These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Quantifying the surface-subsurface biogeochemical coupling during the VERTIGO ALOHA and K2 studies  

SciTech Connect

A central question addressed by the VERTIGO (VERtical Transport In the Global Ocean) study was 'What controls the efficiency of particle export between the surface and subsurface ocean'? Here, we present data from sites at ALOHA (N Central Pacific Gyre) and K2 (NW subarctic Pacific) on phytoplankton processes, and relate them via a simple planktonic foodweb model, to subsurface particle export (150-500 m). Three key factors enable quantification of the surface-subsurface coupling: a sampling design to overcome the temporal lag and spatial displacement between surface and subsurface processes; data on the size-partitioning of Net Primary Production (NPP) and subsequent transformations prior to export; estimates of the ratio of algal- to faecal-mediated vertical export flux. At ALOHA, phytoplankton were characterized by low stocks, NPP, F{sub v}/F{sub m} (N-limited), and were dominated by picoplankton. The HNLC waters at K2 were characterized by both two-fold changes in NPP and floristic shifts (high to low proportion of diatoms) between deployment 1 and 2. Prediction of export exiting the euphotic zone was based on size-partitioning of NPP, a copepod-dominated foodweb and a ratio of 0.2 (ALOHA) and 0.1 (K2) for algal:faecal particle flux. Predicted export was 20-22 mg POC m{sup -2} d{sup -1} at ALOHA (i.e. 10-11% NPP (0-125 m); 1.1-1.2 x export flux at 150 m (E{sub 150}). At K2, export was 111 mg C m{sup -2} d{sup -1} (21% NPP (0-50 m); 1.8 x E{sub 150}) and 33 mg POC m{sup -2} d{sup -1} (11% NPP, 0-55 m); 1.4 x E{sub 150}) for deployments 1 and 2, respectively. This decrease in predicted export at K2 matches the observed trend for E{sub 150}. Also, the low attenuation of export flux from 60 to 150 m is consistent with that between 150 to 500 m. This strong surface-subsurface coupling suggests that phytoplankton productivity and floristics play a key role at K2 in setting export flux, and moreover that pelagic particle transformations by grazers strongly influence to what extent sinking particles are further broken down in the underlying waters of the Twilight Zone.

Boyd, P.W.; Gall, M.P.; Silver, M.W.; Bishop, J.K.B.; Coale, Susan L.; Bidigare, Robert R.

2008-02-25

2

Exploring Dynamics of Land surface-Subsurface Coupling Under Change  

NASA Astrophysics Data System (ADS)

The degree of land surface-subsurface coupling is controlled by complex interactions between the atmosphere, land surface condition and subsurface hydrologic characteristics. Global climate models project increases in temperature and changes in precipitation rates and patterns which in turn alter terrestrial water and energy budgets impacting water resources. However, the degree of land surface-subsurface coupling under scenarios of land cover and climate change has not been fully explored. In this study, we used an integrated groundwater-surface water-land surface model (ParFlow.CLM) across a semi-arid catchment located in the central west New South Wales, Australia to assess variability in water and energy fluxes under historic condition and scenarios of climate and land cover change. The Baldry hydrological observatory situated in a topographically flat terrain has the area of 2 km2 and contains two distinct land cover types of pasture and a regenerated Eucalyptus forest. High resolution groundwater level measurements in the site reveal differences in groundwater connectivity in wet versus dry periods in pasture and Eucalyptus forest for the historic condition. Using downscaled climate forcing obtained from a regional climate model for eastern Australia, the degree of land surface-subsurface coupling within the catchment was examined under various scenarios of climate and changes in land cover types. It is expected that a fully integrated hydrologic model like ParFlow.CLM improve predictions in land-atmospheric feedback processes under changes in hydrologic conditions.

Ajami, Hoori; McCabe, Matthew F.; Evans, Jason P.

2013-04-01

3

A Coupled Surface/Subsurface Model for Hydrological Drought Investigations  

NASA Astrophysics Data System (ADS)

Hydrological droughts occur when storage in the ground and surface-water bodies falls below statistical average. Due to the inclusion of regional groundwater, hydrological droughts evolve relatively slowly. The atmospheric and surface components of the hydrological cycle have been widely studied, are well understood, and their prognoses are fairly accurate. In large-scale land surface models on the other hand, subsurface (groundwater) flow processes are usually assumed unidirectional and limited to the vertically-downward percolation and the horizontal runoffs. The vertical feedback from groundwater to the unsaturated zone as well as the groundwater recharge from surface waters are usually misrepresented, resulting in poor model performance during low-flow periods. The feedback is important during meteorological droughts because it replenishes soil moisture from ground- and surface water, thereby delaying the onset of agricultural droughts. If sustained for long periods however, the depletion can significantly reduce surface and subsurface storage and lead to severe hydrological droughts. We hypothesise that an explicit incorporation of the groundwater component into an existing land surface model would lead to better representation of low flows, which is critical for drought analyses. It would also improve the model performance during low-flow periods. For this purpose, we coupled the process-based mHM surface model (Samaniego et al. 2010) with MODFLOW (Harbaugh 2005) to analyse droughts in the Unstrut catchment, one of the tributaries of the Elbe. The catchment is located in one of the most drought-prone areas of Germany. We present results for stand-alone and coupled mHM simulations for the period 1970-2000. References Arlen W. Harbaugh. MODFLOW-2005, The U.S. Geological Survey Modular Ground-water Model-the Ground-water Flow Process, chapter Modelling techniques, sec. A. Ground water, pages 1:1-9:62. USGS, 2005. Luis Samaniego, Rohini Kumar, and Sabine Attinger. Multiscale parameter regionalization of a grid-based hydrologic model at the mesoscale. Water Resour. Res., 46(W05523), 2010. doi: 10.1029/2008WR007327.

Musuuza, J. L.; Kumar, R.; Samaniego, L. E.; Fischer, T.; Kolditz, O.; Attinger, S.

2013-12-01

4

External iterative coupling strategy for surface-subsurface flow calculations in surface irrigation  

Technology Transfer Automated Retrieval System (TEKTRAN)

Coupling the unsteady open-channel flow equations of surface irrigation with the equation of variably saturated porous media flow is a computationally complex problem, because of the dependence of infiltration on flow depths. Several models of this coupled process have been developed, all of which ...

5

Insights into three-dimensional simulation of coastal flow dynamics using a fully coupled surface-subsurface approach  

NASA Astrophysics Data System (ADS)

Coastal aquifers are complex hydrologic systems because many physical processes interact: (i) variably saturated flow, (ii) spatial-temporal fluid density variations, (iii) tidal fluctuations, (iv) storm surges overtopping dykes, and (v) surface runoff of storm water. The HydroGeoSphere model is used to numerically simulate coastal flow dynamics, assuming a fully coupled surface-subsurface approach, accounting for all processes listed above. The diffusive wave approximation of the St. Venant equation is used to describe surface flow. Surface flow and salt transport are fully coupled with subsurfacial variably saturated, variable-density flow and salt transport through mathematical terms that represent exchange of fluid mass and solute mass, respectively. Tides and storm surges induce a time-variant head that is applied to nodes of the surface domain. The approach is applied to real cases of tide and storm surge events of the coastal catchment area of Unterweser, Northern Germany (ca. 2500 km2). To optimize the simulation and to reduce CPU cost, the actual simulation domain is only a part of the total catchment area: We selected a narrow strip of about 10 km width parallel to the coastline. The catchment area outside of that strip is not affected by saltwater intrusion and does therefore not need to be included in the numerical model. The seaside boundary condition of the reduced simulation domain is obtained from a 3D hydrodynamic-numerical flow model where changes in sea level are being simulated. The landside boundary condition is obtained from a 3D steady-state flow model of the total catchment area. The 3D model is calibrated using field data previously gathered at the study site. Results indicate that the fully coupled approach with a reduced simulation domain is effective in the simulation of 3D coastal flow dynamics.

Yang, Jie; Graf, Thomas

2013-04-01

6

Measuring groundwater flow at the Sanford Laboratory with coupled surface/subsurface time-lapse gravity measurements  

NASA Astrophysics Data System (ADS)

Limited options exist to measure groundwater processes, particularly at large depths. Coupled time-lapse gravity measurements at the surface and underground are one possibility, but despite recent advances in borehole instruments, no repeat underground gravity measurements of water-mass change have been reported. At the Sanford Laboratory-located at the Homestake Mine in Lead, South Dakota, and site of the proposed Deep Underground Science and Engineering Laboratory (DUSEL)-the U.S. Geological Survey has established a network of 19 surface and 5 underground gravity stations to monitor groundwater-storage change over the projected 20-year existence of the underground laboratory. Continuous pumping is planned to dewater the mine to a depth of 2,500 m; the current pumping regime began in 2007 and current water levels (2011) are at a depth of about 1,700 m. Measurements using a field-portable A-10 absolute gravimeter have been made approximately annually at surface stations since 2007. Underground stations forming a vertical profile along the Ross Shaft on the 300, 800, 2000, 4100, and 4850 levels (numbers indicate approximate depth in feet) were established in 2011, and it is expected all stations will be surveyed annually. To date, surface time-lapse measurements show gravity increases of 50 to 100 nm/s^2 (10 nm/s^2 = 1 microgal) at some stations and equivalent decreases at others, indicating little evidence of water-mass change from pumping. Preliminary modeling, in which the dewatered zone is represented by a series of horizontal prisms that undergo mass change equal to the porosity (assumed 0.005, an average of rock porosity and mined-out voids), indicates that this is the expected result. At pumping rates required to maintain drawdown to a depth of 2,500 m, however, the expected gravity change increases from about 50 nm/s^2 at the surface to 250 nm/s^2 at the 4850 level. Gravity stations in the subsurface are advantageous because they are both closer to the water-mass change from pumping and removed from water-mass change at the surface caused by inter-annual climate variability. Furthermore, the predicted gravity response varies along the vertical profile depending on the distribution of water-mass change in the deep subsurface, indicating the subsurface measurements will be useful for calibrating and validating a groundwater flow model. A tunnel on the 300 level that traverses beneath a forested hillslope and exits at the land surface is a significant future opportunity for monitoring hydrologic processes; concurrent surface and subsurface gravity profiles above and below this hillslope, combined with other measurements, would likely lead to new advances in hillslope-scale hydrology.

Kennedy, J.; Murdoch, L.; Long, A. J.; Koth, K.

2011-12-01

7

Coupling a terrestrial biogeochemical model to the common land model  

SciTech Connect

A terrestrial biogeochemical model (CASACNP) was coupled to a land surface model (the Common Land Model, CoLM) to simulate the dynamics of carbon substrate in soil and its limitation on soil respiration. The combined model, CoLM-CASACNP, was able to predict long-term carbon sources and sinks that CoLM alone could not. The coupled model was tested using measurements of belowground respiration and surface fluxes from two forest ecosystems. The combined model simulated reasonably well the diurnal and seasonal variations of net ecosystem carbon exchange, as well as seasonal variation in the soil respiration rate of both the forest sites chosen for this study. However, the agreement between model simulations and actual measurements was poorer under dry conditions. The model should be tested against more measurements before being applied globally to investigate the feedbacks between the carbon cycle and climate change.

Shi, Xiaoying [ORNL; Mao, Jiafu [ORNL; Wang, Yingping [ORNL; Dai, Yongjiu [Beijing Normal University; Tang, Xuli [Chinese Academy of Sciences

2011-01-01

8

Physical/biogeochemical coupled model : impact of an offline vs online strategy  

NASA Astrophysics Data System (ADS)

Mercator-Ocean, the French ocean forecasting center, has been developing several operational forecasting systems and reanalysis of the physical and biogeochemical 3D-Ocean. Here we study the impact of an offline vs online strategy to couple the physical (OPA) and biogeochemical (PISCES) modules included in the NEMO platform. For this purpose, we perform global one-year long simulations at 1° resolution. The model was initialized with global climatologies. The spin-up involved 10 years of biogeochemical off-line simulation forced by a climatology of ocean physics. The online mode consists in running physical and biogeochemical models simultaneously whereas in the offline mode, the biogeochemical model is launched alone, forced by averaged physical forcing (1 day, 7 days,… ). The Mercator operational biogeochemical system is currently using the offline mode with a weekly physical forcing. A special treatment is applied to the vertical diffusivity coefficient (Kz): as it varies of several orders of magnitude, we compute the mean of the LOG10 of Kz. Moreover, a threshold value is applied to remove the highest values corresponding to enhanced convection. To improve this system, 2 directions are explored. First, 3 physical forcing frequencies are compared to quantify errors due to the offline mode: 1 hour (online mode), 1 day and 1 week (offline modes). Secondly, sensitivity tests to the threshold value applied to Kz are performed. The simulations are evaluated by systematically comparing model fields to observations (Globcolour product and World Ocean Atlas 2005) at global and regional scales. We show first that offline simulations are in good agreement with online simulation. As expected, the lower the physical forcing frequency is, the closer to the online solution is the offline simulation. The threshold value on the vertical diffusivity coefficient manages the mixing strength within the mixed layer. A value of 1 m2.s-1 appears to be a good compromise to approach the online solution. Our sensitivity tests show that increasing the temporal resolution of the forcing induces a temporal shift in the surface chlorophyll seasonal cycle: less chlorophyll in winter and a stronger spring bloom in offline mode. We attribute this behavior to the entrainment/detrainment process of chlorophyll and nutrients at the bottom of the mixed layer during winter.

Hameau, Angélique; Perruche, Coralie; Bricaud, Clément; Gutknecht, Elodie; Reffray, Guillaume

2014-05-01

9

Internanual variability of the biogeochemical fluxes in the deep water formation area in the northwestern Mediterranean Sea from a 3D coupled physical-biogeochemical model  

NASA Astrophysics Data System (ADS)

A biogeochemical model was coupled to a regional circulation model to investigate the interannual variability of the biogeochemical fluxes in the northwestern Mediterranean Sea. The physical model is the primitive equation ocean circulation S model [Marsaleix et al., 2011]. The biogeochemical model Eco3M-S [Auger et al., 2011] was used to describe the cycles of carbon, nitrogen, phosphorus and silica. The model results were compared with a set of in-situ and satellite observations available over the 5-year period study, 2004-2008. The comparisons provided a reasonable validation of the model reproducing the recorded spatial and temporal variations and suggested that it can be used to estimate a budget of biogenic elements. A strong variability of the intensity of the deep convection was observed over the study period. We investigated the impact of this variability on (1) the import of nutrients upwelled in the surface layer, (2) the primary production, (3) the export of organic carbon towards the bottom and on (4) the lateral exchanges.

Ulses, Caroline; Auger, Pierre-Amaël; Soetaert, Karline; Diaz, Fredéric; Marsaleix, Patrick; Kessouri, Fayçal; Herrmann, Marine; Estournel, Claude

2014-05-01

10

Carbon sequestration by patch fertilization: A comprehensive assessment using coupled physical-ecological-biogeochemical models  

SciTech Connect

This final report summarizes research undertaken collaboratively between Princeton University, the NOAA Geophysical Fluid Dynamics Laboratory on the Princeton University campus, the State University of New York at Stony Brook, and the University of California, Los Angeles between September 1, 2000, and November 30, 2006, to do fundamental research on ocean iron fertilization as a means to enhance the net oceanic uptake of CO2 from the atmosphere. The approach we proposed was to develop and apply a suite of coupled physical-ecological-biogeochemical models in order to (i) determine to what extent enhanced carbon fixation from iron fertilization will lead to an increase in the oceanic uptake of atmospheric CO2 and how long this carbon will remain sequestered (efficiency), and (ii) examine the changes in ocean ecology and natural biogeochemical cycles resulting from iron fertilization (consequences). The award was funded in two separate three-year installments: • September 1, 2000 to November 30, 2003, for a project entitled “Ocean carbon sequestration by fertilization: An integrated biogeochemical assessment.” A final report was submitted for this at the end of 2003 and is included here as Appendix 1. • December 1, 2003 to November 30, 2006, for a follow-on project under the same grant number entitled “Carbon sequestration by patch fertilization: A comprehensive assessment using coupled physical-ecological-biogeochemical models.” This report focuses primarily on the progress we made during the second period of funding subsequent to the work reported on in Appendix 1. When we began this project, we were thinking almost exclusively in terms of long-term fertilization over large regions of the ocean such as the Southern Ocean, with much of our focus being on how ocean circulation and biogeochemical cycling would interact to control the response to a given fertilization scenario. Our research on these types of scenarios, which was carried out largely during the first three years of our project, led to several major new insights on the interaction between ocean biogeochemistry and circulation. This work, which is described in the following Section II on “Large scale fertilization,” has continued to appear in the literature over the past few years, including two high visibility papers in Nature. Early on in the first three years of our project, it became clear that small "patch-scale" fertilizations over limited regions of order 100 km diameter were much more likely than large scale fertilization, and we carried out a series of idealized patch fertilization simulations reported on in Gnanadesikan et al. (2003). Based on this paper and other results we had obtained by the end of our first three-year grant, we identified a number of important issues that needed to be addressed in the second three-year period of this grant. Section III on “patch fertilization” discusses the major findings of this phase of our research, which is described in two major manuscripts that will be submitted for publication in the near future. This research makes use of new more realistic ocean ecosystem and iron cycling models than our first paper on this topic. We have several major new insights into what controls the efficiency of iron fertilization in the ocean. Section IV on “model development” summarizes a set of papers describing the progress that we made on improving the ecosystem models we use for our iron fertilization simulations.

Jorge L. Sarmiento - Princeton PI, Anand Gnanadesikan - Princeton Co-I, Nicolas Gruber - UCLA PI, Xin Jin - UCLA PostDoc, Robert Armstrong - SUNY/Stony Brook Consultant

2007-06-21

11

Net greenhouse gas balance in response to nitrogen enrichment: perspectives from a coupled biogeochemical model.  

PubMed

Increasing reactive nitrogen (N) input has been recognized as one of the important factors influencing climate system through affecting the uptake and emission of greenhouse gases (GHG). However, the magnitude and spatiotemporal variations of N-induced GHG fluxes at regional and global scales remain far from certain. Here we selected China as an example, and used a coupled biogeochemical model in conjunction with spatially explicit data sets (including climate, atmospheric CO2 , O3 , N deposition, land use, and land cover changes, and N fertilizer application) to simulate the concurrent impacts of increasing atmospheric and fertilized N inputs on balance of three major GHGs (CO2 , CH4 , and N2 O). Our simulations showed that these two N enrichment sources in China decreased global warming potential (GWP) through stimulating CO2 sink and suppressing CH4 emission. However, direct N2 O emission was estimated to offset 39% of N-induced carbon (C) benefit, with a net GWP of three GHGs averaging -376.3 ± 146.4 Tg CO2  eq yr(-1) (the standard deviation is interannual variability of GWP) during 2000-2008. The chemical N fertilizer uses were estimated to increase GWP by 45.6 ± 34.3 Tg CO2  eq yr(-1) in the same period, and C sink was offset by 136%. The largest C sink offset ratio due to increasing N input was found in Southeast and Central mainland of China, where rapid industrial development and intensively managed crop system are located. Although exposed to the rapidly increasing N deposition, most of the natural vegetation covers were still showing decreasing GWP. However, due to extensive overuse of N fertilizer, China's cropland was found to show the least negative GWP, or even positive GWP in recent decade. From both scientific and policy perspectives, it is essential to incorporate multiple GHGs into a coupled biogeochemical framework for fully assessing N impacts on climate changes. PMID:23504794

Lu, Chaoqun; Tian, Hanqin

2013-02-01

12

Observations of physical-biogeochemical coupling in the tropical Northeast Atlantic using a fleet of gliders  

NASA Astrophysics Data System (ADS)

To study the coupling between physical and biogeochemical parameters, high-spatial resolution, multi-parameter measurements are required. This poses a challenge to ocean observing systems. We present results from a study in the tropical Northeast Atlantic, employing simultaneous observations from 5 gliders. Each glider recorded temperature, salinity, chlorophyll, oxygen and turbidity for the duration of 50 days. A 45 by 45 km wide area was sampled using butterfly-shaped courses, to optimize the area coverage of the gliders. Our analysis focuses on the quantification of the spatial scales of variability in the recorded parameters and the demonstration of coupling between physical and biogeochemical parameters. The gliders observed strong variability in form of changes of thermohaline properties including pronounced submesoscale variability. The scale-dependence of the different parameters is presented. Below the mixed layer, changes in oxygen and salinity imply spatio-temporal variability of the ratio of North to South Atlantic waters. We report the passing of an open-ocean salinity front, associated with pronounced changes in both the vertical chlorophyll distribution and the possible communication between the mixed layer base and the sub-surface chlorophyll maximum. Our results imply, that these variations might pose challenges to estimating chlorophyll profiles by remote sensing.Salinity (upper panel) and chlorophyll fluorescence (lower panel), as observed from a glider north of the Cape Verde Islands. Also shown are the mixed laxer base (magenta line) and a potential density surface (black line). Note that the mixed layer base ceases to reach the subsurface chlorophyll maximum after passing through the salinity front.

Kanzow, T.; Krahmann, G.; Karstensen, J.

2012-12-01

13

Modeling Nitrogen Cycle at the Surface-Subsurface Water Interface  

NASA Astrophysics Data System (ADS)

Anthropogenic activities, primarily food and energy production, have altered the global nitrogen cycle, increasing reactive dissolved inorganic nitrogen, Nr, chiefly ammonium NH4+ and nitrate NO3-, availability in many streams worldwide. Increased Nr promotes biological activity often with negative consequences such as water body eutrophication and emission of nitrous oxide gas, N2O, an important greenhouse gas as a by-product of denitrification. The hyporheic zone may play an important role in processing Nr and returning it to the atmosphere. Here, we present a process-based three-dimensional semi-analytical model, which couples hyporheic hydraulics with biogeochemical reactions and transport equations. Transport is solved by means of particle tracking with negligible local dispersion and biogeochemical reactions modeled by linearized Monod's kinetics with temperature dependant reaction rate coefficients. Comparison of measured and predicted N2O emissions from 7 natural stream shows a good match. We apply our model to gravel bed rivers with alternate bar morphology to investigate the role of hyporheic hydraulic, depth of alluvium, relative availability of stream concentration of NO3- and NH4+ and water temperature on nitrogen gradients within the sediment. Our model shows complex concentration dynamics, which depend on hyporheic residence time distribution and consequently on streambed morphology, within the hyporheic zone. Nitrogen gas emissions from the hyporheic zone increase with alluvium depth in large low-gradient streams but not in small steep streams. On the other hand, hyporheic water temperature influences nitrification/denitrification processes mainly in small-steep than large low-gradient streams, because of the long residence times, which offset the slow reaction rates induced by low temperatures in the latter stream. The overall conclusion of our analysis is that river morphology has a major impact on biogeochemical processes such as nitrification and denitrification with a direct impact on the stream nutrient removal and transport.

Marzadri, A.; Tonina, D.; Bellin, A.

2011-12-01

14

HYDROBIOGEOCHEM: A coupled model of HYDROlogic transport and mixed BIOGEOCHEMical kinetic/equilibrium reactions in saturated-unsaturated media  

SciTech Connect

The computer program HYDROBIOGEOCHEM is a coupled model of HYDROlogic transport and BIOGEOCHEMical kinetic and/or equilibrium reactions in saturated/unsaturated media. HYDROBIOGEOCHEM iteratively solves the two-dimensional transport equations and the ordinary differential and algebraic equations of mixed biogeochemical reactions. The transport equations are solved for all aqueous chemical components and kinetically controlled aqueous species. HYDROBIOGEOCHEM is designed for generic application to reactive transport problems affected by both microbiological and geochemical reactions in subsurface media. Input to the program includes the geometry of the system, the spatial distribution of finite elements and nodes, the properties of the media, the potential chemical and microbial reactions, and the initial and boundary conditions. Output includes the spatial distribution of chemical and microbial concentrations as a function of time and space, and the chemical speciation at user-specified nodes.

Yeh, G.T.; Salvage, K.M. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil and Environmental Engineering] [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil and Environmental Engineering; Gwo, J.P. [Oak Ridge National Lab., TN (United States)] [Oak Ridge National Lab., TN (United States); Zachara, J.M.; Szecsody, J.E. [Pacific Northwest National Lab., Richland, WA (United States)] [Pacific Northwest National Lab., Richland, WA (United States)

1998-07-01

15

Finite volume integrated surface-subsurface flow modeling on nonorthogonal grids  

NASA Astrophysics Data System (ADS)

this paper, we present an innovative finite volume surface-subsurface integrated flow model on nonorthogonal grids. The shallow water equation with diffusion wave approximation is used to formulate the surface flow system, while the Richards' equation is used to formulate the saturated-unsaturated subsurface flow system. These two flow systems are discretized using a finite volume method and are then coupled by enforcing the continuity of pressure and flux at the surface-subsurface interface, which does not require unphysical parameters such as the interface permeability and thickness. The numerical instability caused by enforcing the continuity of pressure and flux at the interface is resolved using a cell-centered finite volume discretization. The coupled systems are solved simultaneously by the Newton iterative method. A battery of benchmark analyses and laboratory experiments verify the proposed model's superior performance relative to existing models. Two numerical experiments over irregular terrain show that the nonorthogonal grids and diffusive wave approximation used in the proposed model accurately represent the interaction between surface and subsurface flows for irregular topographies. In particular, they capture the significant topographical effects on runoff discharges, especially where gentle slopes are involved.

An, Hyunuk; Yu, Soonyoung

2014-03-01

16

Towards coupled physical-biogeochemical models of the ocean carbon cycle  

NASA Technical Reports Server (NTRS)

The purpose of this review is to discuss the critical gaps in our knowledge of ocean dynamics and biogeochemical cycles. It is assumed that the ultimate goal is the design of a model of the earth system that can predict the response to changes in the external forces driving climate.

Rintoul, Stephen R.

