Geochemistry and Flux of Terrigenous Dissolved Organic Matter to the Arctic Ocean

NASA Astrophysics Data System (ADS)

Spencer, R. G.; Mann, P. J.; Hernes, P. J.; Tank, S. E.; Striegl, R. G.; Dyda, R. Y.; Peterson, B. J.; McClelland, J. W.; Holmes, R. M.

2011-12-01

Rivers draining into the Arctic Ocean exhibit high concentrations of terrigenous dissolved organic carbon (DOC) and recent studies indicate that DOC export is changing due to climatic warming and alteration in permafrost condition. The fate of exported DOC in the Arctic Ocean is of key importance for understanding the regional carbon cycle and remains a point of discussion in the literature. As part of the Arctic Great Rivers Observatory (Arctic-GRO) project, samples were collected for DOC, chromophoric dissolved organic matter (CDOM) and lignin phenols from the Ob', Yenisey, Lena, Kolyma, Mackenzie and Yukon rivers in 2009 - 2010. DOC and lignin concentrations were elevated during the spring freshet and measurements related to DOC composition indicated an increasing contribution from terrestrial vascular plant sources at this time of year (e.g. lignin carbon-normalized yield, CDOM spectral slope, SUVA254, humic-like fluorescence). CDOM absorption was found to correlate strongly with both DOC (r2=0.83) and lignin concentration (r2=0.92) across the major arctic rivers. Utilizing these relationships we modeled loads for DOC and lignin export from high-resolution CDOM measurements (daily across the freshet) to derive improved flux estimates, particularly from the dynamic spring discharge maxima period when the majority of DOC and lignin export occurs. The new load estimates for DOC and lignin are higher than previous evaluations, emphasizing that if these are more representative of current arctic riverine export, terrigenous DOC is transiting through the Arctic Ocean at a faster rate than previously thought. It is apparent that higher resolution sampling of arctic rivers is exceptionally valuable with respect to deriving accurate fluxes and we highlight the potential of CDOM in this role for future studies and the applicability of in-situ CDOM sensors.

Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

NASA Astrophysics Data System (ADS)

Lawson, E. C.; Wadham, J. L.; Tranter, M.; Stibal, M.; Lis, G. P.; Butler, C. E. H.; Laybourn-Parry, J.; Nienow, P.; Chandler, D.; Dewsbury, P.

2014-07-01

Runoff from small glacier systems contains dissolved organic carbon (DOC) rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr-1). We report high and episodic fluxes of POC and DOC from a large (>600 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70-89% on average), is sourced from the ice sheet bed, and contains a significant bioreactive component (9% carbohydrates). A major source of the "bioavailable" (free carbohydrate) LMW-DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW-DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (26-53%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the approximately two-fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating a supply limitation in suspended sediment in runoff. Scaled to the GrIS, the combined DOC (0.13-0.17 Tg C yr-1 (±13%)) and POC fluxes (mean = 0.36-1.52 Tg C yr-1 (±14%)) are of a similar order of magnitude to a large Arctic river system, and hence may represent an important OC source to the near-coastal North Atlantic, Greenland and Labrador seas.

Influences of glacial melt and permafrost thaw on the age of dissolved organic carbon in the Yukon River basin

USGS Publications Warehouse

Aiken, George R.; Spencer, Robert G.M.; Striegl, Robert G.; Schuster, Paul F.; Raymond, Peter A.

2014-01-01

Responses of near-surface permafrost and glacial ice to climate change are of particular significance for understanding long-term effects on global carbon cycling and carbon export by high-latitude northern rivers. Here we report Δ14C-dissolved organic carbon (DOC) values and dissolved organic matter optical data for the Yukon River, 15 tributaries of the Yukon River, glacial meltwater, and groundwater and soil water end-member sources draining to the Yukon River, with the goal of assessing mobilization of aged DOC within the watershed. Ancient DOC was associated with glacial meltwater and groundwater sources. In contrast, DOC from watersheds dominated by peat soils and underlain by permafrost was typically enriched in Δ14C indicating that degradation of ancient carbon stores is currently not occurring at large enough scales to quantitatively influence bulk DOC exports from those landscapes. On an annual basis, DOC exported was predominantly modern during the spring period throughout the Yukon River basin and became older through summer-fall and winter periods, suggesting that contributions of older DOC from soils, glacial meltwaters, and groundwater are significant during these months. Our data indicate that rapidly receding glaciers and increasing groundwater inputs will likely result in greater contributions of older DOC in the Yukon River and its tributaries in coming decades.

Degradation potentials of dissolved organic carbon (DOC) from thawed permafrost peat

PubMed Central

Panneer Selvam, Balathandayuthabani; Lapierre, Jean-François; Guillemette, Francois; Voigt, Carolina; Lamprecht, Richard E.; Biasi, Christina; Christensen, Torben R.; Martikainen, Pertti J.; Berggren, Martin

2017-01-01

Global warming can substantially affect the export of dissolved organic carbon (DOC) from peat-permafrost to aquatic systems. The direct degradability of such peat-derived DOC, however, is poorly constrained because previous permafrost thaw studies have mainly addressed mineral soil catchments or DOC pools that have already been processed in surface waters. We incubated peat cores from a palsa mire to compare an active layer and an experimentally thawed permafrost layer with regard to DOC composition and degradation potentials of pore water DOC. Our results show that DOC from the thawed permafrost layer had high initial degradation potentials compared with DOC from the active layer. In fact, the DOC that showed the highest bio- and photo-degradability, respectively, originated in the thawed permafrost layer. Our study sheds new light on the DOC composition of peat-permafrost directly upon thaw and suggests that past estimates of carbon-dioxide emissions from thawed peat permafrost may be biased as they have overlooked the initial mineralization potential of the exported DOC. PMID:28378792

The Age of Terrestrial Carbon Export and Rainfall Intensity in a Temperate River Headwater System

NASA Astrophysics Data System (ADS)

Tittel, J.; Büttner, O.; Freier, K.; Heiser, A.; Sudbrack, R.; Ollesch, G.

2013-12-01

Riverine dissolved organic carbon (DOC) supports the production of estuaries and coastal ecosystems, constituting one of the most actively recycled pools of the global carbon cycle. A substantial proportion of DOC entering oceans is highly aged, but its origins remain unclear. Significant fluxes of old DOC have never been observed in temperate headwaters where terrestrial imports take place. Here, we studied the radiocarbon age of DOC in three streams draining forested headwater catchments of the river Mulde (Ore Mountains, Germany). We found modern DOC at moderately dry and moderately wet conditions as well as at high discharges during snowmelt. Old groundwater carbon contributed to stream DOC during the summer drought, although the yield was negligible. However, in a four-week summer precipitation event DOC aged at between 160 and 270 years was delivered into the watershed. In one stream, the DOC was modern but depleted in radiocarbon compared to other hydrological conditions. The yield was substantial and corresponded to 20 to 52% of the annual DOC yields in wet and dry years, respectively. Time-integrating samples of a downstream reservoir also revealed modern DOC ages under moderate conditions and old DOC from the rainfall event. Earlier studies suggested that increasing precipitation escalates the contribution of modern DOC from topsoil layers to surface runoff. Our results demonstrate a step change occurring if rainfall intensities increase and become extreme; then the consequences lead to the mobilization of old carbon in exceptionally high concentrations. The runoff/precipitation ratios of rainfall events indicated that during extreme events upland areas of the catchments were hydrologically connected to the stream and upland DOC was activated. Furthermore, the analysis of long-term data suggested that the DOC export in extreme precipitation events added to the annual yield and was not compensated for by lower exports in remaining periods. We conclude that climate change, along with additional processes associated with human activities, channels old soil carbon into more rapidly cycled carbon pools of the hydrosphere.

Local and regional scale exchanges of dissolved organic carbon (DOC) between tidal wetlands and their adjacent coastal waters

NASA Astrophysics Data System (ADS)

Osburn, C. L.; Joshi, I.; Lebrasse, M. C.; Oviedo-Vargas, D.; Bianchi, T. S.; Bohnenstiehl, D. R.; D'Sa, E. J.; He, R.; Ko, D.; Arellano, A.; Ward, N. D.

2017-12-01

The contribution of blue carbon from tidal wetlands to the coastal ocean in the form of dissolved organic carbon (DOC) represents a terrestrial-aquatic linkage of increasing importance. DOC flux results will be presented from local (tidal creek) and regional (bays) scale studies in which various combinations of field observations, ocean-color satellite observations, and the outputs of high-resolution hydrodynamic models were used to estimate DOC export. The first project was located in Bald Head Creek, a tributary to the Cape Fear River estuary in eastern North Carolina (NC). DOC fluxes were computed using a bathymetric data collected via unmanned surface vehicle (USV) and a numerical hydrodynamic model (SCHISM) based on the relationships between colored dissolved organic matter (CDOM) absorption, DOC concentration, and salinity taken from field observations. Model predictions estimated an annual net export of DOC at 54 g C m-2 yr-1 from the tidal creek to the adjacent estuary. Carbon stable isotope (δ13C) values were used to estimate the contribution of wetland carbon to this export. In the second project, DOC fluxes from the Apalachicola Bay, FL, Barataria Bay, LA, were based on the development of algorithms between DOC and CDOM absorption derived from the VIIRS ocean color sensor. The Navy Coastal Ocean Model (NCOM) was used to compute salt flux estimates from each bay to the Louisiana-Texas shelf. The relationship between salinity and CDOM was used to estimate net annual DOC exports of 8.35 x 106 g C m-2 y-1 (Apalachicola Bay) and 7.14 x 106 g C m-2 yr-1 (Barataria Bay). These values approximate 13% and 9% of the annual loads of DOC from the Mississippi River to the Gulf of Mexico, respectively. CDOM and lignin were used in a mixing model to estimate wetland-derived DOC were 2% for Apalachicola Bay and 13% for Barataria Bay, the latter having one of the highest rates of relative sea level rise in North America. Results from our project demonstrated the utility of CDOM, amenable to high resolution observations from multiple platforms, as a basis for constraining the heterogeneity of DOC exports from tidal wetlands to estuaries and coastal waters using numerical models at local and regional scales.

Landscape controls on dissolved organic carbon export from watersheds of the British Columbia outer-coast

NASA Astrophysics Data System (ADS)

Giesbrecht, I.; Tank, S. E.; Frazer, G. W.; Gonzalez Arriola, S.; Korver, M.; Floyd, B. C.; Oliver, A. A.; Lertzman, K. P.

2016-12-01

Global models suggest that the Pacific Coastal Temperate Rainforest of North America (PCTR) exports significant quantities of dissolved organic carbon (DOC) to the coastal ocean. This aquatic flux from land to sea has implications for marine ecosystems and regional carbon budgets. However, DOC concentrations and flux estimates vary substantially across watersheds and drivers of spatial variation are poorly described for this region. For an outer-coast area of the PCTR, with among the highest per unit area DOC yields in the world (Oliver et al. in prep.), we describe and model landscape controls on DOC exports to the coastal ocean. In 2015 we collected three rounds of synoptic samples on Calvert Island, observing a nine-fold variation in DOC concentration (3.8 - 34.3 mg/L) across 59 watersheds that range in size from 0.26 to 21.12 km2 and reach a maximum elevation of 1012 m. We use standard ecosystem maps (Province of BC), LiDAR and other remote sensing data to measure watershed attributes. We use freshwater cation concentrations to explore geochemical signals of bedrock and surficial deposits that may be poorly represented by available geospatial data. We examine the role of topography, climate, waterbodies, geology and the local ecosystem mosaic in controlling DOC concentration and flux. An improved model of spatial controls on freshwater DOC export from the outer-coast of the PCTR will inform regional carbon modeling efforts and enhance our understanding of ecosystem processes at the coastal margin.

Representation of dissolved organic carbon in the JULES land surface model (vn4.4_JULES-DOCM)

NASA Astrophysics Data System (ADS)

Nakhavali, Mahdi; Friedlingstein, Pierre; Lauerwald, Ronny; Tang, Jing; Chadburn, Sarah; Camino-Serrano, Marta; Guenet, Bertrand; Harper, Anna; Walmsley, David; Peichl, Matthias; Gielen, Bert

2018-02-01

Current global models of the carbon (C) cycle consider only vertical gas exchanges between terrestrial or oceanic reservoirs and the atmosphere, thus not considering the lateral transport of carbon from the continents to the oceans. Therefore, those models implicitly consider all of the C which is not respired to the atmosphere to be stored on land and hence overestimate the land C sink capability. A model that represents the whole continuum from atmosphere to land and into the ocean would provide a better understanding of the Earth's C cycle and hence more reliable historical or future projections. A first and critical step in that direction is to include processes representing the production and export of dissolved organic carbon in soils. Here we present an original representation of dissolved organic C (DOC) processes in the Joint UK Land Environment Simulator (JULES-DOCM) that integrates a representation of DOC production in terrestrial ecosystems based on the incomplete decomposition of organic matter, DOC decomposition within the soil column, and DOC export to the river network via leaching. The model performance is evaluated in five specific sites for which observations of soil DOC concentration are available. Results show that the model is able to reproduce the DOC concentration and controlling processes, including leaching to the riverine system, which is fundamental for integrating terrestrial and aquatic ecosystems. Future work should include the fate of exported DOC in the river system as well as DIC and POC export from soil.

Carbon export and cycling by the Yukon, Tanana, and Porcupine rivers, Alaska, 2001-2005

USGS Publications Warehouse

Striegl, Robert G.; Dornblaser, Mark M.; Aiken, George R.; Wickland, Kimberly P.; Raymond, Peter A.

2007-01-01

Loads and yields of dissolved and particulate organic and inorganic carbon (DOC, POC, DIC, PIC) were measured and modeled at three locations on the Yukon River (YR) and on the Tanana and Porcupine rivers (TR, PR) in Alaska during 2001–2005. Total YR carbon export averaged 7.8 Tg C yr−1, 30% as OC and 70% as IC. Total C yields (0.39–1.03 mol C m−2 yr−1) were proportional to water yields (139–356 mm yr−1; r2 = 0.84) at all locations. Summer DOC had an aged component (fraction modern (FM) = 0.94–0.97), except in the permafrost wetland‐dominated PR, where DOC was modern. POC had FM = 0.63–0.70. DOC had high concentration, high aromaticity, and high hydrophobic content in spring and low concentration, low aromaticity, and high hydrophilic content in winter. About half of annual DOC export occurred during spring. DIC concentration and isotopic composition were strongly affected by dissolution of suspended carbonates in glacial meltwater during summer.

Hydrological processes and permafrost regulate magnitude, source and chemical characteristics of dissolved organic carbon export in a peatland catchment of northeastern China

NASA Astrophysics Data System (ADS)

Guo, Yuedong; Song, Changchun; Tan, Wenwen; Wang, Xianwei; Lu, Yongzheng

2018-02-01

Permafrost thawing in peatlands has the potential to alter the catchment export of dissolved organic carbon (DOC), thus influencing the carbon balance and cycling in linked aquatic and ocean ecosystems. Peatlands along the southern margins of the Eurasian permafrost are relatively underexplored despite the considerable risks associated with permafrost degradation due to climate warming. This study examined dynamics of DOC export from a permafrost peatland catchment located in northeastern China during the 2012 to 2014 growing seasons. The estimated annual DOC loads varied greatly between 3211 and 19 022 kg yr-1, with a mean DOC yield of 4.7 g m-2 yr-1. Although the estimated DOC yield was in the lower range compared with other permafrost regions, it was still significant for the net carbon balance in the studied catchment. There were strong linkages between daily discharge and DOC concentrations in both wet and dry years, suggesting a transport-limited process of DOC delivery from the catchment. Discharge explained the majority of both seasonal and interannual variations of DOC concentrations, which made annual discharge a good indicator of total DOC load from the catchment. As indicated by three fluorescence indices, DOC source and chemical characteristics tracked the shift of flow paths during runoff processes closely. Interactions between the flow path and DOC chemical characteristics were greatly influenced by the seasonal thawing of the soil active layer. The deepening of the active layer due to climate warming likely increases the proportion of microbial-originated DOC in baseflow discharge.

Amounts, isotopic character and ages of organic and inorganic carbon exported from rivers to ocean margins: Assessment of natural and anthropogenic controls

NASA Astrophysics Data System (ADS)

Bauer, J. E.; Hossler, K.

2012-12-01

Riverine exports of carbon (C) and organic matter (OM) are regulated by a variety of natural and anthropogenic factors. Understanding the relationships between these various factors and C and OM exports can help to constrain global C budgets, as well allow assessment of current and future anthropogenic impacts on both riverine and global C cycles. We quantified the effects of multiple natural and anthropogenic controls on riverine export fluxes and compositions of particulate organic C (POC), dissolved organic C (DOC), and dissolved inorganic C (DIC) for a regional group of eight rivers in the northeastern U.S. For allochthonous and aged C contributions to POC, DOC and DIC exports, we first estimated fractional contributions from six potential sources for POC and DOC (i.e., modern C3 plant material (C3-OC), modern C4 plant material (C4-OC), modern algal material (algal OC), slow-turnover soil OC (slow SOC; turnover time 25 yr), passive-turnover soil OC (passive SOC; turnover time 5,000 yr) and fossil OC and four potential sources for DIC (i.e., modern atmospheric CO2 exchange, carbonate dissolution, POC remineralization and DOC remineralization) using a novel time-varying isotope mixing model. Using these estimated source contributions, we then estimated the allochthonous proportions of (a) the POC and DOC pools to be the C3-OC, C4-OC, slow SOC, passive SOC, and fossil OC contributions; and (b) the DIC pools to be the dissolved carbonates, remineralized allochthonous POC, and remineralized allochthonous DOC contributions. We considered aged C to be anything older than ˜ 60 yr, which included passive SOC and fossil OC for POC and DOC and dissolved carbonates and aged fractions of remineralized POC and DOC for DIC. Potential controls related to hydrogeomorphology and regional climate, soil order, soil texture, bedrock lithology, land use, and additional anthropogenic factors were analyzed collectively, individually, and at scales of both local and regional influence. Factors related either to hydrogeomorphology and climate or to anthropogenic factors exhibited the strongest impacts on riverine C exports and compositions, particularly at broader regional scales. The effect of hydrogeomorphology and climate was primarily one of size, as larger watersheds with greater discharge exported more total C and terrestrial C. Principal anthropogenic factors included impacts of wastewater treatment plants (WWTPs) and river impoundments. The presence of WWTPs as well as anthropogenic use of carbonate-based materials (e.g., limestone) may have substantially increased riverine C exports, particularly fossil C exports, in the study region. The presence of nuclear power plants in the associated watersheds is also discussed because of the potential for anthropogenic 14C inputs and subsequent biasing of aquatic C studies utilizing natural abundance 14C.

Temporal-spatial variation of DOC concentration, UV absorbance and the flux estimation in the Lower Dagu River, China

NASA Astrophysics Data System (ADS)

Xi, Min; Kong, Fanlong; Li, Yue; Kong, Fanting

2017-12-01

Dissolved organic carbon (DOC) is an important component for both carbon cycle and energy balance. The concentration, UV absorbance, and export flux of DOC in the natural environment dominate many important transport processes. To better understand the temporal and spatial variation of DOC, 7 sites along the Lower Dagu River were chosen to conduct a comprehensive measurement from March 2013 to February 2014. Specifically, water samples were collected from the Lower Dagu River between the 26th and 29th of every month during the experimental period. The DOC concentration (CDOC) and UV absorbance were analyzed using a total organic carbon analyzer and the ultraviolet-visible absorption spectrum, and the DOC export flux was estimated with a simple empirical model. The results showed that the CDOC of the Lower Dagu River varied from 1.32 to 12.56 mg/L, consistent with global rivers. The CDOC and UV absorbance showed significant spatial variation in the Dagu River during the experiential period because of the upstream natural processes and human activities in the watershed. The spatial variation is mainly due to dam or reservoir constructions, riverside ecological environment changes, and non-point source or wastewater discharge. The seasonal variation of CDOC was mainly related to the source of water DOC, river runoff, and temperature, and the UV absorbance and humification degree of DOC had no obvious differences among months ( P<0.05). UV absorbance was applied to test the CDOC in Lower Dagu River using wave lengths of 254 and 280 nm. The results revealed that the annual DOC export flux varied from 1.6 to 3.76 × 105 g C/km2/yr in a complete hydrological year, significantly lower than the global average. It is worth mentioning that the DOC export flux was mainly concentrated in summer (˜90% of all-year flux in July and August), since the runoff in the Dagu River took place frequently in summer. These observations implied environment change could bring the temporal-spatial variation of DOC and the exports, which would further affect the land-ocean interactions in the Lower Dagu River and the global carbon cycle.

Dissolved Organic Matter Land-Ocean Linkages in the Arctic

NASA Astrophysics Data System (ADS)

Mann, P. J.; Spencer, R. M.; Hernes, P. J.; Tank, S. E.; Striegl, R.; Dyda, R. Y.; Peterson, B. J.; McClelland, J. W.; Holmes, R. M.

2012-04-01

Rivers draining into the Arctic Ocean exhibit high concentrations of terrigenous dissolved organic carbon (DOC), and recent studies indicate that DOC export is changing due to climatic warming and alteration in permafrost condition. The fate of exported DOC in the Arctic Ocean is important for understanding the regional carbon cycle and remains a point of discussion in the literature. As part of the NSF funded Arctic Great Rivers Observatory (Arctic-GRO) project, samples were collected for DOC, chromophoric and fluorescent dissolved organic matter (CDOM & FDOM) and lignin phenols from the Ob', Yenisey, Lena, Kolyma, Mackenzie and Yukon rivers in 2009 - 2010. DOC and lignin concentrations were elevated during the spring freshet and measurements related to DOC composition indicated an increasing contribution from terrestrial vascular plant sources at this time of year (e.g. lignin carbon-normalized yield, CDOM spectral slope, SUVA254, humic-like fluorescence). CDOM absorption was found to correlate strongly with both DOC (r2=0.83) and lignin concentration (r2=0.92) across the major arctic rivers. Lignin composition was also successfully modeled using FDOM measurements decomposed using PARAFAC analysis. Utilizing these relationships we modeled loads for DOC and lignin export from high-resolution CDOM measurements (daily across the freshet) to derive improved flux estimates, particularly from the dynamic spring discharge maxima period when the majority of DOC and lignin export occurs. The new load estimates for DOC and lignin are higher than previous evaluations, emphasizing that if these are more representative of current arctic riverine export, terrigenous DOC is transiting through the Arctic Ocean at a faster rate than previously thought. It is apparent that higher resolution sampling of arctic rivers is exceptionally valuable with respect to deriving accurate fluxes and we highlight the potential of CDOM in this role for future studies and the applicability of in-situ CDOM sensors.

River Export of Dissolved and Particulate Organic Carbon from Permafrost and Peat Deposits across the Siberian Arctic

NASA Astrophysics Data System (ADS)

Wild, B.; Andersson, A.; Bröder, L.; Vonk, J.; Hugelius, G.; McClelland, J. W.; Raymond, P. A.; Gustafsson, O.

2017-12-01

Permafrost and peat deposits of northern high latitudes store more than 1300 Pg of organic carbon. This carbon has been preserved for thousands of years by cold and moist conditions, but is now increasingly mobilized as temperatures rise. While part will be degraded to CO2 and CH4 and amplify global warming, part will be exported by rivers to the Arctic Ocean where it can be degraded or re-buried by sedimentation. We here use the four large Siberian rivers Ob, Yenisey, Lena, and Kolyma as natural integrators of carbon mobilization in their catchments. We apply isotope based source apportionments and Markov Chain Monte Carlo Simulations to quantify contributions of organic carbon from permafrost and peat deposits to organic carbon exported by these rivers. More specifically, we compare the 14C signatures of dissolved and particulate organic carbon (DOC, POC) sampled close to the river mouths with those of five potential carbon sources; (1) recent aquatic and (2) terrestrial primary production, (3) the active layer of permafrost soils, (4) deep Holocene deposits (including thermokarst and peat deposits) and (5) Ice Complex Deposits. 14C signatures of these endmembers were constrained based on extensive literature review. We estimate that the four rivers together exported 2.4-4.5 Tg organic carbon from permafrost and peat deposits per year. While total organic carbon export was dominated by DOC (90%), the export of organic carbon from permafrost and peat deposits was more equally distributed between DOC (56%) and POC (44%). Recent models predict that ca. 200 Pg carbon will be lost as CO2 or CH4 by 2100 (RCP8.5) from the circumarctic permafrost area, of which roughly a quarter is drained by the Ob, Yenisey, Lena, and Kolyma rivers. Our comparatively low estimates of river carbon export thus suggest limited transfer of organic carbon from permafrost and peat deposits to high latitude rivers, or its rapid degradation within rivers. Our findings highlight the importance of both DOC and POC, and its degradation, for the fate of carbon mobilized from high latitude deposits under global warming, and indicate a low potential for its stabilization in the Arctic Ocean.

Submersible UV-Vis Spectroscopy for Quantifying Streamwater Organic Carbon Dynamics: Implementation and Challenges before and after Forest Harvest in a Headwater Stream

PubMed Central

Jollymore, Ashlee; Johnson, Mark S.; Hawthorne, Iain

2012-01-01

Organic material, including total and dissolved organic carbon (DOC), is ubiquitous within aquatic ecosystems, playing a variety of important and diverse biogeochemical and ecological roles. Determining how land-use changes affect DOC concentrations and bioavailability within aquatic ecosystems is an important means of evaluating the effects on ecological productivity and biogeochemical cycling. This paper presents a methodology case study looking at the deployment of a submersible UV-Vis absorbance spectrophotometer (UV-Vis spectro∷lyzer model, s∷can, Vienna, Austria) to determine stream organic carbon dynamics within a headwater catchment located near Campbell River (British Columbia, Canada). Field-based absorbance measurements of DOC were made before and after forest harvest, highlighting the advantages of high temporal resolution compared to traditional grab sampling and laboratory measurements. Details of remote deployment are described. High-frequency DOC data is explored by resampling the 30 min time series with a range of resampling time intervals (from daily to weekly time steps). DOC export was calculated for three months from the post-harvest data and resampled time series, showing that sampling frequency has a profound effect on total DOC export. DOC exports derived from weekly measurements were found to underestimate export by as much as 30% compared to DOC export calculated from high-frequency data. Additionally, the importance of the ability to remotely monitor the system through a recently deployed wireless connection is emphasized by examining causes of prior data losses, and how such losses may be prevented through the ability to react when environmental or power disturbances cause system interruption and data loss. PMID:22666002

Submersible UV-Vis spectroscopy for quantifying streamwater organic carbon dynamics: implementation and challenges before and after forest harvest in a headwater stream.

PubMed

Jollymore, Ashlee; Johnson, Mark S; Hawthorne, Iain

2012-01-01

Organic material, including total and dissolved organic carbon (DOC), is ubiquitous within aquatic ecosystems, playing a variety of important and diverse biogeochemical and ecological roles. Determining how land-use changes affect DOC concentrations and bioavailability within aquatic ecosystems is an important means of evaluating the effects on ecological productivity and biogeochemical cycling. This paper presents a methodology case study looking at the deployment of a submersible UV-Vis absorbance spectrophotometer (UV-Vis spectro::lyzer model, s::can, Vienna, Austria) to determine stream organic carbon dynamics within a headwater catchment located near Campbell River (British Columbia, Canada). Field-based absorbance measurements of DOC were made before and after forest harvest, highlighting the advantages of high temporal resolution compared to traditional grab sampling and laboratory measurements. Details of remote deployment are described. High-frequency DOC data is explored by resampling the 30 min time series with a range of resampling time intervals (from daily to weekly time steps). DOC export was calculated for three months from the post-harvest data and resampled time series, showing that sampling frequency has a profound effect on total DOC export. DOC exports derived from weekly measurements were found to underestimate export by as much as 30% compared to DOC export calculated from high-frequency data. Additionally, the importance of the ability to remotely monitor the system through a recently deployed wireless connection is emphasized by examining causes of prior data losses, and how such losses may be prevented through the ability to react when environmental or power disturbances cause system interruption and data loss.

The role of hydrology in annual organic carbon loads and terrestrial organic matter export from a midwestern agricultural watershed

NASA Astrophysics Data System (ADS)

Dalzell, Brent J.; Filley, Timothy R.; Harbor, Jon M.

2007-03-01

Defining the control that hydrology exerts on organic carbon (OC) export at the watershed scale is important for understanding how the source and quantity of OC in streams and rivers is influenced by climate change or by landscape drainage. To this end, molecular (lignin phenol), stable carbon isotope, and dissolved organic carbon (DOC) data were collected over a range of flow conditions to examine the influence of hydrology on annual OC export from an 850 km 2 Midwestern United States agricultural watershed located in west central Indiana. In years 2002 and 2003, modeled annual DOC loads were 19.5 and 14.1 kg ha -1yr -1, while 71% and 85%, respectively, of the total annual OC was exported in flow events occurring during less than 20% of that time. These results highlight the importance of short-duration, high-discharge events (common in smaller watersheds) in controlling annual OC export. Based on reported increases in annual stream discharge coupled with current estimates of DOC export, annual DOC loads in this watershed may have increased by up to 40% over the past 50 years. Molecular (lignin phenol) characterization of quantity and relative degradation state of terrestrial OC shows as much temporal variability of lignin parameters (in high molecular weight dissolved organic carbon) in this one watershed as that demonstrated in previously published studies of dissolved organic matter in the Mississippi and Amazon Rivers. These results suggest that hydrologic variability is at least as important in determining the nature and extent of OC export as geographic variability. Moreover, molecular and bulk stable carbon isotope data from high molecular weight dissolved organic carbon and colloidal organic carbon showed that increased stream flow from the study watershed was responsible for increased export of agriculturally derived OC. When considered in the context of results from other studies that show the importance of flood events and in-stream processing of terrestrial organic carbon, our results show how hydrologic variability in smaller watersheds can reflect landscape-scale carbon dynamics in ways that cannot necessarily be measured at the outlets of large rivers due to multiple source signals and attenuated hydrology.

A global hotspot for dissolved organic carbon in hypermaritime watersheds of coastal British Columbia

NASA Astrophysics Data System (ADS)

Oliver, Allison A.; Tank, Suzanne E.; Giesbrecht, Ian; Korver, Maartje C.; Floyd, William C.; Sanborn, Paul; Bulmer, Chuck; Lertzman, Ken P.

2017-08-01

The perhumid region of the coastal temperate rainforest (CTR) of Pacific North America is one of the wettest places on Earth and contains numerous small catchments that discharge freshwater and high concentrations of dissolved organic carbon (DOC) directly to the coastal ocean. However, empirical data on the flux and composition of DOC exported from these watersheds are scarce. We established monitoring stations at the outlets of seven catchments on Calvert and Hecate islands, British Columbia, which represent the rain-dominated hypermaritime region of the perhumid CTR. Over several years, we measured stream discharge, stream water DOC concentration, and stream water dissolved organic-matter (DOM) composition. Discharge and DOC concentrations were used to calculate DOC fluxes and yields, and DOM composition was characterized using absorbance and fluorescence spectroscopy with parallel factor analysis (PARAFAC). The areal estimate of annual DOC yield in water year 2015 was 33.3 Mg C km-2 yr-1, with individual watersheds ranging from an average of 24.1 to 37.7 Mg C km-2 yr-1. This represents some of the highest DOC yields to be measured at the coastal margin. We observed seasonality in the quantity and composition of exports, with the majority of DOC export occurring during the extended wet period (September-April). Stream flow from catchments reacted quickly to rain inputs, resulting in rapid export of relatively fresh, highly terrestrial-like DOM. DOC concentration and measures of DOM composition were related to stream discharge and stream temperature and correlated with watershed attributes, including the extent of lakes and wetlands, and the thickness of organic and mineral soil horizons. Our discovery of high DOC yields from these small catchments in the CTR is especially compelling as they deliver relatively fresh, highly terrestrial organic matter directly to the coastal ocean. Hypermaritime landscapes are common on the British Columbia coast, suggesting that this coastal margin may play an important role in the regional processing of carbon and in linking terrestrial carbon to marine ecosystems.

Quantifying and predicting historical and future patterns of carbon fluxes from the North American Continent to Ocean

NASA Astrophysics Data System (ADS)

Tian, H.; Zhang, B.; Xu, R.; Yang, J.; Yao, Y.; Pan, S.; Lohrenz, S. E.; Cai, W. J.; He, R.; Najjar, R. G.; Friedrichs, M. A. M.; Hofmann, E. E.

2017-12-01

Carbon export through river channels to coastal waters is a fundamental component of the global carbon cycle. Changes in the terrestrial environment, both natural (e.g., climatic change, enriched CO2 concentration, and elevated ozone concentration) and anthropogenic (e.g, deforestation, cropland expansion, and urbanization) have greatly altered carbon production, stocks, decomposition, movement and export from land to river and ocean systems. However, the magnitude and spatiotemporal patterns of lateral carbon fluxes from land to oceans and the underlying mechanisms responsible for these fluxes remain far from certain. Here we applied a process-based land model with explicit representation of carbon processes in stream and rivers (Dynamic Land Ecosystem Model: DLEM 2.0) to examine how changes in climate, land use, atmospheric CO2, and nitrogen deposition have affected the carbon fluxes from North American continent to Ocean during 1980-2015. Our simulated results indicated that terrestrial carbon export shows substantially spatial and temporal variability. Of the five sub-regions (Arctic coast, Pacific coast, Gulf of Mexico, Atlantic coast, and Great lakes), the Arctic sub-region provides the highest DOC flux, whereas the Gulf of Mexico sub-region provided the highest DIC flux. However, terrestrial carbon export to the arctic oceans showed increasing trends for both DOC and DIC, whereas DOC and DIC export to the Gulf of Mexico decreased in the recent decades. Future pattern of riverine carbon fluxes would be largely dependent on the climate change and land use scenarios.

Elevated pCO2 enhances bacterioplankton removal of organic carbon

PubMed Central

James, Anna K.; Passow, Uta; Brzezinski, Mark A.; Parsons, Rachel J.; Trapani, Jennifer N.; Carlson, Craig A.

2017-01-01

Factors that affect the removal of organic carbon by heterotrophic bacterioplankton can impact the rate and magnitude of organic carbon loss in the ocean through the conversion of a portion of consumed organic carbon to CO2. Through enhanced rates of consumption, surface bacterioplankton communities can also reduce the amount of dissolved organic carbon (DOC) available for export from the surface ocean. The present study investigated the direct effects of elevated pCO2 on bacterioplankton removal of several forms of DOC ranging from glucose to complex phytoplankton exudate and lysate, and naturally occurring DOC. Elevated pCO2 (1000–1500 ppm) enhanced both the rate and magnitude of organic carbon removal by bacterioplankton communities compared to low (pre-industrial and ambient) pCO2 (250 –~400 ppm). The increased removal was largely due to enhanced respiration, rather than enhanced production of bacterioplankton biomass. The results suggest that elevated pCO2 can increase DOC consumption and decrease bacterioplankton growth efficiency, ultimately decreasing the amount of DOC available for vertical export and increasing the production of CO2 in the surface ocean. PMID:28257422

Utilizing Colored Dissolved Organic Matter to Derive Dissolved Black Carbon Export by Arctic Rivers

NASA Astrophysics Data System (ADS)

Stubbins, Aron; Spencer, Robert; Mann, Paul; Holmes, R.; McClelland, James; Niggemann, Jutta; Dittmar, Thorsten

2015-10-01

Wildfires have produced black carbon (BC) since land plants emerged. Condensed aromatic compounds, a form of BC, have accumulated to become a major component of the soil carbon pool. Condensed aromatics leach from soils into rivers, where they are termed dissolved black carbon (DBC). The transport of DBC by rivers to the sea is a major term in the global carbon and BC cycles. To estimate Arctic river DBC export, 25 samples collected from the six largest Arctic rivers (Kolyma, Lena, Mackenzie, Ob’, Yenisey and Yukon) were analyzed for dissolved organic carbon (DOC), colored dissolved organic matter (CDOM), and DBC. A simple, linear regression between DOC and DBC indicated that DBC accounted for 8.9 ± 0.3% DOC exported by Arctic rivers. To improve upon this estimate, an optical proxy for DBC was developed based upon the linear correlation between DBC concentrations and CDOM light absorption coefficients at 254 nm (a254). Relatively easy to measure a254 values were determined for 410 Arctic river samples between 2004 and 2010. Each of these a254 values was converted to a DBC concentration based upon the linear correlation, providing an extended record of DBC concentration. The extended DBC record was coupled with daily discharge data from the six rivers to estimate riverine DBC loads using the LOADEST modeling program. The six rivers studied cover 53% of the pan-Arctic watershed and exported 1.5 ± 0.1 million tons of DBC per year. Scaling up to the full area of the pan-Arctic watershed, we estimate that Arctic rivers carry 2.8 ± 0.3 million tons of DBC from land to the Arctic Ocean each year. This equates to ~8% of Arctic river DOC export, slightly less than indicated by the simpler DBC vs DOC correlation-based estimate. Riverine discharge is predicted to increase in a warmer Arctic. DBC export was positively correlated with river runoff, suggesting that the export of soil BC to the Arctic Ocean is likely to increase as the Arctic warms.

Bioavailable dissolved and particulate organic carbon flux from coastal temperate rainforest watersheds

NASA Astrophysics Data System (ADS)

Fellman, J.; Hood, E. W.; D'Amore, D. V.; Moll, A.

2017-12-01

Coastal temperate rainforest (CTR) watersheds of southeast Alaska have dense soil carbon stocks ( 300 Mg C ha-1) and high specific discharge (1.5-7 m yr-1) driven by frontal storms from the Gulf of Alaska. As a result, dissolved organic carbon (DOC) fluxes from Alaskan CTR watersheds are estimated to exceed 2 Tg yr-1; however, little is known about the export of particulate organic carbon (POC). The magnitude and bioavailability of this land-to-ocean flux of terrigenous organic matter ultimately determines how much metabolic energy is translocated to downstream and coastal marine ecosystems in this region. We sampled streamwater weekly from May through October from four watersheds of varying landcover (gradient of wetland to glacial coverage) to investigate changes in the concentration and flux of DOC and POC exported to the coastal ocean. We also used headspace analysis of CO2 following 14 day laboratory incubations to determine the flux of bioavailable DOC and POC exported from CTR watersheds. Across all sites, bioavailable DOC concentrations ranged from 0.2 to 1.9 mg L-1 but were on average 0.6 mg L-1. For POC, bioavailable concentrations ranged from below detection to 0.3 mg L-1 but were on average 0.1 mg L-1. The concentration, flux and bioavailability of DOC was higher than for POC highlighting the potential importance of DOC as a metabolic subsidy to downstream and coastal environments. Ratios of DOC to POC decreased during high flow events because the increase in POC concentrations with discharge exceeds that for DOC. Overall, our findings suggest that projected increases in precipitation and storm intensity will drive changes in the speciation, magnitude and bioavailability of the organic carbon flux from CTR watersheds.

Estimating Changes in Runoff and Carbon Exports From Northern Canadian Catchments Under a 2X CO2 Atmosphere

NASA Astrophysics Data System (ADS)

Clair, T. A.; Ehrman, J. M.

2006-12-01

The doubling of atmospheric CO2 on temperature and precipitation will change annual runoff and dissolved organic carbon (DOC) export patterns in northern Canada. Because of the physical size and the range of climatic changes of northern Canada, we found it necessary to model potential changes in river water and carbon exports in the region using a neural network approach. We developed a model for hydrology and one for DOC using as inputs, monthly General Circulation Model temperature and precipitation predictions, historical hydrology and dissolved organic carbon values, as well as catchment size and slope. Mining Environment Canada's historical hydrology and water chemistry databases allowed us to identify 20 sites suitable for our analysis. The site results were summarized within the Canadian Terrestrial Ecozone classification system. Our results show spring melts occurring one month sooner in all northern ecozones except for the Hudson Bay Plains zone, with changes in melt intensity occurring in most regions. The DOC model predicts that exports from catchments will increase by between 10 and 20% depending on the ecozone. Generally, we predict that major changes in both hydrology and carbon cycling should be expected in northern Canadian ecosystems in a warmer planet.

Hydrologically mediated iron reduction/oxidation fluctuations and dissolved organic carbon exports in tidal wetlands

NASA Astrophysics Data System (ADS)

Guimond, J. A.; Seyfferth, A.; Michael, H. A.

2017-12-01

Salt marshes are biogeochemical hotspots where large quantities of carbon are processed and stored. High primary productivity and deposition of carbon-laden sediment enable salt marsh soils to accumulate and store organic carbon. Conversely, salt marshes can laterally export carbon from the marsh platform to the tidal channel and eventually the ocean via tidal pumping. However, carbon export studies largely focus on tidal channels, missing key physical and biogeochemical mechanisms driving the mobilization of dissolved organic carbon (DOC) within the marsh platform and limiting our understanding of and ability to predict coastal carbon dynamics. We hypothesize that iron redox dynamics mediate the mobilization/immobilization of DOC in the top 30 cm of salt marsh sediment near tidal channels. The mobilized DOC can then diffuse into the flooded surface water or be advected to tidal channels. To elucidate DOC dynamics driven by iron redox cycles, we measured porewater DOC, Fe(II), total iron, total sulfate, pH, redox potential, and electrical conductivity (EC) beside the creek, at the marsh levee, and in the marsh interior in a mid-latitude tidal salt marsh in Dover, Delaware. Samples were collected at multiple tide stages during a spring and neap tide at depths of 5-75cm. Samples were also collected from the tidal channel. Continuous Eh measurements were made using in-situ electrodes. A prior study shows that DOC and Fe(II) concentrations vary spatially across the marsh. Redox conditions near the creek are affected by tidal oscillations. High tides saturate the soil and decrease redox potential, whereas at low tide, oxygen enters the sediment and increases the Eh. This pattern is always seen in the top 7-10cm of sediment, with more constant low Eh at depth. However, during neap tides, this signal penetrates deeper. Thus, between the creek and marsh levee, hydrology mediates redox conditions. Based on porewater chemistry, if DOC mobilization can be linked to redox cycles, then hydrologic oscillations can be tied to DOC dynamics and predicted with hydrologic models. By elucidating the mechanisms driving the mobilization of DOC, we can begin to better understand, quantify, and forecast coastal carbon dynamics.

Hydro-ecological controls on dissolved carbon dynamics in groundwater and export to streams in a temperate pine forest

NASA Astrophysics Data System (ADS)

Deirmendjian, Loris; Loustau, Denis; Augusto, Laurent; Lafont, Sébastien; Chipeaux, Christophe; Poirier, Dominique; Abril, Gwenaël

2018-02-01

We studied the export of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from forested shallow groundwater to first-order streams, based on groundwater and surface water sampling and hydrological data. The selected watershed was particularly convenient for such study, with a very low slope, with pine forest growing on sandy permeable podzol and with hydrology occurring exclusively through drainage of shallow groundwater (no surface runoff). A forest plot was instrumented for continuous eddy covariance measurements of precipitation, evapotranspiration, and net ecosystem exchanges of sensible and latent heat fluxes as well as CO2 fluxes. Shallow groundwater was sampled with three piezometers located in different plots, and surface waters were sampled in six first-order streams; river discharge and drainage were modeled based on four gauging stations. On a monthly basis and on the plot scale, we found a good consistency between precipitation on the one hand and the sum of evapotranspiration, shallow groundwater storage and drainage on the other hand. DOC and DIC stocks in groundwater and exports to first-order streams varied drastically during the hydrological cycle, in relation with water table depth and amplitude. In the groundwater, DOC concentrations were maximal in winter when the water table reached the superficial organic-rich layer of the soil. In contrast, DIC (in majority excess CO2) in groundwater showed maximum concentrations at low water table during late summer, concomitant with heterotrophic conditions of the forest plot. Our data also suggest that a large part of the DOC mobilized at high water table was mineralized to DIC during the following months within the groundwater itself. In first-order streams, DOC and DIC followed an opposed seasonal trend similar to groundwater but with lower concentrations. On an annual basis, leaching of carbon to streams occurred as DIC and DOC in similar proportion, but DOC export occurred in majority during short periods of the highest water table, whereas DIC export was more constant throughout the year. Leaching of forest carbon to first-order streams represented a small portion (approximately 2 %) of the net land CO2 sink at the plot. In addition, approximately 75 % of the DIC exported from groundwater was not found in streams, as it returned very fast to the atmosphere through CO2 degassing.

Representation of Dissolved Organic Carbon in the JULES Dynamic Global Vegetation Model

NASA Astrophysics Data System (ADS)

Nakhavali, Mahdi; Friedlingstein, Pierre; Guenet, Bertrand; Ciais, Philip

2017-04-01

Current global models of the carbon cycle consider only vertical gas exchanges between terrestrial or oceanic reservoirs and the atmosphere, hence not considering lateral transport of carbon from the continent to the oceans. This also means that such models implicitly consider that all the CO2 which is not respired to the atmosphere is stored on land, hence overestimating the land sink of carbon. Moving toward a boundless carbon cycle that is integrating the whole continuum from land to ocean to atmosphere is needed in order to better understand Earth's carbon cycle and to make more reliable projection of its future. Here we present an original representation of Dissolved Organic Carbon (DOC) processes in the Joint UK Land Environment Simulator (JULES). The standard version of JULES represent energy, water and carbon cycles and exchanges with the atmosphere, but only account for water run-off, not including export of carbon from terrestrial ecosystems to the aquatic environments. The aim of the project is to include in JULES a representation of DOC production in terrestrial soils, due to incomplete decomposition of organic matter, its decomposition to the atmosphere, and its export to the river network by leaching. In new developed version of JULES (JULES-DOCM), DOC pools, based on their decomposition rate, are classified into labile and recalcitrant within 3 meters of soil. Based on turnover rate, DOC coming from plant material pools and microbial biomass is directed to labile pool, while DOC from humus is directed to recalcitrant pool. Both of these pools have free (dissolved) and locked (adsorbed) form where just the free pool is subjected to decomposition and leaching. DOC production and decomposition are controlled by rate modifiers (moisture, temperature, vegetation fraction and decomposition rate) at each soil layer. Decomposed DOC is released to the atmosphere following a fixed carbon use efficiency. Leaching accounts for both surface (runoff) and subsurface (groundwater) components and is parameterized as Top soil leaching (from top 20cm) and Bottom soil leaching (down to 3 meters) depending on DOC concentration and runoff leaving that layer. The model parameters are calibrated against specific sites (Brasschaat, Hainich and Carlow) for which observations of DOC concentration and leaching are available. Tuning is performed optimizing parameters such as DOC labile and recalcitrant resident time, DOC vertical distribution and CUE. Once this calibration has been performed at the site level, the model is used for global simulations with the major historical forcing (climate, atmospheric CO2 and land-use changes) in order to estimate the changes of DOC export and their attribution to anthropogenic activities.

Examining organic carbon transport by the Orinoco River using SeaWiFS imagery

NASA Astrophysics Data System (ADS)

López, Ramón; Del Castillo, Carlos E.; Miller, Richard L.; Salisbury, Joseph; Wisser, Dominik

2012-09-01

The Orinoco River is the fourth largest in the world in terms of water discharge and organic carbon export to the ocean. River export of organic carbon is a key component of the carbon cycle and the global carbon budget. Here, we examined the seasonal transport of organic carbon by the Orinoco River into the eastern Caribbean using the conservative relationship of colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) in low salinity coastal waters influenced by river plumes. In situ measurements of CDOM absorption, DOC, and salinity were used to develop an empirical model for DOC concentration at the Orinoco River Plume. Satellite remote sensing reflectances were used with empirical models to determine DOC and Particulate organic carbon (POC) river transport. Our estimates of CDOM and DOC significantly correlated with in situ measurements and were within the expected ranges for the river. Total organic carbon transport by the Orinoco River during the period of 1998 to 2010 was 7.10 ×1012 g C y-1, from 5.29 × 1012 g C y-1 of DOC and 1.81 × 1012 g C y-1 of POC, representing ˜6% increase to previous published estimates. The variability in organic carbon transport responded to the seasonality in river flow more than to changes in organic carbon concentration in the river. Our results corroborate that is possible to estimate organic carbon transport using ocean color data at global scales. This is needed to reduce the uncertainties of land-ocean carbon fluxes.

Floodplain influence on carbon speciation and fluxes from the lower Pearl River, Mississippi

NASA Astrophysics Data System (ADS)

Cai, Yihua; Shim, Moo-Joon; Guo, Laodong; Shiller, Alan

2016-08-01

To investigate the floodplain influence on carbon speciation and export to the northern Gulf of Mexico, water samples were collected monthly from two sites in the East Pearl River (EPR) basin during 2006-2008. Additionally, four spatial surveys in the river basin between those two sites were also conducted. Compared with the upstream sampling site at Bogalusa, MS, dissolved inorganic carbon (DIC) and particulate organic carbon (POC) concentrations were 36% and 55% lower, respectively, and dissolved organic carbon (DOC) concentration was 49% higher at the downstream Stennis Space Center (SSC) site. In addition, the bulk DOC pool at SSC had a higher colloidal fraction than at Bogalusa (75% vs. 68%). Detailed spatial surveys revealed the differences between the upstream and downstream stations resulted both from input from Hobolochitto Creek, a tributary of the EPR, and from influence of the swamp-rich floodplain. The contributions from Hobolochitto Creek to the carbon pool in the EPR basin were lowest during a high flow event and reached a maximum during the dry season. Meanwhile, the floodplain in the EPR basin acted as a significant sink for DOC, POC and particulate nitrogen during summer and for suspended sediment during a high flow event. However, the floodplain was converted into a source of suspended sediment, DOC, and POC to the EPR during winter, revealing a dynamic nature and seasonality in the floodplain influence. Consistent with its dominant forest coverage, abundant wetlands along the river corridor, and mild anthropogenic disturbance, the Pearl River basin above Bogalusa generally had higher yields of DOC and POC (1903 and 1386 kg-C km-2 yr-1, respectively), but a lower yield of DIC (2126 kg-C km-2 yr-1) compared to other North American rivers. An estimation based on a mass balance approach suggests the interactions between floodplain and the main river stem could reduce the annual DIC and POC export fluxes from downstream of the EPR by 24% and 40%, respectively, but enhance the annual riverine DOC export by 25%. Similar scenarios likely occur in other wetland-rich coastal rivers and are capable of significantly altering the current estimation of riverine carbon export.

Concentrations, loads, and yields of organic carbon in streams of agricultural watersheds

USGS Publications Warehouse

Kronholm, Scott; Capel, Paul

2012-01-01

Carbon is cycled to and from large reservoirs in the atmosphere, on land, and in the ocean. Movement of organic carbon from the terrestrial reservoir to the ocean plays an important role in the global cycling of carbon. The transition from natural to agricultural vegetation can change the storage and movement of organic carbon in and from a watershed. Samples were collected from 13 streams located in hydrologically and agriculturally diverse watersheds, to better understand the variability in the concentrations and loads of dissolved organic carbon (DOC) and particulate organic carbon (POC) in the streams, and the variability in watershed yields. The overall annual median concentrations of DOC and POC were 4.9 (range: 2.1–6.8) and 1.1 (range: 0.4–3.8) mg C L−1, respectively. The mean DOC watershed yield (± SE) was 25 ± 6.8 kg C ha−1 yr−1. The yields of DOC from these agricultural watersheds were not substantially different than the DOC yield from naturally vegetated watersheds in equivalent biomes, but were at the low end of the range for most biomes. Total organic carbon (DOC + POC) annually exported from the agricultural watersheds was found to average 0.03% of the organic carbon that is contained in the labile plant matter and top 1 m of soil in the watershed. Since the total organic carbon exported from agricultural watersheds is a relatively small portion of the sequestered carbon within the watershed, there is the great potential to store additional carbon in plants and soils of the watershed, offsetting some anthropogenic CO2 emissions.

Organic carbon export from the Greenland Ice Sheet: sources, sinks and downstream fluxes

NASA Astrophysics Data System (ADS)

Wadham, J. L.; Lawson, E.; Tranter, M.; Stibal, M.; Telling, J.; Lis, G. P.; Nienow, P. W.; Anesio, A. M.; Butler, C. E.

2012-12-01

Runoff from small glacier systems has been shown to contain dissolved organic carbon (DOC) rich in low molecular weight (LMW), and hence more labile forms, designating glaciers as an important source of carbon for downstream heterotrophic activity. Here we assess glacier surfaces as potential sources of labile DOC to downstream ecosystems, presenting data from a wide range of glacier systems to determine sources and sinks of DOC in glacial and proglacial systems. We subsequently focus upon the Greenland Ice Sheet (GrIS) which is the largest source of glacial runoff at present (400 km3 yr-1), with predicted increases in future decades. We report high fluxes of particulate organic carbon (POC), DOC and LMW labile fractions from a large GrIS catchment during two contrasting melt seasons. POC dominates OC export, is sourced from the ice sheet bed and contains a significant bioreactive component (~10% carbohydrates). The LMW-DOC "labile" fraction derives almost entirely from microbial activity on the ice sheet surface, which is supported by data from glacier systems also presented here. Annual fluxes of DOC, POC and labile components were lower in 2010 than 2009, despite a ~2 fold increase in runoff fluxes in 2010, suggesting production-limited DOC/POC sources. Scaled to the entire ice sheet, combined DOC and POC fluxes are of a similar order of magnitude to other large Arctic river systems and may represent an important source of organic carbon to the North Atlantic, Greenland and Labrador Seas.

DOC export from a peat extraction site in transition to managed restoration - preliminary results of a long-term research project

NASA Astrophysics Data System (ADS)

Rüggen, Norman; Kutzbach, Lars; Kopelke, Susanne; Pfeiffer, Eva-Maria

2013-04-01

Peatlands play a major role in the global cycles of water and carbon. Budgeting carbon fluxes of temperate man-managed peatlands is limited by few available data. The main carbon compounds exported from such sites are CO2, CH4 and laterally exported C compounds (dissolved organic carbon (DOC) and gases). Without reliable estimates of laterally exported carbon from managed peatlands, overall carbon balances of such geoecosystems remain obscure. The Himmelmoor peatland in Schleswig-Holstein is subject to horticultural peat extraction in transition towards managed restoration. One-third of 130 ha of peatland area are already subject to managed restoration, the remaining part is still intensively used as a peat extraction site. Surface water discharge rates are measured by a water head sensor in combination with a rectangular-shaped weir. An October-November data set (54 days period, 2012) shows a distinct base-flow and precipitation-dependent discharge peaks, which were up to five times higher than the base-flow. The observations indicate a poor water storing capacity of the intensively used areas. During this first observation period, almost 65,000 tons of peatland-DOC-bearing water have been discharged into the adjacent river system. DOC concentrations in the discharge water have been measured every 6-12 days with a Total Carbon Analyzer TOC-L (Shimadzu, Japan). Additionally, a field spectrophotometer (spectro::lyser,s-can, Austria) has been employed, for measuring quasi-continuous concentrations of DOC. During the 54 day period, approximately 1.75 g DOC m-2 (or about 1750 kg DOC km-2) has been laterally exported from the peatland. Average DOC concentration was 35.1 ± 4 g l-1. These values range in the same order of magnitude that have been published from managed UK peatlands (Armstrong et al., 2010; Wilson et al., 2011). Preliminary data evaluation of the in-situ field spectrophotometer show that DOC concentrations of discharge water varied up to 1.5 mg L-1 in less than six hours and up to about 3 mg L-1 in 36 hours. The described recently established hydrological measurements are planned to be continued for the next ten years in combination with continuous eddy covariance measurements of land-atmosphere fluxes of Water, CO2 and CH4. This long-term monitoring of lateral and vertical exchange fluxes will serve as a basis for evaluating the success of the peatland restoration with respect to biogeochemical cycling and greenhouse gas budgets. Literature Armstrong, A., Holden, J., Kay, P., Francis, B., Foulger, M., Gledhill, S., McDonald, A., Walker, A., 2010. The impact of peatland drain-blocking on dissolved organic carbon loss and discolouration of water; results from a national survey. Journal of Hydrology 381, 112-120. Wilson, L., Wilson, J., Holden, J., Johnstone, I., Armstrong, A., Morris, M., 2011. Ditch blocking, water chemistry and organic carbon flux: Evidence that blanket bog restoration reduces erosion and fluvial carbon loss. Science of the Total Environment 409, 2010-2018.

Effects of long-term land use change on dissolved carbon characteristics in the permafrost streams of northeast China.

PubMed

Guo, Yuedong; Song, Changchun; Wan, Zhongmei; Tan, Wenwen; Lu, Yongzheng; Qiao, Tianhua

2014-11-01

Permafrost soils act as large sinks of organic carbon but are highly sensitive to interference such as changes in land use, which can greatly influence dissolved carbon loads in streams. This study examines the effects of long-term land reclamation on seasonal concentrations of dissolved carbons in the upper reaches of the Nenjiang River, northeast China. A comparison of streams in natural and agricultural systems shows that the dissolved organic carbon (DOC) concentration is much lower in the agricultural stream (AG) than in the two natural streams (WAF, wetland dominated; FR, forest dominated), suggesting that land use change is associated with reduced DOC exporting capacity. Moreover, the fluorescence indexes and the ratio of dissolved carbon to nitrogen also differ greatly between the natural and agricultural streams, indicating that the chemical characteristics and the origin of the DOC released from the whole reaches are also altered to some extent. Importantly, the exporting concentration of dissolved inorganic carbon (DIC) and its proportion of total dissolved carbon (TDC) substantially increase following land reclamation, which would largely alter the carbon cycling processes in the downstream fluvial system. Although the strong association between the stream discharge and the DOC concentration was unchanged, the reduction in total soil organic carbon following land reclamation led to remarkable decline of the total flux and exporting coefficient of the dissolved carbons. The results suggest that dissolved carbons in permafrost streams have been greatly affected by changes in land use since the 1970s, and the changes in the concentration and chemical characteristics of dissolved carbons will last until the alteration in both the traditional agriculture pattern and the persistent reclamation activities.

Dissolved black carbon in grassland streams: is there an effect of recent fire history?

PubMed

Ding, Yan; Yamashita, Youhei; Dodds, Walter K; Jaffé, Rudolf

2013-03-01

While the existence of black carbon as part of dissolved organic matter (DOM) has been confirmed, quantitative determinations of dissolved black carbon (DBC) in freshwater ecosystem and information on factors controlling its concentration are scarce. In this study, stream surface water samples from a series of watersheds subject to different burn frequencies in Konza Prairie (Kansas, USA) were collected in order to determine if recent fire history has a noticeable effect on DBC concentration. The DBC levels detected ranged from 0.04 to 0.11 mg L(-1), accounting for ca. 3.32±0.51% of dissolved organic carbon (DOC). No correlation was found between DBC concentration and neither fire frequency nor time since last burn. We suggest that limited DBC flux is related to high burning efficiency, possibly greater export during periods of high discharge and/or the continuous export of DBC over long time scales. A linear correlation between DOC and DBC concentrations was observed, suggesting the export mechanisms determining DOC and DBC concentrations are likely coupled. The potential influence of fire history was less than the influence of other factors controlling the DOC and DBC dynamics in this ecosystem. Assuming similar conditions and processes apply in grasslands elsewhere, extrapolation to a global scale would suggest a global grasslands flux of DBC on the order of 0.14 Mt carbon year(-1). Copyright © 2012 Elsevier Ltd. All rights reserved.

Non-linear, connectivity and threshold-dominated runoff-generation controls DOC and heavy metal export in a small peat catchment

NASA Astrophysics Data System (ADS)

Birkel, Christian; Broder, Tanja; Biester, Harald

2017-04-01

Peat soils act as important carbon sinks, but they also release large amounts of dissolved organic carbon (DOC) to the aquatic system. The DOC export is strongly tied to the export of soluble heavy metals. The accumulation of potentially toxic substances due to anthropogenic activities, and their natural export from peat soils to the aquatic system is an important health and environmental issue. However, limited knowledge exists as to how much of these substances are mobilized, how they are mobilized in terms of flow pathways and under which hydrometeorological conditions. In this study, we report from a combined experimental and modelling effort to provide greater process understanding from a small, lead (Pb) and arsenic (As) contaminated upland peat catchment in northwestern Germany. We developed a minimally parameterized, but process-based, coupled hydrology-biogeochemistry model applied to simulate detailed hydrometric and biogeochemical data. The model was based on an initial data mining analysis, in combination with regression relationships of discharge, DOC and element export. We assessed the internal model DOC-processing based on stream-DOC hysteresis patterns and 3-hourly time step groundwater level and soil DOC data (not used for calibration as an independent model test) for two consecutive summer periods in 2013 and 2014. We found that Pb and As mobilization can be efficiently predicted from DOC transport alone, but Pb showed a significant non-linear relationship with DOC, while As was linearly related to DOC. The relatively parsimonious model (nine calibrated parameters in total) showed the importance of non-linear and rapid near-surface runoff-generation mechanisms that caused around 60% of simulated DOC load. The total load was high even though these pathways were only activated during storm events on average 30% of the monitoring time - as also shown by the experimental data. Overall, the drier period 2013 resulted in increased nonlinearity, but exported less DOC (115 kg C ha-1 yr-1 ± 11 kg C ha-1 yr-1) compared to the equivalent but wetter period in 2014 (189 kg C ha-1 yr-1 ± 38 kg C ha-1 yr-1). The exceedance of a critical water table threshold (-10 cm) triggered a rapid near-surface runoff response with associated higher DOC transport connecting all available DOC pools, and with subsequent dilution. We conclude that the combination of detailed experimental work with relatively simple, coupled hydrology-biogeochemistry models allowed not only the model to be internally constrained, but also provided important insight into how DOC and tightly coupled heavy metals are mobilized.

First dynamic model of dissolved organic carbon derived directly from high-frequency observations through contiguous storms.

PubMed

Jones, Timothy D; Chappell, Nick A; Tych, Wlodek

2014-11-18

The first dynamic model of dissolved organic carbon (DOC) export in streams derived directly from high frequency (subhourly) observations sampled at a regular interval through contiguous storms is presented. The optimal model, identified using the recently developed RIVC algorithm, captured the rapid dynamics of DOC load from 15 min monitored rainfall with high simulation efficiencies and constrained uncertainty with a second-order (two-pathway) structure. Most of the DOC export in the four headwater basins studied was associated with the faster hydrometric pathway (also modeled in parallel), and was soon exhausted in the slower pathway. A delay in the DOC mobilization became apparent as the ambient temperatures increased. These features of the component pathways were quantified in the dynamic response characteristics (DRCs) identified by RIVC. The model and associated DRCs are intended as a foundation for a better understanding of storm-related DOC dynamics and predictability, given the increasing availability of subhourly DOC concentration data.

Rapid Response of Hydrological Loss of DOC to Water Table Drawdown and Warming in Zoige Peatland: Results from a Mesocosm Experiment

PubMed Central

Lou, Xue-Dong; Zhai, Sheng-Qiang; Kang, Bing; Hu, Ya-Lin; Hu, Li-Le

2014-01-01

A large portion of the global carbon pool is stored in peatlands, which are sensitive to a changing environment conditions. The hydrological loss of dissolved organic carbon (DOC) is believed to play a key role in determining the carbon balance in peatlands. Zoige peatland, the largest peat store in China, is experiencing climatic warming and drying as well as experiencing severe artificial drainage. Using a fully crossed factorial design, we experimentally manipulated temperature and controlled the water tables in large mesocosms containing intact peat monoliths. Specifically, we determined the impact of warming and water table position on the hydrological loss of DOC, the exported amounts, concentrations and qualities of DOC, and the discharge volume in Zoige peatland. Our results revealed that of the water table position had a greater impact on DOC export than the warming treatment, which showed no interactive effects with the water table treatment. Both DOC concentration and discharge volume were significantly increased when water table drawdown, while only the DOC concentration was significantly promoted by warming treatment. Annual DOC export was increased by 69% and 102% when the water table, controlled at 0 cm, was experimentally lowered by −10 cm and −20 cm. Increases in colored and aromatic constituents of DOC (measured by Abs254 nm, SUVA254 nm, Abs400 nm, and SUVA400 nm) were observed under the lower water tables and at the higher peat temperature. Our results provide an indication of the potential impacts of climatic change and anthropogenic drainage on the carbon cycle and/or water storage in a peatland and simultaneously imply the likelihood of potential damage to downstream ecosystems. Furthermore, our results highlight the need for local protection and sustainable development, as well as suggest that more research is required to better understand the impacts of climatic change and artificial disturbances on peatland degradation. PMID:25369065

Rapid response of hydrological loss of DOC to water table drawdown and warming in Zoige peatland: results from a mesocosm experiment.

PubMed

Lou, Xue-Dong; Zhai, Sheng-Qiang; Kang, Bing; Hu, Ya-Lin; Hu, Li-Le

2014-01-01

A large portion of the global carbon pool is stored in peatlands, which are sensitive to a changing environment conditions. The hydrological loss of dissolved organic carbon (DOC) is believed to play a key role in determining the carbon balance in peatlands. Zoige peatland, the largest peat store in China, is experiencing climatic warming and drying as well as experiencing severe artificial drainage. Using a fully crossed factorial design, we experimentally manipulated temperature and controlled the water tables in large mesocosms containing intact peat monoliths. Specifically, we determined the impact of warming and water table position on the hydrological loss of DOC, the exported amounts, concentrations and qualities of DOC, and the discharge volume in Zoige peatland. Our results revealed that of the water table position had a greater impact on DOC export than the warming treatment, which showed no interactive effects with the water table treatment. Both DOC concentration and discharge volume were significantly increased when water table drawdown, while only the DOC concentration was significantly promoted by warming treatment. Annual DOC export was increased by 69% and 102% when the water table, controlled at 0 cm, was experimentally lowered by -10 cm and -20 cm. Increases in colored and aromatic constituents of DOC (measured by Abs(254 nm), SUVA(254 nm), Abs(400 nm), and SUVA(400 nm)) were observed under the lower water tables and at the higher peat temperature. Our results provide an indication of the potential impacts of climatic change and anthropogenic drainage on the carbon cycle and/or water storage in a peatland and simultaneously imply the likelihood of potential damage to downstream ecosystems. Furthermore, our results highlight the need for local protection and sustainable development, as well as suggest that more research is required to better understand the impacts of climatic change and artificial disturbances on peatland degradation.

The Spatial and Temporal Distribution of Dissolved Organic Carbon Exported from Three Chinese Rivers to the China Sea

PubMed Central

Shi, Guohua; Peng, Changhui; Wang, Meng; Shi, Shengwei; Yang, Yanzheng; Chu, Junyao; Zhang, Junjun; Lin, Guanghui; Shen, Yan; Zhu, Qiuan

2016-01-01

The lateral transport of dissolved organic carbon (DOC) plays an important role in linking the carbon cycles of terrestrial and aquatic ecosystems. Neglecting the lateral flow of dissolved organic carbon can lead to an underestimation of the organic carbon budget of terrestrial ecosystems. It is thus necessary to integrate DOC concentrations and flux into carbon cycle models, particularly with regard to the development of models that are intended to directly link terrestrial and ocean carbon cycles. However, to achieve this goal, more accurate information is needed to better understand and predict DOC dynamics. In this study, we compiled an inclusive database of available data collected from the Yangtze River, Yellow River and Pearl River in China. The database is collected based on online literature survey and analysed by statistic method. Overall, our results revealed a positive correlation between DOC flux and discharge in all three rivers, whereas the DOC concentration was more strongly correlated with the regional net primary productivity (NPP). We estimated the total DOC flux exported by the three rivers into the China Sea to be approximately 2.73 Tg yr-1. Specifically, the annual flux of DOC from the Yangtze River, Yellow River and Pearl River was estimated to be 1.85 Tg yr-1, 0.06 Tg yr-1 and 0.82 Tg yr-1, respectively, and the average annual DOC concentrations were estimated to be 2.24 ± 0.53 mg L-1, 2.70 ± 0.38 mg L-1 and 1.51 ± 0.09 mg L-1, respectively. Seasonal variations in DOC concentrations are greatly influenced by the interaction between temperature and precipitation. NPP is significantly and positively related to the DOC concentration in the Yangtze River and the Pearl River. In addition, differences in climate and the productivity of the vegetation may influence both the flux and concentrations of DOC transported by the rivers and thus potentially affect estuarine geochemistry. PMID:27755581

Aged dissolved organic carbon exported from rivers of the Tibetan Plateau

PubMed Central

Qu, Bin; Sillanpää, Mika; Kang, Shichang; Stubbins, Aron; Yan, Fangping; Aho, Kelly Sue; Zhou, Feng; Raymond, Peter A.

2017-01-01

The role played by river networks in regional and global carbon cycle is receiving increasing attention. Despite the potential of radiocarbon measurements (14C) to elucidate sources and cycling of different riverine carbon pools, there remain large regions such as the climate-sensitive Tibetan Plateau for which no data are available. Here we provide new 14C data on dissolved organic carbon (DOC) from three large Asian rivers (the Yellow, Yangtze and Yarlung Tsangpo Rivers) running on the Tibetan Plateau and present the carbon transportation pattern in rivers of the plateau versus other river system in the world. Despite higher discharge rates during the high flow season, the DOC yield of Tibetan Plateau rivers (0.41 gC m-2 yr-1) was lower than most other rivers due to lower concentrations. Radiocarbon ages of the DOC were older/more depleted (511±294 years before present, yr BP) in the Tibetan rivers than those in Arctic and tropical rivers. A positive correlation between radiocarbon age and permafrost watershed coverage was observed, indicating that 14C-deplted/old carbon is exported from permafrost regions of the Tibetan Plateau during periods of high flow. This is in sharp contrast to permafrost regions of the Arctic which export 14C-enriched carbon during high discharge periods. PMID:28552976

The geomicrobiology of the Greenland Ice Sheet: impact on DOC export (Invited)

NASA Astrophysics Data System (ADS)

Wadham, J. L.; Stibal, M.; Lawson, E. C.; Barnett, M. J.; Hasan, F.; Telling, J.; Anesio, A.; Lis, G.; Cullen, D.; Butler, C.; Tranter, M.; Nienow, P. W.

2010-12-01

The Greenland Ice Sheet (GrIS) is the largest mass of ice in the northern hemisphere, and contributes ~370 km3 in runoff annually to the Arctic Ocean. While recent work has highlighted runoff increases of up to 100% from the GrIS over the next century, very little is known about the associated impacts upon rates of sediment-bound and dissolved organic carbon export from the ice sheet to the coastal ocean. This is relevant given recent work that has suggested that the high proportion of labile dissolved organic carbon (DOC) present in glacial runoff may be important in sustaining the productivity of ecosystems downstream. Here we report the phylogenetic and functional diversity of micro-organisms inhabiting the surface and basal regions of the Greenland Ice Sheet (at Leverett Glacier, SW Greenland), and whose activity influences the biogeochemical composition of runoff. Real time PCR data on runoff, together with 16S-rRNA bacterial clone libraries on sediments, demonstrate a subglacial microbial community that contrasts phylogenetically and functionally with the ice sheet surface ecosystem. We envisage that large sectors of the subglacial environment are microbially active, with overridden paleosols and in-washed surface organic matter providing a carbon substrate for a range of metabolic pathways. This includes methanogenesis which proceeds at rates similar to deep ocean sediments and via a CO2/H2 pathway. These subglacial microbial communities serve to chemically modify the DOC composition of meltwater inputs from the ice sheet surface and modulate the reactivity of bulk DOC exported in runoff. Evidence for subglacial microbial influences on DOC in runoff includes elevated concentrations of dissolved carbohydrates (e.g. glucose and fructose of up to 1 μmol/L), which are preferentially exported during subglacial outburst events. We examine the temporal changes in DOC export in runoff from the ice sheet over a full melt season, and consider how changes in total runoff over the coming century may perturb this contribution.

Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen: Implications for peat carbon stock stability.

PubMed

Campeau, Audrey; Bishop, Kevin H; Billett, Michael F; Garnett, Mark H; Laudon, Hjalmar; Leach, Jason A; Nilsson, Mats B; Öquist, Mats G; Wallin, Marcus B

2017-12-01

The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content ( 14 C) of dissolved organic carbon (DOC), carbon dioxide (CO 2 ), and methane (CH 4 ) exported from a boreal peatland catchment coupled with 14 C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (<60 years), despite stream DOC, CO 2 , and CH 4 primarily being sourced from deep peat horizons (2-4 m) near the mire's outlet. In fact, the 14 C content of DOC, CO 2 , and CH 4 across the entire peat profile was considerably enriched with postbomb C compared with the solid peat material. Overall, our results demonstrate little to no mobilization of ancient C stocks from this boreal peatland and a relatively large resilience of the source of aquatic C export to forecasted hydroclimatic changes. © 2017 The Authors Global Change Biology Published by John Wiley & Sons Ltd.

Hydro-climatic forcing of dissolved organic carbon in two boreal lakes of Canada.

PubMed

Diodato, Nazzareno; Higgins, Scott; Bellocchi, Gianni; Fiorillo, Francesco; Romano, Nunzio; Guadagno, Francesco M

2016-11-15

The boreal forest of the northern hemisphere represents one of the world's largest ecozones and contains nearly one third of the world's intact forests and terrestrially stored carbon. Long-term variations in temperature and precipitation have been implied in altering carbon cycling in forest soils, including increased fluxes to receiving waters. In this study, we use a simple hydrologic model and a 40-year dataset (1971-2010) of dissolved organic carbon (DOC) from two pristine boreal lakes (ELA, Canada) to examine the interactions between precipitation and landscape-scale controls of DOC production and export from forest catchments to surface waters. Our results indicate that a simplified hydrologically-based conceptual model can enable the long-term temporal patterns of DOC fluxes to be captured within boreal landscapes. Reconstructed DOC exports from forested catchments in the period 1901-2012 follow largely a sinusoidal pattern, with a period of about 37years and are tightly linked to multi-decadal patterns of precipitation. By combining our model with long-term precipitation estimates, we found no evidence of increasing DOC transport or in-lake concentrations through the 20th century. Copyright © 2016 Elsevier B.V. All rights reserved.

Tidally driven export of dissolved organic carbon, total mercury, and methylmercury from a mangrove-dominated estuary

USGS Publications Warehouse

Bergamaschi, B.A.; Krabbenhoft, D.P.; Aiken, G.R.; Patino, E.; Rumbold, D.G.; Orem, W.H.

2012-01-01

The flux of dissolved organic carbon (DOC) from mangrove swamps accounts for 10% of the global terrestrial flux of DOC to coastal oceans. Recent findings of high concentrations of mercury (Hg) and methylmercury (MeHg) in mangroves, in conjunction with the common co-occurrence of DOC and Hg species, have raised concerns that mercury fluxes may also be large. We used a novel approach to estimate export of DOC, Hg, and MeHg to coastal waters from a mangrove-dominated estuary in Everglades National Park (Florida, USA). Using in situ measurements of fluorescent dissolved organic matter as a proxy for DOC, filtered total Hg, and filtered MeHg, we estimated the DOC yield to be 180 (??12.6) g C m -2 yr -1, which is in the range of previously reported values. Although Hg and MeHg yields from tidal mangrove swamps have not been previously measured, our estimated yields of Hg species (28 ?? 4.5 ??g total Hg m -2 yr -1 and 3.1 ?? 0.4 ??g methyl Hg m -2 yr -1) were five times greater than is typically reported for terrestrial wetlands. These results indicate that in addition to the well documented contributions of DOC, tidally driven export from mangroves represents a significant potential source of Hg and MeHg to nearby coastal waters. ?? 2011 American Chemical Society.

Tidally Driven Export of Dissolved Organic Carbon, Total Mercury, and Methylmercury from a Mangrove-Dominated Estuary

PubMed Central

2011-01-01

The flux of dissolved organic carbon (DOC) from mangrove swamps accounts for 10% of the global terrestrial flux of DOC to coastal oceans. Recent findings of high concentrations of mercury (Hg) and methylmercury (MeHg) in mangroves, in conjunction with the common co-occurrence of DOC and Hg species, have raised concerns that mercury fluxes may also be large. We used a novel approach to estimate export of DOC, Hg, and MeHg to coastal waters from a mangrove-dominated estuary in Everglades National Park (Florida, USA). Using in situ measurements of fluorescent dissolved organic matter as a proxy for DOC, filtered total Hg, and filtered MeHg, we estimated the DOC yield to be 180 (±12.6) g C m–2 yr–1, which is in the range of previously reported values. Although Hg and MeHg yields from tidal mangrove swamps have not been previously measured, our estimated yields of Hg species (28 ± 4.5 μg total Hg m–2 yr–1 and 3.1 ± 0.4 μg methyl Hg m–2 yr–1) were five times greater than is typically reported for terrestrial wetlands. These results indicate that in addition to the well documented contributions of DOC, tidally driven export from mangroves represents a significant potential source of Hg and MeHg to nearby coastal waters. PMID:22206226

[Influence of land use change on dissolved organic carbon export in Naoli River watershed. Northeast China].

PubMed

Yin, Xiao-min; Lyu, Xian-guo; Liu, Xing-tu; Xue, Zhen-shan

2015-12-01

The present study was conducted to evaluate the influence of land use change on dissolved organic carbon (DOC) export in Naoli River watershed, Northeast China. Seasonal variation of DOC concentrations of the river water and its relationship with land use in the whole watershed and 100 m riparian zone at the annual average scale were analyzed using the method of field sampling, laboratory analysis, GIS and statistics analysis. The results showed that the concentrations of DOC under base flow conditions in spring and summer were significantly higher than that in fall in the study watershed. The seasonal trend of DOC concentrations in wetland-watersheds was similar to that in all the sub-watersheds, while significantly different from that in non-wetland watersheds. On the annual average scale, percentage of wetland in the whole watershed and paddy field in the 100 m riparian zone had positive relationship with the DOC concentration in the river water, while percentage of forest in the whole watershed had negative relationship with it (P < 0.05). It indicated that wetland in the sub-watershed played a significant role in the seasonal variation of DOC in river water of Naoli River watershed. Wetland in the watershed and paddy field in the 100 m riparian zone significantly promoted DOC export, while forest alleviated it. Land use change in the watershed in the past few decades dramatically changed the DOC balance of river water.

Seasonal variation in the quality of dissolved and particulate organic matter exchanged between a salt marsh and its adjacent estuary

NASA Astrophysics Data System (ADS)

Osburn, Christopher L.; Mikan, Molly P.; Etheridge, J. Randall; Burchell, Michael R.; Birgand, François

2015-07-01

Fluorescence was used to examine the quality of dissolved and particulate organic matter (DOM and POM) exchanging between a tidal creek in a created salt marsh and its adjacent estuary in eastern North Carolina, USA. Samples from the creek were collected hourly over four tidal cycles in May, July, August, and October 2011. Absorbance and fluorescence of chromophoric DOM (CDOM) and of base-extracted POM (BEPOM) served as the tracers for organic matter quality while dissolved organic carbon (DOC) and base-extracted particulate organic carbon (BEPOC) were used to compute fluxes. Fluorescence was modeled using parallel factor analysis (PARAFAC) and principle components analysis (PCA) of the PARAFAC results. Of nine PARAFAC components (C) modeled, C3 represented recalcitrant DOM and C4 represented fresher soil-derived source DOM. Component 1 represented detrital POM, and C6 represented planktonic POM. Based on mass balance, recalcitrant DOC export was 86 g C m-2 yr-1 and labile DOC export was 49 g C m-2 yr-1; no planktonic DOC was exported. The marsh also exported 41 g C m-2 yr-1 of detrital terrestrial POC, which likely originated from lands adjacent to the North River estuary. Planktonic POC export from the marsh was 6 g C m-2 yr-1. Assuming the exported organic matter was oxidized to CO2 and scaled up to global salt marsh area, respiration of salt marsh DOC and POC transported to estuaries could amount to a global CO2 flux of 11 Tg C yr-1, roughly 4% of the recently estimated CO2 release for marshes and estuaries globally.

Relationships between Δ14C and the molecular quality of dissolved organic carbon in rivers draining to the coast from the conterminous United States

USGS Publications Warehouse

Butman, David; Raymond, Peter A.; Butler, Kenna D.; Aiken, George R.

2012-01-01

Dissolved organic carbon (DOC) in natural waters possesses chemical and molecular qualities indicative of its source and age. The apportionment of DOC by age into millennial and decadal pools is necessary to understand the temporal connection between terrestrial and aquatic ecosystems in the global carbon cycle. We measured Δ14C-DOC and chemical composition indices (specific ultraviolet absorbance (SUVA254), fluorescence index (FI), hydrophobic organic acid fraction (HPOA) content) for 15 large river basins in the conterminous United States. Across all rivers the average proportion of HPOA in DOC correlated strongly with SUVA254 (r2 = 0.93 p < 0.001). Individual Δ14C-DOC ranged from a low of −92.9‰ (726 y.b.p.) in the Colorado River to 73.4‰ (>Modern) in the Altamaha River for the year 2009. When adjusted by total discharge, these U.S. Rivers export modern carbon at between 34 and 46‰, a signal dominated by the Mississippi River. The variation in Δ14C correlates to indices of the aromaticity of the DOC measured by the SUVA254 (r2 = 0.87, p < 0.001), and FI (r2 = 0.6; p < 0.001) as well as differences in annual river discharge (r2 = 0.46, p < 0.006). SUVA254 was further correlated to broad scale vegetation phenology estimated from the Enhanced Vegetation Index derived from the NASA Moderate Resolution Imaging Spectrometer (MODIS). We show that basins with high discharge, high proportions of vegetation cover, and low human population densities export DOC enriched in aromatic material that corresponds to recently fixed atmospheric CO2. Conversely old DOC is exported from low discharge watersheds draining arid regions, and watersheds more strongly impacted by humans. The potential influence from fossil carbon from human inputs to aquatic systems may be important and requires more research.

Stable and radiocarbon isotopic composition of dissolved organic matter in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Walker, B. D.; Druffel, E. R. M.; Kolasinski, J.; Roberts, B. J.; Xu, X.; Rosenheim, B. E.

2017-08-01

Dissolved organic carbon (DOC) is of primary importance to marine ecosystems and the global carbon cycle. Stable carbon (δ13C) and radiocarbon (Δ14C) isotopic measurements are powerful tools for evaluating DOC sources and cycling. However, the isotopic signature of DOC in the Gulf of Mexico (GOM) remains almost completely unknown. Here we present the first DOC Δ14C and δ13C depth profiles from the GOM. Our results suggest the Mississippi River exports large amounts of DOC with an anthropogenic "bomb" Δ14C signature. Riverine DOC is removed and recycled offshore, and some marine production of DOC is observed in the river plume. Offshore profiles show that DOC has higher Δ14C than its Caribbean feed waters, indicative of a modern deep DOC source in the GOM basin. Finally, high DOC with negative δ13C and Δ14C values were observed near the Macondo Wellhead, suggesting a transformation of Deepwater Horizon hydrocarbons into a persistent population of DOC.

Modelling hydrological processes and dissolved organic carbon dynamics in a rehabilitated Sphagnum-dominated peatland

NASA Astrophysics Data System (ADS)

Bernard-Jannin, Léonard; Binet, Stéphane; Gogo, Sébastien; Leroy, Fabien; Perdereau, Laurent; Laggoun-Défarge, Fatima

2017-04-01

Sphagnum-dominated peatlands represent a global major stock of carbon (C). Dissolved organic carbon (DOC) exports through runoff and leaching could reduce their potential C sink function and impact downstream water quality. DOC production in peatlands is strongly controlled by the hydrology, especially water table depth (WTD). Therefore, disturbances such as drainage can lead to increase DOC exports by lowering the WTD. Hydrological restoration (e.g. rewetting) can be undertaken to restore peatland functioning with an impact on DOC exports. The objective of this study is to assess the impact of drainage and rewetting on hydrological processes and their interactions with DOC dynamics in a Sphagnum dominated peatland. A hydrological model has been applied to a drained peatland (La Guette, France) which experienced a rewetting action on February 2014 and where WTD has been recorded in four piezometers at a 15 min time step since 2009. In addition, DOC concentrations in the peatland have been measured 6 times a year since 2014. The hydrological model is a WTD dependent reservoir model composed by two reservoirs representing the micro and macro porosity of the peatland (Binet et al., 2013). A DOC production module in both reservoirs was implemented based on temperature and WTD. The model was calibrated against WTD and DOC concentrations for each piezometer. The results show that the WTD in the study area is strongly affected by local meteorological conditions that could hide the effect of the rewetting action. The preliminary results evidenced that an additional source of water, identified as groundwater supply originating from the surrounding sandy layer aquifer, is necessary to maintain the water balance, especially during wet years (NS>0.8). Finally, the DOC module was able to describe DOC concentrations measured in the peatland and could be used to assess the impact of rewetting on DOC dynamics at different locations and to identify the factors of control of DOC exports at the peatland scale before and after the restoration. This simple conceptual model requires few data to operate. Its application on different sites with contrasted settings (hydrological and climatic conditions) could provide insight on the dominant hydrological processes and their impact on DOC dynamics in peatlands. Binet S., Gogo S., Laggoun-Défarge F., A water-table dependent reservoir model to investigate the effect of drought and vascular plant invasion on peatland hydrology, Journal of Hydrology, Volume 499, 30 August 2013, Pages 132-139, ISSN 0022-1694, http://dx.doi.org/10.1016/j.jhydrol.2013.06.035.

Hydrological controls on riverine carbon export in a seasonally wet tropical catchment

NASA Astrophysics Data System (ADS)

Duvert, C.; Hutley, L. B.; Bossa, M.; Bird, M. I.; Munksgaard, N.; Wynn, J. G.; Setterfield, S. A.; Northwood, M.

2017-12-01

Understanding the movement of carbon (C) through the landscape is critical for accurate C accounting. Failure to account for the transport of terrestrially-derived C to aquifers and streams can result in a considerable over-estimation of the C sequestration by the biosphere. Here we report on the magnitude of C export via shallow groundwater and adjacent streams in a savanna-covered seasonally wet tropical catchment of northern Australia. Riverine fluxes of carbon dioxide (CO2), dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) were measured at a high resolution over a full year to gain insight into the drivers of C export in this system. Water and C stable isotopes were also measured in order to elucidate water sources and dominant flow pathways. Our results suggest that CO2 evasion was the major process contributing to riverine C loss in the catchment (111 kg C ha-1 yr-1). The downstream export of C was dominated by DOC (78 kg C ha-1 yr-1), while DIC accounted for 39 kg C ha-1 yr-1 of the annual export. The bulk of annual DOC export was flushed out during the very first high-flow events, with export decreasing throughout the wet season to pre-flood levels. In contrast, the DIC flux was more important during flow recession, upon activation of deeper flowpaths carrying geologically-derived C. Shallow groundwater measured in boreholes was supersaturated with CO2 (15,000 < pCO2 < 55,000 ppm), whereas in-stream concentrations were an order of magnitude lower, suggesting substantial outgassing of CO2. Our findings outline the key role of point-source groundwater discharge in riverine CO2 evasion, with C largely sourced from seasonally productive savanna vegetation. Given the complexity of this pathway and the magnitude of this flux, new methods are needed to more precisely quantify CO2 evasion.

Floodplain Impact on Riverine Dissolved Carbon Cycling in the Mississippi-Atchafalaya River System

NASA Astrophysics Data System (ADS)

DelDuco, E.; Xu, Y. J.

2017-12-01

Studies have shown substantial increases in the export of terrestrial carbon by rivers over the past several decades, and have linked these increases to human activity such as changes in land use, urbanization, and intensive agriculture. The Mississippi River (MR) is the largest river in North America, and is among the largest in the world, making its carbon export globally significant. The Atchafalaya River (AR) receives 25% of the Mississippi River's flow before traveling 189 kilometers through the largest bottomland swamp in North America, providing a unique opportunity to study floodplain impacts on dissolved carbon in a large river. The aim of this study was to determine how dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in the AR change spatially and seasonally, and to elucidate which processes control carbon cycling in this intricate swamp river system. From May 2015 -May 2016, we conducted monthly river sampling from the river's inflow to its outflow, analyzing samples for DOC and DIC concentrations and δ 13C stable isotope composition. During the study period, the river discharged a total of 5.35 Tg DIC and a total of 2.34 Tg DOC into the Gulf of Mexico. Based on the mass inflow-outflow balance, approximately 0.53 Tg ( 10%) of the total DIC exported was produced within the floodplain, while 0.24 Tg ( 10%) of DOC entering the basin was removed. The AR was consistently saturated with pCO2 above atmospheric pressure, indicating that this swamp-river system acts a large source of DIC to the atmosphere as well as to coastal margins. Largest changes in carbon constituents occurred during periods of greatest inundation of the basin, and corresponded with shifts in isotopic composition that indicated large inputs of DIC from floodplains. This effect was particularly pronounced during initial flood stages. This study demonstrates that a major river with extensive floodplains in its coastal margin can act as an important source of DIC as well as a sink for DOC. In light of increased riverine carbon export due to climate change and enhanced hydrological cycling, low-lying floodplain systems such as the AR may need to be looked to in future years for the filtration and removal of organic materials, which impact coastal margins and ocean ecosystems as a whole.

Humic substances-part 7: the biogeochemistry of dissolved organic carbon and its interactions with climate change.

PubMed

Porcal, Petr; Koprivnjak, Jean-François; Molot, Lewis A; Dillon, Peter J

2009-09-01

Dissolved organic matter, measured as dissolved organic carbon (DOC), is an important component of aquatic ecosystems and of the global carbon cycle. It is known that changes in DOC quality and quantity are likely to have ecological repercussions. This review has four goals: (1) to discuss potential mechanisms responsible for recent changes in aquatic DOC concentrations; (2) to provide a comprehensive overview of the interactions between DOC, nutrients, and trace metals in mainly boreal environments; (3) to explore the impact of climate change on DOC and the subsequent effects on nutrients and trace metals; and (4) to explore the potential impact of DOC cycling on climate change. We review recent research on the mechanisms responsible for recent changes in aquatic DOC concentrations, DOC interactions with trace metals, N, and P, and on the possible impacts of climate change on DOC in mainly boreal lakes. We then speculate on how climate change may affect DOC export and in-lake processing and how these changes might alter nutrient and metal export and processing. Furthermore, the potential impacts of changing DOC cycling patterns on climate change are examined. It has been noted that DOC concentrations in lake and stream waters have increased during the last 30 years across much of Europe and North America. The potential reasons for this increase include increasing atmospheric CO(2) concentration, climate warming, continued N deposition, decreased sulfate deposition, and hydrological changes due to increased precipitation, droughts, and land use changes. Any change in DOC concentrations and properties in lakes and streams will also impact the acid-base chemistry of these waters and, presumably, the biological, chemical, and photochemical reactions taking place. For example, the interaction of trace metals with DOC may be significantly altered by climate change as organically complexed metals such as Cu, Fe, and Al are released during photo-oxidation of DOC. The production and loss of DOC as CO(2) from boreal lakes may also be affected by changing climate. Climate change is unlikely to be uniform spatially with some regions becoming wetter while others become drier. As a result, rates of change in DOC export and concentrations will vary regionally and the changes may be non-linear. Climate change models predict that higher temperatures are likely to occur over most of the boreal forests in North America, Europe, and Asia over the next century. Climate change is also expected to affect the severity and frequency of storm and drought events. Two general climate scenarios emerge with which to examine possible DOC trends: warmer and wetter or warmer and drier. Increasing temperature and hydrological changes (specifically, runoff) are likely to lead to changes in the quality and quantity of DOC export from terrestrial sources to rivers and lakes as well as changes in DOC processing rates in lakes. This will alter the quality and concentrations of DOC and its constituents as well as its interactions with trace metals and the availability of nutrients. In addition, export rates of nutrients and metals will also change in response to changing runoff. Processing of DOC within lakes may impact climate depending on the extent to which DOC is mineralized to dissolved inorganic carbon (DIC) and evaded to the atmosphere or settles as particulate organic carbon (POC) to bottom sediments and thereby remaining in the lake. The partitioning of DOC between sediments and the atmosphere is a function of pH. Decreased DOC concentrations may also limit the burial of sulfate, as FeS, in lake sediments, thereby contributing acidity to the water by increasing the formation of H(2)S. Under a warmer and drier scenario, if lake water levels fall, previously stored organic sediments may be exposed to greater aeration which would lead to greater CO(2) evasion to the atmosphere. The interaction of trace metals with DOC may be significantly altered by climate change. Iron enhances the formation of POC during irradiation of lake water with UV light and therefore may be an important pathway for transfer of allochthonous DOC to the sediments. Therefore, changing Fe/DOC ratios could affect POC formation rates. If climate change results in altered DOC chemistry (e.g., fewer and/or weaker binding sites) more trace metals could be present in their toxic and bioavailable forms. The availability of nutrients may be significantly altered by climate change. Decreased DOC concentrations in lakes may result in increased Fe colloid formation and co-incident loss of adsorbable P from the water column. Climate change expressed as changes in runoff and temperature will likely result in changes in aquatic DOC quality and concentration with concomitant effects on trace metals and nutrients. Changes in the quality and concentration of DOC have implications for acid-base chemistry and for the speciation and bioavailability of certain trace metals and nutrients. Moreover, changes in DOC, metals, and nutrients are likely to drive changes in rates of C evasion and storage in lake sediments. The key controls on allochthonous DOC quality, quantity, and catchment export in response to climate change are still not fully understood. More detailed knowledge of these processes is required so that changes in DOC and its interactions with nutrients and trace metals can be better predicted based on changes caused by changing climate. More studies are needed concerning the effects of trace metals on DOC, the effects of changing DOC quality and quantity on trace metals and nutrients, and how runoff and temperature-related changes in DOC export affect metal and nutrient export to rivers and lakes.

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.

Effect of flood events on transport of suspended sediments, organic matter and particulate metals in a forest watershed in the Basque Country (Northern Spain).

PubMed

Peraza-Castro, M; Sauvage, S; Sánchez-Pérez, J M; Ruiz-Romera, E

2016-11-01

An understanding of the processes controlling sediment, organic matter and metal export is critical to assessing and anticipating risk situations in water systems. Concentrations of suspended particulate matter (SPM), dissolved (DOC) and particulate (POC) organic carbon and metals (Cu, Ni, Pb, Cr, Zn, Mn, Fe) in dissolved and particulate phases were monitored in a forest watershed in the Basque Country (Northern Spain) (31.5km(2)) over three hydrological years (2009-2012), to evaluate the effect of flood events on the transport of these materials. Good regression was found between SPM and particulate metal concentration, making it possible to compute the load during the twenty five flood events that occurred during the study period at an annual scale. Particulate metals were exported in the following order: Fe>Mn>Zn>Cr>Pb>Cu>Ni. Annual mean loads of SPM, DOC and POC were estimated at 2267t, 104t and 57t, respectively, and the load (kg) of particulate metals at 76 (Ni), 83 (Cu), 135 (Pb), 256 (Cr), 532 (Zn), 1783 (Mn) and 95170 (Fe). Flood events constituted 91%-SPM, 65%-DOC, 71%-POC, 80%-Cu, 85%-Ni, 72%-Pb, 84%-Cr, 74%-Zn, 87%-Mn and 88%-Fe of total load exported during the three years studied. Flood events were classified into three categories according to their capacity for transporting organic carbon and particulate metals. High intensity flood events are those with high transport capacity of SPM, organic carbon and particulate metals. Most of the SPM, DOC, POC and particulate metal load was exported by this type of flood event, which contributed 59% of SPM, 45% of organic carbon and 54% of metals. Copyright © 2016 Elsevier B.V. All rights reserved.

Rising susceptibility of freshwater DOC inputs to extreme events? The implications of underlying changes in atmospheric deposition and land-management. (Invited)

NASA Astrophysics Data System (ADS)

Evans, C.; Monteith, D.; Jones, T.; Burden, A.; Peacock, M.; Gauci, V.; Page, S. E.; Moore, S.

2013-12-01

Dissolved organic carbon (DOC) represents a significant loss term within the carbon (C) balance of many terrestrial ecosystems, and a quantitatively important and reactive C input to many freshwater ecosystems. DOC concentrations have risen dramatically, over a period of decades, in rivers and lakes draining semi-natural catchments across large areas of Northern Europe and Northeast North America, with wide-ranging consequences for C cycling, aquatic ecosystem functioning and drinking water treatment. These increases have been variously attributed to climatic changes, including increased incidence of extreme events, as well as land-management factors and changes in atmospheric deposition. A growing body of evidence now indicates that the primary driver of rising DOC has been ecosystem recovery from the historic effects of acid deposition, and thus that observed increases - whilst sometimes economically problematic - may represent a return to pre-industrial baseline conditions. In light of the apparent dominance of acidity change as a driver of recent freshwater DOC increases, we consider whether or not other potential drivers of change, including climatic extremes and management-related disturbances, are likely to exert a significant influence on the transport of DOC from catchments to surface waters. We conclude that the alleviation of acidification pressures has now made catchments in regions formerly impacted by sulphur pollution much more susceptible to extreme events and disturbances. Drawing on monitoring and experimental case studies from the UK, we suggest that DOC export from organic soils may be shifting from ';solubility controlled' to ';supply controlled', and that climatic events leading to enhanced DOC production (e.g. high temperatures or drought-rewet cycles) and/or shallow lateral transport (e.g. high flow events) are now generating freshwater DOC peaks that are unprecedented in the monitoring record. We also examine the role of land-management as a control on DOC leaching, focusing on the influence of peatland drainage on sites ranging from the UK to Southeast Asia. Again, we conclude that anthropogenic modification of peat hydrology has contributed both to increases in baseline rates of DOC export, and to the enhanced susceptibility of these ecosystems to extreme events. An example is presented of the impact of an uncontrolled fire on DOC export from a drained peatland in Borneo. We develop a conceptual model of the integrated effect of multiple environmental drivers on DOC export from peats and organo-mineral soils, and consider how projected changes in these drivers might be expected to alter the supply and behaviour of freshwater DOC in future. References Evans CD, Jones TG, Burden A et al. (2012) Acidity controls on dissolved organic carbon mobility in organic soils. Global Change Biology 18, 3317-3331. Monteith DT, Stoddard JL, Evans CD et al. (2007). Rising freshwater dissolved organic carbon driven by changes in atmospheric deposition. Nature 450, 537-540. Moore S, Evans CD, Page SE et al. (2013). Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes, Nature 493, 660-664.

Hydrologic controls on DOC, As and Pb export from a polluted peatland - the importance of heavy rain events, antecedent moisture conditions and hydrological connectivity

NASA Astrophysics Data System (ADS)

Broder, T.; Biester, H.

2015-08-01

Bogs can store large amounts of lead (Pb) and arsenic (As) from atmospheric deposition of anthropogenic emissions. Pb and As are exported along with dissolved organic carbon (DOC) from these organic-rich systems, but it is not yet clear which hydrological (pre)conditions favor their export. This study combines a 1-year monitoring of precipitation, bog water level and pore water concentration changes with bog discharge and DOC, iron, As and Pb stream concentrations. From these data, annual DOC, As, and Pb exports were calculated. Concentrations ranged from 5 to 30 mg L-1 for DOC, 0.2 to 1.9 μg L-1 for As, and 1.3 to 12 μg L-1 for Pb, with highest concentrations in late summer. As and Pb concentrations significantly correlated with DOC concentrations. Fluxes depended strongly on discharge, as 40 % of As and 43 % of Pb were exported during 10 % of the time with the highest discharge, pointing out the over-proportional contribution of short-time, high-discharge events to annual As, Pb and DOC export. Exponential increase in element export from the bog is explained by connection of additional DOC, As and Pb pools in the acrotelm during water table rise, which is most pronounced after drought. Pb, As and DOC concentrations in pore water provide evidence of an increase in the soluble Pb pool as soon as the peat layer becomes hydrologically connected, while DOC and As peak concentrations in runoff lag behind in comparison to Pb. Our data indicate a distinct bog-specific discharge threshold of 8 L s-1, which is thought to depend mainly on the bogs size and drainage conditions. Above this threshold, element concentrations do not further increase and discharge becomes diluted. Combining pore water and discharge data shows that As and Pb exports are dependent on not only the amount of precipitation and discharge but also on the frequency and depth of water table fluctuations. Comparing the annual bog As and Pb export with element inventories indicates that As is much more mobilized than Pb, with annual fluxes accounting for 0.85 and 0.27 ‰ of total As and Pb inventory, respectively.

Hydrologic controls on DOC, As and Pb export from a polluted peatland - the importance of heavy rain events, antecedent moisture conditions and hydrological connectivity

NASA Astrophysics Data System (ADS)

Broder, T.; Biester, H.

2015-03-01

Bogs can store large amounts of lead (Pb) and arsenic (As) attributed to atmospheric deposition of anthropogenic emissions. Pb and As are exported along with dissolved organic carbon (DOC) in these organic-rich systems, but it is not yet clear which hydrological (pre-)conditions favor their export. This study combines one year continuous monitoring of precipitation, bog water level and pore water concentration changes with bog discharge, DOC, As and Pb stream concentrations and fluxes. Concentrations ranged from 5 to 30 mg L-1 for DOC, 0.2 to 1.9 μg L-1 for As and 1.3 to 12 μg L-1 for Pb with highest concentrations in late summer. As and Pb concentrations significantly correlated with DOC concentrations. Fluxes depended strongly on discharge, as 40% of As and 43% of Pb were exported by the upper 10% of discharge, pointing out the over-proportional contribution of heavy rain and high discharge events to annual As, Pb and DOC export. Exponential increase in element export from the bog is explained by connection of additional DOC, As and Pb pools in the acrotelm during water table rise, which is most pronounced after drought. Pb, As and DOC concentrations in pore water provide evidence of an increase of the soluble Pb pool as soon as the peat layer gets hydrologically connected, while DOC and As peak concentrations in runoff lag in comparison to Pb. Our data indicates a distinct bog-specific discharge threshold of 8 L s-1, which is thought to depend mainly on the bogs size and drainage conditions. Above this threshold element concentration do not further increase and discharge gets diluted. Combining pore water and discharge data shows that As and Pb exports are not only dependent on the amount of precipitation and discharge, but on the frequency and depth of water table fluctuations. Comparing the annual bog As and Pb export with element inventories indicates that As is much more mobilized than Pb, with annual fluxes accounting for 0.85 and 0.27‰ of total As and Pb inventory, respectively.

Toward a quantitative and empirical dissolved organic carbon budget for the Gulf of Maine, a semienclosed shelf sea

NASA Astrophysics Data System (ADS)

Balch, William; Huntington, Thomas; Aiken, George; Drapeau, David; Bowler, Bruce; Lubelczyk, Laura; Butler, Kenna

2016-02-01

A time series of organic carbon export from Gulf of Maine (GoM) watersheds was compared to a time series of biological, chemical, bio-optical, and hydrographic properties, measured across the GoM between Yarmouth, NS, Canada, and Portland, ME, U.S. Optical proxies were used to quantify the dissolved organic carbon (DOC) and particulate organic carbon in the GoM. The Load Estimator regression model applied to river discharge data demonstrated that riverine DOC export (and its decadal variance) has increased over the last 80 years. Several extraordinarily wet years (2006-2010) resulted in a massive pulse of chromophoric dissolved organic matter (CDOM; proxy for DOC) into the western GoM along with unidentified optically scattering material (<0.2 µm diameter). A survey of DOC in the GoM and Scotian Shelf showed the strong influence of the Gulf of Saint Lawrence on the DOC that enters the GoM. A deep plume of CDOM-rich water was observed near the coast of Maine which decreased in concentration eastward. The Forel-Ule color scale was derived and compared to the same measurements made in 1912-1913 by Henry Bigelow. Results show that the GoM has yellowed in the last century, particularly in the region of the extension of the Eastern Maine Coastal Current. Time lags between DOC discharge and its appearance in the GoM increased with distance from the river mouths. Algae were also a significant source of DOC but not CDOM. Gulf-wide algal primary production has decreased. Increases in precipitation and DOC discharge to the GoM are predicted over the next century.

Toward a quantitative and empirical dissolved organic carbon budget for the Gulf of Maine, a semienclosed shelf sea

USGS Publications Warehouse

Balch, William; Huntington, Thomas G.; Aiken, George R.; Drapeau, David; Bowler, Bruce; Lubelczyk, Laura; Butler, Kenna D.

2016-01-01

A time series of organic carbon export from Gulf of Maine (GoM) watersheds was compared to a time series of biological, chemical, bio-optical, and hydrographic properties, measured across the GoM between Yarmouth, NS, Canada, and Portland, ME, U.S. Optical proxies were used to quantify the dissolved organic carbon (DOC) and particulate organic carbon in the GoM. The Load Estimator regression model applied to river discharge data demonstrated that riverine DOC export (and its decadal variance) has increased over the last 80 years. Several extraordinarily wet years (2006–2010) resulted in a massive pulse of chromophoric dissolved organic matter (CDOM; proxy for DOC) into the western GoM along with unidentified optically scattering material (<0.2 μm diameter). A survey of DOC in the GoM and Scotian Shelf showed the strong influence of the Gulf of Saint Lawrence on the DOC that enters the GoM. A deep plume of CDOM-rich water was observed near the coast of Maine which decreased in concentration eastward. The Forel-Ule color scale was derived and compared to the same measurements made in 1912–1913 by Henry Bigelow. Results show that the GoM has yellowed in the last century, particularly in the region of the extension of the Eastern Maine Coastal Current. Time lags between DOC discharge and its appearance in the GoM increased with distance from the river mouths. Algae were also a significant source of DOC but not CDOM. Gulf-wide algal primary production has decreased. Increases in precipitation and DOC discharge to the GoM are predicted over the next century.

The Role of Stream Water Carbon Dynamics and Export in the Carbon Balance of a Tropical Seasonal Rainforest, Southwest China

PubMed Central

Zhou, Wen-Jun; Zhang, Yi-Ping; Schaefer, Douglas A.; Sha, Li-Qing; Deng, Yun; Deng, Xiao-Bao; Dai, Kai-Jie

2013-01-01

A two-year study (2009 ∼ 2010) was carried out to investigate the dynamics of different carbon (C) forms, and the role of stream export in the C balance of a 23.4-ha headwater catchment in a tropical seasonal rainforest at Xishuangbanna (XSBN), southwest China. The seasonal volumetric weighted mean (VWM) concentrations of total inorganic C (TIC) and dissolved inorganic C (DIC) were higher, and particulate inorganic C (PIC) and organic C (POC) were lower, in the dry season than the rainy season, while the VWM concentrations of total organic C (TOC) and dissolved organic C (DOC) were similar between seasons. With increased monthly stream discharge and stream water temperature (SWT), only TIC and DIC concentrations decreased significantly. The most important C form in stream export was DIC, accounting for 51.8% of the total C (TC) export; DOC, POC, and PIC accounted for 21.8%, 14.9%, and 11.5% of the TC export, respectively. Dynamics of C flux were closely related to stream discharge, with the greatest export during the rainy season. C export in the headwater stream was 47.1 kg C ha−1 yr−1, about 2.85% of the annual net ecosystem exchange. This finding indicates that stream export represented a minor contribution to the C balance in this tropical seasonal rainforest. PMID:23437195

The role of stream water carbon dynamics and export in the carbon balance of a tropical seasonal rainforest, southwest China.

PubMed

Zhou, Wen-Jun; Zhang, Yi-Ping; Schaefer, Douglas A; Sha, Li-Qing; Deng, Yun; Deng, Xiao-Bao; Dai, Kai-Jie

2013-01-01

A two-year study (2009 ~ 2010) was carried out to investigate the dynamics of different carbon (C) forms, and the role of stream export in the C balance of a 23.4-ha headwater catchment in a tropical seasonal rainforest at Xishuangbanna (XSBN), southwest China. The seasonal volumetric weighted mean (VWM) concentrations of total inorganic C (TIC) and dissolved inorganic C (DIC) were higher, and particulate inorganic C (PIC) and organic C (POC) were lower, in the dry season than the rainy season, while the VWM concentrations of total organic C (TOC) and dissolved organic C (DOC) were similar between seasons. With increased monthly stream discharge and stream water temperature (SWT), only TIC and DIC concentrations decreased significantly. The most important C form in stream export was DIC, accounting for 51.8% of the total C (TC) export; DOC, POC, and PIC accounted for 21.8%, 14.9%, and 11.5% of the TC export, respectively. Dynamics of C flux were closely related to stream discharge, with the greatest export during the rainy season. C export in the headwater stream was 47.1 kg C ha(-1) yr(-1), about 2.85% of the annual net ecosystem exchange. This finding indicates that stream export represented a minor contribution to the C balance in this tropical seasonal rainforest.

Fluvial carbon export from a lowland Amazonian rainforest in relation to atmospheric fluxes

NASA Astrophysics Data System (ADS)

Vihermaa, Leena E.; Waldron, Susan; Domingues, Tomas; Grace, John; Cosio, Eric G.; Limonchi, Fabian; Hopkinson, Chris; da Rocha, Humberto Ribeiro; Gloor, Emanuel

2016-12-01

We constructed a whole carbon budget for a catchment in the Western Amazon Basin, combining drainage water analyses with eddy covariance (EC) measured terrestrial CO2 fluxes. As fluvial C export can represent permanent C export it must be included in assessments of whole site C balance, but it is rarely done. The footprint area of the flux tower is drained by two small streams ( 5-7 km2) from which we measured the dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate organic carbon (POC) export, and CO2 efflux. The EC measurements showed the site C balance to be +0.7 ± 9.7 Mg C ha-1 yr-1 (a source to the atmosphere) and fluvial export was 0.3 ± 0.04 Mg C ha-1 yr-1. Of the total fluvial loss 34% was DIC, 37% DOC, and 29% POC. The wet season was most important for fluvial C export. There was a large uncertainty associated with the EC results and with previous biomass plot studies (-0.5 ± 4.1 Mg C ha-1 yr-1); hence, it cannot be concluded with certainty whether the site is C sink or source. The fluvial export corresponds to only 3-7% of the uncertainty related to the site C balance; thus, other factors need to be considered to reduce the uncertainty and refine the estimated C balance. However, stream C export is significant, especially for almost neutral sites where fluvial loss may determine the direction of the site C balance. The fate of C downstream then dictates the overall climate impact of fluvial export.

Contrasting vulnerability of drained tropical and high-latitude peatlands to fluvial loss of stored carbon

NASA Astrophysics Data System (ADS)

Evans, Chris D.; Page, Susan E.; Jones, Tim; Moore, Sam; Gauci, Vincent; Laiho, Raija; Hruška, Jakub; Allott, Tim E. H.; Billett, Michael F.; Tipping, Ed; Freeman, Chris; Garnett, Mark H.

2014-11-01

Carbon sequestration and storage in peatlands rely on consistently high water tables. Anthropogenic pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of peat-forming vegetation and exposure of previously anaerobic peat to aerobic decomposition. This can shift peatlands from net CO2 sinks to large CO2 sources, releasing carbon held for millennia. Peatlands also export significant quantities of carbon via fluvial pathways, mainly as dissolved organic carbon (DOC). We analyzed radiocarbon (14C) levels of DOC in drainage water from multiple peatlands in Europe and Southeast Asia, to infer differences in the age of carbon lost from intact and drained systems. In most cases, drainage led to increased release of older carbon from the peat profile but with marked differences related to peat type. Very low DOC-14C levels in runoff from drained tropical peatlands indicate loss of very old (centuries to millennia) stored peat carbon. High-latitude peatlands appear more resilient to drainage; 14C measurements from UK blanket bogs suggest that exported DOC remains young (<50 years) despite drainage. Boreal and temperate fens and raised bogs in Finland and the Czech Republic showed intermediate sensitivity. We attribute observed differences to physical and climatic differences between peatlands, in particular, hydraulic conductivity and temperature, as well as the extent of disturbance associated with drainage, notably land use changes in the tropics. Data from the UK Peak District, an area where air pollution and intensive land management have triggered Sphagnum loss and peat erosion, suggest that additional anthropogenic pressures may trigger fluvial loss of much older (>500 year) carbon in high-latitude systems. Rewetting at least partially offsets drainage effects on DOC age.

Dissolved organic carbon in the carbon cycle of the Indian Ocean

NASA Astrophysics Data System (ADS)

Hansell, Dennis A.

Dissolved organic carbon (DOC) is one of the least quantified and least understood bioreactive pools of carbon in the Indian Ocean. Data gaps are large, with much of the central Indian Ocean not yet sampled. Here model results depict the surface distribution of DOC, which is interpreted in terms of anticipated net DOC production (13-26 Tmol C a-1), advective transport, and export to the subsurface with overturning circulation. These interpretations are tested against DOC measurements made on sections in the Arabian Sea, across the Agulhas Current, in the central Indian Ocean, and into the Bay of Bengal. The seasonality of net DOC production and consumption is evaluated in the Arabian Sea, where data density is relatively rich. DOC stocks in the upper 150 m of the western Arabian Sea increased by >1.5 mol C m-2 during the NE monsoon and disappeared rapidly during the SW monsoon. Rapid DOC removal may result in part from aggregation of dust and biogenic particles along with stripping of trace metals and DOC, perhaps as transparent exopolymer particles, from the surrounding waters.

Sunlight Controls Water Column Processing of Carbon in Arctic Freshwaters

NASA Astrophysics Data System (ADS)

Cory, R. M.; Ward, C. P.; Crump, B. C.; Kling, G. W.

2014-12-01

Carbon (C) in thawing permafrost soils may have global impacts on climate change, yet controls on its processing and fate are poorly understood. The dominant fate of dissolved organic C (DOC) released from soils to inland waters is either complete oxidation to CO2 or partial oxidation and river export to oceans. Both processes are most often attributed to bacterial respiration, but we recently showed that photochemical oxidation exceeds rates of respiration and accounts for 70-95% of total DOC processed in the water column of arctic lakes and rivers. While the overall dominance of photochemical processing in streams and lakes remained, the fate of DOC varied consistently by water type. In small streams DOC was mainly mineralized by sunlight to CO2, while in lakes the main fate of DOC was partial photo-oxidation. Large rivers were intermediate between these end members, and photo-mineralization to CO2 was about equal to or less than partial photo-oxidation. We suggest this pattern is a result of light-exposure history, where DOC leached from soils into headwater streams has little prior light exposure and is labile to complete photo-oxidation, but as light exposure increases moving downstream and into lakes with longer residence times the DOC photo-lability declines. Thus as easily photo-mineralized moieties are removed, DOC fate shifts toward partial photo-oxidation and downstream export in rivers and lakes. At the basin scale, photochemical processing of DOC is about one third of the total CO2 released from surface waters, and is thus an important, newly measured component of the Arctic C budget. We also suggest that these photochemical transformations of DOC will occur in any shallow surface water, and could be important for better understanding inland water carbon cycling.

Drought causes step-changes in catchment-scale carbon export from peatland catchments

NASA Astrophysics Data System (ADS)

Howden, Nicholas; Worrall, Fred; Burt, Tim

2015-04-01

Increases in fluvial DOC concentrations in world rivers, particularly those that drain areas of peatland, have been observed for some years, suggesting an increase in carbon loss from the terrestrial biosphere. But it has not been straightforward to identify what causes these increases due to a lack of long-term time series to characterise both observed DOC concentrations and potential drivers. The York Waterworks Company (York, UK) abstracted drinking water from the Yorkshire Ouse just upstream of the city from the late 1800s until 2002. During the period August 1945 to December 2002, records of monthly-average DOC concentrations were kept (using water colour as a surrogate). From January 2003 onwards, the Environment Agency of England and Wales (EA) continued the monitoring, thus providing a 68-year record of monthly-average DOC concentrations in the Yorkshire Ouse, which is the longest DOC time series ever reported for a catchment with significant peat cover. We use the Yorkshire Ouse DOC record to develop a new method that shows how changes in DOC concentration and river flow have influenced carbon fluxes in the Ouse for the latter half of the 20th century and show that the only major changes in DOC flux are caused by step-increases in concentration following severe drought. We then use this method to identify a similar effect in other DOC records for UK rivers. The results suggest that increases in DOC export are due more to discrete events than to the impact of continuous drivers (such as increasing temperatures or changing atmospheric deposition), and also show these increases not to be reversed for at least four decades.

Hydrology or biology? Modeling simplistic physical constraints on lake carbon biogeochemistry to identify when and where biology is likely to matter

NASA Astrophysics Data System (ADS)

Jones, S.; Zwart, J. A.; Solomon, C.; Kelly, P. T.

2017-12-01

Current efforts to scale lake carbon biogeochemistry rely heavily on empirical observations and rarely consider physical or biological inter-lake heterogeneity that is likely to regulate terrestrial dissolved organic carbon (tDOC) decomposition in lakes. This may in part result from a traditional focus of lake ecologists on in-lake biological processes OR physical-chemical pattern across lake regions, rather than on process AND pattern across scales. To explore the relative importance of local biological processes and physical processes driven by lake hydrologic setting, we created a simple, analytical model of tDOC decomposition in lakes that focuses on the regulating roles of lake size and catchment hydrologic export. Our simplistic model can generally recreate patterns consistent with both local- and regional-scale patterns in tDOC concentration and decomposition. We also see that variation in lake hydrologic setting, including the importance of evaporation as a hydrologic export, generates significant, emergent variation in tDOC decomposition at a given hydrologic residence time, and creates patterns that have been historically attributed to variation in tDOC quality. Comparing predictions of this `biologically null model' to field observations and more biologically complex models could indicate when and where biology is likely to matter most.

Dissolved inorganic and organic carbon yields and fluxes in a permafrost catchment on the Qinghai-Tibet Plateau

NASA Astrophysics Data System (ADS)

Wang, G.; Mao, T.; Zhang, T.; Chen, X.

2015-12-01

Riverine transport of carbon from terrestrial to the aquatic ecosystems is an important component of the global carbon cycle. A warming climate can inevitably accelerate the microbial breakdown of organic carbon and the release of carbon dioxide especially in frozen soils (permafrost) within Arctic and sub-Arctic regions. In addition, high hydraulic conductivity and low sorption capacity of the shallow soil active layer overlying impermeable permafrost together lead to quick DOM transport to streams. In different regions, the response of dissolved carbon to climate warming is different due to the differences in hydrology, climatic conditions, soil types, vegetation conditions, permafrost distribution, catchment size, flow paths. The Qinghai-Tibet Plateau (QTP), of which a significant portion is underlain by permafrost, is considered to be more sensitive to climatic warming than other regions. However, the knowledge of dissolved inorganic and organic carbon transport in the QTP is very limited. We compared the yields and fluxes of DIC/DOC in a small tropical permafrost catchment. Our results showed that: (1) the concentrations ranged from 7.8 to 30.9 mg L-1 for the DIC and ranged from 2.3 to 6.4 mg L-1 for the DOC, the ratio of DIC/DOC concentrations ranged from 2.2 to 5.7 with a mean value of 4.3; (2) the annual export approximately 3.56 t km-2 year-1 for the DIC and 0.73 t km-2 year-1 for the DOC, indicating that the dissolved carbon transported in majority under the inorganic form; (3) the seasonal variations in DIC/DOC export are strongly regulated by variability in runoff, meanwhile the concentration of DIC/DOC showed significant positive correlation with the thawing depth of the active layer and vegetation coverage. Our results provided an understanding about the characteristics of riverine dissolved carbons transport at a permafrost catchment scale on the QTP.

Export of dissolved carbonaceous and nitrogenous substances in rivers of the "Water Tower of Asia".

PubMed

Qu, Bin; Sillanpää, Mika; Kang, Shichang; Yan, Fangping; Li, Zhiguo; Zhang, Hongbo; Li, Chaoliu

2018-03-01

Rivers are critical links in the carbon and nitrogen cycle in aquatic, terrestrial, and atmospheric environments. Here riverine carbon and nitrogen exports in nine large rivers on the Tibetan Plateau - the "Water Tower of Asia" - were investigated in the monsoon season from 2013 to 2015. Compared with the world average, concentrations of dissolved inorganic carbon (DIC, 30.7mg/L) were high in river basins of the plateau due to extensive topographic relief and intensive water erosion. Low concentrations of dissolved organic carbon (DOC, 1.16mg/L) were likely due to the low temperature and unproductive land vegetation environments. Average concentrations of riverine DIN (0.32mg/L) and DON (0.35 mg/L) on the Tibetan Plateau were close to the world average. However, despite its predominantly pristine environment, discharge from agricultural activities and urban areas of the plateau has raised riverine N export. In addition, DOC/DON ratio (C/N, ~6.5) in rivers of the Tibetan Plateau was much lower than the global average, indicating that dissolved organic carbon in the rivers of this region might be more bioavailable. Therefore, along with global warming and anthropogenic activities, increasing export of bioavailable riverine carbon and nitrogen from rivers of the Tibetan Plateau can be expected in the future, which will possibly influence the regional carbon and nitrogen cycle. Copyright © 2017. Published by Elsevier B.V.

Photochemical alteration of organic carbon draining permafrost soils shifts microbial metabolic pathways and stimulates respiration.

PubMed

Ward, Collin P; Nalven, Sarah G; Crump, Byron C; Kling, George W; Cory, Rose M

2017-10-03

In sunlit waters, photochemical alteration of dissolved organic carbon (DOC) impacts the microbial respiration of DOC to CO 2 . This coupled photochemical and biological degradation of DOC is especially critical for carbon budgets in the Arctic, where thawing permafrost soils increase opportunities for DOC oxidation to CO 2 in surface waters, thereby reinforcing global warming. Here we show how and why sunlight exposure impacts microbial respiration of DOC draining permafrost soils. Sunlight significantly increases or decreases microbial respiration of DOC depending on whether photo-alteration produces or removes molecules that native microbial communities used prior to light exposure. Using high-resolution chemical and microbial approaches, we show that rates of DOC processing by microbes are likely governed by a combination of the abundance and lability of DOC exported from land to water and produced by photochemical processes, and the capacity and timescale that microbial communities have to adapt to metabolize photo-altered DOC.The role of dissolved organic carbon (DOC) photo-alteration in the microbial respiration of DOC to CO 2 is unclear. Here, the authors show that the impact of this mechanism depends on whether photo-alteration of DOC produces or removes molecules used by native microbial communities prior to light exposure.

Anthropogenic and climatic influences on carbon fluxes from eastern North America to the Atlantic Ocean: A process-based modeling study

NASA Astrophysics Data System (ADS)

Tian, Hanqin; Yang, Qichun; Najjar, Raymond G.; Ren, Wei; Friedrichs, Marjorie A. M.; Hopkinson, Charles S.; Pan, Shufen

2015-04-01

The magnitude, spatiotemporal patterns, and controls of carbon flux from land to the ocean remain uncertain. Here we applied a process-based land model with explicit representation of carbon processes in streams and rivers to examine how changes in climate, land conversion, management practices, atmospheric CO2, and nitrogen deposition affected carbon fluxes from eastern North America to the Atlantic Ocean, specifically the Gulf of Maine (GOM), Middle Atlantic Bight (MAB), and South Atlantic Bight (SAB). Our simulation results indicate that the mean annual fluxes (±1 standard deviation) of dissolved organic carbon (DOC), particulate organic carbon (POC), and dissolved inorganic carbon (DIC) in the past three decades (1980-2008) were 2.37 ± 0.60, 1.06 ± 0.20, and 3.57 ± 0.72 Tg C yr-1, respectively. Carbon export demonstrated substantial spatial and temporal variability. For the region as a whole, the model simulates a significant decrease in riverine DIC fluxes from 1901 to 2008, whereas there were no significant trends in DOC or POC fluxes. In the SAB, however, there were significant declines in the fluxes of all three forms of carbon, and in the MAB subregion, DIC and POC fluxes declined significantly. The only significant trend in the GOM subregion was an increase in DIC flux. Climate variability was the primary cause of interannual variability in carbon export. Land conversion from cropland to forest was the primary factor contributing to decreases in all forms of C export, while nitrogen deposition and fertilizer use, as well as atmospheric CO2 increases, tended to increase DOC, POC, and DIC fluxes.

Assessing Environmental Drivers of DOC Fluxes in the Shark River Estuary: Modeling the Effects of Climate, Hydrology and Water Management

NASA Astrophysics Data System (ADS)

Regier, P.; Briceno, H.; Jaffe, R.

2016-02-01

Urban and agricultural development of the South Florida peninsula has disrupted freshwater flow in the Everglades, a hydrologically connected ecosystem stretching from central Florida to the Gulf of Mexico. Current system-scale restoration efforts aim to restore natural hydrologic regimes to reestablish pre-drainage ecosystem functioning through increased water availability, quality and timing. However, it is uncertain how hydrologic restoration combined with climate change will affect the downstream section of the system, including the mangrove estuaries of Everglades National Park. Aquatic transport of carbon, primarily as dissolved organic carbon (DOC), plays a critical role in biogeochemical cycling and food-web dynamics, and will be affected both by water management policies and climate change. To better understand DOC dynamics in these estuaries and how hydrology, climate and water management may affect them, 14 years of monthly data collected in the Shark River estuary were used to build a DOC flux model. Multi-variate methods were applied to long-term data-sets for hydrology, water quality and climate to untangle the interconnected environmental drivers that control DOC export at intra and inter-annual scales. DOC fluxes were determined to be primarily controlled by hydrology but also by seasonality and long-term climate patterns. Next, a 4-component model (salinity, inflow, rainfall, Atlantic Multidecadal Oscillation) capable of predicting DOC fluxes (R2=0.78, p<0.0001, n=161) was established. Finally, potential climate change scenarios for the Everglades were applied to this model to assess DOC flux variations in response to climate and restoration variables. Although global predictions anticipate that DOC export will generally increase in the future, the majority of scenario runs indicated that DOC export from the Everglades is expected to decrease due to changes in rainfall, evapotranspiration, inflows and sea-level rise.

Biodegradability of dissolved organic carbon in the Yukon River and its tributaries: Seasonality and importance of inorganic nitrogen

USGS Publications Warehouse

Wickland, Kimberly P.; Aiken, George R.; Butler, Kenna D.; Dornblaser, Mark M.; RGM Spencer,; Striegl, Robert G.

2012-01-01

Northern high-latitude rivers transport large amounts of terrestrially derived dissolved organic matter (DOM) from boreal and arctic ecosystems to coastal areas and oceans. Current knowledge of the biodegradability of DOM in these rivers is limited, particularly for large rivers discharging to the Arctic Ocean. We conducted a seasonally comprehensive study of biodegradable dissolved organic carbon (BDOC) dynamics in the Yukon River and two of its tributaries in Alaska, USA. Distinct seasonal patterns of BDOC, consistent across a wide range of watershed size, indicate BDOC is transported year-round. Relative biodegradability (%BDOC) was greatest during winter, and decreased into spring and summer. Due to large seasonal differences in DOC concentration, the greatest concentrations of BDOC (mg C L−1) occurred during spring freshet, followed by winter and summer. While chemical composition of DOM was an important driver of BDOC, the overriding control of BDOC was mineral nutrient availability due to wide shifts in carbon (C) and nitrogen (N) stoichiometry across seasons. We calculated seasonal and annual loads of BDOC exported by the Yukon River by applying measured BDOC concentrations to daily water discharge values, and also by applying an empirical correlation between %BDOC and the ratio of DOC to dissolved inorganic N (DIN) to total DOC loads. The Yukon River exports ∼0.2 Tg C yr−1 as BDOC that is decomposable within 28 days. This corresponds to 12–18% of the total annual DOC export. Furthermore, we calculate that the six largest arctic rivers, including the Yukon River, collectively export ∼2.3 Tg C yr−1 as BDOC to the Arctic Ocean.

Hydrologic and forest management controls on DOC dynamics in the small watersheds of the H.J. Andrews Experimental Forest, OR

NASA Astrophysics Data System (ADS)

Lajtha, K.; Jones, J. A.

2016-12-01

Dissolved organic carbon (DOC) export from hillslopes to streams is an important component of the carbon cycle of a catchment and may be a critical source of energy for the aquatic food web in receiving waters. Using a long-term record of DOC and other dissolved nutrients and elements from paired watersheds from the H.J. Andrews Experimental Forest in Oregon, we explored hydrologic, climatic, and land-use controls on seasonal and inter-annual patterns of DOC flux in a seasonally dry ecosystem. Seasonal patterns of DOC flux demonstrated source limitations to DOC export, with DOC concentrations highest immediately following the first rains after a dry summer, and lowest after winter rains. In contrast, more geochemically-controlled elements showed simple dilution-concentration patterns with no seasonal hysteresis. Inter-annual patterns of DOC flux, however, did not provide evidence of source limitation, with DOC flux within a watershed tightly correlated to total discharge but not temperature. Among watersheds, forest harvest, even over 50 years ago, significantly reduced DOC flux but not fluxes of other elements including N; this response was linked to the loading of coarse woody debris to the forest floor. Chemical fingerprinting of DOC revealed that old-growth watersheds had higher fluxes of DOC characteristic of forest floor organic materials, likely delivered to streams through more surficial preferential flow pathways not subject to microbial alteration, respiration, or sorption losses. Taken together these results suggest that the biogeochemical composition of forested streams reflects both current hydrologic patterns and also processes that occurred many decades ago within the catchment.

High-resolution analysis of the terrestrial influence on DOC and POC export in a Siberian Arctic River during the spring freshet

NASA Astrophysics Data System (ADS)

Myers-Pigg, A.; Teisserenc, R.; Tananaev, N.; Louchouarn, P.

2015-12-01

Arctic Rivers transport vast amounts of terrestrial organic material (TOM) to the Arctic Ocean. The Yenisei River delivers ~18% of total dissolved organic carbon (DOC) exported to the Arctic Ocean each year during peak river discharge (May-June), known as the spring freshet. Previously published DOC fluxes for the freshet period extrapolate from relatively few data points, due to the uniquely difficult sampling conditions during this dynamic period. Here, we present new high resolution data collected from an extensive sampling campaign from April-July 2014 using a reverse osmosis system for DOC isolation. The similarity between the calculated DOC load delivered during the 2014 freshet (2.94 TgC) and the ten-year average from the previous decade (2.92 TgC for 1999-2008) validates the methodological approach used here. In contrast, the total measured load of polymeric lignin phenols (∑8: 643 Gg), an indicator of TOM input, was one order of magnitude higher than a previously estimated load (42 Gg) for May-June. Hence, we may need to re-evaluate the magnitude of terrestrial carbon exported, including the efficiencies of different sampling methods. Additionally, we present the first simultaneous particulate and dissolved lignin analyses in a major Arctic river. Approximately 30% of the total lignin flux in the Yenisei River is delivered in the particulate phase. Particulate lignin export is decoupled from dissolved lignin during the freshet; the initial flush is dominated by dissolved lignin, while the latter portion of the freshet is dominated by particulate lignin. The chemical signatures of lignin in both phases are similar throughout the freshet, suggesting a mobilization of the same source of carbon each spring. This conclusion is at odds with reported isotopic sources signatures (14C age) of bulk organic matter and lignin in these rivers, requiring a multi-faceted approach to fully understand the sources and ages of terrestrial organic matter in Arctic rivers.

How Population Growth and Land-Use Change Increased Fluvial Dissolved Organic Carbon Fluxes over 130 Years in the Thames Basin (UK)

NASA Astrophysics Data System (ADS)

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

2015-12-01

This study investigates drivers of changing dissolved organic carbon (DOC) export in the UK's River Thames basin between 1884 and 2014. Specifically, we consider how the impacts of land-use change and population growth drive increases in DOC concentrations and fluxes at the basin outlet. Such key factors for the long-term increase in riverine DOC in temperate, mineral-soil catchments are still widely debated. First, we estimate soil organic carbon (SOC) stocks in the Thames basin for the period. Second, we convert SOC losses due to land-use change into DOC loss to surface waters through runoff. Finally, we combine this input of DOC with an export coefficient model that considers catchment drivers for DOC release to the river. SOC stocks for each year are calculated from a large database of typical SOC levels for land-uses present in the Thames basin and are combined with literature values of transition times for SOC to adjust to a new level following land-use change. We also account for climate change effects on SOC stock due to temperature increases, which reduces SOC stocks as soil organic matter turnover rates increase. Our work shows that the major driver for DOC increase to the river Thames was the rise in the catchment population, where the increase in urban area was used as a proxy. This highlights the role of sewage effluent in contributing to the rise of fluvial DOC, even though wastewater treatments were in place since the early 1990s. Land-use change had significant but short-term impacts in the increase in DOC, mainly due to massive conversion of permanent grassland into arable land during World War II.

Landscape scale controls on the vascular plant component of dissolved organic carbon across a freshwater delta

USGS Publications Warehouse

Eckard, Robert S.; Hernes, Peter J.; Bergamaschi, Brian A.; Stepanauskas, Ramunas; Kendall, Carol

2007-01-01

Lignin phenol concentrations and compositions were determined on dissolved organic carbon (DOC) extracts (XAD resins) within the Sacramento-San Joaquin River Delta (the Delta), the tidal freshwater portion of the San Francisco Bay Estuary, located in central California, USA. Fourteen stations were sampled, including the following habitats and land-use types: wetland, riverine, channelized waterway, open water, and island drains. Stations were sampled approximately seasonally from December, 1999 through May, 2001. DOC concentrations ranged from 1.3 mg L-1 within the Sacramento River to 39.9 mg L-1 at the outfall from an island drain (median 3.0 mg L-1), while lignin concentrations ranged from 3.0 μL-1 within the Sacramento River to 111 μL-1 at the outfall from an island drain (median 11.6 μL-1). Both DOC and lignin concentrations varied significantly among habitat/land-use types and among sampling stations. Carbon-normalized lignin yields ranged from 0.07 mg (100 mg OC)-1 at an island drain to 0.84 mg (100 mg OC)-1 for a wetland (median 0.36 mg (100 mg OC)-1), and also varied significantly among habitat/land-use types. A simple mass balance model indicated that the Delta acted as a source of lignin during late autumn through spring (10-83% increase) and a sink for lignin during summer and autumn (13-39% decrease). Endmember mixing models using S:V and C:V signatures of landscape scale features indicated strong temporal variation in sources of DOC export from the Delta, with riverine source signatures responsible for 50% of DOC in summer and winter, wetland signatures responsible for 40% of DOC in summer, winter, and late autumn, and island drains responsible for 40% of exported DOC in late autumn. A significant negative correlation was observed between carbon-normalized lignin yields and DOC bioavailability in two of the 14 sampling stations. This study is, to our knowledge, the first to describe organic vascular plant DOC sources at the level of localized landscape features, and is also the first to indicate a significant negative correlation between lignin and DOC bioavailability within environmental samples. Based upon observed trends: (1) Delta features exhibit significant spatial variability in organic chemical composition, and (2) localized Delta features appear to exert strong controls on terrigenous DOC as it passes through the Delta and is exported into the Pacific Ocean.

Characterizing dissolved organic carbon concentrations and export in a boreal forest-peatland landscape under the influence of rapidly degrading discontinuous permafrost

NASA Astrophysics Data System (ADS)

Hanisch, J.; Connon, R.; Templeton, M.; Quinton, W. L.; Olefeldt, D.; Moore, T. R.; Roulet, N. T.; Sonnentag, O.

2014-12-01

Our current understanding of peatland energy, water and carbon (C) cycles implies that northern peatlands are vulnerable to projected climate change, and that the perturbation of these cycles might cause a strong positive or negative net feedback to the climate system. About one third of Canada's northern peatlands contain contain perennialy frozen ground (permafrost). Boreal forest-peatland ecosystems in the discontinuous permafrost zone (50-90% of frozen ground) are especially vulnerable to rising temperatures as permafrost is ice-rich, relatively warm and thin, and thus susceptible to complete disappearance causing ground surface subsidence and a decline in forest cover in response to water-logging. Several recent studies have substantially improved our understanding of northern peatland's role in the climate system by quantifying their net ecosystem C balance which includes atmospheric and aqueous C fluxes generally dominated by the export of dissolved organic C (DOC). We characterize seasonal and diurnal variations in DOC export from five catchments (0.02-0.05 km2) at Scotty Creek, a 152 km2-watershed under the influence of rapidly degrading and disappearing discontinuous permafrost near Fort Simpson, Northwest Territories, Canada. The five catchments are characterized by different fractions of forested peat plateaus with permafrost (38-73%) and permafrost-free collapse bogs (27-62%). Dissolved organic carbon concentrations at Scotty Creek appear to be higher in catchments where the percentage of peat plateaus is higher compared to bogs, independent of catchment size. Average DOC concentration for catchments with a lower percentage of peat plateaus is lower (~43 mg/l) than for those with a higher percentage of plateaus (~60 mg/l). These preliminary results suggest that lateral C losses from this rapidly changing landscape are at least partly controlled by the peat plateau-bog ratio. Over the year, DOC export from the five catchments is limited to around a week due to the relatively dry conditions at Scotty Creek over the hot summer months: only one of the catchments produces continuous measurable surface runoff. However, as indicated through water level recordings, additional unaccounted DOC export may occur through diffuse subsurface flow.

Investigating Forest Harvest Effects on DOC Concentration and Quality: An In Situ, High Resolution Approach to Quantifying DOC Export Dynamics

NASA Astrophysics Data System (ADS)

Jollymore, A. J.; Johnson, M. S.; Hawthorne, I.

2013-12-01

Justification: Forest harvest effects on water quality can signal alterations in hydrologic and ecologic processes incurred as a result of forest harvest activities. Organic matter (OM), specifically dissolved organic carbon (DOC), plays a number of important roles mediating UV-light penetration, redox reactivity and microbial activity within aquatic ecosystems. Quantification of DOC is typically pursued via grab sampling followed by chemical or spectrophotometric analysis, limiting the temporal resolution obtained as well as the accuracy of export calculations. The advent of field-deployable sensors capable of measuring DOC concentration and certain quality characteristics in situ provides the ability to observe dynamics at temporal scales necessary for accurate calculation of DOC flux, as well as the observation of dynamic changes in DOC quality on timescales impossible to observe through grab sampling. Methods: This study utilizes a field deployable UV-Vis spectrophotometer (spectro::lyzer, s::can, Austria) to investigate how forest harvest affects DOC export. The sensor was installed at an existing hydrologic monitoring site at the outlet of a headwater stream draining a small (91 hectare) second growth Douglasfir-dominated catchment near Campbell River on Vancouver Island, British Columbia. Measurement began late in 2009, prior to forest harvest and associated activities such as road building (which commenced in October 2010 and ended in early 2011), and continues to present. During this time - encompassing the pre, during and post-harvest conditions - the absorbance spectrum of stream water from 200 to 750 nm was measured. DOC concentration and spectroscopic indices related to DOC quality (including SUVA, which relates to the concentration of aromatic carbon, and spectral slope) were subsequently calculated for each spectra obtained at 30-minute intervals. Results and conclusions: High frequency measurements of DOC show that overall export of OM increased in the months following harvest. A major advantage of this study is the use of in situ measurements, allowing for high temporal resolution of DOC dynamics occurring within specific hydrologic events. For example, concentration-discharge relationships for both the pre- and post-logging periods demonstrate similar clockwise hysteresis during individual storm events, while the magnitude of change dramatically increased during the post-logging period. However, in situ measurements of SUVA over this period suggest that DOC quality may be less affected by forest harvest than overall DOC concentration, where high frequency data also allows for the observation of SUVA and spectral slope responses to specific hydrologic events during the pre- and post- harvest period.

Sources, bioavailability, and photoreactivity of dissolved organic carbon in the Sacramento-San Joaquin River Delta

USGS Publications Warehouse

Stepanauskas, R.; Moran, M.A.; Bergamaschi, B.A.; Hollibaugh, J.T.

2005-01-01

We analyzed bioavailability, photoreactivity, fluorescence, and isotopic composition of dissolved organic carbon (DOC) collected at 13 stations in the Sacramento-San Joaquin River Delta during various seasons to estimate the persistence of DOC from diverse shallow water habitat sources. Prospective large-scale wetland restorations in the Delta may change the amount of DOC available to the food web as well as change the quality of Delta water exported for municipal use. Our study indicates that DOC contributed by Delta sources is relatively refractory and likely mostly the dissolved remnants of vascular plant material from degrading soils and tidal marshes rather than phytoplankton production. Therefore, the prospective conversion of agricultural land into submerged, phytoplankton-dominated habitats may reduce the undesired export of DOC from the Delta to municipal users. A median of 10% of Delta DOC was rapidly utilizable by bacterioplankton. A moderate dose of simulated solar radiation (286 W m-2 for 4 h) decreased the DOC bioavailability by an average of 40%, with a larger relative decrease in samples with higher initial DOC bioavailability. Potentially, a DOC-based microbial food web could support ???0.6 ?? 109 g C of protist production in the Delta annually, compared to ???17 ?? 109 g C phytoplankton primary production. Thus, DOC utilization via the microbial food web is unlikely to play an important role in the nutrition of Delta zooplankton and fish, and the possible decrease in DOC concentration due to wetland restoration is unlikely to have a direct effect on Delta fish productivity. ?? Springer 2005.

Riverine export of dissolved organic carbon to the Gulf of Maine

NASA Astrophysics Data System (ADS)

Huntington, T. G.; Aiken, G.

2013-12-01

Land-to-sea carbon transport of dissolved organic carbon (DOC) is an important part of the carbon cycle that can affect long-term carbon sequestration, satellite-derived ocean color metrics, and ocean primary productivity and biogeochemistry. Using continuous discharge data and discrete sampling we estimated DOC fluxes from rivers covering about 68% of the watershed that drains to the Gulf of Maine (GoM) for water years (October through September) 2011 and 2012. Estimates for rivers entering the GoM in the USA were made using LOADEST regression software that fits a seasonally-adjusted concentration discharge relation to the data. The basin area-weighted 95% confidence limits about the LOADEST mean fluxes averaged 8.1% for the lower limit and 8.9% for the upper limit. Estimates for rivers entering the GoM in Canada were obtained from previously published estimates. Carbon yield tends to increase from southwest (35 to 36 kg C/ha/yr) to a maximum of 76 kg C/ha/yr for the Penobscot River and then decline further to the northeast (61 kg C/ha/yr in the St. John River and 41 kg C/ha/yr in the rest of New Brunswick and Nova Scotia). The area-weighted average carbon yield for all measured basins was 54.5 kg C/ha/yr. The variation in carbon yield is most closely associated with the amount of runoff and wetland area within a river basin. Simple area-weighted extrapolation to the entire GoM basin resulted in an estimate of 9.8 x 105 metric tons C per year for the WY2011 and WY2012 period. Runoff is the dominant control on intra and inter-annual variation in DOC flux because runoff varies much more than DOC concentration at these temporal scales. Runoff is usually low during the winter, peaks in the spring during snowmelt, decreases to a minimum in late summer and increases again in the fall when transpiration decreases. DOC concentration is low during the winter and snowmelt-dominated spring period, generally increases through the summer, and peaks during the fall. DOC flux to the GoM is characterized by low fluxes in winter, high fluxes during the spring snowmelt and before major increase in transpiration, lower fluxes during summer months and, increasing fluxes in the fall. The increase in spring DOC flux occurs earliest in the major river basins in the southwest and progressively later towards the northeast. Assuming that the seasonally adjusted DOC concentration discharge relationships we obtained have been stable over time we estimated fluxes using historical runoff data to assess potential changes in DOC export from five large river basins with long-term discharge data to the GoM since 1930 (St Croix, Penobscot, Androscoggin, Saco and Merrimack Rivers). DOC export has apparently been increasing over time in association with increasing runoff. The largest increases in DOC in absolute and percentage terms have occurred during October, November, and December. Increases were observed in all months except May when there was a small decrease. The decrease in May and increases in March and April are consistent with earlier snowmelt and earlier onset of transpiration.

Linking aboveground net primary productivity to soil carbon and dissolved organic carbon in complex terrain

NASA Astrophysics Data System (ADS)

Peterson, Fox S.; Lajtha, Kate J.

2013-07-01

Factors influencing soil organic matter (SOM) stabilization and dissolved organic carbon (DOC) content in complex terrain, where vegetation, climate, and topography vary over the scale of a few meters, are not well understood. We examined the spatial correlations of lidar and geographic information system-derived landscape topography, empirically measured soil characteristics, and current and historical vegetation composition and structure versus SOM fractions and DOC pools and leaching on a small catchment (WS1) in the H.J. Andrews Experimental Forest, located in the western Cascades Range of Oregon, USA. We predicted that aboveground net primary productivity (ANPP), litter fall, and nitrogen mineralization would be positively correlated with SOM, DOC, and carbon (C) content of the soil based on the principle that increased C inputs cause C stores in and losses from in the soil. We expected that in tandem, certain microtopographical and microclimatic characteristics might be associated with elevated C inputs and correspondingly, soil C stores and losses. We confirmed that on this site, positive relationships exist between ANPP, C inputs (litter fall), and losses (exportable DOC), but we did not find that these relationships between ANPP, inputs, and exports were translated to SOM stores (mg C/g soil), C content of the soil (% C/g soil), or DOC pools (determined with salt and water extractions). We suggest that the biogeochemical processes controlling C storage and lability in soil may relate to longer-term variability in aboveground inputs that result from a heterogeneous and evolving forest stand.

Urbanization and agriculture increase exports and differentially alter elemental stoichiometry of dissolved organic matter (DOM) from tropical catchments.

PubMed

Gücker, Björn; Silva, Ricky C S; Graeber, Daniel; Monteiro, José A F; Boëchat, Iola G

2016-04-15

Many tropical biomes are threatened by rapid land-use change, but its catchment-wide biogeochemical effects are poorly understood. The few previous studies on DOM in tropical catchments suggest that deforestation and subsequent land use increase stream water dissolved organic carbon (DOC) concentrations, but consistent effects on DOM elemental stoichiometry have not yet been reported. Here, we studied stream water DOC concentrations, catchment DOC exports, and DOM elemental stoichiometry in 20 tropical catchments at the Cerrado-Atlantic rainforest transition, dominated by natural vegetation, pasture, intensive agriculture, and urban land cover. Streams draining pasture could be distinguished from those draining natural catchments by their lower DOC concentrations, with lower DOM C:N and C:P ratios. Catchments with intensive agriculture had higher DOC exports and lower DOM C:P ratios than natural catchments. Finally, with the highest DOC concentrations and exports, as well as the highest DOM C:P and N:P ratios, but the lowest C:N ratios among all land-use types, urbanized catchments had the strongest effects on catchment DOM. Thus, urbanization may have alleviated N limitation of heterotrophic DOM decomposition, but increased P limitation. Land use-especially urbanization-also affected the seasonality of catchment biogeochemistry. While natural catchments exhibited high DOC exports and concentrations, with high DOM C:P ratios in the rainy season only, urbanized catchments had high values in these variables throughout the year. Our results suggest that urbanization and pastoral land use exerted the strongest impacts on DOM biogeochemistry in the investigated tropical catchments and should thus be important targets for management and mitigation efforts. Copyright © 2016 Elsevier B.V. All rights reserved.

Aquatic carbon export from peatland catchments recently undergone wind farm development

NASA Astrophysics Data System (ADS)

Smith, Ben; Waldron, Susan; Henderson, Andrew; Flowers, Hugh; Gilvear, David

2013-04-01

Scotland's peat landscapes are desirable locations for wind-based renewables due to high wind resources and low land use pressures in these areas. The environmental impact of sitting wind-based renewables on peats however, is unknown. Globally, peatlands are important terrestrial carbon stores. Given the topical nature of carbon-related issues, e.g. global warming and carbon footprints, it is imperative we help mitigate their degradation and maintain carbon sequestration. To do so, we need to better understand how peatland systems function with regards to their carbon balance (export versus sequestration) so we can assess their resilience and adaptation to hosting land-based renewable energy projects. Predicting carbon lost as a result of construction of wind farms built on peatland has not been fully characterised and this research will provide data that can supplement current 'carbon payback calculator' models for wind farms that aim to reinforce their 'green' credentials. Transfer of carbon from the terrestrial peatland systems to the aquatic freshwater and oceanic systems is most predominant during periods of high rainfall. It has been estimated that 50% of carbon is exported during only 10% of highest river flows, (Hinton et al., 1998). Furthermore, carbon export from peatlands is known to have a seasonal aspect with highest concentrations of dissolved organic carbon (DOC) found mostly in late summer months of August and September and lowest in December and January, (Dawson et al., 2004). Event sampling, where high intensity sample collection is carried out during high river flow periods, offers a better insight, understanding and estimation of carbon aquatic fluxes from peatland landscapes. The Gordonbush estate, near Brora, has an extensive peatland area where a wind farm development has recently been completed (April 2012). Investigations of aquatic carbon fluxes from this peatland system were started in July 2010, in conjunction with the start of construction of the 35-turbine wind farm, with a strong focus on event sampling. Fieldwork and sample collection is due to continue until at least September 2013 but data collated so far shows seasonal differences of carbon export from similar sized hydrological events. In addition, event sampling has highlighted the different characteristics between DOC and POC export as well as their contribution to the overall aquatic carbon flux. Phosphorous and nitrate concentrations have also been analysed and their export regimes and interactions with carbon export will also be discussed.

Regulation of stream water dissolved organic carbon concentrations ([DOC]) during snowmelt in forest streams; the role of discharge, winter climate and memory effects

NASA Astrophysics Data System (ADS)

Ågren, A.; Haei, M.; Öquist, M.; Buffam, I.; Ottosson-Löfvenius, M.; Kohler, S.; Bishop, K.; Blomkvist, P.; Laudon, H.

2011-12-01

Using 15 year stream records from two forested northern boreal catchments, coupled with soil frost experiments in the riparian zone, we demonstrate the complex inter-annual control on [DOC] and export during snowmelt. Stream [DOC] varied by a factor of 2 during those 15 years with no consistent trend. Based on our long-term analysis, we demonstrate, for the first time, that stream water [DOC] is strongly linked to the climatic conditions during the preceding winter, but that there is also a long-term memory effect in the catchment soils, related to the extent of the previous export from the catchment. Hydrology had a first order control on the inter-annual variation in concentrations, and the length of the winter was more important than the memory effect. By removing the effect of discharge on [DOC], using a conceptual hydrological model, we could detect processes that would otherwise have been overshadowed. A short and intense snowmelt gave higher [DOC] in the stream. During a prolonged snowmelt, one soil layer at the time might have been "flushed" from easily exported DOC, resulting in slightly lower stream [DOC] during such years. We found that longer and colder winters resulted in higher [DOC] during the subsequent snowmelt. A soil frost manipulation experiment in the riparian soils of the study catchment showed that the DOC concentrations in the soil water increased with the duration of the soil frost. A high antecedent DOC export during the preceding summer and autumn resulted in lower concentrations during the following spring, indicating a long-term "memory effect" of the catchment soils. In a nearby stream draining mire, we found a different response to hydrology but similar response to climate and memory effect. The inter-annual variation in snowmelt DOC exports was mostly controlled by the amount of runoff, but the variability in [DOC] also exerted a significant control on the exports, accounting for 15% of the variance in exports. We conclude that winter climatic conditions can play a substantial role in controlling stream [DOC] in ways not previously understood. These findings are especially important for northern latitude regions expected to be most affected by climate change. It's difficult to directly translate this to a future climate change prediction. If warmer winters with less insulating snow cover increase the soil frost, the results from the soil frost manipulation experiment then suggest increasing [DOC] in a future climate. At the same time the statistical analysis of the stream records suggest that a shorter and warmer winter would decrease the [DOC]. Our results do, however, highlight the role of winter climate for regulating DOC in areas with seasonally frozen soils which should be considered when resolving the sensitivity of stream [DOC] to global environmental change.

Effects of wildfire on source-water quality and aquatic ecosystems, Colorado Front Range

USGS Publications Warehouse

Writer, Jeffrey H.; McCleskey, R. Blaine; Murphy, Sheila F.; Stone, Mike; Collins, Adrian; Thoms, Martin C.

2012-01-01

Watershed erosion can dramatically increase after wildfire, but limited research has evaluated the corresponding influence on source-water quality. This study evaluated the effects of the Fourmile Canyon wildfire (Colorado Front Range, USA) on source-water quality and aquatic ecosystems using high- frequency sampling. Dissolved organic carbon (DOC) and nutrient loads in stream water were evaluated for a one-year period during different types of runoff events, including spring snowmelt, and both frontal and summer convective storms. DOC export from the burned watershed did not increase relative to the unburned watershed during spring snowmelt, but substantial increases in DOC export were observed during summer convective storms. Elevated nutrient export from the burned watershed was observed during spring snowmelt and summer convective storms, which increased the primary productivity of stream biofilms. Wildfire effects on source-water quality were shown to be substantial following high-intensity storms, with the potential to affect drinking-water treatment processes.

The spatiotemporal distribution of dissolved carbon in the main stems and their tributaries along the lower reaches of Heilongjiang River Basin, Northeast China.

PubMed

Wang, Lili; Song, Changchun; Guo, Yuedong

2016-01-01

The Heilongjiang River Basin in the eastern Siberia, one of the largest river basins draining to the North Pacific Ocean, is a border river between China, Mongolia, and Russia. In this study, we examined the spatial and seasonal variability in dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved total carbon (DTC) concentrations along lower reaches of Heilongjiang River Basin, China. Water samples were collected monthly along the mouths of main rivers (Heilongjiang River, Wusuli River, and Songhua River) and their ten tributary waters for 2 years. The DOC concentrations of waters ranged from 1.74 to 16.64 mg/L, with a mean value of 8.90 ± 0.27 mg/L (n = 165). Notably, mean DIC concentrations were 9.08 ± 0.31 mg/L, accounting for 13.26∼83.27% of DTC. DIC concentrations increased significantly after the Heilongjiang River passed through Northeast China, while DOC concentrations decreased. Over 50% of DIC concentrations were decreased during exports from groundwater to rice fields and from rice fields to ditches. Water dissolved carbon showed large spatial and temporal variations during the 2-year measurement, suggesting that more frequently samplings were required. Carbon (DIC + DOC) loads from the Heilongjiang River to the Sea of Okhotsk were estimated to be 3.26 Tg C/year in this study, accounting for 0.64% of the global water dissolved carbon flux. DIC export contributed an average of 51.84% of the estimated carbon load in the Heilongjiang River, acting as an important carbon component during riverine transport. Our study could provide some guides on agricultural water management and contribute to more accurately estimate global carbon budgets.

Compositionally heterogeneous dissolved organic matter reflects changing flowpaths in a large ice sheet catchment over the course of the melt season at Leverett Glacier, southwest Greenland

NASA Astrophysics Data System (ADS)

Kellerman, A.; Hawkings, J.; Marshall, M.; Spencer, R.; Wadham, J.

2017-12-01

The Greenland Ice Sheet (GrIS) is losing mass at a remarkable rate. This loss of mass coincides with the export of dissolved organic matter (DOM) and other nutrients from the ice sheet and exerts a primary control on secondary production in downstream ecosystems. However, little is known about the source and composition of DOM exported from these dilute, yet immense, systems. Samples were collected from May 11, 2015 to July 29, 2015 from the outflow of Leverett Glacier, a large, land-terminating glacier of the southwest GrIS. Dissolved organic carbon (DOC) concentrations were measured and the optical properties of DOM were characterized using absorbance and fluorescence spectroscopy. At the beginning of the season, when discharge is <5 m3 sec-1, red-shifted fluorescence suggests terrestrial inputs from either overridden soils or proglacial inputs dominate the DOM pool. With the onset of melt, after an initial pulse in both DOC quantity and red-shifted fluorescence intensity, the DOC concentration and fluorescence intensity is diluted, with little change in DOM composition. The terrestrial signal is lost with the first outburst event in late June, and a single protein-like fluorophore is exhibited for three weeks. On July 10th, a fourth outburst event introduces a second protein-like fluorophore, indicative of production on the ice sheet, and this signature is maintained until the end of the July. These results suggest that subglaical drainage flowpaths and water source influence the exported DOC concentration and DOM composition over a summer melt season. As glacial outflow shifts from higher DOC concentrations early in the season to low DOC concentrations later in the summer, these results impact estimates of carbon export from glaciers. Furthermore, as composition is related to reactivity, the compositional changes observed may indicate shifts in the bioavailability of the DOM upon delivery to coastal systems, a result of changing DOM sources over the course of the season.

Biogeochemistry of the Penobscot River watershed, Maine, USA: nutrient export patterns for carbon, nitrogen, and phosphorus.

PubMed

Cronan, Christopher S

2012-07-01

Watershed exports of carbon, nitrogen, phosphorus, major solutes, and suspended sediments were examined during five water years in the Penobscot River basin, which forms part of the Gulf of Maine watershed. Mean annual exports of dissolved organic carbon (DOC) in the Penobscot River were 58 kg C ha(-1) year(-1), whereas cumulative yearly watershed flux of DOC during the study period ranged from 8.6 to 16.1 × 10(10) g C year(-1) and averaged 11.7 × 10(10) g C year(-1). Watershed exports of total soluble N (TN) and total soluble P in the Penobscot River averaged 1.9 and 0.02 kg ha(-1) year(-1), respectively. Companion studies in two other major Maine rivers indicated that mean annual exports of DOC and TN in the Androscoggin River were 40 kg C ha(-1) year(-1) and 2.0 kg N ha(-1) year(-1), whereas exports in the Kennebec River were 43 kg C ha(-1) year(-1) and 2.2 kg N ha(-1) year(-1). Extrapolation of results from this investigation and a previous complementary study indicates that estuaries and coastal waters in the Gulf of Maine receive at least 1.0 × 10(10) g N year(-1) and 2.5 × 10(11) g C year(-1) in combined runoff from the four largest Maine river basins. Soluble exports of Ca + Mg + Na minus wet deposition inputs of cations in the Penobscot system were approximately 1,840 mol(c) ha(-1) year(-1), which represents a minimum estimate of cation denudation from the watershed. Based on its low N and P export rates, the Penobscot River watershed represents an example of reference conditions for use as a benchmark in ecological assessments of river water quality restoration or impairment. In addition, the biogeochemical metrics from this study provide an historical baseline for analysis of future trends in nutrient exports from the Penobscot watershed as a function of changing climatic and land use patterns.

Dissolved Organic Matter (DOM) Export from Watersheds to Coastal Oceans

NASA Astrophysics Data System (ADS)

Chen, R. F.; Gardner, G. B.; Peri, F.

2016-02-01

Dissolved organic matter (DOM) from terrestrial plants and soils is transported by surface waters and groundwaters to coastal ocean waters. Along the way, photochemical and biological degradation can remove DOM, and in situ processes such as phytoplankton leaching and sediment sources can add to the DOM in the river water. Wetlands, especially coastal wetlands can add significant amounts of DOM that is carried by rivers and is exported through estuaries to coastal systems. We will present observational data from a variety of coastal systems (San Francisco Bay, Boston Harbor, Chesapeake Bay, Hudson River, the Mississippi River, and a small salt marsh in the Gulf of Mexico). High resolution measurements of chromophoric dissolved organic matter (CDOM) can be correlated with dissolved organic carbon (DOC) so can be used to estimate DOC in specific systems and seasons. Gradients in CDOM/DOC combined with water fluxes can be used to estimate DOC fluxes from a variety of coastal watersheds to coastal systems. Influences of land use, system size, residence time, DOM quality, and photochemical and biological degradation will be discussed. The significance of coastal wetlands in the land-to-ocean export of DOC will be emphasized.

Using Eco-hydrologic modeling in the Penobscot River Watershed to explore the role of climate and land use change on DOC concentration and flux

NASA Astrophysics Data System (ADS)

Rouhani, S. F. B. B.; Schaaf, C.; Douglas, E. M.; Huntington, T. G.; Kim, J.

2017-12-01

Dissolved Organic Carbon leaches from the terrestrial watersheds to serve as one of the largest sources of marine DOC. Runoff, slope, soil organic matter and land cover characteristics are the primary spatial factors controlling the variability of fluvial Dissolved Organic Carbon fluxes through the catchment. In large, more heterogeneous catchments, streamflow dissolved organic carbon dynamics are regulated by the combined effect of hydrological mechanisms and the proportion of major landscape elements, such as wetland and forested areas. A number of studies have demonstrated that the amount of wetlands, especially peatlands, controls the watershed level transport of DOC in streams.The Penobscot River Watershed is located in north-central Maine and drains into the Gulf of Maine. It is the second largest watershed in New England. The Penobscot River Watershed is primarily forested but also contains extensive bogs, marshes, and wooded swamps.Studying the spatial and temporal changes in DOC export in the Penobscot River Watershed allows us to better understand and detect carbon sinks to carbon source shifts (or vice versa) in northern forested ecosystems.The Regional Hydro-Ecological Simulation System, is a physical process based terrestrial model that has the ability to simulate both the source and transportation of DOC by combining both hydrological and ecological processes. The study is focused on simulating the DOC concentration and flux with RHESSys in the Penobscot River Watershed. The simulated results are compared with field measurements of DOC from the watershed and the model results from the LOADEST and the temporal DOC export patterns are explored. Future changes in the amount of streamflow DOC will also be investigated by using projected land cover and climate change scenarios. Incremental increases in the loss of wetland areas have been implemented to explore the sensitivity of this watershed to wetland loss and progressive changes in forested land cover have been implemented to understand the role of vegetation types to the DOC flux.The simulated daily streamflow for the period of 2004-2013 corresponded well with observed daily streamflowat USGS gauge station. in addition, the simulated DOC flux and concentration values matched well with observed data and LODEST model results.

Modelling Biogenic Carbon Cycling and Remineralization In The Mesopelagic. 2. Rates and Patterns.

NASA Astrophysics Data System (ADS)

Rivkin, R. B.; Legendre, L.; Nagata, T.; Bussey, H.; Matthews, P.; Churchill, D.

Both dissolved (DOC) and particulate organic carbon (POC) are exported from the surface ocean into the mesopelagic layer (i.e. twilight zone; ~100 to 1000 m). Rela- tively little is known about processes controlling the fate and loss rates of this biogenic carbon (BC). Trap studies suggest that about 90% of the POC that is exported from the euphotic zone is remineralized between 100 and 1000m, however the remineral- ization of DOC is largely uncharacterized. The BC that is transferred or buried below the permanent pycnocline (i.e. sequestration, S) is isolated from the atmosphere for long periods (from hundred to million years) and is therefore of significance to global climate. The sequestration of BC can be computed from euphotic zone export (E) and the subsequent remineralization (R) of BC in the mesopelagic layer. Since both POC and DOC are respired, sequestration can be estimated as S = E - R. Unfortunately there are very few direct measurements of R in the mesopelagic layer. We therefore estimated this property, at the global scale, from a meta-analysis of the distributions of physical, chemical and bacterial properties in the mesopelagic layer. We computed heterotrophic respiration from empirical relationships among temperature, DOC, and bacterial biomass, production and growth efficiency. Preliminary estimates of R are 11 to 35 (mean = 22) Gt C/year for the World Ocean. These values are 28 to 88% of the computed upper ocean respiration of ~40 Gt C/y. These data suggest that global dissolved and particulate primary production may be >75 Gt/y.

Modeling the Dynamics and Export of Dissolved Organic Matter in the Northeastern U.S. Continental Shelf

NASA Technical Reports Server (NTRS)

Druon, J.N.; Mannino, A.; Signorini, Sergio R.; McClain, Charles R.; Friedrichs, M.; Wilkin, J.; Fennel, K.

2009-01-01

Continental shelves are believed to play a major role in carbon cycling due to their high productivity. Particulate organic carbon (POC) burial has been included in models as a carbon sink, but we show here that seasonally produced dissolved organic carbon (DOC) on the shelf can be exported to the open ocean by horizontal transport at similar rates (1-2 mol C/sq m/yr) in the southern U.S. Mid-Atlantic Bight (MAB). The dissolved organic matter (DOM) model imbedded in a coupled circulation-biogeochemical model reveals a double dynamics: the progressive release of dissolved organic nitrogen (DON) in the upper layer during summer increases the regenerated primary production by 30 to 300%, which, in turns ; enhances the DOC production mainly from phytoplankton exudation in the upper layer and solubilization of particulate organic matter (POM) deeper in the water column. This analysis suggests that DOM is a key element for better representing the ecosystem functioning and organic fluxes in models because DOM (1) is a major organic pool directly related to primary production, (2) decouples partially the carbon and nitrogen cycles (through carbon excess uptake, POM solubilization and DOM mineralization) and (3) is intimately linked to the residence time of water masses for its distribution and export.

A study of dissolved organic carbon and nitrate export in Catskill Mountain watersheds

NASA Astrophysics Data System (ADS)

Son, K.; Moore, K. E.; Lin, L.; Schneiderman, E. M.; Band, L. E.

2016-12-01

Watersheds in the Catskill Mountain region of New York State have historically experienced soil and stream acidification due to deposition of acidic compounds created from atmospheric SO2 and NOx. Recent studies in this region, and elsewhere in North America and Europe, have shown increases in dissolved organic carbon (DOC) in streams and lakes. Watersheds in the Catskills are the major source of drinking water for New York City and other communities in the region. Due to use of chlorine for disinfection, there is potential for the increase in DOC to lead to increased levels of disinfection byproducts in treated drinking water. Therefore, developing an improved understanding of the sources, fate and transport mechanisms, and export patterns for nitrate and DOC is important for informing watershed and water supply management. In this study, we analyzed the relationships between watershed characteristics, nitrate, and DOC for 12 gauged streams in the Neversink River watershed. Watershed characteristics included topography (elevation, slope, topographic wetness index), vegetation (leaf area index, species composition), soil (soil hydraulic parameters, soil carbon, wetland soil), atmospheric deposition (SO2, NOx), and climate (precipitation, temperature). Our preliminary analysis showed that both watershed slope and baseflow ratio are negatively correlated with annual median DOC concentration. At Biscuit Brook in the Neversink watershed, annual precipitation explained about 25% of annual DOC median concentration. DOC concentration was highly correlated with storm runoff in spring, summer, and fall, but stream nitrate concentration was weakly correlated with storm runoff in most seasons except summer when it was highly correlated with baseflow. We also applied a process-based ecohydrologic model (Regional Hydrologic Ecologic System Simulation, RHESSys) to the Biscuit Brook watershed to explore sources of nitrate and DOC and their movement within the watershed. We expect that this study will increase our understanding of how, when, and where DOC and nitrate are stored and transported to streams, as well as give insights into the key controls on nitrate and DOC processes in Catskill Mountain watersheds.

Export and losses of blue carbon-derived particulate and dissolved organic carbon (POC and DOC) in blackwater river-dominated and particle-dominated estuaries

NASA Astrophysics Data System (ADS)

Arellano, A. R.; Bianchi, T. S.; Osburn, C. L.; D'Sa, E. J.; Oviedo Vargas, D.; Ward, N. D.; Joshi, I.; Ko, D. S.

2016-12-01

Globally, coastal blue carbon environments (wetlands, seagrass beds and mangroves) sequester an estimated 67-215 Tg C yr-1. While most blue carbon research has focused on carbon burial/stocks and habitat fragmentation of these communities, few studies have examined the export and loss of blue carbon sources of particulate organic matter (POM) and dissolved organic matter (DOM) to adjacent coastal waters. These shifts in losses of DOM and POM are also partly due to large-scale changes in land-use and climate change. Due to the complexity of vascular plant inputs to estuarine systems (e.g. terrestrial vs. blue carbon), being able to separate blue carbon sources of POM and DOM are critical. Here, we investigate the temporal variability of the abundance, sources and breakdown of particulate and dissolved organic carbon (POC and DOC) in particle-dominated (Barataria Bay) and blackwater river-dominated (Apalachicola Bay) estuaries in the northern Gulf of Mexico, using bulk carbon, dissolved lignin phenols, δ13C and dissolved CO2. The range of DOC:POC ratios for Barataria and Apalachicola bays were 0.5-3.1 and 2.3-57.0, respectively. δ13C-POC values were more depleted in Apalachicola (x̅=-27.3‰) compared to those in Barataria (x̅=-24.8‰), and C:N ratios were higher in Apalachicola (x̅=10.8) than in Barataria (x̅=9.3). Although there was no significant temporal variability with δ13C-POC in both systems, Barataria Bay had the highest POC (0.08-0.23 mM) and C:N (7.0-13.4) values during spring, when enhanced southerly winds likely resulted in higher resuspension and marsh erosion rates. Additionally, in Apalachicola, the lowest C:N values (6.2-16.1) were observed during the dry season when fluvial DOM inputs were minimal. The highest dissolved lignin phenol and DOC (0.10-2.98 mM) concentrations in Apalachicola occurred during the wet season, reflecting the importance of riverine inputs to this system. In particular, the Carabelle River plume region had C:V and S:V values that indicated woody inputs (long-leaf pine communities), while the bay proper/East Bay were more indicative of blue carbon sources. Spatial and temporal variability of dissolved CO2 concentrations will be discussed as it relates to possible linkages with the export and losses of blue carbon-derived DOC and POC.

ORCHIDEE-SOM: modeling soil organic carbon (SOC) and dissolved organic carbon (DOC) dynamics along vertical soil profiles in Europe

NASA Astrophysics Data System (ADS)

Camino-Serrano, Marta; Guenet, Bertrand; Luyssaert, Sebastiaan; Ciais, Philippe; Bastrikov, Vladislav; De Vos, Bruno; Gielen, Bert; Gleixner, Gerd; Jornet-Puig, Albert; Kaiser, Klaus; Kothawala, Dolly; Lauerwald, Ronny; Peñuelas, Josep; Schrumpf, Marion; Vicca, Sara; Vuichard, Nicolas; Walmsley, David; Janssens, Ivan A.

2018-03-01

Current land surface models (LSMs) typically represent soils in a very simplistic way, assuming soil organic carbon (SOC) as a bulk, and thus impeding a correct representation of deep soil carbon dynamics. Moreover, LSMs generally neglect the production and export of dissolved organic carbon (DOC) from soils to rivers, leading to overestimations of the potential carbon sequestration on land. This common oversimplified processing of SOC in LSMs is partly responsible for the large uncertainty in the predictions of the soil carbon response to climate change. In this study, we present a new soil carbon module called ORCHIDEE-SOM, embedded within the land surface model ORCHIDEE, which is able to reproduce the DOC and SOC dynamics in a vertically discretized soil to 2 m. The model includes processes of biological production and consumption of SOC and DOC, DOC adsorption on and desorption from soil minerals, diffusion of SOC and DOC, and DOC transport with water through and out of the soils to rivers. We evaluated ORCHIDEE-SOM against observations of DOC concentrations and SOC stocks from four European sites with different vegetation covers: a coniferous forest, a deciduous forest, a grassland, and a cropland. The model was able to reproduce the SOC stocks along their vertical profiles at the four sites and the DOC concentrations within the range of measurements, with the exception of the DOC concentrations in the upper soil horizon at the coniferous forest. However, the model was not able to fully capture the temporal dynamics of DOC concentrations. Further model improvements should focus on a plant- and depth-dependent parameterization of the new input model parameters, such as the turnover times of DOC and the microbial carbon use efficiency. We suggest that this new soil module, when parameterized for global simulations, will improve the representation of the global carbon cycle in LSMs, thus helping to constrain the predictions of the future SOC response to global warming.

Long-term environmental drivers of DOC fluxes: Linkages between management, hydrology and climate in a subtropical coastal estuary

NASA Astrophysics Data System (ADS)

Regier, Peter; Briceño, Henry; Jaffé, Rudolf

2016-12-01

Urban and agricultural development of the South Florida peninsula has disrupted historic freshwater flow in the Everglades, a hydrologically connected ecosystem stretching from central Florida to the Gulf of Mexico, USA. Current system-scale restoration efforts aim to restore natural hydrologic regimes to reestablish pre-drainage ecosystem functioning through increased water availability, quality and timing. Aquatic transport of carbon in this ecosystem, primarily as dissolved organic carbon (DOC), plays a critical role in biogeochemical cycling and food-web dynamics, and will be affected both by water management policies and climate change. To better understand DOC dynamics in South Florida estuaries and how hydrology, climate and water management may affect them, 14 years of monthly data collected in the Shark River estuary were used to examine DOC flux dynamics in a broader environmental context. Multivariate statistical methods were applied to long-term datasets for hydrology, water quality and climate to untangle the interconnected environmental drivers that control DOC export at monthly and annual scales. DOC fluxes were determined to be primarily controlled by hydrology but also by seasonality and long-term climate patterns and episodic weather events. A four-component model (salinity, rainfall, inflow, Atlantic Multidecadal Oscillation) capable of predicting DOC fluxes (R2 = 0.84, p < 0.0001, n = 155) was established and applied to potential climate change scenarios for the Everglades to assess DOC flux response to climate and restoration variables. The majority of scenario runs indicated that DOC export from the Everglades is expected to decrease due to future changes in rainfall, water management and salinity.

Temporal trends in organic carbon content in the main Swiss rivers, 1974-2010.

PubMed

Rodríguez-Murillo, J C; Zobrist, J; Filella, M

2015-01-01

Increases in dissolved organic carbon (DOC) concentrations have often been reported in rivers and lakes of the Northern Hemisphere over the last few decades. High-quality organic carbon (OC) concentration data have been used to study the change in DOC and total (TOC) organic carbon concentrations in the main rivers of Switzerland (Rhône, Rhine, Thur and Aar) between 1974 and 2010. These rivers are characterized by high discharge regimes (due to their Alpine origin) and by running in populated areas. Small long term trends (a general statistically significant decrease in TOC and a less clear increase in DOC concentrations), on the order of 1% of mean OC concentration per year, have been observed. An upward trend before 1999 reversed direction to a more marked downward trend from 1999 to 2010. Of the potential causes of OC temporal variation analysed (water temperature, dissolved reactive phosphorus and river discharge), only discharge explains a significant, albeit still small, part of TOC variability (8-31%), while accounting for barely 2.5% of DOC variability. Estimated anthropogenic TOC and DOC loads (treated sewage) to the rivers could account for a maximum of 4-20% of the temporal trends. Such low predictability is a good example of the limitations faced when studying causality and drivers behind small variations in complex systems. River export of OC from Switzerland has decreased significantly over the period. Since about 5.5% of estimated NEP of Switzerland is exported by the rivers, riverine OC fluxes should be taken into account in a detailed carbon budget of the country. Copyright © 2014 Elsevier B.V. All rights reserved.

Fluvial organic carbon losses from oil palm plantations on tropical peat, Sarawak, Southeast Asia

NASA Astrophysics Data System (ADS)

Cook, Sarah; Page, Susan; Evans, Chris; Whelan, Mick; Gauci, Vincent; Lip Khoon, Kho

2017-04-01

Tropical peatlands are valuable stores of carbon. However, tropical peat swamp forests (TPSFs) in Southeast Asia have increasingly been converted to other land-uses. For example, more than 25% of TPSFs are now under oil palm plantations. This conversion - requiring felling and burning of trees and drainage of the peat - can enhance carbon mineralization, dissolved organic carbon (DOC) losses and can contribute significantly to global anthropogenic greenhouse gas emissions, changing these natural carbon sinks into carbon sources. At present, relatively few scientifically sound studies provide dependable estimates of gaseous and fluvial carbon losses from oil palm plantations or from drained tropical peat in general. Here we present an annual (54 week) estimate of the export of dissolved and particulate organic carbon in water draining two oil palm estates and nearby stands of TPSF in Sarawak, Malaysia, subjected to varying degrees of past anthropogenic disturbance. Spectrophotometric techniques including SUVA254 (Specific Ultra-Violet Absorption) were used to gain insight into the aromaticity and subsequent bioavailability of the exported DOC. Water draining plantation and deforested land had a higher proportion of labile carbon compared to water draining forested areas. Preliminary data suggest a total fluvial DOC flux from plantations of ca. 190 g C m-2 year-1; nearly three times estimates from intact TPSFs (63 g C m-2 year-1). DOC accounted for between 86 % - 94 % of the total organic carbon lost (most of which was bioavailable). Wit et al. (2015) estimates that an average of 53 % of peat-derived DOC is decomposed and emitted as CO2, on a monthly basis. Based on these estimates our data suggests an additional 101 g CO2 m-2 may be emitted indirectly from fluvial organic carbon in degraded TPSFs per year. Overall, these findings emphasize the importance of including fluvial organic carbon fluxes when quantifying the impact of anthropogenic disturbance on the peatland carbon budget. Given the increasing expansion of oil palm plantations on tropical peat, within Southeast Asia, it is essential that fluvial organic carbon data is incorporated into assessment criteria, helping countries to better monitor, report and verify their land-based greenhouse gas emissions.

Carbon isotopes in peat, DOC, CO2, and CH4 in a Holocene peatland on Dartmoor, southwest England

NASA Astrophysics Data System (ADS)

Charman, Dan J.; Aravena, Ramon; Bryant, Charlotte L.; Harkness, Doug D.

1999-06-01

Carbon gases with younger 14C ages than those of the surrounding peat have been reported from continental boreal peatlands, a fact which suggests that significant movement of CO2, CH4, or DOC (dissolved organic carbon) and export of C via subsurface processes are not accounted for in most estimates of contributions to the C cycle. This paper tests the hypothesis that similar processes can occur in oceanic ombrotrophic mires where water and gas movement is theoretically minimal. Measurements of 14C and δ13C in CO2, CH4, and DOC, and of tritium, are reported from depths to 250 cm at Tor Royal, a raised mire in southwest England. Radiocarbon ages of gases are 1460 to 500 yr younger than those of peat from the same depths, and CO2 is consistently younger than CH4. DOC is 1260 to 830 yr younger than the peat, and significant amounts of tritium were found at all depths. Gas ages are mostly intermediate between the age of the peat and that of the DOC, which suggests that C is principally transported as DOC. However, some gases are younger than their associated DOC, which implies that movement of dissolved gases may also take place. δ13C values in gases suggest that CO2 reduction is the major pathway for CH4 production. Transport of C in deep peats is likely to be a significant component in the overall C budget of ombrotrophic oceanic peatlands, and C export via discharge to ground or surface waters may be an important mechanism for gaseous C emissions.

Carbon isotopes in peat, DOC, CO{sub 2}, and CH{sub 4} in a Holocene peatland on Dartmoor, southwest England

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

Charman, D.J.; Aravena, R.; Bryant, C.L.

1999-06-01

Carbon gases with younger {sup 14}C ages than those of the surrounding peat have been reported from continental boreal peatlands, a fact which suggests that significant movement of CO{sub 2}, CH{sub 4}, or DOC (dissolved organic carbon) and export of C via subsurface processes are not accounted for in most estimates of contributions to the C cycle. This paper tests the hypothesis that similar processes can occur in oceanic ombrotrophic mires where water and gas movement is theoretically minimal. Measurements of {sup 14}C and {delta}{sup 13}C in CO{sub 2}, CH{sub 4}, and DOC, and of tritium, are reported from depthsmore » to 250 cm at Tor Royal, a raised mire in southwest England. Radiocarbon ages of gases are 1,460 to 500 yr younger than those of peat from the same depths, and CO{sub 2} is consistently younger than CH{sub 4}. DOC is 1,260 to 830 yr younger than the peat, and significant amounts of tritium were found at all depths. Gas ages are mostly intermediate between the age of the peat and that of the DOC, which suggests that C is principally transported as DOC. However, some gases are younger than their associated DOC, which implies that movement of dissolved gases may also take place. {delta}{sup 13}C values in gases suggest that CO{sub 2} reduction is the major pathway for CH{sub 4} production. Transport of C in deep peats is likely to be a significant component in the overall C budget of ombrotrophic oceanic peatlands, and C export via discharge to ground or surface waters may be an important mechanism for gaseous C emissions.« less

Human impact on long-term organic carbon export to rivers

NASA Astrophysics Data System (ADS)

Noacco, Valentina; Wagener, Thorsten; Worrall, Fred; Burt, Tim P.; Howden, Nicholas J. K.

2017-04-01

Anthropogenic landscape alterations have increased global carbon transported by rivers to oceans since preindustrial times. Few suitable observational data sets exist to distinguish different drivers of carbon increase, given that alterations only reveal their impact on fluvial dissolved organic carbon (DOC) over long time periods. We use the world's longest record of DOC concentrations (130 years) to identify key drivers of DOC change in the Thames basin (UK). We show that 90% of the long-term rise in fluvial DOC is explained by increased urbanization, which released to the river 671 kt C over the entire period. This source of carbon is linked to rising population, due to increased sewage effluent. Soil disturbance from land use change explained shorter-term fluvial responses. The largest land use disturbance was during the Second World War, when almost half the grassland area in the catchment was converted into arable land, which released 45 kt C from soils to the river. Carbon that had built up in soils over decades was released to the river in only a few years. Our work suggests that widespread population growth may have a greater influence on fluvial DOC trends than previously thought.

Association of dissolved mercury with dissolved organic carbon in U.S. rivers and streams: The role of watershed soil organic carbon

NASA Astrophysics Data System (ADS)

Stoken, Olivia M.; Riscassi, Ami L.; Scanlon, Todd M.

2016-04-01

Streams and rivers are important pathways for the export of atmospherically deposited mercury (Hg) from watersheds. Dissolved Hg (HgD) is strongly associated with dissolved organic carbon (DOC) in stream water, but the ratio of HgD to DOC is highly variable between watersheds. In this study, the HgD:DOC ratios from 19 watersheds were evaluated with respect to Hg wet deposition and watershed soil organic carbon (SOC) content. On a subset of sites where data were available, DOC quality measured by specific ultra violet absorbance at 254 nm, was considered as an additional factor that may influence HgD:DOC . No significant relationship was found between Hg wet deposition and HgD:DOC, but SOC content (g m-2) was able to explain 81% of the variance in the HgD:DOC ratio (ng mg-1) following the form: HgD:DOC=17.8*SOC-0.41. The inclusion of DOC quality as a secondary predictor variable explained only an additional 1% of the variance. A mathematical framework to interpret the observed power-law relationship between HgD:DOC and SOC suggests Hg supply limitation for adsorption to soils with relatively large carbon pools. With SOC as a primary factor controlling the association of HgD with DOC, SOC data sets may be utilized to predict stream HgD:DOC ratios on a more geographically widespread basis. In watersheds where DOC data are available, estimates of HgD may be readily obtained. Future Hg emissions policies must consider soil-mediated processes that affect the transport of Hg and DOC from terrestrial watersheds to streams for accurate predictions of water quality impacts.

Nonlinear and threshold-dominated runoff generation controls DOC export in a small peat catchment

NASA Astrophysics Data System (ADS)

Birkel, C.; Broder, T.; Biester, H.

2017-03-01

We used a relatively simple two-layer, coupled hydrology-biogeochemistry model to simultaneously simulate streamflow and stream dissolved organic carbon (DOC) concentrations in a small lead and arsenic contaminated upland peat catchment in northwestern Germany. The model procedure was informed by an initial data mining analysis, in combination with regression relationships of discharge, DOC, and element export. We assessed the internal model DOC processing based on stream DOC hysteresis patterns and 3-hourly time step groundwater level and soil DOC data for two consecutive summer periods in 2013 and 2014. The parsimonious model (i.e., few calibrated parameters) showed the importance of nonlinear and rapid near-surface runoff generation mechanisms that caused around 60% of simulated DOC load. The total load was high even though these pathways were only activated during storm events on average 30% of the monitoring time—as also shown by the experimental data. Overall, the drier period 2013 resulted in increased nonlinearity but exported less DOC (115 kg C ha-1 yr-1 ± 11 kg C ha-1 yr-1) compared to the equivalent but wetter period in 2014 (189 kg C ha-1 yr-1 ± 38 kg C ha-1 yr-1). The exceedance of a critical water table threshold (-10 cm) triggered a rapid near-surface runoff response with associated higher DOC transport connecting all available DOC pools and subsequent dilution. We conclude that the combination of detailed experimental work with relatively simple, coupled hydrology-biogeochemistry models not only allowed the model to be internally constrained but also provided important insight into how DOC and tightly coupled pollutants or trace elements are mobilized.

Export of pre-aged, labile DOM from a central California coastal upwelling system: Insights from D/L amino acids and Δ14C signatures

NASA Astrophysics Data System (ADS)

Walker, B. D.; Shen, Y.; Benner, R. H.; Druffel, E. R. M.

2014-12-01

Coastal upwelling zones are among the most productive regions in the world and play a major role in global carbon and nitrogen cycles. Recent research suggests that a substantial fraction of newly fixed organic matter is exported offshore in the form of dissolved organic matter (DOM). However, to date only a few studies have examined DOM composition in the context of production and export from upwelling systems. The ultimate fate and geochemical impact of coastal DOM exported to offshore and mesopelagic ecosystems also remains largely unknown. Between 2007-2009 we conducted a high-resolution biogeochemical time series at the Granite Canyon Marine Pollution Studies Lab in part to evaluate the seasonal production and export of DOM from the Central CA coast. Our previous work demonstrated substantial, albeit disparate, seasonal production of dissolved organic carbon and nitrogen (DOC, DON) - with high DON (and low C:N ratios) produced during upwelling and high DOC produced during summer/fall water column stratification (Walker and McCarthy, 2012). Here we present new total dissolved D/L amino acid (TDAA) and UV-oxidizable DOC radiocarbon (Δ14C) data with the goal of determining the relative sources (heterotrophic vs. autotrophic), bioavailability, microbial processing and 14C-ages of C-rich vs. N-rich DOM exported from this upwelling system. Our results suggest that C-rich DOM produced during water column stratification carries a large microbial signature (i.e. high D/L AA ratios and non-protein AA abundance), whereas N-rich DOM produced during upwelling appears to be fresh, autotrophic DOM (i.e. lowest D/L AA ratios and highest TDAA abundance). DOM Δ14C signatures also did not approximate in situ dissolved inorganic carbon (DIC), and instead were far more negative and highly correlated to water mass density. Together our results indicate a previously unrecognized source of highly labile yet pre-aged DOM potentially impacting offshore and mesopelagic ecosystems.

Seasonal Variation in the Quality of Dissolved and Particulate Organic Matter Exchanged Between a Salt Marsh and Its Adjacent Estuary

NASA Astrophysics Data System (ADS)

Osburn, C. L.; Mikan, M.; Etheridge, J. R.; Burchell, M. R.; Birgand, F.

2015-12-01

Salt marshes are transitional ecosystems between terrestrial and marine environments. Along with mangroves and other vegetated coastal habitats, salt marshes rank among the most productive ecosystems on Earth, with critical global importance for the planet's carbon cycle. Fluorescence was used to examine the quality of dissolved and particulate organic matter (DOM and POM) exchanging between a tidal creek in a created salt marsh and its adjacent estuary in eastern North Carolina, USA. Samples from the creek were collected hourly over four tidal cycles in May, July, August, and October of 2011. Absorbance and fluorescence of chromophoric DOM (CDOM) and of base-extracted POM (BEPOM) served as the tracers for organic matter quality while dissolved organic carbon (DOC) and base-extracted particulate organic carbon (BEPOC) were used to compute fluxes. Fluorescence was modeled using parallel factor analysis (PARAFAC) and principle components analysis (PCA) of the PARAFAC results. Of nine PARAFAC components modeled, we used multiple linear regression to identify tracers for recalcitrant DOM; labile soil-derived source DOM; detrital POM; and planktonic POM. Based on mass balance, recalcitrant DOC export was 86 g C m-2 yr-1 and labile DOC export was 49 g C m-2 yr-1. The marsh also exported 41 g C m-2 yr-1 of detrital terrestrial POC, which likely originated from lands adjacent to the North River estuary. Planktonic POC export from the marsh was 6 g C m-2 yr-1. Using the DOM and POM quality results obtained via fluorescence measurements and scaling up to global salt marsh area, we estimated that the potential release of CO2 from the respiration of salt marsh DOC and POC transported to estuaries could be 11 Tg C yr-1, roughly 4% of the recently estimated CO2 release for marshes and estuaries globally.

Dissolved Organic Carbon in Headwater Streams and Riparian Soil Organic Carbon along an Altitudinal Gradient in the Wuyi Mountains, China

PubMed Central

Huang, Wei; McDowell, William H.; Zou, Xiaoming; Ruan, Honghua; Wang, Jiashe; Li, Liguang

2013-01-01

Stream water dissolved organic carbon (DOC) correlates positively with soil organic carbon (SOC) in many biomes. Does this relationship hold in a small geographic region when variations of temperature, precipitation and vegetation are driven by a significant altitudinal gradient? We examined the spatial connectivity between concentrations of DOC in headwater stream and contents of riparian SOC and water-soluble soil organic carbon (WSOC), riparian soil C:N ratio, and temperature in four vegetation types along an altitudinal gradient in the Wuyi Mountains, China. Our analyses showed that annual mean concentrations of headwater stream DOC were lower in alpine meadow (AM) than in subtropical evergreen broadleaf forest (EBF), coniferous forest (CF), and subalpine dwarf forest (SDF). Headwater stream DOC concentrations were negatively correlated with riparian SOC as well as WSOC contents, and were unrelated to riparian soil C:N ratio. Our findings suggest that DOC concentrations in headwater streams are affected by different factors at regional and local scales. The dilution effect of higher precipitation and adsorption of soil DOC to higher soil clay plus silt content at higher elevation may play an important role in causing lower DOC concentrations in AM stream of the Wuyi Mountains. Our results suggest that upscaling and downscaling of the drivers of DOC export from forested watersheds when exploring the response of carbon flux to climatic change or other drivers must done with caution. PMID:24265737

Chromophoric Dissolved Organic Matter Export from U.S. Rivers

NASA Astrophysics Data System (ADS)

Spencer, R. G.; Aiken, G.; Dornblaser, M.; Butler, K. D.; Holmes, R. M.; Fiske, G.; Mann, P. J.; Stubbins, A.

2012-12-01

Chromophoric dissolved organic matter (CDOM) fluxes and yields from 15 major U.S. rivers draining an assortment of terrestrial biomes are presented. Utilizing CDOM and dissolved organic carbon (DOC) flux data we establish a robust universal relationship between CDOM and DOC loads. The application of this relationship allows future studies to derive DOC loads from CDOM utilizing emerging in-situ or remote sensing technologies and thus refine river-to-ocean DOC fluxes, as well as exploit historic imagery to examine how fluxes may have changed. Calculated CDOM yields from the 15 U.S. rivers highlight the importance of certain regions with respect to CDOM flux to the coastal ocean. This approach indicates that future studies might predict CDOM and DOC yields for different watershed types that could then be readily converted to loads providing for the estimation of CDOM and DOC export from ungauged watersheds. Examination of CDOM yields also highlights important geographical regions for future study with respect to the role of terrigenous CDOM in ocean color budgets and CDOM's role in biogeochemical processes.

Dissolved organic carbon fluxes from hydropedologic units in Alaskan coastal temperate rainforest watersheds

Treesearch

David V. D' Amore; Rick T. Edwards; Paul A. Herendeen; Eran Hood; Jason B. Fellman

2015-01-01

Dissolved organic C (DOC) transfer from the landscape to coastal margins is a key component of regional C cycles. Hydropedology provides a conceptual and observational framework for linking soil hydrologic function to landscape C cycling. We used hydropedology to quantify the export of DOC from the terrestrial landscape and understand how soil temperature and water...

Regional Groundwater and Storms Are Hydrologic Controls on the Quality and Export of Dissolved Organic Matter in Two Tropical Rainforest Streams, Costa Rica

NASA Astrophysics Data System (ADS)

Osburn, Christopher L.; Oviedo-Vargas, Diana; Barnett, Emily; Dierick, Diego; Oberbauer, Steven F.; Genereux, David P.

2018-03-01

A paired-watershed approach was used to compare the quality and fluxes of dissolved organic matter (DOM) during stormflow and baseflow in two lowland tropical rainforest streams located in northeastern Costa Rica. The Arboleda stream received regional groundwater (RGW) flow, whereas the Taconazo stream did not. DOM quality was assessed with absorbance and fluorescence and stable carbon isotope (δ13C-DOC) values. RGW DOM lacked detectable fluorescence and had specific ultraviolet absorption (SUVA254) and absorbance slope ratio (SR) values consistent with low aromaticity and low molecular weight material, respectively. We attributed these properties to microbial degradation and sorption of humic DOM to mineral surfaces during transport through bedrock. SUVA254 values were lower and SR values were higher in the Arboleda stream during baseflow compared to the Taconazo stream, presumably due to dilution by RGW. However, no significant difference in SUVA254 or SR occurred between the streams during stormflow. SUVA254 was negatively correlated to δ13C-DOC (r2 = 0.61, P < 0.001), demonstrating a strong linkage between stream DOM characteristics and the relative amounts of RGW flow and local watershed runoff containing soil and throughfall C sources. Mean DOC export from the Taconazo stream during the study period was 2.62 ± 0.39 g C m-2 year-1, consistent with other tropical streams, yet mean DOC export from the Arboleda stream was 13.79 ± 2.07 g C m-2 year-1, one of the highest exports reported and demonstrating a substantial impact of old RGW from outside the watershed boundary can have on surface water carbon cycling.

Linking soil DOC production rates and transport processes from landscapes to sub-basin scales

NASA Astrophysics Data System (ADS)

Tian, Y. Q.; Yu, Q.; Li, J.; Ye, C.

2014-12-01

Recent research rejects the traditional perspective that dissolved organic carbon (DOC) component in global carbon cycle are simply trivial, and in fact evidence demonstrates that lakes likely mediate carbon dynamics on a global scale. Riverine and estuarine carbon fluxes play a critical role in transporting and recycling carbon and nutrients, not only within watersheds but in their receiving waters. However, the underlying mechanisms that drive carbon fluxes, from land to rivers, lake and oceans, remain poorly understood. This presentation will report a research result of the scale-dependent DOC production rate in coastal watersheds and DOC transport processes in estuarine regions. We conducted a series of controlled experiments and field measurements for examining biogeochemical, biological, and geospatial variables that regulate downstream processing on global-relevant carbon fluxes. Results showed that increased temperatures and raised soil moistures accelerate decomposition rates of organic matter with significant variations between vegetation types. The measurements at meso-scale ecosystem demonstrated a good correlation to bulk concentration of DOC monitored in receiving waters at the outlets of sub-basins (R2 > 0.65). These field and experimental measurements improved the model of daily carbon exports through below-ground processes as a function of the organic matter content of surface soils, forest litter supply, and temperature. The study demonstrated a potential improvement in modeling the co-variance of CDOM and DOC with the unique terrestrial sources. This improvement indicated a significant promise for monitoring riverine and estuarine carbon flux from satellite images. The technical innovations include deployments of 1) mini-ecosystem (mesocosms) with soil as replicate controlled experiments for DOC production and leaching rates, and 2) aquatic mesocosms for co-variances of DOC and CDOM endmembers, and an instrumented incubation experiment for determining degradation rates.

Winter Ground Temperatures Control Snowmelt DOC Export From a Discontinuous Permafrost Watershed: A Multi-Year Perspective

NASA Astrophysics Data System (ADS)

Carey, S. K.

2006-12-01

For discontinuous and continuous permafrost watersheds, the largest mass flux of dissolved organic carbon (DOC) occurs during the snowmelt period. During this time, available allochtonous organic carbon that has accumulated over the winter in frozen organic soils is rapidly flushed to the basin outlet. While this process has been observed now in many river systems of different size and location, there have been few inter-annual reports on the mass of DOC loss and the factors controlling its variability during freshet. Hydrological and DOC fluxes were recorded for the 2002, 2003 and 2006 snowmelt season with supplementary over-winter data for an 8 square kilometer sub-basin (Granger Basin) of the Wolf Creek Research Basin, Yukon Territory, Canada. Granger Basin is an alpine catchment above treeline underlain with discontinuous permafrost (approximately 70 %) and has widespread surface organic soils up to 0.4 m in thickness. Pre-melt snow water equivalent varied widely throughout the basin, yet was greatest in 2006, followed by 2002 and 2003. Ground temperatures were notably colder throughout the 2003 winter compared with 2006 and 2002. For all years, discharge began in mid-May, and was a continuous event in 2002 and 2006. In 2003 four distinct melt-periods were observed due to rising and falling temperatures. During freshet, stream DOC concentration increased rapidly from < 2 mg C/L to > 15 mg C/L on the first ascending limb of the hydrograph in each year. In 2003, DOC was largely flushed from the catchment several weeks prior to peak freshet. DOC concentration in wells and piezometers followed a similar pattern to streamflow DOC, with 2003 groundwater DOC concentrations less than 2002 and 2006. The total mass flux of DOC during freshet was 0.85, 0.45 and 1.01 g C/m2 for 2002, 2003 and 2006 respectively. Despite differences in pre-melt snow accumulation, the timing of melt and the volume of discharge, it appears that spring DOC export is largely controlled by over-winter ground temperatures. This has important implications for carbon mass balances as warming temperatures in the pan-arctic are largely occurring during the winter months.

Understanding DOC Mobilization Dynamics Through High Frequency Measurements in a Headwater Catchment

NASA Astrophysics Data System (ADS)

Werner, B.; Musolff, A.; Lechtenfeld, O.; de Rooij, G. H.; Fleckenstein, J. H.

2017-12-01

Increasing dissolved organic carbon (DOC) exports from headwater catchments impact the quality of downstream waters and pose challenges to water supply. The importance of riparian zones for DOC export from catchments in humid, temperate climates has generally been acknowledged, but the hydrological controls and biogeochemical factors that govern mobilization of DOC from riparian zones remain elusive. By analyzing high-frequency time series of UV-VIS based water quality we therefore aim at a better understanding on temporal dynamics of DOC mobilization and exports. In a first step a one year high frequency (15 minutes) data set from a headwater catchment in the Harz Mountains (Germany) was systematically analyzed for event-based patterns in DOC concentrations. Here, a simplistic linear model was generated to explain DOC concentration level and variability in the stream. Furthermore, spectral (e.g. slopes and SUVA254) and molecular (FT-ICR-MS) characterization of DOC was used to fingerprint in-stream DOC during events. Continuous DOC concentrations were best predicted (R², NSE = 0.53) by instantaneous discharge (Q) and antecede wetness conditions of the last 30 days (AWC30 = Precip.30/PET30) as well as mean air temperature (Tmean30) and mean discharge (Qmean30) of the preceding 30 days. Analyses of 36 events revealed seasonal trends for the slope, intercept and R² of linear log(DOC)-log(Q) regressions that can be best explained by the mean air temperature of the preceding 15 days. Continuously available optical DOC quality parameters SUVA254 and spectral slope (275 nm - 295 nm) systematically changed with shifts in discharge and in DOC concentration. This is underlined by selected FT-ICR-MS measurements indicating higher DOC aromaticity and oxygen content at high flow conditions. The change of DOC quality parameters during events indicate a shift in the activated source zones: DOC with a different quality was mobilized during high flow conditions when higher groundwater levels connected formerly disconnected DOC source zones to the stream. We conclude that the high concentration variability of DOC can be explained by a few controlling variables only. These variables can be linked to event-based DOC source activation and more seasonal controls of DOC production.

Temperature and precipitation drive temporal variability in aquatic carbon and GHG concentrations and fluxes in a peatland catchment.

PubMed

Dinsmore, K J; Billett, M F; Dyson, K E

2013-07-01

The aquatic pathway is increasingly being recognized as an important component of catchment carbon and greenhouse gas (GHG) budgets, particularly in peatland systems due to their large carbon store and strong hydrological connectivity. In this study, we present a complete 5-year data set of all aquatic carbon and GHG species from an ombrotrophic Scottish peatland. Measured species include particulate and dissolved forms of organic carbon (POC, DOC), dissolved inorganic carbon (DIC), CO2 , CH4 and N2 O. We show that short-term variability in concentrations exists across all species and this is strongly linked to discharge. Seasonal cyclicity was only evident in DOC, CO2 and CH4 concentration; however, temperature correlated with monthly means in all species except DIC. Although the temperature correlation with monthly DOC and POC concentrations appeared to be related to biological productivity in the terrestrial system, we suggest the temperature correlation with CO2 and CH4 was primarily due to in-stream temperature-dependent solubility. Interannual variability in total aquatic carbon concentration was strongly correlated with catchment gross primary productivity (GPP) indicating a strong potential terrestrial aquatic linkage. DOC represented the largest aquatic carbon flux term (19.3 ± 4.59 g C m(-2)  yr(-1) ), followed by CO2 evasion (10.0 g C m(-2)  yr(-1) ). Despite an estimated contribution to the total aquatic carbon flux of between 8 and 48%, evasion estimates had the greatest uncertainty. Interannual variability in total aquatic carbon export was low in comparison with variability in terrestrial biosphere-atmosphere exchange, and could be explained primarily by temperature and precipitation. Our results therefore suggest that climatic change is likely to have a significant impact on annual carbon losses through the aquatic pathway, and as such, aquatic exports are fundamental to the understanding of whole catchment responses to climate change. © 2013 Blackwell Publishing Ltd.

The impact of climate and reservoirs on longitudinal riverine carbon fluxes from two major watersheds in the Central and Intermontane West

USGS Publications Warehouse

Stackpoole, Sarah M.; Stets, Edward G.; Striegl, Robert G.

2014-01-01

A nested sampling network on the Colorado (CR) and Missouri Rivers (MR) provided data to assess impacts of large-scale reservoir systems and climate on carbon export. The Load Estimator (LOADEST) model was used to estimate both dissolved inorganic and organic carbon (DIC and DOC) fluxes for a total of 22 sites along the main stems of the CR and MR. Both the upper CR and MR DIC and DOC fluxes increased longitudinally, but the lower CR fluxes decreased while the lower MRs continued to increase. We examined multiple factors through space and time that help explain these flux patterns. Seasonal variability in precipitation and temperature, along with site-level concentration versus discharge relationships proved to be significant factors explaining much of the difference among sites located below reservoirs as compared to sites located in more free-flowing segments of the river. The characterization of variability in carbon exports over space and time provides a basis for understanding carbon cycling and transport within river basins affected by large reservoir systems, particular in arid-to semi-arid ecosystems.

Simulating C fluxes along the terrestrial-aquatic continuum of the Amazon basin from 1861-2100

NASA Astrophysics Data System (ADS)

Lauerwald, R.; Regnier, P. A. G.; Ciais, P.

2017-12-01

To date, Earth System Models (ESM) ignore the lateral transfers of carbon (C) along the terrestrial-aquatic continuum down to the oceans and thus overestimate the terrestrial C storage. Here, we present the implementation of fluvial transport of dissolved organic carbon (DOC) and CO2 into ORCHIDEE, the land surface scheme of the Institut Pierre-Simon Laplace ESM. This new model branch, called ORCHILEAK, represents DOC production from canopy and soils, DOC and CO2 leaching from soils to streams, DOC decomposition and CO2 evasion to the atmosphere during its lateral transport in rivers, as well as exchange with the soil carbon and litter stocks in riparian wetlands. The model is calibrated and applied to the Amazon basin, including historical simulations starting from 1861 and future projections to the end of the 21st century. The model is found to reproduce well the observed dynamics in lateral DOC fluxes and CO2 evasion from the water surface. According to the simulations, half of the evading CO2 and 2/3 of the DOC transported in the rivers are produced within the water column or in flooded wetlands. We predict an increase in fluvial DOC exports to the coast and CO2 evasion to the atmosphere of about 1/4 over the 21st century (RCP 6.0). These long-term trends are mainly controlled by increasing atmospheric CO2 concentration and its fertilizing effect on terrestrial primary production in the model, while the effects of land-use change and increasing air temperature are minor. Interannual variations and seasonality of CO2 evasion and DOC transported by the river are however mainly controlled by hydrology. Over the simulation period, the actual land C sink represents less than half of the balance between terrestrial production and respiration in the Amazon basin, while the larger proportion is exported through the terrestrial-aquatic interface. These results highlight the importance of the terrestrial-aquatic continuum in the global C cycle.

Hydrological Controls on Dissolved Organic Matter Quality and Export in a Coastal River System in Southeastern USA

NASA Astrophysics Data System (ADS)

Bhattacharya, R.; Osburn, C. L.

2017-12-01

Dissolved organic matter (DOM) exported from river catchments can influence the biogeochemical processes in coastal environments with implications for water quality and carbon budget. High flow conditions are responsible for most DOM export ("pulses") from watersheds, and these events reduce DOM transformation and production by "shunting" DOM from river networks into coastal waters: the Pulse-Shunt Concept (PSC). Subsequently, the source and quality of DOM is also expected to change as a function of river flow. Here, we used stream dissolved organic carbon concentrations ([DOC]) along with DOM optical properties, such as absorbance at 350 nm (a350) and fluorescence excitation and emission matrices modeled by parallel factor analysis (PARAFAC), to characterize DOM source, quality and fluxes under variable flow conditions for the Neuse River, a coastal river system in the southeastern US. Observations were made at a flow gauged station above head of tide periodically between Aug 2011 and Feb 2013, which captured low flow periods in summer and several high flow events including Hurricane Irene. [DOC] and a350 were correlated and varied positively with river flow, implying that a large portion of the DOM was colored, humic and flow-mobilized. During high flow conditions, PARAFAC results demonstrated the higher influx of terrestrial humic DOM, and lower in-stream phytoplankton production or microbial degradation. However, during low flow, DOM transformation and production increased in response to higher residence times and elevated productivity. Further, 70% of the DOC was exported by above average flows, where 3-4 fold increases in DOC fluxes were observed during episodic events, consistent with PSC. These results imply that storms dramatically affects DOM export to coastal waters, whereby high river flow caused by episodic events primarily shunt terrestrial DOM to coastal waters, whereas low flow promotes in-stream DOM transformation and amendment with microbial DOM.

Controls on suspended sediment, particulate and dissolved organic carbon export from two adjacent catchments with contrasting land-uses, Exmoor UK.

NASA Astrophysics Data System (ADS)

Glendell, M.; Brazier, R. E.

2012-04-01

The fluvial export of total organic carbon (particulate and dissolved) plays an important role in the transportation of organic carbon from terrestrial to aquatic ecosystems, with implications for the understanding of the global carbon cycle and calculations of regional carbon budgets. The terrestrial biosphere contains large amounts of stored carbon in the soil and vegetation, thus a small change in the terrestrial carbon pool may have significant implications for atmospheric CO2 concentrations. Since the onset of agriculture, human activities have accelerated soil erosion rates 10- to 100- fold above all estimated natural background levels, especially in the uplands and at lower latitudes, whilst increasing DOC concentrations over the past decades have been reported in rivers across Western Europe and North America, raising concerns about potential destabilisation of the terrestrial soil carbon pool. The increased input of fine sediment and organic carbon into aquatic environments is also an important factor in stream water quality, being responsible for direct ecological effects as well as transport of a range of contaminants. Many factors, such as topography, hydrological regime and vegetation are known to influence the fluvial export of carbon from catchments. However, most work to date has focused on DOC losses from either forested or peaty catchments, with only limited studies examining the controls and rates of TOC (dissolved and particulate) fluxes from agricultural catchments, particularly during flood events. This research aims to: • Quantify the fluxes of total suspended sediment, total dissolved and total particulate carbon in two adjacent catchments with contrasting land-uses and • Examine the controlling factors of total fluvial carbon fluxes in a semi-natural and agricultural catchment in order to assess the impact of agricultural land-use on fluvial carbon export. The two contrasting study catchments (the Aller and Horner), in south-west England, cover 50km2 and comprise a lower lying agricultural sub-catchment and an upland sub-catchment with extensive native woodland and heather moorland. 24 months of monitoring characterised the water quality status in both catchments, including TSS, POC and DOC in both baseflow and stormflow conditions. Results indicate that the agricultural catchment exports higher TSS and TOC concentrations, instantaneous loads and total loads on a storm-by-storm basis, though these exports are short-lived as the catchment is hydrologically very responsive. The upland/woodland catchment displays more attenuated behaviour, with longer response times and longer duration events. In addition to flux data, geospatial sampling at >200 locations across each catchment characterised the carbon and nitrogen content and bulk density of the soils across four land-use categories. Analysis of these data suggests a strong relationship between TSS and TOC loads during stormflow and the spatial distribution of contributing source areas of soil with high carbon content, erodibility and land-use controls such as soil compaction within the two study catchments.

Dissolved organic carbon biodegradability from thawing permafrost stimulated by sunlight rather than inorganic nitrogen

NASA Astrophysics Data System (ADS)

Liu, F.; Chen, L.; Zhang, B.; Wang, G.; Qin, S.; Yang, Y.

2017-12-01

Permafrost thaw could result in a large portion of frozen carbon being laterally transferred to aquatic ecosystems as dissolved organic carbon (DOC). During this delivery process, the size of biodegradable DOC (BDOC) determines the proportion of DOC mineralized by microorganisms and associated carbon loss to the atmosphere, which may further trigger positive carbon-climate feedback. Thermokarst is an abrupt permafrost thaw process that can enhance DOC export and also impact DOC processing through increased inorganic nitrogen (N) and sunlight exposure. However, it remains unclear how thermokarst-impacted BDOC responds to inorganic N addition and ultraviolet (UV) light irradiation. Here we explored the responses of DOC concentration, composition and its biodegradability to inorganic N and UV light in a typical thermokarst on the Tibetan Plateau, by combining field observation and laboratory incubation with spectra analyses (UV-visible absorption and three-dimensional fluorescence spectra) and parallel factor analyses. Our results showed that BDOC in thermokarst feature outflows was significantly higher than in reference water. Furthermore, inorganic N addition had no influence on thermokarst-impacted BDOC, whereas exposure to UV light significantly increased BDOC by as much as 2.3 times higher than the dark-control. Moreover, N addition and UV irradiation did not generate additive effects on BDOC. These results imply that sunlight rather than inorganic N can increase thermokarst-derived BDOC, potentially strengthening the positive permafrost carbon-climate feedback.

Does Litter Impart A Detectable Chemical Signal on Soil DOC? DOC Fluorescence Signatures in Soils Undergoing Long-Term Litter Manipulations

NASA Astrophysics Data System (ADS)

Lajtha, K.; Strid, A.; Lee, B. S.

2015-12-01

Soil dissolved organic carbon (DOC) is a small but crucial part of the forest carbon cycle. Characterizing the relationship between organic matter inputs to soil and DOC chemistry is crucial to understanding the ultimate fate of root carbon, fallen wood and needles. Chemical differences in the DOC pool may help to explain whether fractions are sorbed to mineral surfaces and contribute to accumulation of soil organic carbon, respired as CO2, or exported. Soil solution DOC was sampled from the detrital input and removal treatment (DIRT) plots located in the H.J. Andrews Experimental Forest, OR to determine whether detrital inputs impart a detectable signal on DOC in mineral soil. Multiple types of fresh litter extracts, along with lysimeter and soil extracts from DIRT treatment plots were characterized using UV-Vis and fluorescence spectroscopy coupled with the Cory and McKnight (2005) parallel factor analysis (PARAFAC) model. Principal component analysis of 13 unique fluorophores distinguished using PARAFAC show that litter and soil extracts (needles, wood of decomposition Class 1, Class 3 and Class 5, O-horizon, and A-horizon) each have distinct fluorescence signatures. However, while litter-leached DOC chemistry varies by litter type, neither lysimeter-collected DOC or soil extracts show statistically significant differences in fluorescence signatures among treatments, even after 17 years of litter manipulations. The lack of observed differences among DIRT treatments suggests a "Soil Blender" hypothesis whereby both abiotic and biotic mechanisms effectively homogenize organic carbon constituents within the dissolved pool. The results of this work emphasize the ability of sorption and biodegradation to homogenize soil DOC and demonstrate that fluorescence can be an effective fingerprinting technique for soil DOC composition.

Stream Water, Carbon and Total Nitrogen Load Responses to a Simulated Emerald Ash Borer Infestation in Black Ash Dominated Headwater Wetlands

NASA Astrophysics Data System (ADS)

Van Grinsven, M. J.; Shannon, J.; Noh, N. J.; Kane, E. S.; Bolton, N. W.; Davis, J.; Wagenbrenner, J.; Sebestyen, S. D.; Kolka, R.; Pypker, T. G.

2017-12-01

The rapid and extensive expansion of emerald ash borer (EAB) is considered an important ecological and economic disturbance, and will likely affect critical ecosystem services associated with black ash wetlands. It is unknown how EAB-induced disturbance in wetlands dominated with black ash will impact stream water, dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) export dynamics. We hypothesized that loads of water, DOC and TDN exported from black ash wetlands would be elevated following an EAB-induced disturbance. Stream water, DOC and TDN loads exiting two black ash wetlands in headwater watersheds in Michigan were quantified over a four-year period, and were combined with wetland soil temperature and soil decomposition rate monitoring to better understand the biogeochemical implications of an EAB-induced disturbance. After a two-year baseline monitoring period, an EAB disturbance was simulated by felling (ash-cut) all black ash trees with diameters greater than 2.5-cm in one wetland. When compared to the unaltered control, stream water DOC and TDN concentrations exiting the ash-cut wetland were significantly larger by 39% and 38%, respectively during the post-treatment study period. The significantly elevated DOC and TDN concentrations were likely associated with the higher soil temperatures and increased rates of soil decomposition detected in the ash-cut site during the post-treatment period. No significant mean daily stream discharge differences were detected between treatments during the pre-treatment period, however the 0.46 mm d-1 mean daily stream discharge exiting the ash-cut wetland was significantly smaller than the 1.07 mm d-1 exiting the unaltered control during the post-treatment study period. The significantly smaller daily stream discharge in the ash-cut site likely contributed to the fact no significant differences between treatments for either mean daily DOC loads or TDN loads were detected during the post-treatment period, despite the detection of significantly higher DOC and TDN concentrations. Examination of seasonal stream water, DOC and TDN export dynamics revealed the relative magnitudes of EAB-induced impacts were not evenly distributed throughout the year, and these differences have distinct seasonal implications for downstream waterbodies.

Future export of particulate and dissolved organic carbon from land to coastal zones of the Baltic Sea

NASA Astrophysics Data System (ADS)

Strååt, Kim Dahlgren; Mörth, Carl-Magnus; Undeman, Emma

2018-01-01

The Baltic Sea is a semi-enclosed brackish sea in Northern Europe with a drainage basin four times larger than the sea itself. Riverine organic carbon (Particulate Organic Carbon, POC and Dissolved Organic Carbon, DOC) dominates carbon input to the Baltic Sea and influences both land-to-sea transport of nutrients and contaminants, and hence the functioning of the coastal ecosystem. The potential impact of future climate change on loads of POC and DOC in the Baltic Sea drainage basin (BSDB) was assessed using a hydrological-biogeochemical model (CSIM). The changes in annual and seasonal concentrations and loads of both POC and DOC by the end of this century were predicted using three climate change scenarios and compared to the current state. In all scenarios, overall increasing DOC loads, but unchanged POC loads, were projected in the north. In the southern part of the BSDB, predicted DOC loads were not significantly changing over time, although POC loads decreased in all scenarios. The magnitude and significance of the trends varied with scenario but the sign (+ or -) of the projected trends for the entire simulation period never conflicted. Results were discussed in detail for the "middle" CO2 emission scenario (business as usual, a1b). On an annual and entire drainage basin scale, the total POC load was projected to decrease by ca 7% under this scenario, mainly due to reduced riverine primary production in the southern parts of the BSDB. The average total DOC load was not predicted to change significantly between years 2010 and 2100 due to counteracting decreasing and increasing trends of DOC loads to the six major sub-basins in the Baltic Sea. However, predicted seasonal total loads of POC and DOC increased significantly by ca 46% and 30% in winter and decreased by 8% and 21% in summer over time, respectively. For POC the change in winter loads was a consequence of increasing soil erosion and a shift in duration of snowfall and onset of the spring flood impacting the input of terrestrial litter, while reduced primary production mainly explained the differences predicted in summer. The simulations also showed that future changes in POC and DOC export can vary significantly across the different sub-basins of the Baltic Sea. These changes in organic carbon input may impact future coastal food web structures e.g. by influencing bacterial and phytoplankton production in coastal zones, which in turn may have consequences at higher trophic levels.

Sources and Age of Aquatic DOC, CO2 And CH4 Exported From a Swedish Peatland

NASA Astrophysics Data System (ADS)

Campeau, A.; Wallin, M.; Billett, M. F.; Nilsson, M. B.; Laudon, H.; Oquist, M. G.; Bishop, K. H.

2015-12-01

Northern peatlands store as much organic matter as the equivalent of all the CO2 currently present in the earth's atmosphere. The peat carbon storage results from the progressive accumulation of organic matter since the end of the last glaciation (~10 000 years). The stability of these large carbon storages, under the influence of climate change, is unknown. Runoff represents one of the major C fluxes out of northern peatlands, and is particularly sensitive to changes in climate and hydrological regimes. Identifying the sources and age of aquatic C export will help assess the stability and future role of northern peatlands as active components of the global C cycle. We have characterized both radiogenic (14C) and stable carbon isotopes (δ13C) of DOC, CO2 and CH4 across a four-meter deep ombrotrophic peatland and its stream outlet. Previous studies have shown that about 34% of the estimated net ecosystem exchange from this peatland system, is lost through aquatic C export. We determined that fermentation processes in the peat acts as the main production pathway for stream CO2 (mean δ13C =-4.9‰) and CH4 (mean δ13C = -67.8‰). The seasonal variability in both sources and age of C was high. Despite this dynamism, the application of carbon isotopes allowed us to trace back the origin of aquatic C exports from the peatland.

Increased groundwater to stream discharge from permafrost thawing in the Yukon River basin: Potential impacts on lateral export of carbon and nitrogen

USGS Publications Warehouse

Walvoord, Michelle Ann; Striegl, Robert G.

2007-01-01

Arctic and subarctic watersheds are undergoing climate warming, permafrost thawing, and thermokarst formation resulting in quantitative shifts in surface water - groundwater interaction at the basin scale. Groundwater currently comprises almost one fourth of Yukon River water discharged to the Bering Sea and contributes 5-10% of the dissolved organic carbon (DOC) and nitrogen (DON) and 35-45% of the dissolved inorganic carbon (DIC) and nitrogen (DIN) loads. Long-term strearnflow records (>30 yrs) of the Yukon River basin indicate a general upward trend in groundwater contribution to streamflow of 0.7-0.9%/yr and no pervasive change in annual flow. We propose that the increases in groundwater contributions were caused predominately by climate warming and permafrost thawing that enhances infiltration and supports deeper flowpaths. The increased groundwater fraction may result in decreased DOC and DON and increased DIC and DIN export when annual flow remains unchanged.

Seasonal changes in particulate and dissolved organic matter composition and quality in the Lena River Delta

NASA Astrophysics Data System (ADS)

Mollenhauer, G.; Winterfeld, M.; Hefter, J.; Bodenstab, L.; Morgenstern, A.; Eulenburg, A.; Heim, B.; Koch, B.; Schefuss, E.; Moerth, C. M.; Rethemeyer, J.

2016-12-01

Arctic rivers are known to export large quantities of carbon by discharge of dissolved and particulate organic carbon (DOC, POC), and in a warming and progressively moister Arctic, these exports may increase resulting in a reduction of arctic continental carbon stocks. These rivers have highly variable discharge rates with a pronounced maximum during the spring freshet associated with highest concentrations of DOC and POC. Most studies investigating the isotopic composition and quality of carbon exported by Arctic rivers rely on samples taken in summer during base flow, which is due to the logistical challenges associated with sampling in the remote Arctic permafrost regions. Here we present a record of δ13C and Δ14C of DOC and POC collected between late May during the freshet and late August 2014 in the Lena River Delta. POC Δ14C shows an initial trend towards older values in the spring samples, which is reversed in summer, associated with a shift towards more depleted δ13C values. We interpret this aging trend as reflecting progressive thawing throughout the ice-free season, resulting in mobilization of progressively older carbon from deeper thawed layers. The summer reversal indicates admixture of aquatic organic matter. DOC Δ14C, in contrast, remains at relatively modern levels with rather constant δ13C values throughout the sampling period. We furthermore analysed the biomarker composition of Lena Delta particulate OM collected in spring and summer. From spring to summer, we observe trends in abundance of individual leaf-wax derived biomarkers indicating higher abundance of algal biomass in the summer particles. Trends in soil microbial biomarkers and compound-specific δD of leaf-wax lipids suggest a shift in sources towards higher contributions from the southern catchment in summer. DOC composition investigated with FT-ICR-MS changes from spring with higher abundances of compounds with high H/C and low O/C ratios to late summer, when fewer compounds were found. Our results illustrate the seasonal variability in composition and sources of organic matter discharged by the Lena River. Paired with the strong seassonality of the hydrograph, this implies that total annual discharge of organic matter contains a disproportionally high contribution from the northern part of the catchment.

The biogeochemistry of carbon across a gradient of streams and rivers within the Congo Basin

NASA Astrophysics Data System (ADS)

Mann, P. J.; Spencer, R. G. M.; Dinga, B. J.; Poulsen, J. R.; Hernes, P. J.; Fiske, G.; Salter, M. E.; Wang, Z. A.; Hoering, K. A.; Six, J.; Holmes, R. M.

2014-04-01

Dissolved organic carbon (DOC) and inorganic carbon (DIC, pCO2), lignin biomarkers, and theoptical properties of dissolved organic matter (DOM) were measured in a gradient of streams and rivers within the Congo Basin, with the aim of examining how vegetation cover and hydrology influences the composition and concentration of fluvial carbon (C). Three sampling campaigns (February 2010, November 2010, and August 2011) spanning 56 sites are compared by subbasin watershed land cover type (savannah, tropical forest, and swamp) and hydrologic regime (high, intermediate, and low). Land cover properties predominately controlled the amount and quality of DOC, chromophoric DOM (CDOM) and lignin phenol concentrations (∑8) exported in streams and rivers throughout the Congo Basin. Higher DIC concentrations and changing DOM composition (lower molecular weight, less aromatic C) during periods of low hydrologic flow indicated shifting rapid overland supply pathways in wet conditions to deeper groundwater inputs during drier periods. Lower DOC concentrations in forest and swamp subbasins were apparent with increasing catchment area, indicating enhanced DOC loss with extended water residence time. Surface water pCO2 in savannah and tropical forest catchments ranged between 2,600 and 11,922 µatm, with swamp regions exhibiting extremely high pCO2 (10,598-15,802 µatm), highlighting their potential as significant pathways for water-air efflux. Our data suggest that the quantity and quality of DOM exported to streams and rivers are largely driven by terrestrial ecosystem structure and that anthropogenic land use or climate change may impact fluvial C composition and reactivity, with ramifications for regional C budgets and future climate scenarios.

Estimates of Gelatinous Zooplankton Carbon Flux in the Global Oceans

NASA Astrophysics Data System (ADS)

Luo, J. Y.; Condon, R.; Cowen, R. K.

2016-02-01

Gelatinous zooplankton (GZ), which include the cnidarians, ctenophores, and pelagic tunicates, are a common feature of marine ecosystems worldwide, but their contribution to global biogeochemical fluxes has never been assessed. We constructed a carbon-cycle model with a single, annual time-step and resolved to a 5° spatial grid for the three major GZ groups in order to evaluate the GZ-mediated carbon fluxes and export to depth. Biomass inputs (totaling 0.149 Pg C) were based off of Lucas et al. (2014) and updated using the JeDI database (Condon et al. 2015). From the upper ocean, biomass export flux from cnidarians, ctenophores, and tunicates totaled 2.96 ± 2.82 Pg C y-1, though only 0.199 ± 0.023 Pg C y-1 of GZ carbon were transferred to upper trophic levels, roughly amounting to one-quarter of all mesozooplankton production flux. In contrast, GZ fluxes to DOC only comprised ca. 2% of labile DOC flux. Egestion flux from the upper ocean totaled 2.56 ± 3.35 Pg C y-1, with over 80% being fast-sinking tunicate fecal pellets. Due to fast sinking rates of carcasses and fecal pellets, 26% of all C export from the upper ocean reached the seafloor, such that GZ fecal matter is estimated to comprise between 20-30% of global POC surface export and 11-30% of POC seafloor deposition. Finally, results from sensitivity analyses showed no increase in cnidarian and ctenophore export fluxes with increased temperature and jelly biomass, though tunicate export fluxes showed some increase with both temperature and biomass. These results suggest that current estimates of global POC flux from the surface oceans, which range between 8.6 - 12.9 Pg C y-1, may be underestimated by as much as 20 - 25%, implying a definite need to incorporate GZ mediated flux in estimating the biological pump transfer efficiency. Our study represents the first effort to quantify the role of gelatinous zooplankton in the global marine carbon cycle.

Dissolved organic carbon fluxes in the Middle Atlantic Bight: An integrated approach based on satellite data and ocean model products

NASA Astrophysics Data System (ADS)

Mannino, Antonio; Signorini, Sergio R.; Novak, Michael G.; Wilkin, John; Friedrichs, Marjorie A. M.; Najjar, Raymond G.

2016-02-01

Continental margins play an important role in global carbon cycle, accounting for 15-21% of the global marine primary production. Since carbon fluxes across continental margins from land to the open ocean are not well constrained, we undertook a study to develop satellite algorithms to retrieve dissolved organic carbon (DOC) and combined these satellite data with physical circulation model products to quantify the shelf boundary fluxes of DOC for the U.S. Middle Atlantic Bight (MAB). Satellite DOC was computed through seasonal relationships of DOC with colored dissolved organic matter absorption coefficients, which were derived from an extensive set of in situ measurements. The multiyear time series of satellite-derived DOC stocks (4.9 Teragrams C; Tg) shows that freshwater discharge influences the magnitude and seasonal variability of DOC on the continental shelf. For the 2010-2012 period studied, the average total estuarine export of DOC into the MAB shelf is 0.77 Tg C yr-1 (year). The integrated DOC tracer fluxes across the shelf boundaries are 12.1 Tg C yr-1 entering the MAB from the southwest alongshore boundary, 18.5 Tg C yr-1 entering the MAB from the northeast alongshore boundary, and 29.0 Tg C yr-1 flowing out of the MAB across the entire length of the 100 m isobath. The magnitude of the cross-shelf DOC flux is quite variable in time (monthly) and space (north to south). The highly dynamic exchange of water along the shelf boundaries regulates the DOC budget of the MAB at subseasonal time scales.

Dissolved organic carbon fluxes in the Middle Atlantic Bight: An integrated approach based on satellite data and ocean model products.

PubMed

Mannino, Antonio; Signorini, Sergio R; Novak, Michael G; Wilkin, John; Friedrichs, Marjorie A M; Najjar, Raymond G

2016-02-01

Continental margins play an important role in global carbon cycle, accounting for 15-21% of the global marine primary production. Since carbon fluxes across continental margins from land to the open ocean are not well constrained, we undertook a study to develop satellite algorithms to retrieve dissolved organic carbon (DOC) and combined these satellite data with physical circulation model products to quantify the shelf boundary fluxes of DOC for the U.S. Middle Atlantic Bight (MAB). Satellite DOC was computed through seasonal relationships of DOC with colored dissolved organic matter absorption coefficients, which were derived from an extensive set of in situ measurements. The multiyear time series of satellite-derived DOC stocks (4.9 Teragrams C; Tg) shows that freshwater discharge influences the magnitude and seasonal variability of DOC on the continental shelf. For the 2010-2012 period studied, the average total estuarine export of DOC into the MAB shelf is 0.77 Tg C yr -1 (year). The integrated DOC tracer fluxes across the shelf boundaries are 12.1 Tg C yr -1 entering the MAB from the southwest alongshore boundary, 18.5 Tg C yr -1 entering the MAB from the northeast alongshore boundary, and 29.0 Tg C yr -1 flowing out of the MAB across the entire length of the 100 m isobath. The magnitude of the cross-shelf DOC flux is quite variable in time (monthly) and space (north to south). The highly dynamic exchange of water along the shelf boundaries regulates the DOC budget of the MAB at subseasonal time scales.

Towards an assessment of riverine dissolved organic carbon in surface waters of the western Arctic Ocean based on remote sensing and biogeochemical modeling

NASA Astrophysics Data System (ADS)

Le Fouest, Vincent; Matsuoka, Atsushi; Manizza, Manfredi; Shernetsky, Mona; Tremblay, Bruno; Babin, Marcel

2018-03-01

Future climate warming of the Arctic could potentially enhance the load of terrigenous dissolved organic carbon (tDOC) of Arctic rivers due to increased carbon mobilization within watersheds. A greater flux of tDOC might impact the biogeochemical processes of the coastal Arctic Ocean (AO) and ultimately its capacity to absorb atmospheric CO2. In this study, we show that sea-surface tDOC concentrations simulated by a physical-biogeochemical coupled model in the Canadian Beaufort Sea for 2003-2011 compare favorably with estimates retrieved by satellite imagery. Our results suggest that, over spring-summer, tDOC of riverine origin contributes to 35 % of primary production and that an equivalent of ˜ 10 % of tDOC is exported westwards with the potential of fueling the biological production of the eastern Alaskan nearshore waters. The combination of model and satellite data provides promising results to extend this work to the entire AO so as to quantify, in conjunction with in situ data, the expected changes in tDOC fluxes and their potential impact on the AO biogeochemistry at basin scale.

Export of dissolved organic matter in relation to land use along a European climatic gradient.

PubMed

Mattsson, Tuija; Kortelainen, Pirkko; Laubel, Anker; Evans, Dylan; Pujo-Pay, Mireille; Räike, Antti; Conan, Pascal

2009-03-01

The terrestrial export of dissolved organic matter (DOM) is associated with climate, vegetation and land use, and thus is under the influence of climatic variability and human interference with terrestrial ecosystems, their soils and hydrological cycles. We present a data-set including catchments from four areas covering the major climate and land use gradients within Europe: a forested boreal zone (Finland), a temperate agricultural area (Denmark), a wet and temperate mountain region in Wales, and a warm Mediterranean catchment draining into the Gulf of Lyon. In all study areas, DOC (dissolved organic carbon) was a major fraction of DOM, with much lower proportions of DON (dissolved organic nitrogen) and DOP (dissolved organic phosphorus). A south-north gradient with highest DOC concentrations and export in the northernmost catchments was recorded: DOC concentrations and loads were highest in Finland and lowest in France. These relationships indicate that DOC concentrations/export are controlled by several factors including wetland and forest cover, precipitation and hydrological processes. DON concentrations and loads were highest in the Danish catchments and lowest in the French catchments. In Wales and Finland, DON concentrations increased with the increasing proportion of agricultural land in the catchment, whereas in Denmark and France no such relationship was found. DOP concentrations and loads were low compared to DOC and DON. The highest DOP concentrations and loads were recorded in catchments with a high extent of agricultural land, large urban areas or a high population density, reflecting the influence of human impact on DOP loads.

Reservoirs as hotspots of fluvial carbon cycling in peatland catchments.

PubMed

Stimson, A G; Allott, T E H; Boult, S; Evans, M G

2017-02-15

Inland water bodies are recognised as dynamic sites of carbon processing, and lakes and reservoirs draining peatland soils are particularly important, due to the potential for high carbon inputs combined with long water residence times. A carbon budget is presented here for a water supply reservoir (catchment area~9km 2 ) draining an area of heavily eroded upland peat in the South Pennines, UK. It encompasses a two year dataset and quantifies reservoir dissolved organic carbon (DOC), particulate organic carbon (POC) and aqueous carbon dioxide (CO 2 (aq)) inputs and outputs. The budget shows the reservoir to be a hotspot of fluvial carbon cycling, as with high levels of POC influx it acts as a net sink of fluvial carbon and has the potential for significant gaseous carbon export. The reservoir alternates between acting as a producer and consumer of DOC (a pattern linked to rainfall and temperature) which provides evidence for transformations between different carbon species. In particular, the budget data accompanied by 14 C (radiocarbon) analyses provide evidence that POC-DOC transformations are a key process, occurring at rates which could represent at least ~10% of the fluvial carbon sink. To enable informed catchment management further research is needed to produce carbon cycle models more applicable to these environments, and on the implications of high POC levels for DOC composition. Copyright © 2016 Elsevier B.V. All rights reserved.

Three-Dimensional Water and Carbon Cycle Modeling at High Spatial-Temporal Resolutions

NASA Astrophysics Data System (ADS)

Liao, C.; Zhuang, Q.

2017-12-01

Terrestrial ecosystems in cryosphere are very sensitive to the global climate change due to the presence of snow covers, mountain glaciers and permafrost, especially when the increase in near surface air temperature is almost twice as large as the global average. However, few studies have investigated the water and carbon cycle dynamics using process-based hydrological and biogeochemistry modeling approach. In this study, we used three-dimensional modeling approach at high spatial-temporal resolutions to investigate the water and carbon cycle dynamics for the Tanana Flats Basin in interior Alaska with emphases on dissolved organic carbon (DOC) dynamics. The results have shown that: (1) lateral flow plays an important role in water and carbon cycle, especially in dissolved organic carbon (DOC) dynamics. (2) approximately 2.0 × 104 kg C yr-1 DOC is exported to the hydrological networks and it compromises 1% and 0.01% of total annual gross primary production (GPP) and total organic carbon stored in soil, respectively. This study has established an operational and flexible framework to investigate and predict the water and carbon cycle dynamics under the changing climate.

Relative importance of multiple factors on terrestrial loading of DOC to Arctic river networks

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

Kicklighter, David W.; Hayes, Daniel J; Mcclelland, James W

2014-01-01

Terrestrial carbon dynamics influence the contribution of dissolved organic carbon (DOC) to river networks in addition to controlling carbon fluxes between the land surface and the atmosphere. In this study, we use a biogeochemical process model to simulate the lateral transfer of DOC from land to the Arctic Ocean via riverine transport. We estimate that the pan-arctic watershed has contributed, on average, 32 Tg C/yr of DOC to the Arctic Ocean over the 20th century with most coming from the extensive area of boreal deciduous needle-leaved forests and forested wetlands in Eurasian watersheds. We also estimate that the rate ofmore » terrestrial DOC loading has been increasing by 0.037 Tg C/yr2 over the 20th century primarily as a result of increases in air temperatures and precipitation. These increases have been partially compensated by decreases in terrestrial DOC loading caused by wildfires. Other environmental factors (CO2 fertilization, ozone pollution, atmospheric nitrogen deposition, timber harvest, agriculture) are estimated to have relatively small effects on terrestrial DOC loading to arctic rivers. The effects of the various environmental factors on terrestrial carbon dynamics have both compensated and enhanced concurrent effects on hydrology to influence terrestrial DOC loading. Future increases in riverine DOC concentrations and export may occur from warming-induced increases in terrestrial DOC production associated with enhanced microbial metabolism and the exposure of additional organic matter from permafrost degradation along with decreases in water yield associated with warming-induced increases in evapotranspiration. Improvements in simulating terrestrial DOC loading to pan-arctic rivers in the future will require better information on the spatial distribution of precipitation and its temporal trends, carbon dynamics of larch-dominated ecosystems in eastern Siberia, and the role of industrial organic effluents on carbon budgets of rivers in western Russia.« less

ORCHILEAK (revision 3875): a new model branch to simulate carbon transfers along the terrestrial-aquatic continuum of the Amazon basin

NASA Astrophysics Data System (ADS)

Lauerwald, Ronny; Regnier, Pierre; Camino-Serrano, Marta; Guenet, Bertrand; Guimberteau, Matthieu; Ducharne, Agnès; Polcher, Jan; Ciais, Philippe

2017-10-01

Lateral transfer of carbon (C) from terrestrial ecosystems into the inland water network is an important component of the global C cycle, which sustains a large aquatic CO2 evasion flux fuelled by the decomposition of allochthonous C inputs. Globally, estimates of the total C exports through the terrestrial-aquatic interface range from 1.5 to 2.7 Pg C yr-1 (Cole et al., 2007; Battin et al., 2009; Tranvik et al., 2009), i.e. of the order of 2-5 % of the terrestrial NPP. Earth system models (ESMs) of the climate system ignore these lateral transfers of C, and thus likely overestimate the terrestrial C sink. In this study, we present the implementation of fluvial transport of dissolved organic carbon (DOC) and CO2 into ORCHIDEE (Organising Carbon and Hydrology in Dynamic Ecosystems), the land surface scheme of the Institut Pierre-Simon Laplace ESM. This new model branch, called ORCHILEAK, represents DOC production from canopy and soils, DOC and CO2 leaching from soils to streams, DOC decomposition, and CO2 evasion to the atmosphere during its lateral transport in rivers, as well as exchange with the soil carbon and litter stocks on floodplains and in swamps. We parameterized and validated ORCHILEAK for the Amazon basin, the world's largest river system with regard to discharge and one of the most productive ecosystems in the world. With ORCHILEAK, we are able to reproduce observed terrestrial and aquatic fluxes of DOC and CO2 in the Amazon basin, both in terms of mean values and seasonality. In addition, we are able to resolve the spatio-temporal variability in C fluxes along the canopy-soil-water continuum at high resolution (1°, daily) and to quantify the different terrestrial contributions to the aquatic C fluxes. We simulate that more than two-thirds of the Amazon's fluvial DOC export are contributed by the decomposition of submerged litter. Throughfall DOC fluxes from canopy to ground are about as high as the total DOC inputs to inland waters. The latter, however, are mainly sustained by litter decomposition. Decomposition of DOC and submerged plant litter contributes slightly more than half of the CO2 evasion from the water surface, while the remainder is contributed by soil respiration. Total CO2 evasion from the water surface equals about 5 % of the terrestrial NPP. Our results highlight that ORCHILEAK is well suited to simulate carbon transfers along the terrestrial-aquatic continuum of tropical forests. It also opens the perspective that provided parameterization, calibration and validation is performed for other biomes, the new model branch could improve the quantification of the global terrestrial C sink and help better constrain carbon cycle-climate feedbacks in future projections.

Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment

NASA Astrophysics Data System (ADS)

Spilling, Kristian; Schulz, Kai G.; Paul, Allanah J.; Boxhammer, Tim; Achterberg, Eric P.; Hornick, Thomas; Lischka, Silke; Stuhr, Annegret; Bermúdez, Rafael; Czerny, Jan; Crawfurd, Kate; Brussaard, Corina P. D.; Grossart, Hans-Peter; Riebesell, Ulf

2016-11-01

About a quarter of anthropogenic CO2 emissions are currently taken up by the oceans, decreasing seawater pH. We performed a mesocosm experiment in the Baltic Sea in order to investigate the consequences of increasing CO2 levels on pelagic carbon fluxes. A gradient of different CO2 scenarios, ranging from ambient ( ˜ 370 µatm) to high ( ˜ 1200 µatm), were set up in mesocosm bags ( ˜ 55 m3). We determined standing stocks and temporal changes of total particulate carbon (TPC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC) of specific plankton groups. We also measured carbon flux via CO2 exchange with the atmosphere and sedimentation (export), and biological rate measurements of primary production, bacterial production, and total respiration. The experiment lasted for 44 days and was divided into three different phases (I: t0-t16; II: t17-t30; III: t31-t43). Pools of TPC, DOC, and DIC were approximately 420, 7200, and 25 200 mmol C m-2 at the start of the experiment, and the initial CO2 additions increased the DIC pool by ˜ 7 % in the highest CO2 treatment. Overall, there was a decrease in TPC and increase of DOC over the course of the experiment. The decrease in TPC was lower, and increase in DOC higher, in treatments with added CO2. During phase I the estimated gross primary production (GPP) was ˜ 100 mmol C m-2 day-1, from which 75-95 % was respired, ˜ 1 % ended up in the TPC (including export), and 5-25 % was added to the DOC pool. During phase II, the respiration loss increased to ˜ 100 % of GPP at the ambient CO2 concentration, whereas respiration was lower (85-95 % of GPP) in the highest CO2 treatment. Bacterial production was ˜ 30 % lower, on average, at the highest CO2 concentration than in the controls during phases II and III. This resulted in a higher accumulation of DOC and lower reduction in the TPC pool in the elevated CO2 treatments at the end of phase II extending throughout phase III. The "extra" organic carbon at high CO2 remained fixed in an increasing biomass of small-sized plankton and in the DOC pool, and did not transfer into large, sinking aggregates. Our results revealed a clear effect of increasing CO2 on the carbon budget and mineralization, in particular under nutrient limited conditions. Lower carbon loss processes (respiration and bacterial remineralization) at elevated CO2 levels resulted in higher TPC and DOC pools than ambient CO2 concentration. These results highlight the importance of addressing not only net changes in carbon standing stocks but also carbon fluxes and budgets to better disentangle the effects of ocean acidification.

Export of dissolved organic carbon from the Penobscot River basin in north-central Maine

USGS Publications Warehouse

Huntington, Thomas G.; Aiken, George R.

2013-01-01

Dissolved organic carbon (DOC) flux from the Penobscot River and its major tributaries in Maine was determined using continuous discharge measurements, discrete water sampling, and the LOADEST regression software. The average daily flux during 2004–2007 was 71 kg C ha−1 yr−1 (392 Mt C d−1), an amount larger than measured in most northern temperate and boreal rivers. Distinct seasonal variation was observed in the relation between concentration and discharge (C–Q). During June through December (summer/fall), there was a relatively steep positive C–Q relation where concentration increased by a factor of 2–3 over the approximately 20-fold range of observed stream discharge for the Penobscot River near Eddington, Maine. In contrast, during January through May (winter/spring), DOC concentration did not increase with increasing discharge. In addition, we observed a major shift in the C–Q between 2004–2005 and 2006–2007, apparently resulting from unprecedented rainfall, runoff, and soil flushing beginning in late fall 2005. The relative contribution to the total Penobscot River basin DOC flux from each tributary varied dramatically by season, reflecting the role of large regulated reservoirs in certain basins. DOC concentration and flux per unit watershed area were highest in tributaries containing the largest areas in palustrine wetlands. Tributary DOC concentration and flux was positively correlated to percentage wetland area. Climatic or environmental changes that influence the magnitude or timing of river discharge or the abundance of wetlands will likely affect the export of DOC to the near-coastal ocean.

Dissolved organic carbon export and internal cycling in small, headwater lakes

USGS Publications Warehouse

Stets, Edward G.; Striegl, Robert G.; Aiken, George R.

2010-01-01

Carbon (C) cycling in freshwater lakes is intense but poorly integrated into our current understanding of overall C transport from the land to the oceans. We quantified dissolved organic carbon export (DOCX) and compared it with modeled gross DOC mineralization (DOCR) to determine whether hydrologic or within-lake processes dominated DOC cycling in a small headwaters watershed in Minnesota, USA. We also used DOC optical properties to gather information about DOC sources. We then compared our results to a data set of approximately 1500 lakes in the Eastern USA (Eastern Lake Survey, ELS, data set) to place our results in context of lakes more broadly. In the open-basin lakes in our watershed (n = 5), DOCX ranged from 60 to 183 g C m−2 lake area yr−1, whereas DOCR ranged from 15 to 21 g C m−2 lake area yr−1, emphasizing that lateral DOC fluxes dominated. DOCX calculated in our study watershed clustered near the 75th percentile of open-basin lakes in the ELS data set, suggesting that these results were not unusual. In contrast, DOCX in closed-basin lakes (n = 2) was approximately 5 g C m−2 lake area yr−1, whereas DOCR was 37 to 42 g C m−2 lake area yr−1, suggesting that internal C cycling dominated. In the ELS data set, median DOCX was 32 and 12 g C m−2 yr−1 in open-basin and closed-basin lakes, respectively. Although not as high as what was observed in our study watershed, DOCX is an important component of lake C flux more generally, particularly in open-basin lakes.

Distribution characteristics of dissolved organic carbon in annular wetland soil-water solutions through soil profiles in the Sanjiang Plain, northeast China.

PubMed

Xi, Min; Lu, Xian-Guo; Li, Yue; Kong, Fan-Long

2007-01-01

Overwhelming evidence reveals that concentrations of dissolved organic carbon (DOC) have increased in streams which brings negative environmental impacts. DOC in stream flow is mainly originated from soil-water solutions of watershed. Wetlands prove to be the most sensitive areas as an important DOC reserve between terrestrial and fluvial biogeosystems. This reported study was focused on the distribution characteristics and the controlling factors of DOC in soil-water solutions of annular wetland, i.e., a dishing wetland and a forest wetland together, in the Sanjiang Plain, Northeast China. The results indicate that DOC concentrations in soil-water solutions decreased and then increased with increasing soil depth in the annular wetland. In the upper soil layers of 0-10 cm and 10-20 cm, DOC concentrations in soil-water solutions linearly increased from edge to center of the annular wetland (R2 = 0.3122 and R2 = 0.443). The distribution variations were intimately linked to DOC production and utilization and DOC transport processes in annular wetland soil-water solutions. The concentrations of total organic carbon (TOC), total carbon (TC) and Fe(II), DOC mobility and continuous vertical and lateral flow affected the distribution variations of DOC in soil-water solutions. The correlation coefficients between DOC concentrations and TOC, TC and Fe(II) were 0.974, 0.813 and 0.753 respectively. These distribution characteristics suggested a systematic response of the distribution variations of DOC in annular wetland soil-water solutions to the geometry of closed depressions on a scale of small catchments. However, the DOC in soil pore water of the annular wetland may be the potential source of DOC to stream flow on watershed scale. These observations also implied the fragmentation of wetland landscape could bring the spatial-temporal variations of DOC distribution and exports, which would bring negative environmental impacts in watersheds of the Sanjiang Plain.

Dissolved organic carbon fluxes in the Middle Atlantic Bight: An integrated approach based on satellite data and ocean model products

PubMed Central

Mannino, Antonio; Signorini, Sergio R.; Novak, Michael G.; Wilkin, John; Friedrichs, Marjorie A. M.; Najjar, Raymond G.

2017-01-01

Continental margins play an important role in global carbon cycle, accounting for 15–21% of the global marine primary production. Since carbon fluxes across continental margins from land to the open ocean are not well constrained, we undertook a study to develop satellite algorithms to retrieve dissolved organic carbon (DOC) and combined these satellite data with physical circulation model products to quantify the shelf boundary fluxes of DOC for the U.S. Middle Atlantic Bight (MAB). Satellite DOC was computed through seasonal relationships of DOC with colored dissolved organic matter absorption coefficients, which were derived from an extensive set of in situ measurements. The multiyear time series of satellite-derived DOC stocks (4.9 Teragrams C; Tg) shows that freshwater discharge influences the magnitude and seasonal variability of DOC on the continental shelf. For the 2010–2012 period studied, the average total estuarine export of DOC into the MAB shelf is 0.77 Tg C yr−1 (year). The integrated DOC tracer fluxes across the shelf boundaries are 12.1 Tg C yr−1 entering the MAB from the southwest alongshore boundary, 18.5 Tg C yr−1 entering the MAB from the northeast alongshore boundary, and 29.0 Tg C yr−1 flowing out of the MAB across the entire length of the 100 m isobath. The magnitude of the cross-shelf DOC flux is quite variable in time (monthly) and space (north to south). The highly dynamic exchange of water along the shelf boundaries regulates the DOC budget of the MAB at subseasonal time scales. PMID:29201582

Is the blocking of drainage channels in upland peats an effective means of reducing DOC loss at the catchment scale?

NASA Astrophysics Data System (ADS)

Turner, Kate; Worrall, Fred

2010-05-01

Only 3% of the earths land surface is covered by peatland yet boreal and subarctic peatlands store approximately 15-30% of the World's soil carbon as peat (Limpens et al. 2008). In comparison British bogs store carbon equivalent to 20 years worth of national emissions. The loss of carbon from these areas in the form of dissolved organic carbon (DOC) is increasing and it is expected to have grown by up to 40% by 2018. Extensive drainage of UK peatlands has been associated with dehydration of the peat, an increase in water colour and a loss of carbon storage. It has been considered that the blocking of these drainage channels represents a means of peat restoration and a way of reducing DOC loss. This study aims to assess the effectiveness of this drain blocking at both an individual drain scale and at a larger catchment scale. Gibson et al. (2009) considered the effects of blocking at a solely individual drain scale finding that a 20% drop in DOC export was recorded post blocking however this decrease was due to a reduction in water yield rather than a reduction in DOC concentration with the concentration record showing no significant reduction. The effect of external parameters become more pronounced as the DOC record is examined at larger scales. The catchment is an open system and water chemistry will be influence by mixing with water from other sources. Also it is likely that at some point the drains will cut across slope leading to the flow of any highly coloured water down slope, bypassing the blockages, and entering the surface waters downstream. Degradation of DOC will occur naturally downstream due to the effects of light and microbial activity. There is, consequently, a need to examine the wider effects of drain blocking at a catchment scale to ensure that what is observed for one drain transfers to the whole catchment. A series of blocked and unblocked catchments were studied in Upper Teesdale, Northern England. Drain water samples were taken at least daily at nine localities. These sites were located such that individual drains could be monitored in the context of a larger catchment. Water table depth, flow and weather parameters were recorded along with the collection of runoff and soil water samples. A detailed sampling programme was undertaken in which a series of drains were studied in the 12 months prior to and post blocking. This approach has allowed the effects of blocking on the carbon budget, water balance and flow pathways to be considered. Results indicate that the blocking of zero order drainage channels leads to a decrease in DOC export on an individual drain scale. However, this is due to a reduction in water yield rather than concentration. Concentrations are seen to rise by a small yet statistically significant amount in blocked zero order streams. The effect at a larger scale is more complex. Annual export values in the unblocked control catchment show a rise from zero to first order streams indicating that water is being added to the system at this scale from external spatially variable sources. This pattern is also recognised in the blocked catchment. The DOC concentration record in blocked drains at this larger scale however indicated a reduction relative to the unblocked catchment. This reduction points to a change in flow pathways post blocking as highly coloured water re-navigates its way downstream. References: Gibson H, Worrall F, Burt TP, Adamson JK (2009) DOC budgets of drained peat catchments: implications for DOC production in peat soils, Hydrological Processes 23(13) 1901-1911 Limpens J (2008) Peatlands and the carbon cycle: from local processes to global implications- a synthesis, Biogeosciences 5 1475-1491

Lateral carbon export in the Mississippi River Basin, integrating fluxes from the headwaters to the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Stackpoole, S. M.; Crawford, J.; Santi, L. M.; Stets, E.; Sebestyen, S. D.; Wilson, S.; Striegl, R. G.

2017-12-01

Large-scale river studies have documented that lateral fluxes are an important component of the global carbon cycle. This study focuses on river lateral C fluxes for the Mississippi River Basin (MRB), the largest river in North America. Our lateral river C fluxes are based on data from 23 nested watersheds within the Upper MRB, for water years 2015 and 2016. The study area covers 170,000 km2 and is comprised of both catchment <10 km2 and intermediate-scale watersheds (20,000 to 40,000 km2) in Wisconsin and Minnesota, USA. Total alkalinity yields (flux derived by drainage area) ranged from 0 to 16 g C m2 yr-1 and dissolved organic C (DOC) yields ranged from 1 to 13 g C m2 yr-1. In comparison, published estimates for Mississippi River export to the Gulf of Mexico, estimated at St. Francisville, LA, were 16 g C m-2 yr-1 for alkalinity and 0.6 g m2 yr-1 for DOC. In the Upper MRB, alkalinity yields had a significant negative relationship with DOC yields (R2 = 0.53, p-value<0.0001), and alkalinity yields were significantly higher in basins where the lithology was dominated by carbonates and the land-use was >50% agriculture. There was significant inter-annual variability in the total C fluxes, and the increase in discharge in 2016 relative to 2015 increased the proportion of DOC:alkalinity for watersheds with higher forest and wetland coverage. The integration of these recent C flux estimates for the Upper MRB integrated with the fluxes estimated from the USGS long-term monitoring program dataset provide a comprehensive analysis of alkalinity and DOC fluxes for the entire basin. These results, which represent C fluxes across a gradient of lithology, soil type, and land use, will be used to address questions related to our understanding of carbon sources, transport, and loss that can be applied to other river systems.

Tidal Marshes as Pulsing Systems: New Estimates of Marsh-Carbon Export and Fate

NASA Astrophysics Data System (ADS)

Logozzo, L. A.; Neale, P.; Tzortziou, M.; Nelson, N.; Megonigal, P.

2016-02-01

We investigated wetland-estuarine exchanges of dissolved organic carbon (DOC), chromophoric dissolved organic matter (CDOM), dissolved inorganic carbon (DIC), and chlorophyll a (chl a) in the Chesapeake Bay Kirkpatrick wetlands, an ecosystem that is representative of brackish marshes with organic-rich soils in North America. 1 L water samples were collected every hour over multiple semidiurnal tidal cycles (24 h deployments) and the flow was continuously measured every minute over the course of the study. DIC samples were collected and filtered on site. Fluxes were estimated using the measured flow and concentrations of biogeochemical variables (DOC, DIC, and chl a as a measure of algal biomass). aCDOM(300) was used as a proxy for CDOM amount to observe variations over two semidiurnal tidal cycles. Relative to high tide water, low tide water was consistently enriched in DOC, DIC, and CDOM, whereas it was consistently depleted in chl a. Initial estimates of fluxes over the tidal cycle showed net export of DIC and DOC from the marsh, and net import of chl a into the marsh. These results are consistent with DOC flux estimates from previous studies, but our method utilizes high temporal resolution flow measurements, improving flux estimate accuracy. Transect sampling from the marsh into the sub-estuary during ebbing tide indicated a strong negative gradient in a­CDOM­(300) and non-conservative mixing with salinity. The observed gradients in CDOM absorption spectral shape (slope and slope ratios) and the relative changes in the major fluorescence components identified in 3D fluorescence excitation-emission-matrices, indicated strong photochemical degradation in the estuary and a shift from higher to lower molecular-weight organic compounds. The weaker gradients observed for DOC and DIC compared to aCDOM(300) indicate that while microbial degradation does occur, photobleaching is the dominant degradation mechanism for CDOM in the estuary.

Historical effects of dissolved organic carbon export and land management decisions on the watershed-scale forest carbon budget of a coastal British Columbia Douglas-fir-dominated landscape.

PubMed

Smiley, B P; Trofymow, J A

2017-12-01

To address how natural disturbance, forest harvest, and deforestation from reservoir creation affect landscape-level carbon (C) budgets, a retrospective C budget for the 8500 ha Sooke Lake Watershed (SLW) from 1911 to 2012 was developed using historical spatial inventory and disturbance data. To simulate forest C dynamics, data was input into a spatially-explicit version of the Carbon Budget Model-Canadian Forest Sector (CBM-CFS3). Transfers of terrestrial C to inland aquatic environments need to be considered to better capture the watershed scale C balance. Using dissolved organic C (DOC) and stream flow measurements from three SLW catchments, DOC load into the reservoir was derived for a 17-year period. C stocks and stock changes between a baseline and two alternative management scenarios were compared to understand the relative impact of successive reservoir expansions and sustained harvest activity over the 100-year period. Dissolved organic C flux for the three catchments ranged from 0.017 to 0.057 Mg C ha -1  year -1 . Constraining CBM-CFS3 to observed DOC loads required parameterization of humified soil C losses of 2.5, 5.5, and 6.5%. Scaled to the watershed and assuming none of the exported terrestrial DOC was respired to CO 2 , we hypothesize that over 100 years up to 30,657 Mg C may have been available for sequestration in sediment. By 2012, deforestation due to reservoir creation/expansion resulted in the watershed forest lands sequestering 14 Mg C ha -1 less than without reservoir expansion. Sustained harvest activity had a substantially greater impact, reducing forest C stores by 93 Mg C ha -1 by 2012. However approximately half of the C exported as merchantable wood during logging (~176,000 Mg C) may remain in harvested wood products, reducing the cumulative impact of forestry activity from 93 to 71 Mg C ha -1 . Dissolved organic C flux from temperate forest ecosystems is a small but persistent C flux which may have long term implications for C storage in inland aquatic systems. This is a first step integrating fluvial transport of C into a forest carbon model by parameterizing DOC flux from soil C pools. While deforestation related to successive reservoir expansions did impact the watershed-scale C budget, over multi-decadal time periods, sustained harvest activity was more influential.

Dissolved carbon biogeochemistry and export in mangrove-dominated rivers of the Florida Everglades

NASA Astrophysics Data System (ADS)

Ho, David T.; Ferrón, Sara; Engel, Victor C.; Anderson, William T.; Swart, Peter K.; Price, René M.; Barbero, Leticia

2017-05-01

The Shark and Harney rivers, located on the southwest coast of Florida, USA, originate in the freshwater, karstic marshes of the Everglades and flow through the largest contiguous mangrove forest in North America. In November 2010 and 2011, dissolved carbon source-sink dynamics was examined in these rivers during SF6 tracer release experiments. Approximately 80 % of the total dissolved carbon flux out of the Shark and Harney rivers during these experiments was in the form of inorganic carbon, either via air-water CO2 exchange or longitudinal flux of dissolved inorganic carbon (DIC) to the coastal ocean. Between 42 and 48 % of the total mangrove-derived DIC flux into the rivers was emitted to the atmosphere, with the remaining being discharged to the coastal ocean. Dissolved organic carbon (DOC) represented ca. 10 % of the total mangrove-derived dissolved carbon flux from the forests to the rivers. The sum of mangrove-derived DIC and DOC export from the forest to these rivers was estimated to be at least 18.9 to 24.5 mmol m-2 d-1, a rate lower than other independent estimates from Shark River and from other mangrove forests. Results from these experiments also suggest that in Shark and Harney rivers, mangrove contribution to the estuarine flux of dissolved carbon to the ocean is less than 10 %.

Dynamics of dissolved organic matter in fjord ecosystems: Contributions of terrestrial dissolved organic matter in the deep layer

NASA Astrophysics Data System (ADS)

Yamashita, Youhei; McCallister, S. Leigh; Koch, Boris P.; Gonsior, Michael; Jaffé, Rudolf

2015-06-01

Annually, rivers and inland water systems deliver a significant amount of terrestrial organic matter (OM) to the adjacent coastal ocean in both particulate and dissolved forms; however, the metabolic and biogeochemical transformations of OM during its seaward transport remains one of the least understood components of the global carbon cycle. This transfer of terrestrial carbon to marine ecosystems is crucial in maintaining trophic dynamics in coastal areas and critical in global carbon cycling. Although coastal regions have been proposed as important sinks for exported terrestrial materials, most of the global carbon cycling data, have not included fjords in their budgets. Here we present distributional patterns on the quantity and quality of dissolved OM in Fiordland National Park, New Zealand. Specifically, we describe carbon dynamics under diverse environmental settings based on dissolved organic carbon (DOC) depth profiles, oxygen concentrations, optical properties (fluorescence) and stable carbon isotopes. We illustrate a distinct change in the character of DOC in deep waters compared to surface and mid-depth waters. Our results suggest that, both, microbial reworking of terrestrially derived plant detritus and subsequent desorption of DOC from its particulate counterpart (as verified in a desorption experiment) are the main sources of the humic-like enriched DOC in the deep basins of the studied fjords. While it has been suggested that short transit times and protection of OM by mineral sorption may ultimately result in significant terrestrial carbon burial and preservation in fjords, our data suggests the existence of an additional source of terrestrial OM in the form of DOC generated in deep, fjord water.

Mechanisms and ecological role of carbon transfer within coastal seascapes.

PubMed

Hyndes, Glenn A; Nagelkerken, Ivan; McLeod, Rebecca J; Connolly, Rod M; Lavery, Paul S; Vanderklift, Mathew A

2014-02-01

Worldwide, coastal systems provide some of the most productive habitats, which potentially influence a range of marine and terrestrial ecosystems through the transfer of nutrients and energy. Several reviews have examined aspects of connectivity within coastal seascapes, but the scope of those reviews has been limited to single systems or single vectors. We use the transfer of carbon to examine the processes of connectivity through multiple vectors in multiple ecosystems using four coastal seascapes as case studies. We discuss and compare the main vectors of carbon connecting different ecosystems, and then the natural and human-induced factors that influence the magnitude of effect for those vectors on recipient systems. Vectors of carbon transfer can be grouped into two main categories: detrital particulate organic carbon (POC) and its associated dissolved organic and inorganic carbon (DOC/DIC) that are transported passively; and mobile consumers that transport carbon actively. High proportions of net primary production can be exported over meters to hundreds of kilometers from seagrass beds, algal reefs and mangroves as POC, with its export dependent on wind-generated currents in the first two of these systems and tidal currents for the last. By contrast, saltmarshes export large quantities of DOC through tidal movement, while land run-off plays a critical role in the transport of terrestrial POC and DOC into temperate fjords. Nekton actively transfers carbon across ecosystem boundaries through foraging movements, ontogenetic migrations, or 'trophic relays', into and out of seagrass beds, mangroves or saltmarshes. The magnitude of these vectors is influenced by: the hydrodynamics and geomorphology of the region; the characteristics of the carbon vector, such as their particle size and buoyancy; and for nekton, the extent and frequency of migrations between ecosystems. Through a risk-assessment process, we have identified the most significant human disturbances that affect the integrity of connectivity among ecosystems. Loss of habitat, net primary production (NPP) and overfishing pose the greatest risks to carbon transfer in temperate saltmarsh and tropical estuaries, particularly through their effects on nekton abundance and movement. In comparison, habitat/NPP loss and climate change are likely to be the major risks to carbon transfer in temperate fjords and temperate open coasts through alteration in the amount of POC and/or DOC/DIC being transported. While we have highlighted the importance of these vectors in coastal seascapes, there is limited quantitative data on the effects of these vectors on recipient systems. It is only through quantifying those subsidies that we can effectively incorporate complex interactions into the management of the marine environment and its resources. © 2013 The Authors. Biological Reviews © 2013 Cambridge Philosophical Society.

Watershed export of fine sediment, organic carbon, and chlorophyll-a to Chesapeake Bay: Spatial and temporal patterns in 1984-2016.

PubMed

Zhang, Qian; Blomquist, Joel D

2018-04-01

Chesapeake Bay has long experienced nutrient enrichment and water clarity deterioration. This study provides new quantification of loads and yields for sediment (fine and coarse grained), organic carbon (total, dissolved, and particulate), and chlorophyll-a from the monitored nontidal Chesapeake Bay watershed (MNTCBW), all of which are expected to drive estuarine water clarity. We conducted an integrated analysis of nine major tributaries to the Bay to understand spatial and temporal export patterns over the last thirty years (1984-2016). In terms of spatial pattern, export of these constituents from the MNTCBW was strongly dominated (~90%) by the three largest tributaries (i.e., Susquehanna, Potomac, and James). Among the nine tributaries, the ranking of constituent export generally follows the order of their watershed sizes, with other factors such as land use and reservoir playing important roles in some exceptions. In terms of partitioning, suspended sediment (SS) export was dominated by fine-grained sediment (SS fine ) in all nine tributaries; overall, ~90% of the MNTCBW SS is SS fine . Total organic carbon (TOC) export was dominated by dissolved organic carbon (DOC) in all tributaries except Potomac River; overall, ~60% of the MNTCBW TOC is DOC. A comparison with literature shows that the MNTCBW SS and TOC yields were ~80% and ~60% of the respective medians of worldwide watersheds. In terms of temporal pattern, flow-normalized yields from the MNTCBW show overall increases in SS (both long-term [1984-2016] and short-term [2004-2016]), SS fine (long-term and short-term), TOC (long-term), and chlorophyll-a (short-term). The rises in SS, SS fine , and TOC were largely driven by Susquehanna River where Conowingo Reservoir's trapping efficiency has greatly diminished in the last twenty years. Overall, these new results on the status and trends of sediment, organic carbon, and chlorophyll-a provide the foundation for building potential linkages between riverine inputs and estuarine water clarity patterns. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Meridional fluxes of dissolved organic matter in the North Atlantic Ocean

NASA Technical Reports Server (NTRS)

Walsh, John J.; Carder, Kendall L.; Mueller-Karger, Frank E.

1992-01-01

Biooptical estimates of gelbstoff and a few platinum measurements of dissolved organic carbon (DOCpt) are used to construct a budget of the meridional flux of DOC and dissolved organic nitrogen (DON) across 36 deg 25 min N in the North Atlantic from previous inverse models of water and element transport. Distinct southward subsurface fluxes of dissolved organic matter within subducted shelf water, cabelled slope water, and overturned basin water are inferred. Within two cases of a positive gradient of DOCpt between terrestrial/shelf and offshore stocks, the net equatorward exports of O2 and DOCpt from the northern North Atlantic yield molar ratios of 2.1 to 9.1, compared to the expected Redfield O2/C ratio of 1.3. It is concluded that some shelf export of DOC, with a positive gradient between coastal and oceanic stocks, as well as falling particles, are required to balance carbon, nitrogen, and oxygen budgets of the North Atlantic.

Mercury in stream water at five Czech catchments across a Hg and S deposition gradient

USGS Publications Warehouse

Navrátil, Tomáš; Shanley, James B.; Rohovec, Jan; Oulehle, Filip; Krám, Pavel; Matoušková, Šárka; Tesař, Miroslav; Hojdová, Maria

2015-01-01

The Czech Republic was heavily industrialized in the second half of the 20th century but the associated emissions of Hg and S from coal burning were significantly reduced since the 1990s. We studied dissolved (filtered) stream water mercury (Hg) and dissolved organic carbon (DOC) concentrations at five catchments with contrasting Hg and S deposition histories in the Bohemian part of the Czech Republic. The median filtered Hg concentrations of stream water samples collected in hydrological years 2012 and 2013 from the five sites varied by an order of magnitude from 1.3 to 18.0 ng L− 1. The Hg concentrations at individual catchments were strongly correlated with DOC concentrations r from 0.64 to 0.93 and with discharge r from 0.48 to 0.75. Annual export fluxes of filtered Hg from individual catchments ranged from 0.11 to 13.3 μg m− 2 yr− 1 and were highest at sites with the highest DOC export fluxes. However, the amount of Hg exported per unit DOC varied widely; the mean Hg/DOC ratio in stream water at the individual sites ranged from 0.28 to 0.90 ng mg− 1. The highest stream Hg/DOC ratios occurred at sites Pluhův Bor and Jezeří which both are in the heavily polluted Black Triangle area. Stream Hg/DOC was inversely related to mineral and total soil pool Hg/C across the five sites. We explain this pattern by greater soil Hg retention due to inhibition of soil organic matter decomposition at the sites with low stream Hg/DOC and/or by precipitation of a metacinnabar (HgS) phase. Thus mobilization of Hg into streams from forest soils likely depends on combined effects of organic matter decomposition dynamics and HgS-like phase precipitation, which were both affected by Hg and S deposition histories.

Seasonal Dynamics of Dissolved Organic Carbon Under Complex Circulation Schemes on a Large Continental Shelf: The Northern South China Sea

NASA Astrophysics Data System (ADS)

Meng, Feifei; Dai, Minhan; Cao, Zhimian; Wu, Kai; Zhao, Xiaozheng; Li, Xiaolin; Chen, Junhui; Gan, Jianping

2017-12-01

We examined the distribution and seasonality of dissolved organic carbon (DOC) based on a large data set collected from the northern South China Sea (NSCS) shelf under complex circulation schemes influenced by river plume, coastal upwelling, and downwelling. The highest surface values of ˜117 μmol L-1 were observed nearshore in summer suggesting high DOC supplies from the river inputs, whereas the lowest surface values of ˜62 μmol L-1 were on the outer shelf in winter due to entrainment of DOC-poor subsurface water under strengthened vertical mixing. While the summer coastal upwelling brought lower DOC from offshore depth to the nearshore surface, the winter coastal downwelling delivered higher surface DOC to the midshelf deep waters from the inner shelf fueled by the China Coastal Current (CCC) transporting relatively high DOC from the East China Sea to the NSCS. The intensified winter downwelling generated a cross-shelf DOC transport of 3.1 × 1012 g C over a large shelf area, which induced a significant depression of the NSCS DOC inventory in winter relative to in autumn. In addition to the variable physical controls, net biological production of DOC was semiquantified in both the river plume (2.8 ± 3.0 μmol L-1) and coastal upwelling (3.1 ± 1.3 μmol L-1) in summer. We demonstrated that the NSCS shelf had various origins of DOC including riverine inputs, inter-shelf transport and in situ production. Via cross-shelf transport, the accumulated DOC would be exported to and stored in the deep ocean, suggesting that continental shelves are a potentially effective carbon sink.

The fate of terrigenous dissolved organic carbon on the Eurasian shelves and export to the North Atlantic

NASA Astrophysics Data System (ADS)

Kaiser, K.; Benner, R.; Amon, R. M. W.

2017-01-01

Dissolved lignin phenols, chromophoric dissolved organic matter (CDOM) absorption, and fluorescence were analyzed along cross-slope mooring locations in the Barents, Laptev, and East Siberian Seas to gain a better understanding of terrigenous dissolved organic carbon (tDOC) dynamics in Arctic shelf seas and the Arctic Ocean. A gradient of river water and tDOC was observed along the continental shelf eastward into the East Siberian Sea. Correlations of carbon-normalized yields of lignin-derived phenols supplied by Siberian rivers with river water fractions and known water residence times yielded in situ decay constants of 0.18-0.58 yr-1. Calculations showed ˜50% of annual tDOC discharged by Siberian rivers was mineralized in estuaries and on Eurasian shelves per year indicating extensive removal of tDOC. Bioassay experiments and in situ decay constants indicated a reactivity continuum for tDOC. CDOM parameters and acid/aldehyde ratios of vanillyl (V) and syringyl (S) lignin phenols showed biomineralization was the dominant mechanism for the removal of tDOC. Characteristic ratios of p-hydroxy (P), S, and V phenols (P/V, S/V) also identified shelf regions in the Kara Sea and regions along the Western Laptev Sea shelf where formation of Low Salinity Halocline Waters (LSHW) and Lower Halocline Water (LHW) occurred. The efficient removal of tDOC demonstrates the importance of Eurasian margins as sinks of tDOC derived from the large Siberian Rivers and confirms tDOC mineralization has a major impact on nutrients budgets, air-sea CO2 exchange, and acidification in the Siberian Shelf Seas.

The fate of terrigenous dissolved organic carbon on the Eurasian shelves and export to the North Atlantic

NASA Astrophysics Data System (ADS)

Kaiser, Karl; Amon, Rainer; Benner, Ronald

2017-04-01

Dissolved lignin phenols, chromophoric dissolved organic matter (CDOM) absorption, and fluorescence were analyzed along cross-slope mooring locations in the Barents, Laptev, and East Siberian Seas to gain a better understanding of terrigenous dissolved organic carbon (tDOC) dynamics in Arctic shelf seas and the Arctic Ocean. A gradient of river water and tDOC was observed along the continental shelf eastward into the East Siberian Sea. Correlations of carbon-normalized yields of lignin-derived phenols supplied by Siberian rivers with river water fractions and known water residence times yielded in situ decay constants of 0.18-0.58 per year. Calculations showed about 50% of annual tDOC discharged by Siberian rivers was mineralized in estuaries and on the Eurasian shelves per year indicating extensive removal of tDOC. Bioassay experiments and in situ decay constants indicated a reactivity continuum for tDOC. CDOM parameters and acid/aldehyde ratios of vanillyl (V) and syringyl (S) lignin phenols showed biomineralization was the dominant mechanism for the removal of tDOC. Characteristic ratios of p-hydroxy (P), S, and V phenols (P/V, S/V) also identified shelf regions in the Kara Sea and regions along the Western Laptev Sea shelf where formation of Low Salinity Halocline Waters (LSHW) and Lower Halocline Water (LHW) occurred. The efficient removal of tDOC demonstrates the importance of Eurasian margins as sinks of tDOC derived from the large Siberian Rivers and confirms tDOC mineralization has a major impact on nutrients budgets, air-sea CO2 exchange, and acidification in the Siberian Shelf Seas.

Patterns in DOC Concentration and Composition in Tundra Watersheds in the Kolyma River Basin

NASA Astrophysics Data System (ADS)

Behnke, M. I.; Schade, J. D.; Fiske, G. J.; Whittinghill, K. A.; Zimov, N.

2014-12-01

Much of the world's soil carbon is frozen in permafrost in the Arctic. As the climate warms and permafrost thaws, this carbon will again be actively cycled. Whether it is exported to the ocean or released as greenhouse gases to the atmosphere depends on the form of carbon compounds and conditions encountered during transport, and will determine the strength of permafrost thaw as a feedback on climate change. To better understand the fate of this carbon, we determined how and where in the landscape dissolved organic carbon (DOC) breaks down as water transports it from tundra to ocean. We compared DOC concentration and composition along flowpaths within watersheds and at the mouths of watersheds differing in drainage area. We incubated filtered water samples in light and dark, including filter-sterilized samples, to assess the interactions between light and microbial processing as mechanisms of DOC loss. Composition was assessed using optical measurements associated with the structure of organic compounds. DOC concentration declined along flowpaths within watersheds, with most loss occurring in aquatic environments high in the landscape. We also found a negative correlation between watershed size and DOC concentration. These results suggest that much of the processing of organic carbon occurs in small streams. In addition, the relationship with drainage area suggests that residence time in streams has a large impact on transformation of terrestrial carbon during transport. We found no substantial differences in optical characteristics of DOC, indicating that breakdown processes were not selective, and that light caused much of the breakdown. This conclusion is supported by the incubation experiment, which showed greater breakdown by light, and evidence that light stimulated higher rates of microbial processing. These results highlight the importance of inland aquatic ecosystems as processors of organic matter, and suggest that organic carbon from permafrost thaw is likely to be processed high in the landscape rather than transported to the ocean. Furthermore, the importance of light-induced breakdown as a mechanism for carbon loss suggests that the timing of DOC transport relative to seasonal changes in light intensity may influence the impact of permafrost thaw on climate change.

The influence of hydrologic residence time on lake carbon cycling dynamics following extreme precipitation events

Treesearch

Jacob A. Zwart; Stephen D. Sebestyen; Christopher T. Solomon; Stuart E. Jones

2016-01-01

The frequency and magnitude of extreme events are expected to increase in the future, yet little is known about effects of such events on ecosystem structure and function. We examined how extreme precipitation events affect exports of terrestrial dissolved organic carbon (t-DOC) from watersheds to lakes as well as in-lake heterotrophy in three north-temperate lakes....

Satellite-Derived Distributions, Inventories and Fluxes of Dissolved and Particulate Organic Matter Along the Northeastern U.S. Continental Margin

NASA Technical Reports Server (NTRS)

Mannino, A.; Hooker, S. B.; Hyde, K.; Novak, M. G.; Pan, X.; Friedrichs, M.; Cahill, B.; Wilkin, J.

2011-01-01

Estuaries and the coastal ocean experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine and estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements, optical properties and remote sensing to examine the distributions and inventories of organic carbon in the U.S. Middle Atlantic Bight and Gulf of Maine. Algorithms developed to retrieve colored DOM (CDOM), Dissolved (DOC) and Particulate Organic Carbon (POC) from NASA's MODIS-Aqua and SeaWiFS satellite sensors are applied to quantify the distributions and inventories of DOC and POC. Horizontal fluxes of DOC and POC from the continental margin to the open ocean are estimated from SeaWiFS and MODIS-Aqua distributions of DOC and POC and horizontal divergence fluxes obtained from the Northeastern North Atlantic ROMS model. SeaWiFS and MODIS imagery reveal the importance of estuarine outflow to the export of CDOM and DOC to the coastal ocean and a net community production of DOC on the shelf.

Concurrent estimates of carbon export reveal physical biases in ΔO2/Ar-based net community production estimates in the Southern California Bight

NASA Astrophysics Data System (ADS)

Haskell, William Z.; Fleming, John C.

2018-07-01

Net community production (NCP) represents the amount of biologically-produced organic carbon that is available to be exported out of the surface ocean and is typically estimated using measurements of the O2/Ar ratio in the surface mixed layer under the assumption of negligible vertical transport. However, physical processes can significantly bias NCP estimates based on this in-situ tracer. It is actively debated whether discrepancies between O2/Ar-based NCP and carbon export estimates are due to differences in the location of biological production and export, or the result of physical biases. In this study, we calculate export production across the euphotic depth during two months of upwelling in Southern California in 2014, based on an estimate of the consumption rate of dissolved organic carbon (DOC) and the dissolved: total organic carbon consumption ratio below the euphotic depth. This estimate equals the concurrent O2/Ar-based NCP estimates over the same period that are corrected for physical biases, but is significantly different than NCP estimated without a correction for vertical transport. This comparison demonstrates that concurrent physical transport estimates would significantly improve O2/Ar-based estimates of NCP, particularly in settings with vertical advection. Potential approaches to mitigate this bias are discussed.

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.

Commonalities in Mercury Behavior in Contrasting Northeastern USA Landscapes

NASA Astrophysics Data System (ADS)

Shanley, J. B.; Scherbatskoy, T.; Schuster, P. F.; Reddy, M. M.; Chalmers, A.

2001-05-01

Generally less than 20% of atmospherically deposited mercury is exported from watersheds in streamflow, but the mercury export that does occur is highly episodic. Our research from diverse landscapes in northern New England, including small forested, agricultural, and urban watersheds as well as some larger rivers discharging to Lake Champlain and the Atlantic Ocean, indicates a consistent positive correlation between Hg concentrations and stream discharge. This relation appears to be driven by increased DOC, POC, and suspended sediment concentrations at increased streamflow. Streamwater Hg analyses pooled from 10 watersheds of diverse size and land use during the 2000 snowmelt within the Sleepers River Research Watershed in northeastern Vermont displayed a high correlation between (1) dissolved Hg and DOC, and (2) particulate Hg and POC. The same correlations held at Nettle Brook, a forested Vermont watershed 100 km west of Sleepers River. At Nettle Brook, DOC and dissolved mercury concentrations were both greater than at Sleepers River but the relation at the two sites was co-linear. In an agricultural watershed in northwestern Vermont, particulate Hg concentrations in streamflow were comparable to those at Nettle Brook despite markedly higher suspended sediment (and presumably POC) concentrations, suggesting the soil Hg pool is depleted by more frequent erosional events. The coupling of organic carbon with mercury may originate in the shallow soil zone; high concentrations of DOC and dissolved Hg were observed in O-horizon soil solution both at Nettle Brook and at some sites in the Adirondack Mountains of New York. Our findings underscore the importance of sampling during high-flow to determine accurate fluxes of Hg in streamflow. It is not clear, however, whether organic carbon actually controls Hg mobility, or whether organic carbon and Hg move in tandem simply as a result of their common source in soil organic matter.

Variable flushing mechanisms and landscape structure control stream DOC export during snowmelt in a set of nested catchments

Treesearch

Vincent J. Pacific; Kelsey G. Jencso; Brian L. McGlynn

2010-01-01

Stream DOC dynamics during snowmelt have been the focus of much research, and numerous DOC mobilization and delivery mechanisms from riparian and upland areas have been proposed. However, landscape structure controls on DOC export from riparian and upland landscape elements remains poorly understood. We investigated stream and groundwater DOC dynamics across three...

Dynamics, chemical properties and bioavailability of DOC in an early successional catchment

NASA Astrophysics Data System (ADS)

Risse-Buhl, U.; Hagedorn, F.; Dümig, A.; Gessner, M. O.; Schaaf, W.; Nii-Annang, S.; Gerull, L.; Mutz, M.

2013-01-01

The dynamics of dissolved organic carbon (DOC) have been intensively studied in mature ecosystems, but little is known about DOC dynamics and the significance of DOC as a substrate for microbial activity in early-successional catchments. We determined the concentration, chemical composition, source, radiocarbon age, and bioavailability of DOC along the hydrological flow path from soil solution to a downstream pond in a recently constructed catchment (Chicken Creek Catchment, Germany). Soil solution, upwelling ground water, subsurface water in an alluvial fan, and pond water all had high DOC concentrations (averages of 6.0-11.6 mg DOC L-1), despite small carbon stocks in either vegetation or soil of the early-successional catchment. The mean 14C age of DOC in upwelling ground water was 2600 to 2800 yr. Solid-state CPMAS 13C NMR revealed a higher proportion of aromatic compounds (32%) and a lower proportion of carbohydrates (33%) in upwelling ground water than in pond water (18% and 45%, respectively). The 14C age and 13C NMR spectra suggest that DOC was partly mobilized from charred organic matter of the Quaternary substrate. In an experimental 70-days incubation experiment, 20% of the total DOC was found to be bioavailable, irrespective of the water type. Origin of microbial communities (enriched from soil, stream sediment or pond water) had only marginal effects on overall DOC utilization. Overall, these data suggest that the old DOC can support microbial activity during early ecosystem succession to some extent, although the largest fraction is recalcitrant DOC that is exported from the catchment once it has been mobilized.

Role of Fire and Landscape Position on Dissolved Organic Carbon Composition and Reactivity in the Yukon-Kuskokwim Delta, Alaska

NASA Astrophysics Data System (ADS)

Bristol, E. M.; Dabrowski, J. S.; Jimmie, J. A.; Peter, D. L.; Holmes, R. M.; Mann, P. J.; Natali, S.; Schade, J. D.

2017-12-01

The Yukon-Kuskokwim Delta in southwest, Alaska is characterized by discontinuous permafrost, which is vulnerable to thaw induced by climate change. Recent fires in the delta have caused dramatic changes in the landscape, likely changing carbon dynamics, and potentially altering dissolved organic carbon (DOC) composition and DOC concentrations in aquatic ecosystems. These changes, in turn, likely affect microbial respiration and hydrologic C export from watersheds in the delta. In this study, we investigated how landscape position and fire history drive changes in DOC composition and reactivity in aquatic ecosystems. We surveyed soil pore waters, ponds, fens, and streams at varying landscape positions in burned and unburned landscapes. We also conducted a laboratory experiment to compare the role of photooxidation, photodegradation, and microbial respiration in altering DOC composition and concentration. Surface waters in burned regions were higher in temperature and inorganic nitrogen concentrations. Higher conductivity in burned areas suggests that fire is deepening the water table, causing water to flow through a more mineral soil horizon. While DOC concentrations did not vary significantly by landscape position or fire history, optical properties of DOC suggest that DOC molecular weight is lower in burned regions and decreases along flow paths. Similarly, our incubation experiment indicated that changes in DOC composition are driven by exposure to light more than bacterial respiration, and that photochemical reactivity declines along flow paths. Percent DOC loss was greatest in waters exposed to both light and bacterial, and percent DOC loss from burned watershed waters was correlated with optical properties. Based on our findings, we predict that the combination of increased surface water temperatures, increased inorganic nitrogen concentrations, and lower molecular weight DOC will increase bacterial respiration of DOC in watersheds burned by wildfire. Further research is needed to better understand the changing hydrology in burned tundra, and the relationship between photooxidation and biological mineralization of DOC.

Sources and fate of organic (DOC, POC, CDOM) and inorganic (DIC) carbon in a mangrove dominated estuary (French Guiana)

NASA Astrophysics Data System (ADS)

Ray, R.; Michaud, E.; Vantrepotte, V.; Aller, R. C.; Morvan, S.; Thouzeau, G.

2016-12-01

We studied the mangrove dominated Sinnamary estuarine system in French Guiana during the dry and wet seasons in 2015 to examine the sources, transport and fate of surface water DOC, POC and DIC along the salinity gradient and the effect of tidal fluctuations on carbon dynamics. Elemental ratios, stable isotopes and optical properties (absorption) were applied as proxies to delineate the sources and molecular structure of the organic carbon. Results showed that during the wet season there were significant net inputs of POC and DOC along the salinity gradient from mangroves and enhanced surface runoff. Time series performed during the dry season at a station in channel water adjacent to mangroves revealed mangrove-derived export and exchanges of DOC and POC during the ebb and marine algae import during the flood. DOC was the dominant form of carbon in both seasons with DOC:POC ratios typically between 13 and 40. Both δ13DOC and CDOM descriptors (e.g., S275-295 and a*412) confirmed mangrove litter leaching to be the primary contributor of high molecular weight dissolved organic matter in the wet season which was replaced by marine phytoplanktonic OC during transport offshore in the dry season. CDOM aromaticity is lower in the dry season as mangrove inputs decrease. POC showed similar trends as DOC, with maximum contributions of terrestrial litter in the river and mixing zone, and in situ production dominant in the marine zone. The entire estuary is heterotrophic, exhibiting high pCO2 (837-5575µatm) and oxygen undersaturation (59-86%) in both seasons, and substantial CO2 emission fluxes (278-3671mmol m-2 d-1). Intense local remineralization and laterally transported CO2 originating from mangrove benthic respiration could account for the water column pCO2 enrichment during low tide and night time. Keywords: Organic carbon, stable isotopes, CDOM, pCO2, mangrove, French Guiana

A Source of Terrestrial Organic Carbon to Investigate the Browning of Aquatic Ecosystems

PubMed Central

Lennon, Jay T.; Hamilton, Stephen K.; Muscarella, Mario E.; Grandy, A. Stuart; Wickings, Kyle; Jones, Stuart E.

2013-01-01

There is growing evidence that terrestrial ecosystems are exporting more dissolved organic carbon (DOC) to aquatic ecosystems than they did just a few decades ago. This “browning” phenomenon will alter the chemistry, physics, and biology of inland water bodies in complex and difficult-to-predict ways. Experiments provide an opportunity to elucidate how browning will affect the stability and functioning of aquatic ecosystems. However, it is challenging to obtain sources of DOC that can be used for manipulations at ecologically relevant scales. In this study, we evaluated a commercially available source of humic substances (“Super Hume”) as an analog for natural sources of terrestrial DOC. Based on chemical characterizations, comparative surveys, and whole-ecosystem manipulations, we found that the physical and chemical properties of Super Hume are similar to those of natural DOC in aquatic and terrestrial ecosystems. For example, Super Hume attenuated solar radiation in ways that will not only influence the physiology of aquatic taxa but also the metabolism of entire ecosystems. Based on its chemical properties (high lignin content, high quinone content, and low C:N and C:P ratios), Super Hume is a fairly recalcitrant, low-quality resource for aquatic consumers. Nevertheless, we demonstrate that Super Hume can subsidize aquatic food webs through 1) the uptake of dissolved organic constituents by microorganisms, and 2) the consumption of particulate fractions by larger organisms (i.e., Daphnia). After discussing some of the caveats of Super Hume, we conclude that commercial sources of humic substances can be used to help address pressing ecological questions concerning the increased export of terrestrial DOC to aquatic ecosystems. PMID:24124511

Pushing Boreal Headwaters: Responses of Dissolved Organic Carbon to Increased Hydro-Meteorological Forcing by Forest Harvesting

NASA Astrophysics Data System (ADS)

Schelker, J.; Grabs, T. J.; Bishop, K. H.; Laudon, H.

2012-12-01

Concentrations of dissolved organic carbon (DOC) in stream water show large variations as a response to disturbances such as forestry operations. We used a paired catchment experiment in northern Sweden which shows well quantified increases of DOC concentrations and C-exports as a result of forest harvesting. To identify the drivers of these increases, a physically-based process model (Riparian Flow Integration Model, RIM) was used to inversely simulate the DOC availability in the peat-rich riparian soils of the catchments. DOC availability in soils followed a seasonal signal paralleling the seasonality of soil-temperatures (min: February; max: August) during 2005-2011. Further, high-frequency event sampling of DOC during spring and summer seasons of 2007, 2008 and 2009, respectively, revealed that event size acted as a secondary control of DOC in streams: Spring snowmelt events (as well as one major event in 2009) showed clockwise hysteresis, whereas minor runoff episodes during summer (when DOC availability in soils was highest) were characterized by a counterclockwise behavior. The higher hydro-meteorological forcing consisting of increases of soil temperature and soil moisture after the forest removal governed additional increases in DOC availability in soils. The higher DOC concentrations observed in streams after forest harvesting can therefore be ascribed to i) the increased climatic forcing comprising higher water flows through riparian soils, ii) increased soil temperatures and soil moisture, respectively, favoring an increased production of DOC, and iii) additional variation by event size. Overall these results underline the large impact of forestry operations on stream water quality as well as DOC exports leaving managed boreal forests. Simulated and measured soil water TOC concentration profiles within the three Balsjö catchments (CC-4 = clear-cut with 67% harvest; NO-5 = 35% harvest; NR-7 = northern reference). The simulated curves represent the inversely modeled soil profiles using the average f-parameter calculated for August 2009 for each catchment. Measured values represent TOC concentrations of soil water sampled in mid August 2009. Sample numbers (soil depth in bracket) are given as: n (-0.2m) = 16; n (-0.6m) = 17; n (-0.9m) = 15. Horizontal whiskers indicate the standard deviation of measured values for each soil depth.

Flux and Seasonality of Dissolved Organic Matter From the Northern Dvina (Severnaya Dvina) River, Russia

NASA Astrophysics Data System (ADS)

Johnston, Sarah Ellen; Shorina, Natalia; Bulygina, Ekaterina; Vorobjeva, Taisya; Chupakova, Anna; Klimov, Sergey I.; Kellerman, Anne M.; Guillemette, Francois; Shiklomanov, Alexander; Podgorski, David C.; Spencer, Robert G. M.

2018-03-01

Pan-Arctic riverine dissolved organic carbon (DOC) fluxes represent a major transfer of carbon from land-to-ocean, and past scaling estimates have been predominantly derived from the six major Arctic rivers. However, smaller watersheds are constrained to northern high-latitude regions and, particularly with respect to the Eurasian Arctic, have received little attention. In this study, we evaluated the concentration of DOC and composition of dissolved organic matter (DOM) via optical parameters, biomarkers (lignin phenols), and ultrahigh resolution mass spectrometry in the Northern Dvina River (a midsized high-latitude constrained river). Elevated DOC, lignin concentrations, and aromatic DOM indicators were observed throughout the year in comparison to the major Arctic rivers with seasonality exhibiting a clear spring freshet and also some years a secondary pulse in the autumn concurrent with the onset of freezing. Chromophoric DOM absorbance at a350 was strongly correlated to DOC and lignin across the hydrograph; however, the relationships did not fit previous models derived from the six major Arctic rivers. Updated DOC and lignin fluxes were derived for the pan-Arctic watershed by scaling from the Northern Dvina resulting in increased DOC and lignin fluxes (50 Tg yr-1 and 216 Gg yr-1, respectively) compared to past estimates. This leads to a reduction in the residence time for terrestrial carbon in the Arctic Ocean (0.5 to 1.8 years). These findings suggest that constrained northern high-latitude rivers are underrepresented in models of fluxes based from the six largest Arctic rivers with important ramifications for the export and fate of terrestrial carbon in the Arctic Ocean.

The Relationship Between DOC Partition Coefficient and Mineral Soil C:N Ratio

NASA Astrophysics Data System (ADS)

Aitkenhead-Peterson, J. A.; McDowell, W. H.

2001-12-01

Since our recent publication showing that soil C:N predicts DOC flux at local and global scales, an effort has been made to understand mechanisms controlling the relationship between the two variables. We have approached this at multiple scales, using soil batch experiments, soil column experiments, and long-term field manipulations. We present here the results from our batch adsorption experiment. Mineral soils from tropical (wet and moist) and temperate (coniferous and hardwood) forests were used to assess DOC adsorption by the initial mass isotherm approach. We found that the DOC partition co-efficient (m) which represents a soil's tendency to adsorb DOC is strongly and inversely related to mineral soil C:N ratio (R2 = 0.99 n = 10 p < 0.001). The intercept of the mass isotherm, or the desorption term, was positively related to mineral soil C:N ratio (R2 = 0.80 n = 10 p < 0.01), but we found that desorption of DOC was more closely correlated with equilibrium DOC concentration (R2 = 0.97 n = 10 p < 0.001) than with mineral soil C:N. The mass isotherm approach is also useful in calculating the reactive soil pool (RSP), the fraction of the soil pool of organic carbon that may be lost to leaching. The RSP was not significantly related to mineral soil C:N, but tropical soils tended to have a larger RSP than temperate soils. Although some of the tropical soils came from areas where the natural forest had been cleared, used for plantations and then abandoned, the relationship between DOC adsorption and mineral soil C:N was not compromised. Watershed soil C:N ratio is an excellent predictor of DOC export because soil C:N is related to physiochemical adsorption processes in mineral soils and biotic production of DOC in organic soil horizons. It appears that soil C:N is a relatively robust predictor of soil solution DOC concentration and surface water DOC export for ecosystems undergoing environmental stress.

Wetlands receiving water treated with coagulants improve water quality by removing dissolved organic carbon and disinfection byproduct precursors.

PubMed

Hansen, Angela M; Kraus, Tamara E C; Bachand, Sandra M; Horwath, William R; Bachand, Philip A M

2018-05-01

Constructed wetlands are used worldwide to improve water quality while also providing critical wetland habitat. However, wetlands have the potential to negatively impact drinking water quality by exporting dissolved organic carbon (DOC) that upon disinfection can form disinfection byproducts (DBPs) like trihalomethanes (THMs) and haloacetic acids (HAAs). We used a replicated field-scale study located on organic rich soils in California's Sacramento-San Joaquin Delta to test whether constructed flow-through wetlands which receive water high in DOC that is treated with either iron- or aluminum-based coagulants can improve water quality with respect to DBP formation. Coagulation alone removed DOC (66-77%) and THM (67-70%) precursors, and was even more effective at removing HAA precursors (77-90%). Passage of water through the wetlands increased DOC concentrations (1.5-7.5mgL -1 ), particularly during the warmer summer months, thereby reversing some of the benefits from coagulant addition. Despite this addition, water exiting the wetlands treated with coagulants had lower DOC and DBP precursor concentrations relative to untreated source water. Benefits of the coagulation-wetland systems were greatest during the winter months (approx. 50-70% reduction in DOC and DBP precursor concentrations) when inflow water DOC concentrations were higher and wetland DOC production was lower. Optical properties suggest DOC in this system is predominantly comprised of high molecular weight, aromatic compounds, likely derived from degraded peat soils. Published by Elsevier B.V.

The topographic wetness index as a predictor for hot spots of DOC export from catchments

NASA Astrophysics Data System (ADS)

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

2015-04-01

Dissolved organic carbon (DOC) concentrations in the discharge of many catchments in Europe and North America are rising. This increase is of concern for the drinking water supply from reservoirs since high DOC concentrations cause additional costs in water treatment and potentially the formation of harmful disinfection by-products. A prerequisite for understanding this increase is the knowledge on the spatial distribution of dominant soil DOC sources within catchments and on mobilization as well as transfer processes to the surface water. A number of studies identified wetland soils as the dominant source with fast mobilization and short transit times to the receiving surface water. However, most studies have either focussed on smaller, hillslope and single catchment or on larger scale multi-catchment assessments. Moreover, information on the distribution of soil types in catchments is not always readily available. This study brings together both types of assessment in a data-driven top-down approach: (i) a detailed survey on DOC concentration and loads over the course of one year within two paired data-rich catchments discharging into a large drinking water reservoir in central Germany and (ii) a database of hydrochemistry and physio-geographic characteristics of 113 catchments draining into 58 reservoirs across Germany over the course of 16 years. The objective is to define hot spots of DOC export within the catchments for both types of assessments (i, ii) and to test the suitability of the topographic wetness index (TWI) as a proxy for well-connected wetland soils at various spatial scales. In the sub-catchments of assessment (i) the spatial variability of concentrations and loads was much smaller than expected. None of the studied sub-catchments was a predominant producer of the total DOC loads exported from the catchments. We found the mean concentrations and loads to be positively correlated with the share of groundwater-dominated soils in the sub-catchments. These soils are distributed in riparian wetlands along all streams within the catchments. As a readily available proxy for wetland soils percentiles of the probability distribution of the TWI in the sub-catchments were found to be good predictors for mean DOC concentrations in catchment outlet as well as for loads. In the larger dataset across Germany (ii) we also found a surprisingly good correlation between the TWI within the catchments and mean DOC concentrations. Thus we can show that, despite the wide range of topographies, land use types, geological setups and climatic conditions within this dataset the dominant source zones of DOC export is well captured by the TWI as a proxy for the share of wetland soils and DOC source zones within the catchments.

An investigation of size-fractionated organic matter from Lake Superior and a tributary stream using radiocarbon, stable isotopes and NMR

NASA Astrophysics Data System (ADS)

Zigah, Prosper K.; Minor, Elizabeth C.; Abdulla, Hussain A. N.; Werne, Josef P.; Hatcher, Patrick G.

2014-02-01

This study investigated the concentration and isotopic composition of different size fractions of organic matter (OM) in Lake Superior and in one of its many tributary streams and rivers (Amity Creek, Duluth, Minnesota, USA). Structural compositional drivers of the Δ14C of high molecular weight (HMW, >1 kDa) dissolved organic carbon (DOC) in the lake were also evaluated. Low molecular weight (LMW, <1 kDa) DOC was the fraction containing the largest proportion (68-88%) of organic carbon (OC) in the lake. Particulate organic carbon (POC, >0.7 μm) was generally 13C-depleted (-29 ± 1.2‰) relative to “bulk” (<0.7 μm) DOC (-26.4 ± 0.7‰), “init” (<0.2 μm) DOC (-26.6 ± 0.8‰), HMW DOC (-26.9 ± 0.3‰) and LMW DOC (-26.5 ± 0.9‰), and had more variable 14C content (Δ14C of -94‰ to 53‰; 735 years BP to modern) than the other size fractions. Init DOC (Δ14C of 17-59‰), HMW DOC (Δ14C of 23-64‰) and LMW DOC (Δ14C of 16-62‰) all reflected contemporary (modern) radiocarbon signatures. Bulk DOC (Δ14C of -19‰ to 57‰; 90 years BP to modern) had modern radiocarbon values in the offshore sites (Δ14C of 2-57‰) with pre-aged samples (Δ14C of -8‰ to -19‰) seen at the nearshore site. HMW DOM was relatively N-poor (C:N of 12-19) compared to particulate organic matter (POM, C:N of 8-10) revealing either a more diagenetically altered state or contrasting sources. 13C NMR data showed that biochemical composition of HMW DOC in Lake Superior was dominated by carbohydrates (53-65%) with only trace aromatic components (2-4%). Structurally complex components such as heteropolysaccharides (HPS), amide/peptides and amino sugars (AMS) constitute 75-84% of HMW DOC whereas carboxylic-rich alicyclic molecules (CRAM) made up 16-25% of HMW DOC in the lake. Combined HPS and AMS, O-alkyl carbohydrate carbon, and total carbohydrate carbon contents were significantly positively correlated to the Δ14C of HMW DOC suggesting they contribute a contemporary 14C-enriched component to the HMW DOC in the lake. In contrast, CRAM and aliphatic carbons were significantly inversely correlated with Δ14C of HMW DOC implying that these represent 14C-depleted (older) components of HMW DOC in the lake. At Amity Creek, storm events led to larger loads of bulk DOC and POC, which were both 14C-enriched (modern). However, in baseflow conditions 14C-depleted bulk DOC and POC were exported. LMW DOC from the creek was considerably 14C-depleted compared to concurrent HMW DOC.

Dissolved nutrient balance and net ecosystem metabolism in a Mediterranean-climate coastal lagoon: San Diego Bay

NASA Astrophysics Data System (ADS)

Delgadillo-Hinojosa, F.; Zirino, A.; Holm-Hansen, O.; Hernández-Ayón, J. M.; Boyd, T. J.; Chadwick, B.; Rivera-Duarte, I.

2008-02-01

The temporal and spatial variability of dissolved inorganic phosphate (DIP), nitrogen (DIN), carbon (DIC) and dissolved organic carbon (DOC) were studied in order to determine the net ecosystem metabolism (NEM) of San Diego Bay (SDB), a Mediterranean-climate lagoon. A series of four sampling campaigns were carried out during the rainy (January 2000) and the dry (August 2000 and May and September 2001) seasons. During the dry season, temperature, salinity and DIP, DIC and DOC concentrations increased from oceanic values in the outer bay to higher values at the innermost end of the bay. DIP, DIC and DOC concentrations showed a clear offset from conservative mixing implying production of these dissolved materials inside the bay. During the rainy season, DIP and DOC increased to the head, whereas salinity decreased toward the mouth due to land runoff and river discharges. The distributions of DIP and DOC also showed a deviation from conservative mixing in this season, implying a net addition of these dissolved materials during estuarine mixing within the bay. Mass balance calculations showed that SDB consistently exported DIP (2.8-9.8 × 10 3 mol P d -1), DIC (263-352 × 10 3 mol C d -1) and DOC (198-1233 × 10 3 mol C d -1), whereas DIN (5.5-18.2 × 10 3 mol N d -1) was exported in all samplings except in May 2001 when it was imported (8.6 × 10 3 mol N d -1). The DIP, DIC and DOC export rates along with the strong relationship between DIP, DIC or DOC and salinity suggest that intense tidal mixing plays an important role in controlling their distributions and that SDB is a source of nutrients and DOC to the Southern California Bight. Furthermore, NEM ranged from -8.1 ± 1.8 mmol C m -2 d -1 in September to -13.5 ± 5.8 mmol C m -2 d -1 in January, highlighting the heterotrophic character of SDB. In order to explain the net heterotrophy of this system, we postulate that phytoplankton-derived particulate organic matter, stimulated by upwelling processes in the adjacent coastal waters, is transported into the bay, retained and then remineralized within the system. Our results were compared with those reported for the heterotrophic hypersaline coastal lagoons located in the semi-arid coast of California-Baja California, and with those autotrophic hypersaline systems found in the semi-arid areas of Australia. We point out that the balance between autotrophy and heterotrophy in inverse estuaries is dependent on net external inputs of either inorganic nutrients or organic matter as it has been indicated for positive estuaries.

Constraining the Exchange of Carbon and Nitrogen in Eastern Long Island Sound

NASA Astrophysics Data System (ADS)

Byrd, A.; Warren, J. K.; Vlahos, P.; Whitney, M. M.

2017-12-01

Long Island Sound (LIS) is an urban estuary on the US east coast that undergoes seasonal hypoxia in its western and central regions. Currently, the budgets of both carbon and nitrogen in LIS remain unbalanced, despite their importance to the efficient and strategic management of the health of coastal and aquatic ecosystems. In this study, we evaluated the exchange values of C and N at the mouth of LIS (the Race), in order to constrain export through this important boundary. Discreet water samples were collected during four 15 km transects over the Race at five stations and three depths each station to resolve the temporal variability over a complete tidal cycle, in order to assess both net flux and variations across the tidal period. By evaluating both the particulate and dissolved pools of carbon (POC, PIC, DOC, DIC) and nitrogen (PON, DON, DIN) during the spring, summer and winter (high and low flow conditions) and pairing these measurements with physical data, we were able to identify a variety of forcing and export regimes. Preliminary results indicate the importance of spatial and tidal variability on flux estimates and show little or no export (and sometimes import) of nitrogen and significant export of organic carbon.

Seasonal dynamics and Organic Carbon Flux in the Congo River

NASA Astrophysics Data System (ADS)

Seyler, P.; Coynel, A.; Etcheber, H.; Meybeck, M.

2006-12-01

The Congo (Zaire) River, the second world river in terms of discharges and drainage area (Q=40600 m3/s; A=3.5 106 km2) after the Amazon River, is -up to now- in near-pristine state. For up to two years , the mainstream near river mouth (Kinshasa/Brazzaville station) and some major and minor tributaries (Oubangui, Mpoko and Ngoko-Sangha) were surveyed every month, for total suspended sediment (TSS), particulate organic carbon (POC) and dissolved organic carbon (DOC). In this very flat basin, TSS levels were very low and organic carbon was essentially exported as DOC: 74% of TOC for the tributaries flowing in savannah regions to 86% for those flowing in the rainforest). The seasonal patterns of TSS, POC and DOC showed clockwise hysteresis with river discharges, with maximum levels two to four months before peak flows. At the Kinshasa/Brazzaville station, the DOC distribution is largely influenced by the input of the tributaries draining the marshy forest area (Central depression). In term of fluxes, a marked difference is pointed out between specific fluxes, threefold higher in the forested basin than in savannahs basins. Computation of inputs to Atlantic Ocean showed that the Congo was responsible for 14.4 106 t/yr of TOC of which 12.4 106 t/yr is DOC and 2 106 t/yr is POC. The three biggest tropical rivers (Amazon, Congo and Orinoco) with only 10 percent of the exoreic world area drained to ocean world contribute to 4 percent of its TSS inputs but 29-33 percent of its organic carbon inputs.

Hydrological controls on dissolved organic carbon production and release from UK peatlands

NASA Astrophysics Data System (ADS)

Fenner, Nathalie; Freeman, Chris; Worrall, Fred

Long-term increases in dissolved organic carbon (DOC) release from peatlands to British aquatic ecosystems are widely acknowledged, and are now confirmed to occur in a wide variety of boreal and subboreal settings. Depth to water table is probably the single most important hydrological factor governing that DOC generation and will modulate the response of the system to other environmental factors (such as warming and rising atmospheric carbon dioxide) in a changing climate. Many workers have attempted to attribute the rising DOC trend to a single "universal" driving variable. However, two fundamental problems prevent this: (1) universal theories, i.e., climate change theories that can account for rising trends in diverse catchment types, seem insufficient to account for the large observed increases, and (2) regional theories cannot account for the trend in all catchment types. Here it is suggested that multiple and possibly different drivers can modify DOC exports at four stages, namely, production, diffusion, solubility, and transport, with hydrology undoubtedly having a direct or indirect role in all the potential drivers considered here. These mechanisms, and the interactions between them, need to be more fully understood if we are to predict the response of the United Kingdom and global peatland carbon stores to environmental changes. Moreover, if we are to attempt to ameliorate rising DOC, we will need to fully appreciate the implications of restoration of drained peatlands and land management practices, to ensure that carbon losses are reduced on various temporal scales. These are research topics that remain in their infancy.

The Influence of Wetland Cover and Dissolved Organic Carbon on Mercury Export in Forest Landscapes, Northeastern USA

NASA Astrophysics Data System (ADS)

Dittman, J. A.; Shanley, J. B.; Driscoll, C. T.; Aiken, G.; Chalmers, A.; Towse, J.

2007-12-01

Mercury (Hg) contamination is widespread in remote areas of the northeastern USA. Atmospheric Hg is deposited on terrestrial uplands and subsequently mobilized to downstream aquatic ecosystems. We are investigating the fate of Hg deposited in forested watersheds by quantifying stream transport of Hg, and the interactions with dissolved and particulate organic matter. We hypothesize that the landscape characteristics controlling the production and mobility of organic matter will likewise control the mobility of Hg. This research was conducted at three sites in the Northeast that represent a range of hydrochemical conditions and span a range of wetland cover. Most stream export of Hg occurs at high flow; therefore we collected samples during snowmelt and storms. Mercury concentrations increase with discharge at all three sites; however the partitioning of Hg fractions (dissolved vs. particulate) differs among sites during high flow events. At the Hubbard Brook Experimental Forest, NH (watershed 6), there are no true wetlands and dissolved organic carbon (DOC) and total Hg (THg) concentrations, and suspended sediment concentration (SSC) (mean DOC = 3.1 mg C L-1; THg = 1.5 ng L-1; SSC < 50 mg L-1) are low even during the highest of flow events. At Sleepers River, VT (watershed 9), SSC can be elevated during events (SSC > 500 mg L-1), consequently the particulate Hg fraction can range as high as 95% of the THg concentration (mean particulate Hg concentration = 10.2 ng L- 1). At Archer Creek (Huntington Forest, NY), which has the greatest percent wetland cover (10%) of our three sites, DOC concentrations are high (mean DOC = 7.5 mg C L-1), while SSC are low (SSC < 10 mg L- 1). At Archer Creek, Hg is largely in the dissolved form (~75% of Hg) and strongly correlated with DOC (r2 = 0.90). The hydrophobic organic acid (HPOA) fraction of DOC is most effective at mobilizing Hg and is strongly correlated to Hg concentrations in stream water. This research suggests that high concentrations of Hg can be present in stream water from forest watersheds during high flow events, and that wetlands and suspended sediment favor Hg export. However, it is not clear to what degree this Hg is bioavailable for potential uptake by organisms in aquatic ecosystems following mobilization.

Soil Dissolved Organic Carbon Fluxes are Controlled by both Precipitation and Longer-Term Climate Effects on Boreal Forest Ecosystems

NASA Astrophysics Data System (ADS)

Hotchkiss, E. R.; Ziegler, S. E.; Edwards, K. A.; Bowering, K.

2017-12-01

Water acts as a control on the cycling of organic carbon (OC). Forest productivity responses to climate change are linked to water availability while water residence time is a major control on OC loss in aquatic ecosystems. However, controls on the export of terrestrial OC to the aquatic environment remains poorly understood. Transport of dissolved OC (DOC) through soils both vertically to deeper soil horizons and into aquatic systems is a key flux of terrestrial OC, but the climate drivers controlling OC mobilized from soils is poorly understood. We installed zero-tension lysimeters across similar balsam fir forest sites within three regions that span a MAT gradient of 5.2˚C and MAP of 1050-1500 mm. Using soil water collected over all seasons for four years we tested whether a warmer and wetter climate promotes greater DOC fluxes in ecosystems experiencing relatively high precipitation. Variability within and between years was compared to that observed across climates to test the sensitivity of this flux to shorter relative to longer-term climate effects on this flux. The warmest and wettest southern site exhibited the greatest annual DOC flux (25 to 28 g C m-2 y-1) in contrast to the most northern site (8 to 10 g C m -2 y-1). This flux represented 10% of litterfall C inputs across sites and surpassed the DOC export from associated forested headwater streams (1 to 16 g C m-2 y-1) suggesting terrestrial to aquatic interface processing. Historical climate and increased soil C inputs explain the greater DOC flux in the southern region. Even in years with comparable annual precipitation among regions the DOC flux differed by climate region. Furthermore, neither quantity nor form of precipitation could explain inter-annual differences in DOC flux within each region. Region specific relationships between precipitation and soil water flux instead suggest historical climate effects may impact soil water transport efficiency thereby controlling the regional variation in the DOC flux. As these forests are exposed to a warmer and wetter climate, DOC transport from organic soils will likely increase. Although precipitation changes will impact this C flux, longer-term climate effects impacting soil inputs, composition and structure of these forests will play an important role in controlling DOC transport in a warmer and wetter future.

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.

Controls on stream water dissolved mercury in three mid-Appalachian forested headwater catchments

NASA Astrophysics Data System (ADS)

Riscassi, Ami L.; Scanlon, Todd M.

2011-12-01

Determining the controls on dissolved mercury (HgD) transport is necessary to improve estimations of export from unmonitored watersheds and to forecast responses to changes in deposition and other environmental forcings. Stream water HgD and dissolved organic carbon (DOC) were evaluated over a range of discharge conditions in three streams within Shenandoah National Park, VA. Watersheds are distinguished by stream water pH (ranging from neutral to acidic) and soil size fractioning (ranging from clays to sands). At all sites, discharge was a significant but poor predictor of HgD concentrations (r2 from 0.13-0.52). HgD was strongly coupled with DOC at all sites (r2 from 0.74-0.89). UV absorbance at 254 nm (UV254), a proxy for DOC quantity and quality, slightly improved the predictions of HgD. Mean DOC quality differed between streams, with less aromatic DOC mobilized from the more acidic watershed. The site with less aromatic DOC and sandy soils mobilized more Hg to the stream for the same quantity and quality of DOC, likely due to the reduced capacity of the larger-grained soils to retain Hg, leaving a greater fraction associated with the organic matter. A similar amount of 0.54 ng HgD/mg DOC is transported at all sites, suggesting the less aromatic DOC transports less Hg per unit DOC, offsetting the effects of soil type. This research demonstrates that soil composition and DOC quality influence HgDexport. We also provide evidence that soil organic carbon is a primary control on Hg-DOC ratios (0.12-1.4 ng mg-1) observed across the U.S. and Sweden.

Carbon fluxes in an acid rain impacted boreal headwater catchment

NASA Astrophysics Data System (ADS)

Marx, Anne; Hintze, Simone; Jankovec, Jakub; Sanda, Martin; Dusek, Jaromir; Vogel, Tomas; van Geldern, Robert; Barth, Johannes A. C.

2016-04-01

Terrestrial carbon export via inland aquatic systems is a key process in the budget of the global carbon cycle. This includes loss of carbon to the atmosphere via gas evasion from rivers or reservoirs as well as carbon fixation in freshwater sediments. Headwater streams are the first endmembers of the transition of carbon between soils, groundwater and surface waters and the atmosphere. In order to quantify these processes the experimental catchment Uhlirska (1.78 km2) located in the northern Czech Republic was studied. Dissolved inorganic, dissolved organic and particulate organic carbon (DIC, DOC, POC) concentrations and isotopes were analyzed in ground-, soil -and stream waters between 2014 and 2015. In addition, carbon dioxide degassing was quantified via a stable isotope modelling approach. Results show a discharge-weighted total carbon export of 31.99 g C m-2 yr-1 of which CO2 degassing accounts 79 %. Carbon isotope ratios (δ13C) of DIC, DOC, and POC (in ‰ VPDB) ranged from -26.6 to -12.4 ‰ from -29.4 to -22.7 ‰ and from -30.6 to -26.6 ‰ respectively. The mean values for DIC are -21.8 ±3.8 ‰ -23.6 ±0.9 ‰ and -19.5 ±3.0 ‰ for soil, shallow ground and surface water compartments. For DOC, these compartments have mean values of -27.1 ±0.3 ‰ -27.0 ±0.8 ‰ and -27.4 ±0.7 ‰Ṁean POC value of shallow groundwaters and surface waters are -28.8 ±0.8 ‰ and -29.3 ±0.5 ‰ respectively. These isotope ranges indicate little turnover of organic material and predominant silicate weathering. The degassing of CO2 caused an enrichment of the δ13C-DIC values of up to 6.8 ‰ between a catchment gauge and the catchment outlet over a distance of 866 m. In addition, the Uhlirska catchment has only negligible natural sources of sulphate, yet SO42- accounts for 21 % of major stream water ions. This is most likely a remainder from acid rain impacts in the area.

Dissolved organic carbon in runoff and tile-drain water under corn and forage fertilized with hog manure.

PubMed

Royer, Isabelle; Angers, Denis A; Chantigny, Martin H; Simard, Régis R; Cluis, Daniel

2007-01-01

Dissolved organic carbon (DOC) export from soils can play a significant role in soil C cycling and in nutrient and pollutant transport. However, information about DOC losses from agricultural soils as influenced by management practices is scarce. We compared the effects of mineral fertilizer (MF) and liquid hog manure (LHM) applications on the concentration and molecular size of DOC released in runoff and tile-drain water under corn (Zea mays L.) and forage cropping systems. Runoff and tile-drain water samples were collected during a 2-mo period (October to December 1998) and DOC concentration was measured. Characterization of DOC was performed by tangential ultrafiltration with nominal cut-offs at 3 and 100 kDa. Mean concentration of DOC in runoff water (12.7 mg DOC L(-1)) was higher than in tile-drain water (6.5 mg DOC L(-1)). Incorporation of corn residues increased the DOC concentration by 6- to 17-fold in surface runoff, but this effect was short-lived. In runoff water, the relative size of the DOC molecules increased when corn residues and LHM were applied probably due to partial microbial breakdown of these organic materials and to a faster decomposition or preferential adsorption of the small molecules. The DOC concentration in tile-drain water was slightly higher under forage (7.5 mg DOC L(-1)) than under corn (5.4 mg DOC L(-1)) even though the application rates of LHM were higher in corn plots. We suggest that preferential flow facilitated the migration of DOC to tile drains in forage plots. In conclusion, incorporation of corn residues and LHM increased the concentration of DOC and the relative size of the molecules in surface runoff water, whereas DOC in tile-drain water was mostly influenced by the cropping system with relatively more DOC and larger molecules under forage than corn.

Hillslope nutrient dynamics following upland riparian vegetation disturbance

Treesearch

J. Alan Yeakley; David C. Coleman; Bruce L. Haines; Brian D. Kloeppel; Judy L. Meyer; Wayne T. Swank; Barry W. Argo; James M. Deal; Sharon F. Taylor

2003-01-01

We investigated the effects of removing nearstream Rhododendron and of the natural blowdown of canopy trees on nutrient export to streams in the southern Appalachians. Transects were instrumented on adjacent hillslopes in a first-order watershed at the Coweeta Hydrologic Laboratory (35°03'N, 83°25'W). Dissolved organic carbon (DOC), K+...

Export of dissolved organic carbon and nitrogen from drained and re-wetted bog sites in Lower Saxony (Germany)

NASA Astrophysics Data System (ADS)

Frank, Stefan; Tiemeyer, Bärbel; Freibauer, Annette

2014-05-01

Today, nearly all peatlands in Germany are drained for agriculture, forestry and peat cutting. The export of dissolved organic carbon (C) and nitrogen (N) may be important for the overall C and N balances and affects downstream ecosystems. While drainage generally increases solute losses, there is nearly no C and N export data of raised bogs in Germany which can be used to evaluate both the impact of drainage associated with intensive land use and the re-wetting of peat cutting sites. In the "Ahlenmoor" (North-Western Germany), four sampling points were chosen. Three sampling points represent a deeply drained intensively used grassland at various scales ranging from a drainage pipe (DP, 0.08 ha) and a drainage ditch (DD, 6.8 ha) to a collector ditch (CD, 20 ha). The fourth sampling point (RW) is a former peat cutting site (23 ha) re-wetted 10 years ago. At this site, polder technique was used to establish water tables at the soil surface. Sampling and discharge measurements were conducted bi-weekly from June 2011 to June 2013. Water table levels were recorded with automatic pressure sensors, and rating curves between discharge and water levels were used to calculate continuous discharge values. Samples were analyzed for dissolved organic carbon (DOC), particulate organic carbon (POC), dissolved organic nitrogen (DON), ammonium (NH4+), nitrate (NO3-), sulphate (SO42-), pH, electric conductivity (EC) and specific UV absorbance (SUVA). The discharge did not vary strongly between the sampling points and was slightly lower in the second year. Concentrations of all measured solutes were higher at the intensive grassland (DP, DD and CD) than at the re-wetted site. Surprisingly, SUVA showed no difference between all sites, while the DOC to DON ratio was narrower at DP, DD and CD than at RW. This indicates an export of more degraded dissolved organic matter (DOM) from the drained area. At the grassland sites, no statistical differences were found between the three scales except for SO42-, NO3- and pH. Thus, the grassland shows rather homogenous export patterns over various spatial scales, and there seem to be no fast mineralization or degradation of the exported DOM during the initial stage of export. In total, average losses of DOC (457 kg ha-1 a-1) and POC (40 kg ha-1 a-1) from the drained area were nearly thrice as high as from the re-wetted site (124 and 73 kg ha-1 a-1). The total nitrogen losses were even more reduced by re-wetting and dominated at all sites by DON (19.1 kg ha-1 a-1 at the grassland sites, 3.9 kg ha-1 a-1 at the re-wetted site). NH4+ (drained: 5.2 kg ha-1 a-1, re-wetted: 0.8 kg ha-1 a-1) and NO3- (drained: 1.6 kg ha-1 a-1, re-wetted: not detectable) played a minor role. Overall, differences in the export could rather be explained by differences in solute concentration than in discharge.

Methylmercury production in and export from agricultural wetlands in California, USA: the need to account for physical transport processes into and out of the root zone

USGS Publications Warehouse

Bachand, Philip A.M.; Bachand, Sandra M.; Fleck, Jacob A.; Alpers, Charles N.; Stephenson, Mark; Windham-Myers, Lisamarie

2014-01-01

Concentration and mass balance analyses were used to quantify methylmercury (MeHg) loads from conventional (white) rice, wild rice, and fallowed fields in northern California's Yolo Bypass. These analyses were standardized against chloride to distinguish transport pathways and net ecosystem production (NEP). During summer, chloride loads were both exported with surface water and moved into the root zone at a 2:1 ratio. MeHg and dissolved organic carbon (DOC) behaved similarly with surface water and root zone exports at ~ 3:1 ratio. These trends reversed in winter with DOC, MeHg, and chloride moving from the root zone to surface waters at rates opposite and exceeding summertime root zone fluxes. These trends suggest that summer transpiration advectively moves constituents from surface water into the root zone, and winter diffusion, driven by concentration gradients, subsequently releases those constituents into surface waters. The results challenge a number of paradigms regarding MeHg. Specifically, biogeochemical conditions favoring microbial MeHg production do not necessarily translate to synchronous surface water exports; MeHg may be preserved in the soils allowing for release at a later time; and plants play a role in both biogeochemistry and transport. Our calculations show that NEP of MeHg occurred during both summer irrigation and winter flooding. Wild rice wet harvesting and winter flooding of white rice fields were specific practices that increased MeHg export, both presumably related to increased labile organic carbon and disturbance. Outflow management during these times could reduce MeHg exports. Standardizing MeHg outflow:inflow concentration ratios against natural tracers (e.g. chloride, EC) provides a simple tool to identify NEP periods. Summer MeHg exports averaged 0.2 to 1 μg m− 2 for the different agricultural wetland fields, depending upon flood duration. Average winter MeHg exports were estimated at 0.3 μg m− 2. These exports are within the range reported for other shallow aquatic systems.

Methylmercury production in and export from agricultural wetlands in California, USA: the need to account for physical transport processes into and out of the root zone.

PubMed

Bachand, P A M; Bachand, S M; Fleck, J A; Alpers, C N; Stephenson, M; Windham-Myers, L

2014-02-15

Concentration and mass balance analyses were used to quantify methylmercury (MeHg) loads from conventional (white) rice, wild rice, and fallowed fields in northern California's Yolo Bypass. These analyses were standardized against chloride to distinguish transport pathways and net ecosystem production (NEP). During summer, chloride loads were both exported with surface water and moved into the root zone at a 2:1 ratio. MeHg and dissolved organic carbon (DOC) behaved similarly with surface water and root zone exports at ~3:1 ratio. These trends reversed in winter with DOC, MeHg, and chloride moving from the root zone to surface waters at rates opposite and exceeding summertime root zone fluxes. These trends suggest that summer transpiration advectively moves constituents from surface water into the root zone, and winter diffusion, driven by concentration gradients, subsequently releases those constituents into surface waters. The results challenge a number of paradigms regarding MeHg. Specifically, biogeochemical conditions favoring microbial MeHg production do not necessarily translate to synchronous surface water exports; MeHg may be preserved in the soils allowing for release at a later time; and plants play a role in both biogeochemistry and transport. Our calculations show that NEP of MeHg occurred during both summer irrigation and winter flooding. Wild rice wet harvesting and winter flooding of white rice fields were specific practices that increased MeHg export, both presumably related to increased labile organic carbon and disturbance. Outflow management during these times could reduce MeHg exports. Standardizing MeHg outflow:inflow concentration ratios against natural tracers (e.g. chloride, EC) provides a simple tool to identify NEP periods. Summer MeHg exports averaged 0.2 to 1 μg m(-2) for the different agricultural wetland fields, depending upon flood duration. Average winter MeHg exports were estimated at 0.3 μg m(-2). These exports are within the range reported for other shallow aquatic systems. Copyright © 2013 Elsevier B.V. All rights reserved.

Spatial and seasonal dynamics of total suspended sediment and organic carbon species in the Congo River

NASA Astrophysics Data System (ADS)

Coynel, Alexandra; Seyler, Patrick; Etcheber, Henri; Meybeck, Michel; Orange, Didier

2005-12-01

The Congo (Zaire) River, the world's second largest river in terms both of water discharges and of drainage area after the Amazon River, has remained to date in a near-pristine state. For a period between 2 and 6 years, the mainstream near the river mouth (Brazzaville/Kinshasa station) and some of the major and minor tributaries (the Oubangui, Mpoko, and Ngoko-Sangha) were monitored every month for total suspended sediment (TSS), particulate organic carbon (POC), and dissolved organic carbon (DOC). In this large but relatively flat equatorial basin, TSS levels are very low and organic carbon is essentially exported as DOC: from 74% of TOC for the tributaries flowing in savannah regions and 86% for those flowing in the rain forest. The seasonal patterns of TSS, POC, and DOC show clockwise hysteresis in relation to river discharges, with maximum levels recorded 2 to 4 months before peak flows. At the Kinshasa/Brazzaville station, the DOC distribution is largely influenced by the input from the tributaries draining the large marshy forest area located in the center of the basin. There is a marked difference between specific fluxes, threefold higher in the forest basins than in the savannah basins. The computation of inputs to the Atlantic Ocean demonstrates that the Congo is responsible for 14.4 × 106 t/yr of TOC of which 12.4 × 106 t/yr is DOC and 2 × 106 t/yr is POC. The three biggest tropical rivers (the Amazon, the Congo, and the Orinoco), with only 10% of the exoreic world area drained to world oceans, contribute ˜4% of its TSS inputs but 15-18% of its organic carbon inputs. These proportions may double when considering only world rivers discharging into the open ocean.

Carbon budget for a British upland peat catchment.

PubMed

Worrall, Fred; Reed, Mark; Warburton, Jeff; Burt, Tim

2003-08-01

This study describes the analysis of fluvial carbon flux from an upland peat catchment in the North Pennines. Dissolved organic carbon (DOC), pH, alkalinity and calcium were measured in weekly samples, with particulate organic carbon (POC) measured from the suspended sediment load from the stream outlet of an 11.4-km(2) catchment. For calendar year 1999, regular monitoring of the catchment was supplemented with detailed quasi-continuous measurements of flow and stream temperature, and DOC for the months September through November. The measurements were used to calculate the annual flux of dissolved CO(2), dissolved inorganic carbon, DOC and POC from the catchment and were combined with CO(2) and CH(4) gaseous exchanges calculated from previously published values and the observations of water table height within the peat. The study catchment represents a net sink of 15.4+/-11.9 gC/m(2)/yr. Carbon flows calculated for the study catchment are combined with values in the literature, using a Monte Carlo method, to estimate the carbon budget for British upland peat. For all British upland peat the calculation suggests a net carbon sink of between 0.15 and 0.29 MtC/yr. This is the first study to include a comprehensive study of the fluvial export of carbon within carbon budgets and shows the size of the peat carbon sink to be smaller than previous estimates, although sensitivity analysis shows that the primary productivity rather than fluvial carbon flux is a more important element in estimating the carbon budget in this regard.

Spatial and seasonal variability of dissolved organic matter in the Cariaco Basin

NASA Astrophysics Data System (ADS)

Lorenzoni, Laura; Taylor, Gordon T.; Benitez-Nelson, Claudia; Hansell, Dennis A.; Montes, Enrique; Masserini, Robert; Fanning, Kent; Varela, Ramón; Astor, Yrene; GuzmáN, Laurencia; Muller-Karger, Frank E.

2013-06-01

organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) were measured monthly at the CARIACO Time Series station (10°30'N, 64°40'W) in the southeastern Caribbean Sea between 2005 and 2012. Marked seasonal variability in DOC concentrations was observed, with lower values (~66 µM) in the upper water column (<75 m) during the upwelling season (December-April) due to the injection of cool, DOC-impoverished Subtropical Underwater from the Caribbean Sea. During the rainy season (May-November) waters were stratified and upper layer DOC concentrations increased to ~71 µM. Interannual variability in surface (1 m) concentrations of DOC was also observed in response to the variable strength in upwelling and stratification that the Cariaco Basin experienced. DON and DOP showed no such seasonality. At depths >350 m, DOC concentrations were 56 ± 4.7 µM, roughly 10 µM higher than those in the Caribbean Sea over the same depth range. DON and DOP showed similar vertical profiles to that of DOC, with higher concentrations (6.8 ± 1.2 µM N and 0.15 ±0.09 µM P) in the upper water column and invariant, lower concentrations at depth (4.8 ± 1.6 µM N and 0.10 ± 0.08 µM P). Wind-driven advection of surface DOC out of the Cariaco Basin was estimated to support a net export ~15 Gmol C yr-1 into the Caribbean Sea; this rate is comparable to the flux of settling particulate organic carbon to depths >275 m within the basin.

Changes in the character of DOC in streams during storms in two Midwestern watersheds with contrasting land uses

USGS Publications Warehouse

Vidon, P.; Wagner, L.E.; Soyeux, E.

2008-01-01

Dissolved organic carbon (DOC) dynamics in streams is important, yet few studies focus on DOC dynamics in Midwestern streams during storms. In this study, stream DOC dynamics during storms in two Midwestern watersheds with contrasting land uses, the change in character of stream DOC during storms, and the usability of DOC as a hydrologic tracer in artificially drained landscapes of the Midwest are investigated. Major cation/DOC concentrations, and DOC specific UV absorbance (SUVA) and fluorescence index (FI) were monitored at 2-4 h intervals during three spring storms. Although DOC is less aromatic in the mixed land use watershed than in the agricultural watershed, land use has little impact on stream DOC concentration during storms. For both watersheds, DOC concentration follows discharge, and SUVA and FI values indicate an increase in stream DOC aromaticity and lignin content during storms. The comparison of DOC/major cation flushing dynamics indicates that DOC is mainly exported via overland flow/macropore flow. In both watersheds, the increase in DOC concentration in the streams during storms corresponds to a shift in the source of DOC from DOC originating from mineral soil layers of the soil profile at baseflow, to DOC originating from surficial soil layers richer in aromatic substances and lignin during storms. Results also suggest that DOC, SUVA and FI could be used as hydrologic tracers in artificially drained landscapes of the Midwest. These results underscore the importance of sampling streams for DOC during high flow periods in order to understand the fate of DOC in streams. ?? 2008 Springer Science+Business Media B.V.

Influence of UVB radiation on aquatic ecosystems

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

Lean, D.R.S.

The impact of increased UVB (290--320 nm) radiation due to stratospheric ozone depletion is placed in context with how historical levels of both UVB and UVa (320--400 nm) have influenced the structure of aquatic communities and geochemistry of lakes and their drainage basins. Suggestions for the development of generalized models for predicting the impact of UV radiation are provided and illustrate that both the response of a particular process as a function of wavelength and reliable predictions for underwater spectral irradiance are needed. Direct effects on organisms are discussed in light of problems due to adaptation, avoidance, repair and consequencesmore » of changes from sensitive to tolerant species composition. Indirect effects mediated through photochemically produced highly reactive reduced oxygen species are introduced and related to redox reactions and metal speciation using the mercury cycle as an example. Although neglected in existing global carbon budgets, UV radiation is responsible for significant release of carbon dioxide and carbon monoxide as well as many other organic metabolites from refractory dissolved organic carbon (DOC). Finally, it was argued that some lakes are losing the sun screen provided by DOC, the principal attenuator of UV radiation, due to increased acidification and lower DOC export due to the warmer drier climate conditions.« less

Black Carbon in Estuarine (Coastal) High-molecular-weight Dissolved Organic Matter

NASA Technical Reports Server (NTRS)

Mannino, Antonio; Harvey, H. Rodger

2003-01-01

Dissolved organic matter (DOM) in the ocean constitutes one of the largest pools of organic carbon in the biosphere, yet much of its composition is uncharacterized. Observations of black carbon (BC) particles (by-products of fossil fuel combustion and biomass burning) in the atmosphere, ice, rivers, soils and marine sediments suggest that this material is ubiquitous, yet the contribution of BC to the ocean s DOM pool remains unknown. Analysis of high-molecular-weight DOM isolated from surface waters of two estuaries in the northwest Atlantic Ocean finds that BC is a significant component of DOM, suggesting that river-estuary systems are important exporters of BC to the ocean through DOM. We show that BC comprises 4-7% of the dissolved organic carbon (DOC) at coastal ocean sites, which supports the hypothesis that the DOC pool is the intermediate reservoir in which BC ages prior to sedimentary deposition. Flux calculations suggest that BC could be as important as vascular plant-derived lignin in terms of carbon inputs to the ocean. Production of BC sequesters fossil fuel- and biomass-derived carbon into a refractory carbon pool. Hence, BC may represent a significant sink for carbon to the ocean.

Lateral carbon fluxes and CO2 outgassing from a tropical peat-draining river

NASA Astrophysics Data System (ADS)

Müller, D.; Warneke, T.; Rixen, T.; Müller, M.; Jamahari, S.; Denis, N.; Mujahid, A.; Notholt, J.

2015-07-01

Tropical peatlands play an important role in the global carbon cycle due to their immense carbon storage capacity. However, pristine peat swamp forests are vanishing due to deforestation and peatland degradation, especially in Southeast Asia. CO2 emissions associated with this land use change might not only come from the peat soil directly, but also from peat-draining rivers. So far, though, this has been mere speculation, since there was no data from undisturbed reference sites. We present the first combined assessment of lateral organic carbon fluxes and CO2 outgassing from an undisturbed tropical peat-draining river. Two sampling campaigns were undertaken on the Maludam river in Sarawak, Malaysia. The river catchment is covered by protected peat swamp forest, offering a unique opportunity to study a peat-draining river in its natural state, without any influence from tributaries with different characteristics. The two campaigns yielded consistent results. Dissolved organic carbon (DOC) concentrations ranged between 3222 and 6218 μmol L-1 and accounted for more than 99 % of the total organic carbon (TOC). Radiocarbon dating revealed that the riverine DOC was of recent origin, suggesting that it derives from the top soil layers and surface runoff. We observed strong oxygen depletion, implying high rates of organic matter decomposition and consequently CO2 production. The measured median pCO2 was 7795 and 8400 μatm during the two campaigns, respectively. Overall, we found that only 26 ± 15 % of the carbon was exported by CO2 evasion, while the rest was exported by discharge. CO2 outgassing seemed to be moderated by the short water residence time. Since most Southeast Asian peatlands are located at the coast, this is probably an important limiting factor for CO2 outgassing from most of its peat-draining rivers.

Dissolved organic carbon and major and trace elements in peat porewater of sporadic, discontinuous, and continuous permafrost zones of western Siberia

NASA Astrophysics Data System (ADS)

Raudina, Tatiana V.; Loiko, Sergey V.; Lim, Artyom G.; Krickov, Ivan V.; Shirokova, Liudmila S.; Istigechev, Georgy I.; Kuzmina, Daria M.; Kulizhsky, Sergey P.; Vorobyev, Sergey N.; Pokrovsky, Oleg S.

2017-07-01

Mobilization of dissolved organic carbon (DOC) and related trace elements (TEs) from the frozen peat to surface waters in the permafrost zone is expected to enhance under ongoing permafrost thaw and active layer thickness (ALT) deepening in high-latitude regions. The interstitial soil solutions are efficient tracers of ongoing bio-geochemical processes in the critical zone and can help to decipher the intensity of carbon and metals migration from the soil to the rivers and further to the ocean. To this end, we collected, across a 640 km latitudinal transect of the sporadic to continuous permafrost zone of western Siberia peatlands, soil porewaters from 30 cm depth using suction cups and we analyzed DOC, dissolved inorganic carbon (DIC), and 40 major elements and TEs in 0.45 µm filtered fraction of 80 soil porewaters. Despite an expected decrease in the intensity of DOC and TE mobilization from the soil and vegetation litter to the interstitial fluids with the increase in the permafrost coverage and a decrease in the annual temperature and ALT, the DOC and many major and trace elements did not exhibit any distinct decrease in concentration along the latitudinal transect from 62.2 to 67.4° N. The DOC demonstrated a maximum of concentration at 66° N, on the border of the discontinuous/continuous permafrost zone, whereas the DOC concentration in peat soil solutions from the continuous permafrost zone was equal to or higher than that in the sporadic/discontinuous permafrost zone. Moreover, a number of major (Ca, Mg) and trace (Al, Ti, Sr, Ga, rare earth elements (REEs), Zr, Hf, Th) elements exhibited an increasing, not decreasing, northward concentration trend. We hypothesize that the effects of temperature and thickness of the ALT are of secondary importance relative to the leaching capacity of peat, which is in turn controlled by the water saturation of the peat core. The water residence time in peat pores also plays a role in enriching the fluids in some elements: the DOC, V, Cu, Pb, REEs, and Th were a factor of 1.5 to 2.0 higher in mounds relative to hollows. As such, it is possible that the time of reaction between the peat and downward infiltrating waters essentially controls the degree of peat porewater enrichments in DOC and other solutes. A 2° northward shift in the position of the permafrost boundaries may bring about a factor of 1.3 ± 0.2 decrease in Ca, Mg, Sr, Al, Fe, Ti, Mn, Ni, Co, V, Zr, Hf, Th, and REE porewater concentration in continuous and discontinuous permafrost zones, and a possible decrease in DOC, specific ultraviolet absorbency (SUVA), Ca, Mg, Fe, and Sr will not exceed 20 % of their current values. The projected increase in ALT and vegetation density, northward migration of the permafrost boundary, or the change of hydrological regime is unlikely to modify chemical composition of peat porewater fluids larger than their natural variations within different micro-landscapes, i.e., within a factor of 2. The decrease in DOC and metal delivery to small rivers and lakes by peat soil leachate may also decrease the overall export of dissolved components from the continuous permafrost zone to the Arctic Ocean. This challenges the current paradigm on the increase in DOC export from the land to the ocean under climate warming in high latitudes.

Anthropogenic inputs of dissolved organic matter in New York Harbor

NASA Astrophysics Data System (ADS)

Gardner, G. B.; Chen, R. F.; Olavasen, J.; Peri, F.

2016-02-01

The Hudson River flows into the Atlantic Ocean through a highly urbanized region which includes New York City to the east and Newark, New Jersey to the west. As a result, the export of Dissolved Organic Carbon (DOC) from the Hudson to the Atlantic Ocean includes a significant anthropogenic component. A series of high resolution studies of the DOC dynamics of this system were conducted between 2003 and 2010. These included both the Hudson and adjacent large waterways (East River, Newark Bay, Kill Van Kull and Arthur Kill) using coastal research vessels and smaller tributaries (Hackensack, Pasaic and Raritan rivers) using a 25' boat. In both cases measurements were made using towed instrument packages which could be cycled from near surface to near bottom depths with horizontal resolution of approximately 20 to 200 meters depending on depth and deployment strategy. Sensors on the instrument packages included a CTD to provide depth and salinity information and a chromophoric dissolved organic matter(CDOM) fluorometer to measure the fluorescent fraction of the DOC. Discrete samples allowed calibration of the fluorometer and the CDOM data to be related to DOC. The combined data set from these cruises identified multiple scales of source and transport processes for DOC within the Hudson River/New York Harbor region. The Hudson carries a substantial amount of natural DOC from its 230 km inland stretch. Additional sources exist in fringing salt marshes adjacent to the Hackensack and Raritan rivers. However the lower Hudson/New Harbor region receives a large input of DOC from multiple publically owned treatment works (POTW) discharges. The high resolution surveys allowed us to elucidate the distribution of these sources and the manner in which they are rapidly mixed to create the total export. We estimate that anthropogenic sources account for up to 2.5 times the DOC flux contributed by natural processes.

Using Continuous In-situ Measurement of Fluorescence to Reveal Hot Spots and Hot Moments of Dissolved Organic Matter Dynamics in a Forested Watershed

NASA Astrophysics Data System (ADS)

Ryan, K. A.; Hosen, J. D.; Raymond, P. A.; Stubbins, A.; Shanley, J. B.

2017-12-01

River systems serve as net carbon exporters from land to the ocean, fueling downstream aquatic ecosystem food webs. Fluorescence signatures of aquatic organic matter can be used as a proxy for dissolved organic carbon (DOC) concentration and can characterize DOC composition, reactivity, and source to improve our understanding of ecological processes. In-situ measurement of fluorescence using fifteen-minute interval data logging allows greater temporal resolution than laboratory studies. However, in-situ data must be corrected for interferences from temperature, absorbance and turbidity changes occurring in the field. We installed multiparameter water quality sondes (Eureka Mantas) and in-situ fluorometers (Turner Designs Cyclops) at sites nested within streams and riparian zones in the Sleepers River Research Watershed in Vermont in 2017. We coupled these measurements with simultaneous intensive field sampling campaigns and laboratory analysis of DOC and fluorescence Excitation-Emission Matrices. The data loggers from the nested sites recorded fluorescence peaks responding to discharge events and tracked changes in fluorescence occurring from upstream to downstream sites. Laboratory results confirm a nonlinear, hysteretic relationship between discharge and DOC where peak DOC lags peak discharge. This hysteresis is predicted to be controlled by multiple flow paths and DOC sources (i.e. groundwater, overland flow). We conclude that continuous in-situ records of river water fluorescence can be used to inform ecological processes and test new hypotheses concerning dissolved organic matter dynamics in watersheds.

Salp contributions to vertical carbon flux in the Sargasso Sea

NASA Astrophysics Data System (ADS)

Stone, Joshua P.; Steinberg, Deborah K.

2016-07-01

We developed a one-dimensional model to estimate salp contributions to vertical carbon flux at the Bermuda Atlantic Time-series Study (BATS) site in the North Atlantic subtropical gyre for a 17-yr period (April 1994 to December 2011). We based the model parameters on published rates of salp physiology and experimentally determined sinking and decomposition rates of salp carcasses. Salp grazing was low during non-bloom conditions, but routinely exceeded 100% of chlorophyll standing stock and primary production during blooms. Fecal pellet production was the largest source of salp carbon flux (78% of total), followed by respiration below 200 m (19%), sinking of carcasses (3%), and DOC excretion below 200 m (<0.1%). Thalia democratica, Salpa fusiformis, Salpa aspera, Wheelia cylindrica, and Iasis zonaria were the five highest contributors, accounting for 95% of total salp-mediated carbon flux. Seasonally, salp flux was higher during spring-summer than fall-winter, due to seasonal changes in species composition and abundance. Salp carbon export to 200 m was on average 2.3 mg C m-2 d-1 across the entire time series. This is equivalent to 11% of the mean 200 m POC flux measured by sediment traps in the region. During years with significant salp blooms, however, annually-averaged salp carbon export was the equivalent of up to 60% of trap POC flux at 200 m. Salp carbon flux attenuated slowly, and at 3200 m the average modeled carbon from salps was 109% of the POC flux measured in sediment traps at that depth. Migratory and carcass carbon export pathways should also be considered (alongside fecal pellet flux) as facilitating carbon export to sequestration depths in future studies.

DOC Dynamics in Small Headwater Streams: the Role of Hydrology, Climate, and Land Management

NASA Astrophysics Data System (ADS)

Lajtha, K.; Lee, B. S.; Jones, J. A.

2015-12-01

Dissolved organic carbon (DOC) is a critical component of the carbon (C) cycle of both terrestrial and aquatic systems. For small headwater allochthonous streams, terrestrial C delivery fuels the metabolism of receiving waters and significantly influences biotic diversity and function. While nutrient fluxes in streams have long been used as indicators of terrestrial ecosystem processes, less attention has been given to terrestrial controls on DOC export. We used the long-term stream chemistry records from the H.J. Andrews Forest LTER to examine forest management, climatic, and hydrologic controls on both seasonal and annual DOC fluxes. Within a watershed, annual DOC flux was highly related to annual discharge (Q), although considerable variability in higher discharge years suggested a role for indices of storminess, especially early in the water year. Among watersheds, younger, previously harvested watersheds generally had significantly lower DOC fluxes for a given Q than old-growth watersheds, even 4+ decades after harvest. The exception to this pattern was a harvested watershed that had significant downed wood retained on site, and had densities of coarse woody debris (CWD) close to that of the old-growth watersheds even though live tree biomass was similar to the other harvested watersheds. Other climatic factors did not appear to have significant roles in predicting either seasonal or annual fluxes of DOC. This is in sharp contrast to fluxes of nitrate at our site, which appears to be related most significantly to the presence of alder within the watershed. Taken together, our data suggest a persistent and cascading role for CWD in old-growth forest ecosystems.

Soil Organic Carbon Redistribution by Water Erosion – The Role of CO2 Emissions for the Carbon Budget

PubMed Central

Wang, Xiang; Cammeraat, Erik L. H.; Romeijn, Paul; Kalbitz, Karsten

2014-01-01

A better process understanding of how water erosion influences the redistribution of soil organic carbon (SOC) is sorely needed to unravel the role of soil erosion for the carbon (C) budget from local to global scales. The main objective of this study was to determine SOC redistribution and the complete C budget of a loess soil affected by water erosion. We measured fluxes of SOC, dissolved organic C (DOC) and CO2 in a pseudo-replicated rainfall-simulation experiment. We characterized different C fractions in soils and redistributed sediments using density fractionation and determined C enrichment ratios (CER) in the transported sediments. Erosion, transport and subsequent deposition resulted in significantly higher CER of the sediments exported ranging between 1.3 and 4.0. In the exported sediments, C contents (mg per g soil) of particulate organic C (POC, C not bound to soil minerals) and mineral-associated organic C (MOC) were both significantly higher than those of non-eroded soils indicating that water erosion resulted in losses of C-enriched material both in forms of POC and MOC. The averaged SOC fluxes as particles (4.7 g C m−2 yr−1) were 18 times larger than DOC fluxes. Cumulative emission of soil CO2 slightly decreased at the erosion zone while increased by 56% and 27% at the transport and depositional zone, respectively, in comparison to non-eroded soil. Overall, CO2 emission is the predominant form of C loss contributing to about 90.5% of total erosion-induced C losses in our 4-month experiment, which were equal to 18 g C m−2. Nevertheless, only 1.5% of the total redistributed C was mineralized to CO2 indicating a large stabilization after deposition. Our study also underlines the importance of C losses by particles and as DOC for understanding the effects of water erosion on the C balance at the interface of terrestrial and aquatic ecosystems. PMID:24802350

Carbon Transformations and Source - Sink Dynamics along a River, Marsh, Estuary, Ocean Continuum

NASA Astrophysics Data System (ADS)

Anderson, I. C.; Crosswell, J.; Czapla, K.; Van Dam, B.

2017-12-01

Estuaries, the transition zone between land and the coastal ocean, are highly dynamic systems in which carbon sourced from watersheds, marshes, atmosphere, and ocean may be transformed, sequestered, or exported. The net fate of carbon in estuaries, governed by the interactions of biotic and physical drivers varying on spatial and temporal scales, is currently uncertain because of limited observational data. In this study, conducted in a temperate, microtidal, and shallow North Carolina USA estuary, carbon exchanges via river, tributary, and fringing salt marsh, air-water fluxes, sediment C accumulation, and metabolism were monitored over two-years, with sharply different amounts of rainfall. Air-water CO2 fluxes and metabolic variables were simultaneously measured in channel and shoal by conducting high-resolution surveys at dawn, dusk and the following dawn. Marsh CO2 exchanges, sediment C inputs, and lateral exports of DIC and DOC were also measured. Carbon flows between estuary regions and export to the coastal ocean were calculated by quantifying residual transport of DIC and TOC down-estuary as flows were modified by sources, sinks and internal transformations. Variation in metabolic rates, CO2, TOC and DIC exchanges were large when determined for short time and limited spatial scales. However, when scaled to annual and whole estuarine scales, variation tended to decrease because of counteracting metabolic rates and fluxes between channel and shoal or between seasons. Although overall salt marshes accumulated OC, they were a negligible source of DIC and DOC to the estuary, and net inputs of C to the marsh were mainly derived from sediment OC. These results, as observed in other observational studies of estuaries, show that riverine input, light, temperature and metabolism are major controls on carbon cycling. Comparison of our results with other types of estuaries varying in depth, latitude, and nutrification demonstrates large discrepancies underscoring the limitations of current sampling designs, models and datasets in representing system-scale diversity; thus, a more practical approach may be to choose a small number of representative coastal systems, coordinate research efforts to quantify the relevant fluxes and constrain a range of environmental conditions that influence carbon cycling.

Benthic biogeochemical cycling, nutrient stoichiometry, and carbon and nitrogen mass balances in a eutrophic freshwater bay

USGS Publications Warehouse

Klump, J.V.; Fitzgerald, S.A.; Waplesa, J.T.

2009-01-01

Green Bay, while representing only ,7% of the surface area and ??1.4% of the volume of Lake Michigan, contains one-third of the watershed of the lake, and receives approximately one-third of the total nutrient loading to the Lake Michigan basin, largely from the Fox River at the southern end of the bay. With a history of eutrophic conditions dating back nearly a century, the southern portion of the bay behaves as an efficient nutrient and sediment trap, sequestering much of the annual carbon and nitrogen input within sediments accumulating at up to 1 cm per year. Depositional fluxes of organic matter varied from ??0.1 mol C m-2 yr-1 to >10 mol C m-2 yr-1 and were both fairly uniform in stoichiometric composition and relatively labile. Estimates of benthic recycling derived from pore-water concentration gradients, whole-sediment incubation experiments, and deposition-burial models of early diagenesis yielded an estimated 40% of the carbon and 50% of the nitrogen recycled back into the overlying water. Remineralization was relatively rapid with ??50% of the carbon remineralized within <15 yr of deposition, and a mean residence time for metabolizable carbon and nitrogen in the sediments of 20 yr. On average, organic carbon regeneration occurred as 75% CO2, 15% CH4, and 10% dissolved organic carbon (DOC). Carbon and nitrogen budgets for the southern bay were based upon direct measurements of inputs and burial and upon estimates of export and production derived stoichiometrically from a coupled phosphorus budget. Loadings of organic carbon from rivers were ??3.7 mol m-2 yr-1, 80% in the form of DOC and 20% as particulate organic carbon. These inputs were lost through export to northern Green Bay and Lake Michigan (39%), through sediment burial (26%), and net CO2 release to the atmosphere (35%). Total carbon input, including new production, was 4.54 mol m-2 C yr-1, equivalent to ??10% of the gross annual primary production. Nitrogen budget terms were less well quantified, with nitrogen export ??54% of total inputs and burial ??24%, leaving an unquantified residual loss term in the nitrogen budget of ??22%. ?? 2009.

Monitoring terrestrial dissolved organic carbon export at land-water interfaces using remote sensing

NASA Astrophysics Data System (ADS)

Yu, Q.; Li, J.; Tian, Y. Q.

2017-12-01

Carbon flux from land to oceans and lakes is a crucial component of carbon cycling. However, this lateral carbon flow at land-water interface is often neglected in the terrestrial carbon cycle budget, mainly because observations of the carbon dynamics are very limited. Monitoring CDOM/DOC dynamics using remote sensing and assessing DOC export from land to water remains a challenge. Current CDOM retrieval algorithms in the field of ocean color are not simply applicable to inland aquatic ecosystems since they were developed for coarse resolution ocean-viewing imagery and less complex water types in open-sea. We developed a new semi-analytical algorithm, called SBOP (Shallow water Bio-Optical Properties algorithm) to adapt to shallow inland waters. SBOP was first developed and calibrated based on in situ hyperspectral radiometer data. Then we applied it to the Landsat-8 OLI images and evaluated the effectiveness of the multispectral images on inversion of CDOM absorption based on our field sampling at the Saginaw Bay in the Lake Huron. The algorithm performances (RMSE = 0.17 and R2 = 0.87 in the Saginaw Bay; R2 = 0.80 in the northeastern US lakes) is promising and we conclude the CDOM absorption can be derived from Landsat-8 OLI image in both optically deep and optically shallow waters with high accuracy. Our method addressed challenges on employing appropriate atmospheric correction, determining bottom reflectance influence for shallow waters, and improving for bio-optical properties retrieval, as well as adapting to both hyperspectral and the multispectral remote sensing imagery. Over 100 Landsat-8 images in Lake Huron, northeastern US lakes, and the Arctic major rivers were processed to understand the CDOM spatio-temporal dynamics and its associated driving factors.

Speleothem records of acid sulphate deposition and organic carbon mobilisation

NASA Astrophysics Data System (ADS)

Wynn, Peter; Fairchild, Ian; Bourdin, Clement; Baldini, James; Muller, Wolfgang; Hartland, Adam; Bartlett, Rebecca

2017-04-01

Dramatic increases in measured surface water DOC in recent decades have been variously attributed to either temperature rise, or destabilisation of long-term soil carbon pools following sulphur peak emissions status. However, whilst both drivers of DOC dynamics are plausible, they remain difficult to test due to the restricted nature of the available records of riverine DOC flux (1978 to present), and the limited availability of SO2 emissions inventory data at the regional scale. Speleothems offer long term records of both sulphur and carbon. New techniques to extract sulphur concentrations and isotopes from speleothem calcite have enabled archives of pollution history and environmental acidification to be reconstructed. Due to the large dynamic range in sulphur isotopic values from end member sources (marine aerosol +21 ‰ to continental biogenic emissions -30 ‰) and limited environmental fractionation under oxidising conditions, sulphur isotopes form an ideal tracer of industrial pollution and environmental acidification in the palaeo-record. We couple this acidification history to the carbon record, using organic matter fluorescence and trace metals. Trace metal ratios and abundance can be used to infer the type and size of organic ligand and are therefore sensitive to changes in temperature as a driver of organic carbon processing and biodegradation. This allows fluorescent properties and ratios of trace metals in speleothem carbonate to be used to represent both the flux of organic carbon into the cave as well as the degradation pathway. Here we present some of the first results of this work, exploring sulphur acidification as a mechanistic control on carbon solubility and export throughout the twentieth century.

Identifying dissolved organic carbon sources at a gaged headwater catchment using FDOM sensors

NASA Astrophysics Data System (ADS)

Malzone, J. M.; Shanley, J. B.

2014-12-01

The United States Geological Survey's (USGS) W-9 gage at the headwaters of Sleepers River, Vermont has been monitored for dissolved organic carbon (DOC) concentration for more than 20 years. However, the sources of this DOC during base flow and hydrologic events remain unclear. The major objectives of this research were to identify sources of DOC during storm events and to explain the observed DOC-streamflow counterclockwise hysteresis during hydrologic events. Two main hypotheses to explain hysteresis during hydrologic events were tested: (1) distant headwater wetlands are the major DOC source, which lags behind peak flow due to travel time; and (2) the entire watershed contributes to the DOC at the gage, but the response of DOC lags behind the period when groundwater contributes most to streamflow. Sources of DOC were tracked using fluorescent dissolved organic matter (FDOM) sensors in surface water and groundwater wells. Wells were installed at four depths, 0.3, 0.6, 0.9, and 1.2 m, at four sites: a peaty low-gradient riparian area near the headwaters; a mid-hillslope area on a long hillslope mid-watershed; a near-stream area on a long hillslope mid-watershed; and a low-gradient tributary confluence area just above the gage. During storm events, FDOM and hydraulic head were measured at the nested groundwater wells. Samples for DOC analysis were also taken to determine the relationship between FDOM and DOC. Results suggest that both distant sources and the greater watershed played a role in the transport of DOC to the W-9 gage. Distant peaty sources dominated during large storms and contributed the highest surface water FDOM measurements. The peak FDOM at the gage was therefore best described as a result of transport. However, export from these distant sources terminated rapidly and did not explain continued elevated FDOM at the gage. Groundwater across the watershed exhibited hysteresis analogous to that in the stream itself, with FDOM peaking as head receded. As groundwater is recharged, the water table intersects more carbon rich soil layers. Pre-event water is flushed out first before event water mobilizes DOC, causing the groundwater hysteresis. High FDOM groundwater discharging to the stream likely sustained elevated FDOM at the gage. The gage hysteresis, therefore, seems to be a result of both hypotheses tested.

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.

Lateral, Vertical, and Longitudinal Source Area Connectivity Drive Runoff and Carbon Export Across Watershed Scales

NASA Astrophysics Data System (ADS)

Zimmer, Margaret A.; McGlynn, Brian L.

2018-03-01

Watersheds are three-dimensional hydrologic systems where the longitudinal expansion/contraction of stream networks, vertical connection/disconnection between shallow and deep groundwater systems, and lateral connectivity of these water sources to streams mediate runoff production and nutrient export. The connectivity of runoff source areas during both baseflow and stormflow conditions and their combined influence on biogeochemical fluxes remain poorly understood. Here we focused on a set of 3.3 and 48.4 ha nested watersheds (North Carolina, USA). These watersheds comprise ephemeral and intermittent runoff-producing headwaters and perennial runoff-producing lowlands. Within these landscape elements, we characterized the timing and magnitude of precipitation, runoff, and runoff-generating flow paths. The active surface drainage network (ASDN) reflected connectivity to, and contributions from, source areas that differed under baseflow and stormflow conditions. The baseflow-associated ASDN expanded and contracted seasonally, driven by the rise and fall of the seasonal water table. Superimposed on this were event-activated source area contributions driven by connectivity to surficial and shallow subsurface flow paths. Frequently activated shallow flow paths also caused increased in-stream dissolved organic carbon (DOC) concentrations with increases in runoff across both watershed scales. The spread and variability within this DOC-runoff relationship was driven by a seasonal depletion of DOC from continual shallow subsurface flow path activation and subsequent replenishment from autumn litterfall. Our findings suggest that hydrobiogeochemical signals at larger watershed outlets can be driven by the expansion, contraction, and connection of lateral, longitudinal, and vertical source areas with distinct runoff generation processes.

Contrasting composition of terrigenous organic matter in the dissolved, particulate and sedimentary organic carbon pools on the outer East Siberian Arctic Shelf

NASA Astrophysics Data System (ADS)

Salvadó, Joan A.; Tesi, Tommaso; Sundbom, Marcus; Karlsson, Emma; Kruså, Martin; Semiletov, Igor P.; Panova, Elena; Gustafsson, Örjan

2016-11-01

Fluvial discharge and coastal erosion of the permafrost-dominated East Siberian Arctic delivers large quantities of terrigenous organic carbon (Terr-OC) to marine waters. The composition and fate of the remobilized Terr-OC needs to be better constrained as it impacts the potential for a climate-carbon feedback. In the present study, the bulk isotope (δ13C and Δ14C) and macromolecular (lignin-derived phenols) composition of the cross-shelf exported organic carbon (OC) in different marine pools is evaluated. For this purpose, as part of the SWERUS-C3 expedition (July-September 2014), sediment organic carbon (SOC) as well as water column (from surface and near-bottom seawater) dissolved organic carbon (DOC) and particulate organic carbon (POC) samples were collected along the outer shelves of the Kara Sea, Laptev Sea and East Siberian Sea. The results show that the Lena River and the DOC may have a preferential role in the transport of Terr-OC to the outer shelf. DOC concentrations (740-3600 µg L-1) were 1 order of magnitude higher than POC (20-360 µg L-1), with higher concentrations towards the Lena River plume. The δ13C signatures in the three carbon pools varied from -23.9 ± 1.9 ‰ in the SOC, -26.1 ± 1.2 ‰ in the DOC and -27.1 ± 1.9 ‰ in the POC. The Δ14C values ranged between -395 ± 83 (SOC), -226 ± 92 (DOC) and -113 ± 122 ‰ (POC). These stable and radiocarbon isotopes were also different between the Laptev Sea and the East Siberian Sea. Both DOC and POC showed a depleted and younger trend off the Lena River plume. Further, the Pacific inflow and the sea-ice coverage, which works as a barrier preventing the input of "young" DOC and POC, seem to have a strong influence in these carbon pools, presenting older and more enriched δ13C signatures under the sea-ice extent. Lignin phenols exhibited higher OC-normalized concentrations in the SOC (0.10-2.34 mg g-1 OC) and DOC (0.08-2.40 mg g-1 OC) than in the POC (0.03-1.14 mg g-1 OC). The good relationship between lignin and Δ14C signatures in the DOC suggests that a significant fraction of the outer-shelf DOC comes from "young" Terr-OC. By contrast, the slightly negative correlation between lignin phenols and Δ14C signatures in POC, with higher lignin concentrations in older POC from near-bottom waters, may reflect the off-shelf transport of OC from remobilized permafrost in the nepheloid layer. Syringyl / vanillyl and cinnamyl / vannillyl phenol ratios presented distinct clustering between DOC, POC and SOC, implying that those pools may be carrying different Terr-OC of partially different origin. Moreover, 3,5-dihydroxybenzoic acid to vanillyl phenol ratios and p-coumaric acid to ferulic acid ratios, used as a diagenetic indicators, enhanced in POC and SOC, suggesting more degradation within these pools. Overall, the key contrast between enhanced lignin yields both in the youngest DOC and the oldest POC samples reflects a significant decoupling of terrestrial OC sources and pathways.

Variable C : N : P stoichiometry of dissolved organic matter cycling in the Community Earth System Model

DOE PAGES

Letscher, R. T.; Moore, J. K.; Teng, Y. -C.; ...

2015-01-12

Dissolved organic matter (DOM) plays an important role in the ocean's biological carbon pump by providing an advective/mixing pathway for ~ 20% of export production. DOM is known to have a stoichiometry depleted in nitrogen (N) and phosphorus (P) compared to the particulate organic matter pool, a fact that is often omitted from biogeochemical ocean general circulation models. However the variable C : N : P stoichiometry of DOM becomes important when quantifying carbon export from the upper ocean and linking the nutrient cycles of N and P with that of carbon. Here we utilize recent advances in DOM observationalmore » data coverage and offline tracer-modeling techniques to objectively constrain the variable production and remineralization rates of the DOM C : N : P pools in a simple biogeochemical-ocean model of DOM cycling. The optimized DOM cycling parameters are then incorporated within the Biogeochemical Elemental Cycling (BEC) component of the Community Earth System Model (CESM) and validated against the compilation of marine DOM observations. The optimized BEC simulation including variable DOM C : N : P cycling was found to better reproduce the observed DOM spatial gradients than simulations that used the canonical Redfield ratio. Global annual average export of dissolved organic C, N, and P below 100 m was found to be 2.28 Pg C yr -1 (143 Tmol C yr -1, 16.4 Tmol N yr -1, and 1 Tmol P yr -1, respectively, with an average export C : N : P stoichiometry of 225 : 19 : 1 for the semilabile (degradable) DOM pool. Dissolved organic carbon (DOC) export contributed ~ 25% of the combined organic C export to depths greater than 100 m.« less

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.

Black Carbon in Estuarine and Coastal Ocean Dissolved Organic Matter

NASA Technical Reports Server (NTRS)

Mannino, Antonio; Harvey, H. Rodger

2003-01-01

Black carbon (BC) in ultrafiltered high-molecular-weight DOM (UDOM) was measured in surface waters of Delaware Bay, Chesapeake Bay and the adjacent Atlantic Ocean (USA) to ascertain the importance of riverine and estuarine DOM as a source of BC to the ocean. BC comprised 5-72% of UDOM-C (27+/-l7%) and on average 8.9+/-6.5% of dissolved organic carbon (DOC) with higher values in the turbid region of the Delaware Estuary and lower yields in the river and coastal ocean. The spatial and seasonal distributions of BC along the salinity gradient of Delaware Bay suggest that the higher levels of BC in surface water UDOM originated from localized sources, possibly from atmospheric deposition or released from resuspended sediments. Black carbon comprised 4 to 7% of the DOC in the coastal Atlantic Ocean, revealing that river-estuary systems are important exporters of colloidal BC to the ocean. The annual flux of BC from Delaware Bay UDOM to the Atlantic Ocean was estimated at 2.4x10(exp 10) g BC yr(exp -1). The global river flux of BC through DOM to the ocean could be on the order of 5.5x1O(exp 12)g BC yr (exp -1). These results support the hypothesis that the DOC pool is the intermediate reservoir in which BC ages prior to sedimentary deposition.

Phosphorus and dissolved organic carbon export during peak flow periods in three small homogenous catchments in eastern Germany

NASA Astrophysics Data System (ADS)

Benning, R.; Schwärzel, K.; Feger, K. H.

2012-04-01

Regional climate change scenarios for Central Europe predict both an overall increase in temperature and alterations in annual precipitation regimes. For large parts of Central Europe, climate change is expected to result in an increase in winter precipitation and a decrease in summer precipitation. In addition, an increase in extreme conditions, such as heat waves, prolonged drought periods, and heavy rainfall events are predicted. This research examines the potential impacts of increased heavy rainfall events on matter export from small catchment areas, and how different vegetation cover and land management options effects these exports. In order to evaluate the export of matter from different land-use types in the Eastern Ore Mountains (Saxony, NE Germany, 50° 48'18.06" North, 13° 36'24.54" East), study sites were established in three small catchments with homogeneous land-use. These study areas are each sub-catchments of the Ammelsdorf catchment, which provides inflow to the Lehnmühle reservoir (a major water supply for the city of Dresden). Each sub catchment represents one of the three main land-use types in the catchment area of the reservoir: crops (winter oilseed rape, winter wheat), grasslands, and forests (primarily spruce). Since November 2009 the discharge from these sub catchments has been continuously measured and water quality was analyzed on a weekly basis. During peak flow events, discharge was collected using automatic water samplers, which allowed for high temporal resolution analysis of matter export during these periods to be made. During the 2010 and 2011 hydrological years, several heavy rainfall events occurred which have been evaluated. During a 110-hour long precipitation event (P = 170 mm) between 37 and 81 water samples per sub catchment were collected and analyzed. The resulting export of dissolved phosphorus (ortho-PO4-) and dissolved organic carbon (DOC) from the sub catchments during this event is provided in the results. In addition, the matter export resulting from a 59-hour precipitation event (P = 39 mm, between 31 and 48 analyzed water samples per sub catchment) is presented. The contribution of these two events to the annual export of ortho-PO4- and DOC will be discussed.

Dynamics of dissolved organic matter during four storm events in two forest streams: source, export, and implications for harmful disinfection byproduct formation.

PubMed

Yang, Liyang; Hur, Jin; Lee, Sonmin; Chang, Soon-Woong; Shin, Hyun-Sang

2015-06-01

Dynamics of river dissolved organic matter (DOM) during storm events have profound influences on the downstream aquatic ecosystem and drinking water safety. This study investigated temporal variations in DOM during four storm events in two forest headwater streams (the EH and JH brooks, South Korea) and the impacts on the disinfection byproducts (DBPs) formation potential. The within-event variations of most DOM quantity parameters were similar to the flow rate in the EH but not in the larger JH brook. The dissolved organic carbon (DOC) showed clockwise and counterclockwise hysteresis with the flow rate in the EH and JH brooks, respectively, indicating the importance of both flow path and DOM source pool size in determining the effects of storm events. The stream DOM became less aromatic/humified from the first to the last event in both brooks, probably due to the increasing fresh plant pool and the decreasing leaf litter pool during the course of rainy season. The DOC export during each event increased 1.3-2.7- and 1.1-7.0-fold by stormflows in the EH and JH brooks, respectively. The leaf litter and soil together was the major DOM source, particularly during early events. The enhanced DOM export probably increases the risks of DBPs formation in disinfection, as indicated by a strong correlation observed between DOC and trihalomethanes formation potential (THMFP). High correlations between two humic-like fluorescent components and THMFP further suggested the potential of assessing THMFP with in situ fluorescence sensors during storms.

Isotope geochemistry and fluxes of carbon and organic matter in tropical small mountainous river systems and adjacent coastal waters of the Caribbean

USGS Publications Warehouse

Moyer, Ryan; Bauer, James; Grottoli, Andrea

2012-01-01

Recent studies have shown that small mountainous rivers (SMRs) may act as sources of aged and/or refractory carbon (C) to the coastal ocean, which may increase organic C burial at sea and subsidize coastal food webs and heterotrophy. However, the characteristics and spatial and temporal variability of C and organic matter (OM) exported from tropical SMR systems remain poorly constrained. To address this, the abundance and isotopic character (δ13C and Δ14C) of the three major C pools were measured in two Puerto Rico SMRs with catchments dominated by different land uses (agricultural vs. non-agricultural recovering forest). The abundance and character of C pools in associated estuaries and adjacent coastal waters were also examined. Riverine dissolved and particulate organic C (DOC and POC, respectively) concentrations were highly variable with respect to land use and sampling month, while dissolved inorganic C (DIC) was significantly higher at all times in the agricultural catchment. In both systems, riverine DOC and POC ranged from modern to highly aged (2,340 years before present), while DIC was always modern. The agricultural river and irrigation canals contained very old DOC (1,184 and 2,340 years before present, respectively), which is consistent with findings in temperate SMRs and indicates that these tropical SMRs provide a source of aged DOC to the ocean. During months of high river discharge, OM in estuarine and coastal waters had C isotope signatures reflective of direct terrestrial input, indicating that relatively unaltered OM is transported to the coastal ocean at these times. This is also consistent with findings in temperate SMRs and indicates that C transported to the coastal ocean by SMRs may differ from that of larger rivers because it is exported from smaller catchments that have steeper terrains and fewer land-use types.

Dissolved Organic Matter Composition and Export from U.S. Rivers

NASA Astrophysics Data System (ADS)

Aiken, G.; Butman, D. E.; Spencer, R. G.; Raymond, P.

2012-12-01

Dissolved organic matter (DOM) chemistry and flux are potentially useful indicators of watershed characteristics, climate influences on watershed hydrology and soils, and changes associated with water and land resource management. Organic source materials, watershed geochemistry, oxidative processes and hydrology strongly influence the nature and reactivity of DOM in aquatic systems. The molecules that comprise DOM, in turn, control a number of environmental processes important for ecosystem function including light penetration and photochemistry, microbial activity, mineral dissolution/precipitation, and the transport and reactivity of hydrophobic compounds and metals. In particular, aromatic molecules derived from higher plants exert strong controls on aquatic photochemistry, and on the transport and biogeochemistry of metals. Assessment of DOM composition and transport, therefore, can provide a basis for understanding watershed processes and biogeochemistry of rivers and streams. Here we present results of a multi-year study designed to assess the seasonal and spatial variability of DOM quantity and quality for 15 large North American river basins. Samples were collected from the mouths of the rivers using a sampling program designed to capture hydrologic and seasonal variability of DOM export. DOM concentrations and composition, based on DOM fractionation on XAD resins, chromophoric dissolved organic matter (CDOM) parameters (ultraviolet /visible absorption and fluorescence spectroscopy), specific compound analyses, and DO14C content varied greatly both between sites and seasonally within a given site. DOM in these rivers exhibited a wide range of concentration and carbon specific ultra-violet absorbance at 254 nm (SUVA254), an optical measurement that is an indicator of DOM aromatic carbon content. In almost all systems, CDOM optical parameters correlated strongly with DOC concentration and hydrophobic organic acid (HPOA) content (aquatic humic substances). In particular, SUVA254 was found to correlate strongly with the proportion of HPOA and Δ14C. Relationships between dissolved organic carbon (DOC) concentration and absorbance for individual rivers were quite variable due to differences in the fraction of non-chromophoric DOM. Notably, the relationship between UV absorption coefficients and DOC concentration for four rivers that drain arid regions and/or are heavily influenced by impoundments were statistically weak.although similar trends for these rivers were not observed for Δ14C. Basins with high discharge, high density of vegetation cover, and low population densities exported younger, more aromatic DOM. Conversely, old DOM was exported from low discharge watersheds draining arid regions and watersheds impacted by high population densities. While individual watershed characteristics control DOC concentrations, CDOM parameters and DO14C content, overall discharge dominated the flux of both CDOM and DO14C to coastal waters. The link between the nature and reactivity of DOM and its optical properties can be exploited to provide powerful monitoring tools to assess the impacts of climate change, land-use change, and management practices on overall water quality and on DOM transport and transformation.

Hydro-climatic control of stream dissolved organic carbon in headwater catchment

NASA Astrophysics Data System (ADS)

Humbert, Guillaume; Jaffrezic, Anne; Fovet, Ophélie; Gruau, Gérard; Durand, Patrick

2014-05-01

Dissolved organic matter (DOM) is a key form of the organic matter linking together the water and the carbon cycles and interconnecting the biosphere (terrestrial and marine) and the soil. At the landscape scale, land use and hydrology are the main factors controlling the amount of DOM transferred from soils to the stream. In an intensively cultivated catchment, a recent work using isotopic composition of DOM as a marker has identified two different sources of DOM. The uppermost soil horizons of the riparian wetland appear as a quasi-infinite source while the topsoil of the hillslope forms a limited one mobilized by water-table rise and exported to the stream across the upland-riparian wetland-stream continuum. In addition to the exportation of DOM via water fluxes, climatic factors like temperature and precipitation regulate the DOM production by influencing microbial activity and soil organic matter degradation. The small headwater catchment (5 km²) of Kervidy-Naizin located in Brittany is part of the Environment Research Observatory (ORE) AgrHys. Weather and the hydro-chemistry of the stream, and the groundwater levels are daily recorded since 1993, 2000 and 2001 respectively. Over 13 contrasted hydrological years, the annual flow weighted mean concentration of dissolved organic carbon (DOC) is 5.6 mg.L-1 (sd = 0.7) for annual precipitation varying from 488mm to 1327mm and annual mean temperatures of 11°C (sd = 0.6). Based on this considerable dataset and this annual variability, we tried to understand how the hydro-climatic conditions determinate the stream DOC concentrations along the year. From the fluctuations of water table depth, each hydrologic year has been divided into three main period: i) progressive rewetting of the riparian wetland soils, ii) rising and holding high of the water table in the hillslope, iii) drawdown of the water-table, with less and less topsoil connected to the stream. Within each period base flow and storm flow data were first pooled then treated separately and the influence of preceding periods was tested. This hydrological division of time allowed us to identify climate effect on the topsoil DOM stores of the wetland and hillslope separately. Meteorological and hydro-pedological variables, like soil temperatures or duration of the water saturation in the organo-mineral horizons have been used to interpret the DOC concentrations and fluxes at the outlet within each period. The three hydrological periods contribute respectively to less than 17%, more than 63%, and less than 26% of the annual DOM exportation with flow weighted mean concentration of DOC of 9.5, 6.1, and 3.8 mg.L-1. Considering several DOM sources with different properties of depletion under climatic control, the main output of the work is to provide a modified conceptual model of the DOC dynamics.

Precipitation regime effects on the transport of microbial-derived organic matter from soils to surface waters

NASA Astrophysics Data System (ADS)

Pissarello, Anna; Lechtenfeld, Oliver; Miltner, Anja; Kästner, Matthias

2017-04-01

In the last decades, decreases in soil organic matter (SOM) content and increases of dissolved organic carbon (DOC) concentrations in surface water bodies have been recorded in the northern hemisphere. These have severe consequences for soil fertility and for drinking water purification, respectively. We hypothesize that microbially degraded SOM is a potential source of the additional DOC in the surface water. Recently, rain events have become more extreme, resulting in longer droughts and more intense rain events. These changes in the precipitation regime may increase the input of DOC into surface waters, which occurs mainly directly after heavy rain events. Therefore, our interest was to evaluate the role of variations of the water regime on the mobilization of the DOC from soil organic matter to soil solution. Flow-through column experiments were conducted under extreme precipitation scenarios (from continuously wet to pronounced drying and rewetting) in the laboratory in order to test how fluctuation in the water content influences DOC concentration and composition in the leachates. In our experiment we analyzed both soil respiration and DOM mobilization and found that the increased DOM mobilization after heavy rain events was also an effect of increased microbial activity after the drought stress was relieved. Furthermore, we considered that an important contribution to DOC formation and export may come from microbial processing of microbial biomass residues, residing within the particulate organic matter (POM) fraction. Therefore our aim was to link the necromass contribution to the exported DOC by characterizing DOC leachates of the soil columns at the molecular level and comparing them to fractions of bacterial DOC and POC obtained from an Escherichia coli pure culture, by using ultra-high-resolution methods such as Electrospray Ionization and Matrix assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS and MALDI-FTICR-MS, respectively). The results help to relate the origin of organic matter to typical chemical composition patterns and to allow quantification of the relative contributions of plant and microbe-derived material to NOM and how they are affected by the different water regimes. The results of this experiment consent to link SOM degradation and DOC mobilization and to understand the role of water regime variations for these processes.

Exploring the Disappearing Ocean Micro Plastic Mystery: New Insights from Dissolved Organic Carbon photo production

NASA Astrophysics Data System (ADS)

Zhu, L.; Zhao, S.; Li, D.; Stubbins, A.

2017-12-01

Emerging as a novel planetary threat, plastic waste, dominated by millimeter-sized plastic (microplastic), is omnipresent in the oceans, posing broad environmental threats. However, only 1% of the microplastic waste exported from the land is found in the ocean. Most of the lost fraction is in the form of microplastics. The fate of these buoyant plastic fragments is a fundamental gap in our understanding of the fate and impact of plastics in marine ecosystems. To date, an effective sink for the lost microplastics has not been found. In this study, dissolved organic carbon (DOC) photo-production from the three dominant forms of ocean microplastics was assessed. These plastics were: 1) Polyethylene (PE) both for postconsumer samples and pure standard samples; 2) polypropylene (PP); and, expanded polystyrene (EPS). In addition, a Neustonic microplastic samples from the North Pacific Gyre were irradiated. These real-world samples were dominated by PE ( 80%). All samples were placed in seawater, in quartz flasks, and irradiated in a solar simulator for 2 months. During irradiation, DOC photo-production from PP, EPS, and the PE standard was exponential, while DOC photo-production from postconsumer PE and the Neustonic samples was linear. Scanning electron microscopy indicated surface ablation and micro-fragmentation during the irradiation of the three plastics that showed exponential DOC production (PP, EPS and standard PE), suggesting the increase in photo-reactivity of these plastics was a result of an increase in their surface to volume ratios and therefore their per-unit mass light exposure. Based on DOC production, the half-life of the microplastics ranged from 0.26 years for EPS to 86 years for PE, suggesting sunlight is a major removal term for buoyant oceanic microplastics. With respect to the broader carbon cycle, we conservatively estimate that plastic photodegradation releases 6 to 17 thousand metric tons of radiocarbon dead DOC to the surface ocean each year.

Continuous flux of dissolved black carbon from a vanished tropical forest biome

NASA Astrophysics Data System (ADS)

Dittmar, T.; Rezende, C. E.; Manecki, M.; Niggemann, J.; Coelho Ovalle, A. R.; Bernardes, M. C.

2012-04-01

Humans have extensively used fire as a tool to shape Earth's vegetation. One of the biggest events in this context was the destruction of Brazilian's Atlantic forest, once among the largest tropical forest biomes on Earth. We estimate that the slash-and-burn practice produced 200 to 500 million tons of black carbon from the 1850' to 1973. The fate of this charred organic matter is unknown. Here we show continuous runoff of dissolved black carbon from the cleared forest biome, more than 35 years after the widespread burning of the forest ended. During the 11-year observation period (1997-2008) of this study, on average 0.04 to 0.08 tons of dissolved black carbon were annually exported per square kilometer land. We estimate an annual runoff of 48,000 to 97,000 tons dissolved black carbon from the former Atlantic forest biome. Dissolved black carbon was mobilized by water percolating through the soil during the rainy season. During base flow conditions, dissolved organic carbon (DOC) did not contain black carbon, whereas at peak flow up to 6% of DOC was combustion-derived. If runoff was the only removal mechanism of black carbon from soils, even the highly condensed and presumably refractory component of black carbon would have a half-life of only 440 to 2300 years in the soil. In areas with higher precipitation, stronger runoff and consequently a shorter half-life can be expected. In the deep ocean, dissolved black carbon is virtually inert on this time scale. The disappearance of the Atlantic forest provides a worst-case scenario for tropical forests worldwide, most of which are cleared at increasing rate. Because of the comparably fast mobilization of dissolved black carbon from soils and its resistivity in the deep ocean, an increase of black carbon production on land may alter the size of the global pool of >12 Pg carbon of thermally altered DOC in the ocean on the long term.

Lateral carbon fluxes and CO2 outgassing from a tropical peat-draining river

NASA Astrophysics Data System (ADS)

Müller, D.; Warneke, T.; Rixen, T.; Müller, M.; Jamahari, S.; Denis, N.; Mujahid, A.; Notholt, J.

2015-10-01

Tropical peatlands play an important role in the global carbon cycle due to their immense carbon storage capacity. However, pristine peat swamp forests are vanishing due to deforestation and peatland degradation, especially in Southeast Asia. CO2 emissions associated with this land use change might not only come from the peat soil directly but also from peat-draining rivers. So far, though, this has been mere speculation, since there has been no data from undisturbed reference sites. We present the first combined assessment of lateral organic carbon fluxes and CO2 outgassing from an undisturbed tropical peat-draining river. Two sampling campaigns were undertaken on the Maludam River in Sarawak, Malaysia. The river catchment is covered by protected peat swamp forest, offering a unique opportunity to study a peat-draining river in its natural state, without any influence from tributaries with different characteristics. The two campaigns yielded consistent results. Dissolved organic carbon (DOC) concentrations ranged between 3222 and 6218 μmol L-1 and accounted for more than 99 % of the total organic carbon (TOC). Radiocarbon dating revealed that the riverine DOC was of recent origin, suggesting that it derives from the top soil layers and surface runoff. We observed strong oxygen depletion, implying high rates of organic matter decomposition and consequently CO2 production. The measured median pCO2 was 7795 and 8400 μatm during the first and second campaign, respectively. Overall, we found that only 32 ± 19 % of the carbon was exported by CO2 evasion, while the rest was exported by discharge. CO2 outgassing seemed to be moderated by the short water residence time. Since most Southeast Asian peatlands are located at the coast, this is probably an important limiting factor for CO2 outgassing from most of its peat-draining rivers.

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 chromophoric dissolved organic matter (CDOM) distribution, stocks, and fluxes in Apalachicola Bay using combined field, VIIRS ocean color, and model observations

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

Joshi, Ishan D.; D'Sa, Eurico J.; Osburn, Christopher L.

Understanding the role of estuarine-carbon fluxes is essential to improve estimates of the global carbon budget. Dissolved organic matter (DOM) plays an important role in aquatic carbon cycling. Here, the chromophoric fraction of DOM (CDOM) can be readily detected via in situ and remotely-sensed optical measurements. DOM properties, including CDOM absorption coefficient at 412 nm (a g412) and dissolved organic carbon (DOC) concentrations were examined in Apalachicola Bay, a national estuarine research reserve located in the northeast Gulf of Mexico, using in situ and satellite observations during the spring and fall of 2015. Synoptic and accurate representation of estuarine-scale processesmore » using satellite ocean color imagery necessitates the removal of atmospheric contribu- tion (~90%) to signals received by satellite sensors to successfully link to in situ observations. Three atmospheric correction schemes (e.g., Standard NIR correction, Iterative NIR correction, and SWIR correction) were tested first to find a suitable correction scheme for the VIIRS imagery in low to moderately turbid Apalachicola Bay. The iterative NIR correction performed well, and validation showed high correlation (R 2 = 0.95, N = 25) against in situ light measurements. A VIIRS-based CDOM algorithm was developed (R 2 = 0.87, N = 9) and validated (R 2 = 0.76, N = 20, RMSE = 0.29 m -1) against in situ observations. Subsequently, ag412 was used as a proxy of DOC in March (DOC = 1.08 + 0.94 × a g412,R 2 =0.88, N = 13)and in November (DOC= 1.61 + 1.33 × a g412, R 2 = 0.83, N = 24) to derive DOC maps that provided synoptic views of DOC distribution, sources, and their transport to the coastal waters during the wet and dry seasons. The estimated DOC stocks were ~3.71 × 10 6 kg C in March and ~4.07 × 10 6 kg C in November over an area of ~560 km2. Volume flux (out of the bay) almost doubled for March 24 (735 m 3 s -1) relative to November 4 (378 m 3 s -1). However, estimates of DOC fluxes exported out of the bay from model-derived currents and satellite-derived DOC were only marginally greater in March (0.163 × 10 6 kg C d -1) than in November (0.124 × 10 6 kg C d -1) and reflected greater DOC stocks in the fall. Finally, the combination of satellite-, field-, and model-based observations revealed the strong linkage between the Apalachicola River plume, a major source of DOM, and the overall hydrodynamic forcing that controlled distributions of CDOM abundance, DOC concentration, stocks, and fluxes in the bay.« less

Assessing chromophoric dissolved organic matter (CDOM) distribution, stocks, and fluxes in Apalachicola Bay using combined field, VIIRS ocean color, and model observations

DOE PAGES

Joshi, Ishan D.; D'Sa, Eurico J.; Osburn, Christopher L.; ...

2017-02-06

Understanding the role of estuarine-carbon fluxes is essential to improve estimates of the global carbon budget. Dissolved organic matter (DOM) plays an important role in aquatic carbon cycling. Here, the chromophoric fraction of DOM (CDOM) can be readily detected via in situ and remotely-sensed optical measurements. DOM properties, including CDOM absorption coefficient at 412 nm (a g412) and dissolved organic carbon (DOC) concentrations were examined in Apalachicola Bay, a national estuarine research reserve located in the northeast Gulf of Mexico, using in situ and satellite observations during the spring and fall of 2015. Synoptic and accurate representation of estuarine-scale processesmore » using satellite ocean color imagery necessitates the removal of atmospheric contribu- tion (~90%) to signals received by satellite sensors to successfully link to in situ observations. Three atmospheric correction schemes (e.g., Standard NIR correction, Iterative NIR correction, and SWIR correction) were tested first to find a suitable correction scheme for the VIIRS imagery in low to moderately turbid Apalachicola Bay. The iterative NIR correction performed well, and validation showed high correlation (R 2 = 0.95, N = 25) against in situ light measurements. A VIIRS-based CDOM algorithm was developed (R 2 = 0.87, N = 9) and validated (R 2 = 0.76, N = 20, RMSE = 0.29 m -1) against in situ observations. Subsequently, ag412 was used as a proxy of DOC in March (DOC = 1.08 + 0.94 × a g412,R 2 =0.88, N = 13)and in November (DOC= 1.61 + 1.33 × a g412, R 2 = 0.83, N = 24) to derive DOC maps that provided synoptic views of DOC distribution, sources, and their transport to the coastal waters during the wet and dry seasons. The estimated DOC stocks were ~3.71 × 10 6 kg C in March and ~4.07 × 10 6 kg C in November over an area of ~560 km2. Volume flux (out of the bay) almost doubled for March 24 (735 m 3 s -1) relative to November 4 (378 m 3 s -1). However, estimates of DOC fluxes exported out of the bay from model-derived currents and satellite-derived DOC were only marginally greater in March (0.163 × 10 6 kg C d -1) than in November (0.124 × 10 6 kg C d -1) and reflected greater DOC stocks in the fall. Finally, the combination of satellite-, field-, and model-based observations revealed the strong linkage between the Apalachicola River plume, a major source of DOM, and the overall hydrodynamic forcing that controlled distributions of CDOM abundance, DOC concentration, stocks, and fluxes in the bay.« less

Dynamics and sources of reduced sulfur, humic substances and dissolved organic carbon in a temperate river system affected by agricultural practices.

PubMed

Marie, Lauriane; Pernet-Coudrier, Benoît; Waeles, Matthieu; Gabon, Marine; Riso, Ricardo

2015-12-15

Although reduced organic sulfur substances (RSS) as well as humic substances (HS) are widely suspected to play a role in, for example, metal speciation or used as a model of dissolved organic carbon (DOC) in laboratory studies, reports of their quantification in natural waters are scarce. We have examined the dynamics and sources of reduced sulfur, HS and DOC over an annual cycle in a river system affected by agricultural practices. The new differential pulse cathodic stripping voltammetry was successfully applied to measure glutathione-like compounds (GSHs), thioacetamide-like compounds (TAs) and the liquid chromatography coupled to organic detector to analyze HS and DOC at high frequency in the Penzé River (NW France). The streamflow-concentration patterns, principal components analysis and flux analysis allowed discrimination of the source of each organic compound type. Surprisingly, the two RSS and HS detected in all samples, displayed different behavior. As previously shown, manuring practice is the main source of DOC and HS in this watershed where agricultural activity is predominant. The HS were then transferred to the river systems via runoff, particularly during the spring and autumn floods, which are responsible of >60% of the annual flux. TAs had a clear groundwater source and may be formed underground, whereas GSHs displayed two sources: one aquagenic in spring and summer probably linked to the primary productivity and a second, which may be related to bacterial degradation. High sampling frequency allowed a more accurate assessment of the flux values which were 280 tC y(-1) for DOC representing 20 kg C ha(-1) y(-1). HS, TAs and GSHs fluxes represented 60, 13, and 4% of the total annual DOC export, respectively. Copyright © 2015 Elsevier B.V. All rights reserved.

Variable C : N : P stoichiometry of dissolved organic matter cycling in the Community Earth System Model

DOE PAGES

Letscher, R. T.; Moore, J. K.; Teng, Y. -C.; ...

2014-06-16

Dissolved organic matter (DOM) plays an important role in the ocean's biological carbon pump by providing an advective/mixing pathway for ~ 20% of export production. DOM is known to have a stoichiometry depleted in nitrogen (N) and phosphorus (P) compared to the particulate organic matter pool, a~fact that is often omitted from biogeochemical-ocean general circulation models. However the variable C : N : P stoichiometry of DOM becomes important when quantifying carbon export from the upper ocean and linking the nutrient cycles of N and P with that of carbon. Here we utilize recent advances in DOM observational data coveragemore » and offline tracer-modeling techniques to objectively constrain the variable production and remineralization rates of the DOM C / N / P pools in a simple biogeochemical-ocean model of DOM cycling. The optimized DOM cycling parameters are then incorporated within the Biogeochemical Elemental Cycling (BEC) component of the Community Earth System Model and validated against the compilation of marine DOM observations. The optimized BEC simulation including variable DOM C : N : P cycling was found to better reproduce the observed DOM spatial gradients than simulations that used the canonical Redfield ratio. Global annual average export of dissolved organic C, N, and P below 100 m was found to be 2.28 Pg C yr -1 (143 Tmol C yr -1), 16.4 Tmol N yr -1, and 1 Tmol P yr -1, respectively with an average export C : N : P stoichiometry of 225 : 19 : 1 for the semilabile (degradable) DOM pool. DOC export contributed ~ 25% of the combined organic C export to depths greater than 100 m.« less

Dissolved Organic Matter Compositional Change and Biolability During Two Storm Runoff Events in a Small Agricultural Watershed

NASA Astrophysics Data System (ADS)

Eckard, Robert S.; Pellerin, Brian A.; Bergamaschi, Brian A.; Bachand, Philip A. M.; Bachand, Sandra M.; Spencer, Robert G. M.; Hernes, Peter J.

2017-10-01

Agricultural watersheds are globally pervasive, supporting fundamentally different organic matter source, composition, and concentration profiles in comparison to natural systems. Similar to natural systems, agricultural storm runoff exports large amounts of organic carbon from agricultural land into waterways. But intense management of upper soil layers, waterway channelization, wetland and riparian habitat removal, and postharvest vegetation removal promise to uniquely drive organic matter release to waterways. During a winter first flush and a subsequent storm event, this study investigated the influence of a small agricultural watershed on dissolved organic matter (DOM) source, composition, and biolability. Storm water discharge released strongly terrestrial yet biolabile (23 to 32%) dissolved organic carbon (DOC). Following a 21 day bioassay, a parallel factor analysis identified an 80% reduction in a protein-like (phenylpropyl) component (C2) that was previously correlated to lignin phenol concentration, and a 10% reduction in a humic-like, terrestrially sourced component (C4). Storm-driven releases tripled DOC concentration (from 2.8 to 8.7 mg L-1) during the first flush event in comparison to base flow and were terrestrially sourced, with an eightfold increase in vascular plant derived lignin phenols (23.0 to 185 μg L-1). As inferred from system hydrology, lignin composition, and nitrate as a groundwater tracer, an initial pulse of dilute water from the upstream watershed caused a counterclockwise DOC hysteresis loop. DOC concentrations peaked after 3.5 days, with the delay between peak discharge and peak DOC attributed to storm water hydrology and a period of initial water repellency of agricultural soils, which delayed DOM leaching.

An In situ Study of Seasonal Dissolved Organic Carbon and Nutrient Fluxes from a Spartina alterniflora Salt Marsh in North Carolina

NASA Astrophysics Data System (ADS)

Detweiler, D. J.; Loh, A. N.

2016-02-01

Spartina alterniflora salt marshes are among the most productive and biogeochemically active ecosystems on Earth. While they have been shown to be sources of dissolved organic carbon (DOC) and nutrient export to the coastal ocean via tidal processes, it has not been well quantified experimentally. The purpose of this study was to quantify DOC and nutrient fluxes from a fringing S. alterniflora salt marsh in North Carolina. The experiment was conducted using in situ benthic microcosm chambers filled with seawater during a flooding tide; the chambers were then plugged, and samples were collected during an ebbing tide over the course of 270 minutes while simulating light and dark conditions. Water samples were filtered and analyzed for DOC and nutrient concentrations over time and used to calculate fluxes from vegetated (S. alterniflora) and non-vegetated marsh sediments. Preliminary daily flux calculations show that fluxes from vegetated sediments have a higher magnitude when compared to fluxes from non-vegetated sediments. Daily flux calculations also suggest that vegetated sediments act as a DOC source while non-vegetated sediments act as a DOC sink. Additional flux data for dissolved inorganic and organic nitrogen (DIN, DON) and dissolved inorganic and organic phosphorus (DIP, DOP) as well as marsh sediment characterization will also be presented. Ultimately, these data will provide seasonal daily flux calculations for S. alterniflora salt marshes and insight as to how changing environmental conditions such as wetland modification, wetland destruction, nutrient input, and climate change are affecting coastal biogeochemical cycles.

Assessing colloid-bound metal export in response to short term changes in runoff from a forested catchment

NASA Astrophysics Data System (ADS)

Neubauer, E.; Kammer, F. v. d.; Knorr, K.-H.; Pfeiffer, S.; Reichert, M.; Hofmann, T.

2012-04-01

Soils can act as a source of metals and natural organic matter (NOM) in runoff from catchments. Amounts and intensity of rainfall may influence NOM export from catchments. The presence of NOM and other colloids in water may not only enhance metal export, but also significantly change metal speciation. In this study, we investigated the response of metal-colloid associations to short-term discharge variations in the runoff from a small forested catchment (Lehstenbach, Bavaria, Germany). Here, the discharge from the catchment outlet responds within hours to rain events. Near-surface flow in organic-rich layers and peat soils has been identified to increase dissolved organic carbon (DOC) concentrations during stormwater runoff. Flow Field-Flow Fractionation coupled to ICP-MS (FlowFFF-ICPMS) is a high-resolution size separation technique which was used for the detection and quantification of colloids and associated metals. Colloid-associated metals, dissolved metals and metals associated with low-molecular weight organic ligands were also separated by filtration (0.2 µm) and ultrafiltration (1000 g/mol MWCO). During baseflow DOC concentration was <6 mg/L and the pH ranged between 4.6 and 5.0. The DOC concentration exported at a given discharge was subject to strong seasonal variation and depended on the water level before the discharge event. DOC concentrations were up to 8 fold higher during stormwater runoff compared to baseflow. The export of aluminum, arsenic, rare earth elements (REE) and uranium from the catchment increased during stormwater runoff showing a strong correlation with NOM concentrations. This result was supported by FlowFFF-ICPMS data revealing that NOM was the only colloid type available for metal complexation during all hydrological conditions. A clear temporal pattern in the association with the NOM was observed for most of the metals under study: During baseflow, 70-100% (Fe), 90% (Al), 60-100% (REE) and 80-85% (U) were associated with the NOM. During stormwater runoff, the dissolved species concentration and those associated with small organic ligands (<1000 g/mol) increased. The pH drop during the stormwater runoff (pH <4) is most likely the main factor for weaker metal-NOM binding. However, only 25 to 50% of the arsenic was associated with NOM, but no relation to discharge, or pH was exhibited. The results show that fluxes of most trace metals from the catchment are governed by NOM-colloids, even though substantial concentrations are dissolved or associated to low-molecular weight organic substances during stormwater runoff.

Soil organic carbon redistribution by water erosion: An experimental rainfall simulation approach

NASA Astrophysics Data System (ADS)

Wang, Xiang; Cammeraat, Erik; Romeijn, Paul; Kalbitz, Karsten

2014-05-01

Water erosion influences the redistribution of soil organic carbon (SOC) in landscapes and there is a strong need to better understand these processes with respect to the carbon (C) budget, from local to global scales. We present a study in which the total carbon budget of a loess soil under erosion was determined in an experimental set-up. We measured fluxes of SOC, dissolved organic C (DOC) and CO2 in a climate controlled pseudo-replicated rainfall-simulation laboratory experiment. This approach has been rarely followed to integrate all components of the C budget in one experiment. We characterized different C fractions in soils and redistributed sediments using density fractionation and determined C enrichment ratios (CER) in the transported sediments. Erosion, transport and subsequent deposition resulted in a significantly higher CER of the sediments exported ranging between 1.3 and 4.0. In the exported sediments, C contents (mg per g soil) of particulate organic C (POC, C not bound to soil minerals) and mineral-associated organic C (MOC) were both significantly higher than those of non-eroded soils indicating that water erosion resulted in losses of C-enriched material both in forms of POC and MOC. The averaged SOC fluxes as particles (4.7 g C m-2 yr-1) were 18 times larger than DOC fluxes. Cumulative emission of soil CO2 slightly decreased at the erosion zone while increased by 27% at the deposition zone in comparison to non-eroded soils. Overall, CO2 emission was the predominant form of C loss contributing to about 90.5% of total erosion-induced C losses in our 4-month experiment. However, only 1.5 % of redistributed C was mineralized highlighting that the C sink induced by deposition is much larger than previously assumed. Our study also underlines the importance of C losses by particles and as DOC for understanding effects of water erosion on the C balance at the interface of terrestrial and aquatic systems. Furthermore our study revealed that the sediment and C fluxes showed good correspondence with values obtained in real landscapes as reported in literature. This confirms that a lab-approach, despite its shortcomings with respect to scale, is valuable and gives additional information on processes affecting the soil carbon budget. This is urgently needed and improves our knowledge on the fate of SOC in erosion-depositional systems.

Variation of the isotopic composition of dissolved organic carbon during the runoff cycle in the Amazon River and the floodplains

NASA Astrophysics Data System (ADS)

Albéric, Patrick; Pérez, Marcela A. P.; Moreira-Turcq, Patricia; Benedetti, Marc F.; Bouillon, Steven; Abril, Gwenaël

2018-01-01

Given the relative scarcity of stable isotope data on dissolved organic carbon (DOC) in the Amazon Basin, we hypothesized that the variability in DOC sources may be underestimated in such major river basins. To explore the links between the mainstem and tributaries and the floodplain, particular efforts were made during five distinct cruises at different stages of the hydrograph between October 2008 and January 2011, to document the spatial and temporal variation of DOC concentrations and δ13C-DOC in the central Amazon River system (Brazil). Based on more than 200 data, the spatial and temporal variability of δ13C-DOC values was found to be larger than previously reported in the same area. Although a small range of variation was observed throughout the hydrological cycle in the upper reach of the studied section (-29.2 to -29.5‰ in the Rio Negro and -28.7 to -29.0‰ in the Rio Solimões), a much larger one (-28.0 to -34.6‰) was found in the lower reach of the river, as the proportion of open lakes increased downstream in the floodplains. The low variability in the upper reaches suggests constant and homogeneous DOC sources from upland soils and flooded forest, while lower δ13C-DOC values recorded in the lower reach mainstem at high and falling waters can be attributed to a greater export of plankton-derived 13C-depleted DOC from flooded lakes. Noteworthy are the higher δ13C-DOC values measured in the Rio Madeira and the associated flooded lakes (-26.5 to -28.8‰), which may reflect the imprint from upland headwaters and a weaker density of flooded forest in the watershed. The higher δ13C-DOC values observed in the lower reach during low waters are still not fully understood. Floating meadows principally consisting of C4 macrophytes were found to increase δ13C-DOC values by ∼1.5‰ in their vicinity, but this impact was no longer noticeable at distances of ∼10 m from the plant rafts. This rather modest 13C-enrichment suggests rapid decomposition and/or dilution of this wetland-derived DOC.

Dissolved and particulate organic carbon in the melt water of Icelandic glaciers

NASA Astrophysics Data System (ADS)

Chifflard, Peter; Reiss, Martin

2017-04-01

Recently, glaciers have been recognized as unique ecosystems with potential effects on the global carbon cycle. Among other transport processes organic carbon stored in glacier ecosystems is released from the glaciers through melt at the glaciers surface that discharges into proglacial streams and finally into the ocean. Nevertheless, the potential role of glaciers in the carbon cycle remains poorly understood (Hood et al. 2015). One particular problem in this respect is that there is a lack in regional and global analysis of the total amount of organic carbon released from glaciers. Although, the release of organic carbon has been investigated in proglacial streams in Alaska, the European Alps and Greenland, to our knowledge, there is no information available for Icelandic proglacial streams. Thus, the aims of this study are: 1) to develop a first base information about the concentration of dissolved and particulate organic carbon (DOC and POC) in several Icelandic proglacial streams and 2) to detect the variability of DOC and POC along a proglacial stream from the glacier source to the mouth into the Atlantic Ocean. Therefore, a field trip was conducted between 23 and 31 July 2016, whereby, 25 water samples were taken. The sampling points cover melt water from the following Icelandic glaciers Vatnajökull, Langjökull, Hofsjökull, Myrdalsjökull and Tungnafellsjökull. Further water samples were taken along the river Hvitá starting at the glacier Langjökull and ending at the mouth into the Atlantic ocean in the southwest of Iceland. At every sample point electrical conductivity, water temperate and the pH-value were measured in situ using a calibrated portable water quality meter (Hanna Combo HI98129). The water samples (130 ml) were filtered using pre-combusted GF/F filters (Whatman, pore sizes 0.7 µm) and stored in a cooling box until the shipment to the laboratory of the Department for Geography, Philipps-University of Marburg. The DOC concentrations in the filtered water samples were measured using a TOC analyzer using high-temperature combustion of organic matter (OM) followed by thermal detection of CO2 (TOC-L, Shimadzu, Japan). POC was measured by determining mass lost upon combustion of the samples. Therefore all glass fiber membranes were dried after sampling at 65°C to a constant weight, reweighed to calculate the total suspended solids (TSS), combusted via heating the filter to 550° C and finally reweighed to calculate the amount of particulate organic matter. Spectroscopic characteristics were detected by using a spectrophotometer (ThermoFisher, Genesys 10S) for UV-VIS analysis and a fluorescence spectrometer (Shimadzu RF-6000) for fluorescence analysis. Spectroscopic indices will be calculated based on these UV-VIS and fluorescence data. First results show that the DOC-concentrations are very low and range from 0.113 mg/l to 0.937 mg/l. These concentrations are comparable with values measured in the melt water in other regions (Alaska, Greenland and European Alps) (Hood et al. 2015). POC concentrations range from 0.667 mg/l to 173.333 mg/l and exceed the DOC-concentration at every sampling location. This differences can be compared with results of the Greenland Ice Sheet, but not with some small glaciers in the European Alps, where the concentrations of DOC and POC more or less equal (Hood et al. 2015). Nevertheless, the export of POC plays a very important factor within the organic carbon export budget of glaciers in Iceland and further measurements are required. Hood, E., Battin, T. J., Fellman, J., O'Neel, S., & Spencer, R. G. (2015). Storage and release of organic carbon from glaciers and ice sheets. Nature Geoscience, 8(2), 91-96.

Physical factors controlling carbon cycling dynamics in blackwater river-dominated and particle dominated estuaries

NASA Astrophysics Data System (ADS)

Arellano, A. R.; Bianchi, T. S.; Osburn, C. L.; D'Sa, E. J.; Oviedo-Vargas, D.; Ward, N. D.; Joshi, I.

2017-12-01

While most blue carbon habitat (wetlands, seagrass beds and mangroves) research has focused on carbon burial/stocks and habitat fragmentation of these communities, few studies have examined physical factors that control exports and losses of blue carbon sources of organic matter (OM) to adjacent coastal waters. Here, we report on spatiotemporal changes in the composition and concentration of dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen, pCO2, δ13C-DOC, δ13C-POC, δ13C-CO2, dissolved lignin-phenols (dΣ8), particulate lignin-phenols (pΣ8) and carbon normalized dissolved and particulate lignin phenol yields (dΛ8 and pΛ8) in surface waters of the Apalachicola and Barataria bays in the Gulf of Mexico. Discriminant analysis described spatial variability along canonical axis I (24.4%) while temporal variability was explained by canonical axis II (23.2%). Apalachicola Bay was low in POC concentration and characterized by high values for pCO2, DOC, C:N, dΣ8 and (Ad:Al)V. The latter three parameters indicated a clear terrestrial source of OM at Apalachicola Bay reflecting the importance of riverine DOM inputs in this system. In contrast, Barataria Bay was characterized by high values for POC, C:V, S:V, and δ13C-POC, indicating blue-carbon sources due to a lack of direct river inputs and high prevalence of wetlands, some recently submerged. Extreme weather, such as intense precipitation events in Apalachicola Bay and enhanced northerly winds in Barataria Bay were characterized by δ13C-CO2, dΛ8, C:V (Barataria), and C:N (Apalachicola). Results indicate that such physical factors can exert strong control on OM sources and sinks across the gradient of coastal wetlands and shelf waters and lead to enhanced transfer and degradation of wetland-derived blue carbon in coastal waters.

Spatial and temporal variation in dissolved organic carbon composition in a peaty catchment draining a windfarm

NASA Astrophysics Data System (ADS)

Zheng, Ying; Waldron, Susan; Flowers, Hugh

2015-04-01

Peatlands are an important terrestrial carbon reserve and a principal source of dissolved organic carbon (DOC) to the fluvial environment (Wallage et al. 2006). Recently it has been observed that DOC concentrations [DOC] in surface waters have increased in Europe and North America (Monteith et al. 2007). This has been attributed primarily to reduced acid deposition. However, land use change can also release C from peat soils. A significant land use change in Scotland is hosting windfarms. Whether windfarm construction causes such impacts has been a research focus, particularly considering fluvial losses, but usually assessing if there are changes in DOC concentration rather than composition. Our study area is a peaty catchment that hosts wind turbines, has peat restoration activities and forest felling and is drained by two streams. We are using UV-visible and fluorescence spectrophotometry to assess if there are differences between the two steams or temporal changes in DOC composition. We will present data from samples collected since February 2014. The parameters we are focusing on are SUVA254, E4/E6 and E2/E4 ratios as these are indicators of DOC aromaticity, humic acid (HA): fulvic acid (FA) ratio and the proportion of humic substances in DOC (Weishaar, 2003; Spencer et al. 2007; Graham et al. 2012). To assess these we have measured UV-visible absorbance spectra from 200 nm to 800 nm. Meanwhile sample fluorescence emission and excitation matrix (EEM) will be applied with the PARAFAC model to obtain more information about the variations in humic substances in this catchment. Our current analysis indicates spatial differences not only in DOC concentration but also in composition. For example, the mainstem draining the windfarm area had a smaller [DOC] but higher E4/E6 and lower E2/E4 ratio values than the tributary draining an area of felled forestry. This may be indicative of more HAs in the mainstem DOC. Seasonal variations have also been observed. Both streams had high [DOC] in summer and autumn compared to spring. While E2/E4 ratios were steady in both streams, a more variable E4/E6 ratio in the mainstem may suggest DOC composition changed more over time than in the tributary which had a relatively stable E4/E6 ratio. [DOC] fell in both streams during the summer drought period but a corresponding fall in SUVA254 in the mainstem but not the tributary is further evidence of differences in DOC composition between the two streams. Such spatial and temporal understanding is needed to understand if, and how, land use influences the composition of the DOC exported. References: Graham M. C. et al. 2012. Processes controlling manganese distributions and associations in organic-rich freshwater aquatic systems: The example of Loch Bradan, Scotland. Science of the Total Environment, 424, 239-250. Monteith D. et al. 2007. Dissolved organic carbon trends resulting from changes in atmospheric chemistry. Nature,450, 537-540. Spencer R.G.M, Bolton L. and Baker A. 2007. Freeze/thaw and pH effects on freshwater dissolved organic matter fluorescence and absorbance properties from a number of UK locations.Water Research, 41 (13):2941-2950. Wallage Z.E., Holden, J. and McDonald, A.T. 2006. Drain blocking: An effective treatment for reducing dissolved organic carbon loss and water discolouration in a drained peatland. Science of the total environment, 367, 811-821. Weishaar J.L. et al. 2003. Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon. Environmental Science & Technology 37(20): 4702-4708.

Carbon Fluxes in Dissolved and Gaseous Forms for a Restored Peatland in British Columbia, Canada

NASA Astrophysics Data System (ADS)

D'Acunha, B.; Johnson, M. S.; Lee, S. C.; Christen, A.

2016-12-01

Peatlands are wetlands where gross primary production exceeds organic matter decomposition causing an accumulation of partially decomposed matter, also called peat. These ecosystems can accumulate more carbon than tropical rainforests. However, dissolved and gaseous fluxes of carbon (as dissolved organic carbon (DOC), CO2 and methane (CH4)) must also be considered to determine if these ecosystems are net sinks or sources of greenhouse gases (GHGs) to the atmosphere, which depends in part on the environmental conditions and the state of the ecosystem. We conducted research in Burns Bog, Delta, BC, Canada, a raised domed peat bog located in the Fraser River Delta and one of the largest raised peat bogs on the west coast of the Americas, but which has been heavily impacted by a range of human activities. Currently, ecological restoration efforts are underway by a large-scale ditch blocking program, with the aim to re-establish a high water table. This is approached in partnership with research on the ecosystem services that the bog provides, including its role in a regional GHG inventory. Here we present data on ecosystem-scale fluxes of CO2 and CH4 determined by eddy covariance (EC) on a floating tower platform, and complementary data on (i) evasion fluxes of CO2, CH4 and nitrous oxide (N2O) from the water surface to the atmosphere, and (ii) the flux and composition of dissolved organic carbon in water draining Burns Bog. Concentrations of dissolved CO2, CH4 and N2O were determined by headspace equilibration, and evasion rates from the water surface were quantified and are used to estimate the role of the hydrosphere in the ecosystem-scale measurements. Water samples collected from five saturated areas in the flux tower footprint were analyzed for DOC concentrations and composition. Results indicated that, even though the whole system is a net C sink, the water surface behaved as a source of CO2 and CH4, and a sink for N2O throughout the study period. Drainage waters were high in DOC (> 30 mg L-1). DOC export was found to offset about 20% of the apparent net C uptake determined by EC, indicating that the EC system overestimates carbon accumulation by not accounting for DOC drainage.

Evasion of CO2 from streams - the dominant component of the carbon export through the aquatic conduit in a boreal landscape.

PubMed

Wallin, Marcus B; Grabs, Thomas; Buffam, Ishi; Laudon, Hjalmar; Agren, Ånneli; Öquist, Mats G; Bishop, Kevin

2013-03-01

Evasion of gaseous carbon (C) from streams is often poorly quantified in landscape C budgets. Even though the potential importance of the capillary network of streams as C conduits across the land-water-atmosphere interfaces is sometimes mentioned, low-order streams are often left out of budget estimates due to being poorly characterized in terms of gas exchange and even areal surface coverage. We show that evasion of C is greater than all the total dissolved C (both organic and inorganic) exported downstream in the waters of a boreal landscape. In this study evasion of carbon dioxide (CO2 ) from running waters within a 67 km(2) boreal catchment was studied. During a 4 year period (2006-2009) 13 streams were sampled on 104 different occasions for dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). From a locally determined model of gas exchange properties, we estimated the daily CO2 evasion with a high-resolution (5 × 5 m) grid-based stream evasion model comprising the entire ~100 km stream network. Despite the low areal coverage of stream surface, the evasion of CO2 from the stream network constituted 53% (5.0 (±1.8) g C m(-2)  yr(-1) ) of the entire stream C flux (9.6 (±2.4) g C m(-2)  yr(-1) ) (lateral as DIC, DOC, and vertical as CO2 ). In addition, 72% of the total CO2 loss took place already in the first- and second-order streams. This study demonstrates the importance of including CO2 evasion from low-order boreal streams into landscape C budgets as it more than doubled the magnitude of the aquatic conduit for C from this landscape. Neglecting this term will consequently result in an overestimation of the terrestrial C sink strength in the boreal landscape. © 2012 Blackwell Publishing Ltd.

Chromophoric dissolved organic matter export from U.S. rivers

NASA Astrophysics Data System (ADS)

Spencer, Robert G. M.; Aiken, George R.; Dornblaser, Mark M.; Butler, Kenna D.; Holmes, R. Max; Fiske, Greg; Mann, Paul J.; Stubbins, Aron

2013-04-01

Chromophoric dissolved organic matter (CDOM) fluxes and yields from 15 major U.S. rivers draining an assortment of terrestrial biomes are presented. A robust relationship between CDOM and dissolved organic carbon (DOC) loads is established (e.g., a350 versus DOC; r2 = 0.96, p < 0.001). Calculated CDOM yields are also correlated to watershed percent wetland (e.g. a350; r2 = 0.81, p < 0.001) providing a method for the estimation of CDOM export from ungauged watersheds. A large variation in CDOM yields was found across the rivers. The two rivers in the north-eastern U.S. (Androscoggin and Penobscot), the Edisto draining into the South Atlantic Bight, and some rivers draining into the Gulf of Mexico (Atchafalaya and Mobile) exhibit the highest CDOM yields, linked to extensive wetlands in these watersheds. If the Edisto CDOM yield is representative of other rivers draining into the South Atlantic Bight, this would result in a CDOM load equivalent to that of the Mississippi from a region of approximately 10% of the Mississippi watershed, indicating the importance of certain regions with respect to the role of terrigenous CDOM in ocean color budgets.

Chromophoric dissolved organic matter export from U.S. rivers

USGS Publications Warehouse

Spencer, Robert G. M.; Aiken, George R.; Dornblaser, Mark M.; Butler, Kenna D.; Holmes, R. Max; Fiske, Greg; Mann, Paul J.; Stubbins, Aron

2013-01-01

Chromophoric dissolved organic matter (CDOM) fluxes and yields from 15 major U.S. rivers draining an assortment of terrestrial biomes are presented. A robust relationship between CDOM and dissolved organic carbon (DOC) loads is established (e.g., a350 versus DOC; r2 = 0.96, p < 0.001). Calculated CDOM yields are also correlated to watershed percent wetland (e.g. a350; r2 = 0.81, p < 0.001) providing a method for the estimation of CDOM export from ungauged watersheds. A large variation in CDOM yields was found across the rivers. The two rivers in the north-eastern U.S. (Androscoggin and Penobscot), the Edisto draining into the South Atlantic Bight, and some rivers draining into the Gulf of Mexico (Atchafalaya and Mobile) exhibit the highest CDOM yields, linked to extensive wetlands in these watersheds. If the Edisto CDOM yield is representative of other rivers draining into the South Atlantic Bight, this would result in a CDOM load equivalent to that of the Mississippi from a region of approximately 10% of the Mississippi watershed, indicating the importance of certain regions with respect to the role of terrigenous CDOM in ocean color budgets.

Data-based mechanistic modeling of dissolved organic carbon load through storms using continuous 15-minute resolution observations within UK upland watersheds

NASA Astrophysics Data System (ADS)

Jones, T.; Chappell, N. A.

2013-12-01

Few watershed modeling studies have addressed DOC dynamics through storm hydrographs (notable exceptions include Boyer et al., 1997 Hydrol Process; Jutras et al., 2011 Ecol Model; Xu et al., 2012 Water Resour Res). In part this has been a consequence of an incomplete understanding of the biogeochemical processes leading to DOC export to streams (Neff & Asner, 2001, Ecosystems) & an insufficient frequency of DOC monitoring to capture sometimes complex time-varying relationships between DOC & storm hydrographs (Kirchner et al., 2004, Hydrol Process). We present the results of a new & ongoing UK study that integrates two components - 1/ New observations of DOC concentrations (& derived load) continuously monitored at 15 minute intervals through multiple seasons for replicated watersheds; & 2/ A dynamic modeling technique that is able to quantify storage-decay effects, plus hysteretic, nonlinear, lagged & non-stationary relationships between DOC & controlling variables (including rainfall, streamflow, temperature & specific biogeochemical variables e.g., pH, nitrate). DOC concentration is being monitored continuously using the latest generation of UV spectrophotometers (i.e. S::CAN spectro::lysers) with in situ calibrations to laboratory analyzed DOC. The controlling variables are recorded simultaneously at the same stream stations. The watersheds selected for study are among the most intensively studied basins in the UK uplands, namely the Plynlimon & Llyn Brianne experimental basins. All contain areas of organic soils, with three having improved grasslands & three conifer afforested. The dynamic response characteristics (DRCs) that describe detailed DOC behaviour through sequences of storms are simulated using the latest identification routines for continuous time transfer function (CT-TF) models within the Matlab-based CAPTAIN toolbox (some incorporating nonlinear components). To our knowledge this is the first application of CT-TFs to modelling DOC processes. Furthermore this allows a data-based mechanistic (DBM) modelling philosophy to be followed where no assumptions about processes are defined a priori (given that dominant processes are often not known before analysis) & where the information contained in the time-series is used to identify multiple structures of models that are statistically robust. Within the final stage of DBM, biogeochemical & hydrological processes are interpreted from those models that are observable from the available stream time-series. We show that this approach can simulate the key features of DOC dynamics within & between storms & that some of the resultant response characteristics change with varying DOC processes in different seasons. Through the use of MISO (multiple-input single-output) models we demonstrate the relative importance of different variables (e.g., rainfall, temperature) in controlling DOC responses. The contrasting behaviour of the six experimental catchments is also reflected in differing response characteristics. These characteristics are shown to contribute to understanding of basin-integrated DOC export processes & to the ecosystem service impacts of DOC & color on commercial water treatment within the surrounding water supply basins.

Stoichiometry of hydrological C, N, and P losses across climate and geology: An environmental matrix approach across New Zealand primary forests

NASA Astrophysics Data System (ADS)

McGroddy, M. E.; Baisden, W. T.; Hedin, L. O.

2008-03-01

Hydrologic losses can play a key role in regulating ecosystem nutrient balances, particularly in regions where baseline nutrient cycles are not augmented by industrial deposition. We used first-order streams to integrate hydrologic losses at the watershed scale across unpolluted old-growth forests in New Zealand. We employed a matrix approach to resolve how stream water concentrations of dissolved organic carbon (DOC), organic and inorganic nitrogen (DON and DIN), and organic and inorganic phosphorus (DOP and DIP) varied as a function of landscape differences in climate and geology. We found stream water total dissolved nitrogen (TDN) to be dominated by organic forms (medians for DON, 81.3%, nitrate-N, 12.6%, and ammonium-N, 3.9%). The median stream water DOC:TDN:TDP molar ratio of 1050:21:1 favored C slightly over N and P when compared to typical temperate forest foliage ratios. Using the full set of variables in a multiple regression approach explained approximately half of the variability in DON, DOC, and TDP concentrations. Building on this approach we combined a simplified set of variables with a simple water balance model in a regression designed to predict DON export at larger spatial scales. Incorporating the effects of climate and geologic variables on nutrient exports will greatly aid the development of integrated Earth-climate biogeochemical models which are able to take into account multiple element dynamics and complex natural landscapes.

Tidal wetland fluxes of dissolved organic carbon and sediment at Browns Island, California: initial evaluation

USGS Publications Warehouse

Ganju, N.K.; Bergamaschi, B.; Schoellhamer, D.H.

2003-01-01

Carbon and sediment fluxes from tidal wetlands are of increasing concern in the Sacramento-San Joaquin River Delta (Delta), because of drinking water issues and habitat restoration efforts. Certain forms of dissolved organic carbon (DOC) react with disinfecting chemicals used to treat drinking water, to form disinfection byproducts (DBPs), some of which are potential carcinogens. The contribution of DBP precursors by tidal wetlands is unknown. Sediment transport to and from tidal wetlands determines the potential for marsh accretion, thereby affecting habitat formation.Water, carbon, and sediment flux were measured in the main channel of Browns Island, a tidal wetland located at the confluence of Suisun Bay and the Delta. In-situ instrumentation were deployed between May 3 and May 21, 2002. Water flux was measured using acoustic Doppler current profilers and the index-velocity method. DOC concentrations were measured using calibrated ultraviolet absorbance and fluorescence instruments. Suspended-sediment concentrations were measured using a calibrated nephelometric turbidity sensor. Tidally averaged water flux through the channel was dependent on water surface elevations in Suisun Bay. Strong westerly winds resulted in higher water surface elevations in the area east of Browns Island, causing seaward flow, while subsiding winds reversed this effect. Peak ebb flow transported 36% more water than peak flood flow, indicating an ebb-dominant system. DOC concentrations were affected strongly by porewater drainage from the banks of the channel. Peak DOC concentrations were observed during slack after ebb, when the most porewater drained into the channel. Suspended-sediment concentrations were controlled by tidal currents that mobilized sediment from the channel bed, and stronger tides mobilized more sediment than the weaker tides. Sediment was transported mainly to the island during the 2-week monitoring period, though short periods of export occurred during the spring tide. Future deployments will characterize the seasonal variability of these fluxes.

The Heterotrophic Bacterial Response During the Meso-scale Southern Ocean Iron Experiment (SOFeX)

NASA Astrophysics Data System (ADS)

Oliver, J. L.; Barber, R. T.; Ducklow, H. W.

2002-12-01

Previous meso-scale iron enrichments have demonstrated the stimulatory effect of iron on primary productivity and the accelerated flow of carbon into the surface ocean foodweb. In stratified waters, heterotrophic activity can work against carbon export by remineralizing POC and/or DOC back to CO2, effectively slowing the biological pump. To assess the response of heterotrophic activity to iron enrichment, we measured heterotrophic bacterial production and abundance during the Southern Ocean Iron Experiment (SOFeX). Heterotrophic bacterial processes primarily affect the latter of the two carbon export mechanisms, removal of DOC to the deep ocean. Heterotrophic bacterial production (BP), measured via tritiated thymidine (3H-TdR) and leucine (3H-Leu) incorporation, increased ~40% over the 18-d observation period in iron fertilized waters south of the Polar Front (South Patch). Also, South Patch BP was 61% higher than in the surrounding unfertilized waters. Abundance, measured by flow cytometry (FCM) and acridine orange direct counts (AODC), also increased in the South Patch from 3 to 5 x 108 cells liter-1, a 70% increase. Bacterial biomass increased from ~3.6 to 6.3 μg C liter-1, a clear indication that production rates exceeded removal rates (bactivory, viral lysis) over the course of 18 days. Biomass within the fertilized patch was 11% higher than in surrounding unfertilized waters reflecting a similar trend. This pattern is in contrast to SOIREE where no accumulation of biomass was observed. High DNA-containing (HDNA) cells detected by FCM also increased over time in iron fertilized waters from 20% to 46% relative to the total population suggesting an active subpopulation of cells that were growing faster than the removal rates. In iron fertilized waters north of the Polar Front (North Patch), BP and abundance were ~90% and 80% higher, respectively, than in unfertilized waters. Our results suggest an active bacterial population that responded to iron fertilization by utilizing newly produced DOC and/or iron and which grew at rates that exceeded removal rates. Differences in the microbial response between SOFeX and SOIREE are subtle, and may be related to differences in foodweb structure prior to and during the response to iron enrichment.

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.

Dynamics of Dissolved Organic Matter in Amazon Basin: Insights into Negro River Contribution

NASA Astrophysics Data System (ADS)

Moreira-Turcq, P.; Perez, M. P.; Benedetti, M.; Oliveira, M. A.; Lagane, C.; Seyler, P.; Oliveira, E.

2006-12-01

The study of global carbon cycle requires a precise knowledge of spatial and temporal distributions and exportation from continents to oceans. Organic carbon fluxes represent approximately half of the total carbon budget carried by rivers. Tropical rivers transport two third of the total organic carbon discharged into the world oceans but important gaps still exist in the knowledge of the tropical river carbon biochemistry. The Amazon River is responsible for 10% of the annual amount of organic carbon transported from rivers to oceans. The most important portion of total organic matter transported in the Amazon Basin is the dissolved fraction (between 80% and 95%). Amazonian annual flux of dissolved organic matter is directly related to hydrological variations. All rivers in the Amazon basin are characterized by monomodal hydrograms, with a low water period in october/november and a high water period in may/june. Temporal variations in Amazon dissolved organic carbon (3.0 to 9.1 mg l^{- 1}) are mainly controled by Negro River inputs. DOC and DON contributions from the Negro River can vary between 120 kgC s-1 and 520 kg C s-1, and between 5 kgN s--1 and 15 kgN s-1, during low and high water period, respectivelly. In the Negro River, during high water stages, while DOC concentrations are stable from the upstream stations to the downstream ones (about 11 mg l-1), discharge increases from 16000 to 46000 m3 s-1 and NOD can quintuple from upstream (0.071 mg l-1) to downstream (0.341 mg l-1). Then the nature of dissolved organic matter is variable (C/N ratio varied from 33 to 120 from upstream to downstream). During low water stages DOC concentrations are lower (mean DOC of 8.1 mg l-1) while DON is in the same range, discharge is about 10000 m3 s-1 at downstream stations of Negro River and the C/N ratio is lower and steadier along the River. Finaly, despite a low basin surface (12%) compared with the two other main Amazon tributaries, Solimões and Madeira Rivers, and a mean annual water input to Amazonas of 15%, the Negro River contributes with about 38% of the total organic dissolved carbon transported by the Amazon River.

Mercury methylation, export and bioaccumulation in rice agriculture - model results from comparative and experimental studies in 3 regions of the California Delta, USA

NASA Astrophysics Data System (ADS)

Windham-Myers, L.; Fleck, J.; Eagles-Smith, C.; Ackerman, J.

2013-12-01

Seasonally flooded wetland ecosystems are often poised for mercury (Hg) methylation, thus becoming sources of methylmercury (MeHg) to in situ and downstream biota. The seasonal flooding associated with cultivation of rice (Oryza sativa) also generates MeHg, which may be stored in sediment or plants, bioaccumulated into fauna, degraded or exported, depending on hydrologic and seasonal conditions. While many U.S. waters are regulated for total Hg concentrations based on fish targets, California's Sacramento-San Joaquin Delta (Delta) will soon implement the first MeHg total maximum daily load (TMDL) control program. Since 2007, a conceptual model (DRERIP-MCM) and several ecosystem-level studies have been advanced to better understand the mechanisms behind Hg methylation, export and bioaccumulation within Delta wetlands, including rice agriculture. Three Delta rice-growing regions (Yolo Bypass, Cosumnes River, Central Delta) of varied soil characteristics, mining influences and hydrology, were monitored over full crop years to evaluate annual MeHg dynamics. In addition to fish tissue Hg accumulation, a broad suite of biogeochemical and hydrologic indices were assessed and compared between wetland types, seasons, and regions. In general, Delta rice fields were found to export MeHg during the post-harvest winter season, and promote MeHg uptake in fish and rice grain during the summer growing season. As described in a companion presentation (Eagles-Smith et al., this session), the experimental Cosumnes River study suggests that rice-derived dissolved organic carbon (DOC) fuels MeHg production and uptake into aquatic foodwebs. Explicit DRERIP-MCM linkages for the role of rice-DOC in MeHg production, export and bioaccumulation were verified across two summers (2011, 2012): rice biomass and root productivity influenced porewater DOC availability and microbial processes, which drove sediment MeHg production and flux to surface water, promoting MeHg bioaccumulation in fish. Linkages from plant biomass to fish Hg concentrations were less evident in non-agricultural wetlands (seasonal or permanent flooding), where aromatic DOC and physical controls (e.g. hydrology, photodemethylation) appeared to have a greater role. Winter rice straw management had no measurable impact on summer MeHg dynamics, but wetland data suggest that the inclusion of deepwater cells within fields may reduce MeHg exposure. As concern grows over MeHg concentrations in rice grains, research on cultivars and field management is expanding in China, but ecosystem-level studies remain rare. Broader global monitoring and research are needed to address these pathways of Hg exposure given the global expansion of rice agriculture and ongoing atmospheric Hg deposition. Dense root and canopy structure of California rice fields (Oryza sativa), August 2007

Dynamics of nitrogen and dissolved organic carbon at the Hubbard brook experimental forest.

PubMed

Dittman, Jason A; Driscoll, Charles T; Groffman, Peter M; Fahey, Timothy J

2007-05-01

The factors controlling spatial and temporal patterns in soil solution and streamwater chemistry are highly uncertain in northern hardwood forest ecosystems in the northeastern United States, where concentrations of reactive nitrogen (Nr) in streams have surprisingly declined over recent decades in the face of persistent high rates of atmospheric Nr deposition and aging forests. Reactive nitrogen includes inorganic species (e.g., ammonium [NH4+], nitrate [NO3-]) and some organic forms (e.g., amino acids) available to support the growth of plants and microbes. The objective of this study was to examine controls on the spatial and temporal patterns in the concentrations and fluxes of nitrogen (N) species and dissolved organic carbon (DOC) in a 12-year record of soil solutions and streamwater along an elevational gradient (540-800 m) of a forested watershed at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of New Hampshire, USA. Dissolved organic N and DOC concentrations were elevated in the high-elevation spruce-fir-white birch (SFB) zone of the watershed, while NO3- was the dominant N species in the lower elevation hardwood portion of the watershed. Within the soil profile, N retention was centered in the mineral horizon, and significant amounts of N were retained between the lower mineral soil and the stream, supporting the idea that near- and in-stream processes are significant sinks for N at the HBEF. Temporal analysis suggested that hydrologic flow paths can override both abiotic and biotic retention mechanisms (i.e., during the non-growing season when most hydrologic export occurs, or during years with high rainfall), there appears to be direct flushing of N from the organic horizons into the stream via horizontal flow. Significant correlations between soil NO3- concentrations, nitrification rates and streamwater NO3- exports show the importance of biological production as a regulator of inorganic N export. The lack of internal production response (e.g., mineralization, nitrification) to a severe ice storm in 1998 reinforces the idea that plant uptake is the dominant regulator of export response to disturbance.

Assessing quality and quantity of groundwater DOC in relation to plant export from different over-winter green-cover treatments in tillage farming systems

NASA Astrophysics Data System (ADS)

Premrov, Alina; Coxon, Catherine; Hackett, Richard; Richards, Karl

2010-05-01

The biogeochemistry of nitrogen is often connected to carbon and C/N dynamics. The dissolved organic carbon (DOC) electron donor availability can be related to groundwater denitrification (Buss, et al. 2005). Therefore groundwater nitrate attenuation processes are also frequently linked to carbon availability. In recent years the role of over-winter green cover in tillage farming has been studied extensively. Nevertheless further research on the biogeochemical effect of green cover on soil/sediment and groundwater quality is still needed. In particular plant roots are known to exude different types of organic compounds, but their role in groundwater quality has not been investigated in depth. According to Cannavo et al. (2004a,b), in addition to quantity, the quality of water-extractable soil organic matter (e.g. molecular size/weight) has also an important role for microbial activity. In this study we investigate the effect of over-winter green-cover on potential DOC export to shallow groundwater (2 - 5 m below ground level), located on tillage land in Oak Park, Carlow, Ireland. The experiment includes three over-winter green-cover treatments: natural green-cover, mustard and no-cover (sprayed with herbicide following harvest); and is underlain by a sand and gravel aquifer. The site is equipped with 4 shallow piezometers per treatment (total no. of piezometers is 20, including treatments and surrounding piezometers). In addition to monitoring the quantity of DOC concentrations in shallow groundwater under different green cover treatments over time, an attempt was made to evaluate the quality of dissolved organic matter in shallow groundwater using Excitation Emission Fluorescence Matrix (EEFM) profiles obtained from analyses performed on a Varian Fluorescence Spectrophotometer of a single batch of samples (from all 20 installed piezometers in September 2009). To evaluate the quality of dissolved organic matter in shallow groundwater, computation of the humification index (HIX) was performed. Computation of HIX was adapted from the methodology described in Zsolnay (2003) and Cannavo et al. (2004b) using emission spectra from excitation at 245nm, and the HIX was expressed as the H/L ratio. H/L is defined as the ratio between the area of the higher and lower usable quarter of emission spectrum peak [i.e. H (352 - 382nm), L (450 - 480nm)], corresponding to the pools of high (H) and low (L) organic molecule sizes (Cannavo et al., 2004b). Quantitatively the results showed generally low DOC values (< 3mg/L). However, the groundwater DOC concentrations under mustard-cover were higher if compared to two other treatments, which indicated possible mustard plant DOC export to shallow groundwater (Premrov et al., 2009). Qualitative analyses showed an EEFM profile pattern typical for water extractable organic matter. Mean HIX values were generally low (< 2), as expected for shallow groundwater, corresponding to small organic molecules. The HIX levels obtained in this study were also generally comparable to the low HIX values found by Cannavo (2004b) (e.g. HIX of c. 2 at 1- 2 m unsaturated zone depth). Despite slightly higher mean HIX values under mustard-cover, no clear trend was observed in the quality of dissolved organic matter in groundwater in relation to different green cover treatments: i.e. mean groundwater HIX value under mustard treatment (n=4 per treatment) was 1.84, std.err.= 0.19; while the mean value for natural regeneration was 1.62 (std.err.=0.15) and that for the no-cover treatment was 1.60 (std.err.=0.16). The results indicate the importance of further studies using EEFM analysis to assess the quality of dissolved organic matter in shallow groundwater. Acknowledgements This work was funded by a Teagasc Walsh Fellowship and a Trinity College Dublin One-year Postgraduate Student Award. The authors thank Dr. Norman Allot and Dr. Carlos Rocha from Trinity College Dublin for their support and suggestions regarding the Fluorescence Spectrophotometrical analysis. Literature: Buss, S.R., Rivett, M.O., Morgan, P., Bemment, C.D., 2005. Using science to create a better place: Attenuation of nitrate in the sub-surface environment. Science Report SC030155/SR2. Environment Agency, UK. Cannavo, P., Richaume, A., Lafolie, F., 2004a. Fate of nitrogen and carbon in the vadose zone: in situ and laboratory measurements of seasonal variations in aerobic respiratory and denitrifying activities. Soil Biology and Biochemistry 36, p. 463-478. Cannavo, P., Dudal, Y., Boudenne, J.L., Lafolie, F., 2004b. Potential for Fluorescence Spectroscopy To Assess the Quality of Soil Water-Extracted Organic Matter. Soil Science 169, p. 688-696. Premrov, A., Coxon, C.E., Hackett, R., Brennan D., Sills, P. & Richards, K. 2009. Over-winter green cover in a spring barley system: Role in exporting dissolved organic carbon to shallow groundwater and implications for denitrification. 16th Nitrogen Workshop: Connecting different scales of nitrogen use in agriculture. Turin, Italy. (Eds.: Grignani, C., Acutis, M., Zavattaro, L., Bechini, L., Bertora, C., Gallina, P. M. and Sacco, D.), p. 11-12. Zsolnay, Á., 2003. Dissolved organic matter: artefacts, definitions, and functions. Geoderma 113, p. 187-209.

Chemical and carbon isotopic composition of dissolved organic carbon in a regional confined methanogenic aquifer

USGS Publications Warehouse

Aravena, R.; Wassenaar, L.I.; Spiker, E. C.

2004-01-01

This study demonstrates the advantage of a combined use of chemical and isotopic tools to understand the dissolved organic carbon (DOC) cycle in a regional confined methanogenic aquifer. DOC concentration and carbon isotopic data demonstrate that the soil zone is a primary carbon source of groundwater DOC in areas close to recharge zones. An in-situ DOC source linked to organic rich sediments present in the aquifer matrix is controlling the DOC pool in the central part of the groundwater flow system. DOC fractions, 13C-NMR on fulvic acids and 14C data on DOC and CH4 support the hypothesis that the in-situ DOC source is a terrestrial organic matter and discard the Ordovician bedrock as a source of DOC. ?? 2004 Taylor and Francis Ltd.

Linking major and trace element headwater stream concentrations to DOC release and hydrologic conditions in a bog and peaty riparian zone

NASA Astrophysics Data System (ADS)

Broder, Tanja; Biester, Harald

2017-04-01

Peatlands and organic-rich riparian zones are known to export large amounts of dissolved organic carbon (DOC) to surface water. In organic-rich, acidic headwater streams main carriers for element export are dissolved organic matter (DOM) and organic-iron complexes. In this environment DOM might also act as major carrier for metals, which otherwise may have a low solubility. This study examines annual and short term event-based variations of major and trace elements in a headwater catchment. Patterns are used to trace hydrological pathways and element sources under different hydrologic preconditions. Furthermore, it elucidates the importance of DOC as carrier of different elements in a bog and a peaty riparian catchment. The study was conducted in a small headwater stream draining an ombrotrophic peatland with an adjacent forested area with peaty riparian soils in the Harz Mountains (Germany). Discharge sampling was conducted weekly at two sites from snowmelt to begin of snowfall and in high resolution during selected discharge events in 2013 and 2014. Element concentrations were measured by means of ICP-MS and ICP-OES. A PCA was performed for each site and for annual and event datasets. Results show that a large number of element concentrations strongly correlate with DOC concentrations at the bog site. Even elements like Ca and Mg, which are known to have a low affinity to DOC. Congruently, the first principal component integrates the DOC pattern (element loadings > 0.8: Ca, Fe, Mg, Mn, Zn, As, Sr, Cd, DOC) and explained about 35 % of total variance and even 50 % during rain events (loadings > 0.8: Al, Ca, Fe, Mg, Mn, Zn, Li, Co, As, Sr, Cd, Pb, DOC). The study cannot verify that all correlating elements bind to DOC. It is likely that also a common mobilization pattern in the upper peat layer by plant decomposition causes the same response to changes in hydrologic pathways. Additionally, a low mineral content and an enrichment of elements like Fe and Mn in the upper peat layers due to prevailing redox conditions might play a major role in a bog environment. At the peaty riparian zone only Ca, Fe, and Sr strongly correlated with DOC over the annual record. The PCA of the annual record display no clear DOC component here, but indicates that DOC is influenced by Component one (element loadings > 0.8: Ca, Mg, Zn, Co, Sr) and two (Al, V, La, Pb, U) suggesting different DOC sources in the peaty riparian zone. A large number of elements correlate with DOC during rain event sampling at the riparian zone. In contrast to the bog site the event-based riparian zone PCA distinguished a clear discharge related component with mineral, groundwater related elements (K, Rb, In, Cs, NO3- and SO42-). Pattern of the mineral and DOC components prove that during base flow discharge is generated in a shallow groundwater layer and successively increases upward to the organic-rich upper soil layer with increasing discharge. Contrarily, bog element pattern confirm a dominating surface-near discharge, due to high hydraulic conductivities.

Organic Carbon and Trace Element Cycling in a River-Dominated Tidal Coastal Wetland System (Tampa Bay, FL, USA)

NASA Astrophysics Data System (ADS)

Moyer, R. P.; Smoak, J. M.; Engelhart, S. E.; Powell, C. E.; Chappel, A. R.; Gerlach, M. J.; Kemp, A.; Breithaupt, J. L.

2016-02-01

Tampa Bay is the largest open water, river-fed estuary in Florida (USA), and is characterized by the presence of both mangrove and salt marsh ecosystems. Both coastal wetland systems, and small rivers such as the ones draining into Tampa Bay have historically been underestimated in terms of their role in the global carbon and elemental cycles. Climate change and sea-level rise (SLR) are major threats in Tampa Bay and stand to disrupt hydrologic cycles, compromising sediment accumulation and the rate of organic carbon (OC) burial. This study evaluates organic carbon content, sediment accumulation, and carbon burial rates in salt marsh and mangrove ecosystems, along with measurements of fluxes of dissolved OC (DOC) and trace elements in the water column of the Little Manatee River (LMR) in Tampa Bay. The characterization of OC and trace elements in tidal rivers and estuaries is critical for quantitatively constraining these systems in local-to-regional scale biogeochemical budgets, and provide insight into biogeochemical processes occurring with the estuary and adjacent tidal wetlands. Material fluxes of DOC and trace elements were tied to discharge irrespective of season, and the estuarine habitats removed 15-65% of DOC prior to export to Tampa Bay and the Gulf of Mexico. Thus, material is available for cycling and burial within marsh and mangrove peats, however, LMR mangrove peats have higher OC content and burial rates than adjacent salt marsh peats. Sedimentary accretion rates in LMR marshes are not currently keeping pace with SLR, thus furthering the rapid marsh-to-mangrove conversions that have been seen in Tampa Bay over the past half-century. Additionally, wetlands in Tampa Bay tend to have a lower rate of carbon burial than other Florida tidal wetlands, demonstrating their high sensitivity to climate change and SLR.

Tidal Marsh Outwelling of Dissolved Organic Matter and Resulting Temporal Variability in Coastal Water Optical and Biogeochemical Properties

NASA Technical Reports Server (NTRS)

Tzortziou, Maria; Neale, Patrick J.; Megonigal, J. Patrick; Butterworth, Megan; Jaffe, Rudolf; Yamashita, Youhei

2010-01-01

Coastal wetlands are highly dynamic environments at the land-ocean interface where human activities, short-term physical forcings and intense episodic events result in high biological and chemical variability. Long being recognized as among the most productive ecosystems in the world, tidally-influenced coastal marshes are hot spots of biogeochemical transformation and exchange. High temporal resolution observations that we performed in several marsh-estuarine systems of the Chesapeake Bay revealed significant variability in water optical and biogeochemical characteristics at hourly time scales, associated with tidally-driven hydrology. Water in the tidal creek draining each marsh was sampled every hour during several semi-diurnal tidal cycles using ISCO automated samplers. Measurements showed that water leaving the marsh during ebbing tide was consistently enriched in dissolved organic carbon (DOC), frequently by more than a factor of two, compared to water entering the marsh during flooding tide. Estimates of DOC fluxes showed a net DOC export from the marsh to the estuary during seasons of both low and high biomass of marsh vegetation. Chlorophyll amounts were typically lower in the water draining the marsh, compared to that entering the marsh during flooding tide, suggesting that marshes act as transformers of particulate to dissolved organic matter. Moreover, detailed optical and compositional analyses demonstrated that marshes are important sources of optically and chemically distinctive, relatively complex, high molecular weight, aromatic-rich and highly colored dissolved organic compounds. Compared to adjacent estuarine waters, marsh-exported colored dissolved organic matter (CDOM) was characterized by considerably stronger absorption (more than a factor of three in some cases), larger DOC-specific absorption, lower exponential spectral slope, larger fluorescence signal, lower fluorescence per unit absorbance, and higher fluorescence at visible wavelengths. Observed patterns in water optical and biogeochemical variables were very consistent among different marsh systems and throughout the year, despite continued tidal exchange, implying rapid transformation of marsh DOM in the estuary through both photochemical and microbial processes. These findings illustrate the importance of tidal marsh ecosystems as sources, sinks and/or transformers of biologically important nutrients, carbon and colored dissolved organic compounds, and their influence on short-term biological, optical and biogeochemical variability in coastal waters.

Multi-decadal increases in dissolved organic carbon and alkalinity flux from the Mackenzie drainage basin to the Arctic Ocean

USGS Publications Warehouse

Tank, Suzanne E.; Striegl, Robert G.; McClelland, James W.; Kokelj, Steven V.

2016-01-01

Riverine exports of organic and inorganic carbon (OC, IC) to oceans are intricately linked to processes occurring on land. Across high latitudes, thawing permafrost, alteration of hydrologic flow paths, and changes in vegetation may all affect this flux, with subsequent implications for regional and global carbon (C) budgets. Using a unique, multi-decadal dataset of continuous discharge coupled with water chemistry measurements for the Mackenzie River, we show major increases in dissolved OC (DOC) and IC (as alkalinity) fluxes since the early 1970s, for a watershed that covers 1.8 M km2 of northwestern Canada, and provides substantial inputs of freshwater and biogeochemical constituents to the Arctic Ocean. Over a 39-year period of record, DOC flux at the Mackenzie mouth increased by 39.3% (44.5 ± 22.6 Gmol), while alkalinity flux increased by 12.5% (61.5 ± 60.1 Gmol). Isotopic analyses and substantial increases in sulfate flux indicate that increases in alkalinity are driven by accelerating sulfide oxidation, a process that liberates IC from rock and soils in the absence of CO2 consumption. Seasonal and sub-catchment trends suggest that permafrost thaw plays an important role in the observed increases in DOC and alkalinity: sub-catchment increases for all constituents are confined to northern, permafrost-affected regions, while observed increases in autumn to winter are consistent with documented landscape-scale changes that have resulted from changing thaw dynamics. This increase in DOC and sulfide-derived alkalinity represents a substantial intensification of land-to-ocean C mobilization, at a level that is significant within the regional C budget. The change we observe, for example, is similar to current and projected future rates of CO2 consumption by weathering in the Mackenzie basin.

Hydrologic control of dissolved organic matter concentration and quality in a semiarid artificially drained agricultural catchment

NASA Astrophysics Data System (ADS)

Bellmore, Rebecca A.; Harrison, John A.; Needoba, Joseph A.; Brooks, Erin S.; Kent Keller, C.

2015-10-01

Agricultural practices have altered watershed-scale dissolved organic matter (DOM) dynamics, including in-stream concentration, biodegradability, and total catchment export. However, mechanisms responsible for these changes are not clear, and field-scale processes are rarely directly linked to the magnitude and quality of DOM that is transported to surface water. In a small (12 ha) agricultural catchment in eastern Washington State, we tested the hypothesis that hydrologic connectivity in a catchment is the dominant control over the concentration and quality of DOM exported to surface water via artificial subsurface drainage. Concentrations of dissolved organic carbon (DOC) and humic-like components of DOM decreased while the Fluorescence Index and Freshness Index increased with depth through the soil profile. In drain discharge, these characteristics were significantly correlated with drain flow across seasons and years, with drain DOM resembling deep sources during low-flow and shallow sources during high flow, suggesting that DOM from shallow sources bypasses removal processes when hydrologic connectivity in the catchment is greatest. Assuming changes in streamflow projected for the Palouse River (which contains the study catchment) under the A1B climate scenario (rapid growth, dependence on fossil fuel, and renewable energy sources) apply to the study catchment, we project greater interannual variability in annual DOC export in the future, with significant increases in the driest years. This study highlights the variability in DOM inputs from agricultural soil to surface water on daily to interannual time scales, pointing to the need for a more nuanced understanding of agricultural impacts on DOM dynamics in surface water.

Inter-annual and spatial variability in hillslope runoff and mercury flux during spring snowmelt.

PubMed

Haynes, Kristine M; Mitchell, Carl P J

2012-08-01

Spring snowmelt is an important period of mercury (Hg) export from watersheds. Limited research has investigated the potential effects of climate variability on hydrologic and Hg fluxes during spring snowmelt. The purpose of this research was to assess the potential impacts of inter-annual climate variability on Hg mobility in forested uplands, as well as spatial variability in hillslope hydrology and Hg fluxes. We compared hydrological flows, Hg and solute mobility from three adjacent hillslopes in the S7 watershed of the Marcell Experimental Forest, Minnesota during two very different spring snowmelt periods: one following a winter (2009-2010) with severely diminished snow accumulation (snow water equivalent (SWE) = 48 mm) with an early melt, and a second (2010-2011) with significantly greater winter snow accumulation (SWE = 98 mm) with average to late melt timing. Observed inter-annual differences in total Hg (THg) and dissolved organic carbon (DOC) yields were predominantly flow-driven, as the proportion by which solute yields increased was the same as the increase in runoff. Accounting for inter-annual differences in flow, there was no significant difference in THg and DOC export between the two snowmelt periods. The spring 2010 snowmelt highlighted the important contribution of melting soil frost in the timing of a considerable portion of THg exported from the hillslope, accounting for nearly 30% of the THg mobilized. Differences in slope morphology and soil depths to the confining till layer were important in controlling the large observed spatial variability in hydrological flowpaths, transmissivity feedback responses, and Hg flux trends across the adjacent hillslopes.

Concentration-Discharge Relationships, Nested Reaction Fronts, and the Balance of Oxidative and Acid-Base Weathering Fluxes in an Alpine Catchment, East River, Colorado

NASA Astrophysics Data System (ADS)

Winnick, M.; Carroll, R. W. H.; Williams, K. H.; Maxwell, R. M.; Maher, K.

2016-12-01

Although important for solute production and transport, the varied interactions between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in the headwaters of the East River, CO, a high-elevation shale-dominated catchment system in the Rocky Mountains, using concentration-discharge (C-Q) relationships for major cations, anions, and organic carbon. Dissolved organic carbon (DOC) displays a positive C-Q relationship with well-defined clockwise hysteresis, indicating the mobilization and depletion of DOC in the upper soil horizons and highlighting the importance of shallow flowpaths through the snowmelt period. Cation and anion concentrations demonstrate that carbonate weathering, which dominates solute fluxes, is promoted by both carbonic acid and sulfuric acid derived from oxidation of pyrite in the shale bedrock. Sulfuric acid weathering in the deep subsurface dominates during base flow conditions when waters have infiltrated below the hypothesized pyrite oxidation front, whereas carbonic acid weathering plays a dominant role during the snowmelt period as a result of shallow flowpaths. Differential C-Q relationships between solutes suggest that infiltrating waters approach calcite saturation before reaching the pyrite oxidation front, after which sulfuric acid reduces carbonate alkalinity. This increase in CO2(aq) at the expense of HCO3- results in outgassing of CO2 when waters equilibrate to surface conditions, and reduces the export of carbon and alkalinity from the East River by roughly 33% annually. Future changes in snowmelt dynamics that control the balance of carbonic and sulfuric acid weathering therefore have the capacity to substantially alter the cycling of carbon in the East River catchment. Ultimately, we demonstrate that differential C-Q relationships between major solutes can provide unique insights into the complex subsurface flow and biogeochemical dynamics that operate at catchment scales.

Snowmelt controls on concentration-discharge relationships and the balance of oxidative and acid-base weathering fluxes in an alpine catchment, East River, Colorado: ACID-BASE VERSUS OXIDATIVE WEATHERING FLUXES

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

Winnick, Matthew J.; Carroll, Rosemary W. H.; Williams, Kenneth H.

Although important for riverine solute and nutrient fluxes, the connections between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in the East River, CO, a high-elevation shale-dominated catchment in the Rocky Mountains, using concentration-discharge (C-Q) relationships for major cations, anions, and organic carbon. Dissolved organic carbon (DOC) displays a positive C-Q relationship with clockwise hysteresis, indicating mobilization and depletion of DOC in the upper soil horizons and emphasizing the importance of shallow flowpaths during snowmelt. Cation and anion concentrations demonstrate that carbonate weathering, which dominates solute fluxes, is promoted by both sulfuric acid derived from pyritemore » oxidation in the shale bedrock and carbonic acid derived from subsurface respiration. Sulfuric acid weathering dominates during baseflow conditions when waters infiltrate below the inferred pyrite oxidation front, whereas carbonic acid weathering plays a dominant role during snowmelt as a result of shallow flowpaths. Differential C-Q relationships between solutes suggest that infiltrating waters approach calcite saturation before reaching the pyrite oxidation front, after which sulfuric acid reduces carbonate alkalinity. This reduction in alkalinity results in CO 2 outgassing when waters equilibrate to surface conditions, and reduces the riverine export of carbon and alkalinity by roughly 33% annually. In conclusion, future changes in snowmelt dynamics that control the balance of carbonic and sulfuric acid weathering may substantially alter carbon cycling in the East River. Ultimately, we demonstrate that differential C-Q relationships between major solutes can provide unique insights into the complex subsurface flow and biogeochemical dynamics that operate at catchment scales.« less

Snowmelt controls on concentration-discharge relationships and the balance of oxidative and acid-base weathering fluxes in an alpine catchment, East River, Colorado: ACID-BASE VERSUS OXIDATIVE WEATHERING FLUXES

DOE PAGES

Winnick, Matthew J.; Carroll, Rosemary W. H.; Williams, Kenneth H.; ...

2017-03-01

Although important for riverine solute and nutrient fluxes, the connections between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in the East River, CO, a high-elevation shale-dominated catchment in the Rocky Mountains, using concentration-discharge (C-Q) relationships for major cations, anions, and organic carbon. Dissolved organic carbon (DOC) displays a positive C-Q relationship with clockwise hysteresis, indicating mobilization and depletion of DOC in the upper soil horizons and emphasizing the importance of shallow flowpaths during snowmelt. Cation and anion concentrations demonstrate that carbonate weathering, which dominates solute fluxes, is promoted by both sulfuric acid derived from pyritemore » oxidation in the shale bedrock and carbonic acid derived from subsurface respiration. Sulfuric acid weathering dominates during baseflow conditions when waters infiltrate below the inferred pyrite oxidation front, whereas carbonic acid weathering plays a dominant role during snowmelt as a result of shallow flowpaths. Differential C-Q relationships between solutes suggest that infiltrating waters approach calcite saturation before reaching the pyrite oxidation front, after which sulfuric acid reduces carbonate alkalinity. This reduction in alkalinity results in CO 2 outgassing when waters equilibrate to surface conditions, and reduces the riverine export of carbon and alkalinity by roughly 33% annually. In conclusion, future changes in snowmelt dynamics that control the balance of carbonic and sulfuric acid weathering may substantially alter carbon cycling in the East River. Ultimately, we demonstrate that differential C-Q relationships between major solutes can provide unique insights into the complex subsurface flow and biogeochemical dynamics that operate at catchment scales.« less

Preliminary assessment of DOC and THM precursor loads from a freshwater restored wetland, an agricultural field, and a tidal wetland in the Sacramento-San Joaquin River Delta

USGS Publications Warehouse

Fujii, R.; Bergamaschi, B.A.; Ganju, N.K.; Fleck, J.A.; Burow-Fogg, K.R.; Schoellhamer, D.; Deverel, S.J.

2003-01-01

Water exported from the Sacramento-San Joaquin River Delta supplies drinking water to more than 22 million people in California. At certain times of the year, Delta waters contain relatively high concentrations of dissolved organic carbon (DOC) and bromide. During these times, chlorination of Delta water for drinking water disinfection will form disinfection byproducts, such as trihalomethanes (THMs), that can exceed the U.S. Environmental Protection Agency's maximum contaminant level for THMs of 80 mg/L. Important sources of DOC and THM precursors (types of DOC that form THMs when chlorinated) to the Delta include rivers, drainage water from peat islands, water from wetlands and areas with extensive riparian vegetation, and in-channel growth of algae and macrophytes. Due to proposed ecosystem restoration and creation of wetlands in the Delta, there is an urgent need for information on the relative loads of DOC and THM precursors produced from three different land uses: restored wetlands constructed for subsidence mitigation, tidal wetlands, and agricultural operations. We have been conducting research in the Delta to provide this information. A restored wetland and agricultural field located on Twitchell Island, and a tidal wetland on Browns Island have been monitored for flow, DOC, and THM precursors. Initial results indicate that the loads of DOC and THM precursors are similar for the restored wetland (surface water only) and the agricultural field. These land uses produce DOC loads of about 14 and 11 g C/m2/yr, respectively, and THM precursor loads of about 1.7 and 1.0 g THM/m2/yr, respectively. Estimates of DOC and THM precursor loads for the tidal wetland site on Browns Island and seepage associated with the restored wetland are being developed.

78 FR 68814 - Call for Applications for the International Buyer Program Calendar Year 2015

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-15

... receive DOC assistance in the form of global promotion in foreign markets, provision of export counseling... events and provides practical, hands-on assistance such as export counseling and market analysis to U.S...

Seasonal variation in chromophoric dissolved organic matter and relationships among fluorescent components, absorption coefficients and dissolved organic carbon in the Bohai Sea, the Yellow Sea and the East China Sea

NASA Astrophysics Data System (ADS)

Zhu, Wen-Zhuo; Zhang, Hong-Hai; Zhang, Jing; Yang, Gui-Peng

2018-04-01

The absorption coefficient and fluorescent components of chromophoric dissolved organic matter (CDOM) in the Bohai Sea (BS), Yellow Sea (YS), and East China Sea (ECS) in spring and autumn were analyzed in this study. Excitation-emission matrices (EEMs) combined with parallel factor analysis (PARAFAC) identified three components, namely, humic-like C1, tyrosine-like C2 and tryptophan-like C3. The seasonal variations in the vertical patterns of the CDOM absorption coefficient (aCDOM(355)) and fluorescent components were influenced by the seasonal water mass except for the terrestrial input. The relationship between aCDOM(355) and dissolved organic matter (DOC) was attributed to their own mixing behavior. The correlation of the fluorescent components with DOC was disturbed by other non-conservative processes during the export of CDOM to the open ocean. The different chemical compositions and origins of DOC and CDOM led to variability in carbon-specific CDOM absorption (a*CDOM(355)) and fluorescent component ratios (ICn/IC1). The relationship between a*CDOM(355) and aCDOM(355) demonstrated that dissolved organic matter (DOM) in the BS, but not in the ECS, highly contributed non-absorbing DOC to the total DOC concentration. The photodegradation of dominant terrestrially derived CDOM in the ECS contributed to the positive relationship between a*CDOM(355) and ICn/IC1. By contrast, the abundant autochthonous CDOM in the YS was negatively correlated with ICn/IC1 in autumn. Our established box models showed that water exchange is a potentially important source of the aromatic components in the BS, YS, and ECS. Hence, the seasonal variations in water exchange might contribute to the variability of CDOM chemical composition in the BS, YS, and ECS, and significantly influence the structure and function of their ecosystems.

[Roles of soil dissolved organic carbon in carbon cycling of terrestrial ecosystems: a review].

PubMed

Li, Ling; Qiu, Shao-Jun; Liu, Jing-Tao; Liu, Qing; Lu, Zhao-Hua

2012-05-01

Soil dissolved organic carbon (DOC) is an active fraction of soil organic carbon pool, playing an important role in the carbon cycling of terrestrial ecosystems. In view of the importance of the carbon cycling, this paper summarized the roles of soil DOC in the soil carbon sequestration and greenhouse gases emission, and in considering of our present ecological and environmental problems such as soil acidification and climate warming, discussed the effects of soil properties, environmental factors, and human activities on the soil DOC as well as the response mechanisms of the DOC. This review could be helpful to the further understanding of the importance of soil DOC in the carbon cycling of terrestrial ecosystems and the reduction of greenhouse gases emission.

Hydrologic controls on Congo River particulate organic carbon source and reservoir age

NASA Astrophysics Data System (ADS)

Hemingway, J. D.; Schefuß, E.; Spencer, R. G.; Dinga, B. J.; Eglinton, T. I.; McIntyre, C.; Galy, V.

2016-12-01

Tropical rivers are a major source of organic matter (OM) to the coastal ocean and play a large role in the global carbon cycle. As such, it is critical to understand the sources, sinks, and transformations of OM during fluvial transit over seasonal and inter-annual timescales. Here we present dissolved organic carbon (DOC) concentrations, particulate OM (POM) composition (δ13C, δ15N, Δ14C, N/C), and glycerol dialkyl glycerol tetraether (GDGT) biomarker distributions from a 34-month time-series near the mouth of the Congo River. An end-member mixing model based on δ13C and N/C indicates that exported POM is consistently dominated by C3 tropical rainforest soil inputs, with increasing contributions by C3 tropical plant vegetation and decreasing contributions by autochthonous phytoplankton at high discharge. Calculated Δ14C values of the C3-soil end member reveal significant and variable pre-aging prior to export, especially during the year 2011 when southern-hemisphere discharge reached record lows (mean = -176‰, standard deviation = 93‰). In contrast, Δ14C values were stable near -50‰ between January and June 2013 when southern-hemisphere discharge was highest. These results indicate that headwater POM is diluted and/or overprinted by pre-aged soils during transit through the Cuvette Congolaise swamp forest, while left-bank tributaries export significantly less pre-aged material. GDGT distributions are in agreement, as the methylation and cyclization of branched tetraethers and the GDGT-0/crenarchaeol ratio reflect a significant incorporation of compounds produced in permanently inundated Cuvette Congolaise swamp-forest soils when discharge through this region is high, especially in 2011. This study provides a mechanistic link between hydrology and carbon cycling in the world's second largest tropical river and suggests that, if recent observed decreases in springtime precipitation over the Congo basin persist, future hydrologic conditions will further bias toward export of protracted, swamp-forest-derived OM sources.

Insights from 14C into C loss pathways in degraded peatlands

NASA Astrophysics Data System (ADS)

Evans, Martin; Evans, Chris; Allott, Tim; Stimson, Andrew; Goulsbra, Claire

2016-04-01

Peatlands are important global stores of terrestrial carbon. Lowered water tables due to changing climate and direct or indirect human intervention produce a deeper aerobic zone and have the potential to enhance loss of stored carbon from the peat profile. The quasi continuous accumulation of organic matter in active peatlands means that the age of fluvial dissolved organic carbon exported from peatland systems is related to the source depth in the peat profile. Consequently 14C analysis of DOC in waters draining peatlands has the potential not only to tell us about the source of fluvial carbon and the stability of the peatland but also about the dominant hydrological pathways in the peatland system. This paper will present new radiocarbon determinations from peatland streams draining the heavily eroded peatlands of the southern Pennine uplands in the UK. These blanket peatland systems are highly degraded, with extensive bare peat and gully erosion resulting from air pollution during the industrial revolution, overgrazing, wildfire and climatic changes. Deep and extensive gullying has significantly modified the hydrology of these systems leading to local and more widespread drawdown of water table. 14C data from DOC in drainage waters are presented from two catchments; one with extensive gully erosion and the other with a combination of gully erosion and sheet erosion of the peat. At the gully eroded site DOC in drainage waters is as old as 160 BP but at the site with extensive sheet erosion dates of up to 1069 BP are amongst the oldest recorded from blanket peatland globally These data indicate significant degradation of stored carbon from the eroding peatlands. Initial comparisons of the 14C data with modelled water table for the catchments and depth-age curves for catchment peats suggests that erosion of the peat surface, allowing decomposition of exposed older organic material is a potential mechanism producing aged carbon from the eroded catchment. This mechanism may be as important as changes in hydrological flow pathways within the peat in mobilising aged carbon from the systems.

Source- and degradation-diagnostic of colloidal organic matter exported by rivers across the Eurasian Arctic margin

NASA Astrophysics Data System (ADS)

Karlsson, Emma; Gelting, Johan; Tesi, Tommaso; van Dongen, Bart; Kruså, Martin; Vonk, Jorien; Sanchez-Garcia, Laura; Semiletov, Igor; Charkin, Alexander; Dudarev, Oleg; Gustafsson, Örjan

2013-04-01

Both models and in-situ observations indicate that the Arctic watersheds will experience a significant increase in temperature, resulting in higher runoff and remobilization of the vast carbon reservoirs currently held stable under frozen conditions. However, the sources and degradability of the dissolved organic carbon (DOC) released to this aquatic land-ocean conduit in high latitude regions is still poorly constrained. For example, there is a particular lack in our understanding of the fate of the DOC once it enters the Arctic Ocean. This study therefore investigated the compositional changes of the organic colloidal material along the Arctic land-ocean continuum. Large-volume samples of high-molecular weight DOC (colloids) were isolated as part of the International Siberian Shelf Study 2008 (ISSS-08) using 1000 D cross-flow ultrafiltration outside the mouths of Arctic rivers Ob, Yenisey, Lena, Indigirka and Kolyma as well as on the adjacent continental shelf seas Laptev Sea and the East Siberian Sea. The colloidal fraction was characterized by both bulk isotope parameters (δ13C and Δ14C) and with macromolecular biomarkers such as free lipids (n-alkanes, n-alkanoic acids, n-alkanols) and CuO reaction products (lignin phenols, cutin derived-products, protein and lipid products). In this presentation we will focus on regional differences between contrasting watersheds characterized by different climate and vegetation as well as permafrost conditions. Particular emphasis will be placed on origin, degradation, and dilution of the terrigenous colloidal material during its transport from land to the ocean. Finally, the comparison between the dissolved and particulate fractions will also be presented to highlight differences and similarities between these two pools of aquatic carbon.

Dissolved Organic Carbon 14C in Southern Nevada Groundwater and Implications for Groundwater Travel Times

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

Hershey, Ronald L.; Fereday, Wyall; Thomas, James M

Dissolved inorganic carbon (DIC) carbon-14 ( 14C) ages must be corrected for complex chemical and physical reactions and processes that change the amount of 14C in groundwater as it flows from recharge to downgradient areas. Because of these reactions, DIC 14C can produce unrealistically old ages and long groundwater travel times that may, or may not, agree with travel times estimated by other methods. Dissolved organic carbon (DOC) 14C ages are often younger than DIC 14C ages because there are few chemical reactions or physical processes that change the amount of DOC 14C in groundwater. However, there are several issuesmore » that create uncertainty in DOC 14C groundwater ages including limited knowledge of the initial (A 0) DOC 14C in groundwater recharge and potential changes in DOC composition as water moves through an aquifer. This study examines these issues by quantifying A 0 DOC 14C in recharge areas of southern Nevada groundwater flow systems and by evaluating changes in DOC composition as water flows from recharge areas to downgradient areas. The effect of these processes on DOC 14C groundwater ages is evaluated and DOC and DIC 14C ages are then compared along several southern Nevada groundwater flow paths. Twenty-seven groundwater samples were collected from springs and wells in southern Nevada in upgradient, midgradient, and downgradient locations. DOC 14C for upgradient samples ranged from 96 to 120 percent modern carbon (pmc) with an average of 106 pmc, verifying modern DOC 14C ages in recharge areas, which decreases uncertainty in DOC 14C A 0 values, groundwater ages, and travel times. The HPLC spectra of groundwater along a flow path in the Spring Mountains show the same general pattern indicating that the DOC compound composition does not change along this flow path. Although DOC concentration decreases from recharge-area to downgradient groundwater, the organic compounds are similar, indicating that DOC 14C is unaffected by other processes such as microbial degradation. A small amount of organic carbon was leached from crushed volcanic and carbonate aquifer outcrop rock in rock-leaching experiments. The leached DOC was high in 14C (75 pmc carbonate rocks, 91 pmc volcanic) suggesting that the leached DOC likely came from microbes in the rock samples. The small amount of DOC and high 14C indicates that the amount of old organic carbon in these rocks is low so there should be minimal impact on groundwater DOC 14C ages. Based on the results from this study, DOC 14C ages do not require additional corrections. Several correction models were applied to DIC 14C ages to correct for water-rock reactions along two carbonate and two volcanic flow paths and the corresponding travel times were compare to DOC 14C travel times. The DOC 14C travel times were hundreds to thousands of years shorter than uncorrected and corrected DIC 14C travel times except for the upper section of one carbonate flow path. DOC 14C travel times ranged from 400 to 5,400 years as compared to DIC 14C that ranged from modern to 20,900 years. The DIC 14C ages are greatly influenced by carbonate mineral and gas reactions and other processes such as matrix diffusion, isotope exchange, or adsorption, which are not always adequately accounted for in DIC 14C groundwater age correction models.« less

Dissolved organic matter composition and biodegradability in a permafrost-dominated watershed network in central Siberia

NASA Astrophysics Data System (ADS)

Coble, A. A.; Rodriguez-Cardona, B.; Wymore, A.; Prokishkin, A. S.; Kolosov, R.; McDowell, W. H.

2016-12-01

Thawing permafrost soils can mobilize large quantities of dissolved organic matter (DOM) from soils to headwater streams, and DOM may undergo rapid transformations in streams and rivers in transit to the Arctic Ocean. With climate change an increased frequency of fire is also expected, which will further alter the DOM entering streams, and may contribute to changes in its biodegradability. Elucidating how DOM composition varies across a fire gradient within a river network underlain by continuous permafrost will therefore improve our understanding of the impact of climate change on Arctic ecosystems and its role in the global carbon cycle. To determine DOM composition we measured optical properties via excitation-emission matrices (EEMs) and subsequent parallel factor analysis across a spatially extensive collection of sites in central Siberia. Within a subset of streams in the Nizhnyaya Tunguska watershed network, we also measured biodegradable dissolved organic carbon (BDOC) incubated at in situ temperatures over a 7 day period during spring freshet on two dates in early June. Despite clear changes in optical properties of DOM and background DOC concentration along the fire gradient (range: 3 to >100 y since burn) BDOC did not vary systematically with years since fire for either incubation date. In the first incubation conducted near peak flow BDOC ranged from negligible to 7.6% (BDOC concentration = negligible to 1.4 mg C L-1) within a 7 day period. In the second incubation conducted 5 days later BDOC was negligible across all sites (as both a percentage and a concentration). Our results suggest that DOC exported from permafrost soils in the central Siberian plateau is relatively unreactive at in situ temperatures over 7 day time scales, which contrasts with previous studies conducted in watersheds underlain with Yedoma outcrops where biodegradability comprises a large fraction of DOC. Our preliminary results suggest that melting of permafrost soils in central Siberia may export large quantities of C to the Arctic Ocean that are not rapidly degraded in streams and rivers.

Insights and issues with simulating terrestrial DOC loading of Arctic river networks

USGS Publications Warehouse

Kicklighter, David W.; Hayes, Daniel J.; McClelland, James W.; Peterson, Bruce J.; McGuire, A. David; Melillo, Jerry M.

2013-01-01

Terrestrial carbon dynamics influence the contribution of dissolved organic carbon (DOC) to river networks in addition to hydrology. In this study, we use a biogeochemical process model to simulate the lateral transfer of DOC from land to the Arctic Ocean via riverine transport. We estimate that, over the 20th century, the pan-Arctic watershed has contributed, on average, 32 Tg C/yr of DOC to river networks emptying into the Arctic Ocean with most of the DOC coming from the extensive area of boreal deciduous needle-leaved forests and forested wetlands in Eurasian watersheds. We also estimate that the rate of terrestrial DOC loading has been increasing by 0.037 Tg C/yr2 over the 20th century primarily as a result of climate-induced increases in water yield. These increases have been offset by decreases in terrestrial DOC loading caused by wildfires. Other environmental factors (CO2 fertilization, ozone pollution, atmospheric nitrogen deposition, timber harvest, agriculture) are estimated to have relatively small effects on terrestrial DOC loading to Arctic rivers. The effects of the various environmental factors on terrestrial carbon dynamics have both offset and enhanced concurrent effects on hydrology to influence terrestrial DOC loading and may be changing the relative importance of terrestrial carbon dynamics on this carbon flux. Improvements in simulating terrestrial DOC loading to pan-Arctic rivers in the future will require better information on the production and consumption of DOC within the soil profile, the transfer of DOC from land to headwater streams, the spatial distribution of precipitation and its temporal trends, carbon dynamics of larch-dominated ecosystems in eastern Siberia, and the role of industrial organic effluents on carbon budgets of rivers in western Russia.

Intrinsic Controls of Groundwater-Surface Water Dissolved Organic Carbon Quality and Quantity on Hyporheic Carbon Oxidation.

NASA Astrophysics Data System (ADS)

Garayburu-Caruso, V. A.; Stegen, J.; Graham, E.

2017-12-01

Inputs of dissolved organic carbon (DOC) and nutrients from groundwater (GW) and surface water (SW) to the hyporheic zone strongly influence biogeochemical processes. Despite increased research efforts, we still lack a mechanistic understanding of the conditions driving elevated hyporheic metabolism. This work explores hyporheic carbon oxidation from a thermodynamic perspective by evaluating changes in metabolic rates within hyporheic zone sediments in response to changes on DOC concentration and thermodynamic profiles that are characteristic of GW and SW sources. We hypothesize that GW DOC is protected from microbial oxidation due to low concentration and that SW DOC is protected due low thermodynamic favorability. Further, we propose that GW-SW mixing can simultaneously overcome both limitations and stimulate carbon oxidation. Hyporheic sediments from the Hanford site in Richland, WA were exposed to ambient, 2-,5- and 10-fold concentrations of natural DOC from SW and GW sources, separately, and incubated at in-situ temperature. The two DOC sources supply contrasting thermodynamic profiles, with GW providing lower concentration but more thermodynamically favorable DOC and SW higher concentration, more recalcitrant DOC. Across DOC treatments we characterized time series of oxygen concentration, DOC concentration, and pH as well as endpoint measurements of DOC thermodynamics using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Our results suggest that hyporheic metabolism of distinct carbon pools (GW or SW) can be limited by concentration or thermodynamic favorability. Our work provides an experimental approach to contribute to mechanistic understanding of freshwater carbon oxidation, and a process-based foundation for the development of watershed-scale hydrobiogeochemical models.

A Global Assessment of Rain-Dissolved Organic Carbon

NASA Astrophysics Data System (ADS)

Safieddine, S.; Heald, C. L.

2017-12-01

Precipitation is the largest physical removal pathway of atmospheric organic carbon from the atmosphere. The removed carbon is transferred to the land and ocean in the form of dissolved organic carbon (DOC). Limited measurements have hindered efforts to characterize global DOC. In this poster presentation, we show the first simulated global DOC distribution based on a GEOS-Chem model simulation of the atmospheric reactive carbon budget. Over the ocean, simulated DOC concentrations are between 0.1 to 1 mgCL-1 with a total of 85 TgCyr-1 deposited. DOC concentrations are higher inland, ranging between 1 and 10 mgCL-1, producing a total of 188 TgCyr-1 terrestrial organic wet deposition. We compare the 2010 simulated DOC to a 30-year synthesis of available DOC measurements over different environments. Despite imperfect matching of observational and simulated time intervals, the model is able to reproduce much of the spatial variability of DOC (r= 0.63), with a low bias of 35%. We compare the global average carbon oxidation state (OSc) of both atmospheric and dissolved organic carbon, as a simple metric for describing the chemical composition of organics. In the global atmosphere reactive organic carbon (ROC) is dominated by hydrocarbons and ketones, and OSc, ranges from -1.8 to -0.6. In the dissolved form, formaldehyde, formic acid, primary and secondary semi-volatiles organic aerosol dominate the DOC concentrations. The increase in solubility upon oxidation leads to a global increase in OSc in rainwater with -0.6<=OSc <=0. This simulation provides new insight into the current model representation of the flow of atmospheric and rain-dissolved organic carbon, and new opportunities to use observations and simulations to understand the DOC reaching land and ocean.

The Utility of CDOM for Improving the Resolution of Riverine DOM Fluxes and Biogeochemical Function

NASA Astrophysics Data System (ADS)

Spencer, R. G.; Aiken, G.; Mann, P. J.; Holmes, R. M.; Niggemann, J.; Dittmar, T.; Hernes, P.; Stubbins, A.

2014-12-01

A major historical limitation to geochemical studies assessing fluvial fluxes of dissolved organic matter (DOM) has been the issue of both temporal and spatial scaling. Examples will be presented from watersheds around the world highlighting how chromophoric dissolved organic matter (CDOM) measurements can be utilized as proxies for more intensive and expensive analytical analyses (e.g. molecular-level organic biomarkers). Utilizing these refined CDOM loads for terrigenous biomarkers results in improved temporal resolution and a significant change in flux estimates. Examining CDOM and dissolved organic carbon (DOC) flux data from an assortment of terrestrial biomes we establish a robust relationship between CDOM and DOC loads. The application of this relationship allows future studies to derive DOC loads from CDOM utilizing emerging in-situ or remote sensing technologies and thus refine river-to-ocean DOC fluxes, as well as exploit historic imagery to examine how fluxes may have changed. Calculated CDOM yields from a range of rivers are correlated to watershed percent wetland and highlight the importance of certain regions with respect to CDOM flux to the coastal ocean. This approach indicates that future studies might predict CDOM and DOC yields for different watershed types that could then be readily converted to loads providing for the estimation of CDOM and DOC export from ungauged watersheds. Examination of CDOM yields also highlights important geographical regions for future study with respect to the role of terrigenous CDOM in ocean color budgets and CDOM's role in biogeochemical processes. Finally, examples will be presented linking CDOM parameters to DOM composition and biogeochemical properties with the aim of providing measurements to improve the spatial and especially temporal resolution of the role DOM plays in fluvial networks.

Annual net community production and the biological carbon flux in the ocean

NASA Astrophysics Data System (ADS)

Emerson, Steven

2014-01-01

The flux of biologically produced organic matter from the surface ocean (the biological pump), over an annual cycle, is equal to the annual net community production (ANCP). Experimental determinations of ANCP at ocean time series sites using a variety of different metabolite mass balances have made it possible to evaluate the accuracy of sediment trap fluxes and satellite-determined ocean carbon export. ANCP values at the Hawaii Ocean Time-series (HOT), the Bermuda Atlantic Time-series Study (BATS), Ocean Station Papa (OSP) are 3 ± 1 mol C m-2 yr-1—much less variable than presently suggested by satellite remote sensing measurements and global circulation models. ANCP determined from mass balances at these locations are 3-4 times particulate organic carbon fluxes measured in sediment traps. When the roles of dissolved organic carbon (DOC) flux, zooplankton migration, and depth-dependent respiration are considered these differences are reconciled at HOT and OSP but not at BATS, where measured particulate fluxes are about 3 times lower than expected. Even in the cases where sediment trap fluxes are accurate, it is not possible to "scale up" these measurements to determine ANCP without independent determinations of geographically variable DOC flux and zooplankton migration. Estimates of ANCP from satellite remote sensing using net primary production determined by the carbon-based productivity model suggests less geographic variability than its predecessor (the vertically generalized productivity model) and brings predictions at HOT and OSP closer to measurements; however, satellite-predicted ANCP at BATS is still 3 times too low.

Hidden cycle of dissolved organic carbon in the deep ocean.

PubMed

Follett, Christopher L; Repeta, Daniel J; Rothman, Daniel H; Xu, Li; Santinelli, Chiara

2014-11-25

Marine dissolved organic carbon (DOC) is a large (660 Pg C) reactive carbon reservoir that mediates the oceanic microbial food web and interacts with climate on both short and long timescales. Carbon isotopic content provides information on the DOC source via δ(13)C and age via Δ(14)C. Bulk isotope measurements suggest a microbially sourced DOC reservoir with two distinct components of differing radiocarbon age. However, such measurements cannot determine internal dynamics and fluxes. Here we analyze serial oxidation experiments to quantify the isotopic diversity of DOC at an oligotrophic site in the central Pacific Ocean. Our results show diversity in both stable and radio isotopes at all depths, confirming DOC cycling hidden within bulk analyses. We confirm the presence of isotopically enriched, modern DOC cocycling with an isotopically depleted older fraction in the upper ocean. However, our results show that up to 30% of the deep DOC reservoir is modern and supported by a 1 Pg/y carbon flux, which is 10 times higher than inferred from bulk isotope measurements. Isotopically depleted material turns over at an apparent time scale of 30,000 y, which is far slower than indicated by bulk isotope measurements. These results are consistent with global DOC measurements and explain both the fluctuations in deep DOC concentration and the anomalous radiocarbon values of DOC in the Southern Ocean. Collectively these results provide an unprecedented view of the ways in which DOC moves through the marine carbon cycle.

Hidden cycle of dissolved organic carbon in the deep ocean

PubMed Central

Follett, Christopher L.; Repeta, Daniel J.; Rothman, Daniel H.; Xu, Li; Santinelli, Chiara

2014-01-01

Marine dissolved organic carbon (DOC) is a large (660 Pg C) reactive carbon reservoir that mediates the oceanic microbial food web and interacts with climate on both short and long timescales. Carbon isotopic content provides information on the DOC source via δ13C and age via Δ14C. Bulk isotope measurements suggest a microbially sourced DOC reservoir with two distinct components of differing radiocarbon age. However, such measurements cannot determine internal dynamics and fluxes. Here we analyze serial oxidation experiments to quantify the isotopic diversity of DOC at an oligotrophic site in the central Pacific Ocean. Our results show diversity in both stable and radio isotopes at all depths, confirming DOC cycling hidden within bulk analyses. We confirm the presence of isotopically enriched, modern DOC cocycling with an isotopically depleted older fraction in the upper ocean. However, our results show that up to 30% of the deep DOC reservoir is modern and supported by a 1 Pg/y carbon flux, which is 10 times higher than inferred from bulk isotope measurements. Isotopically depleted material turns over at an apparent time scale of 30,000 y, which is far slower than indicated by bulk isotope measurements. These results are consistent with global DOC measurements and explain both the fluctuations in deep DOC concentration and the anomalous radiocarbon values of DOC in the Southern Ocean. Collectively these results provide an unprecedented view of the ways in which DOC moves through the marine carbon cycle. PMID:25385632

Examining the coupling of carbon and nitrogen cycles in Southern Appalachian streams: Understanding the role of dissolved organic nitrogen

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

Lutz, Brian D; Bernhardt, Emily; Roberts, Brian

Although regional and global models of nitrogen (N) cycling typically focus on nitrate, dissolved organic nitrogen (DON) is the dominant form of nitrogen export from many watersheds and thus the dominant form of dissolved N in many streams. Our understanding of the processes controlling DON export from temperate forests is poor. In pristine systems, where biological N limitation is common, N contained in recalcitrant organic matter (OM) can dominate watershed N losses. This recalcitrant OM often has moderately constrained carbon:nitrogen (C:N) molar ratios ({approx}25-55) and therefore, greater DON losses should be observed in sites where there is greater total dissolvedmore » organic carbon (DOC) loss. In regions where anthropogenic N pollution is high, it has been suggested that increased inorganic N availability can reduce biological demand for organic N and therefore increase watershed DON losses. This would result in a positive correlation between inorganic and organic N concentrations across sites with varying N availability. In four repeated synoptic surveys of stream water chemistry from forested watersheds along an N loading gradient in the southern Appalachians, we found surprisingly little correlation between DON and DOC concentrations. Further, we found that DON concentrations were always significantly correlated with watershed N loading and stream water [NO{sub 3}{sup -}] but that the direction of this relationship was negative in three of the four surveys. The C:N molar ratio of dissolved organic matter (DOM) in streams draining watersheds with high N deposition was very high relative to other freshwaters. This finding, together with results from bioavailability assays in which we directly manipulated C and N availabilities, suggests that heterotrophic demand for labile C can increase as a result of dissolved inorganic N (DIN) loading, and that heterotrophs can preferentially remove N-rich molecules from DOM. These results are inconsistent with the two prevailing hypotheses that dominate interpretations of watershed DON loss. Therefore, we propose a new hypothesis, the indirect carbon control hypothesis, which recognizes that heterotrophic demand for N-rich DOM can keep stream water DON concentrations low when N is not limiting and heterotrophic demand for labile C is high.« less

Solute and sediment export from Amazon forest and soybean headwater streams.

PubMed

Riskin, Shelby H; Neill, Christopher; Jankowski, KathiJo; Krusche, Alex V; McHorney, Richard; Elsenbeer, Helmut; Macedo, Marcia N; Nunes, Darlisson; Porder, Stephen

2017-01-01

Intensive cropland agriculture commonly increases streamwater solute concentrations and export from small watersheds. In recent decades, the lowland tropics have become the world's largest and most important region of cropland expansion. Although the effects of intensive cropland agriculture on streamwater chemistry and watershed export have been widely studied in temperate regions, their effects in tropical regions are poorly understood. We sampled seven headwater streams draining watersheds in forest (n = 3) or soybeans (n = 4) to examine the effects of soybean cropping on stream solute concentrations and watershed export in a region of rapid soybean expansion in the Brazilian state of Mato Grosso. We measured stream flows and concentrations of NO 3 - , PO 4 3- , SO 4 2- , Cl - , NH 4 + , Ca 2+ , Mg 2+ , Na + , K + , Al 3+ , Fe 3+ , and dissolved organic carbon (DOC) biweekly to monthly to determine solute export. We also measured stormflows and stormflow solute concentrations in a subset of watersheds (two forest, two soybean) during two/three storms, and solutes and δ 18 O in groundwater, rainwater, and throughfall to characterize watershed flowpaths. Concentrations of all solutes except K + varied seasonally in streamwater, but only Fe 3+ concentrations differed between land uses. The highest streamwater and rainwater solute concentrations occurred during the peak season of wildfires in Mato Grosso, suggesting that regional changes in atmospheric composition and deposition influence seasonal stream solute concentrations. Despite no concentration differences between forest and soybean land uses, annual export of NH 4 + , PO 4 3- , Ca 2+ , Fe 3+ , Na + , SO 4 2- , DOC, and TSS were significantly higher from soybean than forest watersheds (5.6-fold mean increase). This increase largely reflected a 4.3-fold increase in water export from soybean watersheds. Despite this increase, total solute export per unit watershed area (i.e., yield) remained low for all watersheds (<1 kg NO 3 - N·ha -1 ·yr -1 , <2.1 kg NH 4 + -N·ha -1 ·yr -1 , <0.2 kg PO 4 3- -P·ha -1 ·yr -1 , <1.5 kg Ca 2+ ·ha -1 ·yr -1 ). Responses of both streamflows and solute concentrations to crop agriculture appear to be controlled by high soil hydraulic conductivity, groundwater-dominated hydrologic flowpaths on deep soils, and the absence of nitrogen fertilization. To date, these factors have buffered streams from the large increases in solute concentrations that often accompany intensive croplands in other locations. © 2016 by the Ecological Society of America.

Biogeochemistry of the Amazon River Basin: the role of aquatic ecosystems in the Amazon functioning

NASA Astrophysics Data System (ADS)

Victoria, R. L.; Ballester, V. R.; Krushe, A. V.; Richey, J. E.; Aufdenkampe, A. K.; Kavaguishi, N. L.; Gomes, B. M.; Victoria, D. D.; Montebello, A. A.; Niell, C.; Deegan, L.

2004-12-01

In this study we present the results of an integrated analysis of physical and anthropogenic controls of river biogeochemistry in Amazônia. At the meso-scale level, our results show that both soil properties and land use are the main drivers of river biogeochemistry and metabolism, with pasture cover and soil exchange cation capacity explaining 99% (p < 0.01) of the variability observed in surface water ions and nutrients concentrations. In small rivers, forest clearing can increase cations, P and C inputs. P and light are the main PPL limiting factors in forested streams, while in pasture streams N becomes limiting. P export to streams may increase or remain nearly undetectable after forest-to-pasture conversion, depending on soil type. Pasture streams on Oxisols have very low P export, while on Ultisols P export is increased. Conversions of forest to pasture leads to extensive growth of in channel Paspalum resulting in higher DOC concentrations and respiration rates. Pasture streams have higher DOC fluxes when compared to the forest ones. In pasture areas the soil are compacted, there is less infiltration and higher surface run off, leaching soil superficial layers and caring more DOC to the streams. In forest areas infiltration is deeper into the soils and canopy interaction is higher. Mineralogy and soil properties are key factors determining exports of nutrients to streams. Therefore, land use change effects on nutrient export from terrestrial to aquatic ecosystems and the atmosphere must be understood within the context of varying soil properties across the Amazon Basin.

Distribution and significance of dissolved organic carbon under three land-use systems, NSW, Australia

NASA Astrophysics Data System (ADS)

Fancy, Rubeca; Wilson, Brian R.; Daniel, Heiko; Osanai, Yui

2017-04-01

Carbon accumulation in surface soils is well documented but very little is known about the mechanisms and processes that result in carbon accumulation and long-term storage in the deeper soil profile. Understanding soil carbon storage and distribution mechanisms is critical to evaluate the sequestration potential of the soils of different land uses. Recent investigations have demonstrated that the movement of dissolved organic carbon (DOC) in the soil profile could contribute significantly to the carbon balance of terrestrial ecosystems. However, very little is known regarding the importance of DOC to vertical distribution of soil organic carbon (SOC) pool through the soil profile in different land-use systems, management practices and conditions prevalent in Australia. We investigated the quantity and distribution of SOC and DOC through the profile under three different land-use systems in northern NSW, Australia. A series of site clusters containing a representative range of land-uses (cultivated, improved pasture and woodland) were selected across the region. Within each land use, we determined SOC and DOC concentration and quantity down the soil profile to a depth of 0-100 cm using six soil depth increments. Here we discuss the distribution and relative importance of DOC down the soil profile to the storage and distribution of carbon. We compare and contrast the patterns associated with the different land use systems and explore potential mechanisms of carbon cycling in these soils. Near to the soil surface, SOC had larger concentrations in the order woodland>improved pasture>cropping at all sites studied. However, DOC was found in significantly larger concentrations in the woodland soils at all soil depths. The larger DOC:TOC ratio in woodland and improved pasture soils suggests a direct relationship between TOC and DOC but increased DOC:TOC ratio in deeper soil layers suggests an increasing importance of DOC in soil carbon cycling in these deeper soils under Australian conditions.

Deep nitrogen acquisition in warming permafrost soils: Contributions of belowground plant traits and fungal symbioses in the permafrost carbon feedback to climate

NASA Astrophysics Data System (ADS)

Hartnett, H. E.; Palta, M. M.; Grimm, N. B.; Ruhi, A.; van Shaijik, M.

2016-12-01

Tempe Town Lake (TTL) is a hydrologically-regulated reservoir in Tempe, Arizona. The lake has high primary production and receives dissolved organic carbon (DOC) from rainfall, storm flow, and upstream river discharge. We applied an ARIMA time-series model to a three-year period for which we have high-frequency chemistry, meteorology, and streamflow data and analyzed external (rainfall, stream flow) and internal (dissolved O2) drivers of DOC content and composition. DOC composition was represented by fluorescence-based indices (fluorescence index, humification index, freshness) related to DOC source (microbially- vs. terrestrially-derived) and reactivity DOC. Patterns in DOC concentration and composition suggest carbon cycling in the lake responds to both meteorological events and to anthropogenic activity. The fluorescence-derived DOC composition is consistent with seasonally-distinct inputs of algal- and terrestrially-derived carbon. For example, Tempe Town Lake is supersaturated in O2 over 70% of the time, suggesting the system is autotrophic and primary productivity (i.e., O2 saturation state) was the strongest driver of DOC concentration. In contrast, external drivers (rainfall pattern, streamflow) were the strongest determinants of DOC composition. Biological processes (e.g., algal growth) generate carbon in the lake during spring and summer, and high Fluorescence Index and Freshness values at this time are indicative of algal-derived material; these parameters generally decrease with rain or flow suggesting algal-derived carbon is diluted by external water inputs. During dry periods, carbon builds up on the land surface and subsequent rainfall events deliver terrestrial carbon to the lake. Further evidence that rain and streamflow deliver land-derived material are increases in the Humification Index (an indicator of terrestrial material) following rain/flow events. Our results indicate that Tempe Town Lake generates autochthonous carbon and has the capacity to process allochthonous carbon from the urban environment. Ongoing work is comparing these results to other periods in the 10-year time series to test if the driver-DOC relationships are robust over longer time-scales and evaluating how changes in lake management and climate have altered DOC over time.

Temporal Patterns in Dissolved Organic Carbon Composition in an Urban Lake

NASA Astrophysics Data System (ADS)

Hartnett, H. E.; Palta, M. M.; Grimm, N. B.; Ruhi, A.; van Shaijik, M.

2017-12-01

Tempe Town Lake (TTL) is a hydrologically-regulated reservoir in Tempe, Arizona. The lake has high primary production and receives dissolved organic carbon (DOC) from rainfall, storm flow, and upstream river discharge. We applied an ARIMA time-series model to a three-year period for which we have high-frequency chemistry, meteorology, and streamflow data and analyzed external (rainfall, stream flow) and internal (dissolved O2) drivers of DOC content and composition. DOC composition was represented by fluorescence-based indices (fluorescence index, humification index, freshness) related to DOC source (microbially- vs. terrestrially-derived) and reactivity DOC. Patterns in DOC concentration and composition suggest carbon cycling in the lake responds to both meteorological events and to anthropogenic activity. The fluorescence-derived DOC composition is consistent with seasonally-distinct inputs of algal- and terrestrially-derived carbon. For example, Tempe Town Lake is supersaturated in O2 over 70% of the time, suggesting the system is autotrophic and primary productivity (i.e., O2 saturation state) was the strongest driver of DOC concentration. In contrast, external drivers (rainfall pattern, streamflow) were the strongest determinants of DOC composition. Biological processes (e.g., algal growth) generate carbon in the lake during spring and summer, and high Fluorescence Index and Freshness values at this time are indicative of algal-derived material; these parameters generally decrease with rain or flow suggesting algal-derived carbon is diluted by external water inputs. During dry periods, carbon builds up on the land surface and subsequent rainfall events deliver terrestrial carbon to the lake. Further evidence that rain and streamflow deliver land-derived material are increases in the Humification Index (an indicator of terrestrial material) following rain/flow events. Our results indicate that Tempe Town Lake generates autochthonous carbon and has the capacity to process allochthonous carbon from the urban environment. Ongoing work is comparing these results to other periods in the 10-year time series to test if the driver-DOC relationships are robust over longer time-scales and evaluating how changes in lake management and climate have altered DOC over time.

High soil solution carbon und nitrogen concentrations in a drained Atlantic bog are reduced to natural levels by 10 yr of rewetting

NASA Astrophysics Data System (ADS)

Frank, S.; Tiemeyer, B.; Gelbrecht, J.; Freibauer, A.

2013-10-01

Artificial drainage of peatlands causes dramatic changes in the release of greenhouse gases and in the export of dissolved carbon (C) and nutrients to downstream ecosystems. Rewetting anthropogenically altered peatlands offers a possibility to reduce nitrogen (N) and C losses. In this study, we investigate the impact of drainage and rewetting on the cycling of dissolved C and N as well as on dissolved gases over a period of 1 yr and 4 month, respectively. The peeper technique was used to receive a high vertical sampling resolution. Within one Atlantic bog complex a near natural site, two drained grasslands sites with different mean water table positions, and a former peat cutting area rewetted 10 yr ago were chosen. Our results clearly indicate that drainage increased the concentration of dissolved organic carbon (DOC), ammonia, nitrate and dissolved organic nitrogen (DON) compared to the near natural site. Drainage depth further determined the release and therefore the concentration level of DOC and N species, but the biochemical cycling and therefore dissolved organic matter (DOM) quality and N species composition were unaffected. Thus, especially deep drainage can cause high DOC losses. In general, DOM at drained sites was enriched in aromatic moieties as indicated by SUVA280 and showed a higher degradation status (lower DOC to DON ratio) compared to the near natural site. At the drained sites, equal C to N ratios of uppermost peat layer and DOC to DON ratio of DOM in soil solution suggest that the uppermost degraded peat layer is the main source of DOM. Nearly constant DOC to DON ratios and SUVA280 values with depth furthermore indicated that DOM moving downwards through the drained sites remained largely unchanged. DON and ammonia contributed most to the total dissolved nitrogen (TN). The subsoil concentrations of nitrate were negligible due to strong decline in nitrate around mean water table depth. Methane production during the winter months at the drained sites moved downwards to areas which were mostly water saturated over the whole year (>40 cm). Above these depths, the recovery of the water table in winter months led to the production of nitrous oxide around mean water table depth at drained sites. 10 yr after rewetting, the DOM quality (DOC to DON ratio and SUVA280) and quantity were comparable to the near natural site, indicating the re-establishment of mostly pristine biochemical processes under continuously water logged conditions. The only differences occur in elevated dissolved methane and ammonia concentrations reflecting the former disturbance by drainage and peat extraction. Rewetting via polder technique seems to be an appropriate way to revitalize peatlands on longer timescales and to improve the water quality of downstream water bodies.

Removal of terrestrial DOC in aquatic ecosystems of a temperate river network

USGS Publications Warehouse

Wollheim, W.M.; Stewart, R. J.; Aiken, George R.; Butler, Kenna D.; Morse, Nathaniel B.; Salisbury, J.

2015-01-01

Surface waters play a potentially important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the fate of DOC in aquatic systems is poorly constrained. We used a unique combination of spatially distributed sampling of three DOC fractions throughout a river network and modeling to quantify the net removal of terrestrial DOC during a summer base flow period. We found that aquatic reactivity of terrestrial DOC leading to net loss is low, closer to conservative chloride than to reactive nitrogen. Net removal occurred mainly from the hydrophobic organic acid fraction, while hydrophilic and transphilic acids showed no net change, indicating that partitioning of bulk DOC into different fractions is critical for understanding terrestrial DOC removal. These findings suggest that river systems may have only a modest ability to alter the amounts of terrestrial DOC delivered to coastal zones.

Permafrost thaw and climate warming may decrease the CO2, carbon, and metal concentration in peat soil waters of the Western Siberia Lowland.

PubMed

Raudina, T V; Loiko, S V; Lim, A; Manasypov, R M; Shirokova, L S; Istigechev, G I; Kuzmina, D M; Kulizhsky, S P; Vorobyev, S N; Pokrovsky, O S

2018-09-01

Soil pore waters are a vital component of the ecosystem as they are efficient tracers of mineral weathering, plant litter leaching, and nutrient uptake by vegetation. In the permafrost environment, maximal hydraulic connectivity and element transport from soils to rivers and lakes occurs via supra-permafrost flow (i.e. water, gases, suspended matter, and solutes migration over the permafrost table). To assess possible consequences of permafrost thaw and climate warming on carbon and Green House gases (GHG) dynamics we used a "substituting space for time" approach in the largest frozen peatland of the world. We sampled stagnant supra-permafrost (active layer) waters in peat columns of western Siberia Lowland (WSL) across substantial gradients of climate (-4.0 to -9.1°C mean annual temperature, 360 to 600mm annual precipitation), active layer thickness (ALT) (>300 to 40cm), and permafrost coverage (sporadic, discontinuous and continuous). We analyzed CO 2 , CH 4 , dissolved carbon, and major and trace elements (TE) in 93 soil pit samples corresponding to several typical micro landscapes constituting the WSL territory (peat mounds, hollows, and permafrost subsidences and depressions). We expected a decrease in intensity of DOC and TE mobilization from soil and vegetation litter to the supra-permafrost water with increasing permafrost coverage, decreasing annual temperature and ALT along a latitudinal transect from 62.3°N to 67.4°N. However, a number of solutes (DOC, CO 2 , alkaline earth metals, Si, trivalent and tetravalent hydrolysates, and micronutrients (Mn, Co, Ni, Cu, V, Mo) exhibited a northward increasing trend with highest concentrations within the continuous permafrost zone. Within the "substituting space for time" climate change scenario and northward shift of the permafrost boundary, our results suggest that CO 2 , DOC, and many major and trace elements will decrease their concentration in soil supra-permafrost waters at the boundary between thaw and frozen layers. As a result, export of DOC and elements from peat soil to lakes and rivers of the WSL (and further to the Arctic Ocean) may decrease. Copyright © 2018 Elsevier B.V. All rights reserved.

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

Yang, Qichun; Zhang, Xuesong; Xu, Xingya

Riverine carbon cycling is an important, but insufficiently investigated component of the global carbon cycle. Analyses of environmental controls on riverine carbon cycling are critical for improved understanding of mechanisms regulating carbon processing and storage along the terrestrial-aquatic continuum. Here, we compile and analyze riverine dissolved organic carbon (DOC) concentration data from 1402 United States Geological Survey (USGS) gauge stations to examine the spatial variability and environmental controls of DOC concentrations in the United States (U.S.) surface waters. DOC concentrations exhibit high spatial variability, with an average of 6.42 ± 6.47 mg C/ L (Mean ± Standard Deviation). In general,more » high DOC concentrations occur in the Upper Mississippi River basin and the Southeastern U.S., while low concentrations are mainly distributed in the Western U.S. Single-factor analysis indicates that slope of drainage areas, wetlands, forests, percentage of first-order streams, and instream nutrients (such as nitrogen and phosphorus) pronouncedly influence DOC concentrations, but the explanatory power of each bivariate model is lower than 35%. Analyses based on the general multi-linear regression models suggest DOC concentrations are jointly impacted by multiple factors. Soil properties mainly show positive correlations with DOC concentrations; forest and shrub lands have positive correlations with DOC concentrations, but urban area and croplands demonstrate negative impacts; total instream phosphorus and dam density correlate positively with DOC concentrations. Notably, the relative importance of these environmental controls varies substantially across major U.S. water resource regions. In addition, DOC concentrations and environmental controls also show significant variability from small streams to large rivers, which may be caused by changing carbon sources and removal rates by river orders. In sum, our results reveal that general multi-linear regression analysis of twenty one terrestrial and aquatic environmental factors can partially explain (56%) the DOC concentration variation. In conclusion, this study highlights the complexity of the interactions among these environmental factors in determining DOC concentrations, thus calls for processes-based, non-linear methodologies to constrain uncertainties in riverine DOC cycling.« less

Dissolved organic carbon and its potential predictors in eutrophic lakes.

PubMed

Toming, Kaire; Kutser, Tiit; Tuvikene, Lea; Viik, Malle; Nõges, Tiina

2016-10-01

Understanding of the true role of lakes in the global carbon cycle requires reliable estimates of dissolved organic carbon (DOC) and there is a strong need to develop remote sensing methods for mapping lake carbon content at larger regional and global scales. Part of DOC is optically inactive. Therefore, lake DOC content cannot be mapped directly. The objectives of the current study were to estimate the relationships of DOC and other water and environmental variables in order to find the best proxy for remote sensing mapping of lake DOC. The Boosted Regression Trees approach was used to clarify in which relative proportions different water and environmental variables determine DOC. In a studied large and shallow eutrophic lake the concentrations of DOC and coloured dissolved organic matter (CDOM) were rather high while the seasonal and interannual variability of DOC concentrations was small. The relationships between DOC and other water and environmental variables varied seasonally and interannually and it was challenging to find proxies for describing seasonal cycle of DOC. Chlorophyll a (Chl a), total suspended matter and Secchi depth were correlated with DOC and therefore are possible proxies for remote sensing of seasonal changes of DOC in ice free period, while for long term interannual changes transparency-related variables are relevant as DOC proxies. CDOM did not appear to be a good predictor of the seasonality of DOC concentration in Lake Võrtsjärv since the CDOM-DOC coupling varied seasonally. However, combining the data from Võrtsjärv with the published data from six other eutrophic lakes in the world showed that CDOM was the most powerful predictor of DOC and can be used in remote sensing of DOC concentrations in eutrophic lakes. Copyright © 2016 Elsevier Ltd. All rights reserved.

Soil-solution partitioning of DOC in acid organic soils: Results from a UK field acidification and alkalization experiment

NASA Astrophysics Data System (ADS)

Oulehle, Filip; Jones, Timothy; Burden, Annette; Evans, Chris

2013-04-01

Dissolved organic carbon (DOC) is an important component of the global carbon (C) cycle and has profound impacts on water chemistry and metabolism in lakes and rivers. Reported increases of DOC concentration in surface waters across Europe and Northern America have been attributed to several drivers; from changing climate and land-use to eutrophication and declining acid deposition. The last of these suggests that acidic deposition suppressed the solubility of DOC, and that this historic suppression is now being reversed by reducing emissions of acidifying pollutants. We studied a set of four parallel acidification and alkalization experiments in organic rich soils which, after three years of manipulation, have shown clear soil solution DOC responses to acidity change. We tested whether these DOC concentration changes were related to changes in the acid/base properties of DOC. Based on laboratory determination of DOC site density (S.D. = amount of carboxylic groups per milligram DOC) and charge density (C.D. = organic acid anion concentration per milligram DOC) we found that the change in DOC soil-solution partitioning was tightly related to the change in degree of dissociation (α = C.D./S.D. ratio) of organic acids (R2=0.74, p<0.01). Carbon turnover in soil organic matter (SOM), determined by soil respiration and β-D-glucosidase enzyme activity measurements, also appears to have some impact on DOC leaching, via constraints on the actual supply of available DOC from SOM; when the turnover rate of C in SOM is low, the effect of α on DOC leaching is reduced. Thus, differences in the magnitude of DOC changes seen across different environments might be explained by interactions between physicochemical restrictions of DOC soil-solution partitioning, and SOM carbon turnover effects on DOC supply.

Ocean Biological Pump Sensitivities and Implications for Climate Change Impacts

NASA Technical Reports Server (NTRS)

Romanou, Anastasia

2013-01-01

The ocean is one of the principal reservoirs of CO2, a greenhouse gas, and therefore plays a crucial role in regulating Earth's climate. Currently, the ocean sequesters about a third of anthropogenic CO2 emissions, mitigating the human impact on climate. At the same time, the deeper ocean represents the largest carbon pool in the Earth System and processes that describe the transfer of carbon from the surface of the ocean to depth are intimately linked to the effectiveness of carbon sequestration.The ocean biological pump (OBP), which involves several biogeochemical processes, is a major pathway for transfer of carbon from the surface mixed layer into the ocean interior. About 75 of the carbon vertical gradient is due to the carbon pump with only 25 attributed to the solubility pump. However, the relative importance and role of the two pumps is poorly constrained. OBP is further divided to the organic carbon pump (soft tissue pump) and the carbonate pump, with the former exporting about 10 times more carbon than the latter through processes like remineralization.Major uncertainties about OBP, and hence in the carbon uptake and sequestration, stem from uncertainties in processes involved in OBP such as particulate organicinorganic carbon sinkingsettling, remineralization, microbial degradation of DOC and uptakegrowth rate changes of the ocean biology. The deep ocean is a major sink of atmospheric CO2 in scales of hundreds to thousands of years, but how the export efficiency (i.e. the fraction of total carbon fixation at the surface that is transported at depth) is affected by climate change remains largely undetermined. These processes affect the ocean chemistry (alkalinity, pH, DIC, particulate and dissolved organic carbon) as well as the ecology (biodiversity, functional groups and their interactions) in the ocean. It is important to have a rigorous, quantitative understanding of the uncertainties involved in the observational measurements, the models and the projections of future changes.

Biogeochemistry of a treeline watershed, northwestern Alaska

USGS Publications Warehouse

Stottlemyer, R.

2001-01-01

Since 1950, mean annual temperatures in northwestern Alaska have increased. Change in forest floor and soil temperature or moisture could alter N mineralization rates, production of dissolved organic carbon (DOC) and organic nitrogen (DON), and their export to the aquatic ecosystem. In 1990, we began study of nutrient cycles in the 800-ha Asik watershed, located at treeline in the Noatak National Preserve, northwestern Alaska. This paper summarizes relationships between topographic aspect, soil temperature and moisture, inorganic and organic N pools, C pools, CO2 efflux, growing season net N mineralization rates, and stream water chemistry. Forest floor (O2) C/N ratios, C pools, temperature, and moisture were greater on south aspects. More rapid melt of the soil active layer (zone of annual freeze-thaw) and permafrost accounted for the higher moisture. The O2 C and N content were correlated with moisture, inorganic N pools, CO2 efflux, and inversely with temperature. Inorganic N pools were correlated with temperature and CO2 efflux. Net N mineralization rates were positive in early summer, and correlated with O2 moisture, temperature, and C and N pools. Net nitrification rates were inversely correlated with moisture, total C and N. The CO2 efflux increased with temperature and moisture, and was greater on south aspects. Stream ion concentrations declined and DOC increased with discharge. Stream inorganic nitrogen (DIN) output exceeded input by 70%. Alpine stream water nitrate (NO-3) and DOC concentrations indicated substantial contributions to the watershed DIN and DOC budgets.

Biogeochemistry of a treeline watershed, northwestern Alaska.

PubMed

Stottlemyer, R

2001-01-01

Since 1950, mean annual temperatures in northwestern Alaska have increased. Change in forest floor and soil temperature or moisture could alter N mineralization rates, production of dissolved organic carbon (DOC) and organic nitrogen (DON), and their export to the aquatic ecosystem. In 1990, we began study of nutrient cycles in the 800-ha Asik watershed, located at treeline in the Noatak National Preserve, northwestern Alaska. This paper summarizes relationships between topographic aspect, soil temperature and moisture, inorganic and organic N pools, C pools, CO2 efflux, growing season net N mineralization rates, and stream water chemistry. Forest floor (O2) C/N ratios, C pools, temperature, and moisture were greater on south aspects. More rapid melt of the soil active layer (zone of annual freeze-thaw) and permafrost accounted for the higher moisture. The O2 C and N content were correlated with moisture, inorganic N pools, CO2 efflux, and inversely with temperature. Inorganic N pools were correlated with temperature and CO2 efflux. Net N mineralization rates were positive in early summer, and correlated with O2 moisture, temperature, and C and N pools. Net nitrification rates were inversely correlated with moisture, total C and N. The CO2 efflux increased with temperature and moisture, and was greater on south aspects. Stream ion concentrations declined and DOC increased with discharge. Stream inorganic nitrogen (DIN) output exceeded input by 70%. Alpine stream water nitrate (NO3-) and DOC concentrations indicated substantial contributions to the watershed DIN and DOC budgets.

An Analysis of Terrestrial and Aquatic Environmental Controls of Riverine Dissolved Organic Carbon in the Conterminous United States

DOE PAGES

Yang, Qichun; Zhang, Xuesong; Xu, Xingya; ...

2017-05-29

Riverine carbon cycling is an important, but insufficiently investigated component of the global carbon cycle. Analyses of environmental controls on riverine carbon cycling are critical for improved understanding of mechanisms regulating carbon processing and storage along the terrestrial-aquatic continuum. Here, we compile and analyze riverine dissolved organic carbon (DOC) concentration data from 1402 United States Geological Survey (USGS) gauge stations to examine the spatial variability and environmental controls of DOC concentrations in the United States (U.S.) surface waters. DOC concentrations exhibit high spatial variability, with an average of 6.42 ± 6.47 mg C/ L (Mean ± Standard Deviation). In general,more » high DOC concentrations occur in the Upper Mississippi River basin and the Southeastern U.S., while low concentrations are mainly distributed in the Western U.S. Single-factor analysis indicates that slope of drainage areas, wetlands, forests, percentage of first-order streams, and instream nutrients (such as nitrogen and phosphorus) pronouncedly influence DOC concentrations, but the explanatory power of each bivariate model is lower than 35%. Analyses based on the general multi-linear regression models suggest DOC concentrations are jointly impacted by multiple factors. Soil properties mainly show positive correlations with DOC concentrations; forest and shrub lands have positive correlations with DOC concentrations, but urban area and croplands demonstrate negative impacts; total instream phosphorus and dam density correlate positively with DOC concentrations. Notably, the relative importance of these environmental controls varies substantially across major U.S. water resource regions. In addition, DOC concentrations and environmental controls also show significant variability from small streams to large rivers, which may be caused by changing carbon sources and removal rates by river orders. In sum, our results reveal that general multi-linear regression analysis of twenty one terrestrial and aquatic environmental factors can partially explain (56%) the DOC concentration variation. In conclusion, this study highlights the complexity of the interactions among these environmental factors in determining DOC concentrations, thus calls for processes-based, non-linear methodologies to constrain uncertainties in riverine DOC cycling.« less

How appetizing is the dissolved organic matter (DOM) trees lose during rainfall?

NASA Astrophysics Data System (ADS)

Howard, D.; Van Stan, J. T., II; Whitetree, A.; Zhu, L.; Stubbins, A.

2017-12-01

Dissolved organic carbon (DOC) is the chemical backbone of dissolved organic matter (DOM), which is important because it drives many processes in soils and waterways. Current DOC work has paid little attention to interactions between rain and plant canopies, where rainfall is partitioned into throughfall and stemflow. Even less DOC research has investigated the effect of arboreal epiphytes on throughfall and stemflow DOC. The purpose of this study is twofold: (1) assess the degree and timing of DOC consumption by microbial communities (biolability) in throughfall and stemflow, and (2) determine whether the presence of arboreal epiphytes in the canopy affect DOC biolability. Biolability of stemflow and throughfall DOC from Juniperus virginiana (cedar) was determined by incubating samples for 14 days. Throughfall and stemflow DOC was highly biolabile with DOC concentrations decreasing by 30-60%. Throughfall DOC was more biolabile than stemflow DOC. DOC in both throughfall and stemflow from epiphyte-covered cedars was less biolabile than DOC from trees without epiphytes. The high biolability of tree-derived DOC indicates that its supply provides carbon substrates to the microbial community at the forest floor, in soils and the rhizosphere. Epiphytes appear to be important in determining the biolability of DOC and therefore the size of this carbon subsidy to the soil ecosystem.

75 FR 53639 - Best Practices for Transit, Transshipment, and Reexport of Items Subject to the Export...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-01

... principles and best practices that complement those already identified by BIS in its Web guidance ( http://www.bis.doc.gov/complianceandenforcement/emcp.htm ), and industry outreach regarding export management... application to the EAR. Principles These best practices are based on the following four principles: Industry...

Simulating dissolved organic carbon dynamics at the swedish integrated monitoring sites with the integrated catchments model for carbon, INCA-C.

PubMed

Futter, M N; Löfgren, S; Köhler, S J; Lundin, L; Moldan, F; Bringmark, L

2011-12-01

Surface water concentrations of dissolved organic carbon ([DOC]) are changing throughout the northern hemisphere due to changes in climate, land use and acid deposition. However, the relative importance of these drivers is unclear. Here, we use the Integrated Catchments model for Carbon (INCA-C) to simulate long-term (1996-2008) streamwater [DOC] at the four Swedish integrated monitoring (IM) sites. These are unmanaged headwater catchments with old-growth forests and no major changes in land use. Daily, seasonal and long-term variations in streamwater [DOC] driven by runoff, seasonal temperature and atmospheric sulfate (SO₄(2-)) deposition were observed at all sites. Using INCA-C, it was possible to reproduce observed patterns of variability in streamwater [DOC] at the four IM sites. Runoff was found to be the main short-term control on [DOC]. Seasonal patterns in [DOC] were controlled primarily by soil temperature. Measured SO₄(2-) deposition explained some of the long-term [DOC] variability at all sites.

Uncoupling of Bacterial and Terrigenous Dissolved Organic Matter Dynamics in Decomposition Experiments

PubMed Central

Herlemann, Daniel P. R.; Manecki, Marcus; Meeske, Christian; Pollehne, Falk; Labrenz, Matthias; Schulz-Bull, Detlef; Dittmar, Thorsten; Jürgens, Klaus

2014-01-01

The biodegradability of terrigenous dissolved organic matter (tDOM) exported to the sea has a major impact on the global carbon cycle, but our understanding of tDOM bioavailability is fragmentary. In this study, the effects of preparative tDOM isolation on microbial decomposition were investigated in incubation experiments consisting of mesocosms containing mesohaline water from the Baltic Sea. Dissolved organic carbon (DOC) consumption, molecular DOM composition, bacterial activities, and shifts in bacterial community structure were compared between mesocosms supplemented with riverine tDOM, either as filtered, particle-free river water or as a concentrate obtained by lyophilization/tangential ultrafiltration, and those containing only Baltic Sea water or river water. As shown using ultra-high-resolution mass spectrometry (15 Tesla Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) covering approximately 4600 different DOM compounds, the three DOM preparation protocols resulted in distinct patterns of molecular DOM composition. However, despite DOC losses of 4–16% and considerable bacterial production, there was no significant change in DOM composition during the 28-day experiment. Moreover, tDOM addition affected neither DOC degradation nor bacterial dynamics significantly, regardless of the tDOM preparation. This result suggested that the introduced tDOM was largely not bioavailable, at least on the temporal scale of our experiment, and that the observed bacterial activity and DOC decomposition mainly reflected the degradation of unknown, labile, colloidal and low-molecular weight DOM, both of which escape the analytical window of FT-ICR-MS. In contrast to the different tDOM preparations, the initial bacterial inoculum and batch culture conditions determined bacterial community succession and superseded the effects of tDOM addition. The uncoupling of tDOM and bacterial dynamics suggests that mesohaline bacterial communities cannot efficiently utilize tDOM and that in subarctic estuaries other factors are responsible for the removal of imported tDOM. PMID:24718626

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.

Flux of carbon from 14C-enriched leaf litter throughout a forest soil mesocosm

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

Froberg, Mats J.; Hanson, Paul J; Trumbore, Susan E.

2009-01-01

The role of DOC for the build-up of soil organic carbon pools is still not well known, but it is thought to play a role in the transport of carbon to a greater depth where it becomes more stable. The aim of this study was to elucidate within-year dynamics of carbon transport from litter to the O (Oe and Oa) and A horizons. Mesocosms with constructed soil profiles were used to study dynamics of C transport from 14C-enriched (about 1000 ) leaf litter to the Oe/Oa and A horizons as well as the mineralization of leaf litter. The mesocosms weremore » placed in the field for 17 months during which time fluxes and 14C content of DOC and CO2 were measured. Changes in 14C in leaf litter and bulk soil C pools were also recorded. Significant simultaneous release and immobilization of DOC occurring in both the O and A horizons was hypothesized. Contrary to our hypothesis, DOC released from the labeled Oi horizon was not retained within the Oe/Oa layer. DOC originating in the unlabeled Oe/Oa layer was also released for transport. Extensive retention of DOC occurred in the A horizon. DOC leaching from A horizon consisted of a mix of DOC from different sources, with a main fraction originating in the A horizon and a smaller fraction leached from the overlaying horizons. The C and 14C budget for the litter layer also indicated a surprisingly large amount of carbon with ambient Δ14C-signature to be respired from this layer. Data for this site also suggested significant contributions from throughfall to dissolved organic carbon (DOC) transport into and respiration from the litter layer. The results from this study showed that DOC retentionwas low in the O horizon and therefore not important for the O horizon carbon budget. In the A horizon DOC retention was extensive, but annual DOC input was small compared to C stocks and therefore not important for changes in soil C on an annual timescale.« less

The carbon commute: Effects of urbanization on dissolved organic carbon quality on a suburban New England river network

NASA Astrophysics Data System (ADS)

Balch, E.; Robison, A.; Wollheim, W. M.

2017-12-01

Understanding anthropogenic influence on the sources and fluxes of carbon is necessary for interpreting the carbon cycle and contaminant transport throughout a river system. As urbanization increases worldwide, it is critical to understand how urbanization affects the carbon cycle so that we may be able to predict future changes. Rivers act as both transporters of terrestrial dissolved organic carbon (DOC) to coastal regions, and active transformers of DOC. The character (lability) of the carbon found within a river network is influenced by its sources and fluxes, as determined by the ecological processes, land use, and discharge, which vary throughout the network. We have characterized DOC quantity and quality throughout a suburban New England river network (Ipswich River, MA) in an attempt to provide a detailed picture of how DOC quality varies within a network, and how urbanization influences these changes. We conducted a synoptic survey of 45 sites over two hydrologically similar days in the Ipswich River network in northeast Massachusetts, USA. We collected discrete grab samples for DOC quantity and quality analyses. We also collected dissolved oxygen, conductivity, and nutrients (major anions and cations) as an extension of the synoptic survey. We plan to determine the source of the DOC by using excitation-emission matrices (EEMs), and specific UV absorption (SUVA) at 254 nm. These analyses will provide us with a detailed picture of how DOC quality varies within a network, and how urbanization influences these changes. Using land use data of the Ipswich River watershed, we are able to model the changes in DOC quality throughout the network. In highly urbanized headwaters, through the progressively more forested and wetland dominated main stem reaches, we expect to see the imprint of urbanization throughout the network due to its decreased lability. Studying the imprint of urbanization on DOC throughout a river network helps us complete our understanding of freshwater carbon processes. Rivers are an important component of the global carbon balance, and monitoring the effect of urbanization on the carbon cycle in freshwater systems is integral to understanding their role in the global carbon system.

Ancient low–molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw

USGS Publications Warehouse

Drake, Travis W.; Wickland, Kimberly P.; Spencer, Robert G. M.; McKnight, Diane M.; Striegl, Robert G.

2015-01-01

Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high–temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low–molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2 production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters.

Ancient low-molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw.

PubMed

Drake, Travis W; Wickland, Kimberly P; Spencer, Robert G M; McKnight, Diane M; Striegl, Robert G

2015-11-10

Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high-temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low-molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2 production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters.

Ancient low–molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw

PubMed Central

Drake, Travis W.; Wickland, Kimberly P.; Spencer, Robert G. M.; McKnight, Diane M.; Striegl, Robert G.

2015-01-01

Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high–temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low–molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2 production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters. PMID:26504243

Organic Carbon Mobilisation Mechanisms: Evidence from Globally Distributed Stalagmite Records

NASA Astrophysics Data System (ADS)

Baldini, J. U. L.; Fairchild, I. J.; Wynn, P.; Bourdin, C.; Muller, W.; Hartland, A.; Perrette, Y.; Worrall, F.; Bartlett, R.

2017-12-01

Identifying the cause of widespread increases in surface water dissolved organic carbon (DOC) concentrations in recent years is the subject of a contentious debate. Although DOC trends may partially reflect climate change, in many catchments they may also result from increased soil carbon solubility associated with decreases in acid rain due to lower atmospheric sulphur emissions. However, the lack of long-term DOC records hampers constraining climate's role in modulating DOC trends versus that of recovery from acidification. Here we help clarify the causes of recent DOC increases by using a combination of laboratory soil experiments and new stalagmite geochemical data. Laboratory experiments with soils sampled from above several key caves simulate the effect of acidity, temperature, and soil microbial processes on DOC release. These experiments are used to inform records of DOC encoded within several stalagmites from currently acidified, previously acidified, and unacidified sites, and which collectively yield insights into the timing of DOC change in the past. These records of stalagmite DOC concentration and composition are discussed within the context of the ongoing debate regarding the mechanism responsible for DOC release.

Dissolved organic carbon in Alaskan boreal forest: sources, chemical characteristics, and biodegradability

Treesearch

Kimberly P. Wickland; Jason C. Neff; George R. Aiken

2007-01-01

The fate of terrestrially-derived dissolved organic carbon (DOC) is important to carbon (C) cycling in both terrestrial and aquatic environments, and recent evidence suggests that climate warming is influencing DOC dynamics in northern ecosystems. To understand what determines the fate of terrestrial DOC, it is essential to quantify the chemical nature and potential...

Mangroves, a major source of dissolved organic carbon to the oceans

NASA Astrophysics Data System (ADS)

Dittmar, Thorsten; Hertkorn, Norbert; Kattner, Gerhard; Lara, RubéN. J.

2006-03-01

Organic matter, which is dissolved in low concentrations in the vast waters of the oceans, contains a total amount of carbon similar to atmospheric carbon dioxide. To understand global biogeochemical cycles, it is crucial to quantify the sources of marine dissolved organic carbon (DOC). We investigated the impact of mangroves, the dominant intertidal vegetation of the tropics, on marine DOC inventories. Stable carbon isotopes and proton nuclear magnetic resonance spectroscopy showed that mangroves are the main source of terrigenous DOC in the open ocean off northern Brazil. Sunlight efficiently destroyed aromatic molecules during transport offshore, removing about one third of mangrove-derived DOC. The remainder was refractory and may thus be distributed over the oceans. On a global scale, we estimate that mangroves account for >10% of the terrestrially derived, refractory DOC transported to the ocean, while they cover only <0.1% of the continents' surface.

Potential vulnerability of southeast Alaskan wetland soil carbon stocks to climate warming

NASA Astrophysics Data System (ADS)

Fellman, J.; D'Amore, D. V.; Hood, E. W.

2015-12-01

Carbon cycling along the high latitude coastal margins of Alaska is poorly understood relative to boreal and arctic ecosystems. The perhumid coastal temperate rainforest (PCTR) of southeast Alaska has some of the densest carbon stocks (>300 Mg C ha-1) in the world but the fate of these stocks with continued warming will balance on the poorly constrained rates of carbon accumulation and loss. We quantified the rate of dissolved organic carbon (DOC) and carbon dioxide (CO2) production from four different wetland types (rich fen, poor fen, forested wetland and cedar wetland) using controlled laboratory incubations of surface (10 cm) and subsurface (25 cm) soils incubated at 8 ºC and 15 ºC for 37 weeks. This design allowed us to determine the potential vulnerability of wetland soil carbon stocks to climate warming and partition organic matter mineralization into DOC and CO2 fluxes and its controls (e.g., wetland type and temperature). Furthermore, we used fluorescence characterization of DOC and laboratory bioassays to assess how climate warming may impact the quality and bioavailability of DOC delivered to fluvial systems. Soil depth and temperature strongly influenced carbon loss in all four wetland types with the greatest CO2 fluxes observed in the rich fen and greatest DOC fluxes observed in the poor fen. Of the fluxes, CO2 was the most sensitive to incubation temperature but DOC showed more variation with wetland type. Fluxes of DOC and CO2 were positively correlated only during the last few months of the incubation suggesting strong biotic control of DOC production developed as soil organic matter decomposition progressed. Moreover, bioavailable DOC and protein-like fluorescence were greatest in the initial soil extractions but dramatically decreased over the length of the incubations. Our findings suggest that soil organic matter decomposition will increase as the PCTR continues to warm, but this response will also will vary with wetland type.

Sedimentary sources of old high molecular weight dissolved organic carbon from the ocean margin benthic nepheloid layer

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

Guo, L. Santschi, P.H.

2000-02-01

Average {sup 14}C ages of dissolved organic carbon (DOC) in the ocean are 3--6,000 years, and are influenced by old DOC from continental margins. However, sources of DOC from terrestrial, autochthonous, and sedimentary organic carbon seem to be too young to be responsible for the old DOC observed in the ocean. Since colloidal organic carbon (COC, i.e., high molecular weight DOC), which is chemically very similar to that of bulk DOC, can be effectively isolated from seawater using cross-flow ultrafiltration, it can hold clues to sources and pathways of DOC turnover in the ocean. Radiocarbon measurements on COC in themore » water column and benthic nepheloid layer (BNL) from two continental margin areas (the Middle Atlantic Bight and the Gulf of Mexico) and controlled laboratory experiments were carried out to study sources of old DOC in the ocean margin areas. Vertical distributions of suspended particulate matter (SPM), particulate organic carbon (POC), nitrogen (PON), and DOC in the water column and bottom waters near the sediment-water interface all demonstrate a well developed benthic nepheloid layer in both ocean margin areas. COC from the BNL was much older than COC from the overlying water column. These results, together with strong concentration gradients of SPM, POC, PON, and DOC, suggest a sedimentary source for organic carbon species and possibly for old COC as well in BNL waters. This is confirmed by the results from controlled laboratory experiments. The heterogeneity of {Delta}{sup 14}C signatures in bulk SOC thus points to a preferential release of old organic components from sediment resuspension, which can be the transport mechanism of the old benthic COC observed in ocean margin areas. Old COC from continental margin nepheloid layers may thus be a potential source of old DOC to the deep ocean.« less

Zooplankton diel vertical migration and contribution to deep active carbon flux in the NW Mediterranean

NASA Astrophysics Data System (ADS)

Isla, Alejandro; Scharek, Renate; Latasa, Mikel

2015-03-01

The diel vertical migration (DVM) of zooplankton contributes to the biological pump transporting material from surface to deep waters. We examined the DVM of the zooplankton community in different size fractions (53-200 μm, 200-500 μm, 500-1000 μm, 1000-2000 μm and > 2000 μm) during three cruises carried out in the open NW Mediterranean Sea. We assessed their metabolic rates from empirical published relationships and estimated the active fluxes of dissolved carbon to the mesopelagic zone driven by migrant zooplankton. Within the predominantly oligotrophic Mediterranean Sea, the NW region is one of the most productive ones, with a seasonal cycle characterized by a prominent spring bloom. The study area was visited at three different phases of the seasonal cycle: during the spring bloom, the post-bloom, and strongly stratified oligotrophic conditions. We found seasonal differences in DVM, less evident during the bloom. Changes in DVM intensity were related to the composition of the zooplanktonic assemblage, which also varied between cruises. Euphausiids appeared as the most active migrants in all seasons, and their life cycle conditioned the observed pattern. Immature stages, which are unable to perform large diel vertical movements, dominated during the bloom, in contrast to the higher relative importance of migrating adults in the other two sampling periods. The amount of dissolved carbon exported was determined by the migrant zooplankton biomass, being highest during the post-bloom (2.2 mmol C respired m- 2 d- 1, and up to 3.1 mmol C exported m- 2 d- 1 when DOC release estimations are added). The active transport by diel migrants represented a substantial contribution to total carbon export to deep waters, especially under stratified oligotrophic conditions, revealing the importance of zooplankton in the biological pump operating in the study area.

Influences of organic carbon speciation on hyporheic corridor biogeochemistry and microbial ecology.

PubMed

Stegen, James C; Johnson, Tim; Fredrickson, James K; Wilkins, Michael J; Konopka, Allan E; Nelson, William C; Arntzen, Evan V; Chrisler, William B; Chu, Rosalie K; Fansler, Sarah J; Graham, Emily B; Kennedy, David W; Resch, Charles T; Tfaily, Malak; Zachara, John

2018-02-08

The hyporheic corridor (HC) encompasses the river-groundwater continuum, where the mixing of groundwater (GW) with river water (RW) in the HC can stimulate biogeochemical activity. Here we propose a novel thermodynamic mechanism underlying this phenomenon and reveal broader impacts on dissolved organic carbon (DOC) and microbial ecology. We show that thermodynamically favorable DOC accumulates in GW despite lower DOC concentration, and that RW contains thermodynamically less-favorable DOC, but at higher concentrations. This indicates that GW DOC is protected from microbial oxidation by low total energy within the DOC pool, whereas RW DOC is protected by lower thermodynamic favorability of carbon species. We propose that GW-RW mixing overcomes these protections and stimulates respiration. Mixing models coupled with geophysical and molecular analyses further reveal tipping points in spatiotemporal dynamics of DOC and indicate important hydrology-biochemistry-microbial feedbacks. Previously unrecognized thermodynamic mechanisms regulated by GW-RW mixing may therefore strongly influence biogeochemical and microbial dynamics in riverine ecosystems.

Organic Carbon Loading in Tropical Near-Shore Ecosystems: the Role of Mangrove Lagoons and Channels in Coastal Ocean Acidification

NASA Astrophysics Data System (ADS)

García, E.; Morell, J. M.

2016-02-01

Low energy tropical Caribbean shores are often dominated by highly productive mangrove ecosystems that thrive on land borne inorganic nutrient inputs and whose net production results in significant export of litter and dissolved organic compounds (DOC). These organic matrixes can be effectively transported to nearby ecosystems, including coral reefs whose vulnerability to excessive organic loading has been widely documented. This study documents the seaward transport and transformation of organic carbon from mangrove bays, trough near-shore reef ecosystems and out to open waters in the La Parguera Marine Reserve (LPMR). Considering in-situ colored dissolved organic matter (CDOM) as a tracer for DOC, absorption coefficient values (a350) were observed in the 6.13-0.02 m-1 and 14.08-0.06 m-1 during the dry (from 0 to 0.18 inches of rain) and wet seasons (from 0.68 to 4.76 inches of rain), respectively. Spectral properties (S275-295 and SR) calculations indicate that DOC is predominantly of terrestrial origin and found in high concentrations in enclosed mangrove bays and canals. Data evidences a strong gradient in CDOM concentration decreasing t from inshore to outer shelf waters. Rain precipitation correlated well with high CDOM values (aλ values doubled) and forced LPMR to behave similarly to a river influenced estuary as shown when CDOM is correlated with salinity, contrary to its predominant negative estuary profile. When correlating CDOM with pH and dissolved oxygen concentrations, it is evident that high organic matter content is driving ocean acidification in the nearshore areas. The non-conservative behavior of CDOM implies that other processes besides dilution may play a significant role in its spatial distribution.

Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses

NASA Astrophysics Data System (ADS)

Zigah, Prosper K.; Minor, Elizabeth C.; McNichol, Ann P.; Xu, Li; Werne, Josef P.

2017-07-01

We measured the concentrations and isotopic compositions of solid phase extracted (SPE) dissolved organic carbon (DOC) and high molecular weight (HMW) DOC and their constituent organic components in order to better constrain the sources and cycling of DOC in a large oligotrophic lacustrine system (Lake Superior, North America). SPE DOC constituted a significant proportion (41-71%) of the lake DOC relative to HMW DOC (10-13%). Substantial contribution of 14C-depleted components to both SPE DOC (Δ14C = 25-43‰) and HMW DOC (Δ14C = 22-32‰) was evident during spring mixing, and depressed their radiocarbon values relative to the lake dissolved inorganic carbon (DIC; Δ14C ∼ 59‰). There was preferential removal of 14C-depleted (older) and thermally recalcitrant components from HMW DOC and SPE DOC in the summer. Contemporary photoautotrophic addition to HMW DOC was observed during summer stratification in contrast to SPE DOC, which decreased in concentration during stratification. Serial thermal oxidation radiocarbon analysis revealed a diversity of sources (both contemporary and older) within the SPE DOC, and also showed distinct components within the HMW DOC. The thermally labile components of HMW DOC were 14C-enriched and are attributed to heteropolysaccharides (HPS), peptides/amide and amino sugars (AMS) relative to the thermally recalcitrant components reflecting the presence of older material, perhaps carboxylic-rich alicyclic molecules (CRAM). The solvent extractable lipid-like fraction of HMW DOC was very 14C-depleted (as old as 1270-2320 14C years) relative to the carbohydrate-like and protein-like substances isolated by acid hydrolysis of HMW DOC. Our data constrain relative influences of contemporary DOC and old DOC, and DOC cycling in a modern freshwater ecosystem.

Characterizing Groundwater Sources of Organic Matter to Arctic Coastal Waters

NASA Astrophysics Data System (ADS)

Connolly, C. T.; Spencer, R. G.; Cardenas, M. B.; Bennett, P. C.; McNichol, A. P.; McClelland, J. W.

2016-12-01

The Arctic is projected to transition from a runoff-dominated system to a groundwater-dominated system as permafrost thaws due to climate change. This fundamental shift in hydrology is expected to increase groundwater flow to Arctic coastal waters, which may be a significant source of dissolved organic matter (DOM) to these waters—even under present conditions—that has been largely overlooked. Here we quantify and elucidate sources of groundwater DOM inputs to lagoons along the eastern Alaskan Beaufort Sea coast using an approach that combines concentration measurements and radiocarbon dating of groundwater, soil profiles, and soil leachable dissolved organic carbon (DOC). Samples were collected in late summer, when soil thaw depths (active layer) were near their maximum extent. As anticipated, the radiocarbon age of bulk soil organic matter increased with depth (modern - 6,100 yBP), while the amount of extractable DOC decreased with depth within the active layer. However, amounts of extractable DOC increased dramatically in thawed permafrost samples collected directly below the actively layer. Concentrations of DOM in groundwater (ranging from 902 to 5,118 μmolL-1 DOC) are one to two orders of magnitude higher than those measured in lagoons and nearby river water. In contrast, the 14C-DOC ages of groundwater (1,400 ± 718 s.d. yBP), lagoon water (1,750 yBP), and river water (1,610 yBP) are comparable. Together these results suggest that: (1) groundwater provides a highly concentrated input of old DOC to Arctic coastal waters; (2) groundwater DOM is likely sourced from organic matter spanning the entire soil profile; and (3) the DOM in rivers along the eastern Alaskan Beaufort Sea coast during late summer is strongly influenced by groundwater sources, but is much lower in concentration due to photo-mineralization and/or biological consumption. These results are key for assessing how changes in land-ocean export of organic matter as permafrost thaws will change into the future with clear ramifications for Arctic coastal environments.

Photooxidation and Microbial Processing of Ancient and Modern Dissolved Organic Carbon in the Kolyma River, Siberia.

NASA Astrophysics Data System (ADS)

Behnke, M. I.; Mann, P. J.; Schade, J. D.; Spawn, S.; Zimov, N.

2015-12-01

Permafrost soils in northern high latitudes store large quantities of organic carbon that have remained frozen for thousands of years. As global temperatures increase, permafrost deposits have begun to thaw, releasing previously stored ancient carbon to streams and rivers in the form of dissolved organic carbon (DOC). Newly mobilized DOC is then subjected to processing by photooxidation and microbial metabolism. Permafrost-derived DOC is highly bioavailable directly upon release relative to modern DOC derived from plants and surface active layer soils. Our objectives were to assess the interaction of photodegradation and microbial processing, and to quantify any light priming effect on the microbial consumption of both ancient and modern sourced DOC pools. We exposed sterilized mixtures of ancient and modern DOC to ambient sunlight for six days, and then inoculated mixtures (0, 1, 10, 25, 50 & 100% ancient DOC) with microbes from both modern and ancient water sources. After inoculation, samples were incubated in the dark for five days. We measured biological oxygen demand, changes in absorbance, and DOC concentrations to quantify microbial consumption of DOC and identify shifts in DOC composition and biolability. We found evidence of photobleaching during irradiation (decreasing S275-295, increasing slope ratio, and decreasing SUVA254). Once inoculated, mixtures with more ancient DOC showed initially increased microbial respiration compared to mixtures with primarily modern DOC. During the first 24 hours, the light-exposed mixture with 50% ancient DOC showed 47.6% more oxygen consumption than did the dark 50% mixture, while the purely modern DOC showed 11.5% greater oxygen consumption after light exposure. After 5 days, the modern light priming was comparable to the 50% mixture (31.2% compared to 20.5%, respectively). Our results indicate that natural photoexposure of both modern and newly released DOC increases microbial processing rates over non photo-exposed DOC.

Sources and yields of dissolved carbon in northern Wisconsin stream catchments with differing amounts of Peatland

USGS Publications Warehouse

Elder, J.F.; Rybicki, N.B.; Carter, V.; Weintraub, V.

2000-01-01

In five tributary streams (four inflowing and one outflowing) of 1600-ha Trout Lake in northern Wisconsin, USA, we examined factors that can affect the magnitude of stream flow and transport of dissolved organic and inorganic carbon (DOC and DIC) through the streams to the lake. One catchment, the Allequash Creek basin, was investigated in more detail to describe the dynamics of carbon flow and to identify potential carbon sources. Stream flows and carbon loads showed little or no relation to surface-water catchment area. They were more closely related to ground-water watershed area because ground-water discharge, from both local and regional sources, is a major contributor to the hydrologic budgets of these catchments. An important factor in determining carbon influx to the stream is the area of peatland in the catchment. Peatland porewaters contain DOC concentrations up to 40 mg l-1 and are a significant potential carbon source. Ground-water discharge and lateral flow through peat are the suspected mechanisms for transport of that carbon to the streams. Carbon and nitrogen isotopes suggested that the sources of DOC in Allequash Creek above Allequash Lake were wetland vegetation and peat and that the sources below Allequash Lake were filamentous algae and wild rice. Catchments with high proportions of peatland, including the Allequash Creek catchment, tended to have elevated DOC loads in outflowing stream water. Respiration and carbon mineralization in lakes within the system tend to produce low DOC and low DOC/DIC in lake outflows, especially at Trout Lake. In Allequash Lake, however, the shallow peat island and vegetation-filled west end were sources of DOC. Despite the vast carbon reservoir in the peatlands, carbon yields were very low in these catchments. Maximum yields were on the order of 2.5 g m-2 y-1 DOC and 5.5 g m-2 y-1 DIC. The small yields were attributable to low stream flows due to lack of significant overland runoff and very limited stream channel coverage of the total catchment area.

Advances in the Control System for a High Precision Dissolved Organic Carbon Analyzer

NASA Astrophysics Data System (ADS)

Liao, M.; Stubbins, A.; Haidekker, M.

2017-12-01

Dissolved organic carbon (DOC) is a master variable in aquatic ecosystems. DOC in the ocean is one of the largest carbon stores on earth. Studies of the dynamics of DOC in the ocean and other low DOC systems (e.g. groundwater) are hindered by the lack of high precision (sub-micromolar) analytical techniques. Results are presented from efforts to construct and optimize a flow-through, wet chemical DOC analyzer. This study focused on the design, integration and optimization of high precision components and control systems required for such a system (mass flow controller, syringe pumps, gas extraction, reactor chamber with controlled UV and temperature). Results of the approaches developed are presented.

Carbon dynamics in a Late Quaternary-age coastal limestone aquifer system undergoing saltwater intrusion.

PubMed

Bryan, Eliza; Meredith, Karina T; Baker, Andy; Andersen, Martin S; Post, Vincent E A

2017-12-31

This study investigates the inorganic and organic aspects of the carbon cycle in groundwaters throughout the freshwater lens and transition zone of a carbonate island aquifer and identifies the transformation of carbon throughout the system. We determined 14 C and 13 C carbon isotope values for both DIC and DOC in groundwaters, and investigated the composition of DOC throughout the aquifer. In combination with hydrochemical and 3 H measurements, the chemical evolution of groundwaters was then traced from the unsaturated zone to the deeper saline zone. The data revealed three distinct water types: Fresh (F), Transition zone 1 (T1) and Transition zone 2 (T2) groundwaters. The 3 H values in F and T1 samples indicate that these groundwaters are mostly modern. 14 C DOC values are higher than 14 C DIC values and are well correlated with 3 H values. F and T1 groundwater geochemistry is dominated by carbonate mineral recrystallisation reactions that add dead carbon to the groundwater. T2 groundwaters are deeper, saline and characterised by an absence of 3 H, lower 14 C DOC values and a different DOC composition, namely a higher proportion of Humic Substances relative to total DOC. The T2 groundwaters are suggested to result from either the slow circulation of water within the seawater wedge, or from old remnant seawater caused by past sea level highstands. While further investigations are required to identify the origin of the T2 groundwaters, this study has identified their occurrence and shown that they did not evolve along the same pathway as fresh groundwaters. This study has also shown that a combined approach using 14 C and 13 C carbon isotope values for both DIC and DOC and the composition of DOC, as well as hydrochemical and 3 H measurements, can provide invaluable information regarding the transformation of carbon in a groundwater system and the evolution of fresh groundwater recharge. Copyright © 2017 Elsevier B.V. All rights reserved.

Carbon speciation and surface tension of fog

USGS Publications Warehouse

Capel, P.D.; Gunde, R.; Zurcher, F.; Giger, W.

1990-01-01

The speciation of carbon (dissolved/particulate, organic/inorganic) and surface tension of a number of radiation fogs from the urban area of Zurich, Switzerland, were measured. The carbon species were dominated by "dissolved" organic carbon (DOC; i.e., the fraction that passes through a filter), which was typically present at levels of 40-200 mg/L. Less than 10% of the DOC was identified as specific individual organic compounds. Particulate organic carbon (POC) accounted for 26-41% of the mass of the particles, but usually less than 10% of the total organic carbon mass. Inorganic carbon species were relatively minor. The surface tensions of all the measured samples were less than pure water and were correlated with their DOC concentrations. The combination of high DOC and POC and low surface tension suggests a mechanism for the concentration of hydrophobic organic contaminants in the fog droplet, which have been observed by numerous investigators. ?? 1990 American Chemical Society.

Dynamics of dissolved organic carbon in a stream during a quarter century of forest succession

Treesearch

Judy L. Meyer; Jackson Webster; Jennifer Knoepp; E.F. Benfield

2014-01-01

Dissolved organic carbon (DOC) is a heterogeneous mixture of compounds that makes up a large fraction of the organic matter transported in streams. It plays a significant role in many ecosystems. Riverine DOC links organic carbon cycles of continental and oceanic ecosystems. It is a significant trophic resource in stream food webs. DOC imparts color to lakes,...

Examining the role of dissolved organic nitrogen in stream ecosystems across biomes and Critical Zone gradients

NASA Astrophysics Data System (ADS)

Wymore, A.; Rodriguez-Cardona, B.; Coble, A. A.; Potter, J.; Lopez Lloreda, C.; Perez Rivera, K.; De Jesus Roman, A.; Bernal, S.; Martí Roca, E.; Kram, P.; Hruska, J.; Prokishkin, A. S.; McDowell, W. H.

2016-12-01

Watershed nitrogen exports are often dominated by dissolved organic nitrogen (DON); yet, little is known about the role ambient DON plays in ecosystems. As an organic nutrient, DON may serve as either an energy source or as a nutrient source. One hypothesized control on DON is nitrate (NO3-) availability. Here we examine the interaction of NO3- and DON in streams across temperate forests, tropical rainforests, and Mediterranean and taiga biomes. Experimental streams also drain contrasting Critical Zones which provide gradients of vegetation, soil type and lithology (e.g. volcaniclastic, granitic, ultramafic, Siberian Traps Flood Basalt) in which to explore how the architecture of the Critical Zone affects microbial biogeochemical reactions. Streams ranged in background dissolved organic carbon (DOC) concentration (1-50 mg C/L) and DOC: NO3- ratios (10-2000). We performed a series of ecosystem-scale NO3- additions in multiple streams within each environment and measured the change in DON concentration. Results demonstrate that there is considerable temporal and spatial variation across systems with DON both increasing and decreasing in response to NO3- addition. Ecologically this suggests that DON can serve as both a nutrient source and an energy source to aquatic microbial communities. In contrast, DOC concentrations rarely changed in response to NO3- additions suggesting that the N-rich fraction of the ambient dissolved organic matter pool is more bioreactive than the C-rich fraction. Contrasting responses of the DON and DOC pools indicate different mechanisms controlling their respective cycling. It is likely that DON plays a larger role in ecosystems than previously recognized.

Anthropogenic Impacts on Biological Carbon Sequestration in the Coastal Waters

NASA Astrophysics Data System (ADS)

Jiao, N.

2016-02-01

The well-known biological mechanism for carbon sequestration in the ocean is the biological pump (BP) which is driven by primary production initially in the surface water and then dependent on particulate organic carbon sinking process in the water column. In contrast microbial carbon pump (MCP) depends on microbial transformation of dissolved organic carbon (DOC) to refractory DOC (RDOC).Although the BP and the MCP are distinct mechanisms, they are intertwined. Both mechanisms should be considered regarding maximum sequestration of carbon in the ocean. Recent studies have showed that excess nutrients could facilitate the uptake of DOC and enhance both bacterial production and respiration. Bacterial growth efficiency increases with increasing nitrogen concentration to certain levels and then decreases thereafter, while the remaining DOC in the water usually decreases with increasing nitrogen concentration, suggesting that excess nitrogen could simulate uptake of DOC in the environment and thus have negative impacts on the ocean DOC storage.This is somehow against the case of the BP which is known to increase with increasing availability of nutrients. Another responsible factor is the nature of algal products. If it is labile, the organic carbon cannot be preserved in the environment.On top of that, labile organic carbon has priming effects for river discharged semi-labile DOC for bacterial respiration.That is, labile organic matter will become the incubator for bacteria. While bacteria respire DOC into CO2, they consume oxygen, and finally result in hypoxia. Under anoxic condition, anaerobic bacteria successively work on the rest of the organic carbon and produce harmful gasses such as methane and H2S. Such story did have happened during geological events in the history of the earth. The above processes not only result in ecological disasters but also reduce the capacity of carbon sequestration in the ocean. To achieve maximum carbon sinks, both BP and MCP should be considered in management, especially in the coastal waters where eutrophication and hypoxia are severe. Currently, farm over-fertilization is found world widely to be responsible for coastal water eutrophication. Therefore nutrients input must be under control for optimum outputs of the sum of BP and MCP towards sustainable coastal ecosystems.

Qualitative changes of riverine dissolved organic matter at low salinities due to flocculation

NASA Astrophysics Data System (ADS)

Asmala, Eero; Bowers, David G.; Autio, Riitta; Kaartokallio, Hermanni; Thomas, David N.

2014-10-01

The flocculation of dissolved organic matter (DOM) was studied along transects through three boreal estuaries. Besides the bulk concentration parameters, a suite of DOM quality parameters were investigated, including colored DOM (CDOM), fluorescent DOM, and the molecular weight of DOM as well as associated dissolved iron concentrations. We observed significant deviations from conservative mixing at low salinities (<2) in the estuarine samples of dissolved organic carbon (DOC), UV absorption (a(CDOM254)), and humic-like fluorescence. The maximum deviation from conservative mixing for DOC concentration was -16%, at salinities between 1 and 2. An associated laboratory experiment was conducted where an artificial salinity gradient between 0 and 6 was created. The experiment confirmed the findings from the estuarine transects, since part of the DOC and dissolved iron pools were transformed to particulate fraction (>0.2 µm) and thereby removing them from the dissolved phase. We also measured flocculation of CDOM, especially in the UV region of the absorption spectrum. Protein-like fluorescence of DOM decreased, while humic-like fluorescence increased because of salt-induced flocculation. Additionally, there was a decrease in molecular weight of DOM. Consequently, the quantity and quality of the remaining DOM pool was significantly changed after influenced to flocculation. Based on these results, we constructed a mechanistic, two-component flocculation model. Our findings underline the importance of the coastal filter, where riverine organic matter is flocculated and exported to the sediments.

Isolation, purification and analysis of dissolved organic carbon from Gohagoda uncontrolled open dumpsite leachate, Sri Lanka.

PubMed

Vithanage, Meththika; Wijesekara, Hasintha; Mayakaduwa, S S

2017-07-01

Extract and analysis of the Dissolved Organic Carbon (DOC) fractions were analyzed from the leachate of an uncontrolled dumpsite at Gohagoda, Sri Lanka. DOC fractions, humic acid (HA), fulvic acid (FA) and the hydrophilic (Hyd) fractions were isolated and purified with the resin techniques. Spectroscopic techniques and elemental analysis were performed to characterize DOCs. Maximum TOC and DOC values recorded were 56,955 and 28,493 mg/L, respectively. Based on the total amount of DOC fractionation, Hyd dominated accounting for ∼60%, and HA and FA constituted ∼22% and ∼17%, respectively, exhibiting the mature phase of the dumpsite. The elemental analysis of DOCs revealed carbon variation following HA > FA > Hyd, while hydrogen and nitrogen were similar in each fraction. The N/C ratio for HA was recorded as 0.18, following a similar trend in old dumpsite leachate elsewhere. The O/C ratios for HA and FA were recorded higher as much as 1.0 and 9.3, respectively, indicating high degree of carbon mineralization in the leachates. High content of carboxylic, phenolic and lactone groups in all DOCs was observed disclosing their potential for toxic substances transportation. The results strongly suggest the risk associated with DOCs in dumpsite leachate to the aquatic and terrestrial environment.

Twelve year interannual and seasonal variability of stream carbon export from a boreal peatland catchment

NASA Astrophysics Data System (ADS)

Leach, J. A.; Larsson, A.; Wallin, M. B.; Nilsson, M. B.; Laudon, H.

2016-07-01

Understanding stream carbon export dynamics is needed to accurately predict how the carbon balance of peatland catchments will respond to climatic and environmental change. We used a 12 year record (2003-2014) of continuous streamflow and manual spot measurements of total organic carbon (TOC), dissolved inorganic carbon (DIC), methane (CH4), and organic carbon quality (carbon-specific ultraviolet absorbance at 254 nm per dissolved organic carbon) to assess interannual and seasonal variability in stream carbon export for a peatland catchment (70% mire and 30% forest cover) in northern Sweden. Mean annual total carbon export for the 12 year period was 12.2 gCm-2 yr-1, but individual years ranged between 6 and 18 gCm-2 yr-1. TOC, which was primarily composed of dissolved organic carbon (>99%), was the dominant form of carbon being exported, comprising 63% to 79% of total annual exports, and DIC contributed between 19% and 33%. CH4 made up less than 5% of total export. When compared to previously published annual net ecosystem exchange (NEE) for the studied peatland system, stream carbon export typically accounted for 12 to 50% of NEE for most years. However, in 2006 stream carbon export accounted for 63 to 90% (estimated uncertainty range) of NEE due to a dry summer which suppressed NEE, followed by a wet autumn that resulted in considerable stream export. Runoff exerted a primary control on stream carbon export from this catchment; however, our findings suggest that seasonal variations in biologic and hydrologic processes responsible for production and transport of carbon within the peatland were secondary influences on stream carbon export. Consideration of these seasonal dynamics is needed when predicting stream carbon export response to environmental change.

A Hyporheic Mesocosm Experiment: Influence of Quantity and Quality of stream-source DOC on Rates of Hyporheic Metabolism

NASA Astrophysics Data System (ADS)

Serchan, S. P.; Wondzell, S. M.; Haggerty, R.; Pennington, R.; Feris, K. P.; Sanfilippo, A. R.; Reeder, W. J.; Tonina, D.

2016-12-01

Hyporheic zone biogeochemical processes can influence stream water chemistry. Some estimates show that 50-90% stream water CO2 is produced in the hyporheic zone through heterotrophic metabolism of organic matter, usually supplied from the stream as dissolved organic carbon (DOC). Preliminary results from our well network at the HJ Andrews WS1, indicate that dissolved inorganic carbon (DIC) is 1.5-2 times higher in the hyporheic zone than in stream water. Conversely, DOC (mg/L) is 1.5 times higher in stream water than in the hyporheic zone throughout the year. Overall, the hyporheic zone appears to be a net source of DIC. However, the increase in DIC along hyporheic flow paths is approximately 10-times greater than the loss of DOC, suggesting that metabolism of buried particulate organic carbon (POC) is a major source of organic carbon for microbial metabolism. However, we cannot completely rule out alternative sources of DIC, especially those originating in the overlying riparian soil, because hyporheic processes are difficult to isolate in well networks. To study hyporheic zone biogeochemical processes, particularly the transformation of organic carbon to inorganic carbon species, we designed and built six replicate 2-m long hyporheic mesocosms in which we are conducting DOC amendment experiments. We examine the role of DOC quality and quantity on hyporheic respiration by injecting labile (acetate) and refractory (fulvic acid) organic carbon and comparing rates of O2 consumption, DOC loss, and DIC gains against a control. We expect that stream source DOC is limiting in this small headwater stream, forcing hyporheic metabolism to rely on buried POC. However, the long burial time of POC suggests it is likely of low quality so that supplying labile DOC in stream water should shift hyporheic metabolism away from POC rather than increase the overall rate of metabolism. Future experiments will examine natural sources of DOC (stream periphyton, leaf, and soil humic horizon leachates), the breakdown of wood buried in the hyporheic zone, and the role of temperature and nutrients in controlling the rate at which buried POC is metabolized.

Modeling rates of DOC degradation using DOM composition and hydroclimatic variables

NASA Astrophysics Data System (ADS)

Moody, C. S.; Worrall, F.

2017-05-01

The fluvial fluxes of dissolved organic carbon (DOC) from peatlands form an important part of that ecosystem's carbon cycle, contributing approximately 35% of the overall peatland carbon budget. The in-stream processes acting on the DOC, such as photodegradation and biodegradation, can lead to DOC loss and thus contribute CO2 to the atmosphere. The aim of this study was to understand what controls the rates of DOC degradation. Water samples from a headwater, peat-covered catchment, were collected over a 23 month period and analyzed for the DOC degradation rate and dissolved organic matter (DOM) composition in the context of hydroclimatic monitoring. Measures of DOM composition included 13C solid-state nuclear magnetic resonance spectroscopy, bomb calorimetry, and elemental analysis. Regression analysis showed that there was a significant role for the composition of the DOM in controlling degradation with degradation rates significantly increasing with the proportion of aldehyde and carboxylic acid functional groups but decreasing with the proportion of N-alkyl functional groups. The highest rates of DOC degradation occurred when aldehyde functionality was at its greatest and this occurred on the recession limb of storm hydrographs. Including this knowledge into models of fluvial carbon fate for an 818 km2 catchment gave an annual average DOC removal rate of 67% and 50% for total organic carbon, slightly lower than previously predicted. The compositional controls suggest that DOM is primarily being used as a ready energy source to the aquatic ecosystem rather than as a nutrient source.

Characteristics of wet dissolved carbon deposition in a semi-arid catchment at the Loess Plateau, China

NASA Astrophysics Data System (ADS)

Wang, Linhua; Yen, Haw; Chen, Liding; E, Xinhui; Wang, Yafeng

2018-06-01

Wet dissolved carbon deposition is a critical node of the global carbon cycle, but little is known about dissolved organic and inorganic carbon (DOC and DIC) concentrations and fluxes in the semi-arid areas of the Loess Plateau Region (LPR). In this study, we measured variations in DOC and DIC concentrations in rainfalls at Yangjuangou Ecological Restoration and Soil and Water Observatory. Rainwater samples were collected in 16 rainfall events from July to September and the event-based, monthly concentrations and fluxes of DOC and DIC were quantified. The results showed that the event-based concentrations and fluxes of DOC and DIC were highly variable, ranging from 0.56 to 28.71 mg C L-1 and from 3.47 to 17.49 mg C L-1, respectively. The corresponding event-based fluxes ranged from 0.21-258.36 mg C m-2 and from 4.12 to 42.32 mg C m-2. The monthly concentrations of DOC and DIC were 24.62 and 4.30 (July), 3.58 and 10.52 (August), and 1.01 and 5.89 (September) mg C L-1, respectively. Thus, the monthly deposition fluxes of DOC and DIC were 541.64/94.60, 131.03/385.03, and 44.44/259.16 mg C m-2 for July, August, and September, respectively. In addition, the concentrations of DOC and DIC for the concentrated rainfall season (July-September) in the studied catchment were 7.06 and 7.00 mg C L-1, respectively. The estimated annual wet dissolved carbon depositions were 1.91 and 1.89 g C m-2 yr-1 for DOC and DIC, respectively. The results of this study suggest the variation in concentrations and fluxes of DOC and DIC and explore that these variation may be related to the dissolved carbon source and the rainfall characteristics during the concentrated rainfall season in the semi-arid catchment of the LPR. Furthermore, these results also suggest that dissolved carbon may be an important external input of carbon into terrestrial ecosystems.

Using fluorescence spectroscopy to gain new insights into seasonal patterns of stream DOC concentrations in an alpine, headwater catchment underlain by discontinuous permafrost in Wolf Creek Research Basin, Yukon Territory, Canada

NASA Astrophysics Data System (ADS)

Shatilla, N. J.; Carey, S.; Tang, W.

2017-12-01

The Canadian subarctic is experiencing rapid climate warming resulting in decreased depth and duration of snowcover, decreased permafrost extent and time span of seasonal frozen ground resulting in increased active layer depth, and increased frequency and magnitude of rainfall events during the growing season. These changes challenge our conceptual models of permafrost hydrology as comparisons between recent and historical streamflow records show an emerging secondary post-freshet peak in flow in recent years along with enhanced winter flows. Long-term monitoring of Granger Creek (7.6km2), an alpine watershed underlain by discontinuous permafrost located within Wolf Creek Research Basin (176km2) in Yukon Territory, Canada provided a multi-decadal record of hydro-meteorological measurements. Granger Creek experienced warmer and wetter summers in 2015-6 compared to 2001-8, and an altered streamflow pattern with an earlier spring freshet and peak in dissolved organic carbon (DOC) concentrations. DOC concentrations post-freshet remained low at both the headwater and meso-catchment scale, which contradicts trends of increasing DOC concentrations observed in larger river systems. Hysteresis loops of sub-hourly measurements of streamflow, salinity and chromophoric dissolved organic matter (CDOM) were analyzed to provide new insights into how hydrological connectivity at the headwater scale affected the timing of solute release with supporting information from optical indices calculated from fluorescence spectroscopy. These indices provided a more nuanced view of catchment dynamics than the DOC concentrations. The composition and quality of DOM varied throughout the growing season with the delivery of older, terrestrially-derived material corresponding to high DOC concentrations at the onset of spring freshet when the catchment was initially being flushed. The origin and quality of stream DOM shifted throughout the rest of the season to newer, more easily mobilized DOM. Comparison of historical and current data show a shift from the freshet-driven primary flush of DOC from the system to an increasingly important mobilization of solutes at the end of the growing season that could begin impacting the quantity and quality of solutes exported in the subsequent spring.

Landscape hydrology and scaling of nitrate 15N and 18O isotope composition in a semi-arid agroecosystem

NASA Astrophysics Data System (ADS)

Kelley, C. J.; Martin, R. A.; Keller, C. K.; Orr, C. H.; Huggins, D. R.; Evans, R. D.

2014-12-01

Understanding how pore- to hillslope-scale processes combine to control nutrient export at larger scales is a fundamental challenge in today's agroecosystems as the carbon and contamination footprints of production agriculture come under increasing scrutiny. At the Cook Agronomy Farm (CAF) Long-Term Agricultural Research (LTAR) station near Pullman, WA we are using in-field observations to track how local-scale hydrological routing and biogeochemical processing interact to control landscape-scale water and nutrient exports. Previous research at the CAF has shown that conservative tracers and reactive nutrient quantities (NO3-,and DOC concentrations, DOM quality) in landscape-scale drainage can be explained by straightforward mixing of waters from variably contributing areas. Nitrate stable isotope composition in subsurface drain effluent indicate that most leached nitrate originates from reduced nitrogen fertilizer applied to the CAF in the autumn, which undergoes nitrification and subsequent leaching. This occurs over a timespan of weeks to months. However, water samples from contributing areas exhibit nitrate d15N and d18O significantly greater than subsurface drain effluent at all locations, and time-series consistent with the occurrence of denitrification at some locations. Possible explanations include pore-scale processing of nitrogen that does not affect the other tracers (like EC, DOM quality, and DOC concentration), and landscape-scale transport pathways that bypass our field instruments. Through this work we are contributing to a broader understand of how global change and local factors and management practices interact to affect the fate of fertilizer N, which is a cross-cutting research theme of the national LTAR network.

Where does boreal stream DOC come from? - Quantifying the contribution from different landscape compartments using stable C isotope ratios.

NASA Astrophysics Data System (ADS)

Brink Bylund, J.; Bastviken, D.; Morth, C.; Laudon, H.; Giesler, R.; Buffam, I.

2007-12-01

Stable carbon isotope (δ13C) ratios are frequently used as a source tracer of e.g. organic matter (OM) produced in terrestrial versus aquatic environments. To our knowledge there has been no previous attempt to quantify the relative contribution of dissolved organic carbon (DOC) from various landscape compartments in catchments of different sizes. Here, we test to what extent δ13C values can be used also to quantify the relative contribution of DOC from wetlands/riparian zones along streams, and off stream forest habitats, respectively. We present data on spatial and temporal variability of DOC concentrations and δ13C-DOC values, during the year of 2005 in Krycklan catchment, a boreal stream network in northern Sweden. Ten stream sites, ranging from order 1 to 4, were monitored in sub catchments with different wetland coverage. Spatial variation of DOC concentration showed a weak but statistically significant relationship with wetland area, with higher concentration with increasing percent of wetland in the drainage area. During base flow the difference in δ13C-DOC values was significantly different between forest (-27.5‰) and wetland (-28.1‰). This spatial pattern disappears during spring peak flow when higher discharge flushing upper soil layer and the riparian zone on DOC in the catchments. A simple mixing model using DOC and δ13C-DOC showed that stream water DOC could be describe as a mixture of DOC coming from forest (deep) groundwater and wetland/riparian zone water. The result indicates that during spring peak flow almost all stream DOC (84-100%) is derived from wetlands and riparian zones. The wetland/riparian water dominates the stream DOC flux at all hydrological events, except for two sites, one forest dominated and one mixed catchment, where the forest groundwater dominated the DOC transport during base flow. Although the total wetland area in Krycklan catchment only represent 8.3%, it contributed, together with riparian zones, to as much as 83% of the yearly DOC transport. This study shows that there is a great potential in using stable carbon isotopes to quantify the relative contribution of DOC from various landscape compartments in catchments. Quantitative patterns are crucial for several reasons. It is for example necessary in predicting the response to global warming which will result in a changed hydrology and shifts in the relative area of the landscape compartments in boreal environments. KEY WORDS carbon isotopes; dissolved organic carbon; streams; boreal; landscape compartments; wetland; groundwater

Dissolved Organic Carbon in the Yukon, Tanana and Porcupine Rivers, Alaska

NASA Astrophysics Data System (ADS)

Aiken, G. R.; Striegl, R. G.; Wickland, K. P.; Dornblaser, M. M.; Raymond, P. A.

2006-12-01

The spatial and temporal variability of dissolved organic carbon (DOC) in the Yukon River (YR) and two major tributaries, the Porcupine River (PR), a black water river draining a watershed almost entirely underlain by permafrost, and the Tanana River (TR), a glacial dominated river, are being studied to better define processes controlling DOC in these systems. Five-year seasonal averages indicate DOC concentrations follow the discharge hydrograph, with highest daily and seasonal flux occurring during spring in YR and PR and during summer-autumn in TR. Largest DOC concentrations and specific UV absorption (SUVA) values, a measure of aromatic carbon content of the DOC and an indicator of DOC source, occurred at all locations during spring snowmelt. Lowest DOC concentration and SUVA occurred during low-flow in winter due to greatly reduced contributions of soil organic matter and to relatively greater influences of ground water. While all sites had comparable DOC concentration during winter, DOC concentration was greatest at PR during spring and summer-autumn, whereas TR had the lowest average DOC and SUVA values. Within the YR, average DOC concentration and SUVA values in spring and summer-autumn increase downriver due to contributions from organic carbon rich tributaries, such as PR, that increase in number and significance as the river flows through Alaska. Most the DOC in each system was comprised of hydrophobic organic acids (HPOA) derived from terrestrial vegetation. During winter, the hydrophilic fraction, determined to be the most biodegradable, was a larger percentage of the DOC than during spring-autumn. During spring, HPOA concentration and SUVA increased significantly at all sites, suggesting that most DOC in spring is derived from terrestrial organic matter that was frozen on the land surface over winter. During spring-autumn, PR had the largest concentration of HPOA and TR had the least. Like DOC concentration, HPOA concentration and SUVA increased down river. 14C-DOC values correspond to radiocarbon ages of modern (PR), 282 (TR), and 328 (YR) yrs B.P, indicating the presence of some aged DOC in YR and TR. Comparison of the chemical character of DOC from sites along the YR suggests that most DOC is transported from its source to the Bering Sea with little within river chemical or biological alteration, a result supported by laboratory biodegradation experiments.

Improved automation of dissolved organic carbon sampling for organic-rich surface waters.

PubMed

Grayson, Richard P; Holden, Joseph

2016-02-01

In-situ UV-Vis spectrophotometers offer the potential for improved estimates of dissolved organic carbon (DOC) fluxes for organic-rich systems such as peatlands because they are able to sample and log DOC proxies automatically through time at low cost. In turn, this could enable improved total carbon budget estimates for peatlands. The ability of such instruments to accurately measure DOC depends on a number of factors, not least of which is how absorbance measurements relate to DOC and the environmental conditions. Here we test the ability of a S::can Spectro::lyser™ for measuring DOC in peatland streams with routinely high DOC concentrations. Through analysis of the spectral response data collected by the instrument we have been able to accurately measure DOC up to 66 mg L(-1), which is more than double the original upper calibration limit for this particular instrument. A linear regression modelling approach resulted in an accuracy >95%. The greatest accuracy was achieved when absorbance values for several different wavelengths were used at the same time in the model. However, an accuracy >90% was achieved using absorbance values for a single wavelength to predict DOC concentration. Our calculations indicated that, for organic-rich systems, in-situ measurement with a scanning spectrophotometer can improve fluvial DOC flux estimates by 6 to 8% compared with traditional sampling methods. Thus, our techniques pave the way for improved long-term carbon budget calculations from organic-rich systems such as peatlands. Copyright © 2015 Elsevier B.V. All rights reserved.

Towards a universal microbial inoculum for dissolved organic carbon degradation experiments

NASA Astrophysics Data System (ADS)

Pastor, Ada; Catalán, Núria; Gutiérrez, Carmen; Nagar, Nupur; Casas-Ruiz, Joan P.; Obrador, Biel; von Schiller, Daniel; Sabater, Sergi; Petrovic, Mira; Borrego, Carles M.; Marcé, Rafael

2017-04-01

Dissolved organic carbon (DOC) is the largest biologically available pool of organic carbon in aquatic ecosystems and its degradation along the land-to-ocean continuum has implications for carbon cycling from local to global scales. DOC biodegradability is usually assessed by incubating filtered water inoculated with native microbial assemblages in the laboratory. However, the use of a native inoculum from several freshwaters, without having a microbial-tailored design, hampers our ability to tease apart the relative contribution of the factors driving DOC degradation from the effects of local microbial communities. The use of a standard microbial inoculum would allow researchers to disentangle the drivers of DOC degradation from the metabolic capabilities of microbial communities operating in situ. With this purpose, we designed a bacterial inoculum to be used in experiments of DOC degradation in freshwater habitats. The inoculum is composed of six bacterial strains that easily grow under laboratory conditions, possess a versatile metabolism and are able to grow under both aerobic and anaerobic conditions. The mixed inoculum showed higher DOC degradation rates than those from their isolated bacterial components and the consumption of organic substrates was consistently replicated. Moreover, DOC degradation rates obtained using the designed inoculum were responsive across a wide range of natural water types differing in DOC concentration and composition. Overall, our results show the potential of the designed inoculum as a tool to discriminate between the effects of environmental drivers and intrinsic properties of DOC on degradation dynamics.

Temporal changes in photoreactivity of dissolved organic carbon and implications for aquatic carbon fluxes from peatlands

NASA Astrophysics Data System (ADS)

Pickard, Amy E.; Heal, Kate V.; McLeod, Andrew R.; Dinsmore, Kerry J.

2017-04-01

Aquatic systems draining peatland catchments receive a high loading of dissolved organic carbon (DOC) from the surrounding terrestrial environment. Whilst photo-processing is known to be an important process in the transformation of aquatic DOC, the drivers of temporal variability in this pathway are less well understood. In this study, 8 h laboratory irradiation experiments were conducted on water samples collected from two contrasting peatland aquatic systems in Scotland: a peatland stream and a reservoir in a catchment with high percentage peat cover. Samples were collected monthly at both sites from May 2014 to May 2015 and from the stream system during two rainfall events. DOC concentrations, absorbance properties and fluorescence characteristics were measured to investigate characteristics of the photochemically labile fraction of DOC. CO2 and CO produced by irradiation were also measured to determine gaseous photoproduction and intrinsic sample photoreactivity. Significant variation was seen in the photoreactivity of DOC between the two systems, with total irradiation-induced changes typically 2 orders of magnitude greater at the high-DOC stream site. This is attributed to longer water residence times in the reservoir rendering a higher proportion of the DOC recalcitrant to photo-processing. During the experimental irradiation, 7 % of DOC in the stream water samples was photochemically reactive and direct conversion to CO2 accounted for 46 % of the measured DOC loss. Rainfall events were identified as important in replenishing photoreactive material in the stream, with lignin phenol data indicating mobilisation of fresh DOC derived from woody vegetation in the upper catchment. This study shows that peatland catchments produce significant volumes of aromatic DOC and that photoreactivity of this DOC is greatest in headwater streams; however, an improved understanding of water residence times and DOC input-output along the source to sea aquatic pathway is required to determine the fate of peatland carbon.

Examination of mercury and organic carbon dynamics from a constructed fen in the Athabasca oil sands region, Alberta, Canada using in situ and laboratory fluorescence measurements

NASA Astrophysics Data System (ADS)

Oswald, C.; Carey, S. K.

2013-12-01

In the Athabasca oil sands region, mined landscapes must be reclaimed to a functioning natural ecosystem as part of the mine closure process. To test wetland construction techniques on oil sands tailings, 55 ha of mined landscape on the Syncrude Canada Ltd. property is being reclaimed to a watershed containing a graminoid fen. The 18 ha constructed fen consists of an approximately 50 cm thick peat-mineral soil layer separated from underlying tailings sand by a thin layer of clay till. The water table in the fen is maintained by pumping water into the fen from a nearby lake and controlling outflow with under-drains. The objective of this study was to assess total mercury (THg) and methyl mercury (MeHg) concentration dynamics in water exported from the fen in relation to organic carbon quantity and composition. Water quality data from summer 2012 when the fen pumps were first turned on show that dissolved organic carbon (DOC) concentrations are on average twice as high in water flowing through the underlying tailings sand aquifer (median: 42.0 mg/L) compared to DOC concentrations in water flowing through the fen peat package (median: 20.3 mg/L). Given these DOC concentrations, filtered THg concentrations are very low (median values are 0.81 ng/L and 0.17 ng/L for water flowing through the fen peat and sand tailings, respectively) compared to concentrations reported for other boreal wetlands. Although a relationship was identified between filtered THg and DOC (r2=0.60), its slope (0.06 ng Hg/mg C) is an order-of-magnitude smaller than the typical range of slopes found at other wetland sites potentially suggesting a small pool of mercury in the peat and/or limited partitioning of mercury into solution. Filtered MeHg concentrations in all water samples are near the limit of detection and suggest that biogeochemical conditions conducive to methylation did not exist in the fen peat or tailings sand at the time of sampling. In addition to these baseline THg and MeHg results that will be used to assess the evolution of mercury dynamics in the fen as the hydrology and vegetation become established, we are investigating the composition of dissolved organic matter (DOM) using optical techniques in the water flowing through the fen peat and underlying tailing sand aquifer. During 2013, continuous in situ measurements of chromophoric DOM fluorescence (FDOM) were measured at the fen outlet to identify sources of C and their relative contribution to discharge waters. We compare these field measurements to laboratory measurements of FDOM on discrete water samples using a benchtop spectrofluorometer to develop relationships between FDOM, DOC and filtered THg and MeHg. The use of continuous in situ FDOM measurements as a proxy for DOC and mercury concentrations will improve our understanding of the effects of hydrologic management and natural seasonal variations in fen hydrology on DOC and Hg fluxes from different soil layers in the constructed system. Furthermore, we expect that the modeling of excitation-emission matrices using parallel factor analysis on discrete water samples will provide important information on the sources and reactivity of organic carbon being transported through different soil compartments in the fen.

Dissolved organic carbon in Alaskan boreal forest: Sources, chemical characteristics, and biodegradability

USGS Publications Warehouse

Wickland, K.P.; Neff, J.C.; Aiken, G.R.

2007-01-01

The fate of terrestrially-derived dissolved organic carbon (DOC) is important to carbon (C) cycling in both terrestrial and aquatic environments, and recent evidence suggests that climate warming is influencing DOC dynamics in northern ecosystems. To understand what determines the fate of terrestrial DOC, it is essential to quantify the chemical nature and potential biodegradability of this DOC. We examined DOC chemical characteristics and biodegradability collected from soil pore waters and dominant vegetation species in four boreal black spruce forest sites in Alaska spanning a range of hydrologic regimes and permafrost extents (Well Drained, Moderately Well Drained, Poorly Drained, and Thermokarst Wetlands). DOC chemistry was characterized using fractionation, UV-Vis absorbance, and fluorescence measurements. Potential biodegradability was assessed by incubating the samples and measuring CO2 production over 1 month. Soil pore water DOC from all sites was dominated by hydrophobic acids and was highly aromatic, whereas the chemical composition of vegetation leachate DOC varied significantly with species. There was no seasonal variability in soil pore water DOC chemical characteristics or biodegradability; however, DOC collected from the Poorly Drained site was significantly less biodegradable than DOC from the other three sites (6% loss vs. 13-15% loss). The biodegradability of vegetation-derived DOC ranged from 10 to 90% loss, and was strongly correlated with hydrophilic DOC content. Vegetation such as Sphagnum moss and feathermosses yielded DOC that was quickly metabolized and respired. In contrast, the DOC leached from vegetation such as black spruce was moderately recalcitrant. Changes in DOC chemical characteristics that occurred during microbial metabolism of DOC were quantified using fractionation and fluorescence. The chemical characteristics and biodegradability of DOC in soil pore waters were most similar to the moderately recalcitrant vegetation leachates, and to the microbially altered DOC from all vegetation leachates. ?? 2007 Springer Science+Business Media, LLC.

Organic Matter in Rivers: The Crossroads between Climate and Water Quality

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

Davisson, M L

2001-04-27

All surface waters in the world contain dissolved organic matter and its concentration depends on climate and vegetation. Dissolved organic carbon (DOC) is ten times higher in wetlands and swamps than in surface water of arctic, alpine, or arid climate. Climates of high ecosystem productivity (i.e., tropics) typically have soils with low organic carbon storage, but drain high dissolved organic loads to rivers. Regions with lower productivity (e.g. grasslands) typically have high soil carbon storage while adjacent rivers have high DOC contents. Most DOC in a free-flowing river is derived from leaching vegetation and soil organic matter, whereas in dammedmore » rivers algae may comprise a significant portion. Water chemistry and oxygen-18 abundance of river water, along with radiocarbon and carbon-13 isotope abundance measurements of DOC were used to distinguish water and water quality sources in the Missouri River watershed. Drinking water for the City of St. Louis incorporates these different sources, and its water quality depends mostly on whether runoff is derived from the upper or the lower watershed, with the lower watershed contributing water with the highest DOC. During drinking water chlorination, DOC forms carcinogenic by-products in proportion to the amount of DOC present. This has recently led the USEPA to propose federal regulation standards. Restoration of natural riparian habitat such as wetlands will likely increase DOC concentrations in river water.« less

Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the seawater-brine interface

NASA Astrophysics Data System (ADS)

Shah, S. R.; Joye, S. B.; Brandes, J. A.; McNichol, A. P.

2013-05-01

Orca Basin, an intraslope basin on the Texas-Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200 m in which limited microbial activity has been reported. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to measurements made in the 1970s. Both DIC and DOC are more "aged" within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon remineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC, allowing for only limited oxidation of methane diffusing upwards from sediments. This conclusion is consistent with previous studies that identify the seawater-brine interface as the focus of microbial activity associated with Orca Basin brine. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawater-brine interface region as the likely source region for DOC to the brine as well as DIC.

The Comparison of Different Heterotrophic Bacteria on the Decomposition of DOC molecule

NASA Astrophysics Data System (ADS)

Xie, R.; Zheng, Q.; Jiao, N.

2016-02-01

Marine dissolved organic carbon (DOC) pool is one of the largest reservoirs of organic carbon on Earth. Heterotrophic bacteria are the primary biotic force regulating the fate of marine DOC. Comparison of genomic data, microbes belonging to different clades have diverse DOC molecule utilization genes. That's give us a hint that different microbial groups may have their own pattern to decompose DOC, biosynthesize diverse DOC molecule and contribute to the in situ DOC reservoirs in the ocean. The interaction between marine microbes and DOC molecule is hotspots in current research. We will choose some important microbial groups (e.g., Roseobacter, Altermonas, Halomonas, SAR11 and CFB) to identify their contribution to environmental DOC pool and their specific recalcitrant DOC component using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Combined with the composition of hydrolases, lyases and ligases in their genomes, we try to establish a linkage between the specific DOC composition and microbial genetic information. Future more the environmental metagenomic data would help us understand the relationship between the endemic DOC composition and microbial communities in the environment.

High mobilization of arsenic, metals and rare earth elements in seepage waters driven by respiration of old allochthonous organic carbon.

PubMed

Weiske, Arndt; Schaller, Jörg; Hegewald, Tilo; Machill, Susanne; Werner, Ingo; Dudel, E Gert

2013-12-01

Metal and metalloid mobilization processes within seepage water are of major concern in a range of water reservoir systems. The mobilization process of arsenic and heavy metals within a dam and sediments of a drinking water reservoir was investigated. Principle component analysis (PCA) on time series data of seepage water showed a clear positive correlation of arsenic with iron and DOC (dissolved organic carbon), and a negative correlation with nitrate due to respiratory processes. A relationship of reductive metal and metalloid mobilization with respiration of old carbon was shown. The system is influenced by sediment layers as well as a recent DOC input from degraded ombrotrophic peatbogs in the catchment area. The isotopic composition ((12)C, (13)C and (14)C) of DOC is altered along the path from basin to seepage water, but no significant changes in structural parameters (LC-OCD-OND, FT-IR) could be seen. DIC (dissolved inorganic carbon) in seepage water partly originates from respiratory processes, and a higher relationship of it with sediment carbon than with the DOC inventory of infiltrating water was found. This study revealed the interaction of respiratory processes with metal and metalloid mobilization in sediment water flows. In contrast to the presumption that emerging DOC via respiratory processes mainly controls arsenic and metal mobilization it could be shown that the presence of aged carbon compounds is essential. The findings emphasize the importance of aged organic carbon for DOC, DIC, arsenic and metal turnover.

Relationship between the colored dissolved organic matter and dissolved organic carbon and the application on remote sensing in East China Sea

NASA Astrophysics Data System (ADS)

Qiong, Liu; Pan, Delu; Huang, Haiqing; Lu, Jianxin; Zhu, Qiankun

2011-11-01

A cruise was conducted in the East China Sea (ECS) in autumn 2010 to collect Dissolved Organic Carbon (DOC) and Colored Dissolved Organic Matter (CDOM) samples. The distribution of DOC mainly controlled by the hydrography since the relationship between DOC and salinity was significant in both East China Sea. The biological activity had a significant influence on the concentration of DOC with a close correlation between DOC and Chl a. The absorption coefficient of CDOM (a355) decreased with the salinity increasing in the shelf of East China Sea (R2=0.9045). CDOM and DOC were significantly correlated in ECS where DOC distribution was dominated largely by the Changjiang diluted water. Based on the relationship of CDOM and DOC, we estimated the DOC concentration of the surface in ECS from satellite-derived CDOM images. Some deviations induced by the biological effect and related marine DOC accumulations were discussed.

Overview of a simple model describing variation of dissolved organic carbon in an upland catchment

USGS Publications Warehouse

Boyer, Elizabeth W.; Hornberger, George M.; Bencala, Kenneth E.; McKnight, Diane M.

1996-01-01

Hydrological mechanisms controlling the variation of dissolved organic carbon (DOC) were investigated in the Deer Creek catchment located near Montezuma, CO. Patterns of DOC in streamflow suggested that increased flows through the upper soil horizon during snowmelt are responsible for flushing this DOC-enriched interstitial water to the streams. We examined possible hydrological mechanisms to explain the observed variability of DOC in Deer Creek by first simulating the hydrological response of the catchment using TOPMODEL and then routing the predicted flows through a simple model that accounted for temporal changes in DOC. Conceptually the DOC model can be taken to represent a terrestrial (soil) reservoir in which DOC builds up during low flow periods and is flushed out when infiltrating meltwaters cause the water table to rise into this “reservoir”. Concentrations of DOC measured in the upper soil and in streamflow were compared to model simulations. The simulated DOC response provides a reasonable reproduction of the observed dynamics of DOC in the stream at Deer Creek.

Interlinkages between Carbon and Water Residence Times in Peat

NASA Astrophysics Data System (ADS)

Visser, A.; Wilson, R.; Sebestyen, S.; Griffiths, N.; Chanton, J.; Veale, N.; McFarlane, K. J.; Kolka, R. K.; Guilderson, T.

2016-12-01

Peatlands play an important role in the terrestrial carbon cycle. Understanding their response to climate change is crucial to predict their role as carbon sink or source of methane and carbon dioxide to the atmosphere. The hydrology of the peatland plays a crucial role, providing anoxic conditions for peat accumulation and advective transport of nutrients and dissolved organic carbon (DOC) to methanogens at depth. The interlinkages between the hydrology and carbon-cycling at the S1 bog at the Marcell Experimental Forest were investigated as part of the SPRUCE experiment, using a combination of isotopic techniques characterizing the carbon and water ages to assess the role of advective transport in the peat pore water. Tritium and tritiogenic helium concentrations constrain the age of the pore water to less than 10 years, although gas exchange with the atmosphere complicates direct use of 3H/3He dating methods. The pore water ages further constrain the interpretation of the peat, DOC and DIC ages. While carbon-14 values of solid peat decrease from 0‰ at the surface to -550‰ (corresponding to carbon-14 ages of 8 ka) at 2m depth, the DOC and DIC shift from +50‰ to -50‰ at depth. Knowing that the advective transport time of pore water is negligible on this time scale, the shift in carbon-14 of DOC must result from peat decomposition at depth, rather than in situ aging of DOC. Combined with the DOC concentration data, the carbon-cycling rates at the SPRUCE experiment are further constrained. The integrated application of isotopes in the carbon and water cycle emphasizes the importance of understanding peatland hydrology for understanding carbon-cycle dynamics. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-675107

Sources of dissolved and particulate organic material in Loch Vale Watershed, Rocky Mountain National Park, Colorado, USA

USGS Publications Warehouse

Baron, Jill S.; McKnight, Diane M.; Denning, A. Scott

1991-01-01

The sources of both dissolved organic carbon (DOC) and particulate organic carbon (POC) to an alpine (Sky Pond) and a subalpine lake (The Loch) in Rocky Mountain National Park were explored for four years. The importance of both autochthonous and allochthonous sources of organic matter differ, not only between alpine and subalpine locations, but also seasonally. Overall, autochthonous sources dominate the organic carbon of the alpine lake, while allochthonous sources are a more significant source of organic carbon to the subalpine lake. In the alpine lake, Sky Pond, POC makes up greater than one third of the total organic matter content of the water column, and is related to phytoplankton abundance. Dissolved organic carbon is a product of within-lake activity in Sky Pond except during spring snowmelt and early summer (May–July), when stable carbon isotope ratios suggest a terrestrial source. In the subalpine lake, The Loch, DOC is a much more important constituent of water column organic material than POC, comprising greater than 90% of the spring snowmelt organic matter, and greater than 75% of the organic matter over the rest of the year. Stable carbon isotope ratios and a very strong relation of DOC with soluble Al(tot) indicate DOC concentrations are almost entirely related to flushing of soil water from the surrounding watershed during spring snowmelt. Stable carbon isotope ratios indicate that, for both lakes, phytoplankton is an important source of DOC in the winter, while terrestrial material of plant or microbial origin contributes DOC during snowmelt and summer.

Carbon and nitrogen stoichiometry across stream ecosystems

NASA Astrophysics Data System (ADS)

Wymore, A.; Kaushal, S.; McDowell, W. H.; Kortelainen, P.; Bernhardt, E. S.; Johnes, P.; Dodds, W. K.; Johnson, S.; Brookshire, J.; Spencer, R.; Rodriguez-Cardona, B.; Helton, A. M.; Barnes, R.; Argerich, A.; Haq, S.; Sullivan, P. L.; López-Lloreda, C.; Coble, A. A.; Daley, M.

2017-12-01

Anthropogenic activities are altering carbon and nitrogen concentrations in surface waters globally. The stoichiometry of carbon and nitrogen regulates important watershed biogeochemical cycles; however, controls on carbon and nitrogen ratios in aquatic environments are poorly understood. Here we use a multi-biome and global dataset (tropics to Arctic) of stream water chemistry to assess relationships between dissolved organic carbon (DOC) and nitrate, ammonium and dissolved organic nitrogen (DON), providing a new conceptual framework to consider interactions between DOC and the multiple forms of dissolved nitrogen. We found that across streams the total dissolved nitrogen (TDN) pool is comprised of very little ammonium and as DOC concentrations increase the TDN pool shifts from nitrate to DON dominated. This suggests that in high DOC systems, DON serves as the primary source of nitrogen. At the global scale, DOC and DON are positively correlated (r2 = 0.67) and the average C: N ratio of dissolved organic matter (molar ratio of DOC: DON) across our data set is approximately 31. At the biome and smaller regional scale the relationship between DOC and DON is highly variable (r2 = 0.07 - 0.56) with the strongest relationships found in streams draining the mixed temperate forests of the northeastern United States. DOC: DON relationships also display spatial and temporal variability including latitudinal and seasonal trends, and interactions with land-use. DOC: DON ratios correlated positively with gradients of energy versus nutrient limitation pointing to the ecological role (energy source versus nutrient source) that DON plays with stream ecosystems. Contrary to previous findings we found consistently weak relationships between DON and nitrate which may reflect DON's duality as an energy or nutrient source. Collectively these analyses demonstrate how gradients of DOC drive compositional changes in the TDN pool and reveal a high degree of variability in the C: N ratio (3-100) of stream water dissolved organic matter.

Carbon isotope analysis of dissolved organic carbon in fresh and saline (NaCl) water via continuous flow cavity ring-down spectroscopy following wet chemical oxidation

USGS Publications Warehouse

Conaway, Christopher; Thomas, Randal B.; Saad, Nabil; Thordsen, James J.; Kharaka, Yousif K.

2015-01-01

This work examines the performance and limitations of a wet chemical oxidation carbon analyser interfaced with a cavity ring-down spectrometer (WCO-CRDS) in a continuous flow (CF) configuration for measuring δ13C of dissolved organic carbon (δ13C-DOC) in natural water samples. Low-chloride matrix (<5 g Cl/L) DOC solutions were analysed with as little as 2.5 mg C/L in a 9 mL aliquot with a precision of 0.5 ‰. In high-chloride matrix (10–100 g Cl/L) DOC solutions, bias towards lighter δ13C-DOC was observed because of incomplete oxidation despite using high-concentration oxidant, extended reaction time, or post-wet chemical oxidation gas-phase combustion. However, through a combination of dilution, chloride removal, and increasing the oxidant:sample ratio, high-salinity samples with sufficient DOC (>22.5 µg C/aliquot) may be analysed. The WCO-CRDS approach requires more total carbon (µg C/aliquot) than conventional CF-isotope ratio mass spectrometer, but is nonetheless applicable to a wide range of DOC concentration and water types, including brackish water, produced water, and basinal brines.

Dissolved oxygen as an indicator of bioavailable dissolved organic carbon in groundwater

USGS Publications Warehouse

Chapelle, Francis H.; Bradley, Paul M.; McMahon, Peter B.; Kaiser, Karl; Benner, Ron

2012-01-01

Concentrations of dissolved oxygen (DO) plotted vs. dissolved organic carbon (DOC) in groundwater samples taken from a coastal plain aquifer of South Carolina (SC) showed a statistically significant hyperbolic relationship. In contrast, DO-DOC plots of groundwater samples taken from the eastern San Joaquin Valley of California (CA) showed a random scatter. It was hypothesized that differences in the bioavailability of naturally occurring DOC might contribute to these observations. This hypothesis was examined by comparing nine different biochemical indicators of DOC bioavailability in groundwater sampled from these two systems. Concentrations of DOC, total hydrolysable neutral sugars (THNS), total hydrolysable amino acids (THAA), mole% glycine of THAA, initial bacterial cell counts, bacterial growth rates, and carbon dioxide production/consumption were greater in SC samples relative to CA samples. In contrast, the mole% glucose of THNS and the aromaticity (SUVA254) of DOC was greater in CA samples. Each of these indicator parameters were observed to change with depth in the SC system in a manner consistent with active biodegradation. These results are uniformly consistent with the hypothesis that the bioavailability of DOC is greater in SC relative to CA groundwater samples. This, in turn, suggests that the presence/absence of a hyperbolic DO-DOC relationship may be a qualitative indicator of relative DOC bioavailability in groundwater systems.

Influences of organic carbon speciation on hyporheic corridor biogeochemistry and microbial ecology

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

Stegen, James C.; Johnson, Tim; Fredrickson, James K.

The hyporheic corridor (HC) is a critical component of riverine ecosystems that encompasses the river-11 groundwater continuum. The mixing of groundwater (GW) with river water (RW) in the HC can 12 stimulate biogeochemical activity, and here we (i) propose a novel thermodynamic mechanism 13 underlying this phenomenon, and (ii) reveal broader impacts on dissolved organic carbon (DOC) 14 biogeochemistry and microbial ecology. We show that thermodynamically-favorable DOC 15 accumulates in GW despite decreases in DOC concentration along subsurface flow paths, and that RW 16 contains less thermodynamically-favorable DOC, but at higher concentrations. This indicates that DOC 17 in GW ismore » protected from microbial oxidation by low total energy contained within the DOC pool, while 18 RW DOC is protected by lower thermodynamic favorability of carbon species. We propose that GW-19 RW mixing overcomes these protection mechanisms and stimulates respiration. Mixing models 20 coupled with time-lapse electrical resistance tomography revealed that stimulated respiration leads 21 to tipping points in spatiotemporal dynamics of DOC across the HC. Further, shifts in DOC speciation 22 and biochemical pathways were associated with shifts in microbiome composition, highlighting 23 feedbacks among hydrology, DOC biochemistry, and microbial ecology. These results reveal that 24 previously unrecognized thermodynamic-based mechanisms regulated by GW-RW mixing can strongly 25 influence biogeochemical and microbial dynamics in riverine ecosystems.« less

Influences of organic carbon speciation on hyporheic corridor biogeochemistry and microbial ecology

DOE PAGES

Stegen, James C.; Johnson, Tim; Fredrickson, James K.; ...

2018-02-08

The hyporheic corridor (HC) is a critical component of riverine ecosystems that encompasses the river-11 groundwater continuum. The mixing of groundwater (GW) with river water (RW) in the HC can 12 stimulate biogeochemical activity, and here we (i) propose a novel thermodynamic mechanism 13 underlying this phenomenon, and (ii) reveal broader impacts on dissolved organic carbon (DOC) 14 biogeochemistry and microbial ecology. We show that thermodynamically-favorable DOC 15 accumulates in GW despite decreases in DOC concentration along subsurface flow paths, and that RW 16 contains less thermodynamically-favorable DOC, but at higher concentrations. This indicates that DOC 17 in GW ismore » protected from microbial oxidation by low total energy contained within the DOC pool, while 18 RW DOC is protected by lower thermodynamic favorability of carbon species. We propose that GW-19 RW mixing overcomes these protection mechanisms and stimulates respiration. Mixing models 20 coupled with time-lapse electrical resistance tomography revealed that stimulated respiration leads 21 to tipping points in spatiotemporal dynamics of DOC across the HC. Further, shifts in DOC speciation 22 and biochemical pathways were associated with shifts in microbiome composition, highlighting 23 feedbacks among hydrology, DOC biochemistry, and microbial ecology. These results reveal that 24 previously unrecognized thermodynamic-based mechanisms regulated by GW-RW mixing can strongly 25 influence biogeochemical and microbial dynamics in riverine ecosystems.« less

A Global Assessment of Dissolved Organic Carbon in Precipitation

NASA Astrophysics Data System (ADS)

Safieddine, Sarah A.; Heald, Colette L.

2017-11-01

Precipitation is the largest physical removal pathway of atmospheric reactive organic carbon in the form of dissolved organic carbon (DOC). We present the first global DOC distribution simulated with a global model. A total of 85 and 188 Tg C yr-1 are deposited to the ocean and the land, respectively, with DOC ranging between 0.1 and 10 mg C L-1 in this GEOS-Chem simulation. We compare the 2010 simulated DOC to a 30 year synthesis of measurements. Despite limited measurements and imperfect temporal matching, the model is able to reproduce much of the spatial variability of DOC (r = 0.63), with a low bias of 35%. We present the global average carbon oxidation state (OSc>¯) as a simple metric for describing the chemical composition. In the atmosphere, -1.8≤OSc>¯≤-0.6, and the increase in solubility upon oxidation leads to a global increase in OSc>¯ in precipitation with -0.6≤OSc>¯DOC≤0.

How important are intertidal ecosystems for global biogeochemical cycles? Molecular and isotopic evidence for major outwelling of photo-bleached dissolved organic matter from mangroves.

NASA Astrophysics Data System (ADS)

Dittmar, T.; Cooper, W. T.; Koch, B. P.; Kattner, G.

2006-05-01

Organic matter, which is dissolved in low concentrations in the vast waters of the oceans, contains a total amount of carbon similar to atmospheric carbon dioxide. To understand global biogeochemical cycles it is crucial to quantify the sources of marine dissolved organic carbon (DOC). We investigated the impact of mangroves, the dominant intertidal vegetation of the tropics, on marine DOC inventories. Stable carbon- isotopes, ultrahigh-resolution mass spectrometry (FTICRMS), lignin-derived phenols and proton nuclear magnetic resonance spectroscopy showed that mangroves are the main source of terrigenous DOC on the shelf off Northern Brazil. Sunlight efficiently destroyed aromatic molecules during transport offshore, removing about one third of mangrove-derived DOC. The remainder was refractory and may thus be distributed over the oceans. On a global scale, we estimate that mangroves account for more than 10 percent of the terrestrially- derived, refractory DOC transported to the ocean, while they cover less than 0.1 percent of the continents' surface.

Ocean chemistry. Dilution limits dissolved organic carbon utilization in the deep ocean.

PubMed

Arrieta, Jesús M; Mayol, Eva; Hansman, Roberta L; Herndl, Gerhard J; Dittmar, Thorsten; Duarte, Carlos M

2015-04-17

Oceanic dissolved organic carbon (DOC) is the second largest reservoir of organic carbon in the biosphere. About 72% of the global DOC inventory is stored in deep oceanic layers for years to centuries, supporting the current view that it consists of materials resistant to microbial degradation. An alternative hypothesis is that deep-water DOC consists of many different, intrinsically labile compounds at concentrations too low to compensate for the metabolic costs associated to their utilization. Here, we present experimental evidence showing that low concentrations rather than recalcitrance preclude consumption of a substantial fraction of DOC, leading to slow microbial growth in the deep ocean. These findings demonstrate an alternative mechanism for the long-term storage of labile DOC in the deep ocean, which has been hitherto largely ignored. Copyright © 2015, American Association for the Advancement of Science.

Assessing the contribution of wetlands and subsided islands to dissolved organic matter and disinfection byproduct precursors in the Sacramento-San Joaquin River Delta: A geochemical approach

USGS Publications Warehouse

Kraus, T.E.C.; Bergamaschi, B.A.; Hernes, P.J.; Spencer, R.G.M.; Stepanauskas, R.; Kendall, C.; Losee, R.F.; Fujii, R.

2008-01-01

This study assesses how rivers, wetlands, island drains and open water habitats within the Sacramento-San Joaquin River Delta affect dissolved organic matter (DOM) content and composition, and disinfection byproduct (DBP) formation. Eleven sites representative of these habitats were sampled on six dates to encompass seasonal variability. Using a suite of qualitative analyses, including specific DBP formation potential, absorbance, fluorescence, lignin content and composition, C and N stable isotopic compositions, and structural groupings determined using CPMAS (cross polarization, magic angle spinning) 13C NMR, we applied a geochemical fingerprinting approach to characterize the DOM from different Delta habitats, and infer DOM and DBP precursor sources and estimate the relative contribution from different sources. Although river input was the predominant source of dissolved organic carbon (DOC), we observed that 13-49% of the DOC exported from the Delta originated from sources within the Delta, depending on season. Interaction with shallow wetlands and subsided islands significantly increased DOC and DBP precursor concentrations and affected DOM composition, while deep open water habitats had little discernable effect. Shallow wetlands contributed the greatest amounts of DOM and DBP precursors in the spring and summer, in contrast to island drains which appeared to be an important source during winter months. The DOM derived from wetlands and island drains had greater haloacetic acid precursor content relative to incoming river water, while two wetlands contributed DOM with greater propensity to form trihalomethanes. These results are pertinent to restoration of the Delta. Large scale introduction of shallow wetlands, a proposed restoration strategy, could alter existing DOC and DBP precursor concentrations, depending on their hydrologic connection to Delta channels. ?? 2008 Elsevier Ltd.

Shifts in the Source and Composition of Dissolved Organic Matter in Southwest Greenland Lakes Along a Regional Hydro-climatic Gradient

NASA Astrophysics Data System (ADS)

Osburn, Christopher L.; Anderson, Nicholas J.; Stedmon, Colin A.; Giles, Madeline E.; Whiteford, Erika J.; McGenity, Terry J.; Dumbrell, Alex J.; Underwood, Graham J. C.

2017-12-01

Dissolved organic matter (DOM) concentration and quality were examined from Arctic lakes located in three clusters across south-west (SW) Greenland, covering the regional climatic gradient: cool, wet coastal zone; dry inland interior; and cool, dry ice-marginal areas. We hypothesized that differences in mean annual precipitation between sites would result in a reduced hydrological connectivity between lakes and their catchments and that this concentrates degraded DOM. The DOM in the inland lake group was characterized by a lower aromaticity and molecular weight, a low soil-like fluorescence, and carbon stable isotope (δ13C-DOC) values enriched by 2‰ relative to the coastal group. DOC-specific absorbance (SUVA254) and DOC-specific soil-like fluorescence (SUVFC1) revealed seasonal and climatic gradients across which DOM exhibited a dynamic we term "pulse-process": Pulses of DOM exported from soils to lakes during snow and ice melt were followed by pulses of autochthonous DOM inputs (possibly from macrophytes), and their subsequent photochemical and microbial processing. These effects regulated the dynamics of DOM in the inland lakes and suggested that if circumpolar lakes currently situated in cool wetter climatic regimes with strong hydrological connectivity have reduced connectivity under a drier future climate, they may evolve toward an end-point of large stocks of highly degraded DOC, equivalent to the inland lakes in the present study. The regional climatic gradient across SW Greenland and its influence on DOM properties in these lakes provide a model of possible future changes to lake C cycling in high-latitude systems where climatic changes are most pronounced.

Modelling impacts of temperature, and acidifying and eutrophying deposition on DOC trends

NASA Astrophysics Data System (ADS)

Sawicka, Kasia; Rowe, Ed; Evans, Chris; Monteith, Don; Vanguelova, Elena; Wade, Andrew; Clark, Joanna

2017-04-01

Surface water dissolved organic carbon (DOC) concentrations in large parts of the northern hemisphere have risen over the past three decades, raising concern about enhanced contributions of carbon to the atmosphere and seas and oceans. The effect of declining acid deposition has been identified as a key control on DOC trends in soil and surface waters, since pH and ionic strength affect sorption and desorption of DOC. However, since DOC is derived mainly from recently-fixed carbon, and organic matter decomposition rates are considered sensitive to temperature, uncertainty persists regarding the extent to the relative importance of different drivers that affect these upward trends. We ran the dynamic model MADOC (Model of Acidity and Soil Organic Carbon) for a range of UK soils (podzols, gleysols and peatland), for which the time-series were available, to consider the likely relative importance of decreased deposition of sulphate and chloride, accumulation of reactive N, and higher temperatures, on DOC production in different soils. Modelled patterns of DOC change generally agreed favourably with measurements collated over 10-20 years, but differed markedly between sites. While the acidifying effect of sulphur deposition appeared to be the predominant control on the observed soil water DOC trends in all the soils considered other than a blanket peat, the model suggested that over the long term, the effects of nitrogen deposition on N-limited soils may have been sufficient to elevate the DOC recovery trajectory significantly. The second most influential cause of rising DOC in the model simulations was N deposition in ecosystems that are N-limited and respond with stimulated plant growth. Although non-marine chloride deposition made some contribution to acidification and recovery, it was not amongst the main drivers of DOC change. Warming had almost no effect on modelled historic DOC trends, but may prove to be a significant driver of DOC in future via its influence on nutrient availability and productivity. This suggests that current and future DOC concentrations could also exceed preindustrial levels due to the increased productivity of N enriched ecosystems, having important implications for drinking water catchment management and the setting and pursuit of appropriate restoration targets.

Semiconductor Technology and U.S. National Security

DTIC Science & Technology

2010-04-21

control regime as hindrances to compete in the global market.45 Interestingly, DOD’s Defense Technology Security Administration ( DTSA ) reviews export...licenses and only advises DOS or DOC.46 DTSA has neither compliance nor enforcement authority. There is no lead organization or a centralized...which lists several semiconductor technologies, is out of date and not used, even by DOD’s DTSA .51 In order to remove certain export controls on

Long-term anoxia and release of ancient, labile carbon upon thaw of Pleistocene permafrost

USGS Publications Warehouse

Ewing, Stephanie A.; O'Donnell, Jonathan A.; Aiken, George R.; Butler, Kenna D.; Butman, David; Windham-Myers, Lisamarie; Kanevskiy, Mikhail

2015-01-01

The fate of permafrost carbon upon thaw will drive feedbacks to climate warming. Here we consider the character and context of dissolved organic carbon (DOC) in yedoma permafrost cores from up to 20 m depth in central Alaska. We observed high DOC concentrations (4 to 129 mM) and consistent low molecular weight organic acid concentrations in three cores. We estimate a DOC production rate of 12 µmol DOC m−2 yr−1 based on model ages of up to ~200 kyr derived from uranium isotopes. Acetate C accounted for 24 ± 1% of DOC in all samples. This proportion suggests long-term anaerobiosis and is likely to influence thaw outcomes due to biolability of acetate upon release in many environments. The combination of uranium isotopes, ammonium concentrations, and calcium concentrations explained 86% of the variation in thaw water DOC concentrations, suggesting that DOC production may be related to both reducing conditions and mineral dissolution over time.

Representation of riverine DOC within a GCM: First framework for coupling soil carbon and lateral hydrology in MPI-ESM

NASA Astrophysics Data System (ADS)

Brovkin, V.; Gehlot, S.; Hagemann, S.

2017-12-01

The current state of the art General Circulation Models (GCMs) do not consider the lateral transport of dissolved organic carbon (DOC) from land to ocean via rivers/streams and the global carbon budget is primarily evaluated based only on vertical gas exchange processes between land or ocean carbon reservoirs. In high latitudes, the permafrost plays an important role in contributing to riverine organic carbon. Moreover, the vertical gas exchange processes are active during the lateral riverine carbon transport but are not considered in the impact of thawing permafrost on global climate. The interplay between permafrost and lateral hydrology is a substantial factor impacting the organic carbon inflow to the Arctic and its associated atmospheric exchange. In this research, we propose a framework of coupling the soil carbon transport via rivers using the hydrological discharge scheme (HD-Model) of MPI-ESM (Max-Planck Institute for Meteorology Earth System Model). The soil carbon classification is based on the solubility (YASSO soil carbon pools) and their subsequent attribution to the dissolved organic carbon via runoff (fast carbon pool) and baseflow (slow carbon pool). The HD-model, which simulates the river discharge for all land areas at a resolution of 0.5 degree, will be modified with inclusion of the DOC as tracer over test areas. Evaluation of DOC transport scheme is intended at reservoir level via available site measurements. The analysis will include global river networks for organic carbon transport with focus on permafrost and high latitude areas. Decomposition of DOC en-route land to ocean via vertical gas exchange processes will be included.

Spatiotemporal Variation of Dissolved Carbon in Semi-humid/arid Inland Waters: A Case Study from Songnen Plain, China

NASA Astrophysics Data System (ADS)

Song, K.; Li, L.; Zang, S.; Zhao, Y.

2012-12-01

Spatial and seasonal variations of dissolved organic carbon (DOC) and inorganic carbon (DIC) in 34 waters across the semi-humid/arid Songnen Plain, China were examined with 320 samples collected in 2011-2012. Large variations in both the concentration and quality of DOC are revealed, ranging from 0.47 mgL-1 to 720 mgL-1, which is mainly caused by the hydro-climatic condition in the plain. Large variations of DOC and DIC concentrations are observed between open (mean ± sd: 5.6 ± 2.4 mgL-1, 57.4 ± 34.7 mgL-1) and closed lakes (43.3 ± 7.9 mgL-1, 172.9 ± 113.3 mgL-1). Temporally, higher DOC and DIC concentrations are measured for ice-underlying water in winter than ice-free seasons. Colored dissolved organic matter (CDOM) and DOC concentrations are higher after high discharge events with terrigenous sources of CDOM/DOC dominated, while autochthonous sources also contributed to CDOM/DOC concentrations during algal bloom seasons. An interesting result of this study is that the non-outflow conditions for various water catchments had condensed effects on the dissolved carbon, resulting in close relationships between salinity and dissolved carbon parameters, e.g. salinity vs DOC (R2 = 0.83, p < 0.001), DIC (R2 = 0.96, p < 0.0001) using data set collected in 2011. Independent data set collected in May 2012 also confirmed this finding, yielding high correlation for salinity vs DOC (R2 = 0.79, p < 0.001), salinity vs DIC (R2 = 0.91, p < 0.0001), highlighting the potential of quantifying DOC/DIC from salinity measurements for thousand of waters dispersed in the semi-arid Songnen Plain. Indices based on CDOM absorption spectra, e.g. E250:365, DOC specific CDOM absorption (SUVA254) and spectral slope ratio (Sr, S275-295/S350-400), were applied to characterize DOM components and sources. Our results indicate high molecular weight CDOM fractions are more abundant in open waters than closed waters.

Vegetation and climate controls on potential CO2, DOC and DON production in northern latitude soils

USGS Publications Warehouse

Neff, J.C.; Hooper, D.U.

2002-01-01

Climatic change may influence decomposition dynamics in arctic and boreal ecosystems, affecting both atmospheric CO2 levels, and the flux of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) to aquatic systems. In this study, we investigated landscape-scale controls on potential production of these compounds using a one-year laboratory incubation at two temperatures (10?? and 30??C). We measured the release of CO2, DOC and DON from tundra soils collected from a variety of vegetation types and climatic regimes: tussock tundra at four sites along a latitudinal gradient from the interior to the north slope of Alaska, and soils from additional vegetation types at two of those sites (upland spruce at Fairbanks, and wet sedge and shrub tundra at Toolik Lake in northern Alaska). Vegetation type strongly influenced carbon fluxes. The highest CO2 and DOC release at the high incubation temperature occurred in the soils of shrub tundra communities. Tussock tundra soils exhibited the next highest DOC fluxes followed by spruce and wet sedge tundra soils, respectively. Of the fluxes, CO2 showed the greatest sensitivity to incubation temperatures and vegetation type, followed by DOC. DON fluxes were less variable. Total CO2 and total DOC release were positively correlated, with DOC fluxes approximately 10% of total CO2 fluxes. The ratio of CO2 production to DOC release varied significantly across vegetation types with Tussock soils producing an average of four times as much CO2 per unit DOC released compared to Spruce soils from the Fairbanks site. Sites in this study released 80-370 mg CO2-C g soil C-1 and 5-46 mg DOC g soil C-1 at high temperatures. The magnitude of these fluxes indicates that arctic carbon pools contain a large proportion of labile carbon that could be easily decomposed given optimal conditions. The size of this labile pool ranged between 9 and 41% of soil carbon on a g soil C basis, with most variation related to vegetation type rather than climate.

An effective method of UV-oxidation of dissolved organic carbon in natural waters for radiocarbon analysis by accelerator mass spectrometry

NASA Astrophysics Data System (ADS)

Xue, Yuejun; Ge, Tiantian; Wang, Xuchen

2015-12-01

Radiocarbon (14C) measurement of dissolved organic carbon (DOC) is a very powerful tool to study the sources, transformation and cycling of carbon in the ocean. The technique, however, remains great challenges for complete and successful oxidation of sufficient DOC with low blanks for high precision carbon isotopic ratio analysis, largely due to the overwhelming proportion of salts and low DOC concentrations in the ocean. In this paper, we report an effective UV-Oxidation method for oxidizing DOC in natural waters for radiocarbon analysis by accelerator mass spectrometry (AMS). The UV-oxidation system and method show 95%±4% oxidation efficiency and high reproducibility for DOC in both river and seawater samples. The blanks associated with the method was also low (about 3 µg C) that is critical for 14C analysis. As a great advantage of the method, multiple water samples can be oxidized at the same time so it reduces the sample processing time substantially compared with other UV-oxidation method currently being used in other laboratories. We have used the system and method for 14C studies of DOC in rivers, estuaries, and oceanic environments and have received promise results.

Transport and Degradation of Dissolved Organic Matter and Associated Freshwater Pathways in the Laptev Sea (Siberian Arctic)

NASA Astrophysics Data System (ADS)

Hoelemann, J. A.; Janout, M. A.; Koch, B.; Bauch, D.; Novikhin, A.; Heim, B.; Eulenburg, A.; Kassens, H.; Timokhov, L.

2016-02-01

The Siberian shelves are seasonally ice-covered and characterized by large freshwater runoff rates from some of the largest rivers on earth. These rivers also provide a considerable amount of dissolved organic carbon (DOC) to the Arctic Ocean. With an annual load of about 6 Tg DOC a-1 the Lena River contributes nearly 20 percent of the annual DOC discharge to the Arctic Ocean. We present a comprehensive dataset collected during multiple Laptev Sea expeditions carried out in spring, summer and fall (2010-15) in order to explore the processes controlling the dispersal and degradation of DOM during the river water's passage across the shelf. Our investigations are focused on CDOM (Colored Dissolved Organic Matter), which resembles the DOC concentration, interacts with solar radiation and forms a major fraction of the organic matter pool. Our results show an inverse correlation between salinity and CDOM, which emphasizes its terrigenous source. Further, the spectral slope of CDOM absorption indicates that photochemical bleaching is the main process that reduces the CDOM absorption ( 20%) in freshwater along its transport across the shelf. The distribution of the Lena river water is primarily controlled by winds in summer. During summers with easterly or southerly winds, the plume remains on the central and northern Laptev shelf, and is available for export into the Arctic Basin. The CDOM-rich river water increases the absorption of solar radiation and enhances warming of a shallow surface layer. This emphasizes the importance of CDOM for sea surface temperatures and lateral ice melt on the shelf and adjacent basin. DOC concentrations in freshwater vary seasonally and become larger with increasing discharge. Our data indicate that the CDOM concentrations are highest during the freshet when landfast ice is still present. Subsequent mixing with local sea ice meltwater lowers CDOM to values that are characteristic for the Lena freshwater during the rest of the year.

Transport and degradation of dissolved organic matter and associated freshwater pathways in the Laptev Sea (Siberian Arctic)

NASA Astrophysics Data System (ADS)

Hoelemann, Jens; Janout, Markus; Koch, Boris; Bauch, Dorothea; Hellmann, Sebastian; Eulenburg, Antje; Heim, Birgit; Kassens, Heidemarie; Timokhov, leonid

2016-04-01

The Siberian shelves are seasonally ice-covered and characterized by large freshwater runoff rates from some of the largest rivers on earth. These rivers also provide a considerable amount of dissolved organic carbon (DOC) to the Arctic Ocean. With an annual load of about 6 Tg DOC a-1 the Lena River contributes nearly 20 percent of the annual DOC discharge to the Arctic Ocean. We present a comprehensive dataset collected during multiple Laptev Sea expeditions carried out in spring, summer and fall (2010-15) in order to explore the processes controlling the dispersal and degradation of DOM during the river water's passage across the shelf. Our investigations are focused on CDOM (Colored Dissolved Organic Matter), which resembles the DOC concentration, interacts with solar radiation and forms a major fraction of the organic matter pool. Our results show an inverse correlation between salinity and CDOM, which emphasizes its terrigenous source. Further, the spectral slope of CDOM absorption indicates that photochemical bleaching is the main process that reduces the CDOM absorption (~ 20%) in freshwater along its transport across the shelf. The distribution of the Lena river water is primarily controlled by winds in summer. During summers with easterly or southerly winds, the plume remains on the central and northern Laptev shelf, and is available for export into the Arctic Basin. The CDOM-rich river water increases the absorption of solar radiation and enhances warming of a shallow surface layer. This emphasizes the importance of CDOM for sea surface temperatures and lateral ice melt on the shelf and adjacent basin. DOC concentrations in freshwater vary seasonally and become larger with increasing discharge. Our data indicate that the CDOM concentrations are highest during the freshet when landfast ice is still present. Subsequent mixing with local sea ice meltwater lowers CDOM to values that are characteristic for the Lena freshwater during the rest of the year.

Transformation of molecular weight distributions of dissolved organic carbon and UV-absorbing compounds at full-scale wastewater-treatment plants.

PubMed

Esparza-Soto, Mario; Fox, Peter; Westerhoff, Paul

2006-03-01

The molecular-weight distribution (MWD) of wastewater dissolved-organic carbon (DOC) was determined in samples from seven full-scale wastewater-treatment plants (WWTPs) that use different biological treatments (air activated sludge [air-AS], pure-oxygen AS [O2-AS], and trickling filters). The research objective was to determine how different biological treatments influenced the MWD of wastewater DOC. Primary sedimentation effluent DOC from most of the WWTPs exhibited a skewed distribution toward the low-molecular-weight fraction (MWF) (40 to 50%, < 0.5 K Daltons [KDa]). The Air-AS effluent DOC exhibited a centrally clustered distribution, with the majority of DOC in the intermediate MWF (0.5 to 3 KDa). The O2-AS effluent DOC exhibited a skewed distribution toward the high MWF (> 3 KDa). The removal of DOC by air- and O2-AS bacteria followed trends predicted by a macromolecule degradation model. Trickling-filter effluent DOC exhibited a skewed distribution toward the high MWF (50% DOC, > 3 KDa).

Effect of Photochemical Transformation on Dissolved Organic Carbon Concentration and Bioavailability from Watersheds with Varying Landcover

NASA Astrophysics Data System (ADS)

Vermilyea, A.; Sanders, A.; Vazquez, E.

2017-12-01

The transformation of freshwater dissolved organic carbon (DOC) can have important implications for water quality, aquatic ecosystem health, and our climate. DOC is an important nutrient for heterotrophic microorganisms near the base of the aquatic food chain and the extent of conversion of DOC to CO2 is a critical piece of the global carbon cycle. Photochemical pathways have the potential to transform recalcitrant DOC into more labile forms that can then be converted to smaller DOC molecules and eventually be completely mineralized to CO2. This may lead to a DOC pool with different bioavailability depending on the structural composition of the original DOC pool and the mechanistic pathways undergone during transformation. This study aimed to measure the changes in DOC concentration and bioavailability due solely to photochemical processes in three watersheds of northern Vermont, USA that have varied land cover, land use (LCLU) attributes. Our hypothesis was that photochemical transformations will lead to (1) an overall loss of DOC due to mineralization to CO2 and (2) a relative increase in the bioavailable fraction of DOC. Additionally, the influence of LCLU and base flow versus storm flow on both mineralization rates and changes in DOC bioavailability was investigated. Irradiation of filtered samples in quartz vessels under sunlight led to small changes in DOC concentration over time, but significant changes in DOC bioavailability. In general, fluorescence excitation-emission matrices (EEMs) showed a shift from an initially more humic-like DOC pool, to a more protein-like (bioavailable) DOC pool. Specific UV index (SUVA) along with bioavailable DOC (BDOC) incubations were also used to characterize DOC and its bioavailability. There were only small differences in the DOC transformation that took place among sites, possibly due to only small differences in the initial bioavailability and fluorescent properties between water samples. Photochemical transformation appears to play an important role in the transformation of a more recalcitrant (humic) pool of DOC into a more bioavailable DOC pool that can then be utilized by aquatic heterotrophs and ultimately be converted to CO2.

Dissolved organic carbon in rainwater from areas heavily impacted by sugar cane burning

NASA Astrophysics Data System (ADS)

Coelho, C. H.; Francisco, J. G.; Nogueira, R. F. P.; Campos, M. L. A. M.

This work reports on rainwater dissolved organic carbon (DOC) from Ribeirão Preto (RP) and Araraquara over a period of 3 years. The economies of these two cities, located in São Paulo state (Brazil), are based on agriculture and related industries, and the region is strongly impacted by the burning of sugar cane foliage before harvesting. Highest DOC concentrations were obtained when air masses traversed sugar cane fields burned on the same day as the rain event. Significant increases in the DOC volume weighted means (VWM) during the harvest period, for both sites, and a good linear correlation ( r = 0.83) between DOC and K (a biomass burning marker) suggest that regional scale organic carbon emissions prevail over long-range transport. The DOC VWMs and standard deviations were 272 ± 22 μmol L -1 ( n = 193) and 338 ± 40 μmol L -1 ( n = 80) for RP and Araraquara, respectively, values which are at least two times higher than those reported for other regions influenced by biomass burning, such as the Amazon. These high DOC levels are discussed in terms of agricultural activities, particularly the large usage of biogenic fuels in Brazil, as well as the analytical method used in this work, which includes volatile organic carbon when reporting DOC values. Taking into account rainfall volume, estimated annual rainwater DOC fluxes for RP (4.8 g C m -2 yr -1) and Araraquara (5.4 g C m -2 yr -1) were close to that previously found for the Amazon region (4.8 g C m -2 yr -1). This work also discusses whether previous calculations of the global rainwater carbon flux may have been underestimated, since they did not consider large inputs from biomass combustion sources, and suffered from a possible analytical bias.

Regulation causes nitrogen cycling discontinuities in Mediterranean rivers.

PubMed

von Schiller, Daniel; Aristi, Ibon; Ponsatí, Lídia; Arroita, Maite; Acuña, Vicenç; Elosegi, Arturo; Sabater, Sergi

2016-01-01

River regulation has fundamentally altered large sections of the world's river networks. The effects of dams on the structural properties of downstream reaches are well documented, but less is known about their effect on river ecosystem processes. We investigated the effect of dams on river nutrient cycling by comparing net uptake of total dissolved nitrogen (TDN), phosphorus (TDP) and organic carbon (DOC) in river reaches located upstream and downstream from three reservoir systems in the Ebro River basin (NE Iberian Peninsula). Increased hydromorphological stability, organic matter standing stocks and ecosystem metabolism below dams enhanced the whole-reach net uptake of TDN, but not that of TDP or DOC. Upstream from dams, river reaches tended to be at biogeochemical equilibrium (uptake≈release) for all nutrients, whereas river reaches below dams acted as net sinks of TDN. Overall, our results suggest that flow regulation by dams may cause relevant N cycling discontinuities in rivers. Higher net N uptake capacity below dams could lead to reduced N export to downstream ecosystems. Incorporating these discontinuities could significantly improve predictive models of N cycling and transport in complex river networks. Copyright © 2015. Published by Elsevier B.V.

Dissolved Organic Carbon along the Louisiana coast from MODIS and MERIS satellite data

NASA Astrophysics Data System (ADS)

Chaichi Tehrani, N.; D'Sa, E. J.

2012-12-01

Dissolved organic carbon (DOC) plays a critical role in the coastal and ocean carbon cycle. Hence, it is important to monitor and investigate its the distribution and fate in coastal waters. Since DOC cannot be measured directly through satellite remote sensors, chromophoric dissolved organic matter (CDOM) as an optically active fraction of DOC can be used as an alternative proxy to trace DOC concentrations. Here, satellite ocean color data from MODIS, MERIS, and field measurements of CDOM and DOC were used to develop and assess CDOM and DOC ocean color algorithms for coastal waters. To develop a CDOM retrieval algorithm, empirical relationships between CDOM absorption coefficient at 412 nm (aCDOM(412)) and reflectance ratios Rrs(488)/Rrs(555) for MODIS and Rrs(510)/Rrs(560) for MERIS were established. The performance of two CDOM empirical algorithms were evaluated for retrieval of (aCDOM(412)) from MODIS and MERIS in the northern Gulf of Mexico. Further, empirical algorithms were developed to estimate DOC concentration using the relationship between in situ aCDOM(412) and DOC, as well as using the newly developed CDOM empirical algorithms. Accordingly, our results revealed that DOC concentration was strongly correlated to aCDOM (412) for summer and spring-winter periods (r2 = 0.9 for both periods). Then, using the aCDOM(412)-Rrs and the aCDOM(412)-DOC relationships derived from field measurements, a relationship between DOC-Rrs was established for MODIS and MERIS data. The DOC empirical algorithms performed well as indicated by match-up comparisons between satellite estimates and field data (R2=0.52 and 0.58 for MODIS and MERIS for summer period, respectively). These algorithms were then used to examine DOC distribution along the Louisiana coast.

Just Around the Riverbend: Seasonal hydrologic controls on dynamic hyporheic zone redox biogeochemistry

NASA Astrophysics Data System (ADS)

Saup, C. M.; Sawyer, A. H.; Williams, K. H.; Wilkins, M.

2017-12-01

Upland rivers host exceptionally strong linkages between the terrestrial and aquatic elemental cycles. The weathering of mineral phases, coupled with degradation of organic matter and anthropogenic influences can result in the export of carbon, metals, and nutrients in upland fluvial systems, often decreasing downstream water quality with negative impacts on both human usage and ecosystem functioning. Within these fluvial networks, zones of hyporheic mixing—regions within the riverbed where surface water and groundwater mix—are thought to represent hotspots of biogeochemical activity, thus exerting significant control over elemental cycling and solute export. To investigate how the deeper exchange of oxic river water into the riverbed during snowmelt-driven peak discharge affects microbial degradation (oxidation) of carbon pools, depth resolved pore water samples were recovered from multiple locations around a representative meander on the East River near Crested Butte, CO. At each location, a series of temperature and redox probes were installed in the riverbed to track the extent of hyporheic mixing and the impact of this process on riverbed biogeochemistry. We complemented this real-time data with discrete samples collected during peak flow, intermediate flow, and base flow at a 10 cm resolution over 70 cm vertical profiles for a suite of microbiological and geochemical analyses. Results revealed elevated pore fluid concentrations of dissolved metals and recalcitrant DOC species under reducing conditions induced by base flow, while regions that were more influenced by down-welling oxic surface water hosted distinct microbial communities and lower metal concentrations. Overall, our results indicate that mixing-driven vertical redox gradients exert a strong control on biogeochemical processing in riverbeds, with implications for downstream water quality and solute export from watersheds.

Size and XAD fractionations of trihalomethane precursors from soils.

PubMed

Chow, Alex T; Guo, Fengmao; Gao, Suduan; Breuer, Richard S

2006-03-01

Soil organic matter is an important source of allochthonous dissolved organic matter inputs to the Sacramento-San Joaquin Delta waterways, which is a drinking water source for 22 million people in California, USA. Knowledge of trihalomethane (THM) formation potential of soil-derived organic carbon is important for developing effective strategies for organic carbon removal in drinking water treatment. In this study, soil organic carbon was extracted with electrolytes (deionized H2O and Na- or Ca-based electrolytes) of electrical conductivity bracketing those found in Delta leaching and runoff conditions. The extracts were physically and chemically separated into different fractions: colloidal organic carbon (0.45-0.1 microm), fine colloidal organic carbon (0.1-0.025 microm), and dissolved organic carbon (DOC) (<0.025 microm); hydrophobic acid (HPOA), transphilic acid, and hydrophilic acid. Two representative Delta soils, Rindge Muck (a peat soil) and Scribner Clay Loam (a mineral soil) were examined. Results showed that less than 2% of soil organic carbon was electrolyte-extractable and heterogeneous organic fractions with distinct THM reactivity existed. Regardless of soil and electrolytes, DOC and HPOA fractions were dominant in terms of total concentration and THMFP. The amounts of extractable organic carbon and THMFP were dependent on the cation and to a lesser extent on electrical conductivity of electrolytes. Along with our previous study on temperature and moisture effects on DOC production, we propose a conceptual model to describe the impacts of agricultural practices on DOC production in the Delta. DOC is mainly produced in the surface peat soils during the summer and is immobilized by accumulated salt in the soils. DOC is leached from soils to drainage ditches and finally to the Delta channels during winter salt leaching practices.

Concentration, UV-spectroscopic characteristics and fractionation of DOC in stormflow from an urban stream, Southern California, USA

USGS Publications Warehouse

Izbicki, J.A.; Pimentel, I.M.; Johnson, Russell; Aiken, G.R.; Leenheer, J.

2007-01-01

The composition of dissolved organic carbon (DOC) in stormflow from urban areas has been greatly altered, both directly and indirectly, by human activities and there is concern that there may be public health issues associated with DOC, which has unknown composition from different sources within urban watersheds. This study evaluated changes in the concentration and composition of DOC in stormflow in the Santa Ana River and its tributaries between 1995 and 2004 using a simplified approach based on the differences in the optical properties of DOC and using operationally defined differences in molecular weight and solubility. The data show changes in the composition of DOC in stormflow during the rainy season and differences associated with runoff from different parts of the basin, including extensive upland areas burned prior to the 2004 rainy season.Samples were collected from the Santa Ana River, which drains ~6950 km2 of the densely populated coastal area of southern California, during 23 stormflows between 1995 and 2004. Dissolved organic carbon (DOC) concentrations during the first stormflows of the ‘winter’ (November to March) rainy season increased rapidly with streamflow and were positively correlated with increased faecal indicator bacteria concentrations. DOC concentrations were not correlated with streamflow or with other constituents during stormflows later in the rainy season and DOC had increasing UV absorbance per unit carbon as the rainy season progressed. DOC concentrations in stormflow from an urban drain tributary to the river also increased during stormflow and were greater than concentrations in the river. DOC concentrations in stormflow from a tributary stream, draining urban and agricultural land that contained more than 320 000 animals, mostly dairy cows, were higher than concentrations in stormflow from the river and from the urban drain. Fires that burned large areas of the basin before the 2004 rainy season did not increase DOC concentrations in the river during stormflow after the fires – possibly because the large watershed of the river damped the effect of the fires. However, the fires increased the hydrophobic neutral organic carbon fraction of DOC in stormflow from the urban drain and the tributary stream.

Microbial decomposition of marine dissolved organic matter in cool oceanic crust

NASA Astrophysics Data System (ADS)

Shah Walter, Sunita R.; Jaekel, Ulrike; Osterholz, Helena; Fisher, Andrew T.; Huber, Julie A.; Pearson, Ann; Dittmar, Thorsten; Girguis, Peter R.

2018-05-01

Marine dissolved organic carbon (DOC) is one of the largest active reservoirs of reduced carbon on Earth. In the deep ocean, DOC has been described as biologically recalcitrant and has a radiocarbon age of 4,000 to 6,000 years, which far exceeds the timescale of ocean overturning. However, abiotic removal mechanisms cannot account for the full magnitude of deep-ocean DOC loss. Deep-ocean water circulates at low temperatures through volcanic crust on ridge flanks, but little is known about the associated biogeochemical processes and carbon cycling. Here we present analyses of DOC in fluids from two borehole observatories installed in crustal rocks west of the Mid-Atlantic Ridge, and show that deep-ocean DOC is removed from these cool circulating fluids. The removal mechanism is isotopically selective and causes a shift in specific features of molecular composition, consistent with microbe-mediated oxidation. We suggest organic molecules with an average radiocarbon age of 3,200 years are bioavailable to crustal microbes, and that this removal mechanism may account for at least 5% of the global loss of DOC in the deep ocean. Cool crustal circulation probably contributes to maintaining the deep ocean as a reservoir of `aged' and refractory DOC by discharging the surviving organic carbon constituents that are molecularly degraded and depleted in 14C and 13C into the deep ocean.

High light intensity mediates a shift from allochthonous to autochthonous carbon use in phototrophic stream biofilms

NASA Astrophysics Data System (ADS)

Wagner, Karoline; Bengtsson, Mia M.; Findlay, Robert H.; Battin, Tom J.; Ulseth, Amber J.

2017-07-01

Changes in the riparian vegetation along stream channels, diurnal light availability, and longitudinal fluctuations in the local light regime in streams influence primary production and carbon (C) cycling in benthic stream biofilms. To investigate the influence of light availability on the uptake dynamics of autochthonous and allochthonous dissolved organic carbon (DOC) in benthic biofilms, we experimentally added 13C-labeled allochthonous DOC to biofilms grown under light intensities ranging from 5 to 152 μmol photons m-2 s-1. We calculated the net C flux, which showed that benthic biofilms released autochthonous DOC across the entire light gradient. Light availability and diurnal light patterns influenced C uptake by benthic biofilms. More allochthonous DOC was respired under low light availability and at night, whereas under high light availability and during the day mainly autochthonous C was respired by the benthic biofilm community. Furthermore, phenol oxidase activity (indicative of allochthonous DOC uptake) was more elevated under low light availability, whereas beta-glucosidase activity (indicative of autochthonous DOC use) increased with light intensity. Collectively, our results suggest that biofilms exposed to high light inputs preferentially used autochthonous DOC, whereas biofilms incubated at attenuated levels showed greater use of allochthonous DOC. This has implications for the spatial dynamics of DOC uptake in streams and speaks against the occurrence of priming effects in algal-dominated stream biofilms.

Atmospheric Inputs of Mercury and Organic Carbon into a Forested Upland/Bog Watershed

Treesearch

Randall K. Kolka; E.A. Nater; D.F. Grigal; E.S. Verry

1999-01-01

Inputs of mercury (Hg) and dissolved organic carbon (DOC) in throughfall and stemflow waters were measured for an upland/bog watershed in northern Minnesota, and were compared to the deposition in a nearby opening to determine the influence of tree canopies on Hg and DOC deposition. Twice as much Hg and seven times as much DOC was deposited in the forested watershed...

The Influence of Water Circulation on Dissolved Organic Matter Dynamics in Bald Head Creek

NASA Astrophysics Data System (ADS)

Lebrasse, M. C.; Osburn, C. L.; Bohnenstiehl, D. R.; He, R.

2016-12-01

Dissolved organic matter (DOM) plays an important role in biogeochemical cycles in estuaries such as tidal creeks draining coastal wetlands such as salt marshes. However, significant knowledge gaps remain regarding the quantity and quality of the DOM that tidally exchanges between salt marshes and their adjacent estuaries. Tidal movements play a central role in lateral exchanges of materials and bidirectional flow results in the mixing of DOM from marsh plants and estuarine DOM. The aim of this study was to better understand the role of water circulation on the distribution and quality of DOM in Bald Head Creek, a tributary to the Cape Fear River estuary in eastern North Carolina. Dissolved organic carbon (DOC) concentration, stable carbon isotopes, and chromophoric DOM (CDOM) absorbance at 254 nm (a254) were used to distinguish between DOM quantity and quality at three locations along the creek: Site 3 (upstream), Site 2 (middle stream), and Site 1 (near the creek mouth). Samples were collected over four tidal cycles between March-August 2016 and compared to time series data collected approximately weekly from 2014-2016. DOM characteristics differed substantially over the tidal cycle. Higher CDOM and DOC concentration were observed at low tide than at high tide at all three sites, suggesting greater export of carbon from the marsh into the creek as the tides recede. Analysis of CDOM quality based on specific UV absorbance at 254 nm (SUVA254) and spectral slope ratio (SR) showed that the marsh end-member (Site 3) source of DOM had greater aromaticity and higher molecular weight. Site 1 showed greater variability over the tidal cycle most likely due to a greater tidal influence, being closer to the mouth. Additionally, an unmanned surface vehicle (USV) and a hydrodynamic model were used to map water circulation and DOC concentration along the creek to compute exchanges with the adjacent estuary. Results suggest that estuarine OM dynamics are strongly controlled by the circulation of water, especially for tidal creeks where tidal pumping can dominate lateral fluxes of DOM to adjacent waters.

Variations in abundance and size distribution of carbohydrates in the lower Mississippi River, Pearl River and Bay of St Louis

NASA Astrophysics Data System (ADS)

Wang, Xuri; Cai, Yihua; Guo, Laodong

2013-07-01

Riverine export of dissolved and particulate organic matter to the sea is one of the major components in marine carbon cycles, affecting biogeochemical processes in estuarine and coastal regions. However, the detailed composition of organic material and the relative partitioning among the dissolved, colloidal, and particulate phases are poorly quantified. The abundance of carbohydrate species and their partitioning among dissolved, colloidal, and particulate phases were examined in the waters from the lower Mississippi River (MR), the lower Pearl River (PR), and the Bay of St. Louis (BSL). Particulate carbohydrates (PCHO) represented a small fraction of the particulate organic carbon (POC) pool, with 4.7 ± 3.1%, 4.5 ± 2.4% and 1.8 ± 0.83% in the MR, PR, and BSL, respectively. Dissolved carbohydrates (DCHO) were a major component of the bulk dissolved organic carbon (DOC) pool, comprising 23%, 35%, and 18% in the MR, PR, and BSL, respectively. Differences in the DCHO/DOC ratio between the MR, PR, and BSL were related to their distinct characteristics in drainage basins, anthropogenic impacts, and hydrological conditions, reflecting differences in sources and composition of organic matter in different aquatic environments. Within the total carbohydrates (TCHO) pool, the high-molecular-weight carbohydrates (HMW-CHO, 1 kDa-0.45 μm) were the dominant species, representing 52-71% of the TCHO pool, followed by the low-molecular-weight carbohydrates (LMW-CHO, <1 kDa), representing 14-44% of the TCHO. The PCHO accounted for 4-16% of the bulk TCHO. Variations in the size distribution of carbohydrates among the MR, PR, and BSL were closely linked to the cycling pathway of organic matter and the interactions between different size fractions of the carbohydrates.

Effects of native perennial vegetation buffer strips on dissolved organic carbon in surface runoff from an agricultural landscape

Treesearch

Tomorra E. Smith; Randall K. Kolka; Xiaobo Zhou; Matthew J. Helmers; Richard M. Cruse; Mark D. Tomer

2014-01-01

Dissolved organic carbon (DOC) constitutes a small yet important part of a watershed's carbon budget because it is mobile and biologically active. Agricultural conservation practices such as native perennial vegetation (NPV) strips will influence carbon cycling of an upland agroecosystem, and could affect how much DOC enters streams in runoff, potentially...

Measurement and importance of dissolved organic carbon. Chapter 13

Treesearch

Randall Kolka; Peter Weishampel; Mats Froberg

2008-01-01

The flux of dissolved organic carbon (DOC) from an ecosystem can be a significant component of carbon (C) budgets especially in watersheds containing wetlands. Although internal ecosystem cycling of DOC is generally greater than the fluxes to ground or surface waters, it is the transport out of the system that is a main research focus for carbon accounting. In...

Effects of Land Use on Stable Carbon Isotopic Composition and Concentration of Dissolved Organic Carbon (DOC) and Dissolved Inorganic Carbon (DIC) in Southeastern US Piedmont Headwater Streams

EPA Science Inventory

Stable carbon isotopic composition (delta 13C) and concentrations of DOC and DIC were measured in stream water samples collected monthly in 15 headwater streams from an area with extensive poultry and cattle production and a rapidly growing human population. Linear regression te...

Estimating dissolved organic carbon concentration in turbid coastal waters using optical remote sensing observations

NASA Astrophysics Data System (ADS)

Cherukuru, Nagur; Ford, Phillip W.; Matear, Richard J.; Oubelkheir, Kadija; Clementson, Lesley A.; Suber, Ken; Steven, Andrew D. L.

2016-10-01

Dissolved Organic Carbon (DOC) is an important component in the global carbon cycle. It also plays an important role in influencing the coastal ocean biogeochemical (BGC) cycles and light environment. Studies focussing on DOC dynamics in coastal waters are data constrained due to the high costs associated with in situ water sampling campaigns. Satellite optical remote sensing has the potential to provide continuous, cost-effective DOC estimates. In this study we used a bio-optics dataset collected in turbid coastal waters of Moreton Bay (MB), Australia, during 2011 to develop a remote sensing algorithm to estimate DOC. This dataset includes data from flood and non-flood conditions. In MB, DOC concentration varied over a wide range (20-520 μM C) and had a good correlation (R2 = 0.78) with absorption due to coloured dissolved organic matter (CDOM) and remote sensing reflectance. Using this data set we developed an empirical algorithm to derive DOC concentrations from the ratio of Rrs(412)/Rrs(488) and tested it with independent datasets. In this study, we demonstrate the ability to estimate DOC using remotely sensed optical observations in turbid coastal waters.

Development of a combined isotopic and mass-balance approach to determine dissolved organic carbon sources in eutrophic reservoirs.

PubMed

Pierson-Wickmann, Anne-Catherine; Gruau, Gérard; Jardé, Emilie; Gaury, Nicolas; Brient, Luc; Lengronne, Marion; Crocq, André; Helle, Daniel; Lambert, Thibault

2011-04-01

A combined mass-balance and stable isotope approach was set up to identify and quantify dissolved organic carbon (DOC) sources in a DOC-rich (9mgL(-1)) eutrophic reservoir located in Western France and used for drinking water supply (so-called Rophemel reservoir). The mass-balance approach consisted in measuring the flux of allochthonous DOC on a daily basis, and in comparing it with the effective (measured) DOC concentration of the reservoir. The isotopic approach consisted, for its part, in measuring the carbon isotope ratios (δ(13)C values) of both allochthonous and autochthonous DOC sources, and comparing these values with the δ(13)C values of the reservoir DOC. Results from both approaches were consistent pointing out for a DOC of 100% allochthonous origin. In particular, the δ(13)C values of the DOC recovered in the reservoir (-28.5±0.2‰; n=22) during the algal bloom season (May-September) showed no trace of an autochthonous contribution (δ(13)C in algae=-30.1±0.3‰; n=2) being indistinguishable from the δ(13)C values of allochthonous DOC from inflowing rivers (-28.6±0.1‰; n=8). These results demonstrate that eutrophication is not responsible for the high DOC concentrations observed in the Rophemel reservoir and that limiting eutrophication of this reservoir will not reduce the potential formation of disinfection by-products during water treatment. The methodology developed in this study based on a complementary isotopic and mass-balance approach provides a powerful tool, suitable to identify and quantify DOC sources in eutrophic, DOC-contaminated reservoirs. Copyright © 2010 Elsevier Ltd. All rights reserved.

Degraded Litter Leachates as a Potential Control on Streamwater Nitrogen Dynamics

NASA Astrophysics Data System (ADS)

Hernes, P. J.; O'Geen, A. T.; Dahlgren, R. A.

2008-12-01

Dissolved organic nitrogen (DON) export from catchments is a critical element of overall nutrient cycling. An underlying assumption in most studies investigating DON export is that the source of this DON is from an aged soil organic matter (SOM) pool. However, recent investigations of dissolved organic carbon (DOC) have called into question the idea that dissolved organic matter (DOM) in streams is derived primarily from aged SOM. Evidence includes riverine DOC 14C ages (~5 years) that are much younger than SOM within the catchment as well as the riverine particulate organic matter (POM) pool (decades to 100s of years). Molecular fractionation due to litter leaching and sorption to mineral surfaces can completely account for the degraded molecular signatures observed in dissolved amino acid and dissolved lignin compositions within the DOM pool. Thus it is feasible that a significant portion of exported DON from catchments could come from a younger, less degraded organic matter pool such as litters. To evaluate this potential, we conducted a leaching incubation experiment using litters and degraded "duff" litters (estimated 2-5 yrs of degradation) from four vegetation types (live and blue oak leaves, foothill pine needles, and mixed annual grasses) in an oak woodland ecosystem in the foothills of the Sierra mountains of California. Litters and duffs were placed on sieves within funnels throughout the catchment, and leachates were collected during each rainfall event from Dec. 1, 2006 through May 31, 2007. DON accounted for 50-70% of nitrogen released from litters and DON plus particulate organic nitrogen (PON) constituted >90% of released nitrogen. In contrast, dissolved inorganic nitrogen (DIN) made up 60-80% of released nitrogen in the duff materials with the majority as ammonia. When scaled to the entire watershed, overall yields of dissolved nitrogen in leachates was estimated at 6.0 kg ha-1 for DON, 7.3 kg ha-1 for NH4-N, and 8.8 kg ha-1 for NO3-N, with 90% of the DON and 99% of the DIN derived from the duff materials. Areal yields are up to an order of magnitude greater than reported stream/riverine exports from catchments, indicating that much of this leachate must be degraded or sorbed along hydrologic flowpaths to streams, but that leachates could constitute a significant component of the DON/DOM pool within streams.

Effect of diesel oxidation catalysts on the diesel particulate filter regeneration process.

PubMed

Lizarraga, Leonardo; Souentie, Stamatios; Boreave, Antoinette; George, Christian; D'Anna, Barbara; Vernoux, Philippe

2011-12-15

A Diesel Particulate Filter (DPF) regeneration process was investigated during aftertreatment exhaust of a simulated diesel engine under the influence of a Diesel Oxidation Catalyst (DOC). Aerosol mass spectrometry analysis showed that the presence of the DOC decreases the Organic Carbon (OC) fraction adsorbed to soot particles. The activation energy values determined for soot nanoparticles oxidation were 97 ± 5 and 101 ± 8 kJ mol(-1) with and without the DOC, respectively; suggesting that the DOC does not facilitate elementary carbon oxidation. The minimum temperature necessary for DPF regeneration was strongly affected by the presence of the DOC in the aftertreatment. The conversion of NO to NO(2) inside the DOC induced the DPF regeneration process at a lower temperature than O(2) (ΔT = 30 K). Also, it was verified that the OC fraction, which decreases in the presence of the DOC, plays an important role to ignite soot combustion.

The physiological response of two green calcifying algae from the Great Barrier Reef towards high dissolved inorganic and organic carbon (DIC and DOC) availability.

PubMed

Meyer, Friedrich Wilhelm; Vogel, Nikolas; Teichberg, Mirta; Uthicke, Sven; Wild, Christian

2015-01-01

Increasing dissolved inorganic carbon (DIC) concentrations associated with ocean acidification can affect marine calcifiers, but local factors, such as high dissolved organic carbon (DOC) concentrations through sewage and algal blooms, may interact with this global factor. For calcifying green algae of the genus Halimeda, a key tropical carbonate producer that often occurs in coral reefs, no studies on these interactions have been reported. These data are however urgently needed to understand future carbonate production. Thus, we investigated the independent and combined effects of DIC (pCO2 402 μatm/ pHtot 8.0 and 996 μatm/ pHtot 7.7) and DOC (added as glucose in 0 and 294 μmol L-1) on growth, calcification and photosynthesis of H. macroloba and H. opuntia from the Great Barrier Reef in an incubation experiment over 16 days. High DIC concentrations significantly reduced dark calcification of H. opuntia by 130 % and led to net dissolution, but did not affect H. macroloba. High DOC concentrations significantly reduced daily oxygen production of H. opuntia and H. macroloba by 78 % and 43 %, respectively, and significantly reduced dark calcification of H. opuntia by 70%. Combined high DIC and DOC did not show any interactive effects for both algae, but revealed additive effects for H. opuntia where the combination of both factors reduced dark calcification by 162 % compared to controls. Such species-specific differences in treatment responses indicate H. opuntia is more susceptible to a combination of high DIC and DOC than H. macroloba. From an ecological perspective, results further suggest a reduction of primary production for Halimeda-dominated benthic reef communities under high DOC concentrations and additional decreases of carbonate accretion under elevated DIC concentrations, where H. opuntia dominates the benthic community. This may reduce biogenic carbonate sedimentation rates and hence the buffering capacity against further ocean acidification.

Acid-induced changes in DOC quality in an experimental whole-lake manipulation

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

Donahue, W.F.; Schindler, D.W.; Page, S.J.

1998-10-01

Fluorescence analyses of archived water samples were used to typify dissolved organic carbon (DOC) quality in experimentally acidified lakes and reference lakes at the Experimental Lakes Area, in northwestern Ontario. Carbon-specific DOC fluorescence (CSF) during peak acidification was 40--50% of that for a high-DOC reference lake and similar to a low-DOC reference lake. Reference lakes showed similar but smaller decreases in CSF during several years of prolonged drought in the late 1980s. During the 1990s, recovery from acidification resulted in increased CSF, whereas reference lakes remained unchanged during the same time period. In addition to causing decreased [DOC], acidification causesmore » changes in fluorescence-peak geometry that indicate a switch in DOC quality from allochthonous to autochthonous-like during acidification. The acid-induced change in DOC quality was likely due to increased chemical oxidation or precipitation of the UV-absorbent aromatic portions of allochthonous DOC molecules, leaving more UV-transparent aliphatic chains. The change in the nature of DOC following acidification and drought may have an important role in physical, biological, and chemical processes within these lakes. With recovery from acidification, DOC quality has also recovered.« less

Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysis

USGS Publications Warehouse

Jorien E. Vonk,; Tank, Suzanne E.; Paul J. Mann,; Robert G.M. Spencer,; Treat, Claire C.; Striegl, Robert G.; Benjamin W. Abbott,; Wickland, Kimberly P.

2015-01-01

As Arctic regions warm and frozen soils thaw, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to decomposition or transport. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the degradability of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of the mechanistic controls on DOC biodegradability is currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences commonly used in the literature. We also synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-arctic trends in BDOC.An increasing extent of permafrost across the landscape resulted in higher DOC losses in both soil and aquatic systems. We hypothesize that the unique composition of (yedoma) permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively short flow path lengths and transport times, contributed to a higher overall terrestrial and freshwater DOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January–December) decrease in BDOC in large streams and rivers, but saw no apparent change in smaller streams or soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the thaw season progresses. Our results suggest that future climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC, the amount of BDOC, as well as its variability throughout the Arctic summer. We lastly recommend a standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysis

NASA Astrophysics Data System (ADS)

Vonk, J. E.; Tank, S. E.; Mann, P. J.; Spencer, R. G. M.; Treat, C. C.; Striegl, R. G.; Abbott, B. W.; Wickland, K. P.

2015-12-01

As Arctic regions warm and frozen soils thaw, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to decomposition or transport. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the degradability of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of the mechanistic controls on DOC biodegradability is currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences commonly used in the literature. We also synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher DOC losses in both soil and aquatic systems. We hypothesize that the unique composition of (yedoma) permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively short flow path lengths and transport times, contributed to a higher overall terrestrial and freshwater DOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January-December) decrease in BDOC in large streams and rivers, but saw no apparent change in smaller streams or soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the thaw season progresses. Our results suggest that future climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC, the amount of BDOC, as well as its variability throughout the Arctic summer. We lastly recommend a standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Adsorption and bioadsorption of granular activated carbon (GAC) for dissolved organic carbon (DOC) removal in wastewater.

PubMed

Xing, W; Ngo, H H; Kim, S H; Guo, W S; Hagare, P

2008-12-01

In this study, the performances of GAC adsorption and GAC bioadsorption in terms of dissolved organic carbon (DOC) removal were investigated with synthetic biologically treated sewage effluent (BTSE), synthetic primary treated sewage effluent (PTSE), real BTSE and real PTSE. The main aims of this study are to verify and compare the efficiency of DOC removal by GAC (adsorption) and acclimatized GAC (bioadsorption). The results indicated that the performance of bioadsorption was significantly better than that of adsorption in all cases, showing the practical use of biological granular activated carbon (BGAC) in filtration process. The most significance was observed at a real PTSE with a GAC dose of 5g/L, having 54% and 96% of DOC removal by adsorption and bioadsorption, respectively. In addition, it was found that GAC adsorption equilibrium was successfully predicted by a hybrid Langmuir-Freundlich model whilst integrated linear driving force approximation (LDFA)+hybrid isotherm model could describe well the adsorption kinetics. Both adsorption isotherm and kinetic coefficients determined by these models will be useful to model the adsorption/bioadsorption process in DOC removal of BGAC filtration system.

Stream Mercury Export in Response to Contemporary Timber Harvesting Methods (Pacific Coastal Mountains, Oregon, USA).

PubMed

Eckley, Chris S; Eagles-Smith, Collin; Tate, Michael T; Kowalski, Brandon; Danehy, Robert; Johnson, Sherri L; Krabbenhoft, David P

2018-02-20

Land-use activities can alter hydrological and biogeochemical processes that can affect the fate, transformation, and transport of mercury (Hg). Previous studies in boreal forests have shown that forestry operations can have profound but variable effects on Hg export and methylmercury (MeHg) formation. The Pacific Northwest is an important timber producing region that receives large atmospheric Hg loads, but the impact of forest harvesting on Hg mobilization has not been directly studied and was the focus of our investigation. Stream discharge was measured continuously, and Hg and MeHg concentrations were measured monthly for 1.5 years following logging in three paired harvested and unharvested (control) catchments. There was no significant difference in particulate-bound Hg concentrations or loads in the harvested and unharvested catchments which may have resulted from forestry practices aimed at minimizing erosion. However, the harvested catchments had significantly higher discharge (32%), filtered Hg concentrations (28%), filtered Hg loads (80%), and dissolved organic carbon (DOC) loads (40%) compared to forested catchments. MeHg concentrations were low (mostly <0.05 ng L -1 ) in harvested, unharvested, and downstream samples due to well-drained/unsaturated soil conditions and steep slopes with high energy eroding stream channels that were not conducive to the development of anoxic conditions that support methylation. These results have important implications for the role forestry operations have in affecting catchment retention and export of Hg pollution.

Effect of disinfection upon dissolved organic carbon (DOC) in wastewater: bacterial bioassays.

PubMed

Arana, I; Santorum, P; Muela, A; Barcina, I

2000-08-01

Quantitative and qualitative changes in organic matter content of wastewater effluents attributable to chlorination and ozonation have been analysed using bioassays as well as organic carbon direct measures. Bioassays were carried out using the bacterial populations of wastewater and two Escherichia coli strains as test micro-organisms. Our results indicate that pure strains present some advantages over indigenous bacteria. Although wastewater bacterial populations are better adapted to growth in wastewater, E. coli strains are more sensitive to changes in dissolved organic carbon (DOC) content. Moreover, the use of pure cultures allows estimation of the portion of DOC which can be converted in cell biomass, the assimilable organic carbon (AOC). Finally, the results obtained using prototrophic and the auxotrophic strains of E. coli suggested that ozonation alters the amino acid composition of wastewater while chlorination does not change the quantity nor the quality of the DOC present in effluents.

Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga

USGS Publications Warehouse

Gorski, P.R.; Armstrong, D.E.; Hurley, J.P.; Krabbenhoft, D.P.

2008-01-01

Bioavailability of mercury (Hg) to Selenastrum capricornutum was assessed in bioassays containing field-collected freshwater of varying dissolved organic carbon (DOC) concentrations. Bioconcentration factor (BCF) was measured using stable isotopes of methylmercury (MeHg) and inorganic Hg(II). BCFs for MeHg in low-DOC lake water were significantly larger than those in mixtures of lake water and high-DOC river water. The BCF for MeHg in rainwater (lowest DOC) was the largest of any treatment. Rainwater and lake water also had larger BCFs for Hg(II) than river water. Moreover, in freshwater collected from several US and Canadian field sites, BCFs for Hg(II) and MeHg were low when DOC concentrations were >5 mg L-1. These results suggest high concentrations of DOC inhibit bioavailability, while low concentrations may provide optimal conditions for algal uptake of Hg. However, variability of BCFs at low DOC indicates that DOC composition or other ligands may determine site-specific bioavailability of Hg.

Response Characteristics of Dissolved Organic Carbon Flushing in a Subarctic Alpine Catchment

NASA Astrophysics Data System (ADS)

Carey, S. K.

2002-12-01

Dissolved organic carbon (DOC) is an important part of ecosystem-scale carbon balances and in the transport of contaminants as it interacts with other dissolved substances including trace metals. It also can be used as a surrogate hydrological tracer in permafrost regions as near-surface waters are often DOC enriched due to the presence of thick organic soils. In a small subarctic alpine catchment within the Wolf Creek Research Basin, Yukon, Canada, DOC was studied in the summer of 2001 and spring of 2002 to determine the role frost (both permanent and seasonal), snowmelt and summer storms on DOC flushing. Peak DOC concentrations occurred during the snowmelt period, approximately one week prior to peak discharge. However, peak discharge took place several weeks after snow on south facing exposures had melted. Within the hillslopes, DOC concentrations were three to five times greater in wells underlain with permafrost compared with seasonal frost. Groundwater DOC concentrations declined during snowmelt, yet remained at levels above the streamflow. After peaking, streamflow DOC concentrations declined exponentially suggesting a simple flushing mechanism, however there did not appear to be a relation between DOC and topographic position. Following melt, permafrost underlain slopes had near-surface water tables and retained elevated levels of DOC, whereas slopes without permafrost had rapidly declining water tables at upslope locations with low DOC concentrations at all positions except near-stream riparian zones. The influence of summer rainstorms on DOC was monitored on three occasions. In each case DOC peaked on the ascending limb of the runoff hydrograph and declined exponentially on the receding limb and hysteretic behavior occurred between discharge and DOC during all events. Patterns of DOC within the hillslopes and streams suggest that runoff from permafrost-underlain slopes control DOC flushing within the stream during both snowmelt and summer periods. This flushing mechanism conforms with conceptual models of runoff generation in discontinuous permafrost catchments whereby water tables within permafrost-underlain slopes rise into porous organic-layers, whereupon DOC is leached into the water and rapidly conveyed to the stream.

The influence of dissolved organic carbon on bacterial phosphorus uptake and bacteria-phytoplankton dynamics in two Minnesota lakes

USGS Publications Warehouse

Stets, E.G.; Cotner, J.B.

2008-01-01

The balance of production in any ecosystem is dependent on the flow of limiting nutrients into either the autotrophic or heterotrophic components of the food web. To understand one of the important controls on the flow of inorganic nutrients between phytoplankton and bacterioplankton in lakes, we manipulated dissolved organic carbon (DOC) in two lakes of different trophic status. We hypothesized that labile DOC additions would increase bacterial phosphorus (P) uptake and decrease the response of phytoplankton to nutrient additions. Supplemental nutrients and carbon (C), nitrogen (N, 1.6 ??mol NH4Cl L-1 d-1), P (0.1 ??mol KH 2PO4 L-1 d-1), and DOC (glucose, 15 ??mol C L-1 d-1) were added twice daily to 8-liter experimental units. We tested the effect of added DOC on chlorophyll concentration, bacterial production, biomass, and P uptake using size-fractionated 33P-PO4 uptake. In the oligotrophic lake, DOC additions stimulated bacterial production and increased bacterial biomass-specific P uptake. Bacteria consumed added DOC, and chlorophyll concentrations were significantly lower in carboys receiving DOC additions. In the eutrophic lake, DOC additions had less of a stimulatory effect on bacterial production and biomass-specific P uptake. DOC accumulated over the time period, and there was little evidence for a DOC-induced decrease in phytoplankton biomass. Bacterial growth approached the calculated ??max and yet did not accumulate biomass, indicating significant biomass losses, which may have constrained bacterial DOC consumption. Excess bacterial DOC consumption in oligotrophic lakes may result in greater bacterial P affinity and enhanced nutrient uptake by the heterotrophic compartment of the food web. On the other hand, constraints on bacterial biomass accumulation in eutrophic lakes, from either viral lysis or bacterial grazing, can allow labile DOC to accumulate, thereby negating the effect of excess DOC on the planktonic food web. ?? 2008, by the American Society of Limnology and Oceanography, Inc.

77 FR 3386 - Export and Reexport License Requirements for Certain Microwave and Millimeter Wave Electronic...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-01-24

... electronic components. The two components are packaged high electron mobility transistors and packaged..., 2012, FR Doc. 2012- 135). The two components are packaged high electron mobility transistors (HEMT) and...

Seasonality and flux estimates of dissolved organic carbon in tidal wetlands and estuaries in the U.S. Mid- Atlantic Bight and Gulf of Mexico from ocean color

NASA Astrophysics Data System (ADS)

Cao, F.; Tzortziou, M.; Hu, C.; Najjar, R.

2016-02-01

Tidal wetlands and estuaries are dynamic features of coastal ocean and play critical roles in the global carbon cycle. Exchanges of dissolved organic carbon (DOC) between tidal wetlands and adjacent estuaries have important implications for carbon sequestration in tidal wetlands as well as biogeochemical cycling of wetlands derived material in the coastal zones. Recent studies demonstrated that the absorption coefficients of chromophoric dissolved organic matter at λ= 275 and 295 nm, which can be derived from satellite ocean color observations, can be used to accurately retrieve dissolved organic carbon (DOC) in some coastal waters. Based on a synthesis of existing field observations collected covering wide spatial and temporal variability in the Mid-Atlantic Bight and the Gulf of Mexico, here we developed and validated new empirical models to estimate coastal DOC from remotely sensed bio-optical properties of the surface water. We focused on the interfaces between tidal wetland-estuary and estuary-shelf water domains. The DOC algorithms were applied to SeaWiFs and MODIS observations to generate long-term climatological DOC distributions from 1998 to 2014. Empirical orthogonal function analysis revealed strong seasonality and spatial gradients in the satellite retrieved DOC in the tidal wetlands and estuaries. Combined with field observations and biogeochemical models, satellite retrievals can be used to scale up carbon fluxes from individual marshes and sub-estuaries to the whole estuarine system, and improve understanding of biogeochemical exchanges between terrestrial and aquatic ecosystems.

Monitoring and Predicting the Export and Fate of Global Ocean Net Primary Production: The EXPORTS Field Program

NASA Astrophysics Data System (ADS)

Exports Science Definition Team

2016-04-01

Ocean ecosystems play a critical role in the Earth's carbon cycle and its quantification on global scales remains one of the greatest challenges in global ocean biogeochemistry. The goal of the EXport Processes in the Ocean from Remote Sensing (EXPORTS) science plan is to develop a predictive understanding of the export and fate of global ocean primary production and its implications for the Earth's carbon cycle in present and future climates. NASA's satellite ocean-color data record has revolutionized our understanding of global marine systems. EXPORTS is designed to advance the utility of NASA ocean color assets to predict how changes in ocean primary production will impact the global carbon cycle. EXPORTS will create a predictive understanding of both the export of organic carbon from the euphotic zone and its fate in the underlying "twilight zone" (depths of 500 m or more) where variable fractions of exported organic carbon are respired back to CO2. Ultimately, it is the sequestration of deep organic carbon transport that defines the impact of ocean biota on atmospheric CO2 levels and hence climate. EXPORTS will generate a new, detailed understanding of ocean carbon transport processes and pathways linking upper ocean phytoplankton processes to the export and fate of organic matter in the underlying twilight zone using a combination of field campaigns, remote sensing and numerical modeling. The overarching objective for EXPORTS is to ensure the success of future satellite missions by establishing mechanistic relationships between remotely sensed signals and carbon cycle processes. Through a process-oriented approach, EXPORTS will foster new insights on ocean carbon cycling that will maximize its societal relevance and be a key component in the U.S. investment to understand Earth as an integrated system.

Factors affecting distribution patterns of organic carbon in sediments at regional and national scales in China.

PubMed

Cao, Qingqing; Wang, Hui; Zhang, Yiran; Lal, Rattan; Wang, Renqing; Ge, Xiuli; Liu, Jian

2017-07-14

Wetlands are an important carbon reservoir pool in terrestrial ecosystems. Light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), and dissolved organic carbon (DOC) were fractionated in sediment samples from the four wetlands (ZR: Zhaoniu River; ZRCW: Zhaoniu River Constructed Wetland; XR: Xinxue River; XRCW: Xinxue River Constructed Wetland). Organic carbon (OC) from rivers and coasts of China were retrieved and statistically analyzed. At regional scale, HFOC stably dominates the deposition of OC (95.4%), whereas DOC and LFOC in ZR is significantly higher than in ZRCW. Concentration of DOC is significantly higher in XRCW (30.37 mg/l) than that in XR (13.59 mg/l). DOC and HFOC notably distinguish between two sampling campaigns, and the deposition of carbon fractions are limited by low nitrogen input. At the national scale, OC attains the maximum of 2.29% at precipitation of 800 mm. OC has no significant difference among the three climate zones but significantly higher in river sediments than in coasts. Coastal OC increases from Bohai Sea (0.52%) to South Sea (0.70%) with a decrease in latitude. This study summarizes the factors affecting organic carbon storage in regional and national scale, and have constructive implications for carbon assessment, modelling, and management.

Transcriptional Changes Underlying Elemental Stoichiometry Shifts in a Marine Heterotrophic Bacterium

PubMed Central

Chan, Leong-Keat; Newton, Ryan J.; Sharma, Shalabh; Smith, Christa B.; Rayapati, Pratibha; Limardo, Alexander J.; Meile, Christof; Moran, Mary Ann

2012-01-01

Marine bacteria drive the biogeochemical processing of oceanic dissolved organic carbon (DOC), a 750-Tg C reservoir that is a critical component of the global C cycle. Catabolism of DOC is thought to be regulated by the biomass composition of heterotrophic bacteria, as cells maintain a C:N:P ratio of ∼50:10:1 during DOC processing. Yet a complicating factor in stoichiometry-based analyses is that bacteria can change the C:N:P ratio of their biomass in response to resource composition. We investigated the physiological mechanisms of resource-driven shifts in biomass stoichiometry in continuous cultures of the marine heterotrophic bacterium Ruegeria pomeroyi (a member of the Roseobacter clade) under four element limitation regimes (C, N, P, and S). Microarray analysis indicated that the bacterium scavenged for alternate sources of the scarce element when cells were C-, N-, or P-limited; reworked the ratios of biomolecules when C- and P- limited; and exerted tighter control over import/export and cytoplasmic pools when N-limited. Under S limitation, a scenario not existing naturally for surface ocean microbes, stress responses dominated transcriptional changes. Resource-driven changes in C:N ratios of up to 2.5-fold and in C:P ratios of up to sixfold were measured in R. pomeroyi biomass. These changes were best explained if the C and P content of the cells was flexible in the face of shifting resources but N content was not, achieved through the net balance of different transcriptional strategies. The cellular-level metabolic trade-offs that govern biomass stoichiometry in R. pomeroyi may have implications for global carbon cycling if extendable to other heterotrophic bacteria. Strong homeostatic responses to N limitation by marine bacteria would intensify competition with autotrophs. Modification of cellular inventories in C- and P-limited heterotrophs would vary the elemental ratio of particulate organic matter sequestered in the deep ocean. PMID:22783226

Organic carbon isotope constraints on the dissolved organic carbon (DOC) reservoir at the Cryogenian-Ediacaran transition

NASA Astrophysics Data System (ADS)

Jiang, Ganqing; Wang, Xinqiang; Shi, Xiaoying; Zhang, Shihong; Xiao, Shuhai; Dong, Jin

2010-10-01

Prominent negative carbonate carbon isotope (δ 13C carb) anomalies from some Ediacaran successions are accompanied by invariant or decoupled organic carbon isotope (δ 13C org) values and have been interpreted as resulting from the remineralization of a large dissolved organic carbon (DOC) reservoir capable of buffering carbon isotopes of organic matter. This inferred oceanic DOC reservoir was thought to have initiated with the onset of Cryogenian glaciations (ca. 720 Ma) and lasted for millions of years until the late Ediacaran Period (< 560 Ma). Carbon isotope analyses of the basal Doushantuo Formation (ca. 635 Ma) in south China reveal that (1) the cap carbonate has δ 13C org around -26‰ (VPDB) and relatively low Δδ 13C (22 ± 2‰) and (2) the overlying organic-rich black shale and shaly dolostone have more negative δ 13C org (-28‰ to -35‰) and higher Δδ 13C (28‰-30‰). Both δ 13C carb and δ 13C org show a + 6‰ shift within a 4-m-thick interval overlying the Doushantuo cap carbonate. The δ 13C org values of the cap carbonate are associated with low TOC (mostly < 0.1%); their paleoceanographic significance requires further tests in other Ediacaran basins. The co-varying positive shift in δ 13C carb and δ 13C org following cap carbonate deposition is best interpreted as resulting from a rapid increase in organic carbon burial, which may have resulted in the rise of oxygen and heralded the first appearance of animals a few meters above the Doushantuo cap carbonate. The data suggest that a large oceanic DOC reservoir did not exist in the early Ediacaran ocean. Excess oceanic DOC required to explain the Ediacaran Shuram and upper Doushantuo δ 13C excursions, if it existed, had to be developed during the Ediacaran Period after cap carbonate deposition.

Dissolved organic carbon content and characteristics in relation to carbon dioxide partial pressure across Poyang Lake wetlands and adjacent aquatic systems in the Changjiang basin.

PubMed

Wang, Huaxin; Jiao, Ruyuan; Wang, Fang; Zhang, Lu; Yan, Weijin

2016-12-01

Dissolved organic carbon (DOC) plays diverse roles in carbon biogeochemical cycles. Here, we explored the link between DOC and pCO 2 using high-performance size-exclusion chromatography (HPSEC) with UV 254 detection and excitation emission matrix (EEM) fluorescence spectroscopy to determine the molecular weight distribution (MW) and the spectral characteristics of DOC, respectively. The relationship between DOC and pCO 2 was investigated in the Poyang Lake wetlands and their adjacent aquatic systems. The results indicated significant spatial variation in the DOC concentrations, MW distributions, and pCO 2 . The DOC concentration was higher in the wetlands than in the rivers and lakes. pCO 2 was high in wetlands in which the dominant vegetation was Phragmites australis, whereas it was low in wetlands in which Carex tristachya was the dominant species. DOC was divided into five fractions according to MW, as follows: super-low MW (SLMW, <1 kDa); low MW (LMW, 1-2.5 kDa); intermediate MW (IMW, 2.5-3.5 kDa); high MW (HMW, 3.5-6 kDa); and super-high MW (SMW, > 40 kDa). Rivers contained high proportions of HMW and extremely low amounts of SLMW, whereas wetlands had relatively high proportions of SLMW. The proportion of SMW (SMW p ) was particularly high in wetlands. We found that pCO 2 significantly positively correlated with the proportion of IMW, and significantly negatively correlated with SMW p . These data improve our understanding of the MW of bioavailable DOC and its conversion to CO 2 . The present results demonstrate that both the content and characteristics of DOC significantly affect pCO 2 . pCO 2 and DOC must be studied further to help understanding the role of the wetland on the regional CO 2 budget. Copyright © 2016 Elsevier Ltd. All rights reserved.

The Role of Alpine Wetlands as Hot Spots of Dissolved Organic Carbon Fluxes in the East River, Colorado

NASA Astrophysics Data System (ADS)

Winnick, M.; Rainaldi, G. R.; Lawrence, C. R.; McCormick, M. E.; Hsu, H. T.; Druhan, J. L.; Williams, K. H.; Maher, K.

2016-12-01

Dissolved organic carbon (DOC) is a critical chemical attribute of freshwater systems, affecting nutrient availability, toxicity and solubility of metals, and biological activity via the absorption of light and microbial consumption of O2 during DOC mineralization. Although DOC contributions to streams are distributed across the landscape in the shallow subsurface, many studies have demonstrated area-outsized contributions from riparian zones with high biological productivity and low subsurface O2 concentrations. In the East River, CO, a high-elevation watershed located in the central Rocky Mountains, initial observations show that DOC concentrations of two tributaries, Rock Creek and Gothic Creek, are elevated by 3-10 times compared to concentrations in the main East River and its other tributaries. These elevated concentrations are qualitatively linked to the unique presence of large wetlands in the headwaters of Rock and Gothic creeks, which due to potential anoxic conditions, experience reduced rates of organic matter decomposition and serve as an elevated source of DOC. In this study we quantify the cycling of organic matter in these alpine wetlands and their area-outsized contributions to East River DOC fluxes. We present concentration profiles of DOC along stream reaches and along subsurface flowpaths that span the transition from hillslope to wetland coupled with high-resolution mapping of chronically-saturated zones and calculate area-weighted fluxes of DOC from wetlands to Rock and Gothic creeks at multiple times through the 2016 growing season. Additionally, soil and groundwater DOC fluxes are compared with depth-resolved organic carbon content from soil cores, substrate quality (C:N), and soil surface CO2 fluxes to evaluate organic carbon budgets in the hillslope and wetland areas feeding Rock Creek. The characterization of these hotspots of DOC generation and transport in the East River is vital to the ability to predict nutrient cycling changes into the future.

Laboratory Experiments to Evaluate Matrix Diffusion of Dissolved Organic Carbon Carbon-14 in Southern Nevada Fractured-rock Aquifers

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

Hershey, Ronald L.; Fereday, Wyatt

Dissolved inorganic carbon (DIC) carbon-14 ( 14C) is used to estimate groundwater ages by comparing the DIC 14C content in groundwater in the recharge area to the DIC 14C content in the downgradient sampling point. However, because of chemical reactions and physical processes between groundwater and aquifer rocks, the amount of DIC 14C in groundwater can change and result in 14C loss that is not because of radioactive decay. This loss of DIC 14C results in groundwater ages that are older than the actual groundwater ages. Alternatively, dissolved organic carbon (DOC) 14C in groundwater does not react chemically with aquifermore » rocks, so DOC 14C ages are generally younger than DIC 14C ages. In addition to chemical reactions, 14C ages may also be altered by the physical process of matrix diffusion. The net effect of a continuous loss of 14C to the aquifer matrix by matrix diffusion and then radioactive decay is that groundwater appears to be older than it actually is. Laboratory experiments were conducted to measure matrix diffusion coefficients for DOC 14C in volcanic and carbonate aquifer rocks from southern Nevada. Experiments were conducted using bromide (Br-) as a conservative tracer and 14C-labeled trimesic acid (TMA) as a surrogate for groundwater DOC. Outcrop samples from six volcanic aquifers and five carbonate aquifers in southern Nevada were used. The average DOC 14C matrix diffusion coefficient for volcanic rocks was 2.9 x 10 -7 cm 2/s, whereas the average for carbonate rocks was approximately the same at 1.7 x 10 -7 cm 2/s. The average Br- matrix diffusion coefficient for volcanic rocks was 10.4 x 10 -7 cm 2/s, whereas the average for carbonate rocks was less at 6.5 x 10 -7 cm 2/s. Carbonate rocks exhibited greater variability in DOC 14C and Br- matrix diffusion coefficients than volcanic rocks. These results confirmed, at the laboratory scale, that the diffusion of DOC 14C into southern Nevada volcanic and carbonate aquifers is slower than DIC 14C. Because of the apparent sorption of 14C-labeled TMA in the experiments, matrix diffusion coefficients are likely even lower. The reasons for the higher than expected Br-/ 14C-labeled TMA are unknown. Because the molecular size of TMA is on the low end of the range in molecular size for typical humic substances, the matrix diffusion coefficients for the 14C-labeled TMA likely represent close to the maximum diffusion rates for DOC 14C in the volcanic and carbonate aquifers in southern Nevada.« less

Understanding the fluvial loss of carbon from the UK - implications for terrestrial carbon, greenhouse gases and water quality.

NASA Astrophysics Data System (ADS)

Worrall, F.; Howden, N. J. K.

2016-12-01

We have developed a number of methods to estimate the fate of fluvial organic matter through UK catchments. Here we include dissolved organic matter (DOM), particulate organic matter (POC), and dissolved gases to estimate losses from the terrestrial biosphere; in-stream losses and production (including the role of water and waste treatment); and export to the continental shelf and atmsophere. We use multiple approaches, including: mass balance studies, modelling and experimentation. Mass balance studies suggest that the UK terrestrial biosphere losses 5 Mtonnes C/yr (21.8 tonnes C/km2/yr) in the proportion of 7:22:4 (POC:DOC:diss. CO2). The mass balance studies suggest 3.5 Mtonnes C/yr (15.2 tonnes C/km2/yr) is lost to the atmosphere in the proportion 8:75:17 (POC:DOC:diss. CO2); UK rivers have short residence times (typically 1-2 days) and so the diurnal cycle becomes critical. Experiments show that turnover rates are close to zero overnight but that these can be periods of DOM production from turnover of POM and that the presence of POM may inhibit turnover of DOM; The development and modelling using physically-explicit rate laws showed that the loss of DOC was between 24 and 37% - lower than that estimated from mass balance studies, but that the loss rate of TOC (DOC + POC) was between 57 and 80% - close to that estimated from mass balance studies; The turnover of organic particles within rivers means that any notion that soil erosion leads to net carbon drawdown is entirely negated and the emission factor for gross soil erosion is estimated to be between 0.11 and 0.66 tonnes CO2eq/yr for every 1 tonne of gross erosion; and, Studies of molecular change of DOM and POM along rivers shows that, while POM represents an admixture of its sources (soils and vegetation), the DOM which enters rivers as highly oxidised becomes more reduced in channel. The release of greenhouse gases from UK rivers is now estimated to be between 15,800 - 33,000 ktonnes CO2eq/yr equivalent to between 67 and 131 tonnes CO2eq/km2/yr with fluvial organic matter between 12,328 and 15,922 ktonnes CO2eq/yr in the proportion 5:86:8 - N2O:CO2:CH4. The emissions factor for 1 tonne of organic carbon entering the UK fluvial network has a median value of 3.01 tonnes CO2eq/yr with a 5th to 95th percentile range of 2.60 to 3.59 tonnes CO2eq/yr.

Spatiotemporal characterization of dissolved carbon for inland waters in semi-humid/semi-arid region, China

NASA Astrophysics Data System (ADS)

Song, K. S.; Zang, S. Y.; Zhao, Y.; Li, L.; Du, J.; Zhang, N. N.; Wang, X. D.; Shao, T. T.; Guan, Y.; Liu, L.

2013-10-01

Spatiotemporal variations of dissolved organic carbon (DOC) and inorganic carbon (DIC) in 26 waters across the semi-humid/semi-arid Songnen Plain, China, were examined with data collected during 2008-2011. Fresh (n = 14) and brackish (n = 12) waters were grouped according to electrical conductivity (threshold = 1000 μS cm-1) Significant differences in the average DOC and DIC concentrations were observed between the fresh (5.63 mg L-1, 37.39 mg L-1) and the brackish waters (15.33 mg L-1, 142.93 mg L-1). Colored dissolved organic matter (CDOM) and DOC concentrations were mainly controlled by climatic-hydrologic conditions. The investigation indicated that the outflow conditions in the semi-arid region had condensed effects on the dissolved carbon, resulting in close relationships between salinity vs. DOC (R2 = 0.66), and salinity vs. DIC (R2 = 0.94). An independent data set collected in May 2012 also confirmed this finding (DOC: R2 = 0.79, DIC: R2 = 0.91), highlighting the potential of quantifying DOC and DIC via salinity measurements for waters dispersed in the plain. Indices based on the CDOM absorption spectra (e.g., the DOC-specific CDOM absorption (SUVA254), absorption ratio a250 : a365 (E250 : E365) and the spectral slope ratio (Sr, S275-295/S350-400) were applied to characterize CDOM composition and quality. Our results indicate that high molecular weight CDOM fractions are more abundant in the fresh waters than the brackish waters.

Spatiotemporal characterization of dissolved carbon for inland waters in semi-humid/semiarid region, China

NASA Astrophysics Data System (ADS)

Song, K. S.; Zang, S. Y.; Zhao, Y.; Du, J.; Li, L.; Zhang, N. N.; Wang, X. D.; Shao, T. T.; Guan, Y.; Liu, L.

2013-05-01

Spatiotemporal variations of dissolved organic carbon (DOC), inorganic carbon (DIC) in 26 waters across the semi-humid/semi-arid Songnen Plain, China were examined with data collected during 2008-2011. Fresh (n = 14) and brackish (n = 12) waters were grouped according to electrical conductivity (threshold = 1000 μS cm-1). Significant differences in the mean DOC/DIC concentrations were observed between fresh (5.63 mg L-1, 37.39 mg L-1) and brackish waters (15.33 mg L-1, 142.93 mg L-1). Colored dissolved organic matter (CDOM) and DOC concentrations were mainly controlled by climatic-hydrologic conditions. The observation indicated that the outflow conditions in the semi-endorheic region had condensed effects on the dissolved carbon, resulting in close relationships between salinity vs. DOC (R2 = 0.66), and vs. DIC (R2 = 0.94). Independent data set collected in May 2012 also confirmed this finding (DOC: R2 = 0.79), (DIC: R2 = 0.91), highlighting the potential of quantifying DOC/DIC via salinity measurements for waters dispersed in the plain. Indices based on CDOM absorption spectra, e.g. DOC specific CDOM absorption (SUVA254), absorption ratio a250 : a365 (E250:365) and spectral slope ratio (Sr, S275-295/S350-400), were applied to characterize DOM composition and quality. Our results indicate high molecular weight CDOM fractions are more abundant in fresh waters than brackish waters.

Dissolved oxygen as an indicator of bioavailable dissolved organic carbon in groundwater.

PubMed

Chapelle, Francis H; Bradley, Paul M; McMahon, Peter B; Kaiser, Karl; Benner, Ron

2012-01-01

Concentrations of dissolved oxygen (DO) plotted vs. dissolved organic carbon (DOC) in groundwater samples taken from a coastal plain aquifer of South Carolina (SC) showed a statistically significant hyperbolic relationship. In contrast, DO-DOC plots of groundwater samples taken from the eastern San Joaquin Valley of California (CA) showed a random scatter. It was hypothesized that differences in the bioavailability of naturally occurring DOC might contribute to these observations. This hypothesis was examined by comparing nine different biochemical indicators of DOC bioavailability in groundwater sampled from these two systems. Concentrations of DOC, total hydrolysable neutral sugars (THNS), total hydrolysable amino acids (THAA), mole% glycine of THAA, initial bacterial cell counts, bacterial growth rates, and carbon dioxide production/consumption were greater in SC samples relative to CA samples. In contrast, the mole% glucose of THNS and the aromaticity (SUVA(254)) of DOC was greater in CA samples. Each of these indicator parameters were observed to change with depth in the SC system in a manner consistent with active biodegradation. These results are uniformly consistent with the hypothesis that the bioavailability of DOC is greater in SC relative to CA groundwater samples. This, in turn, suggests that the presence/absence of a hyperbolic DO-DOC relationship may be a qualitative indicator of relative DOC bioavailability in groundwater systems. Ground Water © 2011, National Ground Water Association. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.

Experimental whole-lake increase of dissolved organic carbon concentration produces unexpected increase in crustacean zooplankton density

USGS Publications Warehouse

Kelly, Patrick T.; Craig, Nicola; Solomon, Christopher T.; Weidel, Brian C.; Zwart, Jacob A.; Jones, Stuart E.

2016-01-01

The observed pattern of lake browning, or increased terrestrial dissolved organic carbon (DOC) concentration, across the northern hemisphere has amplified the importance of understanding how consumer productivity varies with DOC concentration. Results from comparative studies suggest these increased DOC concentrations may reduce crustacean zooplankton productivity due to reductions in resource quality and volume of suitable habitat. Although these spatial comparisons provide an expectation for the response of zooplankton productivity as DOC concentration increases, we still have an incomplete understanding of how zooplankton respond to temporal increases in DOC concentration within a single system. As such, we used a whole-lake manipulation, in which DOC concentration was increased from 8 to 11 mg L−1 in one basin of a manipulated lake, to test the hypothesis that crustacean zooplankton production should subsequently decrease. In contrast to the spatially derived expectation of sharp DOC-mediated decline, we observed a small increase in zooplankton densities in response to our experimental increase in DOC concentration of the treatment basin. This was due to significant increases in gross primary production and resource quality (lower seston carbon-to-phosphorus ratio; C:P). These results demonstrate that temporal changes in lake characteristics due to increased DOC may impact zooplankton in ways that differ from those observed in spatial surveys. We also identified significant interannual variability across our study region, which highlights potential difficulty in detecting temporal responses of organism abundances to gradual environmental change (e.g., browning).

Temporal Variability of Stemflow Dissolved Organic Carbon (DOC) Concentrations and Quality from Morphologically Contrasting Deciduous Canopies

NASA Astrophysics Data System (ADS)

van Stan, J. T.; Levia, D. F.; Inamdar, S. P.; Mitchell, M. J.; Mage, S. M.

2010-12-01

Dissolved organic carbon (DOC) inputs from canopy-derived hydrologic fluxes play a significant role in the terrestrial carbon budgets of forested ecosystems. However, no studies known to the authors have examined the variability of both DOC concentrations and quality for stemflow across time scales, nor has any study to date evaluated the effects of canopy structure on stemflow DOC characteristics. This investigation seeks to rectify this knowledge gap by examining the variability of stemflow DOC concentrations and quality across contrasting canopy morphologies and time scales (seasonal, storm and intrastorm). Bulk and intrastorm stemflow samples from a less dense, rough-barked, more plagiophile (Liriodendron tulipifera L. (tulip poplar)) and a denser, thin-barked, more erectophile (Fagus grandifolia Ehrh. (American beech)) canopy were collected and analyzed for DOC quality using metrics derived from UV-vis spectroscopy (E2:E3 ratio, SUVA254, select spectral slope (S), and spectral slope ratios (SR)). Our results suggest that stemflow DOC concentrations and quality change as crown architectural traits enhance or diminish hydrologic retention time within the canopy. The architecture of L. tulipifera canopies likely retards the flow of intercepted water, increasing chemical exchange with bark and foliar surfaces. UV-vis metrics indicated that this increased chemical exchange, particularly with bark surfaces, generally enhanced aromatic hydrocarbon content and increased molecular weight. Because leaf presence influenced DOC quality, stemflow DOC characteristics also varied seasonally in response to canopy condition. At the inter- and intrastorm scale, stemflow DOC concentration and quality varied with meteorological and antecedent canopy conditions. Since recent studies have linked stemflow production to preferential subsurface transport of dissolved chemistries, trends in DOC speciation and fluxes described in this study may impact soil environments within wooded ecosystems.

Hydrologically transported dissolved organic carbon influences soil respiration in a tropical rainforest

NASA Astrophysics Data System (ADS)

Zhou, Wen-Jun; Lu, Hua-Zheng; Zhang, Yi-Ping; Sha, Li-Qing; Schaefer, Douglas Allen; Song, Qing-Hai; Deng, Yun; Deng, Xiao-Bao

2016-10-01

To better understand the effect of dissolved organic carbon (DOC) transported by hydrological processes (rainfall, throughfall, litter leachate, and surface soil water; 0-20 cm) on soil respiration in tropical rainforests, we detected the DOC flux in rainfall, throughfall, litter leachate, and surface soil water (0-20 cm), compared the seasonality of δ13CDOC in each hydrological process, and δ13C in leaves, litter, and surface soil, and analysed the throughfall, litter leachate, and surface soil water (0-20 cm) effect on soil respiration in a tropical rainforest in Xishuangbanna, south-west China. Results showed that the surface soil intercepted 94.4 ± 1.2 % of the annual litter leachate DOC flux and is a sink for DOC. The throughfall and litter leachate DOC fluxes amounted to 6.81 and 7.23 % of the net ecosystem exchange respectively, indicating that the DOC flux through hydrological processes is an important component of the carbon budget, and may be an important link between hydrological processes and soil respiration in a tropical rainforest. Even the variability in soil respiration is more dependent on the hydrologically transported water than DOC flux insignificantly, soil temperature, and soil-water content (at 0-20 cm). The difference in δ13C between the soil, soil water (at 0-20 cm), throughfall, and litter leachate indicated that DOC is transformed in the surface soil and decreased the sensitivity indices of soil respiration of DOC flux to water flux, which suggests that soil respiration is more sensitive to the DOC flux in hydrological processes, especially the soil-water DOC flux, than to soil temperature or soil moisture.

Partitioning of fluorotelomer alcohols to octanol and different sources of dissolved organic carbon.

PubMed

Carmosini, Nadia; Lee, Linda S

2008-09-01

Interest in the environmental fate of fluorotelomer alcohols (FTOHs) has spurred efforts to understand their equilibrium partitioning behavior. Experimentally determined partition coefficients for FTOHs between soil/water and air/water have been reported, but direct measurements of partition coefficients for dissolved organic carbon (DOC)/water (K(doc)) and octanol/ water(K(ow)) have been lacking. Here we measured the partitioning of 8:2 and 6:2 FTOH between one or more types of DOC and water using enhanced solubility or dialysis bag techniques, and also quantified K(ow) values for 4:2 to 8:2 FTOH using a batch equilibration method. The range in measured log K(doc) values for 8:2 FTOH using the enhanced solubility technique with DOC derived from two soils, two biosolids, and three reference humic acids is 2.00-3.97 with the lowest values obtained for the biosolids and an average across all other DOC sources (biosolid DOC excluded) of 3.54 +/- 0.29. For 6:2 FTOH and Aldrich humic acid, a log K(doc) value of 1.96 +/- 0.45 was measured using the dialysis technique. These average values are approximately 1 to 2 log units lower than previously indirectly estimated K(doc) values. Overall, the affinity for DOC tends to be slightly lower than that for particulate soil organic carbon. Measured log K(ow) values for 4:2 (3.30 +/- 0.04), 6:2 (4.54 +/- 0.01), and 8:2 FTOH (5.58 +/- 0.06) were in good agreement with previously reported estimates. Using relationships between experimentally measured partition coefficients and C-atom chain length, we estimated K(doc) and K(ow) values for shorter and longer chain FTOHs, respectively, that we were unable to measure experimentally.

Physical Heterogeneity Increases Biofilm Resource Use and Its Molecular Diversity in Stream Mesocosms

PubMed Central

Singer, Gabriel; Besemer, Katharina; Schmitt-Kopplin, Philippe; Hödl, Iris; Battin, Tom J.

2010-01-01

Background Evidence increasingly shows that stream ecosystems greatly contribute to global carbon fluxes. This involves a tight coupling between biofilms, the dominant form of microbial life in streams, and dissolved organic carbon (DOC), a very significant pool of organic carbon on Earth. Yet, the interactions between microbial biodiversity and the molecular diversity of resource use are poorly understood. Methodology/Principal Findings Using six 40-m-long streamside flumes, we created a gradient of streambed landscapes with increasing spatial flow heterogeneity to assess how physical heterogeneity, inherent to streams, affects biofilm diversity and DOC use. We determined bacterial biodiversity in all six landscapes using 16S-rRNA fingerprinting and measured carbon uptake from glucose and DOC experimentally injected to all six flumes. The diversity of DOC molecules removed from the water was determined from ultrahigh-resolution Fourier Transform Ion Cyclotron Resonance mass spectrometry (FTICR-MS). Bacterial beta diversity, glucose and DOC uptake, and the molecular diversity of DOC use all increased with increasing flow heterogeneity. Causal modeling and path analyses of the experimental data revealed that the uptake of glucose was largely driven by physical processes related to flow heterogeneity, whereas biodiversity effects, such as complementarity, most likely contributed to the enhanced uptake of putatively recalcitrant DOC compounds in the streambeds with higher flow heterogeneity. Conclusions/Significance Our results suggest biophysical mechanisms, including hydrodynamics and microbial complementarity effects, through which physical heterogeneity induces changes of resource use and carbon fluxes in streams. These findings highlight the importance of fine-scale streambed heterogeneity for microbial biodiversity and ecosystem functioning in streams, where homogenization and loss of habitats increasingly reduce biodiversity. PMID:20376323

Watershed scale spatial variability in dissolved and total organic and inorganic carbon in contrasting UK catchments

NASA Astrophysics Data System (ADS)

Cumberland, S.; Baker, A.; Hudson, N. J.

2006-12-01

Approximately 800 organic and inorganic carbon analyses have been undertaken from watershed scale and regional scale spatial surveys in various British catchments. These include (1) a small (<100 sq-km) urban catchment (Ouseburn, N England); (2) a headwater, lowland agricultural catchment (River Tern, C England) (3) a large UK catchment (River Tyne, ~3000 sq-km) and (4) a spatial survey of ~300 analyses from rivers from SW England (~1700 sq-km). Results demonstrate that: (1) the majority of organic and inorganic carbon is in the dissolved (DOC and DIC) fractions; (2) that with the exception of peat rich headwaters, DIC concentration is always greater than DOC; (3) In the rural River Tern, riverine DOC and DIC are shown to follow a simple end- member mixing between DIC (DOC) rich (poor) ground waters and DOC (DIC) rich (poor) riparian wetlands for all sample sites. (4) In the urbanized Ouseburn catchment, although many sample sites also show this same mixing trend, some tributaries follow a pollutant trend of simultaneous increases in both DOC and DIC. The Ouseburn is part of the larger Tyne catchment: this larger catchment follows the simple groundwater DIC- soil water DOC end member mixing model, with the exception of the urban catchments which exhibit an elevated DIC compared to rural sites. (5) Urbanization is demonstrated to increase DIC compared to equivalent rural catchments; this DIC has potential sources including diffuse source inputs from the dissolution of concrete, point sources such as trade effluents and landfill leachates, and bedrock derived carbonates relocated to the soil dissolution zone by urban development. (6) DIC in rural SW England demonstrates that spatial variability in DIC can be attributed to variations in geology; but that DIC concentrations in the SW England rivers dataset are typically lower than the urbanized Tyne catchments despite the presence of carbonate bedrock in many of the sample catchments in the SW England dataset. (7) Recent investigations into carbon fluxes in British rivers have focused on long term increases in DOC in rural and predominantly upland catchments. Our results suggest that research is needed into understanding long term variations in inorganic carbon concentration, as well as total (organic and inorganic) carbon fluxes from British rivers, to obtain total carbon loads. In particular, we provide evidence that DIC concentrations may be greater in urbanized catchments compared to equivalent non-urban catchments, with the implication that increasing urbanization in the future will see increases in riverine DIC and a decrease in the strength of any DOC DIC anti correlation. Further studies of urban catchment DIC sources, within stream processing, long term trends, and potential ecological impacts, are required.

Identification and analysis of low molecular weight dissolved organic carbon in subglacial basal ice ecosystems by ion chromatography

NASA Astrophysics Data System (ADS)

Lawson, E. C.; Wadham, J. L.; Lis, G. P.; Tranter, M.; Pickard, A. E.; Stibal, M.; Dewsbury, P.; Fitzsimons, S.

2015-08-01

Glacial runoff is an important source of dissolved organic carbon (DOC) for downstream heterotrophic activity, despite the low overall DOC concentrations. This is because of the abundance of bioavailable, low molecular weight (LMW) DOC species. However, the provenance and character of LMW-DOC is not fully understood. We investigated the abundance and composition of DOC in subglacial environments via a molecular level DOC analysis of basal ice, which forms by water/sediment freeze-on to the glacier sole. Spectrofluorometry and a novel ion chromatographic method, which has been little utilised in glacial science for LMW-DOC determinations, were employed to identify and quantify the major LMW fractions (free amino acids, carbohydrates and carboxylic acids) in basal ice from four glaciers, each with a different basal debris type. Basal ice from Joyce Glacier (Antarctica) was unique in that 98 % of the LMW-DOC was derived from the extremely diverse FAA pool, comprising 14 FAAs. LMW-DOC concentrations in basal ice were dependent on the bioavailability of the overridden organic carbon (OC), which in turn, was influenced by the type of overridden material. Mean LMW-DOC concentrations in basal ice from Russell Glacier (Greenland), Finsterwalderbreen (Svalbard) and Engabreen (Norway) were low (0-417 nM C), attributed to the relatively refractory nature of the OC in the overridden paleosols and bedrock. In contrast, mean LMW-DOC concentrations were an order of magnitude higher (4430 nM C) in basal ice from Joyce Glacier, a reflection of the high bioavailability of the overridden lacustrine material (>17 % of the sediment OC comprised extractable carbohydrates, a proxy for bioavailable OC). We find that the overridden material may act as a direct (via abiotic leaching) and indirect (via microbial cycling) source of DOC to the subglacial environment and provides a range of LMW-DOC compounds that may stimulate microbial activity in wet sediments in current subglacial environments.

Partial coupling and differential regulation of biologically and photo-chemically labile dissolved organic carbon across boreal aquatic networks

NASA Astrophysics Data System (ADS)

Lapierre, J.-F.; del Giorgio, P. A.

2014-05-01

Despite the rapidly increasing volume of research on the biological and photochemical degradation of DOC in aquatic environments, little is known on the large-scale patterns in biologically and photo-chemically degradable DOC (Bd-DOC and Pd-DOC, respectively) in continental watersheds, and on the links that exist between these two key properties that greatly influence the flow of carbon from continents to oceans. Here we explore the patterns of Bd- and Pd-DOC across hundreds of boreal lakes, rivers and wetlands spanning a large range of system trophy and terrestrial influence, and compared the drivers of these two reactive pools of DOC at the landscape level. Using standardized incubations of natural waters, we found that the concentrations of Bd- and Pd-DOC co-varied across all systems studied but were nevertheless related to different pools of dissolved organic matter (DOM, identified by fluorescence analyses) in ambient waters. A combination of nutrients and protein-like DOM explained nearly half of the variation in Bd-DOC, whereas Pd-DOC was exclusively predicted by DOM optical properties, consistent with the photochemical degradability of specific fluorescent DOM (FDOM) pools that we experimentally determined. The concentrations of colored DOM (CDOM), a proxy of terrestrial influence, almost entirely accounted for the observed relationship between FDOM and the concentrations of both Bd- and Pd-DOC. The concentrations of CDOM and of the putative bio-labile fluorescence component shifted from complete decoupling in clear-water environments to strong coupling in browner streams and wetlands. This suggests a baseline autochthonous Bd-DOC pool fuelled by internal production that is gradually overwhelmed by land-derived Bd-DOC as terrestrial influence increases across landscape gradients. The importance of land as a major source of both biologically and photo-chemically degradable DOC for continental watersheds resulted in a partial coupling of those carbon pools in natural freshwaters, despite fundamental contrasts in terms of their composition and regulation.

Distribution characteristic of soil organic carbon fraction in different types of wetland in Hongze Lake of China.

PubMed

Lu, Yan; Xu, Hongwen

2014-01-01

Soil organic carbon fractions included microbial biomass carbon (MBC), dissolved organic carbon (DOC), and labile organic carbon (LOC), which was investigated over a 0-20 cm depth profile in three types of wetland in Hongze Lake of China. Their ecoenvironmental effect and the relationships with soil organic carbon (SOC) were analyzed in present experiment. The results showed that both active and SOC contents were in order reduced by estuarine wetland, flood plain, and out-of-lake wetland. Pearson correlative analysis indicated that MBC and DOC were positively related to SOC. The lowest ratios of MBC and DOC to SOC in the estuarine wetland suggested that the turnover rate of microbial active carbon pool was fairly low in this kind of wetland. Our results showed that estuarine wetland had a strong carbon sink function, which played important role in reducing greenhouse gas emissions; besides, changes of water condition might affect the accumulation and decomposition of organic carbon in the wetland soils.

Distribution Characteristic of Soil Organic Carbon Fraction in Different Types of Wetland in Hongze Lake of China

PubMed Central

Lu, Yan; Xu, Hongwen

2014-01-01

Soil organic carbon fractions included microbial biomass carbon (MBC), dissolved organic carbon (DOC), and labile organic carbon (LOC), which was investigated over a 0–20 cm depth profile in three types of wetland in Hongze Lake of China. Their ecoenvironmental effect and the relationships with soil organic carbon (SOC) were analyzed in present experiment. The results showed that both active and SOC contents were in order reduced by estuarine wetland, flood plain, and out-of-lake wetland. Pearson correlative analysis indicated that MBC and DOC were positively related to SOC. The lowest ratios of MBC and DOC to SOC in the estuarine wetland suggested that the turnover rate of microbial active carbon pool was fairly low in this kind of wetland. Our results showed that estuarine wetland had a strong carbon sink function, which played important role in reducing greenhouse gas emissions; besides, changes of water condition might affect the accumulation and decomposition of organic carbon in the wetland soils. PMID:24971377

Benthic fluxes of dissolved organic carbon from gas hydrate sediments in the northern South China Sea

PubMed Central

Hung, Chia-Wei; Huang, Kuo-Hao; Shih, Yung-Yen; Lin, Yu-Shih; Chen, Hsin-Hung; Wang, Chau-Chang; Ho, Chuang-Yi; Hung, Chin-Chang; Burdige, David J.

2016-01-01

Hydrocarbon vents have recently been reported to contribute considerable amounts of dissolved organic carbon (DOC) to the oceans. Many such hydrocarbon vents widely exist in the northern South China Sea (NSCS). To investigate if these hydrocarbon vent sites release DOC, we used a real-time video multiple-corer to collect bottom seawater and surface sediments at vent sites. We analyzed concentrations of DOC in these samples and estimated DOC fluxes. Elevated DOC concentrations in the porewaters were found at some sites suggesting that DOC may come from these hydrocarbon vents. Benthic fluxes of DOC from these sediments were 28 to 1264 μmol m−2 d−1 (on average ~321 μmol m−2 d−1) which are several times higher than most DOC fluxes in coastal and continental margin sediments. The results demonstrate that the real-time video multiple-corer can precisely collect samples at vent sites. The estimated benthic DOC flux from the methane venting sites (8.6 × 106 mol y−1), is 24% of the DOC discharge from the Pearl River to the South China Sea, indicating that these sediments make an important contribution to the DOC in deep waters. PMID:27432631

Effects of simulated acid rain on soil and soil solution chemistry in a monsoon evergreen broad-leaved forest in southern China.

PubMed

Qiu, Qingyan; Wu, Jianping; Liang, Guohua; Liu, Juxiu; Chu, Guowei; Zhou, Guoyi; Zhang, Deqiang

2015-05-01

Acid rain is an environmental problem of increasing concern in China. In this study, a laboratory leaching column experiment with acid forest soil was set up to investigate the responses of soil and soil solution chemistry to simulated acid rain (SAR). Five pH levels of SAR were set: 2.5, 3.0, 3.5, 4.0, and 4.5 (as a control, CK). The results showed that soil acidification would occur when the pH of SAR was ≤3.5. The concentrations of NO₃(-)and Ca(2+) in the soil increased significantly when the pH of SAR fell 3.5. The concentration of SO₄(2-) in the soil increased significantly when the pH of SAR was <4.0. The effects of SAR on soil solution chemistry became increasingly apparent as the experiment proceeded (except for Na(+) and dissolved organic carbon (DOC)). The net exports of NO₃(-), SO₄(2-), Mg(2+), and Ca(2+) increased about 42-86% under pH 2.5 treatment as compared to CK. The Ca(2+) was sensitive to SAR, and the soil could release Ca(2+) through mineral weathering to mitigate soil acidification. The concentration of exchangeable Al(3+) in the soil increased with increasing the acidity of SAR. The releases of soluble Al and Fe were SAR pH dependent, and their net exports under pH 2.5 treatment were 19.6 and 5.5 times, respectively, higher than that under CK. The net export of DOC was reduced by 12-29% under SAR treatments as compared to CK. Our results indicate the chemical constituents in the soil are more sensitive to SAR than those in the soil solution, and the effects of SAR on soil solution chemistry depend not only on the intensity of SAR but also on the duration of SAR addition. The soil and soil solution chemistry in this region may not be affected by current precipitation (pH≈4.5) in short term, but the soil and soil leachate chemistry may change dramatically if the pH of precipitation were below 3.5 and 3.0, respectively.

The role of iron and reactive oxygen species in the production of CO2 in arctic soil waters

NASA Astrophysics Data System (ADS)

Trusiak, Adrianna; Treibergs, Lija A.; Kling, George W.; Cory, Rose M.

2018-03-01

Hydroxyl radical (radOH) is a highly reactive oxidant of dissolved organic carbon (DOC) in the environment. radOH production in the dark was observed through iron and DOC mediated Fenton reactions in natural environments. Specifically, when dissolved oxygen (O2) was added to low oxygen and anoxic soil waters in arctic Alaska, radOH was produced in proportion to the concentrations of reduced iron (Fe(II)) and DOC. Here we demonstrate that Fe(II) was the main electron donor to O2 to produce radOH. In addition to quantifying radOH production, hydrogen peroxide (H2O2) was detected in soil waters as a likely intermediate in radOH production from oxidation of Fe(II). For the first time in natural systems we detected carbon dioxide (CO2) production from radOH oxidation of DOC. More than half of the arctic soil waters tested showed production of CO2 under conditions conducive for production of radOH. Findings from this study strongly suggest that DOC is the main sink for radOH, and that radOH can oxidize DOC to yield CO2. Thus, this iron-mediated, dark chemical oxidation of DOC may be an important component of the arctic carbon cycle.

Efficient removal of recalcitrant deep-ocean dissolved organic matter during hydrothermal circulation

NASA Astrophysics Data System (ADS)

Hawkes, Jeffrey A.; Rossel, Pamela E.; Stubbins, Aron; Butterfield, David; Connelly, Douglas P.; Achterberg, Eric P.; Koschinsky, Andrea; Chavagnac, Valérie; Hansen, Christian T.; Bach, Wolfgang; Dittmar, Thorsten

2015-11-01

Oceanic dissolved organic carbon (DOC) is an important carbon pool, similar in magnitude to atmospheric CO2, but the fate of its oldest forms is not well understood. Hot hydrothermal circulation may facilitate the degradation of otherwise un-reactive dissolved organic matter, playing an important role in the long-term global carbon cycle. The oldest, most recalcitrant forms of DOC, which make up most of oceanic DOC, can be recovered by solid-phase extraction. Here we present measurements of solid-phase extractable DOC from samples collected between 2009 and 2013 at seven vent sites in the Atlantic, Pacific and Southern oceans, along with magnesium concentrations, a conservative tracer of water circulation through hydrothermal systems. We find that magnesium and solid-phase extractable DOC concentrations are correlated, suggesting that solid-phase extractable DOC is almost entirely lost from solution through mineralization or deposition during circulation through hydrothermal vents with fluid temperatures of 212-401 °C. In laboratory experiments, where we heated samples to 380 °C for four days, we found a similar removal efficiency. We conclude that thermal degradation alone can account for the loss of solid-phase extractable DOC in natural hydrothermal systems, and that its maximum lifetime is constrained by the timescale of hydrothermal cycling, at about 40 million years.

Water-soluble elements in snow and ice on Mt. Yulong.

PubMed

Niu, Hewen; Kang, Shichang; Shi, Xiaofei; He, Yuanqing; Lu, Xixi; Shi, Xiaoyi; Paudyal, Rukumesh; Du, Jiankuo; Wang, Shijin; Du, Jun; Chen, Jizu

2017-01-01

Melting of high-elevation glaciers can be accelerated by the deposition of light-absorbing aerosols (e.g., organic carbon, mineral dust), resulting in significant reductions of the surface albedo on glaciers. Organic carbon deposited in glaciers is of great significance to global carbon cycles, snow photochemistry, and air-snow exchange processes. In this work, various snow and ice samples were collected at high elevation sites (4300-4850masl) from Mt. Yulong on the southeastern Tibetan Plateau in 2015. These samples were analyzed for water-soluble organic carbon (DOC), total nitrogen (TN), and water-soluble inorganic ions (WSIs) to elucidate the chemical species and compositions of the glaciers in the Mt. Yulong region. Generally, glacial meltwater had the lowest DOC content (0.39mgL -1 ), while fresh snow had the highest (2.03mgL -1 ) among various types of snow and ice samples. There were obvious spatial and temporal trends of DOC and WSIs in glaciers. The DOC and TN concentrations decreased in the order of fresh snow, snow meltwater, snowpit, and surface snow, resulting from the photolysis of DOC and snow's quick-melt effects. The surface snow had low DOC and TN depletion ratios in the melt season; specifically, the ratios were -0.79 and -0.19mgL -1 d -1 , respectively. In the winter season, the ratios of DOC and TN were remarkably higher, with values of -0.20mgL -1 d -1 and -0.08mgL -1 d -1 , respectively. A reduction of the DOC and TN content in glaciers was due to snow's quick melt and sublimation. Deposition of these light-absorbing impurities (LAPs) in glaciers might accelerate snowmelt and even glacial retreat. Copyright © 2016 Elsevier B.V. All rights reserved.

Shifts in vegetation affect organic carbon quality in a coastal marsh along the Hudson River Estuary

NASA Astrophysics Data System (ADS)

Zhang, A. H.; Corbett, J. E.; Tfaily, M. M.; Martin, I.; Ho, L.; Sun, E.; Sevilla, L.; Vincent, S.; Newton, R.; Peteet, D. M.

2015-12-01

To better understand carbon storage in coastal salt marshes, samples were collected from Piermont Marsh, NY (40 ̊00' N, 73 ̊55'W) located within the Hudson River Estuary. Porewater from three different vegetation sites was analyzed to compare the quality of the dissolved organic carbon. Sites contained either native or invasive vegetation with variations in live plant root depth. Porewater was taken from 0-3m in 50cm intervals, and sites were dominated either by invasive Phragmites australis, native Eleocharis , or native mixed vegetation (Spartina patens, Scirpus, and Typha angustifolia). Sites dominated by invasive Phragmites australis were found to have lower dissolved organic carbon (DOC) concentrations, lower cDOM absorption values, and more labile organic carbon compounds. The molecular composition of the DOC was determined with Fourier Transform Ion Cyclotron Mass Spectrometry (FT-ICR-MS). Labile DOC components were defined as proteins, carbohydrates, and amino sugars while recalcitrant DOC components were defined as lipids, unsaturated hydrocarbons, lignins, tannins, and condensed hydrocarbons. For the Phragmites, Eleocharis, and mixed vegetation sites, average DOC concentrations with depth were found to be 1.71 ± 1.06, 4.64 ± 1.73, and 4.62 ± 3.5 (mM), respectively and cDOM absorption values with depth were found to be 13.22 ± 4.81, 49.42 ± 10.8, and 35.74 ± 17.49 (m-1). Additionally, DOC concentrations increased with depth in the mixed vegetation and Eleocharis sites, but remained relatively constant in the Phragmites site. The percent of labile compounds in the surface samples were found to be 19.02, 14.64, and 14.07% for the Phragmites, Eleocharis, and mixed vegetation sites, respectively. These findings suggest that sites dominated by Phragmites may have more reactive DOC substrates than sites dominated by native vegetation. These results indicate that the carbon storage in marshes invaded by Phragmites would be expected to decrease over time.

Effect of Inorganic and Organic Carbon Enrichments (DIC and DOC) on the Photosynthesis and Calcification Rates of Two Calcifying Green Algae from a Caribbean Reef Lagoon.

PubMed

Meyer, Friedrich W; Schubert, Nadine; Diele, Karen; Teichberg, Mirta; Wild, Christian; Enríquez, Susana

2016-01-01

Coral reefs worldwide are affected by increasing dissolved inorganic carbon (DIC) and organic carbon (DOC) concentrations due to ocean acidification (OA) and coastal eutrophication. These two stressors can occur simultaneously, particularly in near-shore reef environments with increasing anthropogenic pressure. However, experimental studies on how elevated DIC and DOC interact are scarce and fundamental to understanding potential synergistic effects and foreseeing future changes in coral reef function. Using an open mesocosm experiment, the present study investigated the impact of elevated DIC (pHNBS: 8.2 and 7.8; pCO2: 377 and 1076 μatm) and DOC (added as 833 μmol L-1 of glucose) on calcification and photosynthesis rates of two common calcifying green algae, Halimeda incrassata and Udotea flabellum, in a shallow reef environment. Our results revealed that under elevated DIC, algal photosynthesis decreased similarly for both species, but calcification was more affected in H. incrassata, which also showed carbonate dissolution rates. Elevated DOC reduced photosynthesis and calcification rates in H. incrassata, while in U. flabellum photosynthesis was unaffected and thalus calcification was severely impaired. The combined treatment showed an antagonistic effect of elevated DIC and DOC on the photosynthesis and calcification rates of H. incrassata, and an additive effect in U. flabellum. We conclude that the dominant sand dweller H. incrassata is more negatively affected by both DIC and DOC enrichments, but that their impact could be mitigated when they occur simultaneously. In contrast, U. flabellum can be less affected in coastal eutrophic waters by elevated DIC, but its contribution to reef carbonate sediment production could be further reduced. Accordingly, while the capacity of environmental eutrophication to exacerbate the impact of OA on algal-derived carbonate sand production seems to be species-specific, significant reductions can be expected under future OA scenarios, with important consequences for beach erosion and coastal sediment dynamics.

Effect of Inorganic and Organic Carbon Enrichments (DIC and DOC) on the Photosynthesis and Calcification Rates of Two Calcifying Green Algae from a Caribbean Reef Lagoon

PubMed Central

Diele, Karen; Teichberg, Mirta; Wild, Christian

2016-01-01

Coral reefs worldwide are affected by increasing dissolved inorganic carbon (DIC) and organic carbon (DOC) concentrations due to ocean acidification (OA) and coastal eutrophication. These two stressors can occur simultaneously, particularly in near-shore reef environments with increasing anthropogenic pressure. However, experimental studies on how elevated DIC and DOC interact are scarce and fundamental to understanding potential synergistic effects and foreseeing future changes in coral reef function. Using an open mesocosm experiment, the present study investigated the impact of elevated DIC (pHNBS: 8.2 and 7.8; pCO2: 377 and 1076 μatm) and DOC (added as 833 μmol L-1 of glucose) on calcification and photosynthesis rates of two common calcifying green algae, Halimeda incrassata and Udotea flabellum, in a shallow reef environment. Our results revealed that under elevated DIC, algal photosynthesis decreased similarly for both species, but calcification was more affected in H. incrassata, which also showed carbonate dissolution rates. Elevated DOC reduced photosynthesis and calcification rates in H. incrassata, while in U. flabellum photosynthesis was unaffected and thalus calcification was severely impaired. The combined treatment showed an antagonistic effect of elevated DIC and DOC on the photosynthesis and calcification rates of H. incrassata, and an additive effect in U. flabellum. We conclude that the dominant sand dweller H. incrassata is more negatively affected by both DIC and DOC enrichments, but that their impact could be mitigated when they occur simultaneously. In contrast, U. flabellum can be less affected in coastal eutrophic waters by elevated DIC, but its contribution to reef carbonate sediment production could be further reduced. Accordingly, while the capacity of environmental eutrophication to exacerbate the impact of OA on algal-derived carbonate sand production seems to be species-specific, significant reductions can be expected under future OA scenarios, with important consequences for beach erosion and coastal sediment dynamics. PMID:27487195

Seasonal variations in production and consumption rates of dissolved organic carbon in an organic-rich coastal sediment

NASA Astrophysics Data System (ADS)

Alperin, M. J.; Albert, D. B.; Martens, C. S.

1994-11-01

Dissolved organic carbon (DOC) concentrations in anoxic marine sediments are controlled by at least three processes: (1) production of nonvolatile dissolved compounds, such as peptides and amino acids, soluble saccharides and fatty acids, via hydrolysis of particulate organic carbon (POC). (2) conversion of these compounds to volatile fatty acids and alcohols by fermentative bacteria. (3) consumption of volatile fatty acids and alcohols by terminal bacteria, such as sulfate reducers and methanogens. We monitored seasonal changes in concentration profiles of total DOC, nonacid-volatile (NAV) DOC and acid-volatile (AV) DOC in anoxic sediment from Cape Lookout Bight, North Carolina, USA, in order to investigate the factors that control seasonal variations in rates of hydrolysis, fermentation, and terminal metabolism. During the winter months, DOC concentrations increased continuously from 0.2 mM in the bottomwater to ~4 mM at a depth of 36 cm in the sediment column. During the summer, a large DOC maximum developed between 5 and 20 cm, with peak concentrations approaching 10 mM. The mid-depth summertime maximum was driven by increases in both NAV- and AV-DOC concentrations. Net NAV-DOC reaction rates were estimated by a diagenetic model applied to NAV-DOC concentration profiles. Depth-integrated production rates of NAV-DOC increased from February through July, suggesting that net rates of POC hydrolysis during this period are controlled by temperature. Net consumption of NAV-DOC during the late summer and early fall suggests reduced gross NAV-DOC production rates, presumably due to a decline in the availability of labile POC. A distinct subsurface peak in AV-DOC concentration developed during the late spring, when the sulfate depletion depth shoaled from 25 to 10 cm. We hypothesize that the AV-DOC maximum results from a decline in consumption by sulfate-reducing bacteria (due to sulfate limitation) and a lag in the development of an active population of methanogenic bacteria. A diagenetic model that incorporates a lag period in the sulfate reducer-methanogen transition successfully simulates the timing, magnitude, depth and shape of the AV-DOC peak.

Controls on dissolved organic carbon quantity and chemical character in temperate rivers of North America

USGS Publications Warehouse

Hanley, Kevin W.; Wollheim, Wilfred M.; Salisbury, Joseph; Huntington, Thomas G.; Aiken, George R.

2013-01-01

Understanding the processes controlling the transfer and chemical composition of dissolved organic carbon (DOC) in freshwater systems is crucial to understanding the carbon cycle and the effects of DOC on water quality. Previous studies have identified watershed-scale controls on bulk DOC flux and concentration among small basins but fewer studies have explored controls among large basins or simultaneously considered the chemical composition of DOC. Because the chemical character of DOC drives riverine biogeochemical processes such as metabolism and photodegradation, accounting for chemical character in watershed-scale studies will improve the way bulk DOC variability in rivers is interpreted. We analyzed DOC quantity and chemical character near the mouths of 17 large North American rivers, primarily between 2008 and 2010, and identified watershed characteristics that controlled variability. We quantified DOC chemical character using both specific ultraviolet absorbance at 254 nm (SUVA254) and XAD-resin fractionation. Mean DOC concentration ranged from 2.1 to 47 mg C L−1 and mean SUVA254 ranged from 1.3 to 4.7 L mg C−1 m−1. We found a significant positive correlation between basin wetland cover and both bulk DOC concentration (R2 = 0.78; p < 0.0001) and SUVA254 (R2 = 0.91; p < 0.0001), while other land use characteristics were not correlated. The strong wetland relationship with bulk DOC concentration is similar to that found by others in small headwater catchments. However, two watersheds with extremely long surface water residence times, the Colorado and St. Lawrence, diverged from this wetland relationship. These results suggest that the role of riverine processes in altering the terrestrial DOC signal at the annual scale was minimal except in river systems with long surface water residence times. However, synoptic DOC sampling of both quantity and character throughout river networks will be needed to more rigorously test this finding. The inclusion of DOC chemical character will be vital to achieving a more complete understanding of bulk DOC dynamics in large river systems.

Dissolved Organic Carbon Mobilisation in a Groundwater System Stressed by Pumping

PubMed Central

Graham, P. W.; Baker, A.; Andersen, M. S.

2015-01-01

The concentration and flux of organic carbon in aquifers is influenced by recharge and abstraction, and surface and subsurface processing. In this study groundwater was abstracted from a shallow fractured rock aquifer and dissolved organic carbon (DOC) was measured in observation bores at different distances from the abstraction bore. Groundwater abstraction at rates exceeding the aquifers yield resulted in increased DOC concentration up to 3,500 percent of initial concentrations. Potential sources of this increased DOC were determined using optical fluorescence and absorbance analysis. Groundwater fluorescent dissolved organic material (FDOM) were found to be a combination of terrestrial-derived humic material and microbial or protein sourced material. Relative molecular weight of FDOM within four metres of the abstraction well increased during the experiment, while the relative molecular weight of FDOM between four and ten metres from the abstraction well decreased. When the aquifer is not being pumped, DOC mobilisation in the aquifer is low. We hypothesise that the physical shear stress on aquifer materials caused by intense abstraction significantly increases the temporary release of DOC from sloughing of biofilms and release of otherwise bound colloidal and sedimentary organic carbon (SOC). PMID:26691238

The conservative behavior of dissolved organic carbon in surface waters of the southern Chukchi Sea, Arctic Ocean, during early summer

PubMed Central

Tanaka, Kazuki; Takesue, Nobuyuki; Nishioka, Jun; Kondo, Yoshiko; Ooki, Atsushi; Kuma, Kenshi; Hirawake, Toru; Yamashita, Youhei

2016-01-01

The spatial distribution of dissolved organic carbon (DOC) concentrations and the optical properties of dissolved organic matter (DOM) determined by ultraviolet-visible absorbance and fluorescence spectroscopy were measured in surface waters of the southern Chukchi Sea, western Arctic Ocean, during the early summer of 2013. Neither the DOC concentration nor the optical parameters of the DOM correlated with salinity. Principal component analysis using the DOM optical parameters clearly separated the DOM sources. A significant linear relationship was evident between the DOC and the principal component score for specific water masses, indicating that a high DOC level was related to a terrigenous source, whereas a low DOC level was related to a marine source. Relationships between the DOC and the principal component scores of the surface waters of the southern Chukchi Sea implied that the major factor controlling the distribution of DOC concentrations was the mixing of plural water masses rather than local production and degradation. PMID:27658444

Inputs of fossil carbon from wastewater treatment plants to U.S. Rivers and oceans

USGS Publications Warehouse

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

2009-01-01

Every day more than 500 million cubic meters of treated wastewater are discharged into rivers, estuaries, and oceans, an amount slightly less than the average flow of the Danube River. Typically, wastewaters have high organic carbon (OC) concentrations and represent a large fraction of total river flow and a higher fraction of river OC in densely populated watersheds. Here, we report the first direct measurements of radiocarbon (14C) in municipal wastewater treatment plant (WWTP) effluent. The radiocarbon ages of particulate and dissolved organic carbon (POC and DOC) in effluent are old and relatively uniform across a range of WWTPs in New York and Connecticut. Wastewater DOC has a mean radiocarbon age of 1630 ?? 500 years B.P. and a mean ??13C of -26.0 ?? 1???. Mass balance calculations indicate that 25% of wastewater DOC is fossil carbon, which is likely derived from petroleumbased household products such as detergents and pharmaceuticals. Thesefindings warrant reevaluation of the "apparent age" of riverine DOC, the total flux of petroleum carbon to U.S. oceans, and OC source assignments in waters impacted by sewage. ?? 2009 American Chemical Society.

Yucca Mountain Area Saturated Zone Dissolved Organic Carbon Isotopic Data

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

Thomas, James; Decker, David; Patterson, Gary

2007-06-25

Groundwater samples in the Yucca Mountain area were collected for chemical and isotopic analyses and measurements of water temperature, pH, specific conductivity, and alkalinity were obtained at the well or spring at the time of sampling. For this project, groundwater samples were analyzed for major-ion chemistry, deuterium, oxygen-18, and carbon isotopes of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). The U.S. Geological Survey (USGS) performed all the fieldwork on this project including measurement of water chemistry field parameters and sample collection. The major ions dissolved in the groundwater, deuterium, oxygen-18, and carbon isotopes of dissolved inorganic carbon (DIC)more » were analyzed by the USGS. All preparation and processing of samples for DOC carbon isotopic analyses and geochemical modeling were performed by the Desert Research Institute (DRI). Analysis of the DOC carbon dioxide gas produced at DRI to obtain carbon-13 and carbon-14 values was conducted at the University of Arizona Accelerator Facility (a NSHE Yucca Mountain project QA qualified contract facility). The major-ion chemistry, deuterium, oxygen-18, and carbon isotopes of DIC were used in geochemical modeling (NETPATH) to determine groundwater sources, flow paths, mixing, and ages. The carbon isotopes of DOC were used to calculate groundwater ages that are independent of DIC model corrected carbon-14 ages. The DIC model corrected carbon-14 calculated ages were used to evaluate groundwater travel times for mixtures of water including water beneath Yucca Mountain. When possible, groundwater travel times were calculated for groundwater flow from beneath Yucca Mountain to down gradient sample sites. DOC carbon-14 groundwater ages were also calculated for groundwaters in the Yucca Mountain area. When possible, groundwater travel times were estimated for groundwater flow from beneath Yucca Mountain to down gradient groundwater sample sites using the DOC calculated groundwater ages. The DIC calculated groundwater ages were compared with DOC calculated groundwater ages and both of these ages were compared to travel times developed in ground-water flow and transport models. If nuclear waste is stored in Yucca Mountain, the saturated zone is the final barrier against the release of radionuclides to the environment. The most recent rendition of the TSPA takes little credit for the presence of the saturated zone and is a testament to the inadequate understanding of this important barrier. If radionuclides reach the saturated zone beneath Yucca Mountain, then there is a travel time before they would leave the Yucca Mountain area and flow down gradient to the Amargosa Valley area. Knowing how long it takes groundwater in the saturated zone to flow from beneath Yucca Mountain to down gradient areas is critical information for potential radionuclide transport. Radionuclide transport in groundwater may be the quickest pathway for radionuclides in the proposed Yucca Mountain repository to reach land surface by way of groundwater pumped in Amargosa Valley. An alternative approach to ground-water flow and transport models to determine the travel time of radionuclides from beneath Yucca Mountain to down gradient areas in the saturated zone is by carbon-14 dating of both inorganic and organic carbon dissolved in the groundwater. A standard method of determining ground-water ages is to measure the carbon-13 and carbon-14 of DIC in the groundwater and then correct the measured carbon-14 along a flow path for geochemical reactions that involve carbon containing phases. These geochemical reactions are constrained by carbon-13 and isotopic fractionations. Without correcting for geochemical reactions, the ground-water ages calculated from only the differences in carbon-14 measured along a flow path (assuming the decrease in carbon-14 is due strictly to radioactive decay) could be tens of thousands of years too old. The computer program NETPATH, developed by the USGS, is the best geochemical program for correcting carbon-14 activities for geochemical reactions. The DIC carbon-14 corrected ages can be further constrained by measuring the carbon isotopes of DOC. Because the only source of organic carbon in aquifers is almost always greater than 40,000 years old, any organic carbon that may be added to the groundwater would contain no carbon-14. Thus, ground-water ages determined by carbon isotopes of DOC should be maximum ages that can be used to constrain DIC corrected ages.« less

Mercury and Organic Carbon Relationships in Streams Draining Forested Upland/Peatland Watersheds

Treesearch

R. K. Kolka; D. F. Grigal; E. S. Verry; E. A. Nater

1999-01-01

We determined the fluxes of total mecury (HgT), total organic carbon (TOC), and dissolved organic carbon (DOC) from five upland/peatland watersheds at the watershed outlet. The difference between TOC and DOC was defined as particulate OC (POC). Concentrations of HgT showed moderate to strong relationships with POC (R2 = 0.77) when all watersheds...

Mercury and Organic Carbon Relationships in Streams Draining Forested Upland/Peatland Watersheds

Treesearch

Randall K. Kolka; D.F. Grigal; E.S. Verry; E.A. Nater

1999-01-01

We determined the fluxes of total mercury (HgT), total organic carbon (TOC), and dissolved organic carbon (DOC) from five upland/peatland watersheds at the watershed outlet. The difference between TOC and DOC was defined as particulate OC (POC). Concentrations of HgT showed moderate to strong relationships with POC (R2 = 0.77) when ah...

Method 415.3, Rev. 1.2: Determination of Total Organic Carbon and Specific UV Absorbance at 254 nm in Source Water and Drinking Water

EPA Science Inventory

This method provides procedures for the determination of total organic carbon (TOC), dissolved organic carbon (DOC), and UV absorption at 254 nm (UVA) in source waters and drinking waters. The DOC and UVA determinations are used in the calculation of the Specific UV Absorbance (S...

Plankton networks driving carbon export in the oligotrophic ocean

PubMed Central

Larhlimi, Abdelhalim; Roux, Simon; Darzi, Youssef; Audic, Stephane; Berline, Léo; Brum, Jennifer; Coelho, Luis Pedro; Espinoza, Julio Cesar Ignacio; Malviya, Shruti; Sunagawa, Shinichi; Dimier, Céline; Kandels-Lewis, Stefanie; Picheral, Marc; Poulain, Julie; Searson, Sarah; Stemmann, Lars; Not, Fabrice; Hingamp, Pascal; Speich, Sabrina; Follows, Mick; Karp-Boss, Lee; Boss, Emmanuel; Ogata, Hiroyuki; Pesant, Stephane; Weissenbach, Jean; Wincker, Patrick; Acinas, Silvia G.; Bork, Peer; de Vargas, Colomban; Iudicone, Daniele; Sullivan, Matthew B.; Raes, Jeroen; Karsenti, Eric; Bowler, Chris; Gorsky, Gabriel

2015-01-01

The biological carbon pump is the process by which CO2 is transformed to organic carbon via photosynthesis, exported through sinking particles, and finally sequestered in the deep ocean. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure driving the process remains largely uncharacterised. Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve our understanding of carbon export in the oligotrophic ocean. We show that specific plankton communities, from the surface and deep chlorophyll maximum, correlate with carbon export at 150 m and highlight unexpected taxa such as Radiolaria, alveolate parasites, as well as Synechococcus and their phages, as lineages most strongly associated with carbon export in the subtropical, nutrient-depleted, oligotrophic ocean. Additionally, we show that the relative abundance of just a few bacterial and viral genes can predict most of the variability in carbon export in these regions. PMID:26863193

Plankton networks driving carbon export in the oligotrophic ocean

NASA Astrophysics Data System (ADS)

2016-04-01

The biological carbon pump is the process by which CO2 is transformed to organic carbon via photosynthesis, exported through sinking particles, and finally sequestered in the deep ocean. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure driving the process remains largely uncharacterized. Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve our understanding of carbon export in the oligotrophic ocean. We show that specific plankton communities, from the surface and deep chlorophyll maximum, correlate with carbon export at 150 m and highlight unexpected taxa such as Radiolaria and alveolate parasites, as well as Synechococcus and their phages, as lineages most strongly associated with carbon export in the subtropical, nutrient-depleted, oligotrophic ocean. Additionally, we show that the relative abundance of a few bacterial and viral genes can predict a significant fraction of the variability in carbon export in these regions.

The effect of drought on dissolved organic carbon (DOC) release from peatland soil and vegetation sources

NASA Astrophysics Data System (ADS)

Ritson, Jonathan P.; Brazier, Richard E.; Graham, Nigel J. D.; Freeman, Chris; Templeton, Michael R.; Clark, Joanna M.

2017-06-01

Drought conditions are expected to increase in frequency and severity as the climate changes, representing a threat to carbon sequestered in peat soils. Downstream water treatment works are also at risk of regulatory compliance failures and higher treatment costs due to the increase in riverine dissolved organic carbon (DOC) often observed after droughts. More frequent droughts may also shift dominant vegetation in peatlands from Sphagnum moss to more drought-tolerant species. This paper examines the impact of drought on the production and treatability of DOC from four vegetation litters (Calluna vulgaris, Juncus effusus, Molinia caerulea and Sphagnum spp.) and a peat soil. We found that mild droughts caused a 39.6 % increase in DOC production from peat and that peat DOC that had been exposed to oxygen was harder to remove by conventional water treatment processes (coagulation/flocculation). Drought had no effect on the amount of DOC production from vegetation litters; however large variation was observed between typical peatland species (Sphagnum and Calluna) and drought-tolerant grassland species (Juncus and Molinia), with the latter producing more DOC per unit weight. This would therefore suggest the increase in riverine DOC often observed post-drought is due entirely to soil microbial processes and DOC solubility rather than litter layer effects. Long-term shifts in species diversity may, therefore, be the most important impact of drought on litter layer DOC flux, whereas pulses related to drought may be observed in peat soils and are likely to become more common in the future. These results provide evidence in support of catchment management which increases the resilience of peat soils to drought, such as ditch blocking to raise water tables.

Experimental investigation and modeling of dissolved organic carbon removal by coagulation from seawater.

PubMed

Jeong, Sanghyun; Sathasivan, Arumugam; Kastl, George; Shim, Wang Geun; Vigneswaran, Saravanamuthu

2014-01-01

Coagulation removes colloidal matters and dissolved organic carbon (DOC) which can cause irreversible membrane fouling. However, how DOC is removed by coagulant is not well-known. Jar test was used to study the removal of hydrophobic and hydrophilic DOC fractions at various doses (0.5-8.0 mg-Fe(+3) L(-1)) of ferric chloride (FeCl3) and pH (5.0-9.0). Natural organic matter (NOM) in seawater and treated seawater were fractionated by liquid chromatography-organic carbon detector (LC-OCD). Compared to surface water, the removal of DOC in seawater by coagulation was remarkably different. Majority of DOC could be easily removed with very low coagulant dose (<5.0 mg-Fe(+3) L(-1)) and the removal efficiency did not vary with pH, but the DOC composition in treated water had significantly changed. Hydrophobic fraction (HB) was better removed at high pH while hydrophilic fraction (HF) was better removed at low pH. A modified model of Kastl et al. (2004) which assumed that the removal occurred by adsorption of un-dissociated compounds onto ferric hydroxide was formulated and successfully validated against the jar test data. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effect of past peat cultivation practices on present dynamics of dissolved organic carbon.

PubMed

Frank, S; Tiemeyer, B; Bechtold, M; Lücke, A; Bol, R

2017-01-01

Peatlands are a major source of dissolved organic carbon (DOC) for aquatic ecosystems. Naturally high DOC concentrations in peatlands may be increased further by drainage. For agricultural purposes, peat has frequently been mixed with sand, but the effect of this measure on the release and cycling of DOC has rarely been investigated. This study examined the effects of (i) mixing peat with sand and (ii) water table depth (WTD) on DOC concentrations at three grassland sites on shallow organic soils. The soil solution was sampled bi-weekly for two years with suction plates at 15, 30 and 60cm depth. Selected samples were analysed for dissolved organic nitrogen (DON), δ 13 C DOM and δ 15 N DOM . Average DOC concentrations were surprisingly high, ranging from 161 to 192mgl -1 . There was no significant impact of soil organic carbon (SOC) content or WTD on mean DOC concentrations. At all sites, DOC concentrations were highest at the boundary between the SOC-rich horizon and the mineral subsoil. In contrast to the mean concentrations, the temporal patterns of DOC concentrations, their drivers and the properties of dissolved organic matter (DOM) differed between peat-sand mixtures and peat. DOC concentrations responded to changes in environmental conditions, but only after a lag period of a few weeks. At the sites with a peat-sand mixture, temperature and therefore probably biological activity determined the DOC concentrations. At the peat site, the contribution of vegetation-derived DOM was higher. The highest concentrations occurred during long, cool periods of waterlogging, suggesting a stronger physicochemical-based DOC mobilisation. Overall, these results indicate that mixing peat with sand does not improve water quality and may result in DOC losses of around 200kg DOCha -1 a -1 . Copyright © 2016 Office national des forêts. Published by Elsevier B.V. All rights reserved.

Nutrient dynamics across a dissolved organic carbon and burn gradient in central Siberia

NASA Astrophysics Data System (ADS)

Rodriguez-Cardona, B.; Coble, A. A.; Prokishkin, A. S.; Kolosov, R.; Spencer, R. G.; Wymore, A.; McDowell, W. H.

2016-12-01

In stream ecosystems, dissolved organic carbon (DOC) and nitrogen (N) processing are tightly linked. In temperate streams, greater DOC concentrations and higher DOC:NO3- ratios promote the greatest nitrate (NO3-) uptake. However, less is known about this relationship in other biomes including the arctic which is undergoing changes due to climate change contributing to thawing of permafrost and alterations in biogeochemical cycles in soils and streams. Headwater streams draining into the N. Tunguska River in the central Siberian plateau are affected by forest fires but little is known about the aquatic biogeochemical implications in both a thawing and burning landscape. There are clear patterns between carbon concentration and fire history where generally DOC concentration in streams decrease after fires and older burn sites have shown greater DOC concentrations and more bioavailable DOC that could promote greater heterotrophic uptake of NO3-. However, the relationship between nutrient dynamics, organic matter composition, and fire history in streams is not very clear. In order to assess the influence of organic matter composition and DOC concentration on nutrient uptake in arctic streams, we conducted a series of short-term nutrient addition experiments following the tracer addition for spiraling curve characterization (TASCC) method, consisting of NO3- and NH4++PO43- additions, across 4 streams that comprise a fire gradient that spans 3- >100 years since the last burn with DOC concentrations ranging between 12-23 mg C/L. We hypothesized that nutrient uptake would be greatest in older burn sites due to greater DOC concentrations and availability. We will specifically examine how nutrient uptake relates to DOC concentration and OM composition (analyzed via FTICR-MS) across the burn gradient. Across the four sites DOC concentration and DOC:NO3- ratios decreased from old burn sites to recently burned sites. Results presented here can elucidate on the potential impacts of permafrost thawing and forest fires on nutrient dynamics in arctic streams.

Organic matter dynamics in a karstic watershed: Example from Santa Fe River, Florida, USA

NASA Astrophysics Data System (ADS)

Jin, J.; Khadka, M. B.; Martin, J. B.; Zimmerman, A. R.

2011-12-01

Organic matter (OM) dynamics in karstic watersheds can involve a range of interactions between organic and inorganic phases of carbon. These interactions include OM remineralization, which will changes its lability, increase dissolved inorganic carbon (DIC) concentrations, reduce pH, and enhance carbonate mineral dissolution. Dissolved organic carbon (DOC) concentrations are elevated in black-water rivers of northern Florida from both allochthonous and autochthonous sources and these rivers flow into and interact with the karstic Floridan Aquifer. One such river, the Santa Fe River, is split into upper confined and lower unconfined watersheds by the Cody Scarp, which represent the erosional edge of a regional confining unit. Water samples were collected from 8 sites across the entire Santa Fe River watershed (SFRW) during 9 sampling trips from December 2009 to May 2011 at flow conditions that ranged from 27 to 39 m3/s, with the highest flow about 45% higher than baseflow. At sites above the Cody Scarp, the river has elevated DOC concentrations, which decrease downstream, while dissolved inorganic carbon (DIC) and δ13C-DIC show opposite trends. At high flow, DOC concentrations progressively decrease downstream from dilution by low-DOC water discharging from the Floridan Aquifer. At low flow, the water chemistry varies little from upstream to downstream, largely because the composition of upstream water becomes similar to that of downstream water. DOC is inversely and linearly correlated with DIC and δ13C-DIC, but the slope of the correlations vary with discharge, with low flow having more negative slopes than high flow. The OM becomes more labile with distance downstream as assessed using two fluorescence indices, biological/autochthonous index (BIX) and humification index (HIX). This increase in lability suggests that DOC is produced in the river, and this production is reflected in a downstream increase in DOC flux regardless of dilution by the influx of low-DOC groundwater. Primary production was 5 to 25 times higher during high and low flow, respectively, in the lower than in the upper SFRW. No decrease in DOC with a concomitant increase in DIC was observed, however, suggesting observations of microbial consumption of OM is masked by primary production and gain of DIC-rich and DOC-poor groundwater. The upper SFRW has lower saturation index (SI; -2.9 and -0.7 for high and low flow, respectively) than the lower SFRW (0.0 and 0.3 for high and low flow, respectively). The downstream shift in SI reflects dissolution of the carbonate minerals and gain of water from the Floridan Aquifer that had equilibrated with carbonate minerals. OM dynamics in the SFRW are closely linked to the allochthonous OM derived from the upper SFRW, as well as primary production in the lower watershed. Both allochthonous and autochthonous OM can be important in abiotic processes such as carbonate mineral dissolution, but flow conditions mediate the magnitudes of the reactions.

Concentrations and characteristics of organic carbon in surface water in Arizona: Influence of urbanization

USGS Publications Warehouse

Westerhoff, P.; Anning, D.

2000-01-01

Dissolved (DOC) and total (TOC) organic carbon concentrations and compositions were studied for several river systems in Arizona, USA. DOC composition was characterized by ultraviolet and visible absorption and fluorescence emission (excitation wavelength of 370 nm) spectra characteristics. Ephemeral sites had the highest DOC concentrations, and unregulated perennial sites had lower concentrations than unregulated intermittent sites, regulated sites, and sites downstream from wastewater-treatment plants (p < 0.05). Reservoir outflows and wastewater-treatment plant effluent were higher in DOC concentration (p < 0.05) and exhibited less variability in concentration than inflows to the reservoirs. Specific ultraviolet absorbance values at 254 nm were typically less than 2 m-1(milligram DOC per liter)-1 and lower than values found in most temperate-region rivers, but specific ultraviolet absorbance values increased during runoff events. Fluorescence measurements indicated that DOC in desert streams typically exhibit characteristics of autochthonous sources; however, DOC in unregulated upland rivers and desert streams experienced sudden shifts from autochthonous to allochthonous sources during runoff events. The urban water system (reservoir systems and wastewater-treatment plants) was found to affect temporal variability in DOC concentration and composition. (C) 2000 Elsevier Science B.V.Dissolved (DOC) and total (TOC) organic carbon concentrations and compositions were studied for several river systems in Arizona, USA. DOC composition was characterized by ultraviolet and visible absorption and fluorescence emission (excitation wavelength of 370 nm) spectra characteristics. Ephemeral sites had the highest DOC concentrations, and unregulated perennial sites had lower concentrations than unregulated intermittent sites, regulated sites, and sites downstream from wastewater-treatment plants (p<0.05). Reservoir outflows and wastewater-treatment plant effluent were higher in DOC concentration (p<0.05) and exhibited less variability in concentration than inflows to the reservoirs. Specific ultraviolet absorbance values at 254 nm were typically less than 2 m-1(milligram DOC per liter)-1 and lower than values found in most temperate-region rivers, but specific ultraviolet absorbance values increased during runoff events. Fluorescence measurements indicated that DOC in desert streams typically exhibit characteristics of autochthonous sources; however, DOC in unregulated upland rivers and desert streams experienced sudden shifts from autochthonous to allochthonous sources during runoff events. The urban water system (reservoir systems and wastewater-treatment plants) was found to affect temporal variability in DOC concentration and composition.The influence of urbanization, becoming increasingly common in arid regions, on dissolved organic carbon (DOC) concentrations in surface water resources was studied. DOC concentration and composition, seasonal watershed runoff events, streamflow variations, water management practices, and urban infrastructure in several Arizona watersheds were monitored. Ephemeral sites had the highest DOC levels, and unregulated perennial sites and lower concentrations than unregulated intermittent sites, regulated sites, and sites downstream from wastewater treatment plants. Reservoir outflows and wastewater treatment plant effluent had higher and less variable DOC concentrations than inflows to reservoirs. UV absorbance values, fluorescence measurements, and other indicators suggest that urban water systems (reservoirs and wastewater treatment plants) affect temporal variability in DOC concentration and composition.

Response of Bacterial Metabolic Activity to Riverine Dissolved Organic Carbon and Exogenous Viruses in Estuarine and Coastal Waters: Implications for CO2 Emission

PubMed Central

Xu, Jie; Sun, Mingming; Shi, Zhen; Harrison, Paul J.; Liu, Hongbin

2014-01-01

A cross-transplant experiment between estuarine water and seawater was conducted to examine the response of bacterial metabolic activity to riverine dissolved organic carbon (DOC) input under virus-rich and virus-free conditions, as well as to exogenous viruses. Riverine DOC input increased bacterial production significantly, but not bacterial respiration (BR) because of its high lability. The bioavailable riverine DOC influenced bulk bacterial respiration in two contrasting ways; it enhanced the bulk BR by stimulating bacterial growth, but simultaneously reduced the cell-specific BR due to its high lability. As a result, there was little stimulation of the bulk BR by riverine DOC. This might be partly responsible for lower CO2 degassing fluxes in estuaries receiving high sewage-DOC that is highly labile. Viruses restricted microbial decomposition of riverine DOC dramatically by repressing the growth of metabolically active bacteria. Bacterial carbon demand in the presence of viruses only accounted for 7–12% of that in the absence of viruses. Consequently, a large fraction of riverine DOC was likely transported offshore to the shelf. In addition, marine bacteria and estuarine bacteria responded distinctly to exogenous viruses. Marine viruses were able to infect estuarine bacteria, but not as efficiently as estuarine viruses, while estuarine viruses infected marine bacteria as efficiently as marine viruses. We speculate that the rapid changes in the viral community due to freshwater input destroyed the existing bacteria-virus relationship, which would change the bacterial community composition and affect the bacterial metabolic activity and carbon cycling in this estuary. PMID:25036641

Response of bacterial metabolic activity to riverine dissolved organic carbon and exogenous viruses in estuarine and coastal waters: implications for CO2 emission.

PubMed

Xu, Jie; Sun, Mingming; Shi, Zhen; Harrison, Paul J; Liu, Hongbin

2014-01-01

A cross-transplant experiment between estuarine water and seawater was conducted to examine the response of bacterial metabolic activity to riverine dissolved organic carbon (DOC) input under virus-rich and virus-free conditions, as well as to exogenous viruses. Riverine DOC input increased bacterial production significantly, but not bacterial respiration (BR) because of its high lability. The bioavailable riverine DOC influenced bulk bacterial respiration in two contrasting ways; it enhanced the bulk BR by stimulating bacterial growth, but simultaneously reduced the cell-specific BR due to its high lability. As a result, there was little stimulation of the bulk BR by riverine DOC. This might be partly responsible for lower CO2 degassing fluxes in estuaries receiving high sewage-DOC that is highly labile. Viruses restricted microbial decomposition of riverine DOC dramatically by repressing the growth of metabolically active bacteria. Bacterial carbon demand in the presence of viruses only accounted for 7-12% of that in the absence of viruses. Consequently, a large fraction of riverine DOC was likely transported offshore to the shelf. In addition, marine bacteria and estuarine bacteria responded distinctly to exogenous viruses. Marine viruses were able to infect estuarine bacteria, but not as efficiently as estuarine viruses, while estuarine viruses infected marine bacteria as efficiently as marine viruses. We speculate that the rapid changes in the viral community due to freshwater input destroyed the existing bacteria-virus relationship, which would change the bacterial community composition and affect the bacterial metabolic activity and carbon cycling in this estuary.

Influence of light, temperature and salinity on dissolved organic carbon exudation rates in Zostera marina L.

PubMed Central

2012-01-01

Background Marine angiosperms, seagrasses, are sentinel species of marine ecosystem health and function. Seagrass carbon budgets provide insight on the minimum requirements needed to maintain this valuable resource. Carbon budgets are a balance between C fixation, growth, storage and loss rates, most of which are well characterized. However, relatively few measurements of dissolved organic carbon (DOC) leaf exudation or rhizodeposition rates exist for most seagrass species. Here I evaluate how eelgrass (Zostera marina L.) DOC exudation is affected by a single factor manipulation (light, temperature or salinity). Eelgrass plants were hydroponically exposed to treatments in experimental chambers (separate leaf and rhizome/root compartments) with artificial seawater medium. Regression analysis of changes in the DOC concentration through time was used to calculate DOC exudation rates. Results Exudation rates were similar across all treatments in all experiments. For all experiments, pooled leaf DOC exudation ranged between 0.032 and 0.069 mg C gdw-1 h-1, while rhizodeposition ranged between 0.024 and 0.045 mg C gdw-1 h-1. These rates are consistent with previously published values and provide first-order estimates for mechanistic models. Conclusions Zostera marina carbon losses from either leaf exudation or rhizodeposition account for a small proportion of gross primary production (1.2-4.6%) and appear to be insensitive to short-term (e.g., hours to days) environmental variations in chamber experiments. Based on these preliminary experiments, I suggest that Z. marina DOC exudation may be a passive process and not an active transport process. PMID:22938529

Fluvial dissolved organic carbon composition varies spatially and seasonally in a small catchment draining a wind farm and felled forestry.

PubMed

Zheng, Ying; Waldron, Susan; Flowers, Hugh

2018-06-01

Assessing whether land use, from activities such as wind farm construction and tree-felling, impacts on terrestrial C delivery to rivers has focused on quantifying the loss of dissolved organic carbon (DOC), and not the composition changes. Here we explore how land use influences DOC composition by considering fluvial DOC concentration, [DOC], and spectrophotometric composition of a river draining a peat-rich catchment. We find that in this 5.7km 2 catchment differences occur in both the concentration and composition of the DOC in its sub-catchments. This is attributed to differences in how land was used: one tributary (D-WF) drains an area with wind farm construction and forestry in the headwaters, and one tributary (D-FF) drains an area with felled plantation trees. Generally, [DOC] in both streams showed similar seasonal variation, and autumn maxima. However, the felled catchment had greater mean [DOC] than the wind farm catchment. The SUVA 254 and E 4 /E 6 indicated DOC in both streams had similar aromaticity and fulvic:humic acid for most of the time, but SUVA 410 and E 2 /E 4 indicated less DOC humification in the felled catchment. This may be due to young DOC from the breakdown of residual branches and roots, or more humification in soils in the wind farm area. During the dry months, DOC composition showed more spatial variation: the D-WF DOC had smaller SUVA 254 (less total aromatic material) and SUVA 410 (fewer humic substances). The decreased E 2 /E 4 in both streams indicated the total aromatic carbon decreased more than humic substances content. Moreover, the larger E 4 /E 6 for D-WF in summer indicated that the humic substances were richer in fulvic acids than humic acids. Soil disturbance associated with forestry-felling likely contributed to the higher [DOC] and release of less-humified material in D-FF. This research indicates drivers of different DOC concentration and composition can exist even in small catchments. Copyright © 2018 Elsevier B.V. All rights reserved.

Considerations of erosion and storage of carbon, focusing on tropical landscapes in Puerto Rico and Panama (Invited)

NASA Astrophysics Data System (ADS)

Stallard, R. F.

2013-12-01

Humid tropical regions are particularly good settings to examine the terrestrial carbon and nutrient cycles because the high average temperatures combined with abundant water and frequent intense storms promote rapid biological activity, weathering, and physical erosion. In studying the human-modified carbon or nutrient cycles on particular landscapes, assessments of the impact of human activities must be compared to prior states of those landscapes with regard to (1) biogeochemical reservoir sizes on the landscape, (2) rates of transport through and out of the landscape, and (3) ultimate fate of the material exported. Ongoing studies in small catchments and larger adjacent watersheds in Puerto Rico (PR) and Panama (PTY) assess which biological, hydrologic, and geomorphic mechanisms have been affected by human activities. The catchments are on older volcanic rocks (6, 2 in PR), granitic rocks (3, all in PR), and one in PTY on limey sediments. Three of the volcanic catchments and one granitic catchment are agricultural. In all these landscapes, landslides, rather than surficial erosion, appear to be the largest regional sediment source, and the biggest landslide-producing storms occur once every few decades. Both landslide-related and surficial erosion are greater in agricultural catchments compared to forested catchments on the same lithology, and granitic landscapes are eroding far more rapidly than volcanic landscapes. Physical erosion on the granitic landscapes appears to be greatly in excess of reasonable equilibrium rates based on mass balances and estimates based on Be-10. The particulate-organic-carbon (POC) yields exceed combined dissolved organic (DOC) and inorganic (DIC) carbon yields in the granitic watersheds, but they are considerably less than the DOC+DIC yields in the volcanic watersheds. Annual yields of DIC and DOC relate linearly to annual runoff, whereas POC has a steep exponential-style increase with increasing runoff, indicating a strong sensitivity to climate change, compared to a linear response. POC yields are tied to sediment yields that are, in turn, far in excess of equilibrium yields. This excess implies that much of the present carbon transport in eastern PR is the result of erosion in excess of equilibrium. In essence, soils that have developed for thousands of years are eroding more rapidly than they are now forming. Carbon accumulation in soil is rapid, and in a landslide scar, which can endure thousands of years, half of the carbon is regenerated in 80 years and all of it in about 200 years. Thus, eroding carbon is being replaced with carbon from the atmosphere. In PR, sediments are delivered to reservoirs or the ocean; in PTY deposition is in reservoirs. These reservoirs are strongly coupled sinks for carbon and nutrients. After landslides, huge quantities of sediment are deposited along with considerable wood and other organic debris. Sediment that deposits in the crenulated arms of the reservoirs is quite rich in organic matter derived from lake productivity that has been greatly augmented by nutrients derived from agricultural lands and domestic wastes. Carbon storage in reservoirs exceeds forest storage, and unlike forests, increases with time.

Dissolved Organic Carbon Degradation in Response to Nutrient Amendments in Southwest Greenland Lakes

NASA Astrophysics Data System (ADS)

Burpee, B. T.; Northington, R.; Simon, K. S.; Saros, J. E.

2014-12-01

Aquatic ecosystems across the Arctic are currently experiencing rapid shifts in biotic, chemical, and physical factors in response to climate change. Preliminary data from multiple lakes in southwestern Greenland indicate decreasing dissolved organic carbon (DOC) concentrations over the past decade. Though several factors may be contributing to this phenomenon, this study attempts to elucidate the potential of heterotrophic bacteria to degrade DOC in the presence of increasing nutrient concentrations. In certain Arctic regions, nutrient subsidies have been released into lakes due to permafrost thaw. If this is occurring in southwestern Greenland, we hypothesized that increased nutrient concentrations will relieve nutrient limitation, thereby allowing heterotrophic bacteria to utilize DOC as an energy source. This prediction was tested using experimental DOC degradation assays from four sample lakes. Four nutrient amendment treatments (control, N, P, and N + P) were used to simulate in situ subsidies. Five time points were sampled during the incubation: days 0, 3, 6, 14, and 60. Total organic carbon (TOC) and parallel factor (PARAFAC) analysis were used to monitor the relative concentrations of different DOC fractions over time. In addition, samples for extracellular enzyme activity (EEA) analysis were collected at every time point. Early analysis of fulvic and humic pools of DOC do not indicate any significant change from days 0 to 14. This could be due to the fact that these DOC fractions are relatively recalcitrant. This study will be important in determining whether bacterial degradation could be a contributing factor to DOC decline in arctic lakes.

Global assessment of ocean carbon export by combining satellite observations and food-web models

NASA Astrophysics Data System (ADS)

Siegel, D. A.; Buesseler, K. O.; Doney, S. C.; Sailley, S. F.; Behrenfeld, M. J.; Boyd, P. W.

2014-03-01

The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of 6 Pg C yr-1. Global export estimates show small variation (typically < 10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean's biological pump.

Radiocarbon and stable-isotope geochemistry of organic and inorganic carbon in Lake Superior

NASA Astrophysics Data System (ADS)

Zigah, Prosper K.; Minor, Elizabeth C.; Werne, Josef P.

2012-03-01

We present a lake-wide investigation of Lake Superior carbon and organic matter biogeochemistry using radiocarbon, stable isotope, and carbon concentrations. Dissolved inorganic carbon (DIC) abundance in the lake was 121-122 Tg C, with offshore concentration andδ13C values being laterally homogenous and tightly coupled to the physical and thermal regime and biochemical processes. Offshore Δ14C of DIC (50-65‰) exhibited lateral homogeneity and was more 14C enriched than co-occurring atmospheric CO2 (˜38‰); nearshore Δ14C of DIC (36-38‰) was similar to atmospheric CO2. Dissolved organic carbon (DOC) abundance was 14.2-16.4 Tg C. DOC's concentration and δ13C were homogenous in June (mixed lake), but varied laterally during August (stratification) possibly due to spatial differences in lake productivity. Throughout sampling, DOC had modern radiocarbon values (14-58‰) indicating a semilabile nature with a turnover time of ≤60 years. Lake particulate organic carbon (POC, 0.9-1.3 Tg C) was consistently 13C depleted relative to DOC. The δ15N of epilimnetic particulate organic nitrogen shifted to more negative values during stratification possibly indicating greater use of nitrate (rather than ammonium) by phytoplankton in August. POC's radiocarbon was spatially heterogeneous (Δ14C range: 58‰ to -303‰), and generally 14C depleted relative to DOC and DIC. POC 14C depletion could not be accounted for by black carbon in the lake but, because of its spatial and temporal distribution, is attributed to sediment resuspension. The presence of old POC within the epilimnion of the open lake indicates possible benthic-pelagic coupling in the lake's organic carbon cycle; the ultimate fate of this old POC bears further investigation.

Tracking the evolution of stream DOM source during storm events using end member mixing analysis based on DOM quality

NASA Astrophysics Data System (ADS)

Yang, Liyang; Chang, Soon-Woong; Shin, Hyun-Sang; Hur, Jin

2015-04-01

The source of river dissolved organic matter (DOM) during storm events has not been well constrained, which is critical in determining the quality and reactivity of DOM. This study assessed temporal changes in the contributions of four end members (weeds, leaf litter, soil, and groundwater), which exist in a small forested watershed (the Ehwa Brook, South Korea), to the stream DOM during two storm events, using end member mixing analysis (EMMA) based on spectroscopic properties of DOM. The instantaneous export fluxes of dissolved organic carbon (DOC), chromophoric DOM (CDOM), and fluorescent components were all enhanced during peak flows. The DOC concentration increased with the flow rate, while CDOM and humic-like fluorescent components were diluted around the peak flows. Leaf litter was dominant for the DOM source in event 2 with a higher rainfall, although there were temporal variations in the contributions of the four end members to the stream DOM for both events. The contribution of leaf litter peaked while that of deeper soils decreased to minima at peak flows. Our results demonstrated that EMMA based on DOM properties could be used to trace the DOM source, which is of fundamental importance for understanding the factors responsible for river DOM dynamics during storm events.

Influences of observation method, season, soil depth, land use and management practice on soil dissolvable organic carbon concentrations: A meta-analysis.

PubMed

Li, Siqi; Zheng, Xunhua; Liu, Chunyan; Yao, Zhisheng; Zhang, Wei; Han, Shenghui

2018-08-01

Quantifications of soil dissolvable organic carbon concentrations, together with other relevant variables, are needed to understand the carbon biogeochemistry of terrestrial ecosystems. Soil dissolvable organic carbon can generally be grouped into two incomparable categories. One is soil extractable organic carbon (EOC), which is measured by extracting with an aqueous extractant (distilled water or a salt solution). The other is soil dissolved organic carbon (DOC), which is measured by sampling soil water using tension-free lysimeters or tension samplers. The influences of observation methods, natural factors and management practices on the measured concentrations, which ranged from 2.5-3970 (mean: 69) mg kg -1 of EOC and 0.4-200 (mean: 12) mg L -1 of DOC, were investigated through a meta-analysis. The observation methods (e.g., extractant, extractant-to-soil ratio and pre-treatment) had significant effects on EOC concentrations. The most significant divergence (approximately 109%) occurred especially at the extractant of potassium sulfate (K 2 SO 4 ) solutions compared to distilled water. As EOC concentrations were significantly different (approximately 47%) between non-cultivated and cultivated soils, they were more suitable than DOC concentrations for assessing the influence of land use on soil dissolvable organic carbon levels. While season did not significantly affect EOC concentrations, DOC concentrations showed significant differences (approximately 50%) in summer and autumn compared to spring. For management practices, applications of crop residues and nitrogen fertilizers showed positive effects (approximately 23% to 91%) on soil EOC concentrations, while tillage displayed negative effects (approximately -17%), compared to no straw, no nitrogen fertilizer and no tillage. Compared to no nitrogen, applications of synthetic nitrogen also appeared to significantly enhance DOC concentrations (approximately 32%). However, further studies are needed in the future to confirm/investigate the effects of ecosystem management practices using standardized EOC measurement protocols or more DOC cases of field experiments. Copyright © 2018 Elsevier B.V. All rights reserved.

Can heterotrophic uptake of dissolved organic carbon and zooplankton mitigate carbon budget deficits in annually bleached corals?

NASA Astrophysics Data System (ADS)

Levas, Stephen; Grottoli, Andréa G.; Schoepf, Verena; Aschaffenburg, Matthew; Baumann, Justin; Bauer, James E.; Warner, Mark E.

2016-06-01

Annual coral bleaching events due to increasing sea surface temperatures are predicted to occur globally by the mid-century and as early as 2025 in the Caribbean, and severely impact coral reefs. We hypothesize that heterotrophic carbon (C) in the form of zooplankton and dissolved organic carbon (DOC) is a significant source of C to bleached corals. Thus, the ability to utilize multiple pools of fixed carbon and/or increase the amount of fixed carbon acquired from one or more pools of fixed carbon (defined here as heterotrophic plasticity) could underlie coral acclimatization and persistence under future ocean-warming scenarios. Here, three species of Caribbean coral— Porites divaricata, P. astreoides, and Orbicella faveolata—were experimentally bleached for 2.5 weeks in two successive years and allowed to recover in the field. Zooplankton feeding was assessed after single and repeat bleaching, while DOC fluxes and the contribution of DOC to the total C budget were determined after single bleaching, 11 months on the reef, and repeat bleaching. Zooplankton was a large C source for P. astreoides, but only following single bleaching. DOC was a source of C for single-bleached corals and accounted for 11-36 % of daily metabolic demand (CHARDOC), but represented a net loss of C in repeat-bleached corals. In repeat-bleached corals, DOC loss exacerbated the negative C budgets in all three species. Thus, the capacity for heterotrophic plasticity in corals is compromised under annual bleaching, and heterotrophic uptake of DOC and zooplankton does not mitigate C budget deficits in annually bleached corals. Overall, these findings suggest that some Caribbean corals may be more susceptible to repeat bleaching than to single bleaching due to a lack of heterotrophic plasticity, and coral persistence under increasing bleaching frequency may ultimately depend on other factors such as energy reserves and symbiont shuffling.

Impact of wetland decline on decreasing dissolved organic carbon concentrations along the Mississippi River continuum

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

Duan, Shuiwang; He, Yuxiang; Kaushal, Sujay S.

Prior to discharging to the ocean, large rivers constantly receive inputs of dissolved organic carbon (DOC) from tributaries or fringing floodplains and lose DOC via continuous in situ processing along distances that span thousands of kilometers. Current concepts predicting longitudinal changes in DOC mainly focus on in situ processing or exchange with fringing floodplain wetlands, while effects of heterogeneous watershed characteristics are generally ignored. We analyzed results from a 17-year time-series of DOC measurements made at seven sites and three expeditions along the entire Mississippi River main channel with DOC measurements made every 17 km. The results show a clearmore » downstream decrease in DOC concentrations that was consistent throughout the entire study period. Downstream DOC decreases were primarily (~63–71%) a result of constant dilutions by low-DOC tributary water controlled by watershed wetland distribution, while in situ processing played a secondary role. We estimate that from 1780 to 1980 wetland loss due to land-use alterations caused a ca. 58% decrease in in DOC concentrations in the tributaries of the Mississippi River. DOC reductions caused by watershed wetland loss likely impacted the capacity for the river to effectively remove nitrogen via denitrification, which can further exacerbate coastal hypoxia. Lastly, these findings highlight the importance of watershed wetlands in regulating DOC longitudinally along the headland to ocean continuum of major rivers.« less

Impact of wetland decline on decreasing dissolved organic carbon concentrations along the Mississippi River continuum

DOE PAGES

Duan, Shuiwang; He, Yuxiang; Kaushal, Sujay S.; ...

2017-01-09

Prior to discharging to the ocean, large rivers constantly receive inputs of dissolved organic carbon (DOC) from tributaries or fringing floodplains and lose DOC via continuous in situ processing along distances that span thousands of kilometers. Current concepts predicting longitudinal changes in DOC mainly focus on in situ processing or exchange with fringing floodplain wetlands, while effects of heterogeneous watershed characteristics are generally ignored. We analyzed results from a 17-year time-series of DOC measurements made at seven sites and three expeditions along the entire Mississippi River main channel with DOC measurements made every 17 km. The results show a clearmore » downstream decrease in DOC concentrations that was consistent throughout the entire study period. Downstream DOC decreases were primarily (~63–71%) a result of constant dilutions by low-DOC tributary water controlled by watershed wetland distribution, while in situ processing played a secondary role. We estimate that from 1780 to 1980 wetland loss due to land-use alterations caused a ca. 58% decrease in in DOC concentrations in the tributaries of the Mississippi River. DOC reductions caused by watershed wetland loss likely impacted the capacity for the river to effectively remove nitrogen via denitrification, which can further exacerbate coastal hypoxia. Lastly, these findings highlight the importance of watershed wetlands in regulating DOC longitudinally along the headland to ocean continuum of major rivers.« less

Designing a dynamic data driven application system for estimating real-time load of dissolved organic carbon in a river

Treesearch

Ying Ouyang

2012-01-01

Understanding the dynamics of naturally occurring dissolved organic carbon (DOC) in a river is central to estimating surface water quality, aquatic carbon cycling, and global climate change. Currently, determination of the DOC in surface water is primarily accomplished by manually collecting samples for laboratory analysis, which requires at least 24 h. In other words...

Dissolved Organic Carbon and Natural Terrestrial Sequestration Potential in Volcanic Terrain, San Juan Mountains, Colorado

NASA Astrophysics Data System (ADS)

Yager, D. B.; Burchell, A.; Johnson, R. H.; Kugel, M.; Aiken, G.; Dick, R.

2009-12-01

The need to reduce atmospheric CO2 levels has stimulated studies to understand and quantify carbon sinks and sources. Soils represent a potentially significant natural terrestrial carbon sequestration (NTS) reservoir. This project is part of a collaborative effort to characterize carbon (C) stability in temperate soils. To examine the potential for dissolved organic carbon (DOC) values as a qualitative indicator of C-stability, peak-flow (1500 ft3/s) and low-flow (200 ft3/s) samples from surface and ground waters were measured for DOC. DOC concentrations are generally low. Median peak-flow values from all sample sites (mg/L) were: streams (0.9); seeps (1.2); wells (0.45). Median low-flow values were: streams (0.7); seeps (0.75); wells (0.5). Median DOC values decrease between June and September 0.45 mg/L for seeps, and 0.2 mg/L for streams. Elevated DOC in some ground waters as compared to surface waters indicates increased contact time with soil organic matter. Elevated peak-flow DOC in areas with propylitically-altered bedrocks, composed of a secondary acid neutralizing assemblage of calcite-chlorite-epidote, reflects increased microbial and vegetation activity as compared to reduced organic matter accumulation in highly-altered terrain composed of an acid generating assemblage with abundant pyrite. Waters sampled in propylitically-altered bedrock terrain exhibit the lowest values during low-flow and suggest bedrock alteration type may influence DOC. Previous studies revealed undisturbed soils sampled have 2 to 6 times greater total organic soil carbon (TOSC) than global averages. Forest soils underlain by intermediate to mafic volcanic bedrock have the highest C (34.15 wt%), C: N (43) and arylsulfatase enzyme activity (ave. 278, high 461 µg p-nitrophenol/g/h). Unreclaimed mine sites have the lowest C (0 to 0.78 wt%), and arylsulfatase enzyme activity (0 to 41). Radiocarbon dates on charcoal collected from paleo-burn horizons illustrate Rocky Mountain soils may represent an old and if undisturbed, stable carbon pool (500 -5,440 ± 40 yrs B.P). Undisturbed and reclaimed soils derived from propylitic bedrocks also exhibit high TOSC (13.5 - 25.6 wt%), C: N (27), arylsulfatase (338). This is consistent with earlier studies in which propylitic bedrocks were identified as having a high acid-neutralizing capacity (ANC). Observations at natural reclamation sites suggest “bio-geo-mimicry” techniques that use ANC rock plus other soil amendments (biochar, nutrients, mycorrhizea, seeding) may aid reclamation measures and support carbon sequestration. The data demonstrate that volcanic-hosted watersheds may exhibit both high TOSC and low DOC. This is attributed to: host rock-weathering release of nutrients important for soil productivity, ANC, formation of secondary mineral carbonates; development of intermediate soil aggregates and adsorption-enhancing clays that stabilize C and N, environmental factors such as climate, moisture retention, and land use. Future work will explore the potential of DOC flux as a proxy for NTS potential.

Land management impacts on dairy-derived dissolved organic carbon in ground water

USGS Publications Warehouse

Chomycia, J.C.; Hernes, P.J.; Harter, T.; Bergamaschi, B.A.

2008-01-01

Dairy operations have the potential to elevate dissolved organic carbon (DOC) levels in ground water, where it may interact with organic and inorganic contaminants, fuel denitrification, and may present problems for drinking water treatment. Total and percent bioavailable DOC and total and carbon-specific trihalomethane (THM) formation potential (TTHMFP and STHMFP, respectively) were determined for shallow ground water samples from beneath a dairy farm in the San Joaquin Valley, California. Sixteen wells influenced by specific land management areas were sampled over 3 yr. Measured DOC concentrations were significantly elevated over the background as measured at an upgradient monitoring well, ranging from 13 to 55 mg L-1 in wells downgradient from wastewater ponds, 8 to 30 mg L-1 in corral wells, 5 to 12 mg L-1 in tile drains, and 4 to 15 mg L-1 in wells associated with manured fields. These DOC concentrations were at the upper range or greatly exceeded concentrations in most surface water bodies used as drinking water sources in California. DOC concentrations in individual wells varied by up to a factor of two over the duration of this study, indicating a dynamic system of sources and degradation. DOC bioavailability over 21 d ranged from 3 to 10%, comparable to surface water systems and demonstrating the potential for dairy-derived DOC to influence dissolved oxygen concentrations (nearly all wells were hypoxic to anoxic) and denitrification. TTHMFP measurements across all management units ranged from 141 to 1731 ??g L-1, well in excess of the maximum contaminant level of 80 ??g L-1 established by the Environmental Protection Agency. STHMFP measurements demonstrated over twofold variation (???4 to ???8 mmol total THM/mol DOC) across the management areas, indicating the dependence of reactivity on DOC composition. The results indicate that land management strongly controls the quantity and quality of DOC to reach shallow ground water and hence should be considered when managing ground water resources and in any efforts to mitigate contamination of ground water with carbon-based contaminants, such as pesticides and pharmaceuticals. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Boreal mire Green House Gas exchange in response to global change perturbations

NASA Astrophysics Data System (ADS)

Nilsson, Mats

2017-04-01

High latitude boreal peatlands contribute importantly to the land-atmosphere-hydrosphere exchange of carbon and GHG, i.e. carbon dioxide, methane and dissolved organic carbon. High latitude biomes are identified as most vulnerable to changing climate. High latitudes are also characterized by a strong seasonality in incoming solar radiation, weather conditions and thus also in biogeochemical processes. The strong seasonality in incoming solar radiation, not to change in response to a changing climate, constitute firm constraints on how changes in air temperature, evapotranspiration and precipitation will affect biogeochemical processes underlying the land atmosphere and land hydrosphere exchange of green house gases. In this presentation I combine data from long-term monitoring, long-term field manipulations and detailed chemical analysis to understand how changes in atmosphere and weather conditions influence the major carbon fluxes of a boreal mire Net Ecosystem Carbon Balance. The long-term monitoring data contains >12 years of continuous Eddy Covariance CO2 data, growing season chamber CH4 data and continuous measurements of discharge export of DOC, CO2 and CH4. Data from long-term field snow removal manipulations and growing season temperature increase manipulations are used to further understand the impact of climate on mire carbon and GHG fluxes. Finally we uses Nuclear Magnetic Spectroscopy (NMR) to reveal how century scale changes in atmospheric CO2 from 300 to 400 pm CO2 and temperature have influenced the net photosynthetic capacity of Sphagnum mosses, the single most important plant genus for boreal mire carbon sequestration.

The characteristics of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) in Antarctic sea ice

NASA Astrophysics Data System (ADS)

Norman, Louiza; Thomas, David N.; Stedmon, Colin A.; Granskog, Mats A.; Papadimitriou, Stathys; Krapp, Rupert H.; Meiners, Klaus M.; Lannuzel, Delphine; van der Merwe, Pier; Dieckmann, Gerhard S.

2011-05-01

An investigation of coloured dissolved organic matter (CDOM) and its relationships to physical and biogeochemical parameters in Antarctic sea ice and oceanic water have indicated that ice melt may both alter the spectral characteristics of CDOM in Antarctic surface waters and serve as a likely source of fresh autochthonous CDOM and labile DOC. Samples were collected from melted bulk sea ice, sea ice brines, surface gap layer waters, and seawater during three expeditions: one during the spring to summer and two during the winter to spring transition period. Variability in both physical (temperature and salinity) and biogeochemical parameters (dissolved and particulate organic carbon and nitrogen, as well as chlorophyll a) was observed during and between studies, but CDOM absorption coefficients measured at 375 nm (a 375) did not differ significantly. Distinct peaked absorption spectra were consistently observed for bulk ice, brine, and gap water, but were absent in the seawater samples. Correlation with the measured physical and biogeochemical parameters could not resolve the source of these peaks, but the shoulders and peaks observed between 260 and 280 nm and between 320 to 330 nm respectively, particularly in the samples taken from high light-exposed gap layer environment, suggest a possible link to aromatic and mycosporine-like amino acids. Sea ice CDOM susceptibility to photo-bleaching was demonstrated in an in situ 120 hour exposure, during which we observed a loss in CDOM absorption of 53% at 280 nm, 58% at 330 nm, and 30% at 375 nm. No overall coincidental loss of DOC or DON was measured during the experimental period. A relationship between the spectral slope (S) and carbon-specific absorption (a *375) indicated that the characteristics of CDOM can be described by the mixing of two broad end-members; and aged material, present in brine and seawater samples characterised by high S values and low a *375; and a fresh material, due to elevated in situ production, present in the bulk ice samples characterised by low S and high a *375. The DOC data reported here have been used to estimate that approximately 8 Tg C yr -1 (˜11% of annual sea ice algae primary production) may be exported to the surface ocean during seasonal sea ice melt in the form of DOC.

Hydrology and landscape structure control subalpine catchment carbon export

Treesearch

Vincent Jerald Pacific

2009-01-01

Carbon export from high elevation ecosystems is a critical component of the global carbon cycle. Ecosystems in northern latitudes have become the focus of much research due to their potential as large sinks of carbon in the atmosphere. However, there exists limited understanding of the controls of carbon export from complex mountain catchments due to strong spatial and...

Pyrolysis temperature-dependent release of dissolved organic carbon from plant, manure, and biorefinery wastes

USDA-ARS?s Scientific Manuscript database

Limited information is available to understand the chemical structure of biochar’s labile dissolved organic carbon (DOC) fraction that will change amended soil’s DOC composition. This study utilized the high sensitivity of fluorescence excitation-emission (EEM) spectrophotometry to understand the s...

Wet Removal of Organic and Black Carbon Aerosols

NASA Astrophysics Data System (ADS)

Torres, A.; Bond, T. C.; Lehmann, C.

2012-12-01

Organic carbon (OC) and black carbon (BC) aerosols derived from the combustion of fossil fuels and biomass are significant atmospheric pollutants that alter the Earth's radiation balance and affect human health. Carbonaceous aerosol lifetime and extent of its effects are mainly controlled by its wet removal, especially by rain. Limited work has been done to measure both BC and OC from rain events even though these aerosols are co-emitted and exist together in the atmosphere. The choices of analytical techniques for measuring OC and BC in water are limited, and researchers often employ the same techniques used for measuring atmospheric carbon particles. There is no agreement in the methods employed for monitoring carbon concentration in precipitation. As part of the method development, the Single Particle Soot Photometer (SP2), Thermal-Optical Analysis (TOA), Ultraviolet/Visible (UV/VIS) Spectrophotometer, and the Total Organic Carbon (TOC) Analyzer were evaluated for measuring BC suspended in water, water insoluble OC (WIOC) and dissolved OC (DOC). The study also monitored the concentration of BC, WIOC, and DOC in rainwater collected at Bondville (Illinois) for 18 months. Results indicated that 34% (±3%) of the BC mass was lost in the SP2 analysis, most probably during the nebulization process. Filtration required for TOA also had large losses (>75%) because quartz fiber filters were ineffective for capturing BC particles from water. Addition of NH4H2PO4 as a coagulant improved (>95%) the capture efficiency of the filters. UV/VIS spectrophotometry had good linearity, but the sensitivity for detecting BC particles (±20 μg/L) suspended in water was inadequate. TOC analysis was a robust technique for measuring both DOC and total carbon (BC + OC). The chosen techniques were TOC analysis for DOC, and TOA with an optimized filtration procedure for BC and WIOC. The mean concentrations in rainwater were 8.72 (±9.84) μg/L of BC, 88.97 (±62.64) μg/L of WIOC, and 1,320 (1,380) μg/L of DOC. DOC contributed, mostly with anions, to the ion balance of rain samples. The total carbon concentration (BC+WIOC+DOC) decreased with increasing precipitation volume and directly correlated with the concentrations of SO42-, NO3-, Ca2+, NH4+, Mg2+, and K+ in rainwater.

Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon

USGS Publications Warehouse

Weishaar, J.L.; Aiken, George R.; Bergamaschi, Brian A.; Fram, Miranda S.; Fujii, Roger; Mopper, K.

2003-01-01

Specific UV absorbance (SUVA) is defined as the UV absorbance of a water sample at a given wavelength normalized for dissolved organic carbon (DOC) concentration. Our data indicate that SUVA, determined at 254 nm, is strongly correlated with percent aromaticity as determined by 13C NMR for 13 organic matter isolates obtained from a variety of aquatic environments. SUVA, therefore, is shown to be a useful parameter for estimating the dissolved aromatic carbon content in aquatic systems. Experiments involving the reactivity of DOC with chlorine and tetramethylammonium hydroxide (TMAH), however, show a wide range of reactivity for samples with similar SUVA values. These results indicate that, while SUVA measurements are good predictors of general chemical characteristics of DOC, they do not provide information about reactivity of DOC derived from different types of source materials. Sample pH, nitrate, and iron were found to influence SUVA measurements.

The temperature-ballast hypothesis explains carbon export efficiency observations in the Southern Ocean

NASA Astrophysics Data System (ADS)

Britten, Gregory L.; Wakamatsu, Lael; Primeau, François W.

2017-02-01

Carbon export from the Southern Ocean exerts a strong control on the ocean carbon sink, yet recent observations from the region demonstrate poorly understood relationships in which carbon export efficiency is weakly related to temperature. These observations conflict with traditional theory where export efficiency increases in colder waters. A recently proposed "temperature-ballast hypothesis" suggests an explanatory mechanism where the effect of temperature-dependent respiration is masked by variation in particle-ballast as upwelling waters move northward from Antarctica. We use observations and statistical models to test this mechanism and find positive support for the hypothesized temperature-ballast interactions. Best fitting models indicate a significant relation between export efficiency and silica-ballast while simultaneously revealing the expected inverse effect of temperature once ballast is accounted for. These findings reconcile model predictions, metabolic theory, and carbon export observations in the Southern Ocean and have consequences for how the ocean carbon sink responds to climate change.

Inorganic carbon speciation and fluxes in the Congo River

NASA Astrophysics Data System (ADS)

Wang, Zhaohui Aleck; Bienvenu, Dinga Jean; Mann, Paul J.; Hoering, Katherine A.; Poulsen, John R.; Spencer, Robert G. M.; Holmes, Robert M.

2013-02-01

Seasonal variations in inorganic carbon chemistry and associated fluxes from the Congo River were investigated at Brazzaville-Kinshasa. Small seasonal variation in dissolved inorganic carbon (DIC) was found in contrast with discharge-correlated changes in pH, total alkalinity (TA), carbonate species, and dissolved organic carbon (DOC). DIC was almost always greater than TA due to the importance of CO2*, the sum of dissolved CO2 and carbonic acid, as a result of low pH. Organic acids in DOC contributed 11-61% of TA and had a strong titration effect on water pH and carbonate speciation. The CO2* and bicarbonate fluxes accounted for ~57% and 43% of the DIC flux, respectively. Congo River surface water released CO2 at a rate of ~109 mol m-2 yr-1. The basin-wide DIC yield was ~8.84 × 104 mol km-2 yr-1. The discharge normalized DIC flux to the ocean amounted to 3.11 × 1011 mol yr-1. The DOC titration effect on the inorganic carbon system may also be important on a global scale for regulating carbon fluxes in rivers.

Designing a Dynamic Data Driven Application System for Estimating Real-Time Load of DOC in a River

NASA Astrophysics Data System (ADS)

Ouyang, Y.; None

2011-12-01

Understanding the dynamics of naturally occurring dissolved organic carbon (DOC) in a river is central to estimating surface water quality, aquatic carbon cycling, and climate change. Currently, determination of DOC in surface water is primarily accomplished by manually collecting samples for laboratory analysis, which requires at least 24 hours. In other words, no effort has been devoted to monitoring real-time variations of DOC in a river due to the lack of suitable and/or cost-effective wireless sensors. However, when considering human health, carbon footprints, and effects of urbanization, industry, and agriculture on water resource supply, timely DOC information may be critical. We have developed here a new paradigm, a dynamic data driven application system (DDDAS), for estimating the real-time load of DOC into a river. This DDDAS consisted of the following four components: (1) a Visual Basic (VB) program for downloading US Geological Survey real-time chlorophyll and discharge data; (2) a STELLA model for evaluating real-time DOC load based on the relationship between chlorophyll a, DOC, and river discharge; (3) a batch file for linking the VB program and STELLA model; and (4) a Microsoft Windows Scheduled Tasks wizard for executing the model and displaying output on a computer screen at selected times. Results show that the real-time load of DOC into the St. Johns River basin near Satsuma, Putnam County, Florida, USA varied over a range from -13,143 to 29,248 kg/h at the selected site in Florida, USA. The negative loads occurred because of the back flow in the estuarine reach of the river. The cumulative load of DOC in the river for the selected site at the end of the simulation (178 hours) was about 1.2 tons. Our results support the utility of the DDDAS developed in this study for estimating the real-time variations of DOC in river ecosystems.

Dynamics of dissolved organic carbon (DOC) through stormwater basins designed for groundwater recharge in urban area: Assessment of retention efficiency.

PubMed

Mermillod-Blondin, Florian; Simon, Laurent; Maazouzi, Chafik; Foulquier, Arnaud; Delolme, Cécile; Marmonier, Pierre

2015-09-15

Managed aquifer recharge (MAR) has been developed in many countries to limit the risk of urban flooding and compensate for reduced groundwater recharge in urban areas. The environmental performances of MAR systems like infiltration basins depend on the efficiency of soil and vadose zone to retain stormwater-derived contaminants. However, these performances need to be finely evaluated for stormwater-derived dissolved organic matter (DOM) that can affect groundwater quality. Therefore, this study examined the performance of MAR systems to process DOM during its transfer from infiltration basins to an urban aquifer. DOM characteristics (fluorescent spectroscopic properties, biodegradable and refractory fractions of dissolved organic carbon -DOC-, consumption by micro-organisms during incubation in slow filtration sediment columns) were measured in stormwater during its transfer through three infiltration basins during a stormwater event. DOC concentrations sharply decreased from surface to the aquifer for the three MAR sites. This pattern was largely due to the retention of biodegradable DOC which was more than 75% for the three MAR sites, whereas the retention of refractory DOC was more variable and globally less important (from 18% to 61% depending on MAR site). Slow filtration column experiments also showed that DOC retention during stormwater infiltration through soil and vadose zone was mainly due to aerobic microbial consumption of the biodegradable fraction of DOC. In parallel, measurements of DOM characteristics from groundwaters influenced or not by MAR demonstrated that stormwater infiltration increased DOC quantity without affecting its quality (% of biodegradable DOC and relative aromatic carbon content -estimated by SUVA254-). The present study demonstrated that processes occurring in soil and vadose zone of MAR sites were enough efficient to limit DOC fluxes to the aquifer. Nevertheless, the enrichments of DOC concentrations measured in groundwater below infiltration basins need to be considered in future studies to especially assess their impact on groundwater quality. Copyright © 2015 Elsevier Ltd. All rights reserved.

Drain blocking: an effective treatment for reducing dissolved organic carbon loss and water discolouration in a drained peatland.

PubMed

Wallage, Zoe E; Holden, Joseph; McDonald, Adrian T

2006-08-31

Peatlands are an important terrestrial carbon store. However, heightened levels of degradation in response to environmental change have resulted in an increased loss of dissolved organic carbon (DOC) and an associated rise in the level of discolouration in catchment waters. A significant threat to peatland sustainability has been the installation of artificial drainage ditches. However, recent restoration schemes have pursued drain blocking as a possible strategy for reducing degradation, fluvial carbon loss and water discolouration. This paper investigates the effect of open cut drainage and the impact of drain blocking on DOC and colour dynamics in blanket peat soil-water solutions. Three treatments (intact peat, drained peat and drain-blocked peat) were monitored in an upland blanket peat catchment in the UK. DOC and colour values were significantly higher on the drained slopes compared with those of the intact peat, which in turn had greater DOC and colour values than the drain-blocked slopes. Consequently, drain blocking is shown to be a highly successful technique in reducing both the DOC concentration and level of discolouration in soil waters, even to values lower than those observed for the intact site, which suggests a process of store exhaustion and flushing may operate. The colour per carbon unit (C/C) ratio was significantly higher at the drain-blocked site than either the intact or the drained treatments, while the E4/E6 ratio (fulvic acid/humic acid) was significantly lower at the blocked site compared to the two other treatments. The high C/C and low E4/E6 ratios indicate that drain blocking also modifies the composition of DOC, such that darker-coloured humic substances become more dominant compared to the intact site. This implies disturbance to DOC production and/or transportation processes operating within the peat.

Dissolved organic carbon in the precipitation of Seoul, Korea: Implications for global wet depositional flux of fossil-fuel derived organic carbon

NASA Astrophysics Data System (ADS)

Yan, Ge; Kim, Guebuem

2012-11-01

Precipitation was sampled in Seoul over a one-year period from 2009 to 2010 to investigate the sources and fluxes of atmospheric dissolved organic carbon (DOC). The concentrations of DOC varied from 15 μM to 780 μM, with a volume-weighted average of 94 μM. On the basis of correlation analysis using the commonly acknowledged tracers, such as vanadium, the combustion of fossil-fuels was recognized to be the dominant source. With the aid of air mass backward trajectory analyses, we concluded that the primary fraction of DOC in our precipitation samples originated locally in Korea, albeit the frequent long-range transport from eastern and northeastern China might contribute substantially. In light of the relatively invariant organic carbon to sulfur mass ratios in precipitation over Seoul and other urban regions around the world, the global magnitude of wet depositional DOC originating from fossil-fuels was calculated to be 36 ± 10 Tg C yr-1. Our study further underscores the potentially significant environmental impacts that might be brought about by this anthropogenically derived component of organic carbon in the atmosphere.

[Response of mineralization of dissolved organic carbon to soil moisture in paddy and upland soils in hilly red soil region].

PubMed

Chen, Xiang-Bi; Wang, Ai-Hua; Hu, Le-Ning; Huang, Yuan; Li, Yang; He, Xun-Yang; Su, Yi-Rong

2014-03-01

Typical paddy and upland soils were collected from a hilly subtropical red-soil region. 14C-labeled dissolved organic carbon (14C-DOC) was extracted from the paddy and upland soils incorporated with 14C-labeled straw after a 30-day (d) incubation period under simulated field conditions. A 100-d incubation experiment (25 degrees C) with the addition of 14C-DOC to paddy and upland soils was conducted to monitor the dynamics of 14C-DOC mineralization under different soil moisture conditions [45%, 60%, 75%, 90%, and 105% of the field water holding capacity (WHC)]. The results showed that after 100 days, 28.7%-61.4% of the labeled DOC in the two types of soils was mineralized to CO2. The mineralization rates of DOC in the paddy soils were significantly higher than in the upland soils under all soil moisture conditions, owing to the less complex composition of DOC in the paddy soils. The aerobic condition was beneficial for DOC mineralization in both soils, and the anaerobic condition was beneficial for DOC accumulation. The biodegradability and the proportion of the labile fraction of the added DOC increased with the increase of soil moisture (45% -90% WHC). Within 100 days, the labile DOC fraction accounted for 80.5%-91.1% (paddy soil) and 66.3%-72.4% (upland soil) of the cumulative mineralization of DOC, implying that the biodegradation rate of DOC was controlled by the percentage of labile DOC fraction.

Fluxes of dissolved organic carbon and nitrogen to the northern Indian Ocean from the Indian monsoonal rivers

NASA Astrophysics Data System (ADS)

Krishna, M. S.; Prasad, V. R.; Sarma, V. V. S. S.; Reddy, N. P. C.; Hemalatha, K. P. J.; Rao, Y. V.

2015-10-01

Dissolved organic carbon (DOC) and nitrogen (DON) were measured in 27 major and medium monsoonal estuaries along the Indian coast during southwest monsoon in order to understand the spatial variability in their concentrations and fluxes to the northern Indian Ocean. A strong spatial variability (~20-fold) in DOC and DON was observed in the Indian monsoonal estuaries due to variable characteristics of the catchment area and volume of discharge. It is estimated that the Indian monsoonal estuaries transport ~2.37 ± 0.47 Tg (1 Tg = 1012 g) of DOC and ~0.41 ± 0.08 Tg of DON during wet period to the northern Indian Ocean. The Bay of Bengal receives 3 times higher DOC and DON (1.82 and 0.30 Tg, respectively) than the Arabian Sea (0.55 and 0.11 Tg). Catchment area normalized fluxes of DOC and DON were found to be higher in the estuaries located in the southwestern than the estuaries from other regions of India. It was attributed to relatively higher soil organic carbon, biomass carbon, and heavy rainfall in catchment areas of the rivers from the former region. It has been noticed that neither catchment area nor discharge volume of the river controls the fluxes of DOC and DON to the northern Indian Ocean. Since the total load of DOC and DON is strongly linked to the volume of discharge, alterations in the freshwater discharge due to natural or anthropogenic activities may have significant influence on organic matter fluxes to the Indian coastal waters and its impact on microbial food web dynamics needs further evaluation.

75 FR 14125 - Submission for OMB Review; Comment Request

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-24

... DEPARTMENT OF COMMERCE Submission for OMB Review; Comment Request The Department of Commerce will..., chambers of commerce, regional groups and other export-oriented groups. The Certified Trade Mission... participate in the Department of Commerce's (DOC) trade promotion events program, identify the products or...

76 FR 30908 - Foreign-Trade Zone 203-Moses Lake, Washington, Export-Only Manufacturing Authority, SGL...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-27

... DEPARTMENT OF COMMERCE Foreign-Trade Zones Board [A(32b)-1-2011] Foreign-Trade Zone 203--Moses Lake, Washington, Export-Only Manufacturing Authority, SGL Automotive Carbon Fibers, LLC, (Carbon Fiber... Automotive Carbon Fibers, LLC (SGL) to manufacture carbon fiber under FTZ procedures solely for export within...

Spatial Variability of Dissolved Organic Carbon in Headwater Wetlands in Central Pennsylvania

NASA Astrophysics Data System (ADS)

Reichert-Eberhardt, A. J.; Wardrop, D.; Boyer, E. W.

2011-12-01

Dissolved organic carbon (DOC) is known to be of an important factor in many microbially mediated biochemical processes, such as denitrification, that occur in wetlands. The spatial variability of DOC within a wetland could impact the microbes that fuel these processes, which in turn can affect the ecosystem services provided by wetlands. However, the amount of spatial variability of DOC in wetlands is generally unknown. Furthermore, it is unknown how disturbance to wetlands can affect spatial variability of DOC. Previous research in central Pennsylvania headwater wetland soils has shown that wetlands with increased human disturbance had decreased heterogeneity in soil biochemistry. To address groundwater chemical variability 20 monitoring wells were installed in a random pattern in a 400 meter squared plot in a low-disturbance headwater wetland and a high-disturbance headwater wetland in central Pennsylvania. Water samples from these wells will be analyzed for DOC, dissolved inorganic carbon, nitrate, ammonia, and sulfate concentrations, as well as pH, conductivity, and temperature on a seasonal basis. It is hypothesized that there will be greater spatial variability of groundwater chemistry in the low disturbance wetland than the high disturbance wetland. This poster will present the initial data concerning DOC spatial variability in both the low and high impact headwater wetlands.

Effect of dissolved organic carbon quality on microbial decomposition and nitrification rates in stream sediments

USGS Publications Warehouse

Strauss, E.A.; Lamberti, G.A.

2002-01-01

1. Microbial decomposition of dissolved organic carbon (DOC) contributes to overall stream metabolism and can influence many processes in the nitrogen cycle, including nitrification. Little is known, however, about the relative decomposition rates of different DOC sources and their subsequent effect on nitrification. 2. In this study, labile fraction and overall microbial decomposition of DOC were measured for leaf leachates from 18 temperate forest tree species. Between 61 and 82% (mean, 75%) of the DOC was metabolized in 24 days. Significant differences among leachates were found for labile fraction rates (P < 0.0001) but not for overall rates (P = 0.088). 3. Nitrification rates in stream sediments were determined after addition of 10 mg C L-1 of each leachate. Nitrification rates ranged from below detection to 0.49 ??g N mL sediment-1 day-1 and were significantly correlated with two independent measures of leachate DOC quality, overall microbial decomposition rate (r = -0.594, P = 0.0093) and specific ultraviolet absorbance (r = 0.469, P = 0.0497). Both correlations suggest that nitrification rates were lower in the presence of higher quality carbon. 4. Nitrification rates in sediments also were measured after additions of four leachates and glucose at three carbon concentrations (10, 30, and 50 mg C L-1). For all carbon sources, nitrification rates decreased as carbon concentration increased. Glucose and white pine leachate most strongly depressed nitrification. Glucose likely increased the metabolism of heterotrophic bacteria, which then out-competed nitrifying bacteria for NH4+. White pine leachate probably increased heterotrophic metabolism and directly inhibited nitrification by allelopathy.

Assessment of potential climate change impacts on peatland dissolved organic carbon release and drinking water treatment from laboratory experiments.

PubMed

Tang, R; Clark, J M; Bond, T; Graham, N; Hughes, D; Freeman, C

2013-02-01

Catchments draining peat soils provide the majority of drinking water in the UK. Over the past decades, concentrations of dissolved organic carbon (DOC) have increased in surface waters. Residual DOC can cause harmful carcinogenic disinfection by-products to form during water treatment processes. Increased frequency and severity of droughts combined with and increased temperatures expected as the climate changes, have potentials to change water quality. We used a novel approach to investigate links between climate change, DOC release and subsequent effects on drinking water treatment. We designed a climate manipulation experiment to simulate projected climate changes and monitored releases from peat soil and litter, then simulated coagulation used in water treatment. We showed that the 'drought' simulation was the dominant factor altering DOC release and affected the ability to remove DOC. Our results imply that future short-term drought events could have a greater impact than increased temperature on DOC treatability. Copyright © 2012 Elsevier Ltd. All rights reserved.

Predicting nitrogen and acidity effects on long-term dynamics of dissolved organic matter.

PubMed

Rowe, E C; Tipping, E; Posch, M; Oulehle, F; Cooper, D M; Jones, T G; Burden, A; Hall, J; Evans, C D

2014-01-01

Increases in dissolved organic carbon (DOC) fluxes may relate to changes in sulphur and nitrogen pollution. We integrated existing models of vegetation growth and soil organic matter turnover, acid-base dynamics, and organic matter mobility, to form the 'MADOC' model. After calibrating parameters governing interactions between pH and DOC dissolution using control treatments on two field experiments, MADOC reproduced responses of pH and DOC to additions of acidifying and alkalising solutions. Long-term trends in a range of acid waters were also reproduced. The model suggests that the sustained nature of observed DOC increases can best be explained by a continuously replenishing potentially-dissolved carbon pool, rather than dissolution of a large accumulated store. The simulations informed the development of hypotheses that: DOC increase is related to plant productivity increase as well as to pH change; DOC increases due to nitrogen pollution will become evident, and be sustained, after soil pH has stabilised. Copyright © 2013 Elsevier Ltd. All rights reserved.

Global patterns of organic carbon export and sequestration in the ocean (Arne Richter Award for Outstanding Young Scientists)

NASA Astrophysics Data System (ADS)

Henson, S.; Sanders, R.; Madsen, E.; Le Moigne, F.; Quartly, G.

2012-04-01

A major term in the global carbon cycle is the ocean's biological carbon pump which is dominated by sinking of small organic particles from the surface ocean to its interior. Here we examine global patterns in particle export efficiency (PEeff), the proportion of primary production that is exported from the surface ocean, and transfer efficiency (Teff), the fraction of exported organic matter that reaches the deep ocean. This is achieved through extrapolating from in situ estimates of particulate organic carbon export to the global scale using satellite-derived data. Global scale estimates derived from satellite data show, in keeping with earlier studies, that PEeff is high at high latitudes and low at low latitudes, but that Teff is low at high latitudes and high at low latitudes. However, in contrast to the relationship observed for deep biomineral fluxes in previous studies, we find that Teff is strongly negatively correlated with opal export flux from the upper ocean, but uncorrelated with calcium carbonate export flux. We hypothesise that the underlying factor governing the spatial patterns observed in Teff is ecosystem function, specifically the degree of recycling occurring in the upper ocean, rather than the availability of calcium carbonate for ballasting. Finally, our estimate of global integrated carbon export is only 50% of previous estimates. The lack of consensus amongst different methodologies on the strength of the biological carbon pump emphasises that our knowledge of a major planetary carbon flux remains incomplete.

Laboratory investigations into the potential for transformation of POC to dissolved and gaseous forms

NASA Astrophysics Data System (ADS)

Goulsbra, Claire; Evans, Martin; Allott, Tim; Evans, Chris; Flint, Rebecca; Mcmorron, Katherine

2014-05-01

In eroding peatland systems POC is the dominant component of the fluvial carbon flux, with POC flux to up to circa 80 g C m-2 yr-1. The fate of this POC has remained uncertain, however, and at present many carbon models exclude POC flux from estimations of atmospherically active carbon budgets. Recent work on headwater systems with high POC concentrations has demonstrated that POC:DOC ratios decrease rapidly downstream, hypothesised to be due the physical and microbial breakdown of POC in the fluvial system and transformation of soil carbon to dissolved and gaseous phases. To assess this hypothesis, laboratory investigations of the potential for transformation of POC to dissolved and gaseous forms were undertaken. POC derived from an exposed gully face was mixed with stream waters collected from Upper North Grain, an eroded peatland catchment in the South Pennines, UK, to simulate typical storm flow suspended sediment concentrations. The solutions were agitated using a magnetic stirring system for one week and subsamples of the solution were extracted at intervals of 0.5, 1, 1.5, 2, 3, 4, 5 and 6 hours, and 1, 2, 3, 4, and 7 days. Samples were analysed for POC and DOC concentration using a Shimadzu total carbon analyser and absorbance was measured spectrophotometrically at 254, 400 465 and 665 nm wavelengths as a proxy for DOC quality. In a parallel experiment CO2 emissions to the mixing flask were measured using an infra-red gas analyser (IRGA). To isolate the role of microbial versus physical breakdown, both experiments were replicated with POM and streamwater which had been sterilised by gamma irradiation. The experiments were further repeated to assess the impact of variations in pH and the initial DOC concentration of the stream water on rates of POC conversion to on DOC and CO2. The results of these experiments will be presented here. Initial results show that peat-derived POC was found to be reactive in streamwater, leading to a rapid in DOC within 24 hours of the start of mixing experiments, thought to occur via physicochemical processes. Mixing of POC with streamwater also led to rapid CO2 emissions, possibly via a DOC intermediary, and overall CO2 production exceeded that of DOC. These results strongly indicate that POC is actively converted to other carbon forms in high-POC waters over the timescale of water residence in typical UK river systems, and that a high proportion of this carbon is emitted to the atmosphere as CO2.

Biodegradability of dissolved organic carbon in permafrost soils and waterways: a meta-analysis

NASA Astrophysics Data System (ADS)

Vonk, J. E.; Tank, S. E.; Mann, P. J.; Spencer, R. G. M.; Treat, C. C.; Striegl, R. G.; Abbott, B. W.; Wickland, K. P.

2015-06-01

As Arctic regions warm, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to thaw and decomposition. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the reactivity and subsequent fate of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism and its biodegradability will determine the extent and rate of carbon release from aquatic ecosystems to the atmosphere. Knowledge of the mechanistic controls on DOC biodegradability is however currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences used as common practice in the literature. We further synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-Arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher BDOC losses in both soil and aquatic systems. We hypothesize that the unique composition of permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively shorter flow path lengths and transport times, resulted in higher overall terrestrial and freshwater BDOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January-December) decrease in BDOC losses in large streams and rivers, but no apparent change in smaller streams and soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the seasons progress. Our results suggest that future, climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC as well as its variability throughout the Arctic summer. We lastly present a recommended standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Dissolved organic carbon loading from the field to watershed scale in tile-drained landscapes

USDA-ARS?s Scientific Manuscript database

Dissolved organic carbon (DOC) is an integral part to the functioning of aquatic ecosystems; yet, there is a paucity of data on DOC delivery and management in tile-drained agricultural headwater watersheds. The objective of this study was to quantify the contribution of subsurface tile drains to wat...

A linear solvation energy relationship model of organic chemical partitioning to dissolved organic carbon.

PubMed

Kipka, Undine; Di Toro, Dominic M

2011-09-01

Predicting the association of contaminants with both particulate and dissolved organic matter is critical in determining the fate and bioavailability of chemicals in environmental risk assessment. To date, the association of a contaminant to particulate organic matter is considered in many multimedia transport models, but the effect of dissolved organic matter is typically ignored due to a lack of either reliable models or experimental data. The partition coefficient to dissolved organic carbon (K(DOC)) may be used to estimate the fraction of a contaminant that is associated with dissolved organic matter. Models relating K(DOC) to the octanol-water partition coefficient (K(OW)) have not been successful for many types of dissolved organic carbon in the environment. Instead, linear solvation energy relationships are proposed to model the association of chemicals with dissolved organic matter. However, more chemically diverse K(DOC) data are needed to produce a more robust model. For humic acid dissolved organic carbon, the linear solvation energy relationship predicts log K(DOC) with a root mean square error of 0.43. Copyright © 2011 SETAC.

Direct analysis of δ13C and concentration of dissolved organic carbon (DOC) in environmental samples by TOC-IRMS

NASA Astrophysics Data System (ADS)

Kirkels, Frédérique; Cerli, Chiara; Federherr, Eugen; Kalbitz, Karsten

2014-05-01

Dissolved organic carbon (DOC) plays an important role in carbon cycling in terrestrial and aquatic systems. Stable isotope analysis (delta 13C) of DOC could provide valuable insights in its origin, fluxes and environmental fate. Precise and routine analysis of delta 13C and DOC concentration are therefore highly desirable. A promising, new system has been developed for this purpose, linking a high-temperature combustion TOC analyzer trough an interface with a continuous flow isotope ratio mass spectrometer (Elementar group, Hanau, Germany). This TOC-IRMS system enables simultaneous stable isotope (bulk delta 13C) and concentration analysis of DOC, with high oxidation efficiency by high-temperature combustion for complex mixtures as natural DOC. To give delta 13C analysis by TOC-IRMS the necessary impulse for broad-scale application, we present a detailed evaluation of its analytical performance for realistic and challenging conditions inclusive low DOC concentrations and environmental samples. High precision (standard deviation, SD predominantly < 0.15 permil) and accuracy (R2 = 0.9997, i.e. comparison TOC-IRMS and conventional EA-IRMS) were achieved by TOC-IRMS for a broad diversity of DOC solutions. This precision is comparable or even slightly better than that typically reported for EA-IRMS systems, and improves previous techniques for δ13C analysis of DOC. Simultaneously, very good precision was obtained for DOC concentration measurements. Assessment of natural abundance and slightly 13C enriched DOC, a wide range of concentrations (0.2-150 mgC/L) and injection volumes (0.05-3 ml), demonstrated good analytical performance with negligible memory effects, no concentration/volume effects and a wide linearity. Low DOC concentrations (< 2 mgC/L), were correctly analyzed without any pre-concentration. Moreover, TOC-IRMS was successfully applied to analyze DOC from diverse terrestrial, freshwater and marine environments (SD < 0.23 permil). In summary, the TOC-IRMS performs fast and reliable analysis of DOC concentration and δ13C in aqueous samples, without any pre-concentration/freeze-drying. Flexible usage is highlighted by automated, online analysis, a variable injection volume, high throughput and no extensive maintenance. Sample analysis is simple, using small aliquots and with minimal sample preparation. Further investigations should focus on complex, saline matrices and very low DOC concentrations, to achieve a potential lower limit of 0.2 mgC/L. High-resolution, routine delta 13C analysis of DOC by TOC-IRMS offers opportunities for wide-scale application in terrestrial, freshwater and marine research to elucidate the role of DOC in biogeochemical processes and ecosystem functioning.

Dynamics, chemical properties and bioavailability of DOC in an early successional catchment

NASA Astrophysics Data System (ADS)

Risse-Buhl, U.; Hagedorn, F.; Dümig, A.; Gessner, M. O.; Schaaf, W.; Nii-Annang, S.; Gerull, L.; Mutz, M.

2013-07-01

The dynamics of dissolved organic carbon (DOC) have been intensively studied in mature ecosystems, but little is known about DOC dynamics and the significance of DOC as a substrate for microbial activity in early-successional catchments. We determined the concentration, chemical composition, source, radiocarbon age, and bioavailability of DOC along the hydrological flow path from soil solution to a downstream pond in a recently constructed catchment (Chicken Creek Catchment, Germany). Soil solution, upwelling ground water, stream water, subsurface water in an alluvial fan, and pond water all had high DOC concentrations (averages: 6.0-11.6 mg DOC L-1), despite small carbon stocks in both vegetation and soil of the catchment. Solid-state CPMAS 13C NMR of DOC in upwelling ground water revealed a higher proportion of aromatic compounds (32%) and a lower proportion of carbohydrates (33%) than in pond water (18% and 45%, respectively). The average 14C age of DOC in upwelling ground water was 2600 to 2900 yr, while organic matter of the Quaternary substrate of the catchment had a 14C age of 3000 to 16 000 yr. Both the 14C age data and 13C NMR spectra suggest that DOC partly derived from organic matter of the Quaternary substrate (about 40 to 90% of the C in the DOC), indicating that both recent and old C of the DOC can support microbial activity during early ecosystem succession. However, in a 70 day incubation experiment, only about 11% of the total DOC was found to be bioavailable. This proportion was irrespective of the water type. Origin of the microbial communities within the catchment (enriched from soil, stream sediment or pond water) also had only a marginal effect on overall DOC utilization.

Contrasting dissolved organic carbon dynamics at two forested catchments interpreted from high-frequency optical sensor measurements

NASA Astrophysics Data System (ADS)

Saraceno, J.; Shanley, J. B.

2015-12-01

Stream dissolved organic carbon (DOC) concentrations can change rapidly during high-flow events. The timing and magnitude of these changes relative to the event hydrograph can yield insights about possible DOC sources its flow paths to the stream. In situ fluorescent dissolved organic matter (FDOM) sensors that generate high-frequency observations enable detailed examination of high-flow DOC- discharge hysteresis. In this presentation, we interpret high-flow DOC dynamics at two of the five U.S. Geological Survey (USGS) Water, Energy, and Biogeochemical Budgets (WEBB) sites - Panola Mountain, Georgia and Sleepers River, Vermont. Based on laboratory analyses of weekly and event grab samples, both USGS WEBB sites had a similar DOC ranges: from ~1 milligrams per liter (mg/L) at base flow to ~11-15 mg/L during the largest events. A curvilinear relationship between DOC and FDOM (corrected for temperature and turbidity interferences) was used to model a continuous time series of DOC. At the Sleepers River site, DOC showed a seasonal pattern of increasing DOC response; from fairly subdued during spring snowmelt, to a maximum during autumn leaf-fall. The DOC response to discharge showed a consistent clockwise hysteresis (DOC peak, lagged discharge peak). At the Panola Mountain site, maximum event DOC response was lower during wet conditions in the winter and spring. Hysteresis was less expressed at Panola Mountain relative to Sleepers River and displayed both clockwise and counterclockwise patterns, which were dependent on antecedent moisture conditions. The greater synchrony of DOC and discharge peaks at Panola Mountain suggests that DOC sources are closer to the stream and (or) move to the stream more quickly, than at Sleepers River.

The soil organic carbon content of anthropogenically altered organic soils effects the dissolved organic matter quality, but not the dissolved organic carbon concentrations

NASA Astrophysics Data System (ADS)

Frank, Stefan; Tiemeyer, Bärbel; Bechtold, Michel; Lücke, Andreas; Bol, Roland

2016-04-01

Dissolved organic carbon (DOC) is an important link between terrestrial and aquatic ecosystems. This is especially true for peatlands which usually show high concentrations of DOC due to the high stocks of soil organic carbon (SOC). Most previous studies found that DOC concentrations in the soil solution depend on the SOC content. Thus, one would expect low DOC concentrations in peatlands which have anthropogenically been altered by mixing with sand. Here, we want to show the effect of SOC and groundwater level on the quantity and quality of the dissolved organic matter (DOM). Three sampling sites were installed in a strongly disturbed bog. Two sites differ in SOC (Site A: 48%, Site B: 9%) but show the same mean annual groundwater level of 15 and 18 cm below ground, respectively. The SOC content of site C (11%) is similar to Site B, but the groundwater level is much lower (-31 cm) than at the other two sites. All sites have a similar depth of the organic horizon (30 cm) and the same land-use (low-intensity sheep grazing). Over two years, the soil solution was sampled bi-weekly in three depths (15, 30 and 60 cm) and three replicates. All samples were analyzed for DOC and selected samples for dissolved organic nitrogen (DON) and delta-13C and delta-15N. Despite differences in SOC and groundwater level, DOC concentrations did not differ significantly (A: 192 ± 62 mg/L, B: 163 ± 55 mg/L and C: 191 ± 97 mg/L). At all sites, DOC concentrations exceed typical values for peatlands by far and emphasize the relevance even of strongly disturbed organic soils for DOC losses. Individual DOC concentrations were controlled by the temperature and the groundwater level over the preceding weeks. Differences in DOM quality were clearer. At site B with a low SOC content, the DOC:DON ratio of the soil solution equals the soil's C:N ratio, but the DOC:DON ratio is much higher than the C:N ratio at site A. In all cases, the DOC:DON ratio strongly correlates with delta-13C. There is no isotope data for site C. Delta-15N is more enriched at site B than at site A, indicating differences in C and N cycling and potential influence of the dominant vegetation (grasses vs. Sphagnum mosses).

Identification and analysis of low-molecular-weight dissolved organic carbon in subglacial basal ice ecosystems by ion chromatography

NASA Astrophysics Data System (ADS)

O'Donnell, Emily C.; Wadham, Jemma L.; Lis, Grzegorz P.; Tranter, Martyn; Pickard, Amy E.; Stibal, Marek; Dewsbury, Paul; Fitzsimons, Sean

2016-07-01

Determining the concentration and composition of dissolved organic carbon (DOC) in glacial ecosystems is important for assessments of in situ microbial activity and contributions to wider biogeochemical cycles. Nonetheless, there is limited knowledge of the abundance and character of DOC in basal ice and the subglacial environment and a lack of quantitative data on low-molecular-weight (LMW) DOC components, which are believed to be highly bioavailable to microorganisms. We investigated the abundance and composition of DOC in basal ice via a molecular-level DOC analysis. Spectrofluorometry and a novel ion chromatographic method, which has been little utilized in glacial science for LMW-DOC determinations, were employed to identify and quantify the major LMW fractions (free amino acids, carbohydrates, and carboxylic acids) in basal ice from four glaciers, each with a different type of overridden material (i.e. the pre-entrainment sedimentary type such as lacustrine material or palaeosols). Basal ice from Joyce Glacier (Antarctica) was unique in that 98 % of the LMW-DOC was derived from the extremely diverse free amino acid (FAA) pool, comprising 14 FAAs. LMW-DOC concentrations in basal ice were dependent on the bioavailability of the overridden organic carbon (OC), which in turn was influenced by the type of overridden material. Mean LMW-DOC concentrations in basal ice from Russell Glacier (Greenland), Finsterwalderbreen (Svalbard), and Engabreen (Norway) were low (0-417 nM C), attributed to the relatively refractory nature of the OC in the overridden palaeosols and bedrock. In contrast, mean LMW-DOC concentrations were an order of magnitude higher (4430 nM C) in basal ice from Joyce Glacier, a reflection of the high bioavailability of the overridden lacustrine material (> 17 % of the sediment OC comprised extractable carbohydrates, a proxy for bioavailable OC). We find that the overridden material may act as a direct (via abiotic leaching) and indirect (via microbial cycling) source of DOC to the subglacial environment and provides a range of LMW-DOC compounds that may stimulate microbial activity in wet subglacial sediments.

Latitudinal distributions of particulate carbon export across the North Western Atlantic Ocean

NASA Astrophysics Data System (ADS)

Puigcorbé, Viena; Roca-Martí, Montserrat; Masqué, Pere; Benitez-Nelson, Claudia; Rutgers van der Loeff, Michiel; Bracher, Astrid; Moreau, Sebastien

2017-11-01

234Th-derived carbon export fluxes were measured in the Atlantic Ocean under the GEOTRACES framework to evaluate basin-scale export variability. Here, we present the results from the northern half of the GA02 transect, spanning from the equator to 64°N. As a result of limited site-specific C/234Th ratio measurements, we further combined our data with previous work to develop a basin wide C/234Th ratio depth curve. While the magnitude of organic carbon fluxes varied depending on the C/234Th ratio used, latitudinal trends were similar, with sizeable and variable organic carbon export fluxes occurring at high latitudes and low to negligible fluxes occurring in oligotrophic waters. Our results agree with previous studies, except at the boundaries between domains, where fluxes were relatively enhanced. Three different models were used to obtain satellite-derived net primary production (NPP). In general, NPP estimates had similar trends along the transect, but there were significant differences in the absolute magnitude depending on the model used. Nevertheless, organic carbon export efficiencies were generally < 25%, with the exception of a few stations located in the transition area between the riverine and the oligotrophic domains and between the oligotrophic and the temperate domains. Satellite-derived organic carbon export models from Dunne et al. (2005) (D05), Laws et al. (2011) (L11) and Henson et al. (2011) (H11) were also compared to our 234Th-derived carbon exports fluxes. D05 and L11 provided estimates closest to values obtained with the 234Th approach (within a 3-fold difference), but with no clear trends. The H11 model, on the other hand, consistently provided lower export estimates. The large increase in export data in the Atlantic Ocean derived from the GEOTRACES Program, combined with satellite observations and modeling efforts continue to improve the estimates of carbon export in this ocean basin and therefore reduce uncertainty in the global carbon budget. However, our results also suggest that tuning export models and including biological parameters at a regional scale is necessary for improving satellite-modeling efforts and providing export estimates that are more representative of in situ observations.