 in 84% of the study catchments; while the runoff is 87%. This paper validates catchments' hedging strategy on evapotranspiration for climate seasonality and shows its potential application for seasonal water balance, which is valuable for water resources planning and management.

An evaluation of Dynamic TOPMODEL in natural and human-impacted catchments for low flow simulation

NASA Astrophysics Data System (ADS)

Coxon, Gemma; Freer, Jim; Lane, Rosanna; Musuuza, Jude; Woods, Ross; Wagener, Thorsten; Howden, Nicholas

2017-04-01

Models of catchment hydrology are essential tools for drought risk management, often providing input to water resource system models, aiding our understanding of low flow processes within catchments and providing low flow simulations and predictions. However, simulating low flows is challenging as hydrological systems often demonstrate threshold effects in connectivity, non-linear groundwater contributions and a greater influence of anthropogenic modifications such as surface and ground water abstractions during low flow periods. These processes are typically not well represented in commonly used hydrological models due to knowledge, data and model limitations. Hence, a better understanding of the natural and human processes that occur during low flows, how these are represented within models and how they could be improved is required to be able to provide robust and reliable predictions of future drought events. The aim of this study is to assess the skill of dynamic TOPMODEL during low flows for both natural and human-impacted catchments. Dynamic TOPMODEL was chosen for this study as it is able to explicitly characterise connectivity and fluxes across landscapes using hydrological response units (HRU's) while still maintaining flexibility in how spatially complex the model is configured and what specific functions (i.e. abstractions or groundwater stores) are represented. We apply dynamic TOPMODEL across the River Thames catchment using daily time series of observed rainfall and potential evapotranspiration data for the period 1999 - 2014, covering two major droughts in the Thames catchment. Significantly, to assess the impact of abstractions on low flows across the Thames catchment, we incorporate functions to characterise over 3,500 monthly surface water and ground water abstractions covering the simulation period into dynamic TOPMODEL. We evaluate dynamic TOPMODEL at over 90 gauging stations across the Thames catchment against multiple signatures of catchment low-flow behaviour in a 'limits of acceptability' GLUE framework. We investigate differences in model performance between signatures, different low flow periods and for natural and human impacted catchments to better understand the ability of dynamic TOPMODEL to represent low flows in space and time. Finally, we discuss future developments of dynamic TOPMODEL to improve low flow simulation and the implications of these results for modelling hydrological extremes in natural and human impacted catchments across the UK and the world.

Regionalization of response routine parameters

NASA Astrophysics Data System (ADS)

Tøfte, Lena S.; Sultan, Yisak A.

2013-04-01

When area distributed hydrological models are to be calibrated or updated, fewer calibration parameters is of a considerable advantage. Based on, among others, Kirchner, we have developed a simple non-threshold response model for drainage in natural catchments, to be used in the gridded hydrological model ENKI. The new response model takes only the hydrogram into account, it has one state and two parameters, and is adapted to catchments that are dominated by terrain drainage. The method is based on the assumption that in catchments where precipitation, evaporation and snowmelt is neglect able, the discharge is entirely determined by the amount of stored water. It can then be characterized as a simple first-order nonlinear dynamical system, where the governing equations can be found directly from measured stream flow fluctuations. This means that the response in the catchment can be modelled by using hydrogram data where all data from periods with rain, snowmelt or evaporation is left out, and adjust these series to a two or three parameter equation. A large number of discharge series from catchments in different regions in Norway are analyzed, and parameters found for all the series. By combining the computed parameters and known catchments characteristics, we try to regionalize the parameters. Then the parameters in the response routine can easily be found also for ungauged catchments, from maps or data bases.

Connections among soil, ground, and surface water chemistries characterize nitrogen loss from an agricultural landscape in the upper Missouri River Basin

NASA Astrophysics Data System (ADS)

Sigler, W. Adam; Ewing, Stephanie A.; Jones, Clain A.; Payn, Robert A.; Brookshire, E. N. Jack; Klassen, Jane K.; Jackson-Smith, Douglas; Weissmann, Gary S.

2018-01-01

Elevated nitrate in shallow aquifers is common in agricultural areas and remediation requires an understanding of nitrogen (N) leaching at a variety of spatial scales. Characterization of the drivers of nitrate leaching at the mesoscale level (102-103 km2) is needed to bridge from field-scale observations to the landscape-scale context, allowing informed water resource management decisions. Here we explore patterns in nitrate leaching rates across a depositional landform in the northern Great Plains within the Upper Missouri Basin, where the predominant land use is non-irrigated small grain production, and nitrate-N concentrations above 10 mg L-1 are common. The shallow Moccasin terrace (260 km2) aquifer is bounded in vertical extent by underlying shale and is isolated from mountain front stream recharge, such that aquifer recharge is dominated by infiltration of precipitation through agricultural soils. This configuration presents a simple landform-scale water balance that we leveraged to estimate leaching rates using groundwater nitrate concentrations and surface water discharge, and quantify uncertainty using a Monte Carlo approach based on spatial variation in observations of groundwater nitrate concentrations. A participatory research approach allowed local farmer knowledge of the landscape to be incorporated into the study design, improved selection of and access to sample sites, and enhanced prospects for addressing nitrate leaching through collaborative understanding of system hydrology. Mean landform-scale nitrate-N leaching rates were 11 and 18 kg ha-1 yr-1 during the 2012-2014 study for the two largest catchments draining the terrace. Over a standard three-year crop rotation, these leaching rates represent 19-31% of typical fertilizer N application rates; however, leaching losses are likely derived not only from fertilizer but also from soil organic N mineralization, and are apparently higher during the post-fallow phase of the crop rotation. Groundwater apparent age is relatively young (0-5 yr) based on tritium-helium analysis, but whole-aquifer turnover time calculations are an order of magnitude longer (20-23 yr), suggesting changes in groundwater may lag behind changes in land management by years to decades.

Influences of Hydrological Regime on Runoff Quality and Pollutant Loadings in Tropical Urban Areas

NASA Astrophysics Data System (ADS)

Chow, M.; Yusop, Z.

2011-12-01

Experience in many developed countries suggests that non point source (NPS) pollution is still the main contributor to pollutant loadings into water bodies in urban areas. However, the mechanism of NPS pollutant transport and the influences of hydrologic regime on the pollutant loading are still unclear. Understanding these interactions will be useful for improving design criteria and strategies for controlling NPS pollution in urban areas. This issue is also extremely relevant in tropical environment because its rainfall and the runoff generation processes are so different from the temperate regions where most of the studies on NPS pollutant have been carried out. In this regard, an intensive study to investigate the extent of this pollution was carried out in Skudai, Johor, Malaysia. Three small catchments, each represents commercial, residential and industrial land use were selected. Stormwater samples and flow rate data were collected at these catchments over 52 storm events from year 2008 to 2009. Samples were analyzed for ten water quality constituents including total suspended solids, 5-day biochemical oxygen demand, chemical oxygen demand, oil and grease, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, soluble phosphorus, total phosphorus and zinc. Quality of stormwater runoff is estimated using Event Mean Concentration (EMC) value. The storm characteristics analyzed included rainfall depth, rainfall duration, mean intensity, max 5 minutes intensity, antecedent dry day, runoff volume and peak flow. Correlation coefficients were determined between storm parameters and EMCs for the residential, commercial and industrial catchments. Except for the antecedent storm mean intensity and antecedent dry days, the other rainfall and runoff variables were negatively correlated with EMCs of most pollutants. This study reinforced the earlier findings on the importance of antecedent dry days for causing greater EMC values with exceptions for oil and grease, nitrate nitrogen, total phosphorus and zinc. There is no positive correlation between rainfall intensity and EMC of constituents in all the studied catchments. In contrast, the pollutant loadings are influenced primarily by the rainfall and runoff characteristics. Rainfall depth, mean intensity, max 5 minute intensity, runoff volume and peak flow were positively correlated with the loadings of most of the constituents. Antecedent storm mean intensity and antecedent dry days seemed to be less important for estimating the pollutant loadings. Such study should be further conducted for acquiring a long term monitoring data related to storm runoff quality during rainfall, in order to have a better understanding on NPS pollution in urban areas.

A temporal-spatial postprocessing model for probabilistic run-off forecast. With a case study from Ulla-Førre with five catchments and ten lead times

NASA Astrophysics Data System (ADS)

Engeland, K.; Steinsland, I.

2012-04-01

This work is driven by the needs of next generation short term optimization methodology for hydro power production. Stochastic optimization are about to be introduced; i.e. optimizing when available resources (water) and utility (prices) are uncertain. In this paper we focus on the available resources, i.e. water, where uncertainty mainly comes from uncertainty in future runoff. When optimizing a water system all catchments and several lead times have to be considered simultaneously. Depending on the system of hydropower reservoirs, it might be a set of headwater catchments, a system of upstream /downstream reservoirs where water used from one catchment /dam arrives in a lower catchment maybe days later, or a combination of both. The aim of this paper is therefore to construct a simultaneous probabilistic forecast for several catchments and lead times, i.e. to provide a predictive distribution for the forecasts. Stochastic optimization methods need samples/ensembles of run-off forecasts as input. Hence, it should also be possible to sample from our probabilistic forecast. A post-processing approach is taken, and an error model based on Box- Cox transformation, power transform and a temporal-spatial copula model is used. It accounts for both between catchment and between lead time dependencies. In operational use it is strait forward to sample run-off ensembles from this models that inherits the catchment and lead time dependencies. The methodology is tested and demonstrated in the Ulla-Førre river system, and simultaneous probabilistic forecasts for five catchments and ten lead times are constructed. The methodology has enough flexibility to model operationally important features in this case study such as hetroscadasety, lead-time varying temporal dependency and lead-time varying inter-catchment dependency. Our model is evaluated using CRPS for marginal predictive distributions and energy score for joint predictive distribution. It is tested against deterministic run-off forecast, climatology forecast and a persistent forecast, and is found to be the better probabilistic forecast for lead time grater then two. From an operational point of view the results are interesting as the between catchment dependency gets stronger with longer lead-times.

Investigating low flow process controls, through complex modelling, in a UK chalk catchment

NASA Astrophysics Data System (ADS)

Lubega Musuuza, Jude; Wagener, Thorsten; Coxon, Gemma; Freer, Jim; Woods, Ross; Howden, Nicholas

2017-04-01

The typical streamflow response of Chalk catchments is dominated by groundwater contributions due the high degree of groundwater recharge through preferential flow pathways. The groundwater store attenuates the precipitation signal, which causes a delay between the corresponding high and low extremes in the precipitation and the stream flow signals. Streamflow responses can therefore be quite out of phase with the precipitation input to a Chalk catchment. Therefore characterising such catchment systems, including modelling approaches, clearly need to reproduce these percolation and groundwater dominated pathways to capture these dominant flow pathways. The simulation of low flow conditions for chalk catchments in numerical models is especially difficult due to the complex interactions between various processes that may not be adequately represented or resolved in the models. Periods of low stream flows are particularly important due to competing water uses in the summer, including agriculture and water supply. In this study we apply and evaluate the physically-based Pennstate Integrated Hydrologic Model (PIHM) to the River Kennet, a sub-catchment of the Thames Basin, to demonstrate how the simulations of a chalk catchment are improved by a physically-based system representation. We also use an ensemble of simulations to investigate the sensitivity of various hydrologic signatures (relevant to low flows and droughts) to the different parameters in the model, thereby inferring the levels of control exerted by the processes that the parameters represent.

Investigating the relationship between a soils classification and the spatial parameters of a conceptual catchment-scale hydrological model

NASA Astrophysics Data System (ADS)

Dunn, S. M.; Lilly, A.

2001-10-01

There are now many examples of hydrological models that utilise the capabilities of Geographic Information Systems to generate spatially distributed predictions of behaviour. However, the spatial variability of hydrological parameters relating to distributions of soils and vegetation can be hard to establish. In this paper, the relationship between a soil hydrological classification Hydrology of Soil Types (HOST) and the spatial parameters of a conceptual catchment-scale model is investigated. A procedure involving inverse modelling using Monte-Carlo simulations on two catchments is developed to identify relative values for soil related parameters of the DIY model. The relative values determine the internal variability of hydrological processes as a function of the soil type. For three out of the four soil parameters studied, the variability between HOST classes was found to be consistent across two catchments when tested independently. Problems in identifying values for the fourth 'fast response distance' parameter have highlighted a potential limitation with the present structure of the model. The present assumption that this parameter can be related simply to soil type rather than topography appears to be inadequate. With the exclusion of this parameter, calibrated parameter sets from one catchment can be converted into equivalent parameter sets for the alternate catchment on the basis of their HOST distributions, to give a reasonable simulation of flow. Following further testing on different catchments, and modifications to the definition of the fast response distance parameter, the technique provides a methodology whereby it is possible to directly derive spatial soil parameters for new catchments.

Modeling the behavior of an ungauged catchment using alternative datasets: a case study of the Caribou catchment in Canada

NASA Astrophysics Data System (ADS)

Labrecque, Geneviève; Boucher, Marie-Amélie; Chesnaux, Romain

2017-04-01

The modelling of ungauged catchments is a long standing problem in hydrology and there is still no general consensus regarding the best practices to adopt in a variety of situations. In addition to flood and drought forecasting, there are other interests of modelling the hydrological behaviour of a catchment, whether it is gauged or not. For instance, estimation of groundwater recharge can be performed through an integrated modeling of the catchment. In this study, the WaSim model is used to model the hydrology of the Caribou River catchment located in the province of Quebec, in Canada. Since this catchment includes an important aquifer that is used both for drinking water, industrial and potential agricultural purposes, an accurate recharge assessment is important and is the long-term objective of the project. The WaSim model was chosen due to its very versatile soil sub-model features which allow to simulate subsurface flows and calculate the groundwater recharge as an output variable. Since the Caribou River is ungauged, alternative means of calibrating the free parameters of WaSim had to be implemented. The implementation of a calibration protocol that can get the most out of the few available data is a secondary objective and is the subject of this presentation. First, a « twin » gauged catchment is selected for its physiographic and hydro-climatic similarities with the Caribou River catchment. Streamflow series from this « twin » catchment are then transferred and used jointly with the dynamically dimensioned search (DDS) algorithm (Tolson and Shoemaker 2007) to obtain a raw calibration of the WaSim model parameters. This initial calibration can be further refined using two available datasets: (1) snow water equivalent data interpolated on a 10 km by 10 km grid and (2) a short and discontinuous time series of streamflow obtained using the land-surface scheme of the environmental multiscale atmospheric model (GEM) at Environment and Climate Change Canada and a unit-hydrograph based routing model. The parameters thus obtained are then validated with a few point measurements of streamflow collected at two locations on the Caribou River during a field campaign realized in 2016-2017. The model performance is assessed using the mean absolute error (MAE) and the results show a satisfactory agreement of the WaSim model with the measured values. References: Tolson, B. A., and C. A. Shoemaker. 2007. "Dynamically dimensioned search algorithm for computationally efficient watershed model calibration." Water Resources Research 43 (1). doi: 10.1029/2005wr004723.

How old is streamwater? Open questions in catchment transit time conceptualization, modeling and analysis

Treesearch

J.J. McDonnell; K. McGuire; P. Aggarwal; K.J. Beven; D. Biondi; G. Destouni; S. Dunn; A. James; J. Kirchner; P. Kraft; S. Lyon; P. Maloszewski; B. Newman; L. Pfister; A. Rinaldo; A. Rodhe; T. Sayama; J. Seibert; K. Solomon; C. Soulsby; M. Stewart; D. Tetzlaff; C. Tobin; P. Troch; M. Weiler; A. Western; A. Wörman; S. Wrede

2010-01-01

The time water spends travelling subsurface through a catchment to the stream network (i.e. the catchment water transit time) fundamentally describes the storage, flow pathway heterogeneity and sources of water in a catchment. The distribution of transit times reflects how catchments retain and release water and solutes that in turn set biogeochemical conditions and...

A long-term data set for hydrologic modeling in a snow-dominated mountain catchment

USDA-ARS?s Scientific Manuscript database

An hourly modeling data set is presented for the water years 1984 through 2008 for a snow-dominated headwater catchment. Meteorological forcing data and GIS watershed characteristics are described and provided. The meteorological data are measured at two sites within the catchment, and include pre...

Effects of harvest on carbon and nitrogen dynamics in a Pacific Northwest forest catchment

EPA Science Inventory

We used a new ecohydrological model, Visualizing Ecosystems for Land Management Assessments (VELMA), to analyze the effects of forest harvest on catchment carbon and nitrogen dynamics. We applied the model to a 10 ha headwater catchment in the western Oregon Cascade Range where t...

Estimation of total nitrogen and total phosphorus in streams of the Middle Columbia River Basin (Oregon, Washington, and Idaho) using SPARROW models, with emphasis on the Yakima River Basin, Washington

USGS Publications Warehouse

Johnson, Henry M.; Black, Robert W.; Wise, Daniel R.

2013-01-01

The watershed model SPARROW (Spatially Related Regressions on Watershed attributes) was used to predict total nitrogen (TN) and total phosphorus (TP) loads and yields for the Middle Columbia River Basin in Idaho, Oregon, and Washington. The new models build on recently published models for the entire Pacific Northwest, and provide revised load predictions for the arid interior of the region by restricting the modeling domain and recalibrating the models. Results from the new TN and TP models are provided for the entire region, and discussed with special emphasis on the Yakima River Basin, Washington. In most catchments of the Yakima River Basin, the TN and TP in streams is from natural sources, specifically nitrogen fixation in forests (TN) and weathering and erosion of geologic materials (TP). The natural nutrient sources are overshadowed by anthropogenic sources of TN and TP in highly agricultural and urbanized catchments; downstream of the city of Yakima, most of the load in the Yakima River is derived from anthropogenic sources. Yields of TN and TP from catchments with nearly uniform land use were compared with other yield values and export coefficients published in the scientific literature, and generally were in agreement. The median yield of TN was greatest in catchments dominated by agricultural land and smallest in catchments dominated by grass and scrub land. The median yield of TP was greatest in catchments dominated by forest land, but the largest yields (90th percentile) of TP were from agricultural catchments. As with TN, the smallest TP yields were from catchments dominated by grass and scrub land.

Identification of the dominant runoff pathways from data-based mechanistic modelling of nested catchments in temperate UK

NASA Astrophysics Data System (ADS)

Ockenden, M. C.; Chappell, N. A.

2011-05-01

SummaryUnderstanding hydrological flow pathways is important for modelling stream response, in order to address a range of environmental problems such as flood prediction, prediction of chemical loads and identification of contaminant pathways for subsequent remediation. This paper describes the use of parametrically efficient, low order models to identify the dominant modes of stream response for catchments within the Upper Eden, UK. A first order linear model adequately identified the dominant mode in all but one of the sub-catchments. A consistent pattern of time constants and pure time delays between catchments was observed over different periods of data. In the nested catchments, time constants increased as the catchment size increased from 1.1 km 2 at Gais Gill (2-7 h) to 69.4 km 2 at Kirkby Stephen (5-10 h) to 223.4 km 2 at Great Musgrave (7-16 h) to 616.4 km 2 at Temple Sowerby (11-22 h), but Blind Beck (a small catchment 8.8 km 2, time constants 11-21 h) had time constants most similar to Temple Sowerby. This was attributed to a combination of the storage role of permeable rock strata, where present, and the effect of scale on sub-surface and channel routing. A first order model could not be identified for the 1.0 km 2 Low Hall catchment, which comprises permeable sandstone overlain by Quaternary sediments. A second-order model of Low Hall stream showed a higher proportion of water taking a slower pathway (76% via a slow pathway; time constant 252 h) than a model with the same structure for the 8.8 km 2 Blind Beck (46% via slow pathway; time constant 60 h), where only 38% of the basin was underlain by the same permeable sandstone. This highlights the need to quantify the role of deep pathways through permeable rock, where present, in addition to the effect of catchment size on response times.

How young water fractions can delineate travel time distributions in contrasting catchments

NASA Astrophysics Data System (ADS)

Lutz, Stefanie; Zink, Matthias; Merz, Ralf

2017-04-01

Travel time distributions (TTDs) are crucial descriptors of flow and transport processes in catchments. Tracking fluxes of environmental tracers such as stable water isotopes offers a practicable method to determine TTDs. The mean transit time (MTT) is the most commonly reported statistic of TTDs; however, MTT assessments are prone to large aggregation biases resulting from spatial heterogeneity and non-stationarity in real-world catchments. Recently, the young water fraction (Fyw) has been introduced as a more robust statistic that can be derived from seasonal tracer cycles. In this study, we aimed at improving the assessment of TTDs by using Fyw as additional information in lumped isotope models. First, we calculated Fyw from monthly δ18O-samples for 24 contrasting sub-catchments in a meso-scale catchment (3300 km2). Fyw ranged from 0.01 to 0.27 (mean= 0.11) and was not significantly correlated with catchment characteristics (e.g., mean slope, catchment area, and baseflow index) apart from the dominant soil type. Second, assuming gamma-shaped TTDs, we determined time-invariant TTDs for each sub-catchment by optimization of lumped isotope models using the convolution integral method. Whereas multiple optimization runs for the same sub-catchment showed a wide range of TTD parameters, the use of Fyw as additional information allowed constraining this range and thus improving the assessment of MTTs. Hence, the best model fit to observed isotope data might not be the desired solution, as the resulting TTD might define a young water fraction non-consistent with the tracer-cycle based Fyw. Given that the latter is a robust descriptor of fast-flow contribution, isotope models should instead aim at accurately describing both Fyw and the isotope time series in order to improve our understanding of flow and transport in catchments.

Quantifying the distribution of tracer discharge from boreal catchments under transient flow using the kinematic pathway approach

NASA Astrophysics Data System (ADS)

Soltani, S. S.; Cvetkovic, V.

2017-07-01

This focuses on solute discharge from boreal catchments with relatively shallow groundwater table and topography-driven groundwater flow. We explore whether a simplified semianalytical approach can be used for predictive modeling of the statistical distribution of tracer discharge. The approach is referred to as the "kinematic pathways approach" (KPA). This approach uses hydrological and tracer inputs and topographical and hydrogeological information; the latter regards average aquifer depth to the less permeable bedrock. A characteristic velocity of water flow through the catchment is further obtained from the overall water balance in the catchment. For the waterborne tracer transport through the catchment, morphological dispersion is accounted for by topographical analysis of the distribution of pathway lengths to the catchment outlet. Macrodispersion is accounted for heuristically by assuming an effective Péclet number. Distribution of water travel times through the catchment reflect the dispersion on both levels and are derived in both a forward mode (transit time from input to outlet) and a backward mode (water age when arriving at outlet arrival). The forward distribution of water travel times is further used for the tracer discharge modeling by convolution. The approach is applied to modeling of a 23 year long chloride data series for a specific catchment Kringlan (Sweden), and for generic modeling to better understand the dependence of the tracer discharge distribution on different dispersion aspects. The KPA is found to provide reasonable estimates of tracer discharge distribution, and particularly of extreme values, depending on method for determining the pathway length distribution. As a possible alternative analytical model of tracer transport through a catchment, the reservoir approach generally results in large tracer dispersion. This implies that tracer discharge distributions obtained from a mixed reservoir approach and from KPA are only compatible under large dispersion conditions.

Modelling of THM formation potential and DOM removal based on drinking water catchment characteristics.

PubMed

Awad, John; Fisk, Claire A; Cox, Jim W; Anderson, Sharolyn J; van Leeuwen, John

2018-09-01

Catchment properties influence the character and concentration of dissolved organic matter (DOM). Surface and subsurface runoff from discrete catchments were collected and DOM was measured and assessed in terms of its treatability by Enhanced Coagulation and potential for disinfection by-product (trihalomethane, THMFP) formation potential. Models were developed of [1] DOM character [i.e. SUVA and SpCoL] and concentration (measured as dissolved organic carbon), [2] treatability of DOM by coagulation/flocculation processes and [3] specific THMFP based on the catchment features including: (a) surface and sub-surface soil texture (% clay: 5-25%), (b) topography (% slope: 5-15%) and (c) vegetation cover [i.e. high photosynthetic vegetation, low photosynthetic vegetation and bare soil] extracted from RapidEye satellite imagery using spectral mixture analysis. From these models, a catchment management decision support tool was designed for application by catchment managers to support decision-making of land-use and expected water quality related to water resources for drinking water supply. Data sets used for models developing presented in this paper have been published in Research Data Australia (RDA) under the title of "Impacts of catchment properties on DOM and nutrients in waters from drinking water catchments". 1 These data sets are available in open access and published in June 2017. A catchment management decision support model (CMDSM) tool was developed. Macros created using Visual Basic for Applications in Excel 2010. Excel 2010 or higher is required to open the CMDSM tool. The tool is provided by the University of South Australia (UniSA) and is not currently available on-line so please contact the corresponding author for access or further information. Crown Copyright © 2018. Published by Elsevier B.V. All rights reserved.

Demonstrating the value of community-based ('citizen science') observations for catchment modelling and characterisation

NASA Astrophysics Data System (ADS)

Starkey, Eleanor; Parkin, Geoff; Birkinshaw, Stephen; Large, Andy; Quinn, Paul; Gibson, Ceri

2017-05-01

Despite there being well-established meteorological and hydrometric monitoring networks in the UK, many smaller catchments remain ungauged. This leaves a challenge for characterisation, modelling, forecasting and management activities. Here we demonstrate the value of community-based ('citizen science') observations for modelling and understanding catchment response as a contribution to catchment science. The scheme implemented within the 42 km2 Haltwhistle Burn catchment, a tributary of the River Tyne in northeast England, has harvested and used quantitative and qualitative observations from the public in a novel way to effectively capture spatial and temporal river response. Community-based rainfall, river level and flood observations have been successfully collected and quality-checked, and used to build and run a physically-based, spatially-distributed catchment model, SHETRAN. Model performance using different combinations of observations is tested against traditionally-derived hydrographs. Our results show how the local network of community-based observations alongside traditional sources of hydro-information supports characterisation of catchment response more accurately than using traditional observations alone over both spatial and temporal scales. We demonstrate that these community-derived datasets are most valuable during local flash flood events, particularly towards peak discharge. This information is often missed or poorly represented by ground-based gauges, or significantly underestimated by rainfall radar, as this study clearly demonstrates. While community-based observations are less valuable during prolonged and widespread floods, or over longer hydrological periods of interest, they can still ground-truth existing traditional sources of catchment data to increase confidence during characterisation and management activities. Involvement of the public in data collection activities also encourages wider community engagement, and provides important information for catchment management.

Conditional flood frequency and catchment state: a simulation approach

NASA Astrophysics Data System (ADS)

Brettschneider, Marco; Bourgin, François; Merz, Bruno; Andreassian, Vazken; Blaquiere, Simon

2017-04-01

Catchments have memory and the conditional flood frequency distribution for a time period ahead can be seen as non-stationary: it varies with the catchment state and climatic factors. From a risk management perspective, understanding the link of conditional flood frequency to catchment state is a key to anticipate potential periods of higher flood risk. Here, we adopt a simulation approach to explore the link between flood frequency obtained by continuous rainfall-runoff simulation and the initial state of the catchment. The simulation chain is based on i) a three state rainfall generator applied at the catchment scale, whose parameters are estimated for each month, and ii) the GR4J lumped rainfall-runoff model, whose parameters are calibrated with all available data. For each month, a large number of stochastic realizations of the continuous rainfall generator for the next 12 months are used as inputs for the GR4J model in order to obtain a large number of stochastic realizations for the next 12 months. This process is then repeated for 50 different initial states of the soil moisture reservoir of the GR4J model and for all the catchments. Thus, 50 different conditional flood frequency curves are obtained for the 50 different initial catchment states. We will present an analysis of the link between the catchment states, the period of the year and the strength of the conditioning of the flood frequency compared to the unconditional flood frequency. A large sample of diverse catchments in France will be used.

Application of a baseflow filter for evaluating model structure suitability of the IHACRES CMD

NASA Astrophysics Data System (ADS)

Kim, H. S.

2015-02-01

The main objective of this study was to assess the predictive uncertainty from the rainfall-runoff model structure coupling a conceptual module (non-linear module) with a metric transfer function module (linear module). The methodology was primarily based on the comparison between the outputs of the rainfall-runoff model and those from an alternative model approach. An alternative model approach was used to minimise uncertainties arising from data and the model structure. A baseflow filter was adopted to better understand deficiencies in the forms of the rainfall-runoff model by avoiding the uncertainties related to data and the model structure. The predictive uncertainty from the model structure was investigated for representative groups of catchments having similar hydrological response characteristics in the upper Murrumbidgee Catchment. In the assessment of model structure suitability, the consistency (or variability) of catchment response over time and space in model performance and parameter values has been investigated to detect problems related to the temporal and spatial variability of the model accuracy. The predictive error caused by model uncertainty was evaluated through analysis of the variability of the model performance and parameters. A graphical comparison of model residuals, effective rainfall estimates and hydrographs was used to determine a model's ability related to systematic model deviation between simulated and observed behaviours and general behavioural differences in the timing and magnitude of peak flows. The model's predictability was very sensitive to catchment response characteristics. The linear module performs reasonably well in the wetter catchments but has considerable difficulties when applied to the drier catchments where a hydrologic response is dominated by quick flow. The non-linear module has a potential limitation in its capacity to capture non-linear processes for converting observed rainfall into effective rainfall in both the wetter and drier catchments. The comparative study based on a better quantification of the accuracy and precision of hydrological modelling predictions yields a better understanding for the potential improvement of model deficiencies.

Prediction of storm transfers and annual loads with data-based mechanistic models using high-frequency data

NASA Astrophysics Data System (ADS)

Ockenden, Mary C.; Tych, Wlodek; Beven, Keith J.; Collins, Adrian L.; Evans, Robert; Falloon, Peter D.; Forber, Kirsty J.; Hiscock, Kevin M.; Hollaway, Michael J.; Kahana, Ron; Macleod, Christopher J. A.; Villamizar, Martha L.; Wearing, Catherine; Withers, Paul J. A.; Zhou, Jian G.; Benskin, Clare McW. H.; Burke, Sean; Cooper, Richard J.; Freer, Jim E.; Haygarth, Philip M.

2017-12-01

Excess nutrients in surface waters, such as phosphorus (P) from agriculture, result in poor water quality, with adverse effects on ecological health and costs for remediation. However, understanding and prediction of P transfers in catchments have been limited by inadequate data and over-parameterised models with high uncertainty. We show that, with high temporal resolution data, we are able to identify simple dynamic models that capture the P load dynamics in three contrasting agricultural catchments in the UK. For a flashy catchment, a linear, second-order (two pathways) model for discharge gave high simulation efficiencies for short-term storm sequences and was useful in highlighting uncertainties in out-of-bank flows. A model with non-linear rainfall input was appropriate for predicting seasonal or annual cumulative P loads where antecedent conditions affected the catchment response. For second-order models, the time constant for the fast pathway varied between 2 and 15 h for all three catchments and for both discharge and P, confirming that high temporal resolution data are necessary to capture the dynamic responses in small catchments (10-50 km2). The models led to a better understanding of the dominant nutrient transfer modes, which will be helpful in determining phosphorus transfers following changes in precipitation patterns in the future.

Advancing Land-Sea Conservation Planning: Integrating Modelling of Catchments, Land-Use Change, and River Plumes to Prioritise Catchment Management and Protection.

PubMed

Álvarez-Romero, Jorge G; Pressey, Robert L; Ban, Natalie C; Brodie, Jon

2015-01-01

Human-induced changes to river loads of nutrients and sediments pose a significant threat to marine ecosystems. Ongoing land-use change can further increase these loads, and amplify the impacts of land-based threats on vulnerable marine ecosystems. Consequently, there is a need to assess these threats and prioritise actions to mitigate their impacts. A key question regarding prioritisation is whether actions in catchments to maintain coastal-marine water quality can be spatially congruent with actions for other management objectives, such as conserving terrestrial biodiversity. In selected catchments draining into the Gulf of California, Mexico, we employed Land Change Modeller to assess the vulnerability of areas with native vegetation to conversion into crops, pasture, and urban areas. We then used SedNet, a catchment modelling tool, to map the sources and estimate pollutant loads delivered to the Gulf by these catchments. Following these analyses, we used modelled river plumes to identify marine areas likely influenced by land-based pollutants. Finally, we prioritised areas for catchment management based on objectives for conservation of terrestrial biodiversity and objectives for water quality that recognised links between pollutant sources and affected marine areas. Our objectives for coastal-marine water quality were to reduce sediment and nutrient discharges from anthropic areas, and minimise future increases in coastal sedimentation and eutrophication. Our objectives for protection of terrestrial biodiversity covered species of vertebrates. We used Marxan, a conservation planning tool, to prioritise interventions and explore spatial differences in priorities for both objectives. Notable differences in the distributions of land values for terrestrial biodiversity and coastal-marine water quality indicated the likely need for trade-offs between catchment management objectives. However, there were priority areas that contributed to both sets of objectives. Our study demonstrates a practical approach to integrating models of catchments, land-use change, and river plumes with conservation planning software to inform prioritisation of catchment management.

Advancing Land-Sea Conservation Planning: Integrating Modelling of Catchments, Land-Use Change, and River Plumes to Prioritise Catchment Management and Protection

PubMed Central

Álvarez-Romero, Jorge G.; Pressey, Robert L.; Ban, Natalie C.; Brodie, Jon

2015-01-01

Human-induced changes to river loads of nutrients and sediments pose a significant threat to marine ecosystems. Ongoing land-use change can further increase these loads, and amplify the impacts of land-based threats on vulnerable marine ecosystems. Consequently, there is a need to assess these threats and prioritise actions to mitigate their impacts. A key question regarding prioritisation is whether actions in catchments to maintain coastal-marine water quality can be spatially congruent with actions for other management objectives, such as conserving terrestrial biodiversity. In selected catchments draining into the Gulf of California, Mexico, we employed Land Change Modeller to assess the vulnerability of areas with native vegetation to conversion into crops, pasture, and urban areas. We then used SedNet, a catchment modelling tool, to map the sources and estimate pollutant loads delivered to the Gulf by these catchments. Following these analyses, we used modelled river plumes to identify marine areas likely influenced by land-based pollutants. Finally, we prioritised areas for catchment management based on objectives for conservation of terrestrial biodiversity and objectives for water quality that recognised links between pollutant sources and affected marine areas. Our objectives for coastal-marine water quality were to reduce sediment and nutrient discharges from anthropic areas, and minimise future increases in coastal sedimentation and eutrophication. Our objectives for protection of terrestrial biodiversity covered species of vertebrates. We used Marxan, a conservation planning tool, to prioritise interventions and explore spatial differences in priorities for both objectives. Notable differences in the distributions of land values for terrestrial biodiversity and coastal-marine water quality indicated the likely need for trade-offs between catchment management objectives. However, there were priority areas that contributed to both sets of objectives. Our study demonstrates a practical approach to integrating models of catchments, land-use change, and river plumes with conservation planning software to inform prioritisation of catchment management. PMID:26714166

An INCA model for pathogens in rivers and catchments: Model structure, sensitivity analysis and application to the River Thames catchment, UK.

PubMed

Whitehead, P G; Leckie, H; Rankinen, K; Butterfield, D; Futter, M N; Bussi, G

2016-12-01

Pathogens are an ongoing issue for catchment water management and quantifying their transport, loss and potential impacts at key locations, such as water abstractions for public supply and bathing sites, is an important aspect of catchment and coastal management. The Integrated Catchment Model (INCA) has been adapted to model the sources and sinks of pathogens and to capture the dominant dynamics and processes controlling pathogens in catchments. The model simulates the stores of pathogens in soils, sediments, rivers and groundwaters and can account for diffuse inputs of pathogens from agriculture, urban areas or atmospheric deposition. The model also allows for point source discharges from intensive livestock units or from sewage treatment works or any industrial input to river systems. Model equations are presented and the new pathogens model has been applied to the River Thames in order to assess total coliform (TC) responses under current and projected future land use. A Monte Carlo sensitivity analysis indicates that the input coliform estimates from agricultural sources and decay rates are the crucial parameters controlling pathogen behaviour. Whilst there are a number of uncertainties associated with the model that should be accounted for, INCA-Pathogens potentially provides a useful tool to inform policy decisions and manage pathogen loading in river systems. Copyright © 2016. Published by Elsevier B.V.

TRANSPORT, AIR-SURFACE EXCHANGE AND LANDSCAPE ACCUMULATION OF AIRBORNE POLLUTANTS DEPOSITED ONTO RURAL CATCHMENTS: THE CASE OF MERCURY

EPA Science Inventory

This paper presents a modeling analysis of airborne mercury fate in rural catchments by coupling components of simulation models developed and published previously by the authors. Results for individual rural catchments are presented and discussed, with a focus on the major mercu...

Modeling of Escherichia coli fluxes on a catchment and the impact on coastal water and shellfish quality

USDA-ARS?s Scientific Manuscript database

We coupled the Soil and Water Assessment Tool (SWAT) with a hydrodynamic model in the Daoulas’ catchment and estuary to estimate daily variations in Escherichia coli fluxes due to catchment activities (manure spreading and wastewater treatment plants discharge) and to assess their impact on coastal ...

Predictive optimal control of sewer networks using CORAL tool: application to Riera Blanca catchment in Barcelona.

PubMed

Puig, V; Cembrano, G; Romera, J; Quevedo, J; Aznar, B; Ramón, G; Cabot, J

2009-01-01

This paper deals with the global control of the Riera Blanca catchment in the Barcelona sewer network using a predictive optimal control approach. This catchment has been modelled using a conceptual modelling approach based on decomposing the catchments in subcatchments and representing them as virtual tanks. This conceptual modelling approach allows real-time model calibration and control of the sewer network. The global control problem of the Riera Blanca catchment is solved using a optimal/predictive control algorithm. To implement the predictive optimal control of the Riera Blanca catchment, a software tool named CORAL is used. The on-line control is simulated by interfacing CORAL with a high fidelity simulator of sewer networks (MOUSE). CORAL interchanges readings from the limnimeters and gate commands with MOUSE as if it was connected with the real SCADA system. Finally, the global control results obtained using the predictive optimal control are presented and compared against the results obtained using current local control system. The results obtained using the global control are very satisfactory compared to those obtained using the local control.

Simulating high frequency water quality monitoring data using a catchment runoff attenuation flux tool (CRAFT).

PubMed

Adams, Russell; Quinn, Paul F; Perks, Matthew; Barber, Nicholas J; Jonczyk, Jennine; Owen, Gareth J

2016-12-01

High resolution water quality data has recently become widely available from numerous catchment based monitoring schemes. However, the models that can reproduce time series of concentrations or fluxes have not kept pace with the advances in monitoring data. Model performance at predicting phosphorus (P) and sediment concentrations has frequently been poor with models not fit for purpose except for predicting annual losses. Here, the data from the Eden Demonstration Test Catchments (DTC) project have been used to calibrate the Catchment Runoff Attenuation Flux Tool (CRAFT), a new, parsimonious model developed with the aim of modelling both the generation and attenuation of nutrients and sediments in small to medium sized catchments. The CRAFT has the ability to run on an hourly timestep and can calculate the mass of sediments and nutrients transported by three flow pathways representing rapid surface runoff, fast subsurface drainage and slow groundwater flow (baseflow). The attenuation feature of the model is introduced here; this enables surface runoff and contaminants transported via this pathway to be delayed in reaching the catchment outlet. It was used to investigate some hypotheses of nutrient and sediment transport in the Newby Beck Catchment (NBC) Model performance was assessed using a suite of metrics including visual best fit and the Nash-Sutcliffe efficiency. It was found that this approach for water quality models may be the best assessment method as opposed to using a single metric. Furthermore, it was found that, when the aim of the simulations was to reproduce the time series of total P (TP) or total reactive P (TRP) to get the best visual fit, that attenuation was required. The model will be used in the future to explore the impacts on water quality of different mitigation options in the catchment; these will include attenuation of surface runoff. Copyright © 2016 Elsevier B.V. All rights reserved.

Impacts of urbanization on nitrogen cycling and aerosol, surface and groundwater transport in semi-arid regions

NASA Astrophysics Data System (ADS)

Lohse, K. A.; Gallo, E.; Carlson, M.; Riha, K. M.; Brooks, P. D.; McIntosh, J. C.; Sorooshian, A.; Michalski, G. M.; Meixner, T.

2011-12-01

Semi-arid regions are experiencing disproportionate increases in human population and land transformation worldwide, taxing limited water resources and altering nitrogen (N) biogeochemistry. How the redistribution of water and N by urbanization affects semi-arid ecosystems and downstream water quality (e.g. drinking water) is unclear. Understanding these interactions and their feedbacks will be critical for developing science-based management strategies to sustain these limited resources. This is especially true in the US where some of the fastest growing urban areas are in semi-arid ecosystems, where N and water cycles are accelerated, and intimately coupled, and where runoff from urban ecosystems is actively managed to augment a limited water supply to the growing human population. Here we synthesize several ongoing studies from the Tucson Basin in Arizona and examine how increasing urban land cover is altering rainfall-runoff relationships, groundwater recharge, water quality, and long range transport of atmospheric N. Studies across 5 catchments varying in impervious land cover showed that only the least impervious catchment responded to antecedent moisture conditions while hydrologic responses were not statistically related to antecedent rainfall conditions at more impervious sites. Regression models indicated that rainfall depth, imperviousness, and their combined effect control discharge and runoff ratios (p < 0.01, r2 = 0.91 and 0.75, respectively). In contrast, runoff quality was not predictably related to imperviousness or catchment size. Rather, rainfall depth and duration, time since antecedent rainfall, and stream channel characteristics and infrastructure controlled runoff chemistry. Groundwater studies showed nonpoint source contamination of CFCs and associated nitrate in areas of rapid recharge along ephemeral channels. Aerosol measurements indicate that both long-range transport of N and N emissions from Tucson are being transported and deposited at high elevation in areas that recharge regional groundwater. Combined, our findings suggest that urbanization in semi-arid regions results in tradeoffs in the redistribution of water and N that have important implications for water management and sustaining water quality.

Patterns and multi-scale drivers of phytoplankton species richness in temperate peri-urban lakes.

PubMed

Catherine, Arnaud; Selma, Maloufi; Mouillot, David; Troussellier, Marc; Bernard, Cécile

2016-07-15

Local species richness (SR) is a key characteristic affecting ecosystem functioning. Yet, the mechanisms regulating phytoplankton diversity in freshwater ecosystems are not fully understood, especially in peri-urban environments where anthropogenic pressures strongly impact the quality of aquatic ecosystems. To address this issue, we sampled the phytoplankton communities of 50 lakes in the Paris area (France) characterized by a large gradient of physico-chemical and catchment-scale characteristics. We used large phytoplankton datasets to describe phytoplankton diversity patterns and applied a machine-learning algorithm to test the degree to which species richness patterns are potentially controlled by environmental factors. Selected environmental factors were studied at two scales: the lake-scale (e.g. nutrients concentrations, water temperature, lake depth) and the catchment-scale (e.g. catchment, landscape and climate variables). Then, we used a variance partitioning approach to evaluate the interaction between lake-scale and catchment-scale variables in explaining local species richness. Finally, we analysed the residuals of predictive models to identify potential vectors of improvement of phytoplankton species richness predictive models. Lake-scale and catchment-scale drivers provided similar predictive accuracy of local species richness (R(2)=0.458 and 0.424, respectively). Both models suggested that seasonal temperature variations and nutrient supply strongly modulate local species richness. Integrating lake- and catchment-scale predictors in a single predictive model did not provide increased predictive accuracy; therefore suggesting that the catchment-scale model probably explains observed species richness variations through the impact of catchment-scale variables on in-lake water quality characteristics. Models based on catchment characteristics, which include simple and easy to obtain variables, provide a meaningful way of predicting phytoplankton species richness in temperate lakes. This approach may prove useful and cost-effective for the management and conservation of aquatic ecosystems. Copyright © 2016 Elsevier B.V. All rights reserved.

Drivers of dissolved organic carbon export in a subarctic catchment: Importance of microbial decomposition, sorption-desorption, peatland and lateral flow.

PubMed

Tang, Jing; Yurova, Alla Y; Schurgers, Guy; Miller, Paul A; Olin, Stefan; Smith, Benjamin; Siewert, Matthias B; Olefeldt, David; Pilesjö, Petter; Poska, Anneli

2018-05-01

Tundra soils account for 50% of global stocks of soil organic carbon (SOC), and it is expected that the amplified climate warming in high latitude could cause loss of this SOC through decomposition. Decomposed SOC could become hydrologically accessible, which increase downstream dissolved organic carbon (DOC) export and subsequent carbon release to the atmosphere, constituting a positive feedback to climate warming. However, DOC export is often neglected in ecosystem models. In this paper, we incorporate processes related to DOC production, mineralization, diffusion, sorption-desorption, and leaching into a customized arctic version of the dynamic ecosystem model LPJ-GUESS in order to mechanistically model catchment DOC export, and to link this flux to other ecosystem processes. The extended LPJ-GUESS is compared to observed DOC export at Stordalen catchment in northern Sweden. Vegetation communities include flood-tolerant graminoids (Eriophorum) and Sphagnum moss, birch forest and dwarf shrub communities. The processes, sorption-desorption and microbial decomposition (DOC production and mineralization) are found to contribute most to the variance in DOC export based on a detailed variance-based Sobol sensitivity analysis (SA) at grid cell-level. Catchment-level SA shows that the highest mean DOC exports come from the Eriophorum peatland (fen). A comparison with observations shows that the model captures the seasonality of DOC fluxes. Two catchment simulations, one without water lateral routing and one without peatland processes, were compared with the catchment simulations with all processes. The comparison showed that the current implementation of catchment lateral flow and peatland processes in LPJ-GUESS are essential to capture catchment-level DOC dynamics and indicate the model is at an appropriate level of complexity to represent the main mechanism of DOC dynamics in soils. The extended model provides a new tool to investigate potential interactions among climate change, vegetation dynamics, soil hydrology and DOC dynamics at both stand-alone to catchment scales. Copyright © 2017 Elsevier B.V. All rights reserved.

Water quality trends in New Zealand rivers: 1989-2009.

PubMed

Ballantine, Deborah J; Davies-Colley, Robert J

2014-03-01

Recent assessments of water quality in New Zealand have indicated declining trends, particularly in the 40 % of the country's area under pasture. The most comprehensive long-term and consistent water quality dataset is the National Rivers Water Quality Network (NRWQN). Since 1989, monthly samples have been collected at 77 NRWQN sites on 35 major river systems that, together, drain about 50 % of New Zealand's land area. Trend analysis of the NRWQN data shows increasing nutrient concentrations, particularly nitrogen (total nitrogen and nitrate), over 21 years (1989-2009). Total nitrogen and nitrate concentrations were increasing significantly over the first 11 years (1989-2000), but for the more recent 10-year period, only nitrate concentrations continued to increase sharply. Also, the increasing phosphorus trends over the first 11 years (1989-2000) levelled off over the later 10-year period (2000-2009). Conductivity has also increased over the 21 years (1989-2009). Visual clarity has increased over the full time period which may be the positive result of soil conservation measures and riparian fencing. NRWQN data shows that concentrations of nutrients increase, and visual clarity decreases (i.e. water quality declines), with increasing proportions of pastoral land in catchments. As such, the increasing nutrient trends may reflect increasing intensification of pastoral agriculture.

Improved parameter inference in catchment models: 1. Evaluating parameter uncertainty

NASA Astrophysics Data System (ADS)

Kuczera, George

1983-10-01

A Bayesian methodology is developed to evaluate parameter uncertainty in catchment models fitted to a hydrologic response such as runoff, the goal being to improve the chance of successful regionalization. The catchment model is posed as a nonlinear regression model with stochastic errors possibly being both autocorrelated and heteroscedastic. The end result of this methodology, which may use Box-Cox power transformations and ARMA error models, is the posterior distribution, which summarizes what is known about the catchment model parameters. This can be simplified to a multivariate normal provided a linearization in parameter space is acceptable; means of checking and improving this assumption are discussed. The posterior standard deviations give a direct measure of parameter uncertainty, and study of the posterior correlation matrix can indicate what kinds of data are required to improve the precision of poorly determined parameters. Finally, a case study involving a nine-parameter catchment model fitted to monthly runoff and soil moisture data is presented. It is shown that use of ordinary least squares when its underlying error assumptions are violated gives an erroneous description of parameter uncertainty.

Conceptual modelling of E. coli in urban stormwater drains, creeks and rivers

NASA Astrophysics Data System (ADS)

Jovanovic, Dusan; Hathaway, Jon; Coleman, Rhys; Deletic, Ana; McCarthy, David T.

2017-12-01

Accurate estimation of faecal microorganism levels in water systems, such as stormwater drains, creeks and rivers, is needed for appropriate assessment of impacts on receiving water bodies and the risks to human health. The underlying hypothesis for this work is that a single conceptual model (the MicroOrganism Prediction in Urban Stormwater model - i.e. MOPUS) can adequately simulate microbial dynamics over a variety of water systems and wide range of scales; something which has not been previously tested. Additionally, the application of radar precipitation data for improvement of the model performance at these scales via more accurate areal averaged rainfall intensities was tested. Six comprehensive Escherichia coli (E. coli) datasets collected from five catchments in south-eastern Australia and one catchment in Raleigh, USA, were used to calibrate the model. The MOPUS rainfall-runoff model performed well at all scales (Nash-Sutcliffe E for instantaneous flow rates between 0.70 and 0.93). Sensitivity analysis showed that wet weather urban stormwater flows can be modelled with only three of the five rainfall runoff model parameters: routing coefficient (K), effective imperviousness (IMP) and time of concentration (TOC). The model's performance for representing instantaneous E. coli fluctuations ranged from 0.17 to 0.45 in catchments drained via pipe or open creek, and was the highest for a large riverine catchment (0.64); performing similarly, if not better, than other microbial models in literature. The model could also capture the variability in event mean concentrations (E = 0.17-0.57) and event loads (E = 0.32-0.97) at all scales. Application of weather radar-derived rainfall inputs caused lower overall performance compared to using gauged rainfall inputs in representing both flow and E. coli levels in urban drain catchments, with the performance improving with increasing catchment size and being comparable to the models that use gauged rainfall inputs at the large riverine catchment. These results demonstrate the potential of the MOPUS model and its ability to be applied to a wide range of catchment scales, including large riverine systems.

Controls on denitrification in riparian soils in headwater catchments of a hardwood forest in the Catskill Mountains, U.S.A.

USGS Publications Warehouse

Ashby, J.A.; Bowden, W.B.; Murdoch, Peter S.

1998-01-01

Denitrification in riparian soils is thought to be an important factor that reduces hydrologic export of nitrate from forested and agricultural catchments. A 2-y study to identify the soil factors most closely associated with denitrification in riparian soils in headwater catchments within the Catskill Mountains of New York, included field surveys of surface and subsurface denitrification rates, and an amendment experiment to assess the relative effects of increases in available carbon and substrate NO-/3 on denitrification rates. Denitrification rates were measured by acetylene inhibition during incubation of intact soil cores from eight soil types representing a range of drainage classes. Soil cores were analyzed for organic matter, total P, extractable NO-/3-N and NH+/4-N, organic N, pH, moisture, porosity, and water-filled pore space, to determine which of these factors were most closely associated with denitrification. The distribution of denitrification rates found during the field surveys was highly skewed, with many low or zero values and few high values. Denitrification rates were positively associated with high soil organic matter, total P, and water-filled pore space, and were highest in seep (poorly-drained) soils, toeslope (seasonally-drained) soils, and stream-edge (poorly- to moderately well-drained) soils in which these three soil characteristics were typically high. Denitrification rates in these wet locations were also positively associated with soil NH+/4-N concentration and pH, but not with NO-/3-N concentration, suggesting that the rate of NO-/3 supply (via nitrification or hydrologic transport) was more important than the instantaneous concentration of NO-/3-N in the soils. The amendment experiment indicated that denitrification in soil types studied was most responsive to added glucose alone or with NO-/3. Thus, in these soils, a combination of slow rates of NO-/3 supply and low available carbon appears to limit denitrification. Annual denitrification rates in spring-fed soils (0.74 to 1.43 kg N ha-1 y-1) were up to 5 times greater than in other surface soils, yet these soils accounted for only 1.8% of the catchment's N loss through denitrification because they represent less than 3% of the catchment area. Dry upland soils constituted 71% of the catchment area and accounted for 91% of the catchment's N loss through denitrification. Annual denitrification in the catchment equaled about 65% of stream NO-/3-N and NH+/4-N export and 14% of precipitation NO-/3-N and NH+/4-N inputs. Denitrification appears to be important relative to N input and export in these Catskill catchments.

Event-based hydrological modeling for detecting dominant hydrological process and suitable model strategy for semi-arid catchments

NASA Astrophysics Data System (ADS)

Huang, Pengnian; Li, Zhijia; Chen, Ji; Li, Qiaoling; Yao, Cheng

2016-11-01

To simulate the hydrological processes in semi-arid areas properly is still challenging. This study assesses the impact of different modeling strategies on simulating flood processes in semi-arid catchments. Four classic hydrological models, TOPMODEL, XINANJIANG (XAJ), SAC-SMA and TANK, were selected and applied to three semi-arid catchments in North China. Based on analysis and comparison of the simulation results of these classic models, four new flexible models were constructed and used to further investigate the suitability of various modeling strategies for semi-arid environments. Numerical experiments were also designed to examine the performances of the models. The results show that in semi-arid catchments a suitable model needs to include at least one nonlinear component to simulate the main process of surface runoff generation. If there are more than two nonlinear components in the hydrological model, they should be arranged in parallel, rather than in series. In addition, the results show that the parallel nonlinear components should be combined by multiplication rather than addition. Moreover, this study reveals that the key hydrological process over semi-arid catchments is the infiltration excess surface runoff, a non-linear component.

A detailed model for simulation of catchment scale subsurface hydrologic processes

NASA Technical Reports Server (NTRS)

Paniconi, Claudio; Wood, Eric F.

1993-01-01

A catchment scale numerical model is developed based on the three-dimensional transient Richards equation describing fluid flow in variably saturated porous media. The model is designed to take advantage of digital elevation data bases and of information extracted from these data bases by topographic analysis. The practical application of the model is demonstrated in simulations of a small subcatchment of the Konza Prairie reserve near Manhattan, Kansas. In a preliminary investigation of computational issues related to model resolution, we obtain satisfactory numerical results using large aspect ratios, suggesting that horizontal grid dimensions may not be unreasonably constrained by the typically much smaller vertical length scale of a catchment and by vertical discretization requirements. Additional tests are needed to examine the effects of numerical constraints and parameter heterogeneity in determining acceptable grid aspect ratios. In other simulations we attempt to match the observed streamflow response of the catchment, and we point out the small contribution of the streamflow component to the overall water balance of the catchment.

Multiple long-term trends and trend reversals dominate environmental conditions in a man-made freshwater reservoir.

PubMed

Znachor, Petr; Nedoma, Jiří; Hejzlar, Josef; Seďa, Jaromír; Kopáček, Jiří; Boukal, David; Mrkvička, Tomáš

2018-05-15

Man-made reservoirs are common across the world and provide a wide range of ecological services. Environmental conditions in riverine reservoirs are affected by the changing climate, catchment-wide processes and manipulations with the water level, and water abstraction from the reservoir. Long-term trends of environmental conditions in reservoirs thus reflect a wider range of drivers in comparison to lakes, which makes the understanding of reservoir dynamics more challenging. We analysed a 32-year time series of 36 environmental variables characterising weather, land use in the catchment, reservoir hydrochemistry, hydrology and light availability in the small, canyon-shaped Římov Reservoir in the Czech Republic to detect underlying trends, trend reversals and regime shifts. To do so, we fitted linear and piecewise linear regression and a regime shift model to the time series of mean annual values of each variable and to principal components produced by Principal Component Analysis. Models were weighted and ranked using Akaike information criterion and the model selection approach. Most environmental variables exhibited temporal changes that included time-varying trends and trend reversals. For instance, dissolved organic carbon showed a linear increasing trend while nitrate concentration or conductivity exemplified trend reversal. All trend reversals and cessations of temporal trends in reservoir hydrochemistry (except total phosphorus concentrations) occurred in the late 1980s and during 1990s as a consequence of dramatic socioeconomic changes. After a series of heavy rains in the late 1990s, an administrative decision to increase the flood-retention volume of the reservoir resulted in a significant regime shift in reservoir hydraulic conditions in 1999. Our analyses also highlight the utility of the model selection framework, based on relatively simple extensions of linear regression, to describe temporal trends in reservoir characteristics. This approach can provide a solid basis for a better understanding of processes in freshwater reservoirs. Copyright © 2017 Elsevier B.V. All rights reserved.

Simulation of filter strips influence on runoff and soil and nutrient losses under different rainfall patterns in a small vineyard catchment

NASA Astrophysics Data System (ADS)

Ramos, Maria C.; Benito, Carolina

2014-05-01

This work presents the analysis of the influence of filter strips on soil and water losses in a small catchment, whose main land use is grape vines. The watershed was located in the municipality of Piera (Barcelona, Spain). Other crops like olive trees, winter barley and alfalfa were also found, as well as some residential areas. Soil and water losses were simulated using the Soil and Water Assessment Tool (SWAT). The model was calibrated and validated using soil water and runoff data collected in the field during the period May 2010- May 2012. Then, the model was run for the period 2000-2011, which included years with different rainfall amounts and characteristics. Soil losses with and without that soil conservation measure was compared. The annual rainfall recorded during the analysed years ranged from 329.8 to 785 mm with different rainfall distributions within the year. Runoff rates ranged from 17 to 141 mm, which represented respectively 4.7 and 21% of total precipitation. Both extreme situations were recorded in the driest years of the series, with precipitation below the average. Soil losses ranged between 0.31 Mg/ha in the driest year and 13.9 Mg/ha, in the wettest. The simulation of soil losses with the introduction of filter strips 3m width in the vineyards resulted in a reduction of soil losses up to 68% in relation to the situation without that soil conservation measure. This soil loss decrease represented an additional nutrient loss reduction (up to 66% for N_organic, up to 64% of P_organic and between 6.5 and 40% of N_nitrate, depending on rainfall characteristics).

Modeling Land Use Change Impacts on Water Resources in a Tropical West African Catchment (dano, Burkina Faso)

NASA Astrophysics Data System (ADS)

Yira, Y.; Diekkrüger, B.; Steup, G.; Bossa, A. Y.

2015-12-01

This study investigates the impacts of land use change on water resources in the Dano catchment, Burkina Faso, using a physically based hydrological simulation model and land use scenarios. Land use dynamic in the catchment was assessed through the analysis of four land use maps corresponding to the land use status in 1990, 2000, 2007 and 2013. A reclassification procedure of the maps permitted to assess the major land use changes in the catchment from 1990 to 2013. The land use maps were used to build five land use scenarios corresponding to different levels of land use change in the catchment. Water balance was simulated by applying the Water flow and balance Simulation Model (WaSiM) using observed discharge, soil moisture, and groundwater level for model calibration and validation. Model statistical quality measures (R2, NSE and KGE) achieved during the calibration and the validation ranged between 0.9 and 0.6 for total discharge, soil moisture, and groundwater level, indicating satisfying to good agreements between observed and simulated variables. After a successful multi-criteria validation the model was run with the land use scenarios. The land use assessment exhibited a decrease of savannah at an annual rate of 2% since 1990. Conversely, cropland and urban areas have increased. Since urban areas occupy only 3% of the catchment in 2013 it can be assumed that savannah was mainly converted to cropland. The increase in cropland area results from the population growth and the farming system in the catchment. A clear increase in total discharge (+17%) and decrease in evapotranspiration (-5%) was observed following land use change in the catchment. A strong relationship was established between savannah degradation, cropland expansion, discharge increase and reduction of evapotranspiration. The increase in total discharge is related to high discharge and peak flow, suggesting (i) an increase in water resources that is not available for plant growth and the population of the catchment and (ii) an alteration of flood risk for both the population within and downstream of the catchment.

Instream Attenuation of Nitrogen and Phosphorus in Non-Point Source Dominated Streams: Hydrologic and Biogeochemical Controls

NASA Astrophysics Data System (ADS)

Bray, E. N.; Chen, X.; Keller, A. A.

2010-12-01

Non-point source inputs of total nitrogen (TN) and total phosphorus (TP) in rivers are the leading causes of water quality degradation in the United States (Turner and Rabalais, 2003; Broussard and Turner, 2009). Yet it remains a challenge to adequately quantify the relative role and influence of physical hydrological processes versus biogeochemical processes on the attenuation of TN and TP for individual river reaches. A watershed-scale study of instream dynamics and attenuation of TN and TP in northeastern U.S. headwater streams demonstrates that physical and hydrological processes exert greater control over nutrient removal than biogeochemical processes. To explore these interactions under various attenuation scenarios, we developed the watershed-scale model (WARMF) for 97 catchments to simulate watershed processes, hydrology, and diffuse source loads of nutrients. We simulated a hypothetical nutrient release at a rate of 1 kg/d of TN (50% as ammonium and 50% as nitrate) and TP (100% as phosphate) to predict response lengths of downstream catchments. Resulting attenuation factors are presented as the change in mean load at a given location, normalized to the change in the catchment in which the load is applied. Results indicate that for most catchments, the TN and TP load increase is attenuated from the stream within a few tens of kilometers. Fifty percent attenuation occurs across length scales ranging from a few hundreds of meters to kilometers if the load is introduced in the headwaters, indicating the most rapid nutrient removal occurs in the smallest headwater streams but generally decreases with distance downstream. There are some differences in the attenuation factors for TN and TP, although the pattern of attenuation is the same. Sensitivity analyses highlight five hydrological parameters of paramount importance to concentrations of N and P, namely precipitation, evaporation coefficients (magnitude and skewness), soil layer thickness, soil saturated moisture and soil hydraulic conductivity. These model parameters have a significant effect on the concentrations of nutrients, with TN exhibiting greater sensitivity. Further, attenuation results suggest that stream depth, flow regime, and density of agriculture in small headwater streams are potentially important controls to nutrient uptake and removal; i.e. during periods of low flow, dilution is reduced, attenuation length increases, and removal processes may be dominated by settling as opposed to biogeochemistry. Instream attenuation and model results can be used to assess 1) the scale and nature of best management practices which must be adopted to result in nutrient reductions, 2) the downstream distance at which load reductions will be effective, and 3) the hydrological characteristics of the river network which exert considerable influence on attenuation lengths and nutrient removal.

The application of GEOtop for catchment scale hydrology in Ireland

NASA Astrophysics Data System (ADS)

Lewis, C.; Xu, X.; Albertson, J.; Kiely, G.

2009-04-01

GEOtop represents the new generation of distributed hydrological model driven by geospatial data (e.g. topography, soils, vegetation, land cover). It estimates rainfall-runoff, evapotranspiration and provides spatially distributed outputs as well as routing water and sediment flows through stream and river networks. The original version of GEOtop designed in Italy, includes a rigorous treatment of the core hydrological processes (e.g. unsaturated and saturated flow and transport, surface energy balances, and streamflow generation/routing). Recently GEOtop was extended to include treatment of shallow landslides. The GEOtop model is built on an open-source programming framework, which makes it well suited for adaptation and extension. GEOtop has been run very successfully in a number of alpine catchments (such as Brenta) but has not been used on Irish catchments before. The cell size used for the spatially distributed inputs varies from catchment to catchment. In smaller catchments (less than 2000ha) 50 by 50m cells have been used and 200 by 200 for larger catchments. Smaller cell sizes have been found to significantly increase the computational time so a larger cell size is used providing it does not significantly affect the performance of the model. Digital elevation model, drainage direction, landuse and soil type maps are the minimum spatial requirements with precipitation, radiation, temperature, atmospheric pressure and wind speed been the minimum meteorological requirements for a successful run. The soil type maps must also contain information regarding texture and hydraulic conductivity. The first trial of GEOtop in Ireland was on a small 1524 ha catchment in the south of Ireland. The catchment ranges from 50 to just over 200m, the land use is predominately agricultural grassland and it receives on average 1400mm of rain per year. Within this catchment there is a meteorological tower which provides the meteorological inputs, soil moisture is also recorded at this location. GEOtop was run from the end of April 2006 to December 2007. A comparison of measured and simulated values of soil moisture showed some good results and proved that the model could be successfully be used in Ireland. Following initial success in modelling soil moisture in a small catchment GEOtop was then used in the much larger 115,000 ha Blackwater catchment. The variation of soil type within the catchment was obtained from a national soils database while Landuse data was obtained from the national Corrine Land use database. Hydraulic properties were estimated by carrying out on site infiltration experiments. As GEOtop can accept multiple rainfall inputs and it was known that the rainfall varies substantially within in the catchment it was decided to make use of a rainfall study on the Blackwater catchment. A total of 21 rain gauges were deployed around the catchment for year 2006. The data from these 21 rain gauges were then added to the inputs which GEOtop interpolated the rainfall using the kriging method. Continuous flow is recorded at the outlet of the Blackwater catchment and as GEOtop simulates stream flows we were able to see how well GEOtop modelled the hydrology of the catchment. Comparisons of simulated versus real flow showed that GEOtop was providing us with satisfactory results. Once we were satisfied that GEOtop was successfully modelling the catchment we were able to see the effects of varying rain fall and land use on many different hydraulic parameters such stream flow, soil suction potential, soil moisture content etc. When this process has been carried out for other parts of the country it is planned to use GEOtop study potential threats to soil quality such as erosion, surface sealing, compaction, landslides and loss of organic matter. New modules will be develop for GEOtop to help understand and quantify these threats. The model will also be used to help understand the interactions between soil hydrology, land use and climate change (with climate projections from the IPCC fourth assessment). These outputs will be combined with Irish geo-spatial data to develop a GIS-based risk assessment tool to predict impacts on soil quality based on hydrology, land use and climate change.

Uncertainty in mixing models: a blessing in disguise?

NASA Astrophysics Data System (ADS)

Delsman, J. R.; Oude Essink, G. H. P.

2012-04-01

Despite the abundance of tracer-based studies in catchment hydrology over the past decades, relatively few studies have addressed the uncertainty associated with these studies in much detail. This uncertainty stems from analytical error, spatial and temporal variance in end-member composition, and from not incorporating all relevant processes in the necessarily simplistic mixing models. Instead of applying standard EMMA methodology, we used end-member mixing model analysis within a Monte Carlo framework to quantify the uncertainty surrounding our analysis. Borrowing from the well-known GLUE methodology, we discarded mixing models that could not satisfactorily explain sample concentrations and analyzed the posterior parameter set. This use of environmental tracers aided in disentangling hydrological pathways in a Dutch polder catchment. This 10 km2 agricultural catchment is situated in the coastal region of the Netherlands. Brackish groundwater seepage, originating from Holocene marine transgressions, adversely affects water quality in this catchment. Current water management practice is aimed at improving water quality by flushing the catchment with fresh water from the river Rhine. Climate change is projected to decrease future fresh water availability, signifying the need for a more sustainable water management practice and a better understanding of the functioning of the catchment. The end-member mixing analysis increased our understanding of the hydrology of the studied catchment. The use of a GLUE-like framework for applying the end-member mixing analysis not only quantified the uncertainty associated with the analysis, the analysis of the posterior parameter set also identified the existence of catchment processes otherwise overlooked.

Modeling diffuse sources of surface water contamination with plant protection products

NASA Astrophysics Data System (ADS)

Wendland, Sandra; Bock, Michael; Böhner, Jürgen; Lembrich, David

2015-04-01

Entries of chemical pollutants in surface waters are a serious environmental problem. Among water pollutants plant protection products (ppp) from farming practice are of major concern not only for water suppliers and environmental agencies, but also for farmers and industrial manufacturers. Lost chemicals no longer fulfill their original purpose on the field, but lead to severe damage of the environment and surface waters. Besides point-source inputs of chemical pollutants, the diffuse-source inputs from agricultural procedures play an important and not yet sufficiently studied role concerning water quality. The two most important factors for diffuse inputs are erosion and runoff. The latter usually occurs before erosion begins, and is thus often not visible in hindsight. Only if it has come to erosion, it is obvious to expect runoff in foresight at this area, too. In addition to numerous erosion models, there are also few applications to model runoff processes available. However, these conventional models utilize approximations of catchment parameters based on long-term average values or theoretically calculated concentration peaks which can only provide indications to relative amounts. Our study aims to develop and validate a simplified spatially-explicit dynamic model with high spatiotemporal resolution that enables to measure current and forecast runoff potential not only at catchment scale but field-differentiated. This method allows very precise estimations of runoff risks and supports risk reduction measures to be targeted before fields are treated. By focusing on water pathways occurring on arable land, targeted risk reduction measures like buffer strips at certain points and adapted ppp use can be taken early and pollution of rivers and other surface waters through transported pesticides, fertilizers and their products could be nearly avoided or largely minimized. Using a SAGA-based physical-parametric modeling approach, major factors influencing runoff (relief, soil properties, weather conditions and crop coverage) are represented. Water balance parameters are modeled in daily steps, taking into account relief determined discharge pathways, runoff velocity and number of field boundaries passed until receiving streams are reached. Model development is based on a comprehensive monitoring campaign at 3 smaller catchments in North Rhine-Westphalia (Germany), equipped with two gauges each, upstream and downstream, an optical Trios probe and four Isco-Samplers. The temporal high resolution monitoring of discharge, ppp, orthophosphate and nitrate-nitrogen enables an evaluation of runoff simulations in relation with rain events. First model results suggest that the simulation of surface runoff pathways enables a spatial-explicit identification of fields contributing to pollutant inputs. We assume that targeted actions on few fields will help solving the problem of diffuse inputs of ppp in our surface water to a considerable extent.

Integrating environmental and socio-economic indicators of a linked catchment-coastal system using variable environmental intensity.

PubMed

Dymond, John R; Davie, Tim J A; Fenemor, Andrew D; Ekanayake, Jagath C; Knight, Ben R; Cole, Anthony O; de Oca Munguia, Oscar Montes; Allen, Will J; Young, Roger G; Basher, Les R; Dresser, Marc; Batstone, Chris J

2010-09-01

Can we develop land use policy that balances the conflicting views of stakeholders in a catchment while moving toward long term sustainability? Adaptive management provides a strategy for this whereby measures of catchment performance are compared against performance goals in order to progressively improve policy. However, the feedback loop of adaptive management is often slow and irreversible impacts may result before policy has been adapted. In contrast, integrated modelling of future land use policy provides rapid feedback and potentially improves the chance of avoiding unwanted collapse events. Replacing measures of catchment performance with modelled catchment performance has usually required the dynamic linking of many models, both biophysical and socio-economic-and this requires much effort in software development. As an alternative, we propose the use of variable environmental intensity (defined as the ratio of environmental impact over economic output) in a loose coupling of models to provide a sufficient level of integration while avoiding significant effort required for software development. This model construct was applied to the Motueka Catchment of New Zealand where several biophysical (riverine water quantity, sediment, E. coli faecal bacteria, trout numbers, nitrogen transport, marine productivity) models, a socio-economic (gross output, gross margin, job numbers) model, and an agent-based model were linked. An extreme set of land use scenarios (historic, present, and intensive) were applied to this modelling framework. Results suggest that the catchment is presently in a near optimal land use configuration that is unlikely to benefit from further intensification. This would quickly put stress on water quantity (at low flow) and water quality (E. coli). To date, this model evaluation is based on a theoretical test that explores the logical implications of intensification at an unlikely extreme in order to assess the implications of likely growth trajectories from present use. While this has largely been a desktop exercise, it would also be possible to use this framework to model and explore the biophysical and economic impacts of individual or collective catchment visions. We are currently investigating the use of the model in this type of application.

Predicting in ungauged basins using a parsimonious rainfall-runoff model

NASA Astrophysics Data System (ADS)

Skaugen, Thomas; Olav Peerebom, Ivar; Nilsson, Anna

2015-04-01

Prediction in ungauged basins is a demanding, but necessary test for hydrological model structures. Ideally, the relationship between model parameters and catchment characteristics (CC) should be hydrologically justifiable. Many studies, however, report on failure to obtain significant correlations between model parameters and CCs. Under the hypothesis that the lack of correlations stems from non-identifiability of model parameters caused by overparameterization, the relatively new parameter parsimonious DDD (Distance Distribution Dynamics) model was tested for predictions in ungauged basins in Norway. In DDD, the capacity of the subsurface water reservoir M is the only parameter to be calibrated whereas the runoff dynamics is completely parameterised from observed characteristics derived from GIS and runoff recession analysis. Water is conveyed through the soils to the river network by waves with celerities determined by the level of saturation in the catchment. The distributions of distances between points in the catchment to the nearest river reach and of the river network give, together with the celerities, distributions of travel times, and, consequently unit hydrographs. DDD has 6 parameters less to calibrate in the runoff module than, for example, the well-known Swedish HBV model. In this study, multiple regression equations relating CCs and model parameters were trained from 84 calibrated catchments located all over Norway and all model parameters showed significant correlations with catchment characteristics. The significant correlation coefficients (with p- value < 0.05) ranged from 0.22-0.55. The suitability of DDD for predictions in ungauged basins was tested for 17 catchments not used to estimate the multiple regression equations. For 10 of the 17 catchments, deviations in Nash-Suthcliffe Efficiency (NSE) criteria between the calibrated and regionalised model were less than 0.1. The median NSE for the regionalised DDD for the 17 catchments, for two different time series was 0.66 and 0.72. Deviations in NSE between calibrated and regionalised models are well explained by the deviations between calibrated and regressed parameters describing spatial snow distribution and snowmelt, respectively. This latter result indicates the topic for further improvements in the model structure of DDD.

Integrating Environmental and Socio-Economic Indicators of a Linked Catchment-Coastal System Using Variable Environmental Intensity

NASA Astrophysics Data System (ADS)

Dymond, John R.; Davie, Tim J. A.; Fenemor, Andrew D.; Ekanayake, Jagath C.; Knight, Ben R.; Cole, Anthony O.; de Oca Munguia, Oscar Montes; Allen, Will J.; Young, Roger G.; Basher, Les R.; Dresser, Marc; Batstone, Chris J.

2010-09-01

Can we develop land use policy that balances the conflicting views of stakeholders in a catchment while moving toward long term sustainability? Adaptive management provides a strategy for this whereby measures of catchment performance are compared against performance goals in order to progressively improve policy. However, the feedback loop of adaptive management is often slow and irreversible impacts may result before policy has been adapted. In contrast, integrated modelling of future land use policy provides rapid feedback and potentially improves the chance of avoiding unwanted collapse events. Replacing measures of catchment performance with modelled catchment performance has usually required the dynamic linking of many models, both biophysical and socio-economic—and this requires much effort in software development. As an alternative, we propose the use of variable environmental intensity (defined as the ratio of environmental impact over economic output) in a loose coupling of models to provide a sufficient level of integration while avoiding significant effort required for software development. This model construct was applied to the Motueka Catchment of New Zealand where several biophysical (riverine water quantity, sediment, E. coli faecal bacteria, trout numbers, nitrogen transport, marine productivity) models, a socio-economic (gross output, gross margin, job numbers) model, and an agent-based model were linked. An extreme set of land use scenarios (historic, present, and intensive) were applied to this modelling framework. Results suggest that the catchment is presently in a near optimal land use configuration that is unlikely to benefit from further intensification. This would quickly put stress on water quantity (at low flow) and water quality ( E. coli). To date, this model evaluation is based on a theoretical test that explores the logical implications of intensification at an unlikely extreme in order to assess the implications of likely growth trajectories from present use. While this has largely been a desktop exercise, it would also be possible to use this framework to model and explore the biophysical and economic impacts of individual or collective catchment visions. We are currently investigating the use of the model in this type of application.

Emergent structures and understanding from a comparative uncertainty analysis of the FUSE rainfall-runoff modelling platform for >1,100 catchments

NASA Astrophysics Data System (ADS)

Freer, J. E.; Odoni, N. A.; Coxon, G.; Bloomfield, J.; Clark, M. P.; Greene, S.; Johnes, P.; Macleod, C.; Reaney, S. M.

2013-12-01

If we are to learn about catchments and their hydrological function then a range of analysis techniques can be proposed from analysing observations to building complex physically based models using detailed attributes of catchment characteristics. Decisions regarding which technique is fit for a specific purpose will depend on the data available, computing resources, and the underlying reasons for the study. Here we explore defining catchment function in a relatively general sense expressed via a comparison of multiple model structures within an uncertainty analysis framework. We use the FUSE (Framework for Understanding Structural Errors - Clark et al., 2008) rainfall-runoff modelling platform and the GLUE (Generalised Likelihood Uncertainty Estimation - Beven and Freer, 2001) uncertainty analysis framework. Using these techniques we assess two main outcomes: 1) Benchmarking our predictive capability using discharge performance metrics for a diverse range of catchments across the UK 2) evaluating emergent behaviour for each catchment and/or region expressed as ';best performing' model structures that may be equally plausible representations of catchment behaviour. We shall show how such comparative hydrological modelling studies show patterns of emergent behaviour linked both to seasonal responses and to different geoclimatic regions. These results have implications for the hydrological community regarding how models can help us learn about places as hypothesis testing tools. Furthermore we explore what the limits are to such an analysis when dealing with differing data quality and information content from ';pristine' to less well characterised and highly modified catchment domains. This research has been piloted in the UK as part of the Environmental Virtual Observatory programme (EVOp), funded by NERC to demonstrate the use of cyber-infrastructure and cloud computing resources to develop better methods of linking data and models and to support scenario analysis for research, policy and operational needs.

Regional Assessment of the Relationship Between Landscape Attributes and Water Quality in Five National Parks of the Rocky Mountains

NASA Astrophysics Data System (ADS)

Nanus, L.; Williams, M. W.; Campbell, D. H.

2005-12-01

Atmospheric deposition of pollutants threatens pristine environments around the world. However, scientifically-based decisions regarding management of these environments has been confounded by spatial variability of atmospheric deposition, particularly across regional scales at which resource management is typically considered. A statistically based methodology coupled within GIS is presented that builds on small alpine lake and sub-alpine catchments scale to identify deposition-sensitive lakes across larger watershed and regional scales. The sensitivity of 874 alpine and subalpine lakes to acidification from atmospheric deposition of nitrogen and sulfur was estimated using statistical models relating water quality and landscape attributes in Glacier National Park, Yellowstone National Park, Grand Teton National Park, Rocky Mountain National Park and Great Sand Dunes National Park and Preserve. Water-quality data measured during synoptic lake surveys were used to calibrate statistical models of lake sensitivity. In the case of nitrogen deposition, water quality data were supplemented with dual isotopic measurements of d15N and d18O of nitrate. Landscape attributes for the lake basins were derived from GIS including the following explanatory variables; topography (basin slope, basin aspect, basin elevation), bedrock type, vegetation type, and soil type. Using multivariate logistic regression analysis, probability estimates were developed for acid-neutralizing capacity, nitrate, sulfate and DOC concentrations, and lakes with a high probability of being sensitive to atmospheric deposition were identified. Water-quality data collected at 60 lakes during fall 2004 were used to validate statistical models. Relationships between landscape attributes and water quality vary by constituent, due to spatial variability in landscape attributes and spatial variation in the atmospheric deposition of pollutants within and among the five National Parks. Predictive ability, model fit and sensitivity were first assessed for each of the five National Parks individually, to evaluate the utility of this methodology for prediction of alpine and sub-alpine lake sensitivity across the catchment scale. A similar assessment was then performed, treating the five parks as a group. Validation results showed that 85 percent of lakes sampled were accurately identified by the model as having a greater than 60 percent probability of acid-neutralizing capacity concentrations less than 200 microequivalents per liter. Preliminary findings indicate good predictive ability and reasonable model fit and sensitivity, suggesting that logistic regression modeling coupled within a GIS framework is an appropriate approach for remote identification of deposition-sensitive lakes across the Rocky Mountain region. To assist resource management decisions regarding alpine and sub-alpine lakes across this region, screening procedures were developed based on terrain and landscape attribute information available to all participating parks. Since the screening procedure is based on publicly available data, our methodology and similar screening procedures may be applicable to other National Parks with deposition-sensitive surface waters.

Using "StorAge Selection" functions and high resolution isotope data to unravel travel time distributions in headwater catchments

NASA Astrophysics Data System (ADS)

Benettin, Paolo; Soulsby, Chris; Birkel, Christian; Tetzlaff, Doerthe; Botter, Gianluca; Rinaldo, Andrea

2017-04-01

We use high resolution tracer data from the Bruntland Burn catchment (UK) to test theoretical approaches that integrate catchment-scale flow and transport processes in a unified framework centered on selective age sampling by streamflow and evapotranspiration fluxes. Hydrologic transport is here described through StorAge Selection (SAS) functions, parametrized as simple power laws. By representing the way in which catchment storage generates outflows composed by water of different ages, the main mechanism regulating the tracer composition of runoff is clearly identified. The calibrated numerical model provides simulations that convincingly reproduce complex measured signals of daily deuterium content in stream waters during wet and dry periods. The results for the catchment under consideration are consistent with other recent studies indicating a tendency for natural catchments to preferentially release younger available water. The model allows estimating transient water age and its related uncertainty, as well as the total catchment storage. This study shows that power-law SAS functions prove a powerful tool to explain catchment-scale transport processes that also has potential in less intensively monitored sites.

Preferential flow across scales: how important are plot scale processes for a catchment scale model?

NASA Astrophysics Data System (ADS)

Glaser, Barbara; Jackisch, Conrad; Hopp, Luisa; Klaus, Julian

2017-04-01

Numerous experimental studies showed the importance of preferential flow for solute transport and runoff generation. As a consequence, various approaches exist to incorporate preferential flow in hydrological models. However, few studies have applied models that incorporate preferential flow at hillslope scale and even fewer at catchment scale. Certainly, one main difficulty for progress is the determination of an adequate parameterization for preferential flow at these spatial scales. This study applies a 3D physically based model (HydroGeoSphere) of a headwater region (6 ha) of the Weierbach catchment (Luxembourg). The base model was implemented without preferential flow and was limited in simulating fast catchment responses. Thus we hypothesized that the discharge performance can be improved by utilizing a dual permeability approach for a representation of preferential flow. We used the information of bromide irrigation experiments performed on three 1m2 plots to parameterize preferential flow. In a first step we ran 20.000 Monte Carlo simulations of these irrigation experiments in a 1m2 column of the headwater catchment model, varying the dual permeability parameters (15 variable parameters). These simulations identified many equifinal, yet very different parameter sets that reproduced the bromide depth profiles well. Therefore, in the next step we chose 52 parameter sets (the 40 best and 12 low performing sets) for testing the effect of incorporating preferential flow in the headwater catchment scale model. The variability of the flow pattern responses at the headwater catchment scale was small between the different parameterizations and did not coincide with the variability at plot scale. The simulated discharge time series of the different parameterizations clustered in six groups of similar response, ranging from nearly unaffected to completely changed responses compared to the base case model without dual permeability. Yet, in none of the groups the simulated discharge response clearly improved compared to the base case. Same held true for some observed soil moisture time series, although at plot scale the incorporation of preferential flow was necessary to simulate the irrigation experiments correctly. These results rejected our hypothesis and open a discussion on how important plot scale processes and heterogeneities are at catchment scale. Our preliminary conclusion is that vertical preferential flow is important for the irrigation experiments at the plot scale, while discharge generation at the catchment scale is largely controlled by lateral preferential flow. The lateral component, however, was already considered in the base case model with different hydraulic conductivities in different soil layers. This can explain why the internal behavior of the model at single spots seems not to be relevant for the overall hydrometric catchment response. Nonetheless, the inclusion of vertical preferential flow improved the realism of internal processes of the model (fitting profiles at plot scale, unchanged response at catchment scale) and should be considered depending on the intended use of the model. Furthermore, we cannot exclude with certainty yet that the quantitative discharge performance at catchment scale cannot be improved by utilizing a dual permeability approach, which will be tested in parameter optimization process.

Recent advances towards a theory of catchment hydrologic transport: age-ranked storage and the Ω-functions

NASA Astrophysics Data System (ADS)

Harman, C. J.

2014-12-01

Models that faithfully represent spatially-integrated hydrologic transport through the critical zone at sub-watershed scales are essential building blocks for large-scale models of land use and climate controls on non-point source contaminant delivery. A particular challenge facing these models is the need to represent the delay between inputs of soluble contaminants (such as nitrate) at the field scale, and the solute load that appears in streams. Recent advances in the theory of time-variable transit time distributions (e.g. Botter et al., GRL 38(L11403), 2011) have provided a rigorous framework for representing conservative solute transport and its coupling to hydrologic variability and partitioning. Here I will present a reformulation of this framework that offers several distinct advantages over existing formulations: 1) the derivation of the governing conservation equation is simple and intuitive, 2) the closure relations are expressed in a convenient and physically meaningful way as probability distributions Ω(ST)Omega(S_T) over the storage ranked by age STS_T, and 3) changes in transport behavior determined by storage-dependent dilution and flow-path dynamics (as distinct from those due only to changes in the rates and partitioning of water flux) are completely encapsulated by these probability distributions. The framework has been implemented to model to the rich dataset of long-term stream and precipitation chloride from the Plynlimon watershed in Wales, UK. With suitable choices for the functional form of the closure relationships, only a small number of free parameters are required to reproduce the observed chloride dynamics as well as previous models with many more parameters, including reproducing the observed fractal 1/f filtering of the streamflow chloride variability. The modeled transport dynamics are sensitive to the input precipitation variability and water balance partitioning to evapotranspiration. Apparent storage-dependent age-sampling suggests that the model can account for shifts in flow pathways across high and low flows. This approach suggests a path forward for catchment-scale coupled flow and transport modeling.

Sensitivity of effective rainfall amount to land use description using GIS tool. Case of a small mediterranean catchment

NASA Astrophysics Data System (ADS)

Payraudeau, S.; Tournoud, M. G.; Cernesson, F.

Distributed modelling in hydrology assess catchment subdivision to take into account physic characteristics. In this paper, we test the effect of land use aggregation scheme on catchment hydrological response. Evolution of intra-subcatchment land use is studied using statistic and entropy methods. The SCS-CN method is used to calculate effective rainfall which is here assimilated to hydrological response. Our purpose is to determine the existence of a critical threshold-area appropriate for the application of hydrological modelling. Land use aggregation effects on effective rainfall is assessed on small mediterranean catchment. The results show that land use aggregation and land use classification type have significant effects on hydrological modelling and in particular on effective rainfall modelling.

The distribution of catchment coverage by stationary rainstorms

NASA Technical Reports Server (NTRS)

Eagleson, P. S.

1984-01-01

The occurrence of wetted rainstorm area within a catchment is modeled as a Poisson arrival process in which each storm is composed of stationary, nonoverlapping, independent random cell clusters whose centers are Poisson-distributed in space and whose areas are fractals. The two Poisson parameters and hence the first two moments of the wetted fraction are derived in terms of catchment average characteristics of the (observable) station precipitation. The model is used to estimate spatial properties of tropical air mass thunderstorms on six tropical catchments in the Sudan.

ArcNLET: A GIS-based software to simulate groundwater nitrate load from septic systems to surface water bodies

NASA Astrophysics Data System (ADS)

Rios, J. Fernando; Ye, Ming; Wang, Liying; Lee, Paul Z.; Davis, Hal; Hicks, Rick

2013-03-01

Onsite wastewater treatment systems (OWTS), or septic systems, can be a significant source of nitrates in groundwater and surface water. The adverse effects that nitrates have on human and environmental health have given rise to the need to estimate the actual or potential level of nitrate contamination. With the goal of reducing data collection and preparation costs, and decreasing the time required to produce an estimate compared to complex nitrate modeling tools, we developed the ArcGIS-based Nitrate Load Estimation Toolkit (ArcNLET) software. Leveraging the power of geographic information systems (GIS), ArcNLET is an easy-to-use software capable of simulating nitrate transport in groundwater and estimating long-term nitrate loads from groundwater to surface water bodies. Data requirements are reduced by using simplified models of groundwater flow and nitrate transport which consider nitrate attenuation mechanisms (subsurface dispersion and denitrification) as well as spatial variability in the hydraulic parameters and septic tank distribution. ArcNLET provides a spatial distribution of nitrate plumes from multiple septic systems and a load estimate to water bodies. ArcNLET's conceptual model is divided into three sub-models: a groundwater flow model, a nitrate transport and fate model, and a load estimation model which are implemented as an extension to ArcGIS. The groundwater flow model uses a map of topography in order to generate a steady-state approximation of the water table. In a validation study, this approximation was found to correlate well with a water table produced by a calibrated numerical model although it was found that the degree to which the water table resembles the topography can vary greatly across the modeling domain. The transport model uses a semi-analytical solution to estimate the distribution of nitrate within groundwater, which is then used to estimate a nitrate load using a mass balance argument. The estimates given by ArcNLET are suitable for a screening-level analysis.

Precipitation chemistry in and ionic loading to an Alpine Basin, Sierra Nevada

NASA Astrophysics Data System (ADS)

Williams, Mark W.; Melack, John M.

1991-07-01

Wet deposition of solutes to an alpine catchment in the southern Sierra Nevada was measured from October 1984 through March 1988. Rainfall had a volume-weighted pH of 4.9, and snowfall had a volume-weighted pH of 5.3. Acetic and formic acids were important components of all wet deposition, contributing 25-30% of the measured anions in snowfall and, through analysis of charge balance deficits, the same percentage in rainfall. The NO3- to SO42- equivalent ratio for all wet deposition was 1.16. Ammonium concentration was tenfold greater than H+ in rainfall; ammonium nitrate and ammonium sulfate appear to be the principal nitrate and sulfate containing aerosols in wet deposition. Snowmelt runoff (1985 and 1986) or snowpack runoff plus rainfall during the period of snowpack runoff (1987) supplied 90% of the annual solute flux from wet deposition to the catchment. The amount of snow water equivalence (mm m-2) and H+, SO42-, and Cl- (eq m-2) in cumulative snowfall measured on snowboards was similar to the accumulated deposition of these parameters measured in snowpils at midwinter and during maximum snow accumulation periods, while about 20% of the NO3- in snowfall was not stored in the winter snowpack. Dry deposition was therefore not an important contributor of H+, NO3-, and SO42- to the winter snowpack. The source of the ions in snowfall was air masses that originated over the Pacific Ocean, while low Cl- and Na+ relative to NO3- and NH4+ in rainfall indicate that local urban and agricultural areas were the major source of the ions in rainfall.

The influence of hydrologic connectivity on ecosystem metabolism and nitrate uptake in an active beaver meadow

NASA Astrophysics Data System (ADS)

Wegener, P.; Covino, T. P.; Wohl, E.; Kampf, S. K.; Lacy, S.

2015-12-01

Wetlands have been widely demonstrated to provide important watershed services, such as the sequestration of carbon (C) and removal of nitrate (NO3-) from through-flowing water. Hydrologic connectivity (degree of water and associated material exchange) between floodplain water bodies (e.g., side channels, ponds) and the main channel influence rates of C accumulation and NO3- uptake, and the degree to which wetlands contribute to enhanced water quality at the catchment scale. However, environmental engineers have largely ignored the role of hydrologic connectivity in providing essential ecosystem services, and constructed wetlands are commonly built using compacted clay and berms that result in less groundwater and surface water exchange than observed in natural wetlands. In a study of an active beaver meadow (multithreaded, riparian wetland) in Rocky Mountain National Park, CO, we show how shifts in hydrology (connectivity, residence times, flow paths) from late spring snowmelt (high connectivity) to autumn/winter baseflow (low connectivity) influence ecosystem metabolism metrics (e.g., gross primary production, ecosystem respiration, and net ecosystem productivity) and NO3- uptake rates. We use a combination of mixing analyses, tracer tests, and hydrometric methods to evaluate shifts in surface and subsurface hydrologic connections between floodplain water bodies from snowmelt to baseflow. In the main channel and three floodplain water bodies, we quantify metabolism metrics and NO3- uptake kinetics across shifting flow regimes. Results from our research indicate that NO3- uptake and metabolism dynamics respond to changing levels of hydrologic connectivity to the main channel, emphasizing the importance of incorporating connectivity in wetland mitigation practices that seek to enhance water quality at the catchment scale.

Least Disturbed Condition for European Mediterranean rivers.

PubMed

Feio, M J; Aguiar, F C; Almeida, S F P; Ferreira, J; Ferreira, M T; Elias, C; Serra, S R Q; Buffagni, A; Cambra, J; Chauvin, C; Delmas, F; Dörflinger, G; Erba, S; Flor, N; Ferréol, M; Germ, M; Mancini, L; Manolaki, P; Marcheggiani, S; Minciardi, M R; Munné, A; Papastergiadou, E; Prat, N; Puccinelli, C; Rosebery, J; Sabater, S; Ciadamidaro, S; Tornés, E; Tziortzis, I; Urbanič, G; Vieira, C

2014-04-01

The present report describes a three-step approach that was used to characterize and define thresholds for the Least Disturbed Condition in Mediterranean streams of four different types, regarding organic pollution and nutrients, hydrological and morphological alterations, and land use. For this purpose, a common database composed of national reference sites (929 records) from seven countries, sampled for invertebrates, diatoms and macrophytes was used. The analyses of reference sites showed that small (catchment <100 km(2)) siliceous and non-siliceous streams were mainly affected by channelization, bank alteration and hydropeaking. Medium-sized siliceous rivers were the most affected by stressors: 25-43% of the samples showed at least slight alterations regarding channelization, connectivity, upstream dam influence, hydropeaking and degradation of riparian vegetation. Temporary streams were the least affected by hydromorphological changes, but they were nevertheless affected by alterations in riparian vegetation. There were no major differences between all permanent stream types regarding water quality, but temporary streams showed lower values for oxygenation (DO) and wider ranges for other variables, such as nitrates. A lower threshold value for DO (60%) was determined for this stream type and can be attributed to the streams' natural characteristics. For all other river types, common limits were found for the remaining variables (ammonium, nitrate, phosphate, total P, % of artificial areas, % of intensive and extensive agriculture, % of semi-natural areas in the catchment). These values were then used to select the list of reference sites. The biological communities were characterized, revealing the existence of nine groups of Mediterranean invertebrate communities, six for diatoms and five for macrophytes: each group was characterized by specific indicator taxa that highlighted the differences between groups. Copyright © 2013 Elsevier B.V. All rights reserved.

Long-term, high-frequency water quality monitoring in an agricultural catchment: insights from spectral analysis

NASA Astrophysics Data System (ADS)

Aubert, Alice; Kirchner, James; Faucheux, Mikael; Merot, Philippe; Gascuel-Odoux, Chantal

2013-04-01

The choice of sampling frequency is a key issue in the design and operation of environmental observatories. The choice of sampling frequency creates a spectral window (or temporal filter) that highlights some timescales and processes, and de-emphasizes others (1). New online measurement technologies can monitor surface water quality almost continuously, allowing the creation of very rich time series. The question of how best to analyze such detailed temporal datasets is an important issue in environmental monitoring. In the present work, we studied water quality data from the AgrHys long-term hydrological observatory (located at Kervidy-Naizin, Western France) sampled at daily and 20-minute time scales. Manual sampling has provided 12 years of daily measurements of nitrate, dissolved organic carbon (DOC), chloride and sulfate (2), and 3 years of daily measurements of about 30 other solutes. In addition, a UV-spectrometry probe (Spectrolyser) provides one year of 20-minute measurements for nitrate and DOC. Spectral analysis of the daily water quality time series reveals that our intensively farmed catchment exhibits universal 1/f scaling (power spectrum slope of -1) for a large number of solutes, confirming and extending the earlier discovery of universal 1/f scaling in the relatively pristine Plynlimon catchment (3). 1/f time series confound conventional methods for assessing the statistical significance of trends. Indeed, conventional methods assume that there is a clear separation of scales between the signal (the trend line) and the noise (the scatter around the line). This is not true for 1/f noise, since it overestimates the occurrence of significant trends. Our results raise the possibility that 1/f scaling is widespread in water quality time series, thus posing fundamental challenges to water quality trend analysis. Power spectra of the 20-minute nitrate and DOC time series show 1/f scaling at frequencies below 1/day, consistent with the longer-term daily measurements. At higher frequencies, however, the spectra steepen to a slope of -2, indicating that at sub-daily time scales the concentration time series become relatively smooth. However, at time scales shorter than 2-3 hours, the spectra flatten to a slope near zero (white noise), reflecting analytical noise in the measurement probe. This result demonstrates that measuring water quality dynamics at high frequencies also requires high measurement precision, because as measurements are taken closer and closer together in time, the real-world differences that must be measured between adjacent measurements become smaller and smaller. Our results highlight the importance of quantifying the spectral properties of analytical noise in environmental measurements, to identify frequency ranges where measurements could be dominated by analytical noise instead of real-world signals. 1. Kirchner, J.W., Feng, X., Neal, C., Robson, A.J., 2004. The fine structure of water-quality dynamics: the (high-frequency) wave of the future. Hydrological Processes, 18(7): 1353-1359 2. Aubert, A.H. et al., 2012. The chemical signature of a livestock farming catchment: synthesis from a high-frequency multi-element long term monitoring. HESSD, 9(8): 9715 - 9741 3. Kirchner, J.W. and Neal, C., 2013. Universal fractal scaling in water quality dynamics across the periodic table. Manuscript in review.

Nitrous oxide and nitrate concentration in under-drainage from arable fields subject to diffuse pollution mitigation measures

NASA Astrophysics Data System (ADS)

Hama-Aziz, Zanist; Hiscock, Kevin; Adams, Christopher; Reid, Brian

2016-04-01

Atmospheric nitrous oxide concentrations are increasing by 0.3% annually and a major source of this greenhouse gas is agriculture. Indirect emissions of nitrous oxide (e.g. from groundwater and surface water) account for about quarter of total nitrous oxide emissions. However, these indirect emissions are subject to uncertainty, mainly due to the range in reported emission factors. It's hypothesised in this study that cover cropping and implementing reduced (direct drill) cultivation in intensive arable systems will reduce dissolved nitrate concentration and subsequently indirect nitrous oxide emissions. To test the hypothesis, seven fields with a total area of 102 ha in the Wensum catchment in eastern England have been chosen for experimentation together with two fields (41 ha) under conventional cultivation (deep inversion ploughing) for comparison. Water samples from field under-drainage have been collected for nitrate and nitrous oxide measurement on a weekly basis from April 2013 for two years from both cultivation areas. A purge and trap preparation line connected to a Shimadzu GC-8A gas chromatograph fitted with an electron capture detector was used for dissolved nitrous oxide analysis. Results revealed that with an oilseed radish cover crop present, the mean concentration of nitrate, which is the predominant form of N, was significantly depleted from 13.9 mg N L-1 to 2.5 mg N L-1. However, slightly higher mean nitrous oxide concentrations under the cover crop of 2.61 μg N L-1 compared to bare fields of 2.23 μg N L-1 were observed. Different inversion intensity of soil tended to have no effect on nitrous oxide and nitrate concentrations. The predominant production mechanism for nitrous oxide was nitrification process and the significant reduction of nitrate was due to plant uptake rather than denitrification. It is concluded that although cover cropping might cause a slight increase of indirect nitrous oxide emission, it can be a highly effective mitigation measure in an agricultural area where high nitrate losses from fields into groundwater or surface water is excessively occurring.

Getting the tail to wag the dog: Incorporating groundwater transport into catchment solute transport models using rank StorAge Selection (rSAS) functions

NASA Astrophysics Data System (ADS)

Harman, C. J.

2015-12-01

Surface water hydrologic models are increasingly used to analyze the transport of solutes through the landscape, such as nitrate. However, many of these models cannot adequately capture the effect of groundwater flow paths, which can have long travel times and accumulate legacy contaminants, releasing them to streams over decades. If these long lag times are not accounted for, the short-term efficacy of management activities to reduce nitrogen loads may be overestimated. Models that adopt a simple 'well-mixed' assumption, leading to an exponential transit time distribution at steady state, cannot adequately capture the broadly skewed nature of groundwater transit times in typical watersheds. Here I will demonstrate how StorAge Selection functions can be used to capture the long lag times of groundwater in a typical subwatershed-based hydrologic model framework typical of models like SWAT, HSPF, HBV, PRMS and others. These functions can be selected and calibrated to reproduce historical data where available, but can also be fitted to the results of a steady-state groundwater transport model like MODFLOW/MODPATH, allowing those results to directly inform the parameterization of an unsteady surface water model. The long tails of the transit time distribution predicted by the groundwater model can then be completely captured by the surface water model. Examples of this application in the Chesapeake Bay watersheds and elsewhere will be given.

Erosivity, surface runoff, and soil erosion estimation using GIS-coupled runoff-erosion model in the Mamuaba catchment, Brazil.

PubMed

Marques da Silva, Richarde; Guimarães Santos, Celso Augusto; Carneiro de Lima Silva, Valeriano; Pereira e Silva, Leonardo

2013-11-01

This study evaluates erosivity, surface runoff generation, and soil erosion rates for Mamuaba catchment, sub-catchment of Gramame River basin (Brazil) by using the ArcView Soil and Water Assessment Tool (AvSWAT) model. Calibration and validation of the model was performed on monthly basis, and it could simulate surface runoff and soil erosion to a good level of accuracy. Daily rainfall data between 1969 and 1989 from six rain gauges were used, and the monthly rainfall erosivity of each station was computed for all the studied years. In order to evaluate the calibration and validation of the model, monthly runoff data between January 1978 and April 1982 from one runoff gauge were used as well. The estimated soil loss rates were also realistic when compared to what can be observed in the field and to results from previous studies around of catchment. The long-term average soil loss was estimated at 9.4 t ha(-1) year(-1); most of the area of the catchment (60%) was predicted to suffer from a low- to moderate-erosion risk (<6 t ha(-1) year(-1)) and, in 20% of the catchment, the soil erosion was estimated to exceed > 12 t ha(-1) year(-1). Expectedly, estimated soil loss was significantly correlated with measured rainfall and simulated surface runoff. Based on the estimated soil loss rates, the catchment was divided into four priority categories (low, moderate, high and very high) for conservation intervention. The study demonstrates that the AvSWAT model provides a useful tool for soil erosion assessment from catchments and facilitates the planning for a sustainable land management in northeastern Brazil.

Using a Data-Driven Approach to Understand the Interaction between Catchment Characteristics and Water Quality Responses

NASA Astrophysics Data System (ADS)

Western, A. W.; Lintern, A.; Liu, S.; Ryu, D.; Webb, J. A.; Leahy, P.; Wilson, P.; Waters, D.; Bende-Michl, U.; Watson, M.

2016-12-01

Many streams, lakes and estuaries are experiencing increasing concentrations and loads of nutrient and sediments. Models that can predict the spatial and temporal variability in water quality of aquatic systems are required to help guide the management and restoration of polluted aquatic systems. We propose that a Bayesian hierarchical modelling framework could be used to predict water quality responses over varying spatial and temporal scales. Stream water quality data and spatial data of catchment characteristics collected throughout Victoria and Queensland (in Australia) over two decades will be used to develop this Bayesian hierarchical model. In this paper, we present the preliminary exploratory data analysis required for the development of the Bayesian hierarchical model. Specifically, we present the results of exploratory data analysis of Total Nitrogen (TN) concentrations in rivers in Victoria (in South-East Australia) to illustrate the catchment characteristics that appear to be influencing spatial variability in (1) mean concentrations of TN; and (2) the relationship between discharge and TN throughout the state. These important catchment characteristics were identified using: (1) monthly TN concentrations measured at 28 water quality gauging stations and (2) climate, land use, topographic and geologic characteristics of the catchments of these 28 sites. Spatial variability in TN concentrations had a positive correlation to fertiliser use in the catchment and average temperature. There were negative correlations between TN concentrations and catchment forest cover, annual runoff, runoff perenniality, soil erosivity and catchment slope. The relationship between discharge and TN concentrations showed spatial variability, possibly resulting from climatic and topographic differences between the sites. The results of this study will feed into the hierarchical Bayesian model of river water quality.

Towards a catchment-scale macro-ecological model to support integrated catchment management in Europe

NASA Astrophysics Data System (ADS)

Lerner, R. N.; Lerner, D. N.; Surridge, B.; Paetzold, A.; Harris, B.; Anderson, C. W.

2005-12-01

In Europe, the Water Framework Directive (WFD) is providing a powerful regulatory driver to adopt integrated catchment management, and so pressurizing researchers to build suitable supporting tools. The WFD requires agencies to drive towards `good ecological quality' by 2015. After the initial step of characterising water bodies and the pressures on them, the next substantive step is the preparation of river basin management plans and proposed programmes of measures by 2009. Ecological quality is a complex concept and poorly defined, unless it is taken as a simple measure such as the abundance of a particular species of organism. There is clearly substantial work to do to build a practical but sound definition of ecological quality; practical in the sense of being easy to measure and explain to stakeholders, and sound in the sense that it reflects ecological complexity within catchments, the variability between catchments, and the conflicts demands for goods and services that human society places upon the ecological system. However ecological quality is defined, it will be driven by four interacting groups of factors. These represent the physical, chemical, ecological and socio-economic environments within and encompassing the catchment. Some of these groupings are better understood than others, for example hydrological processes and the transport of solutes are reasonably understood, even though they remain research areas in their own right. There are much larger gaps in our understanding at the interfaces, i.e. predicting how, for example, hydrological processes such as flow and river morphology influence ecological quality. Overall, it is clear we are not yet in a position to build deterministic models of the overall ecological behaviour of catchment. But we need predictive tools to support catchment management agencies in preparing robust plans. This poster describes our current exploration of soft modelling options to build a comprehensive macro-ecological model of UK catchments. This is taking place within the Catchment Science Centre, a joint venture between the University of Sheffield and the Environment Agency.

Runoff production in a small agricultural catchment in Lao PDR : influence of slope, land-use and observation scale.

NASA Astrophysics Data System (ADS)

Patin, J.; Ribolzi, O.; Mugler, C.; Valentin, C.; Mouche, E.

2009-04-01

We study the surface and sub-surface hydrology of a small agricultural catchment (60ha) located in the Luang Prabang province of Lao PDR. This catchment is representative of the rural mountainous south east Asia. It exhibits steep slopes (up to 100% and more) under a monsoon climate. After years of traditional slash and burn cultures, it is now under high land pressures due to population resettling and environment preservation policies. This evolution leads to rapid land-use changes such as shifting cultivation reduction or growing of teak forest instead of classical crops. This catchment is a benchmark site of the Managing Soil Erosion Consortium since 1998. The international consortium aims to understand the effects of agricultural changes on the catchment hydrology and soil erosion in south east Asia. The Huay Pano catchment is subdivided into small sub-catchments that are gauged and monitored. Differ- ent agricultural practices where tested along the years. At a smaller scale, plot of 1m2 are instrumented to follow runoff and detachment of soil under natural rainfall along the monsoon season. Our modeling work aims to develop a distributed hydrological model integrating experimental data at the different scales. One of the objective is to understand the impact of land-use, soil properties (slope, crust, etc) and rainfall (dry and wet seasons) on surface and subsurface flows. We present here modeling results of the runoff plot experiments (1m2 scale) performed from 2002 to 2007. The plots distribution among the catchment and over the years gives a good representativity of the different runoff responses. The role of crust, slope and land-use on runoff is examined. Finally we discuss how this plot scale will be integrated in a sub-catchment model, with a particular attention on the observed paradox: how to explain that runoff coefficients at the catchment scale are much slower than at the plot scale ?

Scale appropriate modelling to represent dominant pollution processes in agricultural catchments, to underpin management and policy decisions

NASA Astrophysics Data System (ADS)

Adams, Russell; Quinn, Paul

2014-05-01

We present the development of scale appropriate modelling techniques to represent dominant pollution processes in agricultural catchments to underpin catchment management and its implications on policy. A quasi-physically based, spatially lumped macro-model (CRAFT), has been developed to assess mitigation options for nitrogen and phosphorus. CRAFT has been developed to use daily time series data of rainfall, stream flow and nutrient concentration data, and can be applied to catchments varying in size from a few hectares to 100s of square kilometres. If stream flow routing is added to the model then potentially larger catchments and sub-daily time steps could be represented. There are two key issues addressed here. Firstly, the model can be used to assess the usefulness of monitoring data collected at a high temporal resolution at considerable expense compared to routine grab sampling. An earlier study in the Frome catchment in southern England collected sub-daily water quality data for more than 12 months at the catchment outlet, comprising: total oxidised nitrogen (TON); soluble reactive phosphorus (SRP) and total phosphorus (TP) concentrations. The three data sets have quite different temporal signals relating to flow pathways with different residence times and the importance of runoff events in generating acute pollution. The flexible model structure was therefore developed to include different sources of runoff including overland flow from impervious areas in the catchment, where pollution hotspots will be located (e.g. farmyards). The model has been used to assess the value of collecting high resolution monitoring data, in this case by resampling the Frome sub-daily data to a daily timestep, and comparing these model simulations against those calibrated using all the samples. The usefulness of the high resolution data can be assessed on whether a daily model would undepredict (for example) high nutrient concentrations that can be identified in the sub-daily monitoring data. Secondly, the study aims to investigate the mitigation measures that can be used to address the catchment scale sources of N and P, under EU or other governmental legislation designed to reduce their loads. In a complex catchment like the Frome, the mitigation measures are likely to target both point and non-point sources, particularly of SRP (e.g. wastewater treatment plant discharges and soluble fertilizer applications respectively). For a modelling tool to be useful to land holders and policy makers, it is imperative that these stakeholders can investigate different scenarios by easily manipulating the model input parameters, e.g. by reducing the diffuse sources of SRP and TON (by parameter adjustment), or modifying flow pathways through runoff attenuation (e.g. reducing runoff from farmyards), and the model structure reflects this functionality allowing it to be used as a runoff attenuation tool.

Conjunction of wavelet transform and SOM-mutual information data pre-processing approach for AI-based Multi-Station nitrate modeling of watersheds

NASA Astrophysics Data System (ADS)

Nourani, Vahid; Andalib, Gholamreza; Dąbrowska, Dominika

2017-05-01

Accurate nitrate load predictions can elevate decision management of water quality of watersheds which affects to environment and drinking water. In this paper, two scenarios were considered for Multi-Station (MS) nitrate load modeling of the Little River watershed. In the first scenario, Markovian characteristics of streamflow-nitrate time series were proposed for the MS modeling. For this purpose, feature extraction criterion of Mutual Information (MI) was employed for input selection of artificial intelligence models (Feed Forward Neural Network, FFNN and least square support vector machine). In the second scenario for considering seasonality-based characteristics of the time series, wavelet transform was used to extract multi-scale features of streamflow-nitrate time series of the watershed's sub-basins to model MS nitrate loads. Self-Organizing Map (SOM) clustering technique which finds homogeneous sub-series clusters was also linked to MI for proper cluster agent choice to be imposed into the models for predicting the nitrate loads of the watershed's sub-basins. The proposed MS method not only considers the prediction of the outlet nitrate but also covers predictions of interior sub-basins nitrate load values. The results indicated that the proposed FFNN model coupled with the SOM-MI improved the performance of MS nitrate predictions compared to the Markovian-based models up to 39%. Overall, accurate selection of dominant inputs which consider seasonality-based characteristics of streamflow-nitrate process could enhance the efficiency of nitrate load predictions.

Prediction of Baseflow Index of Catchments using Machine Learning Algorithms

NASA Astrophysics Data System (ADS)

Yadav, B.; Hatfield, K.

2017-12-01

We present the results of eight machine learning techniques for predicting the baseflow index (BFI) of ungauged basins using a surrogate of catchment scale climate and physiographic data. The tested algorithms include ordinary least squares, ridge regression, least absolute shrinkage and selection operator (lasso), elasticnet, support vector machine, gradient boosted regression trees, random forests, and extremely randomized trees. Our work seeks to identify the dominant controls of BFI that can be readily obtained from ancillary geospatial databases and remote sensing measurements, such that the developed techniques can be extended to ungauged catchments. More than 800 gauged catchments spanning the continental United States were selected to develop the general methodology. The BFI calculation was based on the baseflow separated from daily streamflow hydrograph using HYSEP filter. The surrogate catchment attributes were compiled from multiple sources including digital elevation model, soil, landuse, climate data, other publicly available ancillary and geospatial data. 80% catchments were used to train the ML algorithms, and the remaining 20% of the catchments were used as an independent test set to measure the generalization performance of fitted models. A k-fold cross-validation using exhaustive grid search was used to fit the hyperparameters of each model. Initial model development was based on 19 independent variables, but after variable selection and feature ranking, we generated revised sparse models of BFI prediction that are based on only six catchment attributes. These key predictive variables selected after the careful evaluation of bias-variance tradeoff include average catchment elevation, slope, fraction of sand, permeability, temperature, and precipitation. The most promising algorithms exceeding an accuracy score (r-square) of 0.7 on test data include support vector machine, gradient boosted regression trees, random forests, and extremely randomized trees. Considering both the accuracy and the computational complexity of these algorithms, we identify the extremely randomized trees as the best performing algorithm for BFI prediction in ungauged basins.

Hochauflösendes Monitoring von Karst-Grundwasserressourcen beiderseits des Jordangrabens - Konzepte und Anwendungsbeispiele

NASA Astrophysics Data System (ADS)

Schmidt, Sebastian; Grimmeisen, Felix; Ries, Fabian; Goldscheider, Nico; Sauter, Martin

2018-03-01

In the semi-arid eastern Mediterranean water supply is highly dependent on karst aquifers. The region is characterized by multi-year dry and wet cycles combined with high hydrological dynamics, especially during intense precipitation events. The investigated karst regions in the West Bank and Jordan are experiencing strong urbanization within the groundwater catchments and hence a rising impact on water quality. Therefore, high resolution monitoring data are required for the assessment of available water resources and the hydrogeological characterization of the karst systems. These measurements are focused on the (natural) meteorological input signals and the system output signals at the karst springs. Also soil moisture and ephemeral runoff dynamics are investigated. The monitoring data enable (1) hydrogeological characterization of the aquifers, (2) estimation of groundwater recharge via soil water balance and reservoir models, and (3) assessment of contamination dynamics in groundwater (e. g. nitrate and E. coli concentrations), allowing an optimized raw water management. Several examples illustrate the importance of high-resolution hydrological monitoring data.

Hydrological similarity approach and rainfall satellite utilization for mini hydro power dam basic design (case study on the ungauged catchment at West Borneo, Indonesia)

NASA Astrophysics Data System (ADS)

Prakoso, W. G.; Murtilaksono, K.; Tarigan, S. D.; Purwanto, Y. J.

2018-05-01

An approach on flow duration and flood design estimation on the ungauged catchment with no rainfall and discharge data availability was been being develop with hydrological modelling including rainfall run off model implemented with watershed characteristic dataset. Near real time Rainfall data from multi satellite platform e.g. TRMM can be utilized for regionalization approach on the ungauged catchment. Watershed hydrologically similarity analysis were conducted including all of the major watershed in Borneo which was predicted to be similar with the Nanga Raun Watershed. It was found that a satisfactory hydrological model calibration could be achieved using catchment weighted time series of TRMM daily rainfall data, performed on nearby catchment deemed to be sufficiently similar to Nanga Raun catchment in hydrological terms. Based on this calibration, rainfall runoff parameters were then transferred to a model. Relatively reliable flow duration curve and extreme discharge value estimation were produced with reasonable several limitation. Further approach may be performed in order to deal with the primary limitations inherent in the hydrological and statistical analysis, especially to give prolongation to the availability of the rainfall and climate data with some novel approach like downscaling of global climate model.

SWAT-CS: Revision and testing of SWAT for Canadian Shield catchments

NASA Astrophysics Data System (ADS)

Fu, Congsheng; James, April L.; Yao, Huaxia

2014-04-01

Canadian Shield catchments are under increasing pressure from various types of development (e.g., mining and increased cottagers) and changing climate. Within the southern part of the Canadian Shield, catchments are generally characterized by shallow forested soils with high infiltration rates and low bedrock infiltration, generating little overland flow, and macropore and subsurface flow are important streamflow generation processes. Large numbers of wetlands and lakes are also key physiographic features, and snow-processes are critical to catchment modeling in this climate. We have revised the existing, publicly available SWAT (version 2009.10.1 Beta 3) to create SWAT-CS, a version representing hydrological processes dominating Canadian Shield catchments, where forest extends over Precambrian Shield bedrock. Prior to this study, very few studies applying SWAT to Canadian Shield catchments exist (we have found three). We tested SWAT-CS using the Harp Lake catchment dataset, an Ontario Ministry of Environment research station located in south-central Ontario. Simulations were evaluated against 30 years of observational data, including streamflow from six headwater sub-catchments (0.1-1.9 km2), outflow from Harp Lake (5.4 km2) and five years of weekly snow water equivalent (SWE). The best Nash-Sutcliffe efficiency (NSE) results for daily streamflow calibration, daily streamflow validation, and SWE were 0.60, 0.65, and 0.87, respectively, for sub-catchment HP4 (with detailed land use and soil data). For this range of catchment scales, land cover and soil properties were found to be transferable across sub-catchments with similar physiographic features, namely streamflow from the remaining five sub-catchments could be modeled well using sub-catchment HP4 parameterization. The Harp Lake outflow was well modeled using the existing reservoir-based target release method, generating NSEs of 0.72 and 0.67 for calibration and verification periods respectively. With significant changes to the infiltration module (introducing macropore flow and reduced bedrock percolation), more than 90% of interflow was generated close to the soil-bedrock interface and the contribution of groundwater flow to total runoff was reduced to small amounts, consistent with hydrological process understanding in this terrain. These two changes also allowed for a positive linear relationship between NSE of SWE and Q, whereas prior to these changes there was a negative relationship. With these key revisions to the infiltration and bedrock percolations modules, it is concluded that SWAT-CS can reasonably capture key hydrological processes within Canadian Shield catchments. Further testing will examine water quality modeling and larger-scale applications.

Impact of modellers' decisions on hydrological a priori predictions

NASA Astrophysics Data System (ADS)

Holländer, H. M.; Bormann, H.; Blume, T.; Buytaert, W.; Chirico, G. B.; Exbrayat, J.-F.; Gustafsson, D.; Hölzel, H.; Krauße, T.; Kraft, P.; Stoll, S.; Blöschl, G.; Flühler, H.

2014-06-01

In practice, the catchment hydrologist is often confronted with the task of predicting discharge without having the needed records for calibration. Here, we report the discharge predictions of 10 modellers - using the model of their choice - for the man-made Chicken Creek catchment (6 ha, northeast Germany, Gerwin et al., 2009b) and we analyse how well they improved their prediction in three steps based on adding information prior to each following step. The modellers predicted the catchment's hydrological response in its initial phase without having access to the observed records. They used conceptually different physically based models and their modelling experience differed largely. Hence, they encountered two problems: (i) to simulate discharge for an ungauged catchment and (ii) using models that were developed for catchments, which are not in a state of landscape transformation. The prediction exercise was organized in three steps: (1) for the first prediction the modellers received a basic data set describing the catchment to a degree somewhat more complete than usually available for a priori predictions of ungauged catchments; they did not obtain information on stream flow, soil moisture, nor groundwater response and had therefore to guess the initial conditions; (2) before the second prediction they inspected the catchment on-site and discussed their first prediction attempt; (3) for their third prediction they were offered additional data by charging them pro forma with the costs for obtaining this additional information. Holländer et al. (2009) discussed the range of predictions obtained in step (1). Here, we detail the modeller's assumptions and decisions in accounting for the various processes. We document the prediction progress as well as the learning process resulting from the availability of added information. For the second and third steps, the progress in prediction quality is evaluated in relation to individual modelling experience and costs of added information. In this qualitative analysis of a statistically small number of predictions we learned (i) that soft information such as the modeller's system understanding is as important as the model itself (hard information), (ii) that the sequence of modelling steps matters (field visit, interactions between differently experienced experts, choice of model, selection of available data, and methods for parameter guessing), and (iii) that added process understanding can be as efficient as adding data for improving parameters needed to satisfy model requirements.

National-Scale Hydrologic Classification & Agricultural Decision Support: A Multi-Scale Approach

NASA Astrophysics Data System (ADS)

Coopersmith, E. J.; Minsker, B.; Sivapalan, M.

2012-12-01

Classification frameworks can help organize catchments exhibiting similarity in hydrologic and climatic terms. Focusing this assessment of "similarity" upon specific hydrologic signatures, in this case the annual regime curve, can facilitate the prediction of hydrologic responses. Agricultural decision-support over a diverse set of catchments throughout the United States depends upon successful modeling of the wetting/drying process without necessitating separate model calibration at every site where such insights are required. To this end, a holistic classification framework is developed to describe both climatic variability (humid vs. arid, winter rainfall vs. summer rainfall) and the draining, storing, and filtering behavior of any catchment, including ungauged or minimally gauged basins. At the national scale, over 400 catchments from the MOPEX database are analyzed to construct the classification system, with over 77% of these catchments ultimately falling into only six clusters. At individual locations, soil moisture models, receiving only rainfall as input, produce correlation values in excess of 0.9 with respect to observed soil moisture measurements. By deploying physical models for predicting soil moisture exclusively from precipitation that are calibrated at gauged locations, overlaying machine learning techniques to improve these estimates, then generalizing the calibration parameters for catchments in a given class, agronomic decision-support becomes available where it is needed rather than only where sensing data are located.lassifications of 428 U.S. catchments on the basis of hydrologic regime data, Coopersmith et al, 2012.

Urban flood simulation and prioritization of critical urban sub-catchments using SWMM model and PROMETHEE II approach

NASA Astrophysics Data System (ADS)

Babaei, Sahar; Ghazavi, Reza; Erfanian, Mahdi

2018-06-01

Urban runoff increased due to augment of impervious surfaces. In order to flood mitigation during rainy season, determination of critical urban sub-catchments is very important for urban planners. Due to lack of information, adopting a simulation approach is one of the practical ways to identify the surcharged junctions and critical sub-catchments. Occurrence of destructive floods in the rainy seasons indicates the inappropriateness of the urban drainage system in Urmia. The main aims of this study were to estimate the surface runoff of urban sub-catchments using SWMM, to evaluate the accuracy of the drainage system of the study urban area and to prioritize sub-catchments using PROMETHEE II approach and SWMM. In the present study, the occurrence of rainfall event of the Urmia city (West Azerbaijan province, Iran) used for estimation of runoff depth. The study area was divided into 22 sub-catchments. For calibration and validation of model parameters, 3 rainfall events and their related runoff were measured. According to sensitivity analysis CN was the most sensitive parameter for model calibration. Amount of surcharged conduits and junctions indicates that the drainage system of the study area has not enough capacity for converting of the runoff and. For 10 year return period, depth of channels should increase by 20% for prevention of flooding in these sub-catchments. Sub-catchments were prioritized using PROMETHEE II approach and its results were compared with SWMM simulation outcomes. Based on SWMM simulation, S11, S7, S18, S16 and S1 sub-catchments are more critical sub-catchments respectively, while according to PROMETHEE method, S1, S11, S16, S14 and S18 are determined as the critical areas.

Development and validation of a runoff and erosion model for lowland drained catchments

NASA Astrophysics Data System (ADS)

Grangeon, Thomas; Cerdan, Olivier; Vandromme, Rosalie; Landemaine, Valentin; Manière, Louis; Salvador-Blanes, Sébastien; Foucher, Anthony; Evrard, Olivier

2017-04-01

Modelling water and sediment transfer in lowland catchments is complex as both hortonian and saturation excess-flow occur in these environments. Moreover, their dynamics was complexified by the installation of tile drainage networks or stream redesign. To the best of our knowledge, few models are able to simulate saturation runoff as well as hortonian runoff in tile-drained catchments. Most of the time, they are used for small scale applications due to their high degree of complexity. In this context, a model of intermediate complexity was developed to simulate the hydrological and erosion processes at the catchment scale in lowland environments. This GIS-based, spatially distributed and lumped model at the event scale uses a theoretical hydrograph to approximate within-event temporal variations. It comprises two layers used to represent surface and subsurface transfers. Observations of soil surface characteristics (i.e. vegetation density, soil crusting and roughness) were used to document spatial variations of physical soil characteristics (e.g. infiltration capacity). Flow was routed depending on the local slope, using LIDAR elevation data. Both the diffuse and the gully erosion are explicitly described. The model ability to simulate water and sediment dynamics at the catchment scale was evaluated using the monitoring of a selection of flood events in a small, extensively cultivated catchment (the Louroux catchment, Loire River basin, central France; 25 km2). In this catchment, five monitoring stations were equipped with water level sensors, turbidity probes, and automatic samplers. Discharge and suspended sediment concentration were deduced from field measurements. One station was installed at the outlet of a tile drain and was used to parameterize fluxes supplied by the drainage network. The selected floods were representative of various rainfall and soil surface conditions (e.g. low-intensity rainfall occurring on saturated soils as well as intense rainfall occurring on dry soils in spring). The model was able to reproduce the runoff volumes for these different situations, and performed well, especially in winter (the relationship between observed and modeled values has R2=0.72) when most of the sediment are transferred. Therefore, future work will evaluate the model ability to reproduce the erosion and sediment dynamics in this catchment in order to provide a tool for sediment management in these lowland environments draining agricultural land where river siltation is problematic.

The changing trend in nitrate concentrations in major aquifers due to historical nitrate loading from agricultural land across England and Wales from 1925 to 2150.

PubMed

Wang, L; Stuart, M E; Lewis, M A; Ward, R S; Skirvin, D; Naden, P S; Collins, A L; Ascott, M J

2016-01-15

Nitrate is necessary for agricultural productivity, but can cause considerable problems if released into aquatic systems. Agricultural land is the major source of nitrates in UK groundwater. Due to the long time-lag in the groundwater system, it could take decades for leached nitrate from the soil to discharge into freshwaters. However, this nitrate time-lag has rarely been considered in environmental water management. Against this background, this paper presents an approach to modelling groundwater nitrate at the national scale, to simulate the impacts of historical nitrate loading from agricultural land on the evolution of groundwater nitrate concentrations. An additional process-based component was constructed for the saturated zone of significant aquifers in England and Wales. This uses a simple flow model which requires modelled recharge values, together with published aquifer properties and thickness data. A spatially distributed and temporally variable nitrate input function was also introduced. The sensitivity of parameters was analysed using Monte Carlo simulations. The model was calibrated using national nitrate monitoring data. Time series of annual average nitrate concentrations along with annual spatially distributed nitrate concentration maps from 1925 to 2150 were generated for 28 selected aquifer zones. The results show that 16 aquifer zones have an increasing trend in nitrate concentration, while average nitrate concentrations in the remaining 12 are declining. The results are also indicative of the trend in the flux of groundwater nitrate entering rivers through baseflow. The model thus enables the magnitude and timescale of groundwater nitrate response to be factored into source apportionment tools and to be taken into account alongside current planning of land-management options for reducing nitrate losses. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Modeling sediment yield in small catchments at event scale: Model comparison, development and evaluation

NASA Astrophysics Data System (ADS)

Tan, Z.; Leung, L. R.; Li, H. Y.; Tesfa, T. K.

2017-12-01

Sediment yield (SY) has significant impacts on river biogeochemistry and aquatic ecosystems but it is rarely represented in Earth System Models (ESMs). Existing SY models focus on estimating SY from large river basins or individual catchments so it is not clear how well they simulate SY in ESMs at larger spatial scales and globally. In this study, we compare the strengths and weaknesses of eight well-known SY models in simulating annual mean SY at about 400 small catchments ranging in size from 0.22 to 200 km2 in the US, Canada and Puerto Rico. In addition, we also investigate the performance of these models in simulating event-scale SY at six catchments in the US using high-quality hydrological inputs. The model comparison shows that none of the models can reproduce the SY at large spatial scales but the Morgan model performs the better than others despite its simplicity. In all model simulations, large underestimates occur in catchments with very high SY. A possible pathway to reduce the discrepancies is to incorporate sediment detachment by landsliding, which is currently not included in the models being evaluated. We propose a new SY model that is based on the Morgan model but including a landsliding soil detachment scheme that is being developed. Along with the results of the model comparison and evaluation, preliminary findings from the revised Morgan model will be presented.

The benefits of daily data and scale up issues in hydrologic models-SWAT and CRAFT

NASA Astrophysics Data System (ADS)

Huang, Yumei; Quinn, Paul; Liang, Qiuhua; Adams, Russell

2017-04-01

When modelling the flow pathways for nutrient transport, the lack of good data and limitation of data resolution become the key cause of low quality output in various hydrologic models. The scale of catchment being studied would present the main issues of the sensitivity and uncertainty expected on the hydrologic modelling. Equally, the time step chosen is also important to nutrient dynamics. This study aims to evaluate the benefits of using both monthly and daily data in hydrologic models, and to address the issues of catchment scale when using the two hydrologic models, the Soil and Water Assessment Tool (SWAT), and Catchment Runoff Attenuation Flux Tool (CRAFT), by comparing the difference between SWAT and CRAFT in flow pathways and sediment transport. The models are different in terms of complexity, therefore the poster will discuss the strengths and weakness of the models. Also we can show the problems of calibration and how the models can be used to support catchment modelling.

Modelling remediation scenarios in historical mining catchments.

PubMed

Gamarra, Javier G P; Brewer, Paul A; Macklin, Mark G; Martin, Katherine

2014-01-01

Local remediation measures, particularly those undertaken in historical mining areas, can often be ineffective or even deleterious because erosion and sedimentation processes operate at spatial scales beyond those typically used in point-source remediation. Based on realistic simulations of a hybrid landscape evolution model combined with stochastic rainfall generation, we demonstrate that similar remediation strategies may result in differing effects across three contrasting European catchments depending on their topographic and hydrologic regimes. Based on these results, we propose a conceptual model of catchment-scale remediation effectiveness based on three basic catchment characteristics: the degree of contaminant source coupling, the ratio of contaminated to non-contaminated sediment delivery, and the frequency of sediment transport events.

Modeling the effects of different N fertilizer rates on N2O emissions and nitrate leaching from arable soils in Korea

NASA Astrophysics Data System (ADS)

Kim, Y.; Berger, S.; Tenhunen, J. D.; Gebauer, G.; Kiese, R.

2012-12-01

Process-based biogeochemical models can be used to predict the impact of various agricultural management practices on plant nitrogen use efficiency and nitrogen losses to the environment such as greenhouse gas emissions and nitrate leaching by analyzing the interactions between management practices, primary drivers such as climate, soil properties, crop types, etc., and biogeochemical reactions. In this study we applied the Landscape-DNDC model, which combines and uniforms functions of the agricultural-DNDC and the Forest-DNDC for simulation of C and N turnover, GHG emissions, nitrate leaching, and plant growth for a Korean arable field cultivated with radish (Raphanus sativus L.). The annual average temperature is app. 8.5°C and the annual precipitation is app. 1,500 mm. According to farmers practice the study field received a basal fertilizer application of app. 200 kg N ha-1 before setting up four fertilizer treatments i.e. additionally 50, 150, 250 and 350 kg N ha-1. All N treatment plots were tilled a week after application of specific N fertilizer in order to make row and interrow. Just before radish seeding rows were covered with black plastic mulch which was removed after harvest. In spite the widespread usage of black mulch in Korea or even Asia; so far biogeochemical models do not consider impacts of mulch on soil environmental conditions and soil biogeochemistry. Based on field measurements we adjusted input information and used only half of the annual precipitation and the maximum temperature for simulation of row conditions, whereas the actual weather data were used for the interrow simulations. Simulated N2O emissions agreed well with measurements; however peak emissions after fertilization were slightly underestimated in row and interrow. Annual N2O emissions of the fertilizer treatments increased with increasing fertilization rates from around 1.5 to 3 kg N ha-1 in the row and lower emissions of app. 1.5 kg N ha-1 (for all N treatments) in the interrow resulting in total direct emissions of about 1.5 to 2.3 kg N ha-1 yr-1 (area weighted average of row and interrow). Compared with the IPCC approach (EF = 0.01) these values are rather low which can be explained by high rates of simulated and measured nitrate leaching across all N treatments (row: 214 - 240 kg N ha-1 yr-1; interrow: 259 - 263 kg N ha-1 yr-1). Seasonal dynamic and magnitude of measured and simulated NO3 concentrations in soil water in different soil depths agreed well which give further evidence for the simulated nitrate leaching. Using the IPCC EF of 0.0075, nitrate leaching results in indirect N2O emissions of additionally 1.8 kg N ha-1 yr-1. Only slight increase of measured and simulated yields (4 to 5.2 t DW ha-1) with higher rates of N fertilization indicate that actual farmer practices can be improved and optimizing agricultural management considering the specific climatic and soil conditions has a high potential to reduce environmental impacts of crop cultivations in the study area of the Haean catchment.

On the use of three hydrological models as hypotheses to investigate the behaviour of a small Mediterranean catchment

NASA Astrophysics Data System (ADS)

Ruiz Pérez, Guiomar; Latron, Jérôme; Llorens, Pilar; Gallart, Francesc; Francés, Félix

2017-04-01

Selecting an adequate hydrological model is the first step to carry out a rainfall-runoff modelling exercise. A hydrological model is a hypothesis of catchment functioning, encompassing a description of dominant hydrological processes and predicting how these processes interact to produce the catchment's response to external forcing. Current research lines emphasize the importance of multiple working hypotheses for hydrological modelling instead of only using a single model. In line with this philosophy, here different hypotheses were considered and analysed to simulate the nonlinear response of a small Mediterranean catchment and to progress in the analysis of its hydrological behaviour. In particular, three hydrological models were considered representing different potential hypotheses: two lumped models called LU3 and LU4, and one distributed model called TETIS. To determine how well each specific model performed and to assess whether a model was more adequate than another, we raised three complementary tests: one based on the analysis of residual errors series, another based on a sensitivity analysis and the last one based on using multiple evaluation criteria associated to the concept of Pareto frontier. This modelling approach, based on multiple working hypotheses, helped to improve our perceptual model of the catchment behaviour and, furthermore, could be used as a guidance to improve the performance of other environmental models.

Review article: Hydrological modeling in glacierized catchments of central Asia - status and challenges

NASA Astrophysics Data System (ADS)

Chen, Yaning; Li, Weihong; Fang, Gonghuan; Li, Zhi

2017-02-01

Meltwater from glacierized catchments is one of the most important water supplies in central Asia. Therefore, the effects of climate change on glaciers and snow cover will have increasingly significant consequences for runoff. Hydrological modeling has become an indispensable research approach to water resources management in large glacierized river basins, but there is a lack of focus in the modeling of glacial discharge. This paper reviews the status of hydrological modeling in glacierized catchments of central Asia, discussing the limitations of the available models and extrapolating these to future challenges and directions. After reviewing recent efforts, we conclude that the main sources of uncertainty in assessing the regional hydrological impacts of climate change are the unreliable and incomplete data sets and the lack of understanding of the hydrological regimes of glacierized catchments of central Asia. Runoff trends indicate a complex response to changes in climate. For future variation of water resources, it is essential to quantify the responses of hydrologic processes to both climate change and shrinking glaciers in glacierized catchments, and scientific focus should be on reducing uncertainties linked to these processes.

Research on Multi Hydrological Models Applicability and Modelling Data Uncertainty Analysis for Flash Flood Simulation in Hilly Area

NASA Astrophysics Data System (ADS)

Ye, L.; Wu, J.; Wang, L.; Song, T.; Ji, R.

2017-12-01

Flooding in small-scale watershed in hilly area is characterized by short time periods and rapid rise and recession due to the complex underlying surfaces, various climate type and strong effect of human activities. It is almost impossible for a single hydrological model to describe the variation of flooding in both time and space accurately for all the catchments in hilly area because the hydrological characteristics can vary significantly among different catchments. In this study, we compare the performance of 5 hydrological models with varying degrees of complexity for simulation of flash flood for 14 small-scale watershed in China in order to find the relationship between the applicability of the hydrological models and the catchments characteristics. Meanwhile, given the fact that the hydrological data is sparse in hilly area, the effect of precipitation data, DEM resolution and their interference on the uncertainty of flood simulation is also illustrated. In general, the results showed that the distributed hydrological model (HEC-HMS in this study) performed better than the lumped hydrological models. Xinajiang and API models had good simulation for the humid catchments when long-term and continuous rainfall data is provided. Dahuofang model can simulate the flood peak well while the runoff generation module is relatively poor. In addition, the effect of diverse modelling data on the simulations is not simply superposed, and there is a complex interaction effect among different modelling data. Overall, both the catchment hydrological characteristics and modelling data situation should be taken into consideration in order to choose the suitable hydrological model for flood simulation for small-scale catchment in hilly area.

Should we trust build-up/wash-off water quality models at the scale of urban catchments?

PubMed

Bonhomme, Céline; Petrucci, Guido

2017-01-01

Models of runoff water quality at the scale of an urban catchment usually rely on build-up/wash-off formulations obtained through small-scale experiments. Often, the physical interpretation of the model parameters, valid at the small-scale, is transposed to large-scale applications. Testing different levels of spatial variability, the parameter distributions of a water quality model are obtained in this paper through a Monte Carlo Markov Chain algorithm and analyzed. The simulated variable is the total suspended solid concentration at the outlet of a periurban catchment in the Paris region (2.3 km 2 ), for which high-frequency turbidity measurements are available. This application suggests that build-up/wash-off models applied at the catchment-scale do not maintain their physical meaning, but should be considered as "black-box" models. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dual nitrate isotopes clarify the role of biological processing and hydrologic flow paths on nitrogen cycling in subtropical low-gradient watersheds

DOE PAGES

Griffiths, Natalie A.; Jackson, C. Rhett; McDonnell, Jeffrey J.; ...

2016-02-08

Nitrogen (N) is an important nutrient as it often limits productivity but in excess can impair water quality. Most studies on watershed N cycling have occurred in upland forested catchments where snowmelt dominates N export; fewer studies have focused on low-relief watersheds that lack snow. We examined watershed N cycling in three adjacent, low-relief watersheds in the Upper Coastal Plain of the southeastern United States to better understand the role of hydrological flow paths and biological transformations of N at the watershed scale. Groundwater was the dominant source of nitrified N to stream water in two of the three watersheds,more » while atmospheric deposition comprised 28% of stream water nitrate in one watershed. The greater atmospheric contribution may have been due to the larger stream channel area relative to total watershed area or the dominance of shallow subsurface flow paths contributing to stream flow in this watershed. There was a positive relationship between temperature and stream water ammonium concentrations and a negative relationship between temperature and stream water nitrate concentrations in each watershed suggesting that N cycling processes (i.e., nitrification and denitrification) varied seasonally. However, there were no clear patterns in the importance of denitrification in different water pools possibly because a variety of factors (i.e., assimilatory uptake, dissimilatory uptake, and mixing) affected nitrate concentrations. In conclusion, together, these results highlight the hydrological and biological controls on N cycling in low-gradient watersheds and variability in N delivery flow paths among adjacent watersheds with similar physical characteristics.« less

Modelling strategies to predict the multi-scale effects of rural land management change

NASA Astrophysics Data System (ADS)

Bulygina, N.; Ballard, C. E.; Jackson, B. M.; McIntyre, N.; Marshall, M.; Reynolds, B.; Wheater, H. S.

2011-12-01

Changes to the rural landscape due to agricultural land management are ubiquitous, yet predicting the multi-scale effects of land management change on hydrological response remains an important scientific challenge. Much empirical research has been of little generic value due to inadequate design and funding of monitoring programmes, while the modelling issues challenge the capability of data-based, conceptual and physics-based modelling approaches. In this paper we report on a major UK research programme, motivated by a national need to quantify effects of agricultural intensification on flood risk. Working with a consortium of farmers in upland Wales, a multi-scale experimental programme (from experimental plots to 2nd order catchments) was developed to address issues of upland agricultural intensification. This provided data support for a multi-scale modelling programme, in which highly detailed physics-based models were conditioned on the experimental data and used to explore effects of potential field-scale interventions. A meta-modelling strategy was developed to represent detailed modelling in a computationally-efficient manner for catchment-scale simulation; this allowed catchment-scale quantification of potential management options. For more general application to data-sparse areas, alternative approaches were needed. Physics-based models were developed for a range of upland management problems, including the restoration of drained peatlands, afforestation, and changing grazing practices. Their performance was explored using literature and surrogate data; although subject to high levels of uncertainty, important insights were obtained, of practical relevance to management decisions. In parallel, regionalised conceptual modelling was used to explore the potential of indices of catchment response, conditioned on readily-available catchment characteristics, to represent ungauged catchments subject to land management change. Although based in part on speculative relationships, significant predictive power was derived from this approach. Finally, using a formal Bayesian procedure, these different sources of information were combined with local flow data in a catchment-scale conceptual model application , i.e. using small-scale physical properties, regionalised signatures of flow and available flow measurements.

Development and Application of a Simple Hydrogeomorphic Model for Headwater Catchments

EPA Science Inventory

We developed a catchment model based on a hydrogeomorphic concept that simulates discharge from channel-riparian complexes, zero-order basins (ZOB, basins ZB and FA), and hillslopes. Multitank models simulate ZOB and hillslope hydrological response, while kinematic wave models pr...

Effects of harvest on carbon and nitrogen dynamics in a Pacific Northwest forest catchment

Treesearch

Alex Abdelnour; Robert B. McKane; Marc Stieglitz; Feifei Pan; Yiwei Cheng

2013-01-01

We used a new ecohydrological model, Visualizing Ecosystems for Land Management Assessments (VELMA), to analyze the effects of forest harvest on catchment carbon and nitrogen dynamics. We applied the model to a 10 ha headwater catchment in the western Oregon Cascade Range where two major disturbance events have occurred during the past 500 years: a stand-replacing fire...

Effects of wildfire on catchment runoff response: a modeling approach to detect changes in snow-dominated forested catchments

Treesearch

Jan Seibert; Jeffrey J. McDonnell; Richard D. Woodsmith

2010-01-01

Wildfire is an important disturbance affecting hydrological processes through alteration of vegetation cover and soil characteristics. The effects of fire on hydrological systems at the catchment scale are not well known, largely because site specific data from both before and after wildfire are rare. In this study a modelling approach was employed for change detection...

A SIMPLE HYDROLOGICAL MODEL FOR WATERSHED CHARACTERIZATION

EPA Science Inventory

Catchment behavior is characterized with a variety of metrics - discharge, chemical export, biological activity, to name a few. Catchments have complex temporal behavior, e.g., summer and winter storm recessions and nutrient export may look nothing alike. Further, catchment res...

Soil erosion rates (particulate and dissolved fluxes) variations in a temperate river basin

NASA Astrophysics Data System (ADS)

Cerdan, Olivier; Gay, Aurore; Négrel, Philippe; Pételet-Giraud, Emmanuelle; Salvador Blanes, Sébastien; Degan, Francesca

2015-04-01

Soil erosion is one of the major drivers of landscape evolution in Western Europe. However, depending on the land use characteristics and on the geological and topographical settings, miscellaneous forms of erosion may lead to a very diverse morphological evolution. To understand these landscape evolutions different scientific questions remain to be answered or quantified. The main difficulty arises from the nonlinear interactions between different erosional processes that act at different temporal and spatial scales. This study proposes to investigate different datasets describing particulate and dissolved sediment fluxes within a French River basin (The Loire River) at different spatial scales and at temporal scales ranging from the flood event to several decades. The particulate sediment load values at the outlet of the catchments range from 2.5 102 to 8.6 105 t yr-1, and the sediment yield values range from 2.9 to 32.4 t km 2 yr-1. Sediment exports from the Loire and Brittany river basins are low compared with mountainous regions and European exports. However, a strong spatial variability within this territory exists. The expected results on the sediment yield spatial pattern distribution and the correlation between SY values and basin sizes are not observed. An analysis of the sediment yield values at different time steps shows a strong effect of the seasonal availability of detached particles to be transported. High concentrations of suspended sediments during the winter and lower values during the summer and autumn are observed. Inter-annual variations are also observed, with export values varying by a factor 2 to 10 between years for one catchment. The influence of rainfall on the sediment exports is predominant, but investigations on physical characteristics of each catchment (e.g., lithology, slope, land use) are required to better understand the production and transfer processes within a drainage basin. These inter-annual variations imply that long-term data are required to provide mean SY values representative of the catchment functioning. From our calculations, 18 complete years of data are required to obtain a mean sediment yield value with less than 10% of variation on average around the mean. The specific dissolved fluxes vary from 13.7 to 199.9 t.km-2. t yr-1. Contrary to particulate matters, the impact of the lithology is illustrated by higher total dissolved solid fluxes on limestone catchments compared with graniteous or schisteous catchments. Nitrates and ammonium are indicators of anthropogenic perturbation and their fluxes vary respectively from 0.4 to 31.4 t.km-2. yr-1 and from 7.8*10-3 to 7.7 t.km-2. yr-1 and evolve differently according to land uses: nitrates fluxes are lower in the upstream Loire and higher downstream in the region where agricultural pressure is higher. The analysis of these datasets at different spatial and temporal scales permits to identify some of the dominant processes, and also to distinguish natural from anthropogenic influences. Concerning upland physical soil surface erosion rates, we find that the average travel distance of eroded particles may be limited, implying a strong decrease in physical erosion rates when moving from the local scale (m²) to the river basin scale (> 103 km²). Chemical erosion rates are less sensitive to scale and can either decrease or increase with increasing area in function of lithology, land management and topography. The results also highlight the predominant role of surface connectivity to characterize the fraction of sediment exported out of river drainage areas by physical soil surface erosion. For the export of dissolved sediment originating from weathering processes, the catchment physiography and connectivity does no longer play the dominant role. A direct link between soil production rates and exported dissolved fluxes tends to show that, contrary to the suspended particles, which are transport-limited, the dissolved matter seems to be supply-limited.

Using large hydrological datasets to create a robust, physically based, spatially distributed model for Great Britain

NASA Astrophysics Data System (ADS)

Lewis, Elizabeth; Kilsby, Chris; Fowler, Hayley

2014-05-01

The impact of climate change on hydrological systems requires further quantification in order to inform water management. This study intends to conduct such analysis using hydrological models. Such models are of varying forms, of which conceptual, lumped parameter models and physically-based models are two important types. The majority of hydrological studies use conceptual models calibrated against measured river flow time series in order to represent catchment behaviour. This method often shows impressive results for specific problems in gauged catchments. However, the results may not be robust under non-stationary conditions such as climate change, as physical processes and relationships amenable to change are not accounted for explicitly. Moreover, conceptual models are less readily applicable to ungauged catchments, in which hydrological predictions are also required. As such, the physically based, spatially distributed model SHETRAN is used in this study to develop a robust and reliable framework for modelling historic and future behaviour of gauged and ungauged catchments across the whole of Great Britain. In order to achieve this, a large array of data completely covering Great Britain for the period 1960-2006 has been collated and efficiently stored ready for model input. The data processed include a DEM, rainfall, PE and maps of geology, soil and land cover. A desire to make the modelling system easy for others to work with led to the development of a user-friendly graphical interface. This allows non-experts to set up and run a catchment model in a few seconds, a process that can normally take weeks or months. The quality and reliability of the extensive dataset for modelling hydrological processes has also been evaluated. One aspect of this has been an assessment of error and uncertainty in rainfall input data, as well as the effects of temporal resolution in precipitation inputs on model calibration. SHETRAN has been updated to accept gridded rainfall inputs, and UKCP09 gridded daily rainfall data has been disaggregated using hourly records to analyse the implications of using realistic sub-daily variability. Furthermore, the development of a comprehensive dataset and computationally efficient means of setting up and running catchment models has allowed for examination of how a robust parameter scheme may be derived. This analysis has been based on collective parameterisation of multiple catchments in contrasting hydrological settings and subject to varied processes. 350 gauged catchments all over the UK have been simulated, and a robust set of parameters is being sought by examining the full range of hydrological processes and calibrating to a highly diverse flow data series. The modelling system will be used to generate flow time series based on historical input data and also downscaled Regional Climate Model (RCM) forecasts using the UKCP09 Weather Generator. This will allow for analysis of flow frequency and associated future changes, which cannot be determined from the instrumental record or from lumped parameter model outputs calibrated only to historical catchment behaviour. This work will be based on the existing and functional modelling system described following some further improvements to calibration, particularly regarding simulation of groundwater-dominated catchments.

Modeling micropollutant fate at the catchment scale: from science to practice

NASA Astrophysics Data System (ADS)

Seuntjens, P.; Desmet, N.; Holvoet, K.; van Griensven, A.; van Hoey, S.; Tang, X. Y.; Nopens, I.

2009-04-01

Micropollutants, such as pesticides, personal care products, veterinary and human pharmaceuticals, pose a possible threat to human and ecological health. Humans and ecosystems may be exposed to these chemicals via the water system. Catchment models can be used to optimise management in view of risk reduction of the chemicals. Along the trajectory of science to practice a number of catchment models are available that simulate the fate and transport of micropollutants. They range from physically-based fully-coupled soil, groundwater, and surface water models, over empirical management models, to purely statistical database-driven models. For assessing effects on ecosystems, models need to be able to predict the observed highly dynamic behaviour of pesticide concentrations in the surface water, since adverse effects will be determined by the number, intensity and frequency of ecological threshold exceedances. For assessing effects on humans, models need to predict the dilution between areas where the pesticide is released and the location of the drinking water intake, sometimes tens or hundreds of kilometres further downstream. We adapted management models to simulate dynamic pesticide behaviour and fate at the catchment scale. The models were also used to illustrate the effects of specific management options on risk reduction and to derive the dominant sources of pollutants in a catchment area. The results show that the concentrations of pesticides in river systems are attributed to (1) fast flow over and in soils or pavements, and to (2) point sources. Therefore, future models for improved estimation of chemical fate at the catchment scale need a combination of stochastic source characterisation, higher spatial resolution and reduced complexity of the mathematical description of fast flow processes. This will be illustrated by recent developments in model simplification coupled to increased spatial detail.

Development of flood routing simulation system of digital Qingjiang based on integrated spatial information technology

NASA Astrophysics Data System (ADS)

Yuan, Yanbin; Zhou, You; Zhu, Yaqiong; Yuan, Xiaohui; Sælthun, N. R.

2007-11-01

Based on digital technology, flood routing simulation system development is an important component of "digital catchment". Taking QingJiang catchment as a pilot case, in-depth analysis on informatization of Qingjiang catchment management being the basis, aiming at catchment data's multi-source, - dimension, -element, -subject, -layer and -class feature, the study brings the design thought and method of "subject-point-source database" (SPSD) to design system structure in order to realize the unified management of catchments data in great quantity. Using the thought of integrated spatial information technology for reference, integrating hierarchical structure development model of digital catchment is established. The model is general framework of the flood routing simulation system analysis, design and realization. In order to satisfy the demands of flood routing three-dimensional simulation system, the object-oriented spatial data model are designed. We can analyze space-time self-adapting relation between flood routing and catchments topography, express grid data of terrain by using non-directed graph, apply breadth first search arithmetic, set up search method for the purpose of dynamically searching stream channel on the basis of simulated three-dimensional terrain. The system prototype is therefore realized. Simulation results have demonstrated that the proposed approach is feasible and effective in the application.

Designing Observation and Modeling Systems to Inform Decisions and Policies on Freshwater Objectives in New Zealand

NASA Astrophysics Data System (ADS)

Baisden, W. T.; Ellis, T.; Rissman, C.; Moore, C.; Matthews, A.

2016-12-01

Declines in New Zealand's freshwater quality have led to legislation - the 2014 National Policy Statement on Freshwater Management (NPS-FM) - which requires regional governments to set "objectives" and design policies accordingly. In most regions, increases in freshwater contaminants are derived largely from intensifying agriculture and come as nitrogen, phosphorous or sediment, or a combination thereof. Here, the development and application of N and O isotopes as natural tracers for nitrate is examined as a case study, in the context of a wider hierarchy of observations such as N concentrations, flow and broader hydrochemistry used for NPS-FM implementation. The analysis of N and O isotopes in nitrate provides specific information on sources and removal processes that cannot be obtained by other measurements. Yet, despite considerable development of the technical methodology and environment-specific interpretation, application of measurements has faced barriers. Many may be typical of science in a small advanced nation with a population of 4.5 million, but others are unique due to New Zealand's limited rural population base and large diversity in physical geography, as well as a unique economic reliance on highly productive pastoral agricultural systems. Seventeen different regional governments are empowered to regulate in ways consistent with local consultation and democracy within their catchment boundaries, but with limited resources to align highly technical observational data to policies and decisions, as well as supporting models. The resulting gaps in communication and technical capability combine with a diversity of approaches to pose both challenges and opportunities for development and application of hierarchical observation systems. Success appears to lie in ensuring decision frameworks can be `mapped', so that different frameworks can be compared, and the benefits of sophisticated observations understood directly in relation to influence on regional policy and on-farm management decisions.

Dynamics of transit times and StorAge Selection functions in four forested catchments from stable isotope data

NASA Astrophysics Data System (ADS)

Rodriguez, Nicolas B.; McGuire, Kevin J.; Klaus, Julian

2017-04-01

Transit time distributions, residence time distributions and StorAge Selection functions are fundamental integrated descriptors of water storage, mixing, and release in catchments. In this contribution, we determined these time-variant functions in four neighboring forested catchments in H.J. Andrews Experimental Forest, Oregon, USA by employing a two year time series of 18O in precipitation and discharge. Previous studies in these catchments assumed stationary, exponentially distributed transit times, and complete mixing/random sampling to explore the influence of various catchment properties on the mean transit time. Here we relaxed such assumptions to relate transit time dynamics and the variability of StoreAge Selection functions to catchment characteristics, catchment storage, and meteorological forcing seasonality. Conceptual models of the catchments, consisting of two reservoirs combined in series-parallel, were calibrated to discharge and stable isotope tracer data. We assumed randomly sampled/fully mixed conditions for each reservoir, which resulted in an incompletely mixed system overall. Based on the results we solved the Master Equation, which describes the dynamics of water ages in storage and in catchment outflows Consistent between all catchments, we found that transit times were generally shorter during wet periods, indicating the contribution of shallow storage (soil, saprolite) to discharge. During extended dry periods, transit times increased significantly indicating the contribution of deeper storage (bedrock) to discharge. Our work indicated that the strong seasonality of precipitation impacted transit times by leading to a dynamic selection of stored water ages, whereas catchment size was not a control on transit times. In general this work showed the usefulness of using time-variant transit times with conceptual models and confirmed the existence of the catchment age mixing behaviors emerging from other similar studies.

Simulating hydrological processes of a typical small mountainous catchment in Tibetan Plateau

NASA Astrophysics Data System (ADS)

Xu, Y. P.; Bai, Z.; Fu, Q.; Pan, S.; Zhu, C.

2017-12-01

Water cycle of small watersheds with seasonal/permanent frozen soil and snow pack in Tibetan Plateau is seriously affected by climate change. The objective of this study is to find out how much and in what way the frozen soil and snow pack will influence the hydrology of small mountainous catchments in cold regions and how can the performance of simulation by a distributed hydrological model be improved. The Dong catchment, a small catchment located in Tibetan Plateau, is used as a case study. Two measurement stations are set up to collect basic meteorological and hydrological data for the modeling purpose. Annual and interannual variations of runoff indices are first analyzed based on historic data series. The sources of runoff in dry periods and wet periods are analyzed respectively. Then, a distributed hydrology soil vegetation model (DHSVM) is adopted to simulate the hydrological process of Dong catchment based on limited data set. Global sensitivity analysis is applied to help determine the important processes of the catchment. Based on sensitivity analysis results, the Epsilon-Dominance Non-Dominated Sorted Genetic Algorithm II (ɛ-NSGAII) is finally added into the hydrological model to calibrate the hydrological model in a multi-objective way and analyze the performance of DHSVM model. The performance of simulation is evaluated with several evaluation indices. The final results show that frozen soil and snow pack do play an important role in hydrological processes in cold mountainous region, in particular in dry periods without precipitation, while in wet periods precipitation is often the main source of runoff. The results also show that although the DHSVM hydrological model has the potential to model the hydrology well in small mountainous catchments with very limited data in Tibetan Plateau, the simulation of hydrology in dry periods is not very satisfactory due to the model's insufficiency in simulating seasonal frozen soil.

Recession-based hydrological models for estimating low flows in ungauged catchments in the Himalayas

NASA Astrophysics Data System (ADS)

Rees, H. G.; Holmes, M. G. R.; Young, A. R.; Kansakar, S. R.

The Himalayan region of Nepal and northern India experiences hydrological extremes from monsoonal floods during July to September, when most of the annual precipitation falls, to periods of very low flows during the dry season (December to February). While the monsoon floods cause acute disasters such as loss of human life and property, mudslides and infrastructure damage, the lack of water during the dry season has a chronic impact on the lives of local people. The management of water resources in the region is hampered by relatively sparse hydrometerological networks and consequently, many resource assessments are required in catchments where no measurements exist. A hydrological model for estimating dry season flows in ungauged catchments, based on recession curve behaviour, has been developed to address this problem. Observed flows were fitted to a second order storage model to enable average annual recession behaviour to be examined. Regionalised models were developed, using a calibration set of 26 catchments, to predict three recession curve parameters: the storage constant; the initial recession flow and the start date of the recession. Relationships were identified between: the storage constant and catchment area; the initial recession flow and elevation (acting as a surrogate for rainfall); and the start date of the recession and geographic location. An independent set of 13 catchments was used to evaluate the robustness of the models. The regional models predicted the average volume of water in an annual recession period (1st of October to the 1st of February) with an average error of 8%, while mid-January flows were predicted to within ±50% for 79% of the catchments in the data set.

The Effect of Rainfall Measurement Technique and Its Spatiotemporal Resolution on Discharge Predictions in the Netherlands

NASA Astrophysics Data System (ADS)

Uijlenhoet, R.; Brauer, C.; Overeem, A.; Sassi, M.; Rios Gaona, M. F.

2014-12-01

Several rainfall measurement techniques are available for hydrological applications, each with its own spatial and temporal resolution. We investigated the effect of these spatiotemporal resolutions on discharge simulations in lowland catchments by forcing a novel rainfall-runoff model (WALRUS) with rainfall data from gauges, radars and microwave links. The hydrological model used for this analysis is the recently developed Wageningen Lowland Runoff Simulator (WALRUS). WALRUS is a rainfall-runoff model accounting for hydrological processes relevant to areas with shallow groundwater (e.g. groundwater-surface water feedback). Here, we used WALRUS for case studies in a freely draining lowland catchment and a polder with controlled water levels. We used rain gauge networks with automatic (hourly resolution but low spatial density) and manual gauges (high spatial density but daily resolution). Operational (real-time) and climatological (gauge-adjusted) C-band radar products and country-wide rainfall maps derived from microwave link data from a cellular telecommunication network were also used. Discharges simulated with these different inputs were compared to observations. We also investigated the effect of spatiotemporal resolution with a high-resolution X-band radar data set for catchments with different sizes. Uncertainty in rainfall forcing is a major source of uncertainty in discharge predictions, both with lumped and with distributed models. For lumped rainfall-runoff models, the main source of input uncertainty is associated with the way in which (effective) catchment-average rainfall is estimated. When catchments are divided into sub-catchments, rainfall spatial variability can become more important, especially during convective rainfall events, leading to spatially varying catchment wetness and spatially varying contribution of quick flow routes. Improving rainfall measurements and their spatiotemporal resolution can improve the performance of rainfall-runoff models, indicating their potential for reducing flood damage through real-time control.

Evaluation of seasonal and spatial variations of lumped water balance model sensitivity to precipitation data errors

NASA Astrophysics Data System (ADS)

Xu, Chong-yu; Tunemar, Liselotte; Chen, Yongqin David; Singh, V. P.

2006-06-01

Sensitivity of hydrological models to input data errors have been reported in the literature for particular models on a single or a few catchments. A more important issue, i.e. how model's response to input data error changes as the catchment conditions change has not been addressed previously. This study investigates the seasonal and spatial effects of precipitation data errors on the performance of conceptual hydrological models. For this study, a monthly conceptual water balance model, NOPEX-6, was applied to 26 catchments in the Mälaren basin in Central Sweden. Both systematic and random errors were considered. For the systematic errors, 5-15% of mean monthly precipitation values were added to the original precipitation to form the corrupted input scenarios. Random values were generated by Monte Carlo simulation and were assumed to be (1) independent between months, and (2) distributed according to a Gaussian law of zero mean and constant standard deviation that were taken as 5, 10, 15, 20, and 25% of the mean monthly standard deviation of precipitation. The results show that the response of the model parameters and model performance depends, among others, on the type of the error, the magnitude of the error, physical characteristics of the catchment, and the season of the year. In particular, the model appears less sensitive to the random error than to the systematic error. The catchments with smaller values of runoff coefficients were more influenced by input data errors than were the catchments with higher values. Dry months were more sensitive to precipitation errors than were wet months. Recalibration of the model with erroneous data compensated in part for the data errors by altering the model parameters.

Natural flood risk management in flashy headwater catchments: managing runoff peaks, timing, water quality and sediment regimes

NASA Astrophysics Data System (ADS)

Wilkinson, Mark; Addy, Steve; Ghimire, Sohan; Kenyon, Wendy; Nicholson, Alex; Quinn, Paul; Stutter, Marc; Watson, Helen

2013-04-01

Over the past decade many European catchments have experienced an unusually high number of flood events. A large number of these events are the result of intense rainfall in small headwater catchments which are dominated by surface runoff generation, resulting in flash flooding of local communities. Soil erosion and related water quality issues, among others, are typically associated with such rapid runoff generation. The hazard of flooding is increasing owing to impacts of changing climatic patterns (including more intense summer storms), intensification of agriculture within rural catchments and continued pressure to build on floodplains. Concurrently, the cost of constructing and maintaining traditional flood defences in small communities outweigh the potential benefits. Hence, there is a growing interest in more cost effective natural approaches that also have multipurpose benefits in terms of sediment, water quality, and habitat creation. Many catchments in Europe are intensively farmed and there is great potential for agriculture to be part of the solution to flood risk management. Natural flood management (NFM) is the alteration, restoration or use of landscape features with the aim of reducing flood risk by slowing down, storing (and filtering) rapid surface runoff. NFM includes measures such as temporarily storing water in ponds/wetlands, increasing soil infiltration, planting trees on floodplains and within catchments, re-meandering and wood placements in streams/ditches. In this presentation we highlight case studies from densely instrumented research sites across the UK (which could be typical of many European catchments) where NFM measures have been installed in small scale flashy catchments. The presentation will give an overview of the function of these measures in these catchments and how other multiple benefits are being accrued. Study catchments include the headwater catchments of the Bowmont (3 to 8 km2) and Belford Burn (6 km2) catchments. These catchments are known for their rapid runoff generation and have downstream local communities at risk of flash flooding. In Bowmont, NFM measures are currently being put in place to restore river bars and to store water more effectively on the flood plains during these flashy events. For example, Apex engineered wood structure in the river channel and riparian zones are designed to trap sediment and log bank protection structures are being installed to stop bank erosion. Tree planting in the catchment is also taking place. In the Belford catchment storage ponds and woody debris have been installed over the past five years to help to reduce the flood risk to the village of Belford. A dense instrumentation network has provided data for analysis and modelling which shows evidence of local scale flood peak reductions along with the collection of large amounts of sediment. A modelling study carried out (using a pond network model) during an intense summer storm showed that 30 small scale pond features used in sequence could reduce the flood peak by ~35% at the local scale. Findings show that managing surface runoff and local ditch flow at local scale headwater catchments is a cost effective way of managing flashy catchment for flood risk and sediment control. Working with catchment stakeholders is vital. Information given by the local community post flooding has been useful in placing NFM measures throughout the catchments. Involving the local communities in these projects and giving them access to the data and model outputs has helped to develop these projects further.

Gene Flow within and between Catchments in the Threatened Riparian Plant Myricaria germanica

PubMed Central

Werth, Silke; Scheidegger, Christoph

2014-01-01

One of the major distinctions of riparian habitats is their linearity. In linear habitats, gene flow is predicted to follow a one-dimensional stepping stone model, characterized by bidirectional gene flow between neighboring populations. Here, we studied the genetic structure of Myricaria germanica, a threatened riparian shrub which is capable of both wind and water dispersal. Our data led us to reject the ‘one catchment – one gene pool’ hypothesis as we found support for two gene pools, rather than four as expected in a study area including four catchments. This result also implies that in the history of the studied populations, dispersal across catchments has occurred. Two contemporary catchment-crossing migration events were detected, albeit between spatially proximate catchments. Allelic richness and inbreeding coefficients differed substantially between gene pools. There was significant isolation by distance, and our data confirmed the one-dimensional stepping-stone model of gene flow. Contemporary migration was bidirectional within the studied catchments, implying that dispersal vectors other than water are important for M. germanica. PMID:24932520

Diffuse pollution (pesticides and nitrate) at catchment scale on two constrasted sites: mass balances and characterization of the temporal variability of groundwater quality.

NASA Astrophysics Data System (ADS)

Baran, N.; Gutierrez, A.

2009-04-01

Enhanced monitoring of groundwater quality over several years has revealed a nitrate and /or pesticide contamination of aquifers in North America and Europe (Gilliom et al., 2006; Ifen, 2004). In many countries (France, United Kingdom, Denmark, Switzerland), drinking water is partly or dominantly supplied by groundwater. Assessing the extent of nitrate or pesticide contamination in aquifer and understanding the transport of the solutes to groundwater is, therefore, of major importance for the management of groundwater resources. Besides, the objective set by the European Water Framework Directive (WFD - 2000/60/EC, OJEC 2000) is for "all groundwater bodies to achieve the good quantitative and chemical status … at the latest by 2015". The Directive demands that European Union Member States not only characterize their levels of groundwater contamination, but also that they study the evolutionary trends of their pollutant concentrations. Monitoring groundwater quality for nitrate and pesticide is thus particularly relevant as well as the characterization of the transfer of solutes to and in groundwater is essential for effective water resource management. Several countries have approached the stage of characterization of their groundwater bodies either by using data derived from various measurement networks, as in France or by establishing specific sampling and analysis protocols (NAQUA network in Switzerland; NAWQA network in the United States). Pesticide monitoring networks, where they exist, are often less than 10 years old with a fairly low measurement frequency (1 to 4 analyses per year). Chemical status and trend interpretations are thus difficult and limited. Characterizing an entire groundwater body from observations limited in time and space remains a challenge. Little published data exists concerning intensive monitoring over several years, whether at the catchment outlet or at observation points spread over a basin, that would allow these characterizations. Notable changes in the use of pesticides generally result from the evolution of regulations. In Europe, the herbicides atrazine and isoproturon have been classified as priority substances (2455/2001/EC, OJEC 2001). The use of atrazine was forbidden in France since September 2003 following restrictions already in force since 1991. In January 2004 the maximum permitted application of isoproturon was reduced from 2500 to 1800 g ha-1. In France, two contrasted hydrogeological systems located in agricultural contexts were intensively monitored for at least a decade in order to i) characterize the spatial and temporal variability of groundwater contamination by different pesticides with varied physical and chemical characteristics (atrazine, isoproturon and their metabolites and chloroacetanilides used as atrazine substitutes) and nitrate, ii) calculate annual pesticide mass balances for a long period including years with contrasted climatic conditions and to iii) identify the different mechanisms influencing water and solute transfer. Although both sites (Brévilles and 3 Fontaines) have very different hydrogeological characteristics (4 vs. 50 sq km, sandy vs. chalky saturated zone, non karstic vs. karstic, …) the monitoring of the major springs representing the outlet of the catchments revealed similarities. For example, atrazine and its metabolite deethylatrazine have been both systematically quantified at the outlet springs despite the stop of atrazine use on the Brévilles and 3 Fontaines catchments since April1999 and September 2003, respectively. For both sites, the mass balances (comparison of inputs and outfluxes) indicated that only few percents of the applied quantity of atrazine reached the spring but led to concentrations higher than the allowed limit for drinkable water. At the opposite, isoproturon which is the pesticide applied with the highest quantities for the last decade on both sites, is detected in a very limited number of samples. The different tools used on these sites complementarily to the monitoring (modelling, isotope and classical geochemistry approaches, dating) enabled a better understanding of the hydrodynamic of the hydrogeological systems and gave explanation on the observed temporal variability of groundwater quality and the time transfer of solutes. These intensive monitoring gave also insight on the representativeness of a sample (location in the catchment, date of sampling, depth of the aquifer sampled, …). The results of these studies also raise questions on how efficient and how fast will the positive impact of product substitution or environmental regulations be. Taking into consideration these aspects is of primary importance to conform to the requirements of the European Water Framework Directive regarding good status assessment of groundwater bodies. References IFEN, 2004. Les pesticides dans les eaux - Sixième bilan annuel - données 2002. Collection Etudes et travaux, n°42, Ifen, Orléans, 32 p. ISBN : 2-911089-70-7. (Detailed results on CD-Rom). Gilliom, R.J., Barbash, J.E., Crawford, C.G., Hamilton, P.A., Martin, J.D., Nakagaki, N., Nowell, L.H, Scott, J.C., Stackelberg, P.E., Thelin, G.P., Wolock D.M., 2006. The quality of our Nation's waters - Pesticides in the Nation's streams and ground water, 1992-2001. U.S. Geological Survey circular 1291, 172p. Official Journal of the European Communities, 2000. Directive 2000/60/EC of the European Parliament and of the council of 23 October 2000 establishing a framework for Community action in the field of water policy. 72p. Official Journal of the European Communities, 2001. Decision n° 2455/2001/EC of the European Parliament and of the Council of 20 November 2001 establishing the list of priority substances in the field of water policy and amending Directive 2000/60/EC. 5p. Acknowledgements These works were supported by BRGM research projects, European projects PEGASE (FP5 - EVK1-CT1999-00028) and AQUATERRA (FP6 - 505428 - GOCE), and conventions with the Seine River Basin Water Authority (AESN) and Centre Regional Council (Conseil Régional Centre).

Inverse Geochemical Reaction Path Modelling and the Impact of Climate Change on Hydrologic Structure in Snowmelt-Dominated Catchments in the Southwestern USA

NASA Astrophysics Data System (ADS)

Driscoll, J. M.; Meixner, T.; Molotch, N. P.; Sickman, J. O.; Williams, M. W.; McIntosh, J. C.; Brooks, P. D.

2011-12-01

Snowmelt from alpine catchments provides 70-80% of the American Southwest's water resources. Climate change threatens to alter the timing and duration of snowmelt in high elevation catchments, which may also impact the quantity and the quality of these water resources. Modelling of these systems provides a robust theoretical framework to process the information extracted from the sparse physical measurement available in these sites due to their remote locations. Mass-balance inverse geochemical models (via PHREEQC, developed by the USGS) were applied to two snowmelt-dominated catchments; Green Lake 4 (GL4) in the Rockies and Emerald Lake (EMD) in the Sierra Nevada. Both catchments primarily consist of granite and granodiorite with a similar bulk geochemistry. The inputs for the models were the initial (snowpack) and final (catchment output) hydrochemistry and a catchment-specific suite of mineral weathering reactions. Models were run for wet and dry snow years, for early and late time periods (defined hydrologically as 1/2 of the total volume for the year). Multiple model solutions were reduced to a representative suite of reactions by choosing the model solution with the fewest phases and least overall phase change. The dominant weathering reactions (those which contributed the most solutes) were plagioclase for GL4 and albite for EMD. Results for GL4 show overall more plagioclase weathering during the dry year (214.2g) than wet year (89.9g). Both wet and dry years show more weathering in the early time periods (63% and 56%, respectively). These results show that the snowpack and outlet are chemically more similar during wet years than dry years. A possible hypothesis to explain this difference is a change in contribution from subsurface storage; during the wet year the saturated catchment reduces contact with surface materials that would result in mineral weathering reactions by some combination of reduced infiltration and decreased subsurface transit time. By contrast, during the dry year infiltration and subsequent displacement of stored water that has had longer contact time with minerals and therefore has become more geochemically evolved to produce a greater difference between snowmelt and catchment outlet hydrochemistry. The results for EMD show little distinction between albite weathering for wet and dry years (55.9g and 66.0g, relatively). A hypothesis for this lack of difference in mineral phase changes may be due to less subsurface storage capacity in EMD relative to GL4. The spatial distribution of snowmelt has also been shown to influence the integrated watershed response, and future work includes using the Alpine Hydrochemical Model (AHM) to further investigate catchment response to these spatial data. The AHM will also provide further insight of surface-groundwater interactions through a more integrated model which includes hydrochemical, biological and physical processes to elucidate catchment response to changes in snowmelt dynamics.

Interactive Effects of Storms, Drought, and Weekly Land Cover Changes on Water Quality Patterns in an Agricultural-dominated Subtropical Catchment in New Zealand

NASA Astrophysics Data System (ADS)

Julian, J.; Owsley, B.; de Beurs, K.; Hughes, A.

2013-12-01

Rivers are the funnels of landscapes, with the quality of water at the catchment outlet reflecting interactions among geomorphic processes, vegetation characteristics, weather patterns, and anthropogenic land uses. The impacts of changing climate and land cover on water quality are not straightforward; but instead, are set by the interaction of numerous landscape components at multiple spatiotemporal scales. In agricultural-dominated subtropical landscapes such as the Hoteo River Catchment in northern North Island of New Zealand, the land surface can be very dynamic, responding quickly to storms, drought, forest clearings, and grazing practices. In order to capture these short-term fluctuations, we created an 8-day land disturbance index for the catchment using MODIS Nadir BRDF-adjusted reflectance (NBAR) data (500 meter resolution) from 2000 to 2013. We also fused this time-series with Landsat TM/ETM surface reflectance data (30 meter resolution) to more precisely capture the location and extent of these land disturbances. This high-resolution land disturbance time-series was then compared to daily rainfall, daily river discharge, and monthly water samples to assess the effects of changing weather and land cover on a suite of water quality variables including water clarity, turbidity, ammonium (NH4), nitrate (NO3), total nitrogen (TN), dissolved reactive phosphate (DRP), total phosphorus (TP), and fecal coliforms. Forest clearings in the early part of our study period created the most intense land disturbances, which led to elevated turbidity and DRP during subsequent storms. Pasture areas during drought were also characterized by high disturbance indices, particularly in 2013 - the worst drought on record for northern New Zealand. Seasonal effects on land disturbance and water quality were also detected, especially for water clarity and turbidity. From 2011 to 2013, river discharge and turbidity from three sub-catchments were measured at 5-minute intervals to capture rainfall event-based water quality patterns. Together, the event-based and monthly turbidity data suggest that intense land disturbances in the Hoteo Catchment have the ability to switch the catchment from supply-limited (river loadings are dictated by what is available from the landscape) to transport-limited (loadings from the landscape are abundant, and thus dictated by water runoff). The findings from this research can be used to assess (1) the vulnerability of agricultural land uses to climate changes, particularly the impact of severe droughts from intensifying ENSO phenomena; and (2) the interactive effects of changing climate and land use on water quality across multiple spatiotemporal scales.

Let's put this in perspective: using dynamic simulation modelling to assess the impacts of farm-scale land management change on catchment-scale water quality

NASA Astrophysics Data System (ADS)

Rivers, Mark; Clarendon, Simon; Coles, Neil

2013-04-01

Natural Resource Management and Agri-industry development groups in Australia have invested considerable resources into the investigation of the economic, social and, particularly, environmental impacts of varying farming activities in a "catchment context". This research has resulted in the development of a much-improved understanding of the likely impacts of changed management practices at the farm-scale as well as the development of a number of conceptual models which place farming within this broader catchment context. The project discussed in this paper transformed a conceptual model of dairy farm phosphorus (P) management and transport processes into a more temporally and spatially dynamic model. This was then loaded with catchment-specific data and used as a "policy support tool" to allow the Australian dairy industry to examine the potential farm and catchment-scale impacts of varying dairy farm management practices within some key dairy farming regions. Models were developed, validated and calibrated using "STELLA©" dynamic modelling software for three catchments in which dairy is perceived as a significant land use. The models describe P movement and cycling within and through dairy farms in great detail and also estimate P transport through major source, sink and flow sectors of the catchments. A series of scenarios were executed for all three catchments which examined three main "groups" of tests: changes to farm P input rates; implementation of perceived environmental "Best Management Practices" (BMPs), and; changes to land use mosaics. Modifications to actual P input rates into dairy farms (not surprisingly) had a major effect on nutrient transport within and from the farms with a significant rise in nutrient loss rates at all scales with increasing fertiliser use. More surprisingly, however, even extensive environmental BMP implementation did not have marked effects on off-farm nutrient loss rates. On and off-farm riparian management implemented over entire catchments, for example, only reduced P losses by approximately 20%. Most importantly, changes to land use mosaics within the catchments provided great insight into the relative roles within the catchment P system of the various land uses. While dairying uses large amounts of P, the effects that dairy farm management can have at the catchment scale when these farms represent only a small proportion of the landscape are limited. The most important conclusions from the research are that: • While State and regional environmental management and regulatory agencies continue to set optimistic goals for water quality protection, this research shows that these targets are not achievable within current landscape paradigms even after broadscale BMP implementation, and that either these targets must be re-considered or that significant land use change (rather than simply improved management within current systems) must occur to meet the targets. • Catchment-scale effects of P losses at the farm scale are a complex function of P-use efficiency, landscape position and landscape footprint. Simply targetting those landuses perceived to have high nutrient loss rates does not adequately address the problem. • Catchment P management must be considered in a more inclusive and holistic way, and these assessments should be used to inform future planning policies and development plans if environmental goals as well as community expectations about the productive use of agricultural land are to be met.

Interpretation of concentration‐discharge patterns in acid‐neutralizing capacity during storm flow in three small, forested catchments in Shenandoah National Park, Virginia

USGS Publications Warehouse

Rice, Karen C.; Chanat, Jeffrey G.; Hornberger, George M.; Webb, James R.

2004-01-01

Episodic concentration‐discharge (c‐Q) plots are a popular tool for interpreting the hydrochemical response of small, forested catchments. Application of the method involves assuming an underlying conceptual model of runoff processes and comparing observed c‐Q looping patterns with those predicted by the model. We analyzed and interpreted c‐Q plots of acid‐neutralizing capacity (ANC) for 133 storms collected over a 7‐year period from three catchments in Shenandoah National Park, Virginia. Because of their underlying lithologies the catchments represent a gradient in both hydrologic and geochemical behavior, ranging from a flashy, acidic, poorly buffered catchment to a moderate, neutral, well‐buffered catchment. The relative frequency of observed anticlockwise c‐Q loops in each catchment decreased along this gradient. Discriminant function analysis indicated that prestorm base flow ANC was an important predictor of loop rotation direction; however, the strength of the predictive relationship decreased along the same gradient. The trends were consistent with several equally plausible three‐component mixing models. Uncertainty regarding end‐member timing and relative volume and possible time variation in end‐member concentrations were key factors precluding identification of a unique model. The inconclusive results obtained on this large data set suggest that identification of underlying runoff mechanisms on the basis of a small number of c‐Q plots without additional supporting evidence is likely to be misleading.

Water and Solute Flux Simulation Using Hydropedology Survey Data in South African Catchments

NASA Astrophysics Data System (ADS)

Lorentz, Simon; van Tol, Johan; le Roux, Pieter

2017-04-01

Hydropedology surveys include linking soil profile information in hillslope transects in order to define dominant subsurface flow mechanisms and pathways. This information is useful for deriving hillslope response functions, which aid storage and travel time estimates of water and solute movement in the sub-surface. In this way, the "soft" data of the hydropedological survey can be included in simple hydrological models, where detailed modelling of processes and pathways is prohibitive. Hydropedology surveys were conducted in two catchments and the information used to improve the prediction of water and solute responses. Typical hillslope response functions are then derived using a 2-D finite element model of the hydropedological features. Similar response types are mapped. These mapped response units are invoked in a simple SCS based, hydrological and solute transport model to yield water and solute fluxes at the catchment outlets. The first catchment (1.6 km2) comprises commercial forestry in a sedimentary geology of sandstone and mudstone formation while the second catchment (6.1 km2) includes mine waste impoundments in a granitic geology. In this paper, we demonstrate the method of combining hydropedological interpretation with catchment hydrology and solute transport simulation. The forested catchment, with three dominant hillslope response types, have solute response times in excess of 90 days, whereas the granitic responses occur within 10 days. The use of the hydropedological data improves the solute distribution response and storage simulation, compared to simulations without the hydropedology interpretation. The hydrological responses are similar, with and without the use of the hydropedology data, but the simulated distribution of water in the catchment is improved using the techniques demonstrated.

Managing salinity in Upper Colorado River Basin streams: Selecting catchments for sediment control efforts using watershed characteristics and random forests models

USGS Publications Warehouse

Tillman, Fred; Anning, David W.; Heilman, Julian A.; Buto, Susan G.; Miller, Matthew P.

2018-01-01

Elevated concentrations of dissolved-solids (salinity) including calcium, sodium, sulfate, and chloride, among others, in the Colorado River cause substantial problems for its water users. Previous efforts to reduce dissolved solids in upper Colorado River basin (UCRB) streams often focused on reducing suspended-sediment transport to streams, but few studies have investigated the relationship between suspended sediment and salinity, or evaluated which watershed characteristics might be associated with this relationship. Are there catchment properties that may help in identifying areas where control of suspended sediment will also reduce salinity transport to streams? A random forests classification analysis was performed on topographic, climate, land cover, geology, rock chemistry, soil, and hydrologic information in 163 UCRB catchments. Two random forests models were developed in this study: one for exploring stream and catchment characteristics associated with stream sites where dissolved solids increase with increasing suspended-sediment concentration, and the other for predicting where these sites are located in unmonitored reaches. Results of variable importance from the exploratory random forests models indicate that no simple source, geochemical process, or transport mechanism can easily explain the relationship between dissolved solids and suspended sediment concentrations at UCRB monitoring sites. Among the most important watershed characteristics in both models were measures of soil hydraulic conductivity, soil erodibility, minimum catchment elevation, catchment area, and the silt component of soil in the catchment. Predictions at key locations in the basin were combined with observations from selected monitoring sites, and presented in map-form to give a complete understanding of where catchment sediment control practices would also benefit control of dissolved solids in streams.

Assessing the effect of land use change on catchment runoff by combined use of statistical tests and hydrological modelling: Case studies from Zimbabwe

NASA Astrophysics Data System (ADS)

Lørup, Jens Kristian; Refsgaard, Jens Christian; Mazvimavi, Dominic

1998-03-01

The purpose of this study was to identify and assess long-term impacts of land use change on catchment runoff in semi-arid Zimbabwe, based on analyses of long hydrological time series (25-50 years) from six medium-sized (200-1000 km 2) non-experimental rural catchments. A methodology combining common statistical methods with hydrological modelling was adopted in order to distinguish between the effects of climate variability and the effects of land use change. The hydrological model (NAM) was in general able to simulate the observed hydrographs very well during the reference period, thus providing a means to account for the effects of climate variability and hence strengthening the power of the subsequent statistical tests. In the test period the validated model was used to provide the runoff record which would have occurred in the absence of land use change. The analyses indicated a decrease in the annual runoff for most of the six catchments, with the largest changes occurring for catchments located within communal land, where large increases in population and agricultural intensity have taken place. However, the decrease was only statistically significant at the 5% level for one of the catchments.

Catchment classification by runoff behaviour with self-organizing maps (SOM)

NASA Astrophysics Data System (ADS)

Ley, R.; Casper, M. C.; Hellebrand, H.; Merz, R.

2011-09-01

Catchments show a wide range of response behaviour, even if they are adjacent. For many purposes it is necessary to characterise and classify them, e.g. for regionalisation, prediction in ungauged catchments, model parameterisation. In this study, we investigate hydrological similarity of catchments with respect to their response behaviour. We analyse more than 8200 event runoff coefficients (ERCs) and flow duration curves of 53 gauged catchments in Rhineland-Palatinate, Germany, for the period from 1993 to 2008, covering a huge variability of weather and runoff conditions. The spatio-temporal variability of event-runoff coefficients and flow duration curves are assumed to represent how different catchments "transform" rainfall into runoff. From the runoff coefficients and flow duration curves we derive 12 signature indices describing various aspects of catchment response behaviour to characterise each catchment. Hydrological similarity of catchments is defined by high similarities of their indices. We identify, analyse and describe hydrologically similar catchments by cluster analysis using Self-Organizing Maps (SOM). As a result of the cluster analysis we get five clusters of similarly behaving catchments where each cluster represents one differentiated class of catchments. As catchment response behaviour is supposed to be dependent on its physiographic and climatic characteristics, we compare groups of catchments clustered by response behaviour with clusters of catchments based on catchment properties. Results show an overlap of 67% between these two pools of clustered catchments which can be improved using the topologic correctness of SOMs.

Catchment classification by runoff behaviour with self-organizing maps (SOM)

NASA Astrophysics Data System (ADS)

Ley, R.; Casper, M. C.; Hellebrand, H.; Merz, R.

2011-03-01

Catchments show a wide range of response behaviour, even if they are adjacent. For many purposes it is necessary to characterise and classify them, e.g. for regionalisation, prediction in ungauged catchments, model parameterisation. In this study, we investigate hydrological similarity of catchments with respect to their response behaviour. We analyse more than 8200 event runoff coefficients (ERCs) and flow duration curves of 53 gauged catchments in Rhineland-Palatinate, Germany, for the period from 1993 to 2008, covering a huge variability of weather and runoff conditions. The spatio-temporal variability of event-runoff coefficients and flow duration curves are assumed to represent how different catchments "transform" rainfall into runoff. From the runoff coefficients and flow duration curves we derive 12 signature indices describing various aspects of catchment response behaviour to characterise each catchment. Hydrological similarity of catchments is defined by high similarities of their indices. We identify, analyse and describe hydrologically similar catchments by cluster analysis using Self-Organizing Maps (SOM). As a result of the cluster analysis we get five clusters of similarly behaving catchments where each cluster represents one differentiated class of catchments. As catchment response behaviour is supposed to be dependent on its physiographic and climatic characteristics, we compare groups of catchments clustered by response behaviour with clusters of catchments based on catchment properties. Results show an overlap of 67% between these two pools of clustered catchments which can be improved using the topologic correctness of SOMs.

Concentration-discharge responses to storm events in coastal California watersheds

NASA Astrophysics Data System (ADS)

Aguilera, R.; Melack, J. M.

2017-12-01

Storm events in montane catchments are the main cause of mobilization of solutes and particulates into and within stream channels in coastal California. Non-linear behavior of nutrients and suspended sediments during storms is evident in the hysteresis that arises in concentration-discharge (C-Q) relationships. We examined patterns in the C-Q hysteresis of nutrients (NO3-, NH4+, DON and PO43-) and total suspended solids (TSS) during storms across ten sites and water years 2002 to 2015 by quantifying the slope of the C-Q relationship and the rotational pattern of the hysteresis loop. We observed several hysteresis types: constituents associated with sediment transport (PO43- and TSS) were flushed during storm events, whereas nitrogen species had hysteretic responses such as dilution with clockwise rotation in urban sites and enrichment with anti-clockwise rotation in undeveloped sites. The wide range of C-Q responses that occurred among sites and seasons reflected the variable hydrological and biogeochemical characteristics of catchments and storms. Storm responses for nitrate in nested catchments differed in slope and rotation of C-Q hysteresis. Upland undeveloped and lowland urban sites had anti-clockwise rotation at the onset of the rainy season following a dry year, which implied a delay in the transport of this solute to the streams. By the middle of the season, the urban site switched from dilution to enrichment, and then again to dilution with clockwise rotation, which implied high initial concentrations and proximal sources by the end of the season.

An updated model for nitrate uptake modelling in plants. I. Functional component: cross-combination of flow–force interpretation of nitrate uptake isotherms, and environmental and in planta regulation of nitrate influx

PubMed Central

Le Deunff, Erwan; Malagoli, Philippe

2014-01-01

Background and Aims In spite of major breakthroughs in the last three decades in the identification of root nitrate uptake transporters in plants and the associated regulation of nitrate transport activities, a simplified and operational modelling approach for nitrate uptake is still lacking. This is due mainly to the difficulty in linking the various regulations of nitrate transport that act at different levels of time and on different spatial scales. Methods A cross-combination of a Flow–Force approach applied to nitrate influx isotherms and experimentally determined environmental and in planta regulation is used to model nitrate in oilseed rape, Brassica napus. In contrast to ‘Enzyme–Substrate’ interpretations, a Flow–Force modelling approach considers the root as a single catalytic structure and does not infer hypothetical cellular processes among nitrate transporter activities across cellular layers in the mature roots. In addition, this approach accounts for the driving force on ion transport based on the gradient of electrochemical potential, which is more appropriate from a thermodynamic viewpoint. Key Results and Conclusions Use of a Flow–Force formalism on nitrate influx isotherms leads to the development of a new conceptual mechanistic basis to model more accurately N uptake by a winter oilseed rape crop under field conditions during the whole growth cycle. This forms the functional component of a proposed new structure–function mechanistic model of N uptake. PMID:24638820

A simple distributed sediment delivery approach for rural catchments

NASA Astrophysics Data System (ADS)

Reid, Lucas; Scherer, Ulrike

2014-05-01

The transfer of sediments from source areas to surface waters is a complex process. In process based erosion models sediment input is thus quantified by representing all relevant sub processes such as detachment, transport and deposition of sediment particles along the flow path to the river. A successful application of these models requires, however, a large amount of spatially highly resolved data on physical catchment characteristics, which is only available for a few, well examined small catchments. For the lack of appropriate models, the empirical Universal Soil Loss Equation (USLE) is widely applied to quantify the sediment production in meso to large scale basins. As the USLE provides long-term mean soil loss rates, it is often combined with spatially lumped models to estimate the sediment delivery ratio (SDR). In these models, the SDR is related to data on morphological characteristics of the catchment such as average local relief, drainage density, proportion of depressions or soil texture. Some approaches include the relative distance between sediment source areas and the river channels. However, several studies showed that spatially lumped parameters describing the morphological characteristics are only of limited value to represent the factors of influence on sediment transport at the catchment scale. Sediment delivery is controlled by the location of the sediment source areas in the catchment and the morphology along the flow path to the surface water bodies. This complex interaction of spatially varied physiographic characteristics cannot be adequately represented by lumped morphological parameters. The objective of this study is to develop a simple but spatially distributed approach to quantify the sediment delivery ratio by considering the characteristics of the flow paths in a catchment. We selected a small catchment located in in an intensively cultivated loess region in Southwest Germany as study area for the development of the SDR approach. The flow pathways were extracted in a geographic information system. Then the sediment delivery ratio for each source area was determined using an empirical approach considering the slope, morphology and land use properties along the flow path. As a benchmark for the calibration of the model parameters we used results of a detailed process based erosion model available for the study area. Afterwards the approach was tested in larger catchments located in the same loess region.

Time series and recurrence interval models to predict the vulnerability of streams to episodic acidification in Shenandoah National Park, Virginia

USGS Publications Warehouse

Deviney, Frank A.; Rice, Karen C.; Hornberger, George M.

2006-01-01

Acid rain affects headwater streams by temporarily reducing the acid‐neutralizing capacity (ANC) of the water, a process termed episodic acidification. The increase in acidic components in stream water can have deleterious effects on the aquatic biota. Although acidic deposition is uniform across Shenandoah National Park (SNP) in north central Virginia, the stream water quality response during rain events varies substantially. This response is a function of the catchment's underlying geology and topography. Geologic and topographic data for SNP's 231 catchments are readily available; however, long‐term measurements (tens of years) of ANC and accompanying discharge are not and would be prohibitively expensive to collect. Transfer function time series models were developed to predict hourly ANC from discharge for five SNP catchments with long‐term water‐quality and discharge records. Hourly ANC predictions over short time periods (≤1 week) were averaged, and distributions of the recurrence intervals of annual water‐year minimum ANC values were model‐simulated for periods of 6, 24, 72, and 168 hours. The distributions were extrapolated to the rest of the SNP catchments on the basis of catchment geology and topography. On the basis of the models, large numbers of SNP streams have 6‐ to 168‐hour periods of low‐ANC values, which may stress resident fish populations. Smaller catchments are more vulnerable to episodic acidification than larger catchments underlain by the same bedrock. Catchments with similar topography and size are more vulnerable if underlain by less basaltic/carbonate bedrock. Many catchments are predicted to have successive years of low‐ANC values potentially sufficient to extirpate some species.

Dynamic regression modeling of daily nitrate-nitrogen concentrations in a large agricultural watershed.

PubMed

Feng, Zhujing; Schilling, Keith E; Chan, Kung-Sik

2013-06-01

Nitrate-nitrogen concentrations in rivers represent challenges for water supplies that use surface water sources. Nitrate concentrations are often modeled using time-series approaches, but previous efforts have typically relied on monthly time steps. In this study, we developed a dynamic regression model of daily nitrate concentrations in the Raccoon River, Iowa, that incorporated contemporaneous and lags of precipitation and discharge occurring at several locations around the basin. Results suggested that 95 % of the variation in daily nitrate concentrations measured at the outlet of a large agricultural watershed can be explained by time-series patterns of precipitation and discharge occurring in the basin. Discharge was found to be a more important regression variable than precipitation in our model but both regression parameters were strongly correlated with nitrate concentrations. The time-series model was consistent with known patterns of nitrate behavior in the watershed, successfully identifying contemporaneous dilution mechanisms from higher relief and urban areas of the basin while incorporating the delayed contribution of nitrate from tile-drained regions in a lagged response. The first difference of the model errors were modeled as an AR(16) process and suggest that daily nitrate concentration changes remain temporally correlated for more than 2 weeks although temporal correlation was stronger in the first few days before tapering off. Consequently, daily nitrate concentrations are non-stationary, i.e. of strong memory. Using time-series models to reliably forecast daily nitrate concentrations in a river based on patterns of precipitation and discharge occurring in its basin may be of great interest to water suppliers.

Getting a feel for parameters: using interactive parallel plots as a tool for parameter identification in the new rainfall-runoff model WALRUS

NASA Astrophysics Data System (ADS)

Brauer, Claudia; Torfs, Paul; Teuling, Ryan; Uijlenhoet, Remko

2015-04-01

Recently, we developed the Wageningen Lowland Runoff Simulator (WALRUS) to fill the gap between complex, spatially distributed models often used in lowland catchments and simple, parametric models which have mostly been developed for mountainous catchments (Brauer et al., 2014ab). This parametric rainfall-runoff model can be used all over the world in both freely draining lowland catchments and polders with controlled water levels. The open source model code is implemented in R and can be downloaded from www.github.com/ClaudiaBrauer/WALRUS. The structure and code of WALRUS are simple, which facilitates detailed investigation of the effect of parameters on all model variables. WALRUS contains only four parameters requiring calibration; they are intended to have a strong, qualitative relation with catchment characteristics. Parameter estimation remains a challenge, however. The model structure contains three main feedbacks: (1) between groundwater and surface water; (2) between saturated and unsaturated zone; (3) between catchment wetness and (quick/slow) flowroute division. These feedbacks represent essential rainfall-runoff processes in lowland catchments, but increase the risk of parameter dependence and equifinality. Therefore, model performance should not only be judged based on a comparison between modelled and observed discharges, but also based on the plausibility of the internal modelled variables. Here, we present a method to analyse the effect of parameter values on internal model states and fluxes in a qualitative and intuitive way using interactive parallel plotting. We applied WALRUS to ten Dutch catchments with different sizes, slopes and soil types and both freely draining and polder areas. The model was run with a large number of parameter sets, which were created using Latin Hypercube Sampling. The model output was characterised in terms of several signatures, both measures of goodness of fit and statistics of internal model variables (such as the percentage of rain water travelling through the quickflow reservoir). End users can then eliminate parameter combinations with unrealistic outcomes based on expert knowledge using interactive parallel plots. In these plots, for instance, ranges can be selected for each signature and only model runs which yield signature values in these ranges are highlighted. The resulting selection of realistic parameter sets can be used for ensemble simulations. C.C. Brauer, A.J. Teuling, P.J.J.F. Torfs, R. Uijlenhoet (2014a): The Wageningen Lowland Runoff Simulator (WALRUS): a lumped rainfall-runoff model for catchments with shallow groundwater, Geoscientific Model Development, 7, 2313-2332, www.geosci-model-dev.net/7/2313/2014/gmd-7-2313-2014.pdf C.C. Brauer, P.J.J.F. Torfs, A.J. Teuling, R. Uijlenhoet (2014b): The Wageningen Lowland Runoff Simulator (WALRUS): application to the Hupsel Brook catchment and Cabauw polder, Hydrology and Earth System Sciences, 18, 4007-4028, www.hydrol-earth-syst-sci.net/18/4007/2014/hess-18-4007-2014.pdf

The River EdenDTC Project: A National Demonstration Test Catchment

NASA Astrophysics Data System (ADS)

Benskin, C.; Surridge, B.; Deasy, C.; Woods, C.; Rimmer, D.; Lees, E.; Owens, G.; Jonczyk, J.; Quinton, J.; Wilkinson, M.; Perks, M.; Quinn, P.; Barker, P.; Haygarth, P.; Burke, S.; Reaney, S.; Watson, N.

2012-04-01

Our environment is a complex system of interactions between natural process and anthropogenic activities that disrupt them. It is crucial to manage the balance for continued food production whilst maintaining the quality of the environment. The challenges we face include managing the impact of agricultural land use on aquatic quality and biodiversity as an integral system, rather than as separate issues. In order to do this, it is critical to understand how the different components are linked - how does land use affect our water courses and ground water, and their associated ecosystems, and how can the impact of agricultural land use on these systems be minimised? Regulating farm nutrient management through measures that minimise sources, their exposure to mobilisation, and reduce drainage pathways to water courses are all fundamental to the UK's approach to meeting the Water Framework Directive objective of achieving 'good ecological status' in all surface and groundwater bodies by 2015. The EdenDTC project is part of a 5-year national Demonstration Test Catchments (DTC) environmental scheme, aiming to understand the above issues through combining scientific research with local knowledge and experience from multiple stakeholders. The DTC project is a 5-year initiative by Defra, Welsh Assembly Government and the Environment Agency, which encompasses a research platform covering three distinct river catchments: the Eden in Cumbria; the Wensum in Norfolk; and the Avon in Hampshire. Within the EdenDTC, the impact and effects of multiple diffuse pollutants on ecosystems and sustainable food production are being studied on a river catchment scale. Three 10 km2 focus catchments, selected to represent the different farming practices and geologies observed across the Eden, have been instrumented to record the dynamics of agricultural diffuse pollution at multiple scales. Within each focus catchment, two sub-catchments were selected: one control and one mitigation, in which a number of existing and novel mitigation measures will be tested. A number of on-farm measures, aimed at reducing agricultural diffuse pollution, will be evaluated by monitoring their effect on water quality and associated biodiversity. In order to achieve this, state of the art hydro-meteorological logging systems have been installed. The outlets of the focus catchments each have a 'high-tech' multi-parameter station that will provide data for total P, soluble reactive P, nitrate, ammonium, temperature, conductivity, dissolved oxygen, turbidity, pH and flow. At the sub-catchment scale are 10 sub-stations, which provide a record of turbidity and water level. All are continuously sampling at 15 minute intervals and are telemetered. The goal is to give an abundance of high quality, multi-scale continuous data provided in real time. Additional storm sampling is being performed at all stations using automatic water samplers, and monthly spot samples are also analysed for each site. The information gathered at these different scales is hoped to improve the effectiveness/efficiency of schemes such as the England Catchment Sensitive Farming Delivery Initiative (ECSFDI). It is also hoped that many of the mitigation features will be multipurpose, having positive effects on flooding, carbon sequestration, habitat creation and biodiversity.

Prediction of hydrographs and flow-duration curves in almost ungauged catchments: Which runoff measurements are most informative for model calibration?

NASA Astrophysics Data System (ADS)

Pool, Sandra; Viviroli, Daniel; Seibert, Jan

2017-11-01

Applications of runoff models usually rely on long and continuous runoff time series for model calibration. However, many catchments around the world are ungauged and estimating runoff for these catchments is challenging. One approach is to perform a few runoff measurements in a previously fully ungauged catchment and to constrain a runoff model by these measurements. In this study we investigated the value of such individual runoff measurements when taken at strategic points in time for applying a bucket-type runoff model (HBV) in ungauged catchments. Based on the assumption that a limited number of runoff measurements can be taken, we sought the optimal sampling strategy (i.e. when to measure the streamflow) to obtain the most informative data for constraining the runoff model. We used twenty gauged catchments across the eastern US, made the assumption that these catchments were ungauged, and applied different runoff sampling strategies. All tested strategies consisted of twelve runoff measurements within one year and ranged from simply using monthly flow maxima to a more complex selection of observation times. In each case the twelve runoff measurements were used to select 100 best parameter sets using a Monte Carlo calibration approach. Runoff simulations using these 'informed' parameter sets were then evaluated for an independent validation period in terms of the Nash-Sutcliffe efficiency of the hydrograph and the mean absolute relative error of the flow-duration curve. Model performance measures were normalized by relating them to an upper and a lower benchmark representing a well-informed and an uninformed model calibration. The hydrographs were best simulated with strategies including high runoff magnitudes as opposed to the flow-duration curves that were generally better estimated with strategies that captured low and mean flows. The choice of a sampling strategy covering the full range of runoff magnitudes enabled hydrograph and flow-duration curve simulations close to a well-informed model calibration. The differences among such strategies covering the full range of runoff magnitudes were small indicating that the exact choice of a strategy might be less crucial. Our study corroborates the information value of a small number of strategically selected runoff measurements for simulating runoff with a bucket-type runoff model in almost ungauged catchments.

Moments of catchment storm area

NASA Technical Reports Server (NTRS)

Eagleson, P. S.; Wang, Q.

1985-01-01

The portion of a catchment covered by a stationary rainstorm is modeled by the common area of two overlapping circles. Given that rain occurs within the catchment and conditioned by fixed storm and catchment sizes, the first two moments of the distribution of the common area are derived from purely geometrical considerations. The variance of the wetted fraction is shown to peak when the catchment size is equal to the size of the predominant storm. The conditioning on storm size is removed by assuming a probability distribution based upon the observed fractal behavior of cloud and rainstorm areas.

Impacts of intensive agricultural irrigation and livestock farming on a semi-arid Mediterranean catchment.

PubMed

Martín-Queller, Emi; Moreno-Mateos, David; Pedrocchi, César; Cervantes, Juan; Martínez, Gonzalo

2010-08-01

Irrigation return flows (IRF) are a major contributor of non-point source pollution to surface and groundwater. We evaluated the effects of irrigation on stream hydrochemistry in a Mediterranean semi-arid catchment (Flumen River, NE Spain). The Flumen River was separated into two zones based on the intensity of irrigation activities in the watershed. General linear models were used to compare the two zones. Relevant covariables (urban sewage, pig farming, and gypsum deposits in the basin) were quantified with the help of geographic information system techniques, accompanied by ground-truthing. High variability of the water quality parameters and temporal dynamics caused by irrigation were used to distinguish the two river reaches. Urban activity and livestock farming had a significant effect on water chemistry. An increase in the concentration of salts (240-541 microS.cm(-1) more in winter) and nitrate (average concentrations increased from 8.5 to 20.8 mg.l(-1) during irrigation months) was associated with a higher level of IRF. Those river reaches more strongly influenced by urban areas tended to have higher phosphorus (0.19-0.42 mg.l(-1) more in winter) concentrations. These results support earlier research about the significant consequences to water quality of both urban expansion and intensive agricultural production in arid and semi-arid regions. Data also indicate that salinization of soils, subsoils, surface water, and groundwater can be an unwelcome result of the application of pig manure for fertilization (increase in sodium concentration in 77.9 to 138.6 mg.l(-1)).

The road to NHDPlus — Advancements in digital stream networks and associated catchments

USGS Publications Warehouse

Moore, Richard B.; Dewald, Thomas A.

2016-01-01

A progression of advancements in Geographic Information Systems techniques for hydrologic network and associated catchment delineation has led to the production of the National Hydrography Dataset Plus (NHDPlus). NHDPlus is a digital stream network for hydrologic modeling with catchments and a suite of related geospatial data. Digital stream networks with associated catchments provide a geospatial framework for linking and integrating water-related data. Advancements in the development of NHDPlus are expected to continue to improve the capabilities of this national geospatial hydrologic framework. NHDPlus is built upon the medium-resolution NHD and, like NHD, was developed by the U.S. Environmental Protection Agency and U.S. Geological Survey to support the estimation of streamflow and stream velocity used in fate-and-transport modeling. Catchments included with NHDPlus were created by integrating vector information from the NHD and from the Watershed Boundary Dataset with the gridded land surface elevation as represented by the National Elevation Dataset. NHDPlus is an actively used and continually improved dataset. Users recognize the importance of a reliable stream network and associated catchments. The NHDPlus spatial features and associated data tables will continue to be improved to support regional water quality and streamflow models and other user-defined applications.

Simulating the effect of vegetation cover on the sediment yield of mediterranean catchments using SHETRAN

NASA Astrophysics Data System (ADS)

Lukey, B. T.; Sheffield, J.; Bathurst, J. C.; Lavabre, J.; Mathys, N.; Martin, C.

1995-08-01

The sediment yield of two catchments in southern France was modelled using the newly developed sediment code of SHETRAN. A fire in August 1990 denuded the Rimbaud catchment, providing an opportunity to study the effect of vegetation cover on sediment yield by running the model for both pre-and post-fire cases. Model output is in the form of upper and lower bounds on sediment discharge, reflecting the uncertainty in the erodibility of the soil. The results are encouraging since measured sediment discharge falls largely between the predicted bounds, and simulated sediment yield is dramatically lower for the catchment before the fire which matches observation. SHETRAN is also applied to the Laval catchment, which is subject to Badlands gulley erosion. Again using the principle of generating upper and lower bounds on sediment discharge, the model is shown to be capable of predicting the bulk sediment discharge over periods of months. To simulate the effect of reforestation, the model is run with vegetation cover equivalent to a neighbouring fully forested basin. The results obtained indicate that SHETRAN provides a powerful tool for predicting the impact of environmental change and land management on sediment yield.

Nested Tracer Studies In Catchment Hydrology: Towards A Multiscale Understanding of Runoff Generation and Catchment Funtioning

NASA Astrophysics Data System (ADS)

Soulsby, C.; Rodgers, P.; Malcolm, I. A.; Dunn, S.

Geochemical and isotopic tracers have been shown to have widespread utility in catch- ment hydrology in terms of identifying hydrological source areas and characterising residence time distributions. In many cases application of tracer techniques has pro- vided insights into catchment functioning that could not be obtained from hydromet- ric and/or modelling studies alone. This paper will show how the use of tracers has contributed to an evolving perceptual model of hydrological pathways and runoff gen- eration processes in catchments in the Scottish highlands. In particular the paper will focus on the different insights that are gained at three different scales of analysis; (a) nested sub-catchments within a mesoscale (ca. 200 square kilometers) experimen- tal catchment; (b) hillslope-riparian interactions and (c) stream bed fluxes. Nested hydrometric and hydrochemical monitoring within the mesoscale Feugh catchment identified three main hydrological response units: (i) plateau peatlands which gener- ated saturation overland flow in the catchment headwaters, (ii) steep valley hillslopes which drain from the plateaux into (iii) alluvial and drift aquifers in the valley bottoms. End Member Mixing Analysis (EMMA) in 8 nested sub-catchments indicated that that stream water tracer concentrations can be modelled in terms of 2 dominant runoff pro- cesses; overland flow from the peat and groundwater from the drift aquifers. Ground- water contributions generally increased with catchment size, though this was moder- ated by the characteristics of individual sub-basins, with drift cover being particularly important. Hillslope riparian interactions were also examined using tracers, hydromet- ric data and a semi-distributed hydrological model. This revealed that in the glaciated, drift covered terrain of the Scottish highlands, extensive valley bottom aquifers effec- tively de-couple hillslope waters from the river channel. Thus, riparian groundwater appears to significantly contribute to storm runoff as well as sustain base flows. Water from steeper hillslopes appears to primarily recharge valley bottom aquifers. Fluxes from the drift aquifers into the stream bed were investigated using hydrometric and tracer techniques. Groundwater fluxes through the stream bed appear to be relatively localized relating to geological boundaries or changes in drift characteristics. How- ever, these fluxes are also controlled by morphological features in the river channel which exert a strong control on localized groundwater U surface water interactions. 1 If catchment hydrology is to contribute to a functional understanding of freshwater ecosystems it is argued that integrated tracer studies, at different scales and incorpo- rating both observations from field work and modelling applications, have a key role to play. 2

Factors influencing protein tyrosine nitration – structure-based predictive models

PubMed Central

Bayden, Alexander S.; Yakovlev, Vasily A.; Graves, Paul R.; Mikkelsen, Ross B.; Kellogg, Glen E.

2010-01-01

Models for exploring tyrosine nitration in proteins have been created based on 3D structural features of 20 proteins for which high resolution X-ray crystallographic or NMR data are available and for which nitration of 35 total tyrosines has been experimentally proven under oxidative stress. Factors suggested in previous work to enhance nitration were examined with quantitative structural descriptors. The role of neighboring acidic and basic residues is complex: for the majority of tyrosines that are nitrated the distance to the heteroatom of the closest charged sidechain corresponds to the distance needed for suspected nitrating species to form hydrogen bond bridges between the tyrosine and that charged amino acid. This suggests that such bridges play a very important role in tyrosine nitration. Nitration is generally hindered for tyrosines that are buried and for those tyrosines where there is insufficient space for the nitro group. For in vitro nitration, closed environments with nearby heteroatoms or unsaturated centers that can stabilize radicals are somewhat favored. Four quantitative structure-based models, depending on the conditions of nitration, have been developed for predicting site-specific tyrosine nitration. The best model, relevant for both in vitro and in vivo cases predicts 30 of 35 tyrosine nitrations (positive predictive value) and has a sensitivity of 60/71 (11 false positives). PMID:21172423

Groundwater biofilm dynamics grown in situ along a nutrient gradient.

PubMed

Williamson, Wendy M; Close, Murray E; Leonard, Margaret M; Webber, Judith B; Lin, Susan

2012-01-01

This paper describes the in situ response of groundwater biofilms in an alluvial gravel aquifer system on the Canterbury Plains, New Zealand. Biofilms were developed on aquifer gravel, encased in fine mesh bags and suspended in protective columns in monitoring wells for at least 20 weeks. Four sites were selected in the same groundwater system where previous analyses indicated a gradient of increasing nitrate down the hydraulic gradient from Sites 1 to 4. Measurements during the current study classified the groundwater as oligotrophic. Biofilm responses to the nutrient gradients were assessed using bioassays, with biomass determined using protein and cellular and nucleic acid staining and biofilm activity using enzyme assays for lipid, carbohydrate, phosphate metabolism, and cell viability. In general, biofilm activity decreased as nitrate levels increased from Sites 1 to 4, with the opposite relationship for carbon and phosphorus concentrations. These results showed that the groundwater system supported biofilm growth and that the upper catchment supported efficient and productive biofilms (high ratio of activity per unit biomass). © 2012, Institute of Environmental Science & Research Ltd (ESR). Ground Water © 2012, National Ground Water Association.

Identifying dominant controls on hydrologic parameter transfer from gauged to ungauged catchments: a comparative hydrology approach

USGS Publications Warehouse

Singh, R.; Archfield, S.A.; Wagener, T.

2014-01-01

Daily streamflow information is critical for solving various hydrologic problems, though observations of continuous streamflow for model calibration are available at only a small fraction of the world’s rivers. One approach to estimate daily streamflow at an ungauged location is to transfer rainfall–runoff model parameters calibrated at a gauged (donor) catchment to an ungauged (receiver) catchment of interest. Central to this approach is the selection of a hydrologically similar donor. No single metric or set of metrics of hydrologic similarity have been demonstrated to consistently select a suitable donor catchment. We design an experiment to diagnose the dominant controls on successful hydrologic model parameter transfer. We calibrate a lumped rainfall–runoff model to 83 stream gauges across the United States. All locations are USGS reference gauges with minimal human influence. Parameter sets from the calibrated models are then transferred to each of the other catchments and the performance of the transferred parameters is assessed. This transfer experiment is carried out both at the scale of the entire US and then for six geographic regions. We use classification and regression tree (CART) analysis to determine the relationship between catchment similarity and performance of transferred parameters. Similarity is defined using physical/climatic catchment characteristics, as well as streamflow response characteristics (signatures such as baseflow index and runoff ratio). Across the entire US, successful parameter transfer is governed by similarity in elevation and climate, and high similarity in streamflow signatures. Controls vary for different geographic regions though. Geology followed by drainage, topography and climate constitute the dominant similarity metrics in forested eastern mountains and plateaus, whereas agricultural land use relates most strongly with successful parameter transfer in the humid plains.

Combining Neural Networks with Existing Methods to Estimate 1 in 100-Year Flood Event Magnitudes

NASA Astrophysics Data System (ADS)

Newson, A.; See, L.

2005-12-01

Over the last fifteen years artificial neural networks (ANN) have been shown to be advantageous for the solution of many hydrological modelling problems. The use of ANNs for flood magnitude estimation in ungauged catchments, however, is a relatively new and under researched area. In this paper ANNs are used to make estimates of the magnitude of the 100-year flood event (Q100) for a number of ungauged catchments. The data used in this study were provided by the Centre for Ecology and Hydrology's Flood Estimation Handbook (FEH), which contains information on catchments across the UK. Sixteen catchment descriptors for 719 catchments were used to train an ANN, which was split into a training, validation and test data set. The goodness-of-fit statistics on the test data set indicated good model performance, with an r-squared value of 0.8 and a coefficient of efficiency of 79 percent. Data for twelve ungauged catchments were then put through the trained ANN to produce estimates of Q100. Two other accepted methodologies were also employed: the FEH statistical method and the FSR (Flood Studies Report) design storm technique, both of which are used to produce flood frequency estimates. The advantage of developing an ANN model is that it provides a third figure to aid a hydrologist in making an accurate estimate. For six of the twelve catchments, there was a relatively low spread between estimates. In these instances, an estimate of Q100 could be made with a fair degree of certainty. Of the remaining six catchments, three had areas greater than 1000km2, which means the FSR design storm estimate cannot be used. Armed with the ANN model and the FEH statistical method the hydrologist still has two possible estimates to consider. For these three catchments, the estimates were also fairly similar, providing additional confidence to the estimation. In summary, the findings of this study have shown that an accurate estimation of Q100 can be made using the catchment descriptors of an ungauged catchment as inputs to an ANN. It also demonstrated how the ANN Q100 estimates can be used in conjunction with a number of other estimates in order to provide a more accurate and confident estimate of Q100 at an ungauged catchment. This clearly exploits the strengths of existing methods in combination with the latest soft computing tools.

How is the River Water Quality Response to Climate Change Impacts?

NASA Astrophysics Data System (ADS)

Nguyen, T. T.; Willems, P.

2015-12-01

Water quality and its response to climate change have been become one of the most important issues of our society, which catches the attention of many scientists, environmental activists and policy makers. Climate change influences the river water quality directly and indirectly via rainfall and air temperature. For example, low flow decreases the volume of water for dilution and increases the residence time of the pollutants. By contrast, high flow leads to increases in the amount of pollutants and sediment loads from catchments to rivers. The changes in hydraulic characteristics, i.e. water depth and velocity, affect the transportation and biochemical transformation of pollutants in the river water body. The high air temperature leads to increasing water temperature, shorter growing periods of different crops and water demands from domestic households and industries, which eventually effects the level of river pollution. This study demonstrates the quantification of the variation of the water temperature and pollutant concentrations along the Molse Neet river in the North East of Belgium as a result of the changes in the catchment rainfall-runoff, air temperature and nutrient loads. Firstly, four climate change scenarios were generated based on a large ensemble of available global and regional climate models and statistical downscaling based on a quantile perturbation method. Secondly, the climatic changes to rainfall and temperature were transformed to changes in the evapotranspiration and runoff flow through the conceptual hydrological model PDM. Thirdly, the adjustment in nutrient loads from agriculture due to rainfall and growing periods of crops were calculated by means of the semi-empirical SENTWA model. Water temperature was estimated from air temperature by a stochastic model separating the temperature into long-term annual and short-term residual components. Next, hydrodynamic and water quality models of the river, implemented in InfoWorks RS, were simulated for both historical (2000-2010) and projected future periods (2050-2060). The advection movement and physico-biochemical processes were considered for simulation of the following water quality variables: water temperature, dissolved oxygen, biological oxygen demand, ammonium, nitrate, nitrite and organic nitrogen.

Impact of modellers' decisions on hydrological a priori predictions

NASA Astrophysics Data System (ADS)

Holländer, H. M.; Bormann, H.; Blume, T.; Buytaert, W.; Chirico, G. B.; Exbrayat, J.-F.; Gustafsson, D.; Hölzel, H.; Krauße, T.; Kraft, P.; Stoll, S.; Blöschl, G.; Flühler, H.

2013-07-01

The purpose of this paper is to stimulate a re-thinking of how we, the catchment hydrologists, could become reliable forecasters. A group of catchment modellers predicted the hydrological response of a man-made 6 ha catchment in its initial phase (Chicken Creek) without having access to the observed records. They used conceptually different model families. Their modelling experience differed largely. The prediction exercise was organized in three steps: (1) for the 1st prediction modellers received a basic data set describing the internal structure of the catchment (somewhat more complete than usually available to a priori predictions in ungauged catchments). They did not obtain time series of stream flow, soil moisture or groundwater response. (2) Before the 2nd improved prediction they inspected the catchment on-site and attended a workshop where the modellers presented and discussed their first attempts. (3) For their improved 3rd prediction they were offered additional data by charging them pro forma with the costs for obtaining this additional information. Holländer et al. (2009) discussed the range of predictions obtained in step 1. Here, we detail the modeller's decisions in accounting for the various processes based on what they learned during the field visit (step 2) and add the final outcome of step 3 when the modellers made use of additional data. We document the prediction progress as well as the learning process resulting from the availability of added information. For the 2nd and 3rd step, the progress in prediction quality could be evaluated in relation to individual modelling experience and costs of added information. We learned (i) that soft information such as the modeller's system understanding is as important as the model itself (hard information), (ii) that the sequence of modelling steps matters (field visit, interactions between differently experienced experts, choice of model, selection of available data, and methods for parameter guessing), and (iii) that added process understanding can be as efficient as adding data for improving parameters needed to satisfy model requirements.

Estimating of the impact of land use changes using the conceptual hydrological model THESEUS??a case study

NASA Astrophysics Data System (ADS)

Wegehenkel, Martin

As a result of a new agricultural funding policy established in 1992 by the European Community, it was assumed that up to 15-20% of arable land would have been set aside in the next years in the new federal states of north-eastern Germany, for example, Brandenburg. As one potential land use option, afforestation of these set aside areas was discussed to obtain deciduous forests. Since the mean annual precipitation in north-eastern Germany, Brandenburg is relatively low (480-530 mm y -1), an increase in interception and evapotranspiration loss by forests compared to arable land would lead to a reduction in ground water recharge. Experimental evidence to determine effects of such land use changes are rarely available. Therefore, there is a need for indirect methods to estimate the impact of afforestation on the water balance of catchments. In this paper, a conceptual hydrological model was verified and calibrated in two steps using data from the Stobber-catchment located in Brandenburg. In the first step, model outputs like daily evapotranspiration rates and soil water contents were verified on the basis of experimental data sets from two test locations. One test site with the land use arable land was located within the Stobber-catchment. The other test site with pine forest was located near by the catchment. In the second step, the model was used to estimate the impact of afforestation on catchment water balance and discharge. For that purpose, the model was calibrated against daily discharge measurements for the period 1995-1997. For a simple afforestation scenario, it was assumed that the area of forest increases from 34% up to 80% of the catchment area. The impact of this change in forest cover proportion was analyzed using the calibrated model. In case of increasing the proportion of forest cover in the catchment due to the scenario afforestation, the model predicts a reduction in discharge and an increase in evapotranspiration.

Forecasting the effects of EU policy measures on the nitrate pollution of groundwater and surface waters

NASA Astrophysics Data System (ADS)

Kunkel, R.; Kreins, P.; Tetzlaff, B.; Wendland, F.

2009-04-01

The fundamental objectives of the European Union-Water Framework Directive and the EU Groundwater Directive are to attain a good status of water and groundwater resources in the member states of the EU by 2015. Following the implementation time table, the EU member States carried out a review about the qualitative and quantitative status for all river basins in the EU. For river basins, whose good status cannot be guaranteed by 2015, catchment wide operational plans and measurement programs are to be drafted and implemented until 2009. In the river basin district Weser, Germany, which comprises a catchment area of ca. 49.000 km2, the achievement of the good status is unclear, or rather unlikely for 63% of the groundwater bodies. Inputs from diffuse sources and most of all nitrogen losses from agriculturally used land have been identified as the main reasons for exceeding the groundwater threshold value for nitrate (50 mg/l) and for failing the „good qualitative status" of groundwater in 2015. For this reason the drafting and implementation of measurement programs in the Weser basin are primarily focused on nitrate. The achievement of good qualitative status of groundwater bodies entails a particular challenge especially for large river basins as the complex ecological, hydrological, hydrogeological and agro-economic relationships have to be considered simultaneously. Integrated large scale agroeconomic- hydrologic models are powerful tools to analyze the actual pollution loads and "hot spot" areas and to predict the temporal and spatial effects of reduction measures. We used the interdisciplinary model network REGFLUD to predict the nitrogen intakes into groundwater and the nitrogen losses to surface waters by different pathways at the regional scale using an area differentiated approach. The model system combines the agro-economic model RAUMIS for estimating nitrogen surpluses from agriculture and the hydrological models GROWA/DENUZ/WEKU for describing the reactive nitrate transport in the soil-groundwater system. Nitrogen transport by groundwater runoff, surface runoff, drainage runoff and natural interflow is considered. In a first step the model is used to analyze the present situation using N surpluses from agriculture for the year 2003. In many region of the Weser basin, particularly in the northwestern part which is characterized by high livestock densities, predicted nitrate concentrations in percolation water exceed the EU groundwater quality standard of 50 mg/L by far. In parallel, high nitrogen outputs to surface waters via the different pathways are predicted for these areas. The regional importance of a specific outtake pathway for nitrogen, however, may vary significantly depending on the individual site characteristics. Based on the results of the analysis of the present situation regionally adapted and hence effective agri-environmental reduction measures need to be derived and implemented to improve groundwater and surface water quality by 2015. These measures include both single measures and combination of measures, which will be analyzed with regard to their impact on the regional quality of percolation water and on their impacts on the regional agricultural income. In this context it is very important to distinguish between the effects of measures, which have already been implemented by current agricultural policy and measures which have to be additionally implemented to meet the environmental targets of the EU Water Framework Directive. For this purpose a baseline scenario is developed, which projects the effects of modified general conditions of the agricultural sector on the nitrogen surpluses to the year 2015. In this baseline scenario the effects of the common agricultural policy (CAP) of the EU, already implemented agri-environmental measures of the Federal States and the expected developments of agriculture are considered. According to this scenario the nitrogen surpluses for agricultural areas can be expected to be reduced only by about 10 kg N ha-1 a-1 on average for the whole Weser basin. However, for the agriculturally intensive used regions the expected N surpluses reduction may be much higher and can amount 40 kg N ha-1 a-1 or more. The REGLUD model system is used to quantify the potential effects of these projected N surpluses on the intakes into the groundwater the nitrogen pollution of surface waters. A comparison to the present situation shows that the potential nitrate concentration in the leachate will decrease in almost all regions of the Weser basin, mostly by about 10 mg NO3/L. In the agriculturally intensive used regions much higher reductions in the order of 40 mg NO3/L may be expected. Consequently, reduced nitrogen outflows to surface waters via the different pathways are obtained. Using environmental target values for groundwater and surface waters, e.g. a concentration of 50 mg NO3/L in the leachate as a target for groundwater protection, the model results can be used directly to identify those regions where additional agri-environmental reduction measures are required. Additionally, a backward calculation by the REGFLUD allows the quantification of maximal permissible nitrogen surplus levels, which can be used as a reference for the derivation of additional regionally adapted and hence effective nitrogen reduction measures. The research work presented here is carried out in the framework of the still ongoing AGRUM Weser project which is funded on behalf of the German Federal Ministry of Food, Agriculture and Consumer protection (BMELV) and the River Basin Commission Weser (FGG).

The effectiveness and resilience of phosphorus management practices in the Lake Simcoe watershed, Ontario, Canada

NASA Astrophysics Data System (ADS)

Crossman, J.; Futter, M. N.; Palmer, M.; Whitehead, P. G.; Baulch, H. M.; Woods, D.; Jin, L.; Oni, S. K.; Dillon, P. J.

2016-09-01

Uncertainty surrounding future climate makes it difficult to have confidence that current nutrient management strategies will remain effective. This study used monitoring and modeling to assess current effectiveness (% phosphorus reduction) and resilience (defined as continued effectiveness under a changing climate) of best management practices (BMPs) within five catchments of the Lake Simcoe watershed, Ontario. The Integrated Catchment Phosphorus model (INCA-P) was used, and monitoring data were used to calibrate and validate a series of management scenarios. To assess current BMP effectiveness, models were run over a baseline period 1985-2014 with and without management scenarios. Climate simulations were run (2070-2099), and BMP resilience was calculated as the percent change in effectiveness between the baseline and future period. Results demonstrated that livestock removal from water courses was the most effective BMP, while manure storage adjustments were the least. Effectiveness varied between catchments, influenced by the dominant hydrological and nutrient transport pathways. Resilience of individual BMPs was associated with catchment sensitivity to climate change. BMPs were most resilient in catchments with high soil water storage capacity and small projected changes in frozen-water availability and in soil moisture deficits. Conversely, BMPs were less resilient in catchments with larger changes in spring melt magnitude and in overland flow proportions. Results indicated that BMPs implemented are not always those most suited to catchment flow pathways, and a more site-specific approach would enhance prospects for maintaining P reduction targets. Furthermore, BMP resilience to climate change can be predicted from catchment physical properties and present-day hydrochemical sensitivity to climate forcing.

Downscaling catchment scale flood risk to contributing sub-catchments to determine the optimum location for flood management.

NASA Astrophysics Data System (ADS)

Pattison, Ian; Lane, Stuart; Hardy, Richard; Reaney, Sim

2010-05-01

The recent increase in flood frequency and magnitude has been hypothesised to have been caused by either climate change or land management. Field scale studies have found that changing land management practices does affect local runoff and streamflow, but upscaling these effects to the catchment scale continues to be problematic, both conceptually and more importantly methodologically. The impact on downstream flood risk is highly dependent upon where the changes are in the catchment, indicating that some areas of the catchment are more important in determining downstream flood risk than others. This is a major flaw in the traditional approach to studying the effect of land use on downstream flood risk: catchment scale hydrological models, which treat every cell in the model equally. We are proposing an alternative ideological approach for doing flood management research, which is underpinned by downscaling the downstream effect (problem i.e. flooding) to the upstream causes (contributing sub-catchments). It is hoped that this approach could have several benefits over the traditional upscaling approach. Firstly, it provides an efficient method to prioritise areas for land use management changes to be implemented to reduce downstream flood risk. Secondly, targets for sub-catchment hydrograph change can be determined which will deliver the required downstream effect. Thirdly, it may be possible to detect the effect of land use changes in upstream areas on downstream flood risk, by weighting the areas of most importance in hydrological models. Two methods for doing this downscaling are proposed; 1) data-based statistical analysis; and 2) hydraulic modelling-based downscaling. These will be outlined using the case study of the River Eden, Cumbria, NW England. The data-based methodology uses the timing and magnitude of floods for each sub-catchment. Principal components analysis (PCA) is used to simplify sub-catchment interactions and optimising stepwise regression is used to predict downstream flood magnitude from the significant principal components. Two particular sub-catchments, the Eamont and the Upper Eden were highlighted as explaining the highest proportion of downstream flood risk, with 21.0% and 19.6% respectively. This approach uses the concept of data mining, whereby commonly available discharge data is used in an innovative way to learn about catchment behaviour. An alternative downscaling approach is hydraulic modelling whereby the input hydrographs from each tributary are changed in turn, both in terms of the magnitudes and the timing of the flows. This basic scenario testing approach can be used to assess the sensitivity of downstream flood risk to upstream contributing tributaries. This approach also highlighted the Upper Eden and Eamont as the most sensitive sub-catchments. A 25% reduction in the flows from these sub-catchments resulted in a 33.1cm and 21.9cm stage reduction downstream respectively, while an 8 hour delay of the peak flow caused a 32.3cm and 27.4cm decrease in downstream stage respectively. This alternative flood management approach is not a replacement to traditional hydrological modelling (upscaling), but a pre-step which allows for more focussed and informed investigation of land management scenarios, in the area where they are most likely to have beneficial impacts on downstream flooding.

Applying A Multi-Objective Based Procedure to SWAT Modelling in Alpine Catchments

NASA Astrophysics Data System (ADS)

Tuo, Y.; Disse, M.; Chiogna, G.

2017-12-01

In alpine catchments, water management practices can lead to conflicts between upstream and downstream stakeholders, like in the Adige river basin (Italy). A correct prediction of available water resources plays an important part, for example, in defining how much water can be stored for hydropower production in upstream reservoirs without affecting agricultural activities downstream. Snow is a crucial hydrological component that highly affects seasonal behavior of streamflow. Therefore, a realistic representation of snow dynamics is fundamental for water management operations in alpine catchments. The Soil and Water Assessment Tool (SWAT) model has been applied in alpine catchments worldwide. However, during model calibration of catchment scale applications, snow parameters were generally estimated based on streamflow records rather than on snow measurements. This may lead to streamflow predictions with wrong snow melt contribution. This work highlights the importance of considering snow measurements in the calibration of the SWAT model for alpine hydrology and compares various calibration methodologies. In addition to discharge records, snow water equivalent time series of both subbasin scale and monitoring station were also utilized to evaluate the model performance by comparing with the SWAT subbasin and elevation band snow outputs. Comparing model results obtained calibrating the model using discharge data only and discharge data along with snow water equivalent data, we show that the latter approach allows us to improve the reliability of snow simulations while maintaining good estimations of streamflow. With a more reliable representation of snow dynamics, the hydrological model can provide more accurate references for proposing adequate water management solutions. This study offers to the wide SWAT user community an effective approach to improve streamflow predictions in alpine catchments and hence support decision makers in water allocation.

Comparison of estuarine sediment record with modelled rates of sediment supply from a western European catchment since 1500

NASA Astrophysics Data System (ADS)

Poirier, Clément; Poitevin, Cyril; Chaumillon, Éric

2016-09-01

Marine and estuarine sediment records reporting impacts of historical land use changes exist worldwide, but they are rarely supported by direct quantified evidence of changes in denudation rates on the related catchments. Here we implement a spatially-resolved RUSLE soil erosion model on the 10 000 km2 Charente catchment (France), supplied with realistic scenarios of land-cover and climate changes since 1500, and compare the results to a 14C-dated estuarine sediment record. Despite approximations, the model correctly predicts present-day Charente river sediment load. Back-cast modelling suggests that the Charente catchment is an interesting case where the sediment supply did not change despite increase in soil erosion resulting from 18th-century deforestation because it was mitigated by drier climate during the same period. Silt-sand alternations evidenced in the sediment record were correlated with sub-decadal rainfall variability.

Effects of spatial variability and scale on areal -average evapotranspiration

NASA Technical Reports Server (NTRS)

Famiglietti, J. S.; Wood, Eric F.

1993-01-01

This paper explores the effect of spatial variability and scale on areally-averaged evapotranspiration. A spatially-distributed water and energy balance model is employed to determine the effect of explicit patterns of model parameters and atmospheric forcing on modeled areally-averaged evapotranspiration over a range of increasing spatial scales. The analysis is performed from the local scale to the catchment scale. The study area is King's Creek catchment, an 11.7 sq km watershed located on the native tallgrass prairie of Kansas. The dominant controls on the scaling behavior of catchment-average evapotranspiration are investigated by simulation, as is the existence of a threshold scale for evapotranspiration modeling, with implications for explicit versus statistical representation of important process controls. It appears that some of our findings are fairly general, and will therefore provide a framework for understanding the scaling behavior of areally-averaged evapotranspiration at the catchment and larger scales.

Benthic metabolism and nitrogen dynamics in an urbanised tidal creek: Domination of DNRA over denitrification as a nitrate reduction pathway

NASA Astrophysics Data System (ADS)

Dunn, Ryan J. K.; Robertson, David; Teasdale, Peter R.; Waltham, Nathan J.; Welsh, David T.

2013-10-01

Benthic oxygen and nutrient fluxes and nitrate reduction rates were determined seasonally under light and dark conditions at three sites in a micro-tidal creek within an urbanised catchment (Saltwater Creek, Australia). It was hypothesized that stormwater inputs of organic matter and inorganic nitrogen would stimulate rates of benthic metabolism and nutrient recycling and preferentially stimulate dissimilatory nitrate reduction to ammonium (DNRA) over denitrification as a pathway for nitrate reduction. Stormwaters greatly influenced water column dissolved inorganic nitrogen (DIN) and suspended solids concentrations with values following a large rainfall event being 5-20-fold greater than during the preceding dry period. Seasonally, maximum and minimum water column total dissolved nitrogen (TDN) and DIN concentrations occurred in the summer (wet) and winter (dry) seasons. Creek sediments were highly heterotrophic throughout the year, and strong sinks for oxygen, and large sources of dissolved organic and inorganic nitrogen during both light and dark incubations, although micro-phytobenthos (MPB) significantly decreased oxygen consumption and N-effluxes during light incubations due to photosynthetic oxygen production and photoassimilation of nutrients. Benthic denitrification rates ranged from 3.5 to 17.7 μmol N m2 h-1, denitrification efficiencies were low (<1-15%) and denitrification was a minor process compared to DNRA, which accounted for ˜75% of total nitrate reduction. Overall, due to the low denitrification efficiencies and high rates of N-regeneration, Saltwater Creek sediments would tend to increase rather than reduce dissolved nutrient loads to the downstream Gold Coast Broadwater and Moreton Bay systems. This may be especially true during wet periods when increased inputs of particulate organic nitrogen (PON) and suspended solids could respectively enhance rates of N-regeneration and decrease light availability to MPB, reducing their capacity to ameliorate N-effluxes through photoassimilation.

Application of Temperature Index Model to Assess the Future Hydrological Regime of the Glacierized Catchments in Nepal.

NASA Astrophysics Data System (ADS)

Kayastha, R.; Kayastha, R. B.

2017-12-01

Unavailability of hydro meteorological data in the Himalayan regions is challenging on understanding the flow regimes. Temperature index model is simple yet the powerful glacio-hydrological model to simulate the discharge in the glacierized basin. Modified Positive Degree Day (MPDD) Model Version 2.0 is a grid-ded based semi distributed model with baseflow module is a robust melt modelling tools to estimate the discharge. MPDD model uses temperature and precipitation as a forcing datasets to simulate the discharge and also to obtain the snowmelt, icemelt, rain and baseflow contribution on total discharge. In this study two glacierized, Marsyangdi and Langtang catchment were investigated for the future hydrological regimes. Marsyangdi encompasses an area of 4026.19 sq. km with 20% glaciated area, whereas Langtang catchment with area of 354.64 sq. km with 36% glaciated area is studied to examine for the future climatic scenarios. The model simulates discharge well for the observed period; (1992-1998) in Marsyangdi and from (2007-2013) in Langtang catchment. The Nash-Sutcliffe Efficiency (NSE) for the both catchment were above 0.75 with the volume difference less than - 8 %. The snow and ice melts contribution in Marsyangdi were 4.7% and 10.2% whereas in Langtang the contribution is 15.3% and 23.4%, respectively. Rain contribution ( 40%) is higher than the baseflow contribution in total discharge in both basins. The future river discharge is also predicted using the future climate data from the regional climate models (RCMs) of CORDEX South Asia experiments for the medium stabilization scenario RCP4.5 and very high radiative forcing scenario RCP8.5 after bias correction. The projected future discharge of both catchment shows slightly increase in both scenarios with increase of snow and ice melt contribution on discharge. The result generated from the model can be utilized to understand the future hydrological regimes of the glacierized catchment also the impact of climate change on the snow and ice contribution on discharge. The future discharge projection is also helpful for the water resource management and also for the strategic planners.

The GREAT-ER model in China: Evaluating the risk of both treated and untreated wastewater discharges and a consideration to the future.

NASA Astrophysics Data System (ADS)

Jackson, Benjamin; Jones, Kevin; Sweetman, Andrew

2016-04-01

As a result of rapid economic development, the production and usage of chemicals in China has risen significantly. This has resulted in China's environment becoming degraded. The Chinese government has attempted to ease these problems with significant investment towards upgrading the wastewater network. These efforts have initially focused upon large cities; progressing towards smaller populations within the most recent 5 year plan. However rural populations were largely overlooked, ~90% of rural settlements do not have treatment facilities for their wastewater. The next (13th) five year plan is a great opportunity to improve upon wastewater infrastructure. This transition is particularly important and it is essential for the government to prioritise settlements to provide treatment facilities and to improve water quality in receiving waters. This study focuses upon the use of a catchment model in order make progress towards this goal. A reliable model which can capture the complexity of the catchment is needed, but one without complexity in itself, in order for it to be developed and validated without an excessive requirement for data. The Geo-referenced Regional Exposure Assessment Tool for European Rivers (GREAT-ER) model is a catchment-scale stochastic-deterministic GIS model. It is primarily used for higher-tier chemical risk assessment. Emissions are from point source only and are calculated based upon population and calculated emission rates per capita. Dilution and transportation are determined using low-flow statistics within each stretch; calculated based upon catchment soil and topographic properties. Removal of the contaminant can occur prior to emission and in-stream. The lowest tier methodology applies a simple 1st-order removal rate and a flat percentage removal for in-stream and sewage treatment work removal respectively. The data requirements are relatively low, although still challenging for many situations. Many authors have reported reasonable agreement between modelled and observed concentrations. Unlike many other water quality models, GREAT-ER is relatively simple to setup and use. This provides value for catchment managers, and for chemical end-users and manufacturers alike. As of yet, GREAT-ER has not been used in Chinese catchments, but there is much potential. Our study involves the creation and validation of a model for the Dongjiang catchment, South China. The Dongjiang catchment is a highly populated area, draining into Guangzhou and the Pearl River delta. The catchment area is 25,325 km2 (above Boluo gauging station), of which approximately 90% resides in Guangdong Province. The downstream section of the catchment is densely populated, whilst upstream there is a more significant rural population. This study focuses upon chemical ingredients found in personal care products and pharmaceuticals and the potential risk they may impose upon the catchment. The relative impact of rural discharges has also been examined along with the potential effect of a range of future wastewater upgrade scenarios. The model has been validated with measurement data collected over a number of sampling campaigns. We believe that this study provides insights into the challenges faced by China as it drives to improve water quality.

Which catchment characteristics control the temporal dependence structure of daily river flows?

NASA Astrophysics Data System (ADS)

Chiverton, Andrew; Hannaford, Jamie; Holman, Ian; Corstanje, Ron; Prudhomme, Christel; Bloomfield, John; Hess, Tim

2014-05-01

A hydrological classification system would provide information about the dominant processes in the catchment enabling information to be transferred between catchments. Currently there is no widely-agreed upon system for classifying river catchments. This paper developed a novel approach to assess the influence that catchment characteristics have on the precipitation-to-flow relationship, using a catchment classification based on the average temporal dependence structure in daily river flow data over the period 1980 to 2010. Temporal dependence in river flow data is driven by the flow pathways, connectivity and storage within the catchment. Temporal dependence was analysed by creating temporally averaged semi-variograms for a set of 116 near-natural catchments (in order to prevent direct anthropogenic disturbances influencing the results) distributed throughout the UK. Cluster analysis, using the variogram, classified the catchments into four well defined clusters driven by the interaction of catchment characteristics, predominantly characteristics which influence the precipitation-to-flow relationship. Geology, depth to gleyed layer in soils, slope of the catchment and the percentage of arable land were significantly different between the clusters. These characteristics drive the temporal dependence structure by influencing the rate at which water moves through the catchment and / or the storage in the catchment. Arable land is correlated with several other variables, hence is a proxy indicating the residence time of the water in the catchment. Finally, quadratic discriminant analysis was used to show that a model with five catchment characteristics is able to predict the temporal dependence structure for un-gauged catchments. This work demonstrates that a variogram-based approach is a powerful and flexible methodology for grouping catchments based on the precipitation-to-flow relationship which could be applied to any set of catchments with a relatively complete daily river flow record.

SWMM Modeling Methods for Simulating Green Infrastructure at a Suburban Headwatershed: User’s Guide

EPA Science Inventory

Urban stormwater runoff quantity and quality are strongly dependent upon catchment properties. Models are used to simulate the runoff characteristics, but the output from a stormwater management model is dependent on how the catchment area is subdivided and represented as spatial...

How much complexity is warranted in a rainfall-runoff model?

Treesearch

A.J. Jakeman; G.M. Hornberger

1993-01-01

Development of mathmatical models relating the precipitation incident upon a catchment to the streamflow emanating from the catchment has been a major focus af surface water hydrology for decades. Generally, values for parameters in such models must be selected so that runoff calculated from the model "matches" recorded runoff from some historical period....

Plan of study to determine if the isotopic ratios [delta]15 N and [delta]18 O can reveal the sources of nitrate discharged by the Mississippi River into the Gulf of Mexico

USGS Publications Warehouse

Battaglin, William A.; Kendall, Carol; Goolsby, Donald A.; Boyer, Laurie L.

1997-01-01

Nitrate and other nutrients discharged from the Mississippi River basin are suspected of causing a zone of depleted dissolved oxygen (hypoxic zone) in the Gulf of Mexico each summer. The hypoxic zone may have an adverse effect on aquatic life and commercial fisheries. Commercial fertilizers are the dominant source of nitrogen input to the Mississippi basin. Other nitrogen sources include animal waste, fixation of atmospheric nitrogen by legumes, precipitation, domestic and industrial effluent, and the soil. The inputs of nitrogen from most of these sources to the Mississippi basin can be estimated and the outputs in surface water can be measured. However, nitrogen from each source is affected differently by physical, chemical, and biological processes that control nitrogen cycling in terrestrial and aquatic systems. Hence, the relative contributions from the various sources of nitrogen to nitrate load in the Mississippi River are unknown because the different sources may not contribute proportionally to their inputs in the basin. It may be possible to determine the relative contributions of the major sources of nitrate in river water using the stable isotopic ratios d15N and d18O of the nitrate ion. A few researchers have used the d15N and/or d18O isotope ratios to determine sources of nitrate in ground water, headwater catchments, and small rivers, but little is known about the isotopic composition of nitrate in larger rivers. The objective of this study is to measure the isotopic composition of nitrate and suspended organic matter in the Mississippi River and its major tributaries, in discharge to the Gulf of Mexico, and in streamflow from smaller watersheds that have distinct sources of nitrogen (row crops, animal wastes, and urban effluents) or are minimally impacted by man (undeveloped). Samples from seven sites on the Mississippi River and its tributaries and from 17 sites in smaller watersheds within the Mississippi River basin will be analyzed for d15N and d18O of dissolved nitrate. Suspended sediment collected from these sites will also be analyzed to determine the d15N, d13C, and d34S of the suspended organic material. Six samples will be collected at each site during the winter, spring, and summer of 1996-97. Results from these samples will be used to identify seasonal and flow-related variability in d15N and d18O ratios from each site and may also help determine the principal sources of the nitrate entering the Gulf of Mexico.

Landscape structure and climate influences on hydrologic response

NASA Astrophysics Data System (ADS)

Nippgen, Fabian; McGlynn, Brian L.; Marshall, Lucy A.; Emanuel, Ryan E.

2011-12-01

Climate variability and catchment structure (topography, geology, vegetation) have a significant influence on the timing and quantity of water discharged from mountainous catchments. How these factors combine to influence runoff dynamics is poorly understood. In this study we linked differences in hydrologic response across catchments and across years to metrics of landscape structure and climate using a simple transfer function rainfall-runoff modeling approach. A transfer function represents the internal catchment properties that convert a measured input (rainfall/snowmelt) into an output (streamflow). We examined modeled mean response time, defined as the average time that it takes for a water input to leave the catchment outlet from the moment it reaches the ground surface. We combined 12 years of precipitation and streamflow data from seven catchments in the Tenderfoot Creek Experimental Forest (Little Belt Mountains, southwestern Montana) with landscape analyses to quantify the first-order controls on mean response times. Differences between responses across the seven catchments were related to the spatial variability in catchment structure (e.g., slope, flowpath lengths, tree height). Annual variability was largely a function of maximum snow water equivalent. Catchment averaged runoff ratios exhibited strong correlations with mean response time while annually averaged runoff ratios were not related to climatic metrics. These results suggest that runoff ratios in snowmelt dominated systems are mainly controlled by topography and not by climatic variability. This approach provides a simple tool for assessing differences in hydrologic response across diverse watersheds and climate conditions.

The role of pesticide fate modelling in a prevention-led approach to potable water quality management

NASA Astrophysics Data System (ADS)

Dolan, Tom; Pullan, Stephanie; Whelan, Mick; Parsons, David

2013-04-01

Diffuse inputs from agriculture are commonly the main source of pesticide contamination in surface water and may have implications for the quality of treated drinking water. After privatisation in 1991, UK water companies primarily focused on the provision of sufficient water treatment to reduce the risk of non-compliance with the European Drinking Water Directive (DWD), under which all pesticide concentrations must be below 0.1µg/l and UK Water Supply Regulations for the potable water they supply. Since 2000, Article 7 of the Water Framework Directive (WFD) has begun to drive a prevention-led approach to compliance with the DWD. As a consequence water companies are now more interested in the quality of 'raw' (untreated) water at the point of abstraction. Modelling (based upon best available estimates of cropping, pesticide use, weather conditions, pesticide characteristics, and catchment characteristics) and monitoring of raw water quality can both help to determine the compliance risks associated with the quality of this 'raw' water resource. This knowledge allows water companies to prioritise active substances for action in their catchments, and is currently used in many cases to support the design of monitoring programmes for pesticide active substances. Additional value can be provided if models are able to help to identify the type and scale of catchment management interventions required to achieve DWD compliance for pesticide active substances through pollution prevention at source or along transport pathways. These questions were explored using a simple catchment-scale pesticide fate and transport model. The model employs a daily time-step and is semi-lumped with calculations performed for soil type and crop combinations, weighted by their proportions within the catchment. Soil properties are derived from the national soil database and the model can, therefore, be applied to any catchment in England and Wales. Various realistic catchment management intervention scenarios were explored (including changes to land use and pesticide usage) with the aim of providing a useful input to the debate between water companies, their regulators and pesticide users over the scale of catchment management required to support both DWD and WFD Article 7 compliance.

Reactive transport model for bioremediation of nitrate using fumarate in groundwater system: verification and field application

NASA Astrophysics Data System (ADS)

Lee, S.; Yeo, I. W.; Yeum, Y.; Kim, Y.

2016-12-01

Previous studies showed that groundwater of rural areas in Korea is often contaminated with nitrate highly exceeding the drinking water standard of 10 mg/L (NO3-N), which poses a major threat in human and livestock health. In-situ bioremediation method has been developed to reduce high nitrate-nitrogen concentration in groundwater using slowly released encapsulated carbon source. Collaborative research of this study revealed that fumarate was found to be a very effective carbon source in terms of cost and nitrate reduction against formate, propionate, and lactate. For reactive transport modeling of the bioremediation of nitrate using fumarate, the BTEX module of RT3D incorporated in GMS, a commercial groundwater modeling software developed by AQUAVEO, was adopted, where BTEX was replaced with fumarate as a carbon source. Column tests were carried out to determine transport and reaction parameters for numerical modeling such as dispersity and first order degradation rate of nitrate by fumarate. The calibration of the numerical model against column tests strongly indicated that nitrate, known to be not reactive in groundwater system, appeared to be retarded due to sorption by fumarate. The calibrated model was tested for field-scale application to the composting facility in Gimje, Korea. The numerical results showed that the model could simulate the nitrate reduction by fumarate in field scale groundwater system. The reactive transport model for nitrate can be used as a tool for optimum design of in-situ nitrate bioremediation system, such as released depth and amount of fumarate and the spacing of wells that encapsulated fumarate is released through.

Application of Water Evaluation and Planning Model for Integrated Water Resources Management: Case Study of Langat River Basin, Malaysia

NASA Astrophysics Data System (ADS)

Leong, W. K.; Lai, S. H.

2017-06-01

Due to the effects of climate change and the increasing demand on water, sustainable development in term of water resources management has become a major challenge. In this context, the application of simulation models is useful to duel with the uncertainty and complexity of water system by providing stakeholders with the best solution. This paper outlines an integrated management planning network is developed based on Water Evaluation and Planning (WEAP) to evaluate current and future water management system of Langat River Basin, Malaysia under various scenarios. The WEAP model is known as an integrated decision support system investigate major stresses on demand and supply in terms of water availability in catchment scale. In fact, WEAP is applicable to simulate complex systems including various sectors within a single catchment or transboundary river system. To construct the model, by taking account of the Langat catchment and the corresponding demand points, we defined the hydrological model into 10 sub-hydrological catchments and 17 demand points included the export of treated water to the major cities outside the catchment. The model is calibrated and verified by several quantitative statistics (coefficient of determination, R2; Nash-Sutcliffe efficiency, NSE and Percent bias, PBIAS). The trend of supply and demand in the catchment is evaluated under three scenarios to 2050, 1: Population growth rate, 2: Demand side management (DSM) and 3: Combination of DSM and reduce non-revenue water (NRW). Results show that by reducing NRW and proper DSM, unmet demand able to reduce significantly.

Insights on the impact of systematic model errors on data assimilation performance in changing catchments

NASA Astrophysics Data System (ADS)

Pathiraja, S.; Anghileri, D.; Burlando, P.; Sharma, A.; Marshall, L.; Moradkhani, H.

2018-03-01

The global prevalence of rapid and extensive land use change necessitates hydrologic modelling methodologies capable of handling non-stationarity. This is particularly true in the context of Hydrologic Forecasting using Data Assimilation. Data Assimilation has been shown to dramatically improve forecast skill in hydrologic and meteorological applications, although such improvements are conditional on using bias-free observations and model simulations. A hydrologic model calibrated to a particular set of land cover conditions has the potential to produce biased simulations when the catchment is disturbed. This paper sheds new light on the impacts of bias or systematic errors in hydrologic data assimilation, in the context of forecasting in catchments with changing land surface conditions and a model calibrated to pre-change conditions. We posit that in such cases, the impact of systematic model errors on assimilation or forecast quality is dependent on the inherent prediction uncertainty that persists even in pre-change conditions. Through experiments on a range of catchments, we develop a conceptual relationship between total prediction uncertainty and the impacts of land cover changes on the hydrologic regime to demonstrate how forecast quality is affected when using state estimation Data Assimilation with no modifications to account for land cover changes. This work shows that systematic model errors as a result of changing or changed catchment conditions do not always necessitate adjustments to the modelling or assimilation methodology, for instance through re-calibration of the hydrologic model, time varying model parameters or revised offline/online bias estimation.