1992-01-01

17

Three-dimensional approach using two coupled models for description of hydrological and biogeochemical processes at the catchment scale  

NASA Astrophysics Data System (ADS)

Hydrological and biogeochemical transport through changing landscapes has been well described during the past years in literature. However, the uncertainties of combined water quality and water quantity models are still challenging, both due to a lack in process understanding as well to spatiotemporal heterogeneity of environmental conditions driving the processes. In order to reduce the uncertainty in water quality and runoff predictions at the catchment scale, a variety of different model approaches from empirical-conceptual to fully physical and process based models have been developed. In this study we present a new modelling approach for the investigation of hydrological processes and nutrient cycles, with a focus on nitrogen in a small catchment from Hessen, Germany. A hydrological model based on the model toolbox Catchment Modelling Framework (CMF) has been coupled with the process based biogeochemical model LandscapeDNDC. States, fluxes and parameters are exchanged between the models at high temporal and spatial resolution using the Python scripting language in order to obtain a 3-dimensional model application. The transport of water and nutrients through the catchment is modelled using a 3D Richards/Darcy approach for subsurface fluxes, a kinematic wave approach for surface runoff and a Penman-Monteith based calculation of evapotranspiration. Biogeochemical processes are modelled by Landscape-DNDC, including plant growth and biomass allocation, organic matter mineralisation, nitrification, denitrification and associated nitrous oxide emissions. The interactions and module connectivity between the two coupled models, as well as the model application on a 3.7 km² catchment with the runoff results and nitrogen quantification will be presented in this study.

Plesca, Ina; Kraft, Philipp; Haas, Edwin; Klatt, Steffen; Butterbach-Bahl, Klaus; Frede, Hans-Georg; Breuer, Lutz

2014-05-01

18

A Coupled Biogeochemical Reactive Transport Model in Bed Sediments and Water Column of Riverine Systems  

Microsoft Academic Search

ABSTRACT: A multi-scale, quasi-two-dimensional, biogeochemical reactive theoretical and numerical model is presented, able to simulating sediment associated transport and transformations of contaminants in the water column and bed sediments of riverine systems as a result of sediment associated transport, as well as resuspension, deposition and burial. The model considers contaminant mass exchange between sediments and aqueous phase both in benthic

A. Massoudieh; F. A. Bombardelli; S. S. Sengor; T. R. Ginn

2007-01-01

19

Coupled Hydrological and Biogeochemical Controls on Methylmercury Production and Export from a Boreal Wetland  

NASA Astrophysics Data System (ADS)

Through long-term addition of a mercury (Hg) stable isotope to a wetland, we have begun to unravel the complexity of Hg and methylmercury (MeHg) cycling in a Boreal wetland. As part of the METAALICUS project being conducted at the Experimental Lakes Area, the lake 658 wetland was annually amended from 2001-2006 with a mercury isotope at a level approximately 5 times the annual anthropogenic deposition. However, wetlands not only receive Hg directly from atmospheric deposition, but also from upland runoff and from adjacent water bodies during periods of inundation. As METAALICUS is a whole watershed experiment, both the adjacent lake and uplands were each amended with a different mercury isotope. This has allowed us to study the cycling of Hg within the wetland in a watershed context. What is clear from this integrated approach is Hg cycling is dependent on the complex interplay of hydrodynamic and biogeochemical factors which will form the focus of this presentation. The Lake 658 wetland is classified as a basin oligotrophic swamp, and is surrounded on three sides by steeply sloping uplands and on the fourth by a lake. The morphology of the wetland causes large portions of the wetland to be hydrologically disconnected for long periods during dry periods in the summer and by ice in winter. When flow occurs, it is along defined channels rather than by sheet flow, which is partially an artifact of the basin morphology. Thus, wetland form influences the wetland volume that contributes to Hg and MeHg export. The majority of the Hg isotope added to the wetland has been retained in the vegetation and upper few centimeters of peat, with less than 1% exported despite the substantial export of both inorganic ambient Hg and MeHg. As little newly deposited Hg, represented by the amended isotope has been exported, we hypothesize that Hg export from wetlands is strongly coupled to decomposition and the fate of dissolved organic carbon which binds both Hg and MeHg. While MeHg is found throughout the wetland, MeHg concentrations and potentials (measured by short-term assays) were greatest in areas that are hydrologically connected to the lake or upland. These methylation assays correlate well with sulfate reduction and methane production. However, high concentrations of MeHg can be present in areas of the wetland when methylation assays reveal no measurable activity suggesting a pool of recalcitrant MeHg exists in wetlands. We hypothesize that the hydrologically interconnected areas of the wetland are most important in producing and exporting MeHg. However, the slow release of Hg isotope from the 658 wetland indicates Hg retention, thus response to changes in Hg deposition, is at least on the order of years and probably decades.

Heyes, A.; Krabbenhoft, D. P.; Branfireun, B. A.; Gilmour, C. C.; Mitchell, C. P.; Tate, M. T.; Richardson, M.

2007-12-01

20

Coupled physical/biogeochemical modeling including O2-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela  

NASA Astrophysics Data System (ADS)

The Eastern Boundary Upwelling Systems (EBUS) contribute to one fifth of the global catches in the ocean. Often associated with Oxygen Minimum Zones (OMZs), EBUS represent key regions for the oceanic nitrogen (N) cycle. Important bioavailable N loss due to denitrification and anammox processes as well as greenhouse gas emissions (e.g, N2O) occur also in these EBUS. However, their dynamics are currently crudely represented in global models. In the climate change context, improving our capability to properly represent these areas is crucial due to anticipated changes in the winds, productivity, and oxygen content. We developed a biogeochemical model (BioEBUS) taking into account the main processes linked with EBUS and associated OMZs. We implemented this model in a 3-D realistic coupled physical/biogeochemical configuration in the Namibian upwelling system (northern Benguela) using the high-resolution hydrodynamic ROMS model. We present here a validation using in situ and satellite data as well as diagnostic metrics and sensitivity analyses of key parameters and N2O parameterizations. The impact of parameter values on the OMZ off Namibia, on N loss, and on N2O concentrations and emissions is detailed. The model realistically reproduces the vertical distribution and seasonal cycle of observed oxygen, nitrate, and chlorophyll a concentrations, and the rates of microbial processes (e.g, NH4+ and NO2- oxidation, NO3- reduction, and anammox) as well. Based on our sensitivity analyses, biogeochemical parameter values associated with organic matter decomposition, vertical sinking, and nitrification play a key role for the low-oxygen water content, N loss, and N2O concentrations in the OMZ. Moreover, the explicit parameterization of both steps of nitrification, ammonium oxidation to nitrate with nitrite as an explicit intermediate, is necessary to improve the representation of microbial activity linked with the OMZ. The simulated minimum oxygen concentrations are driven by the poleward meridional advection of oxygen-depleted waters offshore of a 300 m isobath and by the biogeochemical activity inshore of this isobath, highlighting a spatial shift of dominant processes maintaining the minimum oxygen concentrations off Namibia. In the OMZ off Namibia, the magnitude of N2O outgassing and of N loss is comparable. Anammox contributes to about 20% of total N loss, an estimate lower than currently assumed (up to 50%) for the global ocean.

Gutknecht, E.; Dadou, I.; Le Vu, B.; Cambon, G.; Sudre, J.; Garçon, V.; Machu, E.; Rixen, T.; Kock, A.; Flohr, A.; Paulmier, A.; Lavik, G.

2013-06-01

21

Coupled physical/biogeochemical modeling including O2-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela  

NASA Astrophysics Data System (ADS)

The Eastern Boundary Upwelling Systems (EBUS) contribute to one fifth of the global catches in the ocean. Often associated with Oxygen Minimum Zones (OMZs), EBUS represent key regions for the oceanic nitrogen (N) cycle. Important bioavailable N loss due to denitrification and anammox processes as well as greenhouse gas emissions (e.g, N2O) occur also in these EBUS. However, their dynamics are currently crudely represented in global models. In the climate change context, improving our capability to properly represent these areas is crucial, due to anticipated changes in the winds, productivity, and oxygen content. We developed a biogeochemical model (BioEBUS) taking into account the main processes linked with EBUS and associated OMZs. We implemented this model in a 3-D realistic coupled physical/biogeochemical configuration in the Namibian upwelling system (Northern Benguela) using the high-resolution hydrodynamical model ROMS. We present here a validation using in situ and satellite data as well as diagnostic metrics, and sensitivity analyses of key parameters and N2O parameterizations. The impact of parameter values on the OMZ off Namibia, on N loss, and on N2O concentrations and emissions is detailed. The model realistically reproduces the vertical distribution and seasonal cycle of observed oxygen, nitrate and Chl a concentrations, and the rates of microbial processes (e.g. NH4+ and NO2- oxidation, NO3- reduction and anammox) as well. Based on our sensitivity analyses, biogeochemical parameter values associated with organic matter decomposition, vertical sinking and nitrification play a key role for the low-oxygen water content, N loss and N2O concentrations in the OMZ. Moreover, the importance of both steps of nitrification, ammonium oxidation to nitrate with nitrite as an explicit intermediate, is highlighted to improve the representation of microbial activity linked with OMZ. The simulated minimum oxygen concentrations are driven by the poleward meridional advection of oxygen-depleted waters offshore of 300 m isobath and by the biogeochemical activity inshore of this isobath, highlighting a spatial shift of dominant processes maintaining the minimum oxygen concentrations off Namibia. In the OMZ off Namibia, N2O emissions to the atmosphere are comparable with N loss. Anammox contributes to about 20% of total N loss, an estimate lower than currently assumed (up to 50%) for the global ocean.

Gutknecht, E.; Dadou, I.; Le Vu, B.; Cambon, G.; Sudre, J.; Garçon, V.; Machu, E.; Rixen, T.; Kock, A.; Flohr, A.; Paulmier, A.; Lavik, G.

2012-10-01

22

A Coupled Ocean General Circulation, Biogeochemical, and Radiative Model of the Global Oceans: Seasonal Distributions of Ocean Chlorophyll and Nutrients  

NASA Technical Reports Server (NTRS)

A coupled ocean general circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. Biogeochemical processes in the model are determined from the influences of circulation and turbulence dynamics, irradiance availability. and the interactions among three functional phytoplankton groups (diatoms. chlorophytes, and picoplankton) and three nutrients (nitrate, ammonium, and silicate). Basin scale (greater than 1000 km) model chlorophyll results are in overall agreement with CZCS pigments in many global regions. Seasonal variability observed in the CZCS is also represented in the model. Synoptic scale (100-1000 km) comparisons of imagery are generally in conformance although occasional departures are apparent. Model nitrate distributions agree with in situ data, including seasonal dynamics, except for the equatorial Atlantic. The overall agreement of the model with satellite and in situ data sources indicates that the model dynamics offer a reasonably realistic simulation of phytoplankton and nutrient dynamics on synoptic scales. This is especially true given that initial conditions are homogenous chlorophyll fields. The success of the model in producing a reasonable representation of chlorophyll and nutrient distributions and seasonal variability in the global oceans is attributed to the application of a generalized, processes-driven approach as opposed to regional parameterization and the existence of multiple phytoplankton groups with different physiological and physical properties. These factors enable the model to simultaneously represent many aspects of the great diversity of physical, biological, chemical, and radiative environments encountered in the global oceans.

Gregg, Watson W.; Busalacchi, Antonio (Technical Monitor)

2000-01-01

23

Modeling distinct vertical biogeochemical structure of the Black Sea: Dynamical coupling of the oxic, suboxic, and anoxic layers  

NASA Astrophysics Data System (ADS)

A one-dimensional, vertically resolved, physical-biogeochemical model is used to provide a unified representation of the dynamically coupled oxic-suboxic-anoxic system for the interior Black Sea. The model relates the annual cycle of plankton production in the form of a series of successive phytoplankton, mesozooplankton, and higher consumer blooms to organic matter generation and to the remineralization-ammonification-nitrification-denitrification chain of the nitrogen cycle as well as to anaerobic sulfide oxidation in the suboxic-anoxic interface zone. The simulations indicate that oxygen consumption during remineralization and nitrification, together with a lack of ventilation of subsurface waters due to the presence of strong stratification, are the two main factors limiting aerobic biogeochemical activity to the upper ˜75 m of the water column, which approximately corresponds to the level of nitrate maximum. The position of the upper boundary and thus the thickness of the suboxic layer are controlled by upper layer biological processes. The quasi-permanent character of this layer and the stability of the suboxic-anoxic interface within the last several decades are maintained by a constant rate of nitrate supply from the nitrate maximum zone. Nitrate is consumed to oxidize sinking particulate organic matter as well as hydrogen sulfide and ammonium transported upward from deeper levels.

Oguz, Temel; Ducklow, Hugh W.; Malanotte-Rizzoli, Paola

2000-12-01

24

Hierarchical framework for coupling a biogeochemical trace gas model to a general circulation model  

SciTech Connect

A scheme is described for the computation of terrestrial biogeochemical trace gas fluxes in the context of a general circulation model. This hierarchical system flux scheme (HSFS) incorporates five major components: (1) a general circulation model (GCM), which provides a medium-resolution (i.e., 1{degrees} by 1{degrees}) simulation of the atmospheric circulation; (2) a procedure for identifying regions of defined homogeneity of surface type within GCM grid cells; (3) a set of surface process models, to be run within each homogeneous region, which include a biophysical model, the Biosphere Atmospheric Transfer Scheme (BATS), and a biogeochemical model (BGCM); (4) an interpolation/integration system that transfers information between the GCM and surface process models with finer resolution; and (5) an interactive data array based on a geographic information system (GIS), which provides land characteristic information via the interpolator. The goals of this detailed investigation are to compute the local and global sensitivities of trace gas fluxes to GCM and BATS variables, the effects of trace gas fluxes on global climate, and the effects of global climate on specific biomes.

Miller, N.L.; Foster, I.T.

1994-04-01

25

A spatial and temporal continuous surface-subsurface hydrologic model  

NASA Astrophysics Data System (ADS)

A hydrologic model integrating surface-subsurface processes was developed based on spatial and temporal continuity theory. The raster-based mass balance hydrologic model consists of several submodels which determine spatial and temporal patterns in precipitation, surface flow, infiltration, subsurface flow, and the linkages between these submodels. Model parameters and variables are derived directly or indirectly from satellite remote sensing data, topographic maps, soil maps, literature, and weather station data and are stored in a Geographic Information System (GIS) database used for visualization. Surface resolution of cells in the model is 20 m by 20 m (pixel resolution of the Systeme Probatoire d'Observation de la Terre (SPOT) satellite image) over a 2511 km2 study area around the Crazy Mountains, Alaska, a watershed on the Arctic Circle draining into the Yukon River. The outputs from this model illustrate the interaction of physical and biologic factors on the partitioning of hydrologic components in a complex landscape.

Xiao, Qing-Fu; Ustin, Susan L.; Wallender, Wesley W.

1996-12-01

26

A Coupled Biogeochemical Reactive Transport Model in Bed Sediments and Water Column of Riverine Systems  

NASA Astrophysics Data System (ADS)

ABSTRACT: A multi-scale, quasi-two-dimensional, biogeochemical reactive theoretical and numerical model is presented, able to simulating sediment associated transport and transformations of contaminants in the water column and bed sediments of riverine systems as a result of sediment associated transport, as well as resuspension, deposition and burial. The model considers contaminant mass exchange between sediments and aqueous phase both in benthic sediments and water column as a kinetically controlled process. It also takes into account the effect of microbially-mediated redox reactions affecting the speciation of chemicals. Transport of species in the sediments is modeled using a set of vertical one-dimensional sub-models which take into account the reactive transport of chemicals, burial, sorption/desorption to/from the solid phase, and diffusive transport of aqueous species. An innovative multi-time step approach is used to model the fully kinetic nonlinear reaction terms using a non-iterative explicit method. This approach enables the model to handle fast and near- equilibrium reactions without a significant increase in computational burden. Ongoing and planned applications of this multiscale modeling strategy to two cases, multiple metal transport in Lake Coeur d'Alene, Idaho, and Mercury Cycling in Walker Creek, California, are discussed.

Massoudieh, A.; Bombardelli, F. A.; Sengor, S. S.; Ginn, T. R.

2007-12-01

27

Seasonal Distributions of Global Ocean Chlorophyll and Nutrients: Analysis with a Coupled Ocean General Circulation Biogeochemical, and Radiative Model  

NASA Technical Reports Server (NTRS)

A coupled general ocean circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. The model is driven by climatological meteorological conditions, cloud cover, and sea surface temperature. Biogeochemical processes in the model are determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among three functional phytoplankton groups (diatoms, chorophytes, and picoplankton) and three nutrient groups (nitrate, ammonium, and silicate). Phytoplankton groups are initialized as homogeneous fields horizontally and vertically, and allowed to distribute themselves according to the prevailing conditions. Basin-scale model chlorophyll results are in very good agreement with CZCS pigments in virtually every global region. Seasonal variability observed in the CZCS is also well represented in the model. Synoptic scale (100-1000 km) comparisons of imagery are also in good conformance, although occasional departures are apparent. Agreement of nitrate distributions with in situ data is even better, including seasonal dynamics, except for the equatorial Atlantic. The good agreement of the model with satellite and in situ data sources indicates that the model dynamics realistically simulate phytoplankton and nutrient dynamics on synoptic scales. This is especially true given that initial conditions are homogenous chlorophyll fields. The success of the model in producing a reasonable representation of chlorophyll and nutrient distributions and seasonal variability in the global oceans is attributed to the application of a generalized, processes-driven approach as opposed to regional parameterization, and the existence of multiple phytoplankton groups with different physiological and physical properties. These factors enable the model to simultaneously represent the great diversity of physical, biological, chemical, and radiative environments encountered in the global oceans.

Gregg, Watson W.

1999-01-01

28

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

29

Control of mass balance error in a detailed model of surface-subsurface flow interaction  

NASA Astrophysics Data System (ADS)

Several process-based catchment-scale hydrologic models have been developed in recent years to describe the interactions and feedbacks between different components of the water cycle, but few studies have considered the sources of coupling error in these models. In this work we analyze the sequential iterative coupling scheme of the distributed model CATHY (CATchment HYdrology) in order to identify the different sources of mass balance error and to examine how these are influenced by topography, hydraulic properties, and atmospheric forcing. A pair of adimensional indices that quantify the degree of coupling and of flux partitioning is presented. Our analysis shows that mass balance errors increase during the flood recession limb because of the exchange of information between surface and subsurface water flow. Surface water propagation is cell centered, while the subsurface flow equation is solved on the vertices of surface cells. Evaluation of surface pressure heads and exchange fluxes is critical on this staggered surface-subsurface mesh, especially during transitions from unsaturated to saturated conditions and vice versa. A modified version of the flux exchange algorithm is introduced that considers the effective availability of water on surface cells. The performance of the model is also improved by introducing a heuristic procedure to control and adapt the time step interval. Starting from numerical stability and convergence constraints, this procedure varies the computational interval as a function of the rate of change of surface saturation via the coupling degree index. A final improvement made to the sequential coupling scheme in CATHY is to solve the surface routing equation after rather than before the subsurface module. We find that the modified version improves the water balance by more than 50% in most of the tests considered for a simple v-shaped catchment. The results so far obtained for the synthetic v-catchment indicate the need for a more comprehensive analysis including real catchments.

Fiorentini, Marcello; Orlandini, Stefano; Paniconi, Claudio; Putti, Mario

2014-05-01

30

Global Biogeochemical Cycle of Si: Its Coupling to the Perturbed C-N-P cycles in Industrial Time  

NASA Astrophysics Data System (ADS)

The importance of silicon (Si) in global biogeochemical cycles is demonstrated by its abundance in the land and aquatic biomass, where Si/C is 0.02 in land plants and 0.15 in marine organisms. Estimates show that Si-bioproduction accounts for ~1.5% of terrestrial primary production, and ~4.5% in the coastal ocean. Human land-use activities have substantially changed regional patterns of vegetation distribution, soil conditions, and nutrient fluxes via runoff to the coastal ocean. Anthropogenic chemical fertilization of the land has caused a significant increase in fluvial nitrogen (N) and phosphorus (P) transport, whereas land-use and vegetation mass changes have caused variations in the riverine Si input, all eventually affecting the cycling of nutrients in the marine environment. We developed a global biogeochemical model of the Si cycle as coupled to the global C-N-P cycle model, TOTEM II (Terrestrial-Ocean-aTmosphere-Ecosystem-Model). In the model analysis from year 1700, taken as the start of the Anthropocene, to 2050, the bioproduction of Si on land and in the ocean is coupled to the bioproduction of C, perturbed by the atmospheric CO2 rise, land-use changes, and chemical fertilization. Also, temperature rise affects the Si cycling on land through bioproduction rates, terrestrial organic matter remineralization, and weathering, thereby affecting its delivery to the coastal zone. The results show that biouptake and subsequent release of Si on land strongly affect the Si river flux to the coastal ocean. During the 350-year period, Si river discharge has increased by ~10% until ~1940, decreasing since then to below its 1700 value and continuing to drop, under the current IPCC IS92 projections of CO2, temperature and other forcings. From 1700 to ~1950, land-use changes, associated with slash and burn of large areas of high-productivity land, caused a decrease of global land vegetation. Dissolution of Si in soil humus and weathering of silicate minerals are the main dissolved Si sources for rivers and groundwater. The decrease in Si uptake by land biomass made more Si available for river discharge, causing an increase in the Si river input until an increase in the land primary production reversed the process. Around 1950, the use of fertilizer on land, especially N and P, increased, driving the growth of coastal marine primary producers, including such Si organisms as diatoms, silicoflagellates, and sponge spicules, and thus causing a decrease of dissolved Si in the surface ocean. The percent decrease of coastal dissolved Si due to increased primary production is greater than that of surface open ocean due to the shorter residence time of Si in coastal water (~2.7 years) compared to that of surface open ocean (~10 years. The combination of the relatively small size and location of the coastal ocean at the junction of the land, atmosphere, and open ocean make it important to changes in water chemistry, in situ biological production, and sedimentary storage. Its buffer effect and fast response to perturbations are also shown in the results of this coupling study of the C-N-P-Si cycles.

Lerman, A.; Li, D. D.; MacKenzie, F. T.

2010-12-01

31

A parallel computational framework for integrated surface-subsurface flow and transport simulations  

NASA Astrophysics Data System (ADS)

HydroGeoSphere is a 3D control-volume finite element hydrologic model describing fully-integrated surface and subsurface water flow and solute and thermal energy transport. Because the model solves tighly-coupled highly-nonlinear partial differential equations, often applied at regional and continental scales (for example, to analyze the impact of climate change on water resources), high performance computing (HPC) is essential. The target parallelization includes the composition of the Jacobian matrix for the iterative linearization method and the sparse-matrix solver, a preconditioned Bi-CGSTAB. The matrix assembly is parallelized by using a coarse-grained scheme in that the local matrix compositions can be performed independently. The preconditioned Bi-CGSTAB algorithm performs a number of LU substitutions, matrix-vector multiplications, and inner products, where the parallelization of the LU substitution is not trivial. The parallelization of the solver is achieved by partitioning the domain into equal-size subdomains, with an efficient reordering scheme. The computational flow of the Bi-CGSTAB solver is also modified to reduce the parallelization overhead and to be suitable for parallel architectures. The parallelized model is tested on several benchmark simulations which include linear and nonlinear flow problems involving various domain sizes and degrees of hydrologic complexities. The performance is evaluated in terms of computational robustness and efficiency, using standard scaling performance measures. The results of simulation profiling indicate that the efficiency becomes higher with an increasing number of nodes/elements in the mesh, for increasingly nonlinear transient simulations, and with domains of irregular geometry. These characteristics are promising for the large-scale analysis water resources problems involved integrated surface/subsurface flow regimes.

Park, Y.; Hwang, H.; Sudicky, E. A.

2010-12-01

32

Significant Findings: Seasonal Distributions of Global Ocean Chlorophyll and Nutrients With a Coupled Ocean General Circulation, Biogeochemical, and Radiative Model. 2; Comparisons With Satellite and In Situ Data  

NASA Technical Reports Server (NTRS)

A coupled ocean general circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. Biogeochemical processes in the model were determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among three functional phytoplankton groups (diatoms, chlorophytes, and picoplankton) and three nutrients (nitrate, ammonium, and silicate). Basin scale (>1000 km) model chlorophyll seasonal distributions were statistically positively correlated with CZCS chlorophyll in 10 of 12 major oceanographic regions, and with SeaWiFS in all 12. Notable disparities in magnitudes occurred, however, in the tropical Pacific, the spring/summer bloom in the Antarctic, autumn in the northern high latitudes, and during the southwest monsoon in the North Indian Ocean. Synoptic scale (100-1000 km) comparisons of satellite and in situ data exhibited broad agreement, although occasional departures were apparent. Model nitrate distributions agreed with in situ data, including seasonal dynamics, except for the equatorial Atlantic. The overall agreement of the model with satellite and in situ data sources indicated that the model dynamics offer a reasonably realistic simulation of phytoplankton and nutrient dynamics on basin and synoptic scales.

Gregg, Watson W.; Busalacchi, Antonio (Technical Monitor)

2000-01-01

33

Coupling the multi-layer land surface model ACASA with a biogeochemical model TEM to better represent carbon and nitrogen dynamics  

NASA Astrophysics Data System (ADS)

The newest generation of General Circulation Models has been pushed to better represent the main biogeochemical cycles controlling the global environment. Similarly, Regional Climate Models (RCMs) have also been modified to include biogeochemical cycles such as carbon-nitrogen dynamics, since they highly dependent on the land surface composition. UC Davis is developing a more advanced land surface model coupled to a soil biogeochemistry module, which may be coupled to any RCM in order to better represent complex land-atmospheric feedbacks. This model is being developed based on the UC Davis Advanced Canopy-Atmosphere-Soil Model (ACASA), which was recently fully coupled to the Weather Research and Forecasting (WRF) Model. ACASA is one of the most advanced ecosystem atmosphere models, using higher-order turbulence closure methods in a 10-layer plant canopy representation, linked to state-of-the-art plant physiological algorithms, soil transport algorithms, radiation transfer equations, and snow hydrology sub-models. The biogeochemistry module is based on the Terrestrial Ecosystem Model (TEM), a process-based ecosystem model that uses spatially referenced information on climate, elevation, soils, vegetation and water availability to make estimates of vegetation and soil carbon and nitrogen fluxes and pool sizes. This new framework will provide a credible tool to better understand terrestrial ecosystem feedback within the climate system, such as nitrogen limitation effects on carbon uptake including net ecosystem exchange (NEE), latent heat fluxes, among other variable outputs. Here, we assess the capabilities of this new approach and present preliminary results of the ACASA-TEM model development. We compare model output with observations from selected AmeriFlux sites and from some TEM data sets. We found that nitrogen limitations might reduce NEE up to a 30% depending on the assumptions considered in the model. Issues regarding the disparate temporal scales embodied in the models are also discussed.

Bambach-Ortiz, N. E.; Paw U, K.; Felzer, B. S.

2013-12-01

34

Biogeochemical Coupling of Fe and Tc Speciation in Subsurface Sediments: Implications to Long-Term Tc Immobilization  

SciTech Connect

The project has been focused on biochemical processes in subsurface sediments involving Fe that control the valence state, solubility, and effective mobility of 99Tc. Our goal has been to understand the Tc biogeochemistry as it may occur in suboxic and biostimulated subsurface environments. Two objectives have been pursued: (1) To determine the relative reaction rates of 99Tc(VII)O2(aq) with metal reducing bacteria and biogenic Fe(II); and to characterize the identity, structure, and molecular speciation of Tc(IV) products formed through reaction with both biotic and abiotic reductants. (2) To quantify the biogeochemical factors controlling the reaction rate of O2 with Tc(IV)O2?nH2O in sediment resulting from the direct enzymatic reduction of Tc(VII) by DIRB and/or the reaction of Tc(VII) with the various types of biogenic Fe(II) produced by DIRB.

Jim K. Fredrickson; C. I. Steefel; R. K. Kukkadapu; S. M. Heald

2006-06-01

35

Fully integrated modeling of surface-subsurface solute transport and the effect of dispersion in tracer hydrograph separation  

NASA Astrophysics Data System (ADS)

hydrograph separation has been widely applied to identify streamflow components, often indicating that pre-event water comprises a large proportion of stream water. Previous work using numerical modeling suggests that hydrodynamic mixing in the subsurface inflates the pre-event water contribution to streamflow when derived from tracer-based hydrograph separation. This study compares the effects of hydrodynamic dispersion, both within the subsurface and at the surface-subsurface boundary, on the tracer-based pre-event water contribution to streamflow. Using a fully integrated surface-subsurface code, we simulate two hypothetical 2-D hillslopes with surface-subsurface solute exchange represented by different solute transport conceptualizations (i.e., advective and dispersive conditions). Results show that when surface-subsurface solute transport occurs via advection only, the pre-event water contribution from the tracer-based separation agrees well with the hydraulically determined value of pre-event water from the numerical model, despite dispersion occurring within the subsurface. In this case, subsurface dispersion parameters have little impact on the tracer-based separation results. However, the pre-event water contribution from the tracer-based separation is larger when dispersion at the surface-subsurface boundary is considered. This work demonstrates that dispersion within the subsurface may not always be a significant factor in apparently large pre-event water fluxes over a single rainfall event. Instead, dispersion at the surface-subsurface boundary may increase estimates of pre-event water contribution. This work also shows that solute transport in numerical models is highly sensitive to the representation of the surface-subsurface interface. Hence, models of catchment-scale solute dynamics require careful treatment and sensitivity testing of the surface-subsurface interface to avoid misinterpretation of real-world physical processes.

Liggett, Jessica E.; Werner, Adrian D.; Smerdon, Brian D.; Partington, Daniel; Simmons, Craig T.

2014-10-01

36

Significant Findings: Tracking the SeaWiFS Record with a Coupled Physical/Biogeochemical/Radiative Model of the Global Oceans  

NASA Technical Reports Server (NTRS)

The Sea-Viewing Wide Field-of-view Sensor (SeaWiFS) has observed 2.5 years of routine global chlorophyll observations from space. The mission was launched into a record El Nino event, which eventually gave way to one of the most intensive and longest-lasting La Nina events ever recorded. The SeaWiFS chlorophyll record captured the response of ocean phytoplankton to these significant events in the tropical Indo-Pacific basins, but also indicated significant interannual variability unrelated to the El Nino/La Nina events. This included large variability in the North Atlantic and Pacific basins, in the North Central and equatorial Atlantic, and milder patterns in the North Central Pacific. This SeaWiFS record was tracked with a coupled physical/biogeochemical/radiative model of the global oceans using near-real-time forcing data such as wind stresses, sea surface temperatures, and sea ice. This provided an opportunity to offer physically and biogeochemically meaningful explanations of the variability observed in the SeaWiFS data set, since the causal mechanisms and interrelationships of the model are completely understood. The coupled model was able to represent the seasonal distributions of chlorophyll during the SeaWiFS era, and was capable of differentiating among the widely different processes and dynamics occurring in the global oceans. The model was also reasonably successful in representing the interannual signal, especially when it was large, such as, the El Nino and La Nina events in the tropical Pacific and Indian Oceans. The model provided different phytoplankton group responses for the different events in these regions: diatoms were predominant in the tropical Pacific during the La Nina but other groups were predominant during El Nino. The opposite condition occurred in the tropical Indian Ocean. Both situations were due to the different responses of the basins to El Nino. The interannual variability in the North Atlantic, which was exhibited in SeaWiFS data as a decline in the spring/summer bloom in 1999 relative to 1998, resulted in the model from a more slowly shoaling mixed layer, allowing herbivore populations to keep pace with increasing phytoplankton populations. However, several aspects of the interannual cycle were not well-represented by the model. Explanations ranged from inherent model deficiencies, to monthly averaging of forcing fields, to biases in SeaWiFS atmospheric correction procedures.

Watson, Gregg W.

2000-01-01

37

Quantifying methane emissions from rice fields in Tai-Lake region, China by coupling detailed soil database with biogeochemical model  

NASA Astrophysics Data System (ADS)

China's paddy rice accounts for about 22% of the world's rice fields, therefore it is crucial to accurately estimate the CH4 emissions at regional scale to gauge their contribution to global greenhouse gas effect. This paper reports an application of a biogeochemical model, DeNitrification and DeComposition or DNDC, for quantifying CH4 emissions from rice fields in Tai-Lake region of China by linking DNDC to a 1:50 000 soil database, which was derived from 1107 paddy soil profiles in the Second National Soil Survey of China in the 1980s-1990s. The modeled results estimate that the 2.34 M ha of paddy rice fields in Tai-Lake region emitted about CH4 of 5.67 Tg C for the period of 1982-2000, with the average CH4 flux ranged from 114 to 138 kg C ha-1y-1. The highest emission rate (659.24 kg C ha-1 y-1) occurred in the subgroup of "gleyed paddy soils", while the lowest (90.72 kg C ha-1y-1) were associated with the subgroup "degleyed paddy soils". The subgroup "hydromorphic paddy soils" accounted for about 52.82% of the total area of paddy soils, the largest of areas of all the soil subgroups, with the CH4 flux rate of 106.47 kg C ha-1y-1. On a sub-regional basis, the annual average CH4 flux in the Tai-Lake plain soil region and alluvial plain soil region was higher than that in low mountainous and hilly soil region and polder soil region. The model simulation was conducted with two databases using polygon or county as the basic unit. The county-based database contained soil information coarser than the polygon system built based on the 1:50 000 soil database. The modeled results with the two databases found similar spatial patterns CH4 emissions in Tai-Lake region. However, discrepancies exist between the results from the two methods, the relative deviation is -42.10% for the entire region, and the relative deviation ranged from -19.53% to 97.30% for most counties, which indicates that the more precise soil database was necessary to better simulate CH4 emissions from rice fields in Tai-Lake region using the DNDC model.

Zhang, L.; Yu, D.; Shi, X.; Zhao, L.; Ding, W.; Wang, H.; Pan, J.; Li, C.

2008-12-01

38

Simulation of radar echoes from Mars' surface/subsurface and inversion of surface media parameters  

NASA Astrophysics Data System (ADS)

two-layer model of Mars' regolith/bedrock media with a cratered rough surface/subsurface is presented for radar echo simulation of planetary exploration research. The numerical approach of geometric ray tracing for the scattering of rough surfaces, which is digitized by the triangulated network, is applied to the calculation of the scattering and imaging simulation of radar range echoes. Numerical simulations of a cratered rough surface generated by the Monte Carlo method are used to analyze the functional dependence of radar range echoes at 1-50 MHz center frequencies upon the surface/subsurface feature and the parameters of the layering media, that is, layer depth and dielectric properties. The radar range echoes from two areas of the real Mars surface, which is described by digital elevation model data with a resolution of 1 m × 1 m and a vertical error of less than 1 m, are also simulated and analyzed. Based on these simulations, this study presents a numerical imaging test of radar sounder at center frequencies 1-50 MHz for exploration of different dielectric regolith and bedrock media. The channel 50 MHz with high resolution might be an optimal frequency. Finally, inversion of the dielectric constants of the two-layer media and the regolith layer thickness are developed.

Liu, Chuan; Ye, Hongxia; Jin, Ya-Qiu

2014-07-01

39

Quantifying the effects of nutrient loading on dissolved O2 cycling and hypoxia in Chesapeake Bay using a coupled hydrodynamic-biogeochemical model  

NASA Astrophysics Data System (ADS)

The Regional Ocean Modeling System (ROMS) was coupled to a biogeochemical model (RCA) to understand the controls on dissolved oxygen (O2) depletion in Chesapeake Bay. The model was calibrated to observational data in the year 2000 and subsequent simulations were performed for a 10-year period, where water-column state variables were validated against observations using multiple error metrics and model-simulated rate processes were compared to available measurements. ROMS-RCA captured observed seasonal and regional dynamics of water-column chlorophyll-a, dissolved O2, and nutrient concentrations, as well as sediment-water nutrient and oxygen fluxes and community respiration rates, but for the year 2000, the model over-predicted surface-water chlorophyll-a and bottom-water O2 in some regions. A series of model experiments were made using the physical regime for the year 2000 to understand ecosystem responses to altered loads of nitrogen and phosphorus and to quantify the spatial and temporal response of Chesapeake Bay to altered nutrient loading. Nutrient loading experiments revealed a non-linear response of hypoxia to nitrogen load, where hypoxic-volume-days maximized at nitrogen loads twice of that observed in the year 2000. O2 levels were more sensitive to nitrogen loads than phosphorus loads, consistent with the preponderance of nitrogen limitation in Chesapeake Bay in late spring and summer months. Expanded hypoxic volumes under higher nitrogen loads were associated with increases in water-column production and respiration in seaward regions of Chesapeake Bay during summer (June to August) months. Analysis of the 10-year model run with realistic hydrodynamics and nutrient loading revealed a similar pattern, emphasizing phytoplankton growth during summer in more nitrogen-limited, lower-Bay regions as a mechanism supporting elevated summer hypoxic volumes. This analysis (1) presents ROMS-RCA as a tool for investigating linked biogeochemical processes in coastal ecosystems, (2) identifies phytoplankton growth in seaward Bay regions as a key link between nitrogen loading and hypoxic volume, and (3) suggests that given similar climatic conditions, nutrient load reductions will lead to reduced hypoxic volumes.

Testa, Jeremy M.; Li, Yun; Lee, Younjoo J.; Li, Ming; Brady, Damian C.; Di Toro, Dominic M.; Kemp, W. Michael; Fitzpatrick, James J.

2014-11-01

40

One-Dimensional Coupled Ecosystem-Carbon Flux Model for the Simulation of Biogeochemical Parameters at Ocean Weather Station P  

NASA Technical Reports Server (NTRS)

In this Technical Publication, we describe the model functionality and analyze its application to the seasonal and interannual variations of phytoplankton, nutrients, pCO2 and CO2 concentrations in the eastern subarctic Pacific at Ocean Weather Station P (OWSP, 50 deg. N 145 deg. W). We use a verified one-dimensional ecosystem model, coupled with newly incorporated carbon flux and carbon chemistry components, to simulate 22 years (1958-1980) of pCO2 and CO2 variability at Ocean Weather Station P (OWS P). This relatively long period of simulation verifies and extends the findings of previous studies using an explicit approach for the biological component and realistic coupling with the carbon flux dynamics. The slow currents and the horizontally homogeneous ocean in the subarctic Pacific make OWS P one of the best available candidates for modeling the chemistry of the upper ocean in one dimension. The chlorophyll and ocean currents composite for 1998 illustrates this premise. The chlorophyll concentration map was derived from SeaWiFS data and the currents are from an OGCM simulation (from R. Murtugudde).

Signorini, S.; McClain, C.; Christian, J.; Wong, C. S.

2000-01-01

41

Coupled effects of biogeochemical and hydrological processes on C, N, and P export during extreme rainfall events in a purple soil watershed in southwestern China  

NASA Astrophysics Data System (ADS)

As global warming and extreme weather events increase and intensify across the globe, it becomes ever more urgent to study and understand the effects of extreme rainfall events on carbon (C), nitrogen (N), and phosphorus (P) export from terrestrial to riverine ecosystems. There is still much to learn regarding C, N, and P non-point source discharge that results from extremely heavy rainfall as well as their effects on downstream ecosystems. This study aimed to shed light on C, N, and P biogeochemical and hydrological coupling processes. Long-term and short-term water composition monitoring research was carried out within a purple soil watershed in China's Sichuan Province. This study captured both base flow from long-term observations and dynamic runoff under extreme rainfall events that took place during the 2012 rainy season. Dissolved total nitrogen (DTN) was the largest percentage of total nitrogen (TN) in storm runoff. DTN exceeded particulate nitrogen (PN), which itself exceeded dissolved organic nitrogen (DON). Under site conditions, particulate phosphorus (PP) formed the largest constituent of total phosphorus (TP) followed by dissolved total phosphorus (DTP) and dissolved organic phosphorus (DOP). Furthermore, results showed that C, N, and P loads increased sharply in response to heavy rainfall. Although P abundance in purple soils is limited, it was nevertheless shown that C:N:P ratios measured during rainstorms corresponded much more closely to the Redfield ratio than to ratios measured in base flows. This adds to the evidence that suggests that increased storm runoff will increase eutrophication likelihood in ecosystems further downstream.

Gao, Yang; Zhu, Bo; Yu, Guirui; Chen, Weiliang; He, Nianpeng; Wang, Tao; Miao, Chiyuan

2014-04-01

42

Global Biogeochemical Cycles and the Physical Climate System  

NSDL National Science Digital Library

This module focuses on the biogeochemical cycles of five of the major elements important to life - carbon, nitrogen, phosphorus, sulfur, and oxygen - and their role in climatic change. The chapters include: Biogeochemical Processes, Biogeochemical Cycles and Climate, The Modern Coupled C-N-P-S-O System, Carbon Cycles, The Important Nutrient Nitrogen, Phosphorus and Sulfur, and The Water Cycle. Study questions and answers are also available.

Mackenzie, Fred

1999-01-01

43

The application of a coupled hydrological and biogeochemical model (CHANGE) for modeling of energy, water, and CO2 exchanges over a larch forest in eastern Siberia  

NASA Astrophysics Data System (ADS)

A coupled hydrological and biogeochemical model (CHANGE) that evaluates heat, water, and CO2 exchange between the biosphere and atmosphere across a spectrum of various time and space scales is described in this paper. The CHANGE model, which merges important components and functions in Arctic terrestrial ecosystems, is a process model with a self-constrained nature that is based on a complex and nonlinear interplay among hydrological, physiological, biochemical, ecological, and edaphic factors and meteorological conditions. This model was applied to a larch forest in eastern Siberia for the period of 1998-2006. A key objective was to assess the seasonal and interannual variability of the surface water, energy, and carbon fluxes over the larch forest in order to understand the responses of this ecosystem to climate change and to provide their controlling factors. Two types of simulations were performed with half-hourly and daily forcing data, and temporal correlation and other statistical measures supported the agreement between the simulations and observations. The simulated annual evapotranspiration (ET) ranged from 125 to 196 mm with a mean of 164 mm, 67% of which was contributed by transpiration. The simulated annual mean net ecosystem exchange (NEE) was -138.6 g C m-2 y-1 with a range of -79 to -195 g C m-2 y-1. The NEE variation was closely correlated with the net primary production (NPP). The simulation showed 23-43% interannual variability in heterotrophic respiration (Rh) for a mean of 273.1 g C m-2 y-1. Soil water was found to be a determinant that influences ET and CO2 fluxes in the larch forest. NEE was largely correlated to precipitation (PG). Thicker snow depth in the previous winter season contributed to higher NEE. The contribution of snow depth to NEE was significant in the dry years. The combination of summer PG and snow water resulted in higher NEE, which was found since 2004. In dry years, the access of roots to soil-thawed water alleviated soil water deficit and contributed to ecosystem net C uptake. The model sensitivity addressed the potential importance of the dynamic soil organic carbon on soil temperature.

Park, Hotaek; Iijima, Yoshihiro; Yabuki, Hironori; Ohta, Takeshi; Walsh, John; Kodama, Yuji; Ohata, Tetsuo

2011-08-01

44

Improving surface-subsurface water budgeting using high resolution satellite imagery applied on a brownfield.  

PubMed

The estimation of surface-subsurface water interactions is complex and highly variable in space and time. It is even more complex when it has to be estimated in urban areas, because of the complex patterns of the land-cover in these areas. In this research a modeling approach with integrated remote sensing analysis has been developed for estimating water fluxes in urban environments. The methodology was developed with the aim to simulate fluxes of contaminants from polluted sites. Groundwater pollution in urban environments is linked to patterns of land use and hence it is essential to characterize the land cover in a detail. An object-oriented classification approach applied on high-resolution satellite data has been adopted. To assign the image objects to one of the land-cover classes a multiple layer perceptron approach was adopted (Kappa of 0.86). Groundwater recharge has been simulated using the spatially distributed WetSpass model and the subsurface water flow using MODFLOW in order to identify and budget water fluxes. The developed methodology is applied to a brownfield case site in Vilvoorde, Brussels (Belgium). The obtained land use map has a strong impact on the groundwater recharge, resulting in a high spatial variability. Simulated groundwater fluxes from brownfield to the receiving River Zenne were independently verified by measurements and simulation of groundwater-surface water interaction based on thermal gradients in the river bed. It is concluded that in order to better quantify total fluxes of contaminants from brownfields in the groundwater, remote sensing imagery can be operationally integrated in a modeling procedure. PMID:21112074

Dujardin, J; Batelaan, O; Canters, F; Boel, S; Anibas, C; Bronders, J

2011-01-15

45

Physical mechanisms of anomalous transport in rivers: Implications of surface-porewater flow coupling for downstream solute transport and stream biogeochemistry  

NASA Astrophysics Data System (ADS)

Connectivity between rivers and pore waters greatly influences both hydrological and biogeochemical processes. Conventionally, surface and subsurface transport have been considered separately, and the effects of porewater flow have often been parameterized as added terms in the advection-dispersion equation for downstream transport. However, this approach does not sufficiently represent the full range of important transport dynamics. We believe that general solutions can be obtained by assessing transport holistically over the entire surface-subsurface flow continuum. We used a two-dimensional particle tracking scheme to evaluate the effect of flow coupling across the sediment-water interface on downstream solute transport. These simulations indicate that classic advection-dispersion behavior occurs only in impermeable stream channels, where turbulent mixing is sufficient to homogenize transport over the in-stream velocity profile, thereby meeting the assumptions of classic Taylor dispersion theory. Even in this case, incomplete vertical mixing causes preasymptotic exponential tails that eventually decay to the canonical Gaussian solution. In streams underlain by alluvium, transport becomes anomalous owing to the wide velocity distribution spanning the surface-subsurface flow continuum. In this case, in-stream and subsurface mixing cannot be parameterized independently, as parameters commonly used to describe in-stream mixing (such as the dispersion coefficient) depend on interactions with porewater. These findings are especially important to interpretation of tracer injections used to infer biogeochemical processes, which often occur predominantly at stream channel boundaries or in the subsurface. In this talk, we will review the classic theory for solute transport in rivers, show spatially explicit particle-tracking simulations of solute transport, relate the resulting ensemble solute dynamics to macro-scale continuum transport equations, and discuss the implications for estimates of benthic and hyporheic biogeochemical process rates.

Aubeneau, A. F.; Paster, A.; Bolster, D.; Schumer, R.; Packman, A. I.

2012-12-01

46

Simulating temporal variations of nitrogen losses in river networks with a dynamic transport model unravels the coupled effects of hydrological and biogeochemical processes  

SciTech Connect

The importance of lotic systems as sinks for nitrogen inputs is well recognized. A fraction of nitrogen in streamflow is removed to the atmosphere via denitrification with the remainder exported in streamflow as nitrogen loads. At the watershed scale, there is a keen interest in understanding the factors that control the fate of nitrogen throughout the stream channel network, with particular attention to the processes that deliver large nitrogen loads to sensitive coastal ecosystems. We use a dynamic stream transport model to assess biogeochemical (nitrate loadings, concentration, temperature) and hydrological (discharge, depth, velocity) effects on reach-scale denitrification and nitrate removal in the river networks of two watersheds having widely differing levels of nitrate enrichment but nearly identical discharges. Stream denitrification is estimated by regression as a nonlinear function of nitrate concentration, streamflow, and temperature, using more than 300 published measurements from a variety of US streams. These relations are used in the stream transport model to characterize nitrate dynamics related to denitrification at a monthly time scale in the stream reaches of the two watersheds. Results indicate that the nitrate removal efficiency of streams, as measured by the percentage of the stream nitrate flux removed via denitrification per unit length of channel, is appreciably reduced during months with high discharge and nitrate flux and increases during months of low-discharge and flux. Biogeochemical factors, including land use, nitrate inputs, and stream concentrations, are a major control on reach-scale denitrification, evidenced by the disproportionately lower nitrate removal efficiency in streams of the highly nitrate-enriched watershed as compared with that in similarly sized streams in the less nitrate-enriched watershed. Sensitivity analyses reveal that these important biogeochemical factors and physical hydrological factors contribute nearly equally to seasonal and stream-size related variations in the percentage of the stream nitrate flux removed in each watershed.

Mulholland, Patrick J [ORNL; Alexander, Richard [U.S. Geological Survey; Bohlke, John [U.S. Geological Survey; Boyer, Elizabeth [Pennsylvania State University; Harvey, Judson [U.S. Geological Survey; Seitzinger, Sybil [Rutgers University; Tobias, Craig [University of North Carolina, Wilmington; Tonitto, Christina [Cornell University; Wollheim, Wilfred [University of New Hampshire

2009-01-01

47

A dynamic marine iron cycle module coupled to the University of Victoria Earth System Model: the Kiel Marine Biogeochemical Model 2 (KMBM2) for UVic 2.9  

NASA Astrophysics Data System (ADS)

Marine biological production and the associated biotic uptake of carbon in many ocean regions depend on the availability of nutrients in the euphotic zone. While large areas are limited by nitrogen and/or phosphorus, the micronutrient iron is considered the main limiting nutrient in the North Pacific, equatorial Pacific and Southern Ocean. Changes in iron availability via changes in atmospheric dust input are discussed to play an important role in glacial/interglacial cycles via climate feedbacks caused by changes in biological ocean carbon sequestration. Although many aspects of the iron cycle remain unknown, its incorporation into marine biogeochemical models is needed to test our current understanding and better constrain its role in the Earth system. In the University of Victoria Earth System Climate Model (UVic) iron limitation in the ocean was, until now, simulated pragmatically with an iron concentration masking scheme that did not allow a consistent interactive response to perturbations of ocean biogeochemistry or iron cycling sensitivity studies. Here, we replace the iron masking scheme with a dynamic iron cycle and compare the results to available observations and the previous marine biogeochemical model. Sensitivity studies are also conducted with the new model to test the importance of considering the variable solubility of iron in dust deposition, the importance of considering high resolution bathymetry for the sediment release of iron, the effect of scaling the sedimentary iron release with temperature and the sensitivity of the iron cycle to a climate change scenario.

Nickelsen, L.; Keller, D. P.; Oschlies, A.

2014-12-01

48

Biogeochemical control of the coupled CO2-O 2 system of the Baltic Sea: a review of the results of Baltic-C.  

PubMed

Past, present, and possible future changes in the Baltic Sea acid-base and oxygen balances were studied using different numerical experiments and a catchment-sea model system in several scenarios including business as usual, medium scenario, and the Baltic Sea Action Plan. New CO2 partial pressure data provided guidance for improving the marine biogeochemical model. Continuous CO2 and nutrient measurements with high temporal resolution helped disentangle the biogeochemical processes. These data and modeling indicate that traditional understandings of the nutrient availability-organic matter production relationship do not necessarily apply to the Baltic Sea. Modeling indicates that increased nutrient loads will not inhibit future Baltic Sea acidification; instead, increased mineralization and biological production will amplify the seasonal surface pH cycle. The direction and magnitude of future pH changes are mainly controlled by atmospheric CO2 concentration. Apart from decreasing pH, we project a decreasing calcium carbonate saturation state and increasing hypoxic area. PMID:24414804

Omstedt, Anders; Humborg, Christoph; Pempkowiak, Janusz; Perttilä, Matti; Rutgersson, Anna; Schneider, Bernd; Smith, Benjamin

2014-02-01

49

Soil Biogeochemical Cycles  

NSDL National Science Digital Library

This group activity charges students with teaching their colleagues about the biogeochemical cycle of one key soil element (e.g., either C, N, S, P, Ca, or Fe). Students are given a single class period to summarize their knowledge and to develop a lesson that includes (1) an organized, 5-8 minute oral presentation, (2) a graphical, conceptual model of their assigned element's soil-biogeochemical cycle, and (3) a list of discussion questions with which to engage their colleagues on the other teams. A second class session is used to refine and to expand upon the submitted models as necessary.

Colin Robins

50

Biogeochemical Processes in Microbial Ecosystems  

NASA Technical Reports Server (NTRS)

The hierarchical organization of microbial ecosystems determines process rates that shape Earth's environment, create the biomarker sedimentary and atmospheric signatures of life and define the stage upon which major evolutionary events occurred. In order to understand how microorganisms have shaped the global environment of Earth and potentially, other worlds, we must develop an experimental paradigm that links biogeochemical processes with ever-changing temporal and spatial distributions of microbial population, and their metabolic properties. Photosynthetic microbial mats offer an opportunity to define holistic functionality at the millimeter scale. At the same time, their Biogeochemistry contributes to environmental processes on a planetary scale. These mats are possibly direct descendents of the most ancient biological communities; communities in which oxygenic photosynthesis might have been invented. Mats provide one of the best natural systems to study how microbial populations associate to control dynamic biogeochemical gradients. These are self-sustaining, complete ecosystems in which light energy absorbed over a diel (24 hour) cycle drives the synthesis of spatially-organized, diverse biomass. Tightly-coupled microorganisms in the mat have specialized metabolisms that catalyze transformations of carbon, nitrogen. sulfur, and a host of other elements.

DesMarais, David J.; DeVincenzi, Donald L. (Technical Monitor)

2001-01-01

51

Cave Formation: Biogeochemical Cycles  

NSDL National Science Digital Library

This video explores the role of biogeochemical cycles in the formation of caves. It discusses a radical new theory that identifies sulfuric acid as a cave-forming agent. The video, adapted from a NOVA broadcast, identifies the source of the sulfuric acid, which, unlike carbonic acid, the typical cave-forming agent, does not readily form in nature. The segment is 5 minutes and forty seconds in length.

52

Numerical modeling of the nitrogen retention and turnover at the surface-subsurface interface of riffle-pool sequences  

NASA Astrophysics Data System (ADS)

Quantification of the retention and turnover of constituents in the hyporheic zone of rivers and streams is very challenging as a result of complex physical and biogeochemical processes. There is a tremendous potential of using processes based numerical models to advance our understanding of hyporheic processes. The presentation aims at the calibration and validation procedure for the NH4 and NO3 profiles at various section of a reach and specification of parameters of major significance among large number of parameters involved in the modeling procedure. A case study was conducted on a riffle-pool sequence of the river Lahn, Germany. Using the hydrodynamic TELEMAC2D model, the surface water profile was calibrated. The groundwater flow model, MODFLOW with its reaction module RT3D, was used for the analysis in the subsurface. The first order reaction module was coded for NH4-NO3-N2 conversion process. The water surface elevation data from the hydrodynamic model is integrated into the subsurface flow and reactive transport model. The measured concentration profile (over depth), at various points of River Lahn were calibrated and parameter sensitivity analysis were performed. The model is found to be highly sensitive to hydraulic conductivity, reaction parameters, specific storage, and longitudinal dispersivity; moderately sensitive to conductance; and slightly sensitive to specific yield and molecular dispersion coefficient. It was found that the beginning of the riffle is the location of the highest concentration gradient. The locations of highest hydraulic gradient as a result of morphological change (riffle), is the location of the highest water exchange and nitrogen transformation. In spite of uncertainties involved in the process-based models (data, parameters, and model structure) valuable conclusions can be made towards focused theoretical and experimental studies for new process understating. There is a need to improve the process based numerical models in a more sophisticated manner by stronger coupling of the surface and subsurface process, with due consideration the difficulties in data acquisition and parameter estimation.

Kebede Gurmessa, T.; Borchardt, D.; Rode, M.

2009-04-01

53

Polar Front around the Kerguelen Islands: An up-to-date determination and associated circulation of surface/subsurface waters  

NASA Astrophysics Data System (ADS)

circulation of iron-rich shelf waters around the Kerguelen Islands plays a crucial role for a climatically important, annually recurrent phytoplankton spring bloom over the sluggish shelf region and its downstream plume area along the Antarctic circumpolar flow. However, there is a long-standing confusion about the Polar Front (PF) in the Kerguelen region due to diverse suggestions in the literature for its geographical location with an extreme difference over 10° of latitude. Based on abundant historical hydrographic data, the in situ hydrographic and current measurements during the 2011 KEOPS2 cruise, satellite chlorophyll images, and altimetry-derived surface velocity fields, we determine and validate an up-to-date location of the PF around the Kerguelen Islands. Artificial Lagrangian particle trajectories computed from altimetric velocity time series are analyzed for the possible pathways and sources of different surface/subsurface waters advected into the chlorophyll bloom area east off the islands studied during the KEOPS2 cruise. The PF location determined as the northernmost boundary of the Winter Water colder than 2°C, which is also associated with a band of strong currents, appears to be primarily controlled by topography. The PF rounds the Kerguelen Islands from the south to deflect northward along the eastern escarpment up to the northeastern corner of the Kerguelen Plateau before making its southward retroflection. It is shown that the major surface/subsurface waters found within the deep basin east of the Kerguelen Islands originate from the shelf around the Heard Island, rather than from the shallow shelf north of the Kerguelen Islands.

Park, Young-Hyang; Durand, Isabelle; Kestenare, Elodie; Rougier, Gilles; Zhou, Meng; d'Ovidio, Francesco; Cotté, Cédric; Lee, Jae-Hak

2014-10-01

54

Quantifying methane emissions from rice fields in the Taihu Lake region, China by coupling a detailed soil database with biogeochemical model  

NASA Astrophysics Data System (ADS)

As China has approximately 22% of the world's rice paddies, the regional quantification of CH4 emissions from these paddies is important in determining their contribution to the global greenhouse gas effect. This paper reports the use of a biogeochemical model (DeNitrification and DeComposition or DNDC) for quantifying CH4 emissions from rice fields in the Taihu Lake region of China. For this application, the DNDC model was linked to a 1:50 000 soil database derived from 1107 paddy soil profiles compiled during the Second National Soil Survey of China in the 1980s-1990s. The simulated results showed that the 2.3 Mha of paddy rice fields in the Taihu Lake region emitted the equivalent of 5.7 Tg C from 1982-2000, with the average CH4 flux ranging from 114 to 138 kg C ha-1 y-1. As for soil subgroups, the highest emission rate (660 kg C ha-1 y-1) was linked to gleyed paddy soils accounting for about 4.4% of the total area of paddy soils. The lowest emission rate (91 kg C ha-1 y-1) was associated with degleyed paddy soils accounting for about 18% of the total area of paddy soils. The most common soil in the area was hydromorphic paddy soils, which accounted for about 53% of the total area of paddy soils with a CH4 flux of 106 kg C ha-1 y-1. On a regional basis, the annual averaged CH4 flux in the Taihu Lake plain soil region and alluvial plain soil region were higher than that in the low mountainous and hilly soil region and the polder soil region. The model simulation was conducted with two databases using polygons or counties as the basic units. The county-based database contained soil information coarser than the polygon system built based on the 1:50 000 soil database. The modeled results with the two databases found similar spatial patterns of CH4 emissions in the Taihu Lake region. However, discrepancies exist between the results from the two methods. The total CH4 emissions generated from the polygon-based database is 2.6 times the minimum CH4 emissions generated from the county-based database, and is 0.98 times the maximum CH4 emissions generated from the county-based database. The average value of the relative deviation ranged from -20% to 98% for most counties, which indicates that a more precise soil database is necessary to better simulate CH4 emissions from rice fields in the Taihu Lake region using the DNDC model.

Zhang, L.; Yu, D.; Shi, X.; Weindorf, D.; Zhao, L.; Ding, W.; Wang, H.; Pan, J.; Li, C.

2009-05-01

55

Subsurface Uranium Fate and Transport: Integrated Experiments and Modeling of Coupled Biogeochemical Mechanisms of Nanocrystalline Uraninite Oxidation by Fe(III)-(hydr)oxides - Project Final Report  

SciTech Connect

Subsurface bacteria including sulfate reducing bacteria (SRB) reduce soluble U(VI) to insoluble U(IV) with subsequent precipitation of UO2. We have shown that SRB reduce U(VI) to nanometer-sized UO2 particles (1-5 nm) which are both intra- and extracellular, with UO2 inside the cell likely physically shielded from subsequent oxidation processes. We evaluated the UO2 nanoparticles produced by Desulfovibrio desulfuricans G20 under growth and non-growth conditions in the presence of lactate or pyruvate and sulfate, thiosulfate, or fumarate, using ultrafiltration and HR-TEM. Results showed that a significant mass fraction of bioreduced U (35-60%) existed as a mobile phase when the initial concentration of U(VI) was 160 µM. Further experiments with different initial U(VI) concentrations (25 - 900 ?M) in MTM with PIPES or bicarbonate buffers indicated that aggregation of uraninite depended on the initial concentrations of U(VI) and type of buffer. It is known that under some conditions SRB-mediated UO2 nanocrystals can be reoxidized (and thus remobilized) by Fe(III)-(hydr)oxides, common constituents of soils and sediments. To elucidate the mechanism of UO2 reoxidation by Fe(III) (hydr)oxides, we studied the impact of Fe and U chelating compounds (citrate, NTA, and EDTA) on reoxidation rates. Experiments were conducted in anaerobic batch systems in PIPES buffer. Results showed EDTA significantly accelerated UO2 reoxidation with an initial rate of 9.5?M day-1 for ferrihydrite. In all cases, bicarbonate increased the rate and extent of UO2 reoxidation with ferrihydrite. The highest rate of UO2 reoxidation occurred when the chelator promoted UO2 and Fe(III) (hydr)oxide dissolution as demonstrated with EDTA. When UO2 dissolution did not occur, UO2 reoxidation likely proceeded through an aqueous Fe(III) intermediate as observed for both NTA and citrate. To complement to these laboratory studies, we collected U-bearing samples from a surface seep at the Rifle field site and have measured elevated U concentrations in oxic iron-rich sediments. To translate experimental results into numerical analysis of U fate and transport, a reaction network was developed based on Sani et al. (2004) to simulate U(VI) bioreduction with concomitant UO2 reoxidation in the presence of hematite or ferrihydrite. The reduction phase considers SRB reduction (using lactate) with the reductive dissolution of Fe(III) solids, which is set to be microbially mediated as well as abiotically driven by sulfide. Model results show the oxidation of HS– by Fe(III) directly competes with UO2 reoxidation as Fe(III) oxidizes HS– preferentially over UO2. The majority of Fe reduction is predicted to be abiotic, with ferrihydrite becoming fully consumed by reaction with sulfide. Predicted total dissolved carbonate concentrations from the degradation of lactate are elevated (log(pCO2) ~ –1) and, in the hematite system, yield close to two orders-of-magnitude higher U(VI) concentrations than under initial carbonate concentrations of 3 mM. Modeling of U(VI) bioreduction with concomitant reoxidation of UO2 in the presence of ferrihydrite was also extended to a two-dimensional field-scale groundwater flow and biogeochemically reactive transport model for the South Oyster site in eastern Virginia. This model was developed to simulate the field-scale immobilization and subsequent reoxidation of U by a biologically mediated reaction network.

Peyton, Brent M. [Montana State University; Timothy, Ginn R. [University of California Davis; Sani, Rajesh K. [South Dakota School of Mines and Technology

2013-08-14

56

Hyporheic flow and transport processes: Mechanisms, models, and biogeochemical implications  

NASA Astrophysics Data System (ADS)

years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed.

Boano, F.; Harvey, J. W.; Marion, A.; Packman, A. I.; Revelli, R.; Ridolfi, L.; Wörman, A.

2014-12-01

57

Vegetation Influence on Regional Climate Change: A 3D Integrated Atmospheric-Surface-Subsurface Analysis  

NASA Astrophysics Data System (ADS)

Human induced land-use change has been shown to be one of the major contributing factors to anthropogenic regional climate change. The transition from densely vegetated forests with deep root zones to shallow rooted agricultural ecosystems drastically limits the natural buffering capacity of deep groundwater during severe drought conditions. In order to quantify the magnitude of climate change from altered ecosystems, we employed the 3D model HydroGeoSphere, an integrated variably-saturated subsurface/surface flow and heat transport model, coupled with a simplified zero-dimensional atmospheric boundary layer model to simulate an extended seasonal drought period. It is found that during drought conditions, trees with deep root zones are capable of maintaining higher evapotranspiration rates, higher latent heat fluxes, and a damped atmospheric temperature response. In contrast, grasses with shallow root zones have minimal evapotranspiration rates, lower latent heat fluxes, and a rapid and sharp atmospheric temperature response. On the whole, converting a naturally wooded ecosystem to a farmland or pasture effectively decreases the available water in the subsurface for transpiration subsequently amplifying the atmospheric response to severe weather.

Davison, J. H.; Hwang, H.; Sudicky, E. A.; Lin, J. C.

2013-12-01

58

Effects of the Tide on the Marine Ecosystem in the Northwestern Pacific Marginal Seas using a 3-dimensional Coupled Physico-Biogeochemical Model  

NASA Astrophysics Data System (ADS)

Tide is a crucial factor for the proper simulation of the ocean circulation in the Northwestern Pacific Marginal Seas, especially in the Yellow Sea. The different physical status due to the inclusion (or exclusion) of tide in the coupled ocean physics and biogeochemistry system also produces a different ecosystem. In this study, we have applied 3-dimensional coupled ocean system model based on POLCOMS (Proudman Oceanographic Laboratory Coastal Ocean Modelling System) and ERSEM (European Regional Seas Ecosystem Model) to the Northwestern Pacific Marginal Seas and have investigated the influences of the tide in the marine system model on the ecosystem. The model covers the Yellow and the East China Seas (YES), the East/Japan Sea (EJS) and the Okhotsk Sea (OS) as well as the major western boundary currents, the Kuroshio and the Oyashio currents. The effects of tide in the physical system, as expected, are prominent in the YES circulation pattern change in terms of the Changiang Diluted Water (CDW) dispersion path, the Yellow Sea Warm Current (YSWC), the Yellow Sea Bottom Cold Water (YSBCW) distribution as well as local influences driven by tidal mixing. These changes of physical status control the changes of nutrients as well as plankton distributions in the YES. It is noteworthy that the ecosystem in the southern EJS is also highly affected by the lateral transport of different nutrients conditions and changed ecosystem from the YES. The changes of the OS ecosystem and physical status due to the tide are not notable compared to the YES but there are local changes especially in the northern shelf region. It is concluded that the tide is very important not only for the local ecosystem but also for the remote ecosystem, though the local tide seems not so much crucial, if it is linked with the strong tidal regime inflow region.

Kang, Hyoun-Woo; Kim, Hanna; Kwi So, Jae; Butenschon, Momme; Allen, Icarus

2014-05-01

59

Numerical simulation of in-situ chemical oxidation (ISCO) and biodegradation of petroleum hydrocarbons using a coupled model for bio-geochemical reactive transport  

NASA Astrophysics Data System (ADS)

Petroleum hydrocarbons (PHCs) are a major source of groundwater contamination, being a worldwide and well-known problem. Formed by a complex mixture of hundreds of organic compounds (including BTEX - benzene, toluene, ethylbenzene and xylenes), many of which are toxic and persistent in the subsurface and are capable of creating a serious risk to human health. Several remediation technologies can be used to clean-up PHC contamination. In-situ chemical oxidation (ISCO) and intrinsic bioremediation (IBR) are two promising techniques that can be applied in this case. However, the interaction of these processes with the background aquifer geochemistry and the design of an efficient treatment presents a challenge. Here we show the development and application of BIONAPL/Phreeqc, a modeling tool capable of simulating groundwater flow, contaminant transport with coupled biological and geochemical processes in porous or fractured porous media. BIONAPL/Phreeqc is based on the well-tested BIONAPL/3D model, using a powerful finite element simulation engine, capable of simulating non-aqueous phase liquid (NAPL) dissolution, density-dependent advective-dispersive transport, and solving the geochemical and kinetic processes with the library Phreeqc. To validate the model, we compared BIONAPL/Phreeqc with results from the literature for different biodegradation processes and different geometries, with good agreement. We then used the model to simulate the behavior of sodium persulfate (NaS2O8) as an oxidant for BTEX degradation, coupled with sequential biodegradation in a 2D case and to evaluate the effect of inorganic geochemistry reactions. The results show the advantages of a treatment train remediation scheme based on ISCO and IBR. The numerical performance and stability of the integrated BIONAPL/Phreeqc model was also verified.

Marin, I. S.; Molson, J. W.

2013-05-01

60

Simulation of Marine Nitrogen Cycling as Function of Atmospheric Oxygen: Results of a Coupled C,N,P,O,S Biogeochemical Model Including d15N  

NASA Astrophysics Data System (ADS)

Bioavailable nitrogen is a critical limiting nutrient in the modern marine biosphere. We expect that the rate of denitrification may have been higher in the geologic past due to decreased atmospheric O2 and expanded ocean anoxia. To examine the consequences of this idea, we present numerical simulations of coupled carbon, nitrogen, phosphorus, oxygen, and sulfur cycling as a function of atmospheric oxygen in an ocean with circulation similar to modern conditions. The model has been specifically developed to function over a wide range of ocean redox conditions and has been successfully tested in simulations of both the modern global ocean and Black Sea. Global rates of nitrogen fixation and pelagic denitrification, which are strongly coupled in our default model, reach maximum rates between 25% and 50% of the present atmospheric level of O2 (PAL O2). At 40% PAL O2, the simulated steady-state pelagic denitrification rate is 82.1 Tmol/yr, and the N- fixation rate is 85.7 Tmol/yr. These rates are 8-15× greater than modern estimates. The maximum simulated rate of N-fixation is determined by the N flux required to entirely support export production. At mid- levels of atmospheric oxygen, large areas of the oceans are characterized by a suboxic to anoxic "oxygen minimum zone" between 100m and 1000m depth which is over- and underlain by oxic water. Under these conditions, denitrification in the upper water column is nearly complete, suppressing the ?15N isotopic signal for this process. To test the impact of limitation of N-fixation (e.g. by trace metals, light, temperature) we imposed a cap on the global N-fixation rate. In these simulations, limitation of N-fixation below 50% PAL O2 results in severe N limitation of primary production and low mean oceanic N:P. Our results imply that N limitation may have been chronic at intermediate levels of atmospheric O2. At the same time, low N:P conditions would create evolutionary pressure for efficient N-fixation pathways and high N use efficiency in non-fixing marine phytoplankton, testing the limits of plasticity in the Redfield ratio. If N-fixation were unable to keep up with high rates of denitrification at intermediate levels of atmospheric O2, intense N limitation of Proterozoic marine primary production may have strongly inhibited any further rise of atmospheric O2, thus stabilizing atmospheric O2 at <25% PAL.

Romaniello, S. J.; Derry, L. A.

2008-12-01

61

National Wetlands Biogeochemical Database (NWBD)  

NSDL National Science Digital Library

The National Wetland Biogeochemical Database (NWBD) is "an effort to locate, collect and compile existing biogeochemical information on wetlands of the United States including Hawaii and Alaska." Funded in part by the Environmental Protection Agency (EPA), the database will be used to develop a Nutrient Criteria Technical Guidance Manual for US Wetlands -- for use in assessing potential nutrient-related trophic state impairment and pollution problems. Presently focused on water column and soil biogeochemical parameters (e.g., N, P, C, Metals, temp., DO, pH, etc.), the completed NWBD will act as a reference data set for biogeochemical parameters at different regional, community, and temporal scales. Data contributors are invited to participate using NWBD's on-site contact information.

62

Biogeochemical Cycles in Degraded Lands  

NASA Technical Reports Server (NTRS)

The objectives of this project were to define and describe the types of landscapes that fall under the broad category of "degraded lands" and to study biogeochemical cycles across this range of degradation found in secondary forests. We define degraded land as that which has lost part of its capacity of renovation of a productive ecosystem, either in the context of agroecosystems or as native communities of vegetation. This definition of degradation permits evaluation of biogeochemical constraints to future land uses.

Davidson, Eric A.; Vieira, Ima Celia G.; ReisdeCarvalho, Claudio Jose; DeaneDeAbreuSa, Tatiana; deSpozaMoutinho, Paulo R.; Figueiredo, Ricardo O.; Stone, Thomas A.

2003-01-01

63

Biogeochemical Cycles in Degraded Lands  

NASA Technical Reports Server (NTRS)

The objectives of this project were to define and describe the types of landscapes that fall under the broad category of "degraded lands" and to study biogeochemical cycles across this range of degradation found in secondary forests. We define degraded land as that which has lost part of its capacity of renovation of a productive ecosystem, either in the context of agroecosystems or as native communities of vegetation. This definition of degradation permits evaluation of biogeochemical constraints to future land uses.

Davidson, Eric A.; Vieira, Ima Celia G.; ReisdeCarvalho, Claudio Jose; DeanedeAbreuSa, Tatiana; deSouzaMoutinho, Paulo R.; Figueiredo, Ricardo O.; Stone, Thomas A.

2004-01-01

64

A hierarchical framework for coupling surface fluxes to atompsheric general circulation models: The homogeneity test  

SciTech Connect

The atmosphere and the biosphere are inherently coupled to one another. Atmospheric surface state variables such as temperature, winds, water vapor, precipitation, and radiation control biophysical, biogeochemical, and ecological processes at the surface and subsurface. At the same time, surface fluxes of momentum, moisture, heat, and trace gases act as time-dependent boundary conditions providing feedback on atmospheric processes. To understand such phenomena, a coupled set of interactive models is required. Costs are still prohibitive for computing surface/subsurface fluxes directly for medium-resolution atmospheric general circulation models (AGCMs), but a technique has been developed for testing large-scale homogeneity and accessing surface parameterizations and models to reduce this computational cost and maintain accuracy. This modeling system potentially bridges the observed spatial and temporal ranges yet allows the incorporation of necessary details about individual ecological community types or biomes and simulates the net momentum, heat, moisture, and trace gas fluxes. This suite of coupled models is defined here as the hierarchical systems flux scheme (HSFS).

Miller, N.L.

1993-12-31

65

A hierarchical framework for coupling surface fluxes to atompsheric general circulation models: The homogeneity test  

SciTech Connect

The atmosphere and the biosphere are inherently coupled to one another. Atmospheric surface state variables such as temperature, winds, water vapor, precipitation, and radiation control biophysical, biogeochemical, and ecological processes at the surface and subsurface. At the same time, surface fluxes of momentum, moisture, heat, and trace gases act as time-dependent boundary conditions providing feedback on atmospheric processes. To understand such phenomena, a coupled set of interactive models is required. Costs are still prohibitive for computing surface/subsurface fluxes directly for medium-resolution atmospheric general circulation models (AGCMs), but a technique has been developed for testing large-scale homogeneity and accessing surface parameterizations and models to reduce this computational cost and maintain accuracy. This modeling system potentially bridges the observed spatial and temporal ranges yet allows the incorporation of necessary details about individual ecological community types or biomes and simulates the net momentum, heat, moisture, and trace gas fluxes. This suite of coupled models is defined here as the hierarchical systems flux scheme (HSFS).

Miller, N.L.

1993-01-01

66

Interpreting streamflow generation mechanisms from integrated surface-subsurface flow models of a riparian wetland and catchment  

NASA Astrophysics Data System (ADS)

The understanding of streamflow generation processes is vitally important in the management of water resources. In the absence of the data required to achieve this, Integrated Surface-Subsurface Hydrological Models (ISSHM) can be used to assist with the development of this understanding. However, the standard outputs from these models only enable elicitation of information about hydrological drivers and hydrological responses that occur at the same time. This generally limits the applicability of ISSHMs for the purposes of obtaining an improved understanding of streamflow generation processes to catchment areas that do not exhibit significant storage, travel times or flow depletion mechanisms. In order to overcome this limitation, a previously published Hydraulic Mixing-Cell (HMC) method is improved so that it can be used to follow surface water derived from direct rainfall and groundwater discharge to the stream and adjacent overland flow areas. The developed approach was applied to virtual experiments (based on the Lehstenbach catchment in southeastern Germany), which are composed of two ISSHMs of contrasting scales: (1) a riparian wetland of area 210 m2 and (2) a catchment of area 4.2 km2. For the two models, analysis of modeling results for a large storm event showed complex spatiotemporal variability in streamflow generation and surface water-groundwater interaction. Further analysis with the HMC method elucidated in-stream and overland flow generation mechanisms. This study showed within a modeling framework that identification and quantification of in-stream and overland flow generation better informed understanding of catchment functioning through decomposition of streamflow hydrographs, and analysis of spatiotemporal variability of flow generation mechanisms.

Partington, D.; Brunner, P.; Frei, S.; Simmons, C. T.; Werner, A. D.; Therrien, R.; Maier, H. R.; Dandy, G. C.; Fleckenstein, J. H.

2013-09-01

67

Topographic controls on soil moisture scaling properties in polygonal ground using idealized high-resolution surface-subsurface simulations  

NASA Astrophysics Data System (ADS)

Microtopographic features, such as polygonal ground, are characteristic sources of landscape heterogeneity in the Alaskan Arctic coastal plain. Here, we analyze the hypothesis that microtopography is a dominant controller of soil moisture in polygonal landscapes. We perform multi-year surface-subsurface isothermal flow simulations using the PFLOTRAN model for summer months at six spatial resolutions (0.25-8 m, in increments of a factor of 2). Simulations are performed for four study sites near Barrow, Alaska that are part of the NGEE-Arctic project. Results indicate a non-linear scaling relationship for statistical moments of soil moisture. Mean soil moisture for all study sites is accurately captured in coarser resolution simulations, but soil moisture variance is significantly under-estimated in coarser resolution simulations. The decrease in soil moisture variance in coarser resolution simulations is greater than the decrease in soil moisture variance obtained by coarsening out the fine resolution simulations. We also develop relationships to estimate the fine-resolution soil moisture probability distribution function (PDF) using coarse resolution simulations and topography. Although the estimated soil moisture PDF is underestimated during very wet conditions, the moments computed from the inferred soil moisture PDF had good agreement with the full model solutions (bias < ± 4 % and correlation > 0.99) for all four sites. Lastly, we develop two spatially-explicit methods to downscale coarse-resolution simulations of soil moisture. The first downscaling method requires simulation of soil moisture at fine and coarse resolution, while the second downscaling approach uses only topographical information at the two resolutions. Both downscaling approaches are able to accurately estimate fine-resolution soil moisture spatial patterns when compared to fine-resolution simulations (mean error for all study sites are < ± 1 %), but the first downscaling method more accurately estimates soil moisture variance.

Bisht, G.; Riley, W. J.

2014-11-01

68

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

69

Emergent Archetype Hydrological-Biogeochemical Response Patterns in Heterogeneous Catchments  

NASA Astrophysics Data System (ADS)

What can spatiotemporally integrated patterns observed in stream hydrologic and biogeochemical signals generated in response to transient hydro-climatic and anthropogenic forcing tell us about the interactions between spatially heterogeneous soil-mediated hydrological and biogeochemical processes? We seek to understand how the spatial structure of solute sources coupled with hydrologic responses affect observed concentration-discharge (C-Q) patterns. These patterns are expressions of the spatiotemporal structure of solute loads exported from managed catchments, and their likely ecological consequences manifested in receiving water bodies (e.g., wetlands, rivers, lakes, and coastal waters). We investigated the following broad questions: (1) How does the correlation between flow-generating areas and biogeochemical source areas across a catchment evolve under stochastic hydro-climatic forcing? (2) What are the feasible hydrologic and biogeochemical responses that lead to the emergence of the observed archetype C-Q patterns? and; (3) What implications do these coupled dynamics have for catchment monitoring and implementation of management practices? We categorize the observed temporal signals into three archetypical C-Q patterns: dilution; accretion, and constant concentration. We introduce a parsimonious stochastic model of heterogeneous catchments, which act as hydrologic and biogeochemical filters, to examine the relationship between spatial heterogeneity and temporal history of solute export signals. The core concept of the modeling framework is considering the types and degree of spatial correlation between solute source zones and flow generating zones, and activation of different portions of the catchments during rainfall events. Our overarching hypothesis is that each of the archetype C-Q patterns can be generated by explicitly linking landscape-scale hydrologic responses and spatial distributions of solute source properties within a catchment. The model simulations reproduce the three major C-Q patterns observed in published data, offering valuable insight into coupled catchment processes. The findings have important implications for effective catchment management for water quality improvement, and stream monitoring strategies.

Jawitz, J. W.; Gall, H. E.; Rao, P.

2013-12-01

70

Presidential address Geomycology: biogeochemical transformations  

E-print Network

­soil interface. The geochemical transformations that take place can influence plant productivity and the mobilityPresidential address Geomycology: biogeochemical transformations of rocks, minerals, metals history: Received 21 November 2006 Received in revised form 26 November 2006 Accepted 12 December 2006

Ahmad, Sajjad

71

[Application and development of terrestrial biogeochemical model].  

PubMed

Biogeochemical modeling plays a role as important as experimental measurement in ecosystem research. This paper analyzed the development of biogeochemical model using TEM and DNDC model as cases. Current biogeochemical models were classified according to modeling method, application purpose, element concerned, ecosystem type, and spatial scale. The basic framework (three component: plant, air and soil, and three interface: plantair, plant-soil, and soil-air) and interior fundamental processes (physical, chemical and biological processes) of biogeochemical models were reviewed, and some important problems concerning biogeochemical modeling, such as scale upping, integrating GIS and remote sensing, involved human activity, and comparison study were focused. PMID:12682987

Wang, Xiaoke; Bai, Yanying; Ouyang, Zhiyun; Miao, Hong

2002-12-01

72

Mechanistic Biogeochemical Model Applications for Everglades Restoration: A Review of Case Studies and Suggestions for Future Modeling Needs  

Microsoft Academic Search

Mechanistic biogeochemical model applications for freshwater wetland ecosystems are reviewed with an emphasis on applications in the Florida Everglades. Two significant human impacts on the Everglades have been hydrologic alteration and phosphorus (P) enrichment. Thus, it is important for research conducted in support of Everglades restoration to integrate understanding of the coupled effects of hydrologic and biogeochemical processes. Models are

Joong-Hyuk Min; Rajendra Paudel; James W. Jawitz

2011-01-01

73

Biogeochemical Processes in Microbial Ecosystems  

NASA Technical Reports Server (NTRS)

The hierarchical organization of microbial ecosystems determines process rates that shape Earth's environment, create the biomarker sedimentary and atmospheric signatures of life, and define the stage upon which major evolutionary events occurred. In order to understand how microorganisms have shaped the global environment of Earth and, potentially, other worlds, we must develop an experimental paradigm that links biogeochemical processes with ever-changing temporal and spatial distributions of microbial populations and their metabolic properties. Additional information is contained in the original extended abstract.

DesMarais, David J.

2001-01-01

74

Parameterization of biogeochemical sediment-water fluxes using in-situ measurements and a steady-state diagenetic model  

NASA Astrophysics Data System (ADS)

Sediment biogeochemical processes are important drivers of water column biogeochemistry in coastal areas. For example, sediment oxygen consumption can be an important driver of bottom water oxygen depletion in hypoxic systems, and sediment-water nutrient fluxes support primary productivity in the overlying water column. Yet, biogeochemical sediment-water fluxes are often parameterized crudely and only poorly constrained in coupled physical-biogeochemical models. Here, we present a method for parameterizing biogeochemical sediment-water fluxes realistically and efficiently, using in-situ measurements and a steady state diagenetic model. We apply this method to the Louisiana Shelf where high primary production induced by excess nutrient loads from the Mississippi-Atchafalaya River system promotes the development of hypoxic bottom waters in summer. The implementation of the parameterizations in a coupled circulation-biogeochemical model of the northern Gulf of Mexico results in realistic sediment-water fluxes that enable a sediment-water column feedback at low bottom oxygen concentrations.

Laurent, Arnaud; Fennel, Katja; Wilson, Robin; Lehrter, John; Devereux, Richard

2014-05-01

75

Ocean fronts drive marine fishery production and biogeochemical cycling.  

PubMed

Long-term changes in nutrient supply and primary production reportedly foreshadow substantial declines in global marine fishery production. These declines combined with current overfishing, habitat degradation, and pollution paint a grim picture for the future of marine fisheries and ecosystems. However, current models forecasting such declines do not account for the effects of ocean fronts as biogeochemical hotspots. Here we apply a fundamental technique from fluid dynamics to an ecosystem model to show how fronts increase total ecosystem biomass, explain fishery production, cause regime shifts, and contribute significantly to global biogeochemical budgets by channeling nutrients through alternate trophic pathways. We then illustrate how ocean fronts affect fishery abundance and yield, using long-term records of anchovy-sardine regimes and salmon abundances in the California Current. These results elucidate the fundamental importance of biophysical coupling as a driver of bottom-up vs. top-down regulation and high productivity in marine ecosystems. PMID:25624488

Woodson, C Brock; Litvin, Steven Y

2015-02-10

76

Ocean fronts drive marine fishery production and biogeochemical cycling  

PubMed Central

Long-term changes in nutrient supply and primary production reportedly foreshadow substantial declines in global marine fishery production. These declines combined with current overfishing, habitat degradation, and pollution paint a grim picture for the future of marine fisheries and ecosystems. However, current models forecasting such declines do not account for the effects of ocean fronts as biogeochemical hotspots. Here we apply a fundamental technique from fluid dynamics to an ecosystem model to show how fronts increase total ecosystem biomass, explain fishery production, cause regime shifts, and contribute significantly to global biogeochemical budgets by channeling nutrients through alternate trophic pathways. We then illustrate how ocean fronts affect fishery abundance and yield, using long-term records of anchovy–sardine regimes and salmon abundances in the California Current. These results elucidate the fundamental importance of biophysical coupling as a driver of bottom–up vs. top–down regulation and high productivity in marine ecosystems. PMID:25624488

Woodson, C. Brock; Litvin, Steven Y.

2015-01-01

77

The concept of dual-boundary forcing in land surface-subsurface interactions of the terrestrial hydrologic and energy cycles  

NASA Astrophysics Data System (ADS)

hydrological processes interact in a complex, nonlinear fashion. It is important to quantify these interactions to understand the overall mechanisms of the coupled water and energy cycles. In this study, the concept of a dual-boundary forcing is proposed that connects the variability of atmospheric (upper boundary) and subsurface (lower boundary) processes to the land surface mass and energy balance components. According to this concept, the space-time patterns of land surface mass and energy fluxes can be explained by the variability of the dominating boundary condition for the exchange processes, which is determined by moisture and energy availability. A coupled subsurface-land surface model is applied on the Rur catchment, Germany, to substantiate the proposed concept. Spectral and geostatistical analysis on the observations and model results show the coherence of different processes at various space-time scales in the hydrological cycle. The spectral analysis shows that atmospheric radiative forcing generally drives the variability of the land surface energy fluxes at the daily time scale, while influence of subsurface hydrodynamics is significant at monthly to multimonth time scales under moisture-limited conditions. The geostatistical analysis demonstrates that atmospheric forcing and groundwater control the spatial variability of land surface processes under energy and moisture-limited conditions, respectively. These results suggest that under moisture-limited conditions, groundwater influences the variability of the land surface mass and energy fluxes. Under energy-limited conditions, on the contrary, variability of land surface processes can be explained by atmospheric forcing alone.

Rahman, M.; Sulis, M.; Kollet, S. J.

2014-11-01

78

Tidal sands as biogeochemical reactors  

NASA Astrophysics Data System (ADS)

Sandy sediments of continental shelves and most beaches are often thought of as geochemical deserts because they are usually poor in organic matter and other reactive substances. The present study focuses on analyses of dissolved biogenic compounds of surface seawater and pore waters of Aquitanian coastal beach sediments. To quantitatively assess the biogeochemical reactions, we collected pore waters at low tide on tidal cross-shore transects unaffected by freshwater inputs. We recorded temperature, salinity, oxygen saturation state, and nutrient concentrations. These parameters were compared to the values recorded in the seawater entering the interstitial environment during floods. Cross-shore topography and position of piezometric level at low tide were obtained from kinematics GPS records. Residence time of pore waters was estimated by a tracer approach, using dissolved silica concentration and kinetics estimate of quartz dissolution with seawater. Kinetics parameters were based on dissolved silica concentration monitoring during 20-day incubations of sediment with seawater. We found that seawater that entered the sediment during flood tides remained up to seven tidal cycles within the interstitial environment. Oxygen saturation of seawater was close to 100%, whereas it was as low as 80% in pore waters. Concentrations of dissolved nutrients were higher in pore waters than in seawater. These results suggest that aerobic respiration occurred in the sands. We propose that mineralised organic matter originated from planktonic material that infiltrated the sediment with water during flood tides. Therefore, the sandy tidal sediment of the Aquitanian coast is a biogeochemical reactor that promotes or accelerates remineralisation of coastal pelagic primary production. Mass balance calculations suggest that this single process supplies about 37 kmol of nitrate and 1.9 kmol of dissolved inorganic phosphorus (DIP) to the 250-km long Aquitanian coast during each semi-diurnal tidal cycle. It represents about 1.5% of nitrate and 5% of DIP supplied by the nearest estuary.

Anschutz, Pierre; Smith, Thomas; Mouret, Aurélia; Deborde, Jonathan; Bujan, Stéphane; Poirier, Dominique; Lecroart, Pascal

2009-08-01

79

Combining high resolution space- and air-borne data with borehole monitoring to investigate surface-subsurface water relations in landslide-prone slopes  

NASA Astrophysics Data System (ADS)

Water still seems to be a relatively little studied environmental factor in applications of multispectral space- and air-borne data to landslide investigations, even though stagnated drainage conditions have long been used as diagnostic elements for landslide recognition and mapping based on airphoto interpretation. Here we use both satellite imagery and airphotos, focusing on water as a critical factor of the recurrent instability of poorly drained slopes in a 15.6 km2 catchment area in the Apennine mountains (Italy) characterized by predominance of clay-rich flysch units and agricultural land use. We expand on our recent study (Wasowski et al., 2012) that exploited high resolution multispectral satellite imagery from early spring of 2006 for mapping active landslides, investigating their close association with seasonally wet zones (areas covered by free surface-water including ponds, migrating surface-water, seeps), and for inferring surface-subsurface relationships in unstable slopes. In particular, we use sub-meter resolution multispectral orthophotos acquired in late winter of 2011 to map the distributions of active landslides and wet zones. Considerable spatial-temporal recurrence of these features is indicated from a comparison of the 2011 and 2006 inventories. Furthermore, using the extensive subsurface dataset from piezometer boreholes (ongoing monitoring since 2009) we show that a number of remotely sensed wet zones are indicative of sites with seasonally persistent very high groundwater levels within landslide-prone slopes and on intermittently active landslides. Where such surface-subsurface water linkage can be established, the appearance of the wet zones (fully saturated ground/soil) resulting from groundwater discharge or seepage can be used as a forewarning signal of the increased susceptibility to landsliding, since the hillslopes with shallow groundwater tables are generally more prone to failure. However, the feasibility of retrieving reliable information about surface-water conditions from high resolution optical data, and the degree of its usefulness can be site-specific. This work suggests that useful results can be obtained in settings with similar topography (shallow slopes), lithology (clay-rich) and land use/land cover (agricultural soils with little woodland). A critical factor that will influence the results is the suitable timing of the imagery acquisition, in our case during wet season and early in vegetation period. Furthermore, acquisitions shortly after intense rainfall should be avoided if the focus is on wet zones indicative of shallow groundwater tables, that is those resulting from groundwater discharge and not just from accumulations of surface-water runoff. References Wasowski J., Lamanna C., Gigante G., Casarano D. 2012. High resolution satellite imagery analysis for inferring surface-subsurface water relationships in unstable slopes. Remote Sensing of Environment, 124, 135-148. doi: 10.1016/j.rse.2012.05.007

Wasowski, Janusz; Lamanna, Caterina; Dipalma Lagreca, Marina; Pasquariello, Guido

2013-04-01

80

Proterozoic ocean redox and biogeochemical stasis  

PubMed Central

The partial pressure of oxygen in Earth’s atmosphere has increased dramatically through time, and this increase is thought to have occurred in two rapid steps at both ends of the Proterozoic Eon (?2.5–0.543 Ga). However, the trajectory and mechanisms of Earth’s oxygenation are still poorly constrained, and little is known regarding attendant changes in ocean ventilation and seafloor redox. We have a particularly poor understanding of ocean chemistry during the mid-Proterozoic (?1.8–0.8 Ga). Given the coupling between redox-sensitive trace element cycles and planktonic productivity, various models for mid-Proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients, with potential ecological constraints on emerging eukaryotic life. Here, we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates. We find that the metal enrichment record implies a Proterozoic deep ocean characterized by pervasive anoxia relative to the Phanerozoic (at least ?30–40% of modern seafloor area) but a relatively small extent of euxinic (anoxic and sulfidic) seafloor (less than ?1–10% of modern seafloor area). Our model suggests that the oceanic Mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of Mo and chromium enrichments through time is consistent with the possibility of a Mo–N colimited marine biosphere during many periods of Earth’s history. PMID:23515332

Reinhard, Christopher T.; Planavsky, Noah J.; Robbins, Leslie J.; Partin, Camille A.; Gill, Benjamin C.; Lalonde, Stefan V.; Bekker, Andrey; Konhauser, Kurt O.; Lyons, Timothy W.

2013-01-01

81

The global troposphere - Biogeochemical cycles, chemistry, and remote sensing  

NASA Technical Reports Server (NTRS)

The chemical composition of the troposphere is controlled by various biogeochemical cycles that couple the atmosphere with the oceans, the solid earth and the biosphere, and by atmospheric photochemical/chemical reactions. These cycles and reactions are discussed and a number of key questions concerning tropospheric composition and chemistry for the carbon, nitrogen, oxygen and sulfur species are identified. Next, various remote sensing techniques and instruments capable of measuring and monitoring tropospheric species from the ground, aircraft and space to address some of these key questions are reviewed. Future thrusts in remote sensing of the troposphere are also considered.

Levine, J. S.; Allario, F.

1982-01-01

82

Ecological and Biogeochemical Interactions Constrain Planktonic  

E-print Network

Ecological and Biogeochemical Interactions Constrain Planktonic Nitrogen Fixation in Estuaries Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA; 2 Ecosystems nitrogen (N) is strongly limiting to primary production. Estuaries generally fit this pat- tern

Pace, Michael L.

83

Geophysical Monitoring of Hydrological and Biogeochemical  

E-print Network

Geophysical Monitoring of Hydrological and Biogeochemical Transformations Associated with Cr explored the use of geophysical approaches for monitoring the spatiotemporal distribution of hydrological first integrated hydrological wellbore and geophysical tomographic data sets to estimate hydrological

Hubbard, Susan

84

Modeling the biogeochemical cycling of nitrogen and phosphorus in the Eastern Mediterranean Sea: 1950-2000  

E-print Network

Modeling the biogeochemical cycling of nitrogen and phosphorus in the Eastern Mediterranean Sea and remains ultra-oligotrophic. A mass balance model of the coupled N & P cycles synthesizing our conceptual in the model confirms that nitrogen fixation plays a minor role, in agreement with field measurements

Simon, Emmanuel

85

Factors driving the biogeochemical budget of the Amazon River and its statistical modelling  

E-print Network

Factors driving the biogeochemical budget of the Amazon River and its statistical modelling the period 1982­1984 during the Carbon in the AMazon River Experiment (CAMREX) project. The relevant factors-regressive model coupled to variance analysis. Basically, the compositional fluctuations in the Amazon River

Paris-Sud XI, Université de

86

Microbialites and microbial communities: Biological diversity, biogeochemical functioning, diagenetic  

E-print Network

Microbialites and microbial communities: Biological diversity, biogeochemical functioning is dedicated to microbialites and microbial communities and addresses their biological diversity the study of microbial communities and microbialites: their biological diversity, their biogeochemical

Paris-Sud XI, Université de

87

Molecular biogeochemical provinces in the Atlantic Surface Ocean  

NASA Astrophysics Data System (ADS)

One of the most important aspects to understand marine organic carbon fluxes is to resolve the molecular mechanisms which convert fresh, labile biomolecules into semi-labile and refractory dissolved and particulate organic compounds in the ocean. In this interdisciplinary project, which was performed on a cruise with RV Polarstern, we carried out a detailed molecular characterisation of dissolved organic matter (DOM) on a North-South transect in the Atlantic surface ocean in order to relate the data to different biological, climatic, oceanographic, and meteorological regimes as well as to terrestrial input from riverine and atmospheric sources. Our goal was to achieve a high resolution data set for the biogeochemical characterisation of the sources and reactivity of DOM. We applied ultrahigh resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS), nutrient, trace element, amino acid, and lipid analyses and other biogeochemical measurements for 220 samples from the upper water column (0-200m) and eight deep profiles. Various spectroscopic techniques were applied continuously in a constant sample water flow supplied by a fish system and the moon pool. Radiocarbon dating enabled assessing DOC residence time. Bacterial abundance and production provided a metabolic context for the DOM characterization work and pCO2 concentrations. Combining molecular organic techniques and inductively coupled plasma mass spectrometry (ICP-MS) established an important link between organic and inorganic biogeochemical studies. Multivariate statistics, primarily based on FT-ICR-MS data for 220 samples, allowed identifying geographical clusters which matched ecological provinces proposed previously by Longhurst (2007). Our study demonstrated that marine DOM carries molecular information reflecting the “history” of ocean water masses. This information can be used to define molecular biogeochemical provinces and to improve our understanding of element fluxes in the ocean. Future “organic geotraces” studies should focus on extracting and establishing new organic proxies which are suitable to characterize and, in particular, quantify organic matter sources and transformation processes in the ocean. Longhurst AR (2007) Ecological geography of the sea. Academic Press, San Diego, 542 pp.

Koch, B. P.; Flerus, R.; Schmitt-Kopplin, P.; Lechtenfeld, O. J.; Bracher, A.; Cooper, W.; Frka, S.; Gašparovi?, B.; Gonsior, M.; Hertkorn, N.; Jaffe, R.; Jenkins, A.; Kuss, J.; Lara, R. J.; Lucio, M.; McCallister, S. L.; Neogi, S. B.; Pohl, C.; Roettgers, R.; Rohardt, G.; Schmitt, B. B.; Stuart, A.; Theis, A.; Ying, W.; Witt, M.; Xie, Z.; Yamashita, Y.; Zhang, L.; Zhu, Z. Y.; Kattner, G.

2010-12-01

88

Biogeochemical Indicators of Aquatic Ecosystem Pollution by Heavy Metals  

Microsoft Academic Search

The present-day environmental state of some artificial (Irkutsk, Bratsk, and Novosibirsk reservoirs) and natural (lakes in Altai Territory and Yamal-Nenets Autonomous Okrug and the Tom River) water bodies in Western and Eastern Siberia was evaluated using biogeochemical indicators. The biogeochemical approach is presented as the best for establishing zones of risk and environmental disaster, since biogeochemical cycles play important role

G. A. Leonova

2004-01-01

89

Plankton Functional Types in a New Generation of Biogeochemical Models  

Microsoft Academic Search

Integration of Plankton Abundance Data for the Evaluation of Marine Biogeochemical Models; Cambridge, United Kingdom, 1-3 October 2008; It has long been recognized that biological activity has a large influence on biogeochemical cycles in the ocean. However, the recognition that the ecosystem composition may also be significant is more recent. The newest generation of biogeochemical models used to study climate-ocean

Corinne Le Quéré; Stéphane Pesant

2009-01-01

90

Temporal dynamics of biogeochemical processes at the Norman Landfill site  

USGS Publications Warehouse

The temporal variability observed in redox sensitive species in groundwater can be attributed to coupled hydrological, geochemical, and microbial processes. These controlling processes are typically nonstationary, and distributed across various time scales. Therefore, the purpose of this study is to investigate biogeochemical data sets from a municipal landfill site to identify the dominant modes of variation and determine the physical controls that become significant at different time scales. Data on hydraulic head, specific conductance, ?2H, chloride, sulfate, nitrate, and nonvolatile dissolved organic carbon were collected between 1998 and 2000 at three wells at the Norman Landfill site in Norman, OK. Wavelet analysis on this geochemical data set indicates that variations in concentrations of reactive and conservative solutes are strongly coupled to hydrologic variability (water table elevation and precipitation) at 8 month scales, and to individual eco-hydrogeologic framework (such as seasonality of vegetation, surface-groundwater dynamics) at 16 month scales. Apart from hydrologic variations, temporal variability in sulfate concentrations can be associated with different sources (FeS cycling, recharge events) and sinks (uptake by vegetation) depending on the well location and proximity to the leachate plume. Results suggest that nitrate concentrations show multiscale behavior across temporal scales for different well locations, and dominant variability in dissolved organic carbon for a closed municipal landfill can be larger than 2 years due to its decomposition and changing content. A conceptual framework that explains the variability in chemical concentrations at different time scales as a function of hydrologic processes, site-specific interactions, and/or coupled biogeochemical effects is also presented.

Arora, Bhavna; Mohanty, Binayak P.; McGuire, Jennifer T.; Cozzarelli, Isabelle M.

2013-01-01

91

Temporal dynamics of biogeochemical processes at the Norman Landfill site  

NASA Astrophysics Data System (ADS)

The temporal variability observed in redox sensitive species in groundwater can be attributed to coupled hydrological, geochemical, and microbial processes. These controlling processes are typically nonstationary, and distributed across various time scales. Therefore, the purpose of this study is to investigate biogeochemical data sets from a municipal landfill site to identify the dominant modes of variation and determine the physical controls that become significant at different time scales. Data on hydraulic head, specific conductance, ?2H, chloride, sulfate, nitrate, and nonvolatile dissolved organic carbon were collected between 1998 and 2000 at three wells at the Norman Landfill site in Norman, OK. Wavelet analysis on this geochemical data set indicates that variations in concentrations of reactive and conservative solutes are strongly coupled to hydrologic variability (water table elevation and precipitation) at 8 month scales, and to individual eco-hydrogeologic framework (such as seasonality of vegetation, surface-groundwater dynamics) at 16 month scales. Apart from hydrologic variations, temporal variability in sulfate concentrations can be associated with different sources (FeS cycling, recharge events) and sinks (uptake by vegetation) depending on the well location and proximity to the leachate plume. Results suggest that nitrate concentrations show multiscale behavior across temporal scales for different well locations, and dominant variability in dissolved organic carbon for a closed municipal landfill can be larger than 2 years due to its decomposition and changing content. A conceptual framework that explains the variability in chemical concentrations at different time scales as a function of hydrologic processes, site-specific interactions, and/or coupled biogeochemical effects is also presented.

Arora, Bhavna; Mohanty, Binayak P.; McGuire, Jennifer T.; Cozzarelli, Isabelle M.

2013-10-01

92

Biogeochemical tracers of the marine cyanobacterium Trichodesmium  

Microsoft Academic Search

We examined the utility of several biogeochemical tracers for following the fate of the planktonic diazotrophic cyanobacterium Trichodesmium in the sea. The presence of a (CIO) fatty acid previously reported was observed in a culture of Trichodesmium but was not found in natural samples. This cyanobacterium had high concentrations of C14 and C16 acids, with lesser amounts of several saturated

Edward J. Carpenter; H. Rodger Harvey; Brian Fry; Douglas G. Capone

1997-01-01

93

The interaction between biogeophysical and biogeochemical processes and their feedback on permafrost soil carbon stocks  

NASA Astrophysics Data System (ADS)

Our current understanding of the full suite of processes and their responses to recent warming in terrestrial high-latitudes are far from complete. While continued research on development of more detailed Earth system models (ESMs) is essential to understand the interactions and feedbacks between vegetation, soils and climate change in the Northern high latitudes (NHL), one of the major challenges is the treatment of the biophysical and biogeochemical processes and feedback in the ESM and their impact on soil organic carbon. We used a land surface model, the Integrated Science Assessment Model (ISAM), which coupled carbon-nitrogen biogeochemical and energy and hydrology biogeophysical processes, to investigate the effects of feedbacks between the biogeochemical and biogeophysical processes on the model estimated soil organic carbon (SOC) for the NHL permafrost region. We not only focused on recent improvement in the ISAM biogeophysical processes that are deemed important for the high latitude soils/snow; such as deep soil column, modulation of soil thermal and hydrological properties, wind compaction of snow, and depth hoar formation; on permafrost SOC, but also biogeochemical processes; such as dynamic phenology and root distribution, litter carbon decomposition rates and nitrogen amount remaining; on soil biogeochemistry. We selected multiple sites representative of different high latitude biomes to calibrate and evaluate the model. We then carried out several ISAM model simulations to study the effects of feedbacks between biogeochemical and biogeophysical processes on SOC. Our model analysis shows that including the biogeophysical processes alone could increase modeled Northern high-latitude permafrost carbon by about 30% compared to measurements. Accounting for the biogeochmical processes further improve the NHL soil carbon. This study demonstrates that improvements in biogeophysical or biogeochemical processes alone does not help to improve the modeled SOC, instead we emphasis on the importance of biogeophysical and biophysical processes and feedbacks between them in modeling permafrost carbon stocks.

ElMasri, B.; Barman, R.; Jain, A. K.

2013-12-01

94

Coastal-zone biogeochemical dynamics under global warming  

SciTech Connect

The coastal zone, consisting of the continental shelves to a depth of 200 meters, including bays, lagoons, estuaries, and near-shore banks, is an environment that is strongly affected by its biogeochemical and physical interactions with reservoirs in the adjacent domains of land, atmosphere, open ocean, and marine sediments. Because the coastal zone is smaller in volume and area coverage relative to the open ocean, it traditionally has been studied as an integral part of the global oceans. In this paper, the authors show by numerical modeling that it is important to consider the coastal zone as an entity separate from the open ocean in any assessment of future Earth-system response under human perturbation. Model analyses for the early part of the 21st century suggest that the coastal zone plays a significant modifying role in the biogeochemical dynamics of the carbon cycle and the nutrient cycles coupled to it. This role is manifested in changes in primary production, storage, and/or export of organic matter, its remineralization, and calcium carbonate precipitation--all of which determine the state of the coastal zone with respect to exchange of CO{sub 2} with the atmosphere. Under a scenario of future reduced or complete cessation of the thermohaline circulation (THC) of the global oceans, coastal waters become an important sink for atmospheric CO{sub 2}, as opposed to the conditions in the past and present, when coastal waters are believed to be a source of CO{sub 2} to the atmosphere. Profound changes in coastal-zone primary productivity underscore the important role of phosphorus as a limiting nutrient. In addition, calculations indicate that the saturation state of coastal waters with respect to carbonate minerals will decline by {approximately}15% by the year 2030. Any future slowdown in the THC of the oceans will increase slightly the rate of decline in saturation state.

Mackenzie, F.T.; Ver, L.M.; Lerman, A.

2000-03-01

95

Apparatus for Cold, Pressurized Biogeochemical Experiments  

NASA Technical Reports Server (NTRS)

A laboratory apparatus has been devised as a means of studying plausible biogeochemical reactions under high-pressure, low-temperature aqueous, anaerobic conditions like those conjectured to prevail in a liquid water ocean on Europa (the fourth largest moon of the planet Jupiter). The experiments to be performed by use of this apparatus are intended to enhance understanding of how life (if any) could originate and evolve in the Europa ocean environment. Inasmuch as terrestrial barophilic, psychrophilic organisms that thrive under anaerobic conditions are used in the experiments, the experiments may also contribute to terrestrial biogeochemistry. The apparatus (see figure) includes a bolt-closure reaction vessel secured inside a refrigerator that maintains a temperature of 4 C. Pressurized water is supplied to the interior of the vessel by a hydrostatic pump, which is attached to the vessel via high-pressure fittings. The terrestrial organisms used in the experiments thus far have been several facultative barophilic, psychrophilic stains of Shewanella bacteria. In the experiments, these organisms have been tested for reduction of ferric ion by growing them in the presence of a ferric food source under optimized terrestrial conditions. The short-term goal of these experiments has been to select Shewanella strains that exhibit iron-reduction capability and test their ability to facilitate biogeochemical reduction of iron under temperature and pressure conditions imitating those in Europa s ocean. It is anticipated, that, once growth under Europa-like conditions has been achieved, the selected Shewanella strains will be used to facilitate biogeochemical reactions of sulfate and carbonate with hydrogen gas. Any disequilibrium of the products with the environment would be interpreted as signifying biogenic activity and the possibility of life in Europa s ocean.

Amashukeli, Xenia; Pappalardo, Robert T.; Connon, Stephanie A.; Gleeson, Damhnait F.

2010-01-01

96

Monterey Bay Time Series Biogeochemical Data  

NSDL National Science Digital Library

This dataset includes a broad suite of biogeochemical measurements, particularly dissolvable iron. The measurements span the time period from August 1998 to December 2004 and were taken at the most inshore station of a set of three which are maintained by the Monterey Bay Aquarium Research Institute (MBARI). The data show a large pulse of dissolvable iron consistently occurring during the first spring upwelling event of each year that is derived from resuspended sediment. Iron concentrations then drop rapidly at all three stations. During the summer months, only the most inshore station (C1) maintains iron concentrations in excess of nitrate.

97

Modelling physical and biogeochemical state of the Mediterranean Sea under contemporary and future climate  

NASA Astrophysics Data System (ADS)

A validated 3D coupled transport-biogeochemical model is used to assess the impact of future climatic and management scenarios on biogeochemical and ecological properties of the Mediterranean Sea. Results are discussed in term of temporal and spatial distribution of parameters and indicators related to the carbonate system and the cycles of carbon and inorganic nutrients through dissolved and particulate phases, as simulated by a multi nutrient multi plankton numerical model under current and future conditions. Simulations span the period 2000-2040 and are performed by forcing a three-dimensional off-line coupled eco-hydrodynamical model (BFM and OPA-tracer model, http://bfm-community.eu/) with marine circulation fields produced by ad hoc implementation of the NEMO modelling system and with river input of nutrient and freshwater computed in recent European fp7 projects. The model properly describes available experimental information on contemporary seasonal dynamic and spatial distribution at the basin and sub-basin scale of major biogeochemical parameters, as well as primary production and carbon fluxes at the air-ocean interface. Model projections suggest that future Mediterranean sea will be globally warmer, more productive, and more acidic, but with significant space variability. The relative importance of different biotic and abiotic parameters in defining such a change is explored through several numerical experiments. Potential implications in terms of ecological and higher trophic level organisms dynamics are explored as well, by integrating niche properties of selected organisms and suggestions provided by food web models.

Solidoro, Cosimo; Lazzari, Paolo; Cossarini, Gianpiero; Melaku Canu, Donata; Lovato, Tomas; Vichi, Marcello

2014-05-01

98

Reanalysis of biogeochemical properties in the Mediterranean Sea  

NASA Astrophysics Data System (ADS)

In the 3D variational (3DVAR) assimilation approach the error covariance matrix can be decomposed in a series of operators. The decomposition makes the 3DVAR particularly suitable for marine biogeochemistry data assimilation, because of the reduced computational costs of the method and its modularity, which allows to define the covariance among the biogeochemical variables in a specific operator. In the present work, the results of 3DVAR assimilation of surface chlorophyll concentration in a multi-annual simulation of the Mediterranean Sea biogeochemistry are presented. The assimilated chlorophyll concentrations are obtained from satellite observations (Volpe et al. 2012). The multi-annual simulation is carried out using the OPATM-BFM model (Lazzari et al. 2012), which describes the low trophic web dynamics and is offline coupled with the MFS physical model (Oddo et al. 2009). In the OPATM-BFM four types of phytoplankton are simulated in terms of their content in carbon, nitrogen, phosphorous, silicon and chlorophyll. In the 3DVAR the error covariance matrix has been decomposed in three different operators, which account for the vertical, the horizontal and the biogeochemical covariance (Teruzzi et al. 2014). The biogeochemical operator propagates the result of the assimilation to the OPATM-BFM variables, providing innovation for the components of the four phytoplankton types. The biogeochemical covariance has been designed supposing that the assimilation preserves the physiological status and the relative abundances of phytoplankton types. Practically, the assimilation preserves the internal quotas of the components for each phytoplankton as long as the optimal growth rate condition are maintained. The quotas preservation is not applied when the phytoplankton is in severe declining growth phase, and the correction provided by the assimilation is set equal to zero. Moreover, the relative abundances among the phytoplankton functional types are preserved. The 3DVAR has been applied to the Mediterranean Sea for the period 1999-2010 with weekly assimilation. The results of the multi-annual run show that the assimilation improves the model skill in terms of a better representation of the mean chlorophyll concentrations over the Mediterranean Sea sub-regions and also in terms of spatial and temporal definition of local bloom events. Furthermore, the comparison with nutrients climatology based on in situ measurements show that the non assimilated variables are consistent with observations. The application of the 3DVAR revealed that in specific cases the correction introduced by the assimilation is not maintained by the model dynamics. In these cases, the satellite observations are characterized by local patchy bloom events, which are not well captured by the model. It has been observed that, since the bloom events are strongly affected by the vertical mixing dynamics, which support nutrients to the surface layer, a possible source of error are the mixing conditions provided by the physical model. Oddo et al. 2009. Ocean Science, 5(4), 461-473, doi:10.5194/os-5-461-2009. Lazzari et al. 2012. Biogeosciences, 9(1), 217-233, doi:10.5194/bg-9-217-2012. Teruzzi et al. 2014. Journal of Geophysical Research, 119, 1-18, doi:10.1002/2013JC009277. Volpe et al. 2012. Ocean Science Discussions, 9(2), 1349-1385, doi:10.5194/osd-9-1349-2012.

Cossarini, Gianpiero; Teruzzi, Anna; Salon, Stefano; Solidoro, Cosimo

2014-05-01

99

Biogeochemical Cycles of Carbon and Sulfur  

NASA Technical Reports Server (NTRS)

The elements carbon (C) and sulfur (S) interact with each other across a network of elemental reservoirs that are interconnected by an array of physical, chemical and biological processes. These networks are termed the biogeochemical C and S cycles. The compounds of C are highly important, not only as organic matter, but also as atmospheric greenhouse gases, pH buffers in seawater, oxidation-reduction buffers virtually everywhere, and key magmatic constituents affecting plutonism and volcanism. The element S assumes important roles as an oxidation-reduction partner with C and Fe in biological systems, as a key constituent in magmas and volcanic gases, and as a major influence upon pH in certain environments. This presentation describes the modern biogeochemical C and S cycles. Measurements are described whereby stable isotopes can help to infer the nature and quantitative significance of biological and geological processes involved in the C and S cycles. This lecture also summarizes the geological and climatologic aspects of the ancient C and S cycles, as well as the planetary and extraterrestrial processes that influenced their evolution over millions to billions of years.

DesMarais, David J.; DeVincenzi, D. (Technical Monitor)

2002-01-01

100

Global Biology Research Program: Biogeochemical Processes in Wetlands  

NASA Technical Reports Server (NTRS)

The results of a workshop examining potential NASA contributions to research on wetland processes as they relate to global biogeochemical cycles are summarized. A wetlands data base utilizing remotely sensed inventories, studies of wetland/atmosphere exchange processes, and the extrapolation of local measurements to global biogeochemical cycling processes were identified as possible areas for NASA support.

Bartlett, D. S. (editor)

1984-01-01

101

Community plans for future of ocean biogeochemical research  

Microsoft Academic Search

Members of the biogeochemical research community are taking steps to keep their work thriving in the next millennium. Since 1984, major questions in ocean biogeochemical research have been studied in a concerted manner in the Joint Global Ocean Flux Study (JGOFS) program. This effort as well as the World Ocean Circulation Experiment (WOCE) and Global Ocean Ecosystem Dynamics program (GOED)

James W. Murray; Gustav-Adolf Paffenhofer

1998-01-01

102

Biogeochemical Filtering of Solute Signals Explored as a Function of Transport and Reaction Time Scales  

NASA Astrophysics Data System (ADS)

Catchment biogeochemical responses are the result of superposition of diverse dynamic components, which can be related to climate forcing, water flow, and biogeochemical reactions. The interactions among these components are highly non-linear and contribute to the generation of emergent patterns at multiple spatial and temporal scales. The aim of this work is to explore the following biogeochemical signatures arising from such interactions: (1) the relationship between contaminant loads (L) and discharge (Q) at the annual timescale, leading to an apparent chemostatic relationship (i.e., linear L-Q plots) for different contaminants and at different spatial scales; (2) spatial patterns in the slope and the scatter of the L-Q relationships; and (3) correlation between the intra-annual flow duration curves (FDC) and the load duration curves (LDC). Exploring this relationship necessitates the use of a parsimonious model, with few spatially uniform time constants, that can generate synthetic time series of load and flow at the outlet of river basins. The Mass Response Functions (MRF) approach (Rinaldo et al., 2006), lends itself suitable for the purpose since it relies on the assumption that the evolution of solute concentration in the water pulses depends only on the residence time, and not on its trajectory - thus space is replaced by time. The model simulates the episodic delivery of water and contaminant pulses from the hillslopes to the stream network in response to temporally random but spatially uniform effective rainfall patterns. The domain is described by an immobile source zone in which first order biogeochemical reactions (degradation rate constant ke) alter the solute mass, while multiple mobile rainfall pulses exchange mass with the source zone following linear kinetics (mass transfer rate constant ?). The biogeochemical module of MRF, that was originally written to simulate non-reactive tracer and nitrate transport, was modified to include the more complex biogeochemistry of pesticides. We calibrated and validated the model against nitrate and atrazine data collected in the Little Vermillion River basin (~400 km2; Illinois, IN). Comparison with data showed an excellent agreement of the model outputs with the observed hydrographs and chemographs. The model was then used to explore the effect of time constants on biogeochemical signatures. Four time constants were used to characterize the coupling of hydrologic and biogeochemical processes considered in the model: 1) mean rainfall frequency; 2) mean residence time; 3) mass-transfer rate constant; 4) degradation rate constant. The effect of the four temporal constants on the hillslope biogeochemical response was explored through a sesnsitivity analyses. We hypothesize that a single dimensionless number, a combination of all four temporal constants, could explain the observed patterns. Because this dimensionless number embeds all of the relevant time scales, relative significance of the hydrologic and biogeochemical processes can be examined.

Zanardo, S.; Basu, N. B.; Rao, P. C.

2009-12-01

103

Oceanographic and Biogeochemical Insights from Diatom Genomes  

NASA Astrophysics Data System (ADS)

Diatoms are the most successful group of eukaryotic phytoplankton in the modern ocean and have risen to dominance relatively quickly over the last 100 million years. Recently completed whole genome sequences from two species of diatom, Thalassiosira pseudonana and Phaeodactylum tricornutum, have revealed a wealth of information about the evolutionary origins and metabolic adaptations that have led to their ecological success. A major finding is that they have incorporated genes both from their endosymbiotic ancestors and by horizontal gene transfer from marine bacteria. This unique melting pot of genes encodes novel capacities for metabolic management, for example, allowing the integration of a urea cycle into a photosynthetic cell. In this review we show how genome-enabled approaches are being leveraged to explore major phenomena of oceanographic and biogeochemical relevance, such as nutrient assimilation and life histories in diatoms. We also discuss how diatoms may be affected by climate change-induced alterations in ocean processes.

Bowler, Chris; Vardi, Assaf; Allen, Andrew E.

2010-01-01

104

Biogeochemical cycling in the Strait of Georgia.  

PubMed

The papers in this special issue present the results of a five-year project to study sedimentary biogeochemical processes in the Strait of Georgia, with special emphasis on the near-field of a large municipal outfall. Included in this special issue are overviews of the sedimentology, benthic biology, status of siliceous sponge reefs and distribution of organic carbon in the water column. Other papers address the cycling of contaminants (PCBs, PBDEs) and redox metals in the sediment, a method to map the extent of the influence of municipal effluent from staining on benthic bivalves, and the relationships among geochemical conditions and benthic abundance and diversity. The latter set of papers addresses the role of municipal effluent as a pathway of organic carbon and other contaminants into the Strait of Georgia and the effect of the effluent on benthic geochemistry and biology. PMID:19022498

Johannessen, S C; Macdonald, R W; Burd, B; van Roodselaar, A

2008-12-01

105

An Integrated Biogeochemical and Biophysical Analysis of Bioenergy Crops  

NASA Astrophysics Data System (ADS)

Bioenergy crops are becoming increasingly important with growing concerns about the energy demand and climate change and the need to replace fossil fuels with carbon-neutral renewable sources of energy. The transition to a biofuel-based energy supply raises many questions such as: how and where to grow energy crops, what will be the impacts of growing large scale biofuel crops on climate system, the hydrological cycle and soil biogeochemistry. We are developing and applying an integrated system modeling framework to investigate the biophysical, physiological, and biogeochemical systems governing important processes that regulate crop growth such as water, energy and nutrient cycles. The framework has a two-big-leaf canopy scheme for photosynthesis, stomatal conductance, leaf temperature and energy fluxes. The soil/snow hydrology consists of 10 layers for soil and up to 5 layers for snow. The biogeochemistry component explicitly accounts for coupled carbon and nitrogen dynamics. The feedstocks currently considered include corn stover, Miscanthus and switchgrass. The parameters used for simulation of each crop have been calibrated using field experimental data from the US. The use of this modeling capability will be demonstrated through its applications to study the environmental effects (through changes in albedo and evapotranspiration) of biofuel production as well as the effective management practice in the United States.

Liang, M.; Song, Y.; Barman, R.; Jain, A. K.

2010-12-01

106

River restoration: morphological, hydrological, biogeochemical and ecological changes and challenges  

NASA Astrophysics Data System (ADS)

River restoration is essential as a means to enhance river dynamics, environmental heterogeneity and biodiversity. The underlying processes governing the dynamic changes need to be understood thoroughly to ensure that restoration projects meet their goals. In particular, we need to understand quantitatively how hydromorphological variability relates to ecosystem functioning and services, biodiversity and (ground)water quality in restored river corridors. Here, we provide a short overview on the literature and present a study of a restored river corridor in Switzerland combining physical, chemical, and biological observations with modeling. The results show complex spatial patterns of bank infiltration, habitat-type, biotic communities and biogeochemical processes. In particular, we found an increase in taxonomic and functional diversity for earthworms, testate amoebae and bacteria in the restored part of the river. This complexity is driven by river hydrology and morphodynamics, which are in turn actively coupled to riparian vegetation processes. Given this complexity and the multiple constraints on the uses and management of floodplains, a multi-disciplinary approach is needed to monitor the success of restoration measures and to make recommendations for future restoration projects.

Schirmer, M.; Luster, J.; Linde, N.; Perona, P.; Mitchell, E. A. D.; Barry, D. A.; Cirpka, O. A.; Schneider, P.; Vogt, T.; Durisch-Kaiser, E.

2013-08-01

107

A generic biogeochemical module for Earth system models: Next Generation BioGeoChemical Module (NGBGC), version 1.0  

NASA Astrophysics Data System (ADS)

Physical and biogeochemical processes regulate soil carbon dynamics and CO2 flux to and from the atmosphere, influencing global climate changes. Integration of these processes into Earth system models (e.g., community land models (CLMs)), however, currently faces three major challenges: (1) extensive efforts are required to modify modeling structures and to rewrite computer programs to incorporate new or updated processes as new knowledge is being generated, (2) computational cost is prohibitively expensive to simulate biogeochemical processes in land models due to large variations in the rates of biogeochemical processes, and (3) various mathematical representations of biogeochemical processes exist to incorporate different aspects of fundamental mechanisms, but systematic evaluation of the different mathematical representations is difficult, if not impossible. To address these challenges, we propose a new computational framework to easily incorporate physical and biogeochemical processes into land models. The new framework consists of a new biogeochemical module, Next Generation BioGeoChemical Module (NGBGC), version 1.0, with a generic algorithm and reaction database so that new and updated processes can be incorporated into land models without the need to manually set up the ordinary differential equations to be solved numerically. The reaction database consists of processes of nutrient flow through the terrestrial ecosystems in plants, litter, and soil. This framework facilitates effective comparison studies of biogeochemical cycles in an ecosystem using different conceptual models under the same land modeling framework. The approach was first implemented in CLM and benchmarked against simulations from the original CLM-CN code. A case study was then provided to demonstrate the advantages of using the new approach to incorporate a phosphorus cycle into CLM. To our knowledge, the phosphorus-incorporated CLM is a new model that can be used to simulate phosphorus limitation on the productivity of terrestrial ecosystems. The method presented here could in theory be applied to simulate biogeochemical cycles in other Earth system models.

Fang, Y.; Huang, M.; Liu, C.; Li, H.; Leung, L. R.

2013-11-01

108

Hydrological Perturbations Drive Biogeochemical Processes in Experimental Soil Columns from the Norman Landfill Site  

NASA Astrophysics Data System (ADS)

Fate and transport of contaminants in saturated and unsaturated zones is governed by biogeochemical processes that are complex and non-linearly coupled to each other. A fundamental understanding of the interactions between transport and reaction processes is essential to better characterize contaminant movement in the subsurface. The objectives of this study are to: i) develop quantitative relationships between hydrological (initial and boundary conditions, hydraulic conductivity ratio, and soil layering), geochemical (mineralogy, surface area, redox potential, and organic matter) and microbiological factors (MPN) that alter the biogeochemical processes, and ii) characterize the effect of hydrologic perturbations on coupled processes occurring at the column scale. The perturbations correspond to rainfall intensity, duration of wet and dry conditions, and water chemistry (pH). Soils collected from two locations with significantly different geochemistry at the Norman landfill site are used in this study. Controlled flow experiments were conducted on: i) two homogeneous soil columns, ii) a layered soil column, iii) a soil column with embedded clay lenses, and iv) a soil column with embedded clay lenses and one central macropore. Experimental observations showed enhanced biogeochemical activity at the interface of the layered and lensed columns over the texturally homogeneous soil columns. Multivariate statistical analysis showed that the most important processes were microbial reduction of Fe(III) and SO42-, and oxidation of reduced products in the columns. Modeling results from HP1 indicate least redox activity in the homogeneous sand column while the structurally heterogeneous columns utilize oxygen and nitrate from recharge as well as iron sulfide minerals already present in the columns as electron acceptors. Furthermore, the interface of the layered and lensed soil columns acts as a hotspot of biogeochemical activity due to increased transport timescale as a result of reduced hydraulic conductivity of loam and clay in these columns. Although the coupled HP1 model was able to effectively capture redox dynamics in the experimental soil columns, findings suggest the need to incorporate: i) reduction in hydraulic conductivity due to the formation of iron sulfide precipitates, and ii) transport of aqueous iron sulfide clusters observed in all columns except homogeneous sand in such contaminant fate and transport models. Results indicate that textural differences across the layered, lensed, and macropore columns were directly responsible for redox gradient across these interfaces. Also, quantitative relationships observed between pH and total carbon, pe and redox couples, etc. are most significantly affected by wetting and drying cycles of the soil moisture regime for the different soil columns.

Arora, B.; Mohanty, B. P.; McGuire, J. T.

2010-12-01

109

[DNDC model, a model of biogeochemical processes: Research progress and applications].  

PubMed

Denitrification-decomposition (DNDC) model can estimate the emission fluxes of soil trace gases such as carbon dioxide (CO2), methane (CH4) , and nitrous oxide (N2O) via the coupling of the denitrification and decomposition processes driven by soil environmental factors. At present, DNDC model is one of the most successful models in the world in simulating the terrestrial biogeochemical cycles. This paper mainly reviewed the development process of the DNDC model, its structure, model validation, and sensitive factor analysis, and summarized the hot fields in the applications of the model. PMID:23705407

Guo, Jia-Wei; Zou, Yuan-Chun; Huo, Li-Li; Lü, Xian-Guo

2013-02-01

110

Assessment of climate change impacts at the catchment scale with a detailed hydrological model of surface-subsurface interactions and comparison with a land surface model  

NASA Astrophysics Data System (ADS)

A process-based model that incorporates hydrodynamic feedbacks between the land surface, soil, and groundwater zones is used to assess the sensitivity of the hydrological response (river discharge, aquifer recharge, and soil water storage) to future climate conditions. The analysis is based on the Intergovernmental Panel on Climate Change Special Report on Emissions Scenario A2 and the des Anglais catchment in southwestern Quebec (Canada). Application of the coupled hydrological model (CATHY) to the study basin revealed significant spatiotemporal variations in the river discharge response to climate change owing to a different partitioning between the overland runoff and base flow components of the hydrograph, with the latter alleviating the marked decrease in discharge during the summer period. A spatial analysis of recharge patterns shows that the greatest variations are expected to occur, throughout the year, in the southern portion of the catchment, where the elevations are highest. Compared to river discharge and aquifer recharge, the soil water storage volumes are less sensitive to climate changes. From a spatial analysis of soil moisture variations it was possible to observe organizational patterns that follow the topographic and pedologic characteristics of the catchment. In addition to these analyses, we also compare predictions obtained with the land surface scheme (CLASS) that is coupled to the regional climate model (CRCM) to those from the detailed catchment model for past and future climate change projections. An examination of the runoff revealed that CLASS produces higher estimates than CATHY of surface and subsurface runoff throughout the annual cycle for both past and future projections. For soil water storage, the two models are in general agreement in terms of the intra-annual variability of moisture content at shallower soil layers, whereas a larger difference is found for the deepest layer, with CATHY predicting wetter soil conditions over the entire simulation period and moisture fluctuations of much smaller amplitude.

Sulis, M.; Paniconi, C.; Rivard, C.; Harvey, R.; Chaumont, D.

2011-01-01

111

Temporal Scaling of Biogeochemical Reaction Rates  

NASA Astrophysics Data System (ADS)

In at least two disparate areas of organic and inorganic geochemistry---the microbial degradation of detritus and the dissolution of minerals in sediments and soils---apparent rate constants k have been observed to diminish with the "age" t of the substrate like k(t) ~eq a t-b, where a ~eq 0.2 and b ~eq 1.0. Published reports display up to ten orders of magnitude in time [1,2]. Because the accuracy of biogeochemical models typically depends crucially on the specification of such rates, an understanding of this scaling law has important implications for predicting the evolution of biogeochemical cycles, especially the cycles of carbon and oxygen. The power-law decay of rates likely derives from a combination of chemical and physical heterogeneity. In a purely chemical scenario, an intrinsically heterogeneous substrate (e.g., a mixture of organic matter ranging from "labile" to "recalcitrant") is assumed to produce the observed slowdown of k(t). In contrast, a physical model assumes a homogeneous substrate in which rates nevertheless vary microscopically due to spatially varying physical constraints. Here we consider the extreme case of a purely physical origin and test its consistency with observations [3]. We first show how a diffusion-limited reaction-diffusion system leads to a logarithmic decay of the substrate. We then show how the power-law for k(t) derives from this logarithmic decay. We obtain not only the correct exponent b=1 but also a good approximation of the prefactor a. By constructing an extensive database of previously published measurements, we show that observations compare well to predictions. The particular way in which diffusion-limitation manifests itself varies from problem to problem. In the case of detrital decay in sediments, we suggest that rates are limited by contact of substrate with extracellular enzymes [3]. Mechanisms in soils are likely similar. For mineral dissolution is sediments, we suggest that rates are limited by diffusion of reactants from the seafloor. [1] J.~J.~Middelburg, Geochim.~Cosmochim.~Acta 53, 1577 (1989). [2] K.~Maher, D.~J.~DePaolo, J.~C.-F.~Lin, Geochim.~Cosmochim.~Acta 68, 4629. [3] D.~H.~Rothman and D.~C.~Forney, Science 316, 1325 (2004).

Rothman, D. H.; Forney, D. C.

2007-12-01

112

Review Paper/ Biogeochemical Evolution of a Landfill Leachate  

E-print Network

Review Paper/ Biogeochemical Evolution of a Landfill Leachate Plume, Norman, Oklahoma by I the relative recalcitrance of NVDOC to biodegradation, the center of the plume was depleted in sulfate, which

113

Doctoral Defense "Biogeochemical evaluation of disposal options for arsenic-  

E-print Network

Lutgarde Raskin Professor, Civil & Environmental Engineering Arsenic contamination of drinking water of arsenic. Arsenic contamination is particularly severe in Bangladesh and India, where access to landfillsDoctoral Defense "Biogeochemical evaluation of disposal options for arsenic- bearing wastes

Kamat, Vineet R.

114

Climate change effects on watershed hydrological and biogeochemical processes  

EPA Science Inventory

Projected changes in climate are widely expected to alter watershed processes. However, the extent of these changes is difficult to predict because complex interactions among affected hydrological and biogeochemical processes will likely play out over many decades and spatial sc...

115

Terrestrial ecosystems and the global biogeochemical silica cycle  

NASA Astrophysics Data System (ADS)

Most research on the global Si cycle has focused nearly exclusively on weathering or the oceanic Si cycle and has not explored the complexity of the terrestrial biogeochemical cycle. The global biogeochemical Si cycle is of great interest because of its impact on global CO2 concentrations through the combined processes of weathering of silicate minerals and transfer of CO2 from the atmosphere to the lithosphere. A sizable pool of Si is contained as accumulations of amorphous silica, or biogenic silica (BSi), in living tissues of growing plants, known as phytoliths, and, after decomposition of organic material, as remains in the soil. The annual fixation of phytolith silica ranges from 60-200 Tmol yr-1 and rivals that fixed in the oceanic biogeochemical cycle (240 Tmol yr-1). Internal recycling of the phytolith pool is intense with riverine fluxes of dissolved silicate to the oceans buffered by the terrestrial biogeochemical Si cycle, challenging the ability of weathering models to predict rates of weathering and consequently, changes in global climate. Consideration must be given to the influence of the terrestrial BSi pool on variations in the global biogeochemical Si cycle over geologic time and the influence man has had on modifying both the terrestrial and aquatic biogeochemical cycles.

Conley, Daniel J.

2002-12-01

116

Redox chemistry in the phosphorus biogeochemical cycle.  

PubMed

The element phosphorus (P) controls growth in many ecosystems as the limiting nutrient, where it is broadly considered to reside as pentavalent P in phosphate minerals and organic esters. Exceptions to pentavalent P include phosphine--PH3--a trace atmospheric gas, and phosphite and hypophosphite, P anions that have been detected recently in lightning strikes, eutrophic lakes, geothermal springs, and termite hindguts. Reduced oxidation state P compounds include the phosphonates, characterized by C-P bonds, which bear up to 25% of total organic dissolved phosphorus. Reduced P compounds have been considered to be rare; however, the microbial ability to use reduced P compounds as sole P sources is ubiquitous. Here we show that between 10% and 20% of dissolved P bears a redox state of less than +5 in water samples from central Florida, on average, with some samples bearing almost as much reduced P as phosphate. If the quantity of reduced P observed in the water samples from Florida studied here is broadly characteristic of similar environments on the global scale, it accounts well for the concentration of atmospheric phosphine and provides a rationale for the ubiquity of phosphite utilization genes in nature. Phosphine is generated at a quantity consistent with thermodynamic equilibrium established by the disproportionation reaction of reduced P species. Comprising 10-20% of the total dissolved P inventory in Florida environments, reduced P compounds could hence be a critical part of the phosphorus biogeochemical cycle, and in turn may impact global carbon cycling and methanogenesis. PMID:25313061

Pasek, Matthew A; Sampson, Jacqueline M; Atlas, Zachary

2014-10-28

117

Redox chemistry in the phosphorus biogeochemical cycle  

PubMed Central

The element phosphorus (P) controls growth in many ecosystems as the limiting nutrient, where it is broadly considered to reside as pentavalent P in phosphate minerals and organic esters. Exceptions to pentavalent P include phosphine—PH3—a trace atmospheric gas, and phosphite and hypophosphite, P anions that have been detected recently in lightning strikes, eutrophic lakes, geothermal springs, and termite hindguts. Reduced oxidation state P compounds include the phosphonates, characterized by C?P bonds, which bear up to 25% of total organic dissolved phosphorus. Reduced P compounds have been considered to be rare; however, the microbial ability to use reduced P compounds as sole P sources is ubiquitous. Here we show that between 10% and 20% of dissolved P bears a redox state of less than +5 in water samples from central Florida, on average, with some samples bearing almost as much reduced P as phosphate. If the quantity of reduced P observed in the water samples from Florida studied here is broadly characteristic of similar environments on the global scale, it accounts well for the concentration of atmospheric phosphine and provides a rationale for the ubiquity of phosphite utilization genes in nature. Phosphine is generated at a quantity consistent with thermodynamic equilibrium established by the disproportionation reaction of reduced P species. Comprising 10–20% of the total dissolved P inventory in Florida environments, reduced P compounds could hence be a critical part of the phosphorus biogeochemical cycle, and in turn may impact global carbon cycling and methanogenesis. PMID:25313061

Pasek, Matthew A.; Sampson, Jacqueline M.; Atlas, Zachary

2014-01-01

118

Biogeochemical tracers of the marine cyanobacterium Trichodesmium  

NASA Astrophysics Data System (ADS)

We examined the utility of several biogeochemical tracers for following the fate of the planktonic diazotrophic cyanobacterium Trichodesmium in the sea. The presence of a (CIO) fatty acid previously reported was observed in a culture of Trichodesmium but was not found in natural samples. This cyanobacterium had high concentrations of C 14 and C 16 acids, with lesser amounts of several saturated and unsaturated C 18 fatty acids. This composition was similar to that of other marine cyanobacteria. The major hydrocarbon identified was the C 17n-alkane, which was present in all samples from the five stations examined. Sterols common to algae and copepods were observed in many samples along with hopanoids representative of bacteria, suggesting a varied community structure in colonies collected from different stations. We found no unique taxonomic marker of Trichodesmium among the sterols. Measurements of the ? 15N and ? 13C in Trichodesmium samples from the SW Sargasso and NW Caribbean Seas averaged -0.4960 (range from -0.7 to -0.25960) and -12.9%0 (range from -15.2 to -11.9960), respectively, thus confirming previous observations that this cyanobacterial diazotroph has both the lowest ? 15N and highest ? 13C of any marine phytoplankter observed to date. A culture of Trichodesmium grown under diazotrophic conditions had a ? 15N between -1.3 and -3.6960. Our results support the supposition that the relatively low ? 15N and high ? 13C values observed in suspended and sediment-trapped material from some tropical and subtropical seas result from substantial input of C and N by Trichodesmium.

Carpenter, Edward J.; Harvey, H. Rodger; Fry, Brian; Capone, Douglas G.

1997-01-01

119

Restoration of biogeochemical function in mangrove forests  

USGS Publications Warehouse

Forest structure of mangrove restoration sites (6 and 14 years old) at two locations (Henderson Creek [HC] and Windstar [WS]) in southwest Florida differed from that of mixed-basin forests (>50 years old) with which they were once contiguous. However, the younger site (HC) was typical of natural, developing forests, whereas the older site (WS) was less well developed with low structural complexity. More stressful physicochemical conditions resulting from incomplete tidal flushing (elevated salinity) and variable topography (waterlogging) apparently affected plant survival and growth at the WS restoration site. Lower leaf fall and root production rates at the WS restoration site, compared with that at HC were partly attributable to differences in hydroedaphic conditions and structural development. However, leaf and root inputs at each restoration site were not significantly different from that in reference forests within the same physiographic setting. Macrofaunal consumption of tethered leaves also did not differ with site history, but was dramatically higher at HC compared with WS, reflecting local variation in leaf litter processing rates, primarily by snails (Melampus coffeus). Degradation of leaves and roots in mesh bags was slow overall at restoration sites, however, particularly at WS where aerobic decomposition may have been more limited. These findings indicate that local or regional factors such as salinity regime act together with site history to control primary production and turnover rates of organic matter in restoration sites. Species differences in senescent leaf nitrogen content and degradation rates further suggest that restoration sites dominated by Laguncularia racemosa and Rhizophora mangle should exhibit slower recycling of nutrients compared with natural basin forests where Avicennia germinans is more abundant. Structural development and biogeochemical functioning of restored mangrove forests thus depend on a number of factors, but site-specific as well as regional or local differences in hydrology and concomitant factors such as salinity and soil waterlogging will have a strong influence over the outcome of restoration projects.

McKee, K.L.; Faulkner, P.L.

2000-01-01

120

A generic biogeochemical module for earth system models  

NASA Astrophysics Data System (ADS)

Physical and biogeochemical processes regulate soil carbon dynamics and CO2 flux to and from the atmosphere, influencing global climate changes. Integration of these processes into earth system models (e.g. community land models - CLM), however, currently faces three major challenges: (1) extensive efforts are required to modify modeling structures and to rewrite computer programs to incorporate new or updated processes as new knowledge is being generated, (2) computational cost is prohibitively expensive to simulate biogeochemical processes in land models due to large variations in the rates of biogeochemical processes, and (3) various mathematical representations of biogeochemical processes exist to incorporate different aspects of fundamental mechanisms, but systematic evaluation of the different mathematical representations is difficult, if not impossible. To address these challenges, we propose a new computational framework to easily incorporate physical and biogeochemical processes into land models. The new framework consists of a new biogeochemical module with a generic algorithm and reaction database so that new and updated processes can be incorporated into land models without the need to manually set up the ordinary differential equations to be solved numerically. The reaction database consists of processes of nutrient flow through the terrestrial ecosystems in plants, litter and soil. This framework facilitates effective comparison studies of biogeochemical cycles in an ecosystem using different conceptual models under the same land modeling framework. The approach was first implemented in CLM and benchmarked against simulations from the original CLM-CN code. A case study was then provided to demonstrate the advantages of using the new approach to incorporate a phosphorus cycle into the CLM model. To our knowledge, the phosphorus-incorporated CLM is a new model that can be used to simulate phosphorus limitation on the productivity of terrestrial ecosystems.

Fang, Y.; Huang, M.; Liu, C.; Li, H.-Y.; Leung, L. R.

2013-06-01

121

A cost-efficient biogeochemical model for estuaries: a case-study of a funnel-shaped system  

NASA Astrophysics Data System (ADS)

The hydrodynamics exerts an important influence on the biogeochemical functioning of estuarine systems. Comparative studies have long recognized this tight coupling and, for instance, have attempted to correlate key estuarine biogeochemical processes to simple hydrodynamic properties, such as the residence time or the tidal forcing. Yet, these correlations fail to resolve the estuarine spatio-temporal variability and do not provide powerful means to disentangle the complex interplay of multiple reaction and transport processes. In this context, reaction-transport models (RTMs) are useful tools to resolve the variability inherent to the estuarine environment. They ideally complement field observations, because their integrative power provides the required extrapolation means for a system-scale analysis over the entire spectrum of changing forcing conditions, including the long-term response to land-use and climate changes. However, RTM simulations are associated with high computational costs, especially when the biogeochemical dynamics are to be resolved on a regional or global scale. Furthermore, specific data requirements, such as boundary conditions or bathymetric and geometric information may limit their applicability. Here, a generic one-dimensional RTM approach which relies on idealized geometries to support the estuarine physics is used to quantify the biogeochemical dynamics. The model is cost-efficient and requires only a limited number of readily available input data. The approach is applied to a case-study of a funnel-shaped estuary (The Scheldt, BE/NL) and is tested by comparing integrative measures of the estuarine biogeochemical functioning (e.g. Net Ecosystem Metabolism, integrated CO2 fluxes) with those derived from observations (Frankignoulle et al., 1996, 1998) and highly-resolved model simulations (Vanderborght et al., 2002; Arndt et al., 2009). The method provides a robust quantitative tool to carry sensitivity and uncertainty analyses and to investigate the estuarine biogeochemistry at the regional scale.

Volta, Chiara; Arndt, Sandra; Regnier, Pierre

2013-04-01

122

A Generic Biogeochemical Module for Earth System Models: Next Generation BioGeoChemical Module (NGBGC), Version 1.0  

SciTech Connect

Physical and biogeochemical processes regulate soil carbon dynamics and CO2 flux to and from atmosphere, influencing global climate changes. Integration of these processes into earth system models (e.g., community land models (CLM)), however, currently faces three major challenges: 1) extensive efforts are required to modify modeling structures and to rewrite computer programs to incorporate new or updated processes as new knowledge is being generated, 2) computational cost is prohibitively expensive to simulate biogeochemical processes in land models due to large variations in the rates of biogeochemical processes, and 3) various mathematical representations of biogeochemical processes exist to incorporate different aspects of fundamental mechanisms, but systematic evaluation of the different mathematical representations is difficult, if not possible. To address these challenges, we propose a new computational framework to easily incorporate physical and biogeochemical processes into land models. The new framework consists of a new biogeochemical module with a generic algorithm and reaction database so that new and updated processes can be incorporated into land models without the need to manually set up the ordinary differential equations to be solved numerically. The reaction database consists of processes of nutrient flow through the terrestrial ecosystems in plants, litter and soil. This framework facilitates effective comparison studies of biogeochemical cycles in an ecosystem using different conceptual models under the same land modeling framework. The approach was first implemented in CLM and benchmarked against simulations from the original CLM-CN code. A case study was then provided to demonstrate the advantages of using the new approach to incorporate a phosphorus cycle into the CLM model. To our knowledge, the phosphorus-incorporated CLM is a new model that can be used to simulate phosphorus limitation on the productivity of terrestrial ecosystems.

Fang, Yilin; Huang, Maoyi; Liu, Chongxuan; Li, Hongyi; Leung, Lai-Yung R.

2013-11-13

123

Biogeochemical drivers of phosphatase activity in salt marsh sediments  

NASA Astrophysics Data System (ADS)

Although nitrogen has become a major concern for wetlands scientists dealing with eutrophication problems, phosphorous represents another key element, and consequently its biogeochemical cycling has a crucial role in eutrophication processes. Microbial communities are a central component in trophic dynamics and biogeochemical processes on coastal systems, since most of the processes in sediments are microbial-mediated due to enzymatic action, including the mineralization of organic phosphorus carried out by acid phosphatase activity. In the present work, the authors investigate the biogeochemical sediment drivers that control phosphatase activities. Authors also aim to assess biogeochemical factors' influence on the enzyme-mediated phosphorous cycling processes in salt marshes. Plant rhizosediments and bare sediments were collected and biogeochemical features, including phosphatase activities, inorganic and organic phosphorus contents, humic acids content and pH, were assessed. Acid phosphatase was found to give the highest contribution for total phosphatase activity among the three pH-isoforms present in salt marsh sediments, favored by acid pH in colonized sediments. Humic acids also appear to have an important role inhibiting phosphatase activity. A clear relation of phosphatase activity and inorganic phosphorous was also found. The data presented reinforces the role of phosphatase in phosphorous cycling.

Freitas, Joana; Duarte, Bernardo; Caçador, Isabel

2014-10-01

124

Europa: Geological activity and surface - subsurface exchange  

NASA Astrophysics Data System (ADS)

Jupiter's moon Europa has a geologically young surface, allowing the possibility of current, ongoing geological activity. We are searching the Galileo database for overlapping images taken during the 5-year mission, and are comparing images using an iterative coregistration technique to look for changes due to geological activity. We will also discuss methods by which such activity could occur on Europa. We are particularly interested in the ability of geological processes to bring surface material down into the subsurface, and to bring subsurface material up to the surface. We are continuing a survey of such processes, including endogenic tectonic and cryovolcanic activity, and exogenic processes such as gardening and impact cratering.

Phillips, C. B.; Cowell, W.

2005-12-01

125

Oceanic ventilation and biogeochemical cycling: Understanding the physical mechanisms that produce realistic distributions of tracers and  

E-print Network

Oceanic ventilation and biogeochemical cycling: Understanding the physical mechanisms that produce circulation support different rates of ventilation, which in turn produce different distributions. Matsumoto, J. L. Sarmiento, R. D. Slater, and P. S. Swathi (2004), Oceanic ventilation and biogeochemical

Matsumoto, Katsumi

126

Coupled assimilation for an intermediated coupled ENSO prediction model  

NASA Astrophysics Data System (ADS)

The value of coupled assimilation is discussed using an intermediate coupled model in which the wind stress is the only atmospheric state which is slavery to model sea surface temperature (SST). In the coupled assimilation analysis, based on the coupled wind-ocean state covariance calculated from the coupled state ensemble, the ocean state is adjusted by assimilating wind data using the ensemble Kalman filter. As revealed by a series of assimilation experiments using simulated observations, the coupled assimilation of wind observations yields better results than the assimilation of SST observations. Specifically, the coupled assimilation of wind observations can help to improve the accuracy of the surface and subsurface currents because the correlation between the wind and ocean currents is stronger than that between SST and ocean currents in the equatorial Pacific. Thus, the coupled assimilation of wind data can decrease the initial condition errors in the surface/subsurface currents that can significantly contribute to SST forecast errors. The value of the coupled assimilation of wind observations is further demonstrated by comparing the prediction skills of three 12-year (1997-2008) hindcast experiments initialized by the ocean-only assimilation scheme that assimilates SST observations, the coupled assimilation scheme that assimilates wind observations, and a nudging scheme that nudges the observed wind stress data, respectively. The prediction skills of two assimilation schemes are significantly better than those of the nudging scheme. The prediction skills of assimilating wind observations are better than assimilating SST observations. Assimilating wind observations for the 2007/2008 La Niña event triggers better predictions, while assimilating SST observations fails to provide an early warning for that event.

Zheng, Fei; Zhu, Jiang

2010-10-01

127

Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico  

NASA Astrophysics Data System (ADS)

A three-dimensional coupled physical-biogeochemical model is applied to simulate and examine temporal and spatial variability of circulation and biogeochemical cycling in the Gulf of Mexico (GoM). The model is driven by realistic atmospheric forcing, open boundary conditions from a data assimilative global ocean circulation model, and observed freshwater and terrestrial nitrogen input from major rivers. A 7 yr model hindcast (2004-2010) was performed, and validated against satellite observed sea surface height, surface chlorophyll, and in situ observations including coastal sea level, ocean temperature, salinity, and dissolved inorganic nitrogen (DIN) concentration. The model hindcast revealed clear seasonality in DIN, phytoplankton and zooplankton distributions in the GoM. An empirical orthogonal function analysis indicated a phase-locked pattern among DIN, phytoplankton and zooplankton concentrations. The GoM shelf nitrogen budget was also quantified, revealing that on an annual basis the DIN input is largely balanced by the removal through denitrification (an equivalent of ~ 80% of DIN input) and offshore exports to the deep ocean (an equivalent of ~ 17% of DIN input).

Xue, Z.; He, R.; Fennel, K.; Cai, W.-J.; Lohrenz, S.; Hopkinson, C.

2013-11-01

128

Hyporheic transport and biogeochemical reactions in pool-riffle systems under varying ambient groundwater flow conditions  

NASA Astrophysics Data System (ADS)

the interface between stream water, groundwater, and the hyporheic zone (HZ), important biogeochemical processes that play a crucial role in fluvial ecology occur. Solutes that infiltrate into the HZ can react with each other and possibly also with upwelling solutes from the groundwater. In this study, we systematically evaluate how variations of gaining and losing conditions, stream discharge, and pool-riffle morphology affect aerobic respiration (AR) and denitrification (DN) in the HZ. For this purpose, a computational fluid dynamics model of stream water flow is coupled to a reactive transport model. Scenarios of variations of the solute concentration in the upwelling groundwater were conducted. Our results show that solute influx, residence time, and the size of reactive zones strongly depend on presence, magnitude, and direction of ambient groundwater flow. High magnitudes of ambient groundwater flow lower AR efficiency by up to 4 times and DN by up to 3 orders of magnitude, compared to neutral conditions. The influence of stream discharge and morphology on the efficiency of AR and DN are minor, in comparison to that of ambient groundwater flow. Different scenarios of O2 and NO3 concentrations in the upwelling groundwater reveal that DN efficiency of the HZ is highest under low upwelling magnitudes accompanied with low concentrations of O2 and NO3. Our results demonstrate how ambient groundwater flow influences solute transport, AR, and DN in the HZ. Neglecting groundwater flow in stream-groundwater interactions would lead to a significant overestimation of the efficiency of biogeochemical reactions in fluvial systems.

Trauth, Nico; Schmidt, Christian; Vieweg, Michael; Maier, Uli; Fleckenstein, Jan H.

2014-05-01

129

Modeling carbon cycle responses to tree mortality: linking microbial and biogeochemical changes  

NASA Astrophysics Data System (ADS)

Amid a worldwide increase in tree mortality, mountain pine beetles (Dendroctonus ponderosae Hopkins) have killed billions of trees from Mexico to Alaska in the last 13 years. This mortality is predicted to influence important carbon, water and energy balance feedbacks on the Earth system. We studied changes in soil biogeochemical cycling and microbial community structure after tree mortality. We show, using a decade long chronosequence, that tree mortality causes no increase in total respiration from local to watershed scales, with corresponding changes in biogeochemical pools of nitrogen and phosphorus. We also found comparable declines in both gross primary productivity and respiration suggesting little change in net flux. We tested the mechanisms controlling these patterns using an ecosystem model; contrasting a simplified microbial subroutine with a 'dead soil' model. We coupled our modeling work with direct measurements of microbial biomass, enzyme kinetics and community structure. The transitory recovery of respiration 6-7 years after mortality was associated with increased microbial biomass, increased incorporation of leaf litter carbon into soil organic matter, and was followed by a secondary decline in respiration during years 8-10. Our findings are consistent with the mechanism of reduced input of new carbon causing a decline in microbial biomass rather than an increased output of older carbon.

Moore, D. J.; Trahan, N. A.; Dynes, E. L.; Zobitz, J. M.; Gallery, R.

2013-12-01

130

PHOTOREACTIONS IN SURFACE WATERS AND THEIR ROLE IN BIOGEOCHEMICAL CYCLES  

EPA Science Inventory

During the past decade significant interest has developed in the influence of photochemical reactions on biogeochemical cycles in surface waters of lakes and the sea. A major portion of recent research on these photoreactions has focused on the colored component of dissolved org...

131

The identification and biogeochemical interpretation of fossil magnetotactic bacteria  

E-print Network

The identification and biogeochemical interpretation of fossil magnetotactic bacteria Robert E. Available online 14 August 2007. Abstract Magnetotactic bacteria, which most commonly live within the oxic, specifically magnetite or greigite. The crystals cause the bacteria to orient themselves passively with respect

132

Watershed Management and Mercury Biogeochemical Cycling in Lake Zapotlan, Mexico  

Microsoft Academic Search

Lake Zapotlan is an endorheic subtropical eutrophic lake located in Jalisco State, Mexico. The lake supports a small but important local fishery for carp (Cyprinus sp.) and tilapia (Oreochromis sp.) and is an internationally recognized RAMSAR site. Very little research exists in these regions regarding mercury biogeochemical cycling. The lake receives considerable untreated municipal wastewater discharge that is elevated in

E. A. Malczyk; B. A. Branfireun

2009-01-01

133

The role of phytoplankton photosynthesis in global biogeochemical cycles  

Microsoft Academic Search

Phytoplankton biomass in the world's oceans amounts to only ?1–2% of the total global plant carbon, yet these organisms fix between 30 and 50 billion metric tons of carbon annually, which is about 40% of the total. On geological time scales there is profound evidence of the importance of phytoplankton photosynthesis in biogeochemical cycles. It is generally assumed that present

Paul G. Falkowski

1994-01-01

134

Biogeochemical Changes Accompanying Woody Plant Encroachment in a Subtropical Savanna  

Microsoft Academic Search

Ecosystem properties of surficial (0-10 cm) soils in remnant herbaceous patches were compared to those of contrasting woody plant patch types (upland discrete cluster, upland grove, and lowland woodland) where shifting land cover is known to have occurred over the past 50-77 yr. The purpose of this study was to evaluate and quantify the biogeochemical consequences and subsequent developmental rates

K. A. Hibbard; S. Archer; D. S. Schimel; D. W. Valentine

2001-01-01

135

EFFECTS OF INCREASED SOLAR ULTRAVIOLET RADIATION ON BIOGEOCHEMICAL CYCLES  

EPA Science Inventory

Increases in solar UV radiation could affect terrestrial and aquatic biogeochemical cycles thus altering both sources and sinks of greenhouse and chemically important trace gases (e.g., carbon dioxide (CO2), carbon monoxide (CO), carbonyl sulfide (COS)). n terrestrial ecosystems,...

136

Biogeochemical Controls and Feedbacks on Ocean Primary Production  

Microsoft Academic Search

Changes in oceanic primary production, linked to changes in the network of global biogeochemical cycles, have profoundly influenced the geochemistry of Earth for over 3 billion years. In the contemporary ocean, photosynthetic carbon fixation by marine phytoplankton leads to formation of ;45 gigatons of organic carbon per annum, of which 16 gigatons are ex- ported to the ocean interior. Changes

Paul G. Falkowski; Richard T. Barber; Victor Smetacek

1998-01-01

137

Physical Ecosystem Engineers as Agents of Biogeochemical Heterogeneity  

NSDL National Science Digital Library

This peer-reviewed article form BioScience is about organisms that act as agents of biogeochemical heterogeneity. Physical ecosystem engineers are organisms that physically modify the abiotic environment. They can affect biogeochemical processing by changing the availability of resources for microbes (e.g., carbon, nutrients) or by changing abiotic conditions affecting microbial process rates (e.g., soil moisture or temperature). Physical ecosystem engineers can therefore create biogeochemical heterogeneity in soils and sediments. They do so via general mechanisms influencing the flows of materials (i.e., modification of fluid dynamic properties, fluid pumping, and material transport) or the transfer of heat (i.e., modification of heat transfer properties, direct heat transfer, and convective forcing). The consequences of physical ecosystem engineering for biogeochemical processes can be predicted by considering the resources or abiotic conditions that limit or promote a reaction, and the effect of physical ecosystem engineering on these resources or abiotic conditions via the control they exert on material flows and heat transfer.

JORGE L. GUTIÃÂÃÂRREZ and CLIVE G. JONES (;)

2006-03-01

138

Editorial: Organic wastes in soils: Biogeochemical and Environmental Aspects  

Technology Transfer Automated Retrieval System (TEKTRAN)

This special issue of Soil Biology and Biochemistry presents papers from the Second General Annual Conference of European Geosciences Union, Session SSS12 Recycling of Organic Wastes in Soils: Biogeochemical and Environmental Issues, held at the Austria Center Vienna, 24-29 April 2005. Session SSS12...

139

Developing biogeochemical tracers of apatite weathering by ectomycorrhizal fungi  

NASA Astrophysics Data System (ADS)

Chronic acid deposition has depleted calcium (Ca) from many New England forest soils, and intensive harvesting may reduce phosphorus (P) available to future rotations. Thin glacial till soils contain trace amounts of apatite, a primary calcium phosphate mineral, which may be an important long-term source of both P and Ca to ecosystems. The extent to which ECM fungi enhance the weathering rate of primary minerals in soil which contain growth-limiting nutrients remains poorly quantified, in part due to biogeochemical tracers which are subsequently masked by within-plant fractionation. Rare earth elements (REEs) and Pb isotope ratios show some potential for revealing differences in soil apatite weathering rates across forest stands and silvicultural treatments. To test the utility of these tracers, we grew birch seedlings semi-hydroponically under controlled P-limited conditions, supplemented with mesh bags containing granite chips. Our experimental design included nonmycorrhizal (NM) as well as ectomycorrhizal cultures (Cortinarius or Leccinum). Resulting mycorrhizal roots and leachates of granite chips were analyzed for these tracers. REE concentrations in roots were greatly elevated in treatments with granite relative to those without granite, demonstrating uptake of apatite weathering products. Roots with different mycorrhizal fungi accumulated similar concentrations of REEs and were generally elevated compared to the NM cultures. Ammonium chloride leaches of granite chips grown in contact with mycorrhizal hyphae show elevated REE concentrations and significantly radiogenic Pb isotope signatures relative to bulk rock, also supporting enhanced apatite dissolution. Our results in culture are consistent with data from field-collected sporocarps from hardwood stands in the Bartlett Experimental Forest in New Hampshire, in which Cortinarius sporocarp Pb isotope ratios were more radiogenic than those of other ectomycorrhizal sporocarps. Taken together, the experimental and field results imply that the coupled approach of REE and Pb isotopic values afford a means to quantify the degree to which primary mineral weathering inputs are contributing to ecosystem nutrient budgets and potentially the role of different types of ECM fungi in the weathering process.

Vadeboncoeur, M. A.; Bryce, J. G.; Hobbie, E. A.; Meana-Prado, M. F.; Blichert-Toft, J.

2012-12-01

140

Earth's Early Biosphere and the Biogeochemical Carbon Cycle  

NASA Technical Reports Server (NTRS)

Our biosphere has altered the global environment principally by influencing the chemistry of those elements most important for life, e g., C, N, S, O, P and transition metals (e.g., Fe and Mn). The coupling of oxygenic photosynthesis with the burial in sediments of photosynthetic organic matter, and with the escape of H2 to space, has increased the state of oxidation of the Oceans and atmosphere. It has also created highly reduced conditions within sedimentary rocks that have also extensively affected the geochemistry of several elements. The decline of volcanism during Earth's history reduced the flow of reduced chemical species that reacted with photosynthetically produced O2. The long-term net accumulation of photosynthetic O2 via biogeochemical processes has profoundly influenced our atmosphere and biosphere, as evidenced by the O2 levels required for algae, multicellular life and certain modem aerobic bacteria to exist. When our biosphere developed photosynthesis, it tapped into an energy resource that was much larger than the energy available from oxidation-reduction reactions associated with weathering and hydrothermal activity. Today, hydrothermal sources deliver globally (0.13-1.1)x10(exp l2) mol yr(sup -1) of reduced S, Fe(2+), Mn(2+), H2 and CH4; this is estimated to sustain at most about (0.2-2)xl0(exp 12)mol C yr(sup -1) of organic carbon production by chemautotrophic microorganisms. In contrast, global photosynthetic productivity is estimated to be 9000x10(exp 12) mol C yr(sup -1). Thus, even though global thermal fluxes were greater in the distant geologic past than today, the onset of oxygenic photosynthesis probably increased global organic productivity by some two or more orders of magnitude. This enormous productivity materialized principally because oxygenic photosynthesizers unleashed a virtually unlimited supply of reduced H that forever freed life from its sole dependence upon abiotic sources of reducing power such as hydrothermal emanations and weathering. Communities sustained by oxygenic photosynthesis apparently thrived wherever supplies of sunlight, moisture and nutrients were sufficient. Prior to the development of oxygenic photosynthesis, the net global effect of the ancient global biosphere was to facilitate chemical equilibrium between reduced species from thermal activity and weathering and more oxidized constituents in the surface environment. But even this ancient biosphere might have been globally pervasive. The global geothermal heat flow was substantially higher during Earth's first billion years, and thus reduced chemical species might have persisted in sunlit aquatic environments. Perhaps the substantial decline in thermal activity between 4000 and 3000 Ma created a driver for oxygenic photosynthesis to develop.

DesMarais, David

2004-01-01

141

Adapting to life: ocean biogeochemical modelling and adaptive remeshing  

NASA Astrophysics Data System (ADS)

An outstanding problem in biogeochemical modelling of the ocean is that many of the key processes occur intermittently at small scales, such as the sub-mesoscale, that are not well represented in global ocean models. This is partly due to their failure to resolve sub-mesoscale phenomena, which play a significant role in vertical nutrient supply. Simply increasing the resolution of the models may be an inefficient computational solution to this problem. An approach based on recent advances in adaptive mesh computational techniques may offer an alternative. Here the first steps in such an approach are described, using the example of a simple vertical column (quasi-1-D) ocean biogeochemical model. We present a novel method of simulating ocean biogeochemical behaviour on a vertically adaptive computational mesh, where the mesh changes in response to the biogeochemical and physical state of the system throughout the simulation. We show that the model reproduces the general physical and biological behaviour at three ocean stations (India, Papa and Bermuda) as compared to a high-resolution fixed mesh simulation and to observations. The use of an adaptive mesh does not increase the computational error, but reduces the number of mesh elements by a factor of 2-3. Unlike previous work the adaptivity metric used is flexible and we show that capturing the physical behaviour of the model is paramount to achieving a reasonable solution. Adding biological quantities to the adaptivity metric further refines the solution. We then show the potential of this method in two case studies where we change the adaptivity metric used to determine the varying mesh sizes in order to capture the dynamics of chlorophyll at Bermuda and sinking detritus at Papa. We therefore demonstrate that adaptive meshes may provide a suitable numerical technique for simulating seasonal or transient biogeochemical behaviour at high vertical resolution whilst minimising the number of elements in the mesh. More work is required to move this to fully 3-D simulations.

Hill, J.; Popova, E. E.; Ham, D. A.; Piggott, M. D.; Srokosz, M.

2014-05-01

142

Adapting to life: ocean biogeochemical modelling and adaptive remeshing  

NASA Astrophysics Data System (ADS)

An outstanding problem in biogeochemical modelling of the ocean is that many of the key processes occur intermittently at small scales, such as the sub-mesoscale, that are not well represented in global ocean models. As an example, state-of-the-art models give values of primary production approximately two orders of magnitude lower than those observed in the ocean's oligotrophic gyres, which cover a third of the Earth's surface. This is partly due to their failure to resolve sub-mesoscale phenomena, which play a significant role in nutrient supply. Simply increasing the resolution of the models may be an inefficient computational solution to this problem. An approach based on recent advances in adaptive mesh computational techniques may offer an alternative. Here the first steps in such an approach are described, using the example of a~simple vertical column (quasi 1-D) ocean biogeochemical model. We present a novel method of simulating ocean biogeochemical behaviour on a vertically adaptive computational mesh, where the mesh changes in response to the biogeochemical and physical state of the system throughout the simulation. We show that the model reproduces the general physical and biological behaviour at three ocean stations (India, Papa and Bermuda) as compared to a high-resolution fixed mesh simulation and to observations. The simulations capture both the seasonal and inter-annual variations. The use of an adaptive mesh does not increase the computational error, but reduces the number of mesh elements by a factor of 2-3, so reducing computational overhead. We then show the potential of this method in two case studies where we change the metric used to determine the varying mesh sizes in order to capture the dynamics of chlorophyll at Bermuda and sinking detritus at Papa. We therefore demonstrate adaptive meshes may provide a~suitable numerical technique for simulating seasonal or transient biogeochemical behaviour at high spatial resolution whilst minimising computational cost.

Hill, J.; Popova, E. E.; Ham, D. A.; Piggott, M. D.; Srokosz, M.

2013-11-01

143

The Land\\/Ocean Biogeochemical Observatory: A robust networked mooring system for continuously monitoring complex biogeochemical cycles in estuaries  

Microsoft Academic Search

An ocean observatory that consists of an array of moored sensor platforms, telemetry, and data collection and dissemination software was designed for monitoring the biogeochemistry and physical dynamics of coastal and estuarine ecosystems. The Land-Ocean Biogeochemical Observatory (LOBO) consists of robust moorings that can withstand tidal currents and weather. The moorings are highly configurable, can be deployed in waters as

Hans W. Jannasch; Luke J. Coletti; Kenneth S. Johnson; Stephen E. Fitzwater; Joseph A. Needoba; Joshua N. Plant

144

3D Modeling of influence of oxygenated inflows on biogeochemical structure of redox-layer of enclosed seas  

NASA Astrophysics Data System (ADS)

In this study we used a coupled hydrophysical-biogeochemical model. Biogeochemical processes were described with O-N-S-P-Mn-Fe ROLM model (Yakushev et al, 2007), designed to study processes of organic matter (OM) formation and decay, reduction and oxidation of species of nitrogen, sulphur, manganese and iron, transformation of phosphorus species. Phytoplankton, zooplankton and bacteria were also parameterized and divided into four groups according to their relation to particular energy source and to OM transformation. Hydrophysical processes where described with 3D General Estuarine Transport Model (Burchard et al, 2004). We modeled the influence of oxygenated intrusions on the vertical biogeochemical structure of the central Gotland Sea. The model simulations demonstrate that a complete ventilation of the Gotland Deep bottom water caused by massive inflows of oxygenated North Sea water led to substantial changes of the vertical biogeochemical structure within this basin. During the inflow events large amounts of iron and manganese precipitate and discharge from the water column. In this phase redox reactions are accelerated and growth of bacteria leads to an increase of particulate matter content and consecutive particle sedimentation. An unbalanced structure of water column exists during the period of reestablishment of anoxic conditions. Its appearance is related to the absence of Mn species that play the dominant role in the oxidation-reduction reactions at the pelagic redox interfaces. This unbalanced structure can serve as a biotope for a development of untypical microbial redox-cline reactions (i.e. anammox). According to the model simulations the duration of the reestablishment period for a steady state of biogeochemistry after a complete flushing is about 1.5 years.

Podymov, O.

2009-04-01

145

Novel Imaging Techniques, Integrated with Mineralogical, Geochemical and Microbiological Characterization to Determine the Biogeochemical Controls....  

SciTech Connect

Tc(VII) will be reduced and precipitated in FRC sediments under anaerobic conditions in batch experiments (progressive microcosms). The complementary microcosm experiments using low pH/nigh nitrate sediments from 3 (near FW 009) are imminent, with the sediment cores already shipped to Manchester. HYPOTHESIS 2. Tc(VII) reduction and precipitation can be visualized in discrete biogeochemical zones in sediment columns using 99mTc and a gamma-camera. Preliminary experiments testing the use of 99mTc as a radiotracer to address hypotheses 2 and 3 have suggested that the 99mTc associates with Fe(II)-bearing sediments in microcosms and stratified columns containing FRC sediments. Initial proof of concept microcosms containing Fe(II)-bearing, microbially-reduced FRC sediments were spiked with 99mTc and imaged using a gamma-camera. In comparison with oxic controls, 99mTc was significantly partitioned in the solid phase in Fe(III)-reducing sediments in batch experiments. Column experiments using FRC background area soil with stratified biogeochemical zones after stimulation of anaerobic processes through nutrient supplementation, suggested that 99mTc transport was retarded through areas of Fe(III) reduction. HYPOTHESIS 3. Sediment-bound reduced 99mTc can be solubilized by perturbations including oxidation coupled to biological nitrate reduction, and mobilization visualized in real-time using a gamma-camera. Significant progress has been made focusing on the impact of nitrate on the biogeochemical behavior of technetium. Additions of 100 mM nitrate to FRC sediment microcosms, which could potentially compete for electrons during metal reduction, inhibited the reduction of both Fe(III) and Tc(VII) completely. Experiments have also addressed the impact of high nitrate concentrations on Fe(II) and Tc(IV) in pre-reduced sediments, showing no significant resolubilization of Tc with the addition of 25 mM nitrate. A parallel set of experiments addressing the impact of aerobic conditions on the stability/solubility of Fe(II) and Tc(IV), found 80 % resolubilization of the Tc. Column experiments exploring this behavior are being planned. HYPOTHESIS 4 The mobility of 99mTc in the sediment columns can be modeled using a coupled speciation and transport code. Microbiological and geochemical characterization of the column experiments is ongoing and transport and geochemical modeling experiments are being planned.

Lloyd, Jonathan R.

2005-06-01

146

Incorporating microbes into large-scale biogeochemical models  

NASA Astrophysics Data System (ADS)

Micro-organisms, including Bacteria, Archaea, and Fungi, control major processes throughout the Earth system. Recent advances in microbial ecology and microbiology have revealed an astounding level of genetic and metabolic diversity in microbial communities. However, a framework for interpreting the meaning of this diversity has lagged behind the initial discoveries. Microbial communities have yet to be included explicitly in any major biogeochemical models in terrestrial ecosystems, and have only recently broken into ocean models. Although simplification of microbial communities is essential in complex systems, omission of community parameters may seriously compromise model predictions of biogeochemical processes. Two key questions arise from this tradeoff: 1) When and where must microbial community parameters be included in biogeochemical models? 2) If microbial communities are important, how should they be simplified, aggregated, and parameterized in models? To address these questions, we conducted a meta-analysis to determine if microbial communities are sensitive to four environmental disturbances that are associated with global change. In all cases, we found that community composition changed significantly following disturbance. However, the implications for ecosystem function were unclear in most of the published studies. Therefore, we developed a simple model framework to illustrate the situations in which microbial community changes would affect rates of biogeochemical processes. We found that these scenarios could be quite common, but powerful predictive models cannot be developed without much more information on the functions and disturbance responses of microbial taxa. Small-scale models that explicitly incorporate microbial communities also suggest that process rates strongly depend on microbial interactions and disturbance responses. The challenge is to scale up these models to make predictions at the ecosystem and global scales based on measurable parameters. We argue that meeting this challenge will require a coordinated effort to develop a series of nested models at scales ranging from the micron to the globe in order to optimize the tradeoff between model realism and feasibility.

Allison, S. D.; Martiny, J. B.

2008-12-01

147

Accelerated parameter identification in a 3D marine biogeochemical model using surrogate-based optimization  

NASA Astrophysics Data System (ADS)

We present the application of the Surrogate-based Optimization (SBO) method on a parameter identification problem for a 3-D biogeochemical model. SBO is a method for acceleration of optimization processes when the underlying model itself is of very high computational complexity. In these cases, coupled simulation runs require large amounts of computer time, where optimization runs may become unfeasible even with high-performance hardware. As a consequence, the key idea of SBO is to replace the original and computationally expensive (high-fidelity) model by a so-called surrogate, which is created from a less accurate but computationally cheaper (low-fidelity) model and a suitable correction approach to increase its accuracy. To date, the SBO approach has been widely and successfully used in engineering applications and also for parameter identification in a 1-D marine ecosystem model of NPZD type. In this paper, we apply the approach onto a two-component biogeochemical model. The model is spun-up into a steady seasonal cycle via the Transport Matrix Approach. The low-fidelity model we use consists of a reduced number of spin-up iterations (several decades instead of millennia used for the original model). A multiplicative correction operator is further exploited to extrapolate the rather inaccurate low-fidelity model onto the original one. This corrected model builds our surrogate. We validate this SBO method by twin-experiments that use synthetic observations generated by the original model. We motivate our choice of the low-fidelity model and the multiplicative correction and discuss the computational advantage of SBO in comparison to an expensive parameter optimization in the context of the high-fidelity model. The proposed SBO technique is shown to yield a solution close to the target at a significant gain of computational efficiency. Without further regularization techniques, the method is able to identify most model parameters. The method is simple to implement and presents a promising and pragmatic tool to calibrate biogeochemical models in a global three-dimensional setting.

Prieß, M.; Piwonski, J.; Koziel, S.; Oschlies, A.; Slawig, T.

2013-08-01

148

Investigating the Impact of Pore Scale Microenvironments on Contaminant Biogeochemical Reactive Transport  

NASA Astrophysics Data System (ADS)

Microenvironments and transition zones dominate the subsurface biogeochemical cycling of key contaminants, with strong effects resulting from the coupling of chemical reactions, physical transport and microbiological processes. Understanding the impact of pore-scale environments (e.g. spatial heterogeneity, chemical gradients, and redox potential) is essential for modeling contaminant fate and transport in the subsurface. The driver for biogeochemical processes at the pore scale changes from macroscopic advection to microscale diffusion, and this has a significant effect on the retention of soluble, highly mobile contaminants such as U(VI). Here, etched-silicon microfluidic models with defined chemistry, mineralogy, microbiology, and flow regimes are used for the incremental development of complex microenvironments that approach real-world systems. We demonstrate the colonization of such pore spaces by an anaerobic Fe(III)-reducing bacterium, the enzymatic reduction of a bioavailable Fe(III) phase within this environment, and the subsequent effects of both oxidized and reduced Fe phases on uranium biogeochemistry under flow conditions using both X-ray Microprobe (XMP) and X-ray Absorption Spectroscopy (XAS). Precipitated Fe(III) phases within the microfluidic model were most effectively reduced in the presence of an electron shuttle (e.g. AQDS), with Fe(II) ions adsorbing onto mineral precipitates and surfaces. In the absence of Fe, U(VI) was effectively reduced by the microbial population to insoluble U(IV), which was precipitated in discrete regions associated within biomass. In the presence of both oxidized and reduced Fe phases however, differing effects were observed with regards to U behavior; oxidized U(VI) was frequently adsorbed to poorly crystalline Fe(III), and reduced U(IV) associated with more reduced regions of the microscale flow cell. In the future, the flexibility in the design of the microfluidic models, in combination with advanced characterization techniques, will allow us to further probe a range of pore-structures with distinctive physical, chemical and biological properties to provide a better understanding of biogeochemical redox processes occurring at the pore scale and their impact on contaminant transport.

Wilkins, M. J.; Pearce, C.; Zhang, C.; Heald, S.; Fredrickson, J. K.; Zachara, J. M.

2011-12-01

149

Biogeochemical mass balances in a turbid tropical reservoir. Field data and modelling approach  

NASA Astrophysics Data System (ADS)

The turbid tropical Cointzio reservoir, located in the Trans Mexican Volcanic Belt (TMVB), behaves as a warm monomictic water body (area = 6 km2, capacity 66 Mm3, residence time ~ 1 year). It is strategic for the drinking water supply of the city of Morelia, capital of the state of Michoacán, and for downstream irrigation during the dry season. This reservoir is a perfect example of a human-impacted system since its watershed is mainly composed of degraded volcanic soils and is subjected to high erosion processes and agricultural loss. The reservoir is threatened by sediment accumulation and nutrients originating from untreated waters in the upstream watershed. The high content of very fine clay particles and the lack of water treatment plants lead to serious episodes of eutrophication (up to 70 ?g chl. a L-1), high levels of turbidity (Secchi depth < 30 cm) and a long period of anoxia (from May to October). Based on intensive field measurements in 2009 (deposited sediment, benthic chamber, water vertical profiles, reservoir inflow and outflow) we determined suspended sediment (SS), carbon (C), nitrogen (N) and phosphorus (P) mass balances. Watershed SS yields were estimated at 35 t km2 y-1 of which 89-92 % were trapped in the Cointzio reservoir. As a consequence the reservoir has already lost 25 % of its initial storage capacity since its construction in 1940. Nutrient mass balances showed that 50 % and 46 % of incoming P and N were retained by sedimentation, and mainly eliminated through denitrification respectively. Removal of C by 30 % was also observed both by sedimentation and through gas emission. To complete field data analyses we examined the ability of vertical one dimensional (1DV) numerical models (Aquasim biogeochemical model coupled with k-? mixing model) to reproduce the main biogeochemical cycles in the Cointzio reservoir. The model can describe all the mineralization processes both in the water column and in the sediment. The values of the entire mass balance of nutrients and of the mineralization rates (denitrification and aerobic benthic mineralization) calculated from the model fitted well to the field measurements. Furthermore, this analysis indicates that the benthic mineralizations are the dominant processes involved in the nutrients release. This is the first implementation of a biogeochemical model applied to a highly productive reservoir in the TMVB in order to estimate nutrients release from sediments. It could be used for scenarios of reduction of eutrophication in the reservoir. This study provides a good example of the behavior of a small tropical reservoir under intense human pressure and it will help stakeholders to adopt appropriate strategies for the management of turbid tropical reservoirs.

Phuong Doan, Thuy Kim; Némery, Julien; Gratiot, Nicolas; Schmid, Martin

2014-05-01

150

Variably saturated flow and multicomponent biogeochemical reactive transport modeling of a uranium bioremediation field experiment  

NASA Astrophysics Data System (ADS)

Three-dimensional, coupled variably saturated flow and biogeochemical reactive transport modeling of a 2008 in situ uranium bioremediation field experiment is used to better understand the interplay of transport and biogeochemical reactions controlling uranium behavior under pulsed acetate amendment, seasonal water table variation, spatially variable physical (hydraulic conductivity, porosity) and geochemical (reactive surface area) material properties. While the simulation of the 2008 Big Rusty acetate biostimulation field experiment in Rifle, Colorado was generally consistent with behaviors identified in previous field experiments at the Rifle IFRC site, the additional process and property detail provided several new insights. A principal conclusion from this work is that uranium bioreduction is most effective when acetate, in excess of the sulfate-reducing bacteria demand, is available to the metal-reducing bacteria. The inclusion of an initially small population of slow growing sulfate-reducing bacteria identified in proteomic analyses led to an additional source of Fe(II) from the dissolution of Fe(III) minerals promoted by biogenic sulfide. The falling water table during the experiment significantly reduced the saturated thickness of the aquifer and resulted in reactants and products, as well as unmitigated uranium, in the newly unsaturated vadose zone. High permeability sandy gravel structures resulted in locally high flow rates in the vicinity of injection wells that increased acetate dilution. In downgradient locations, these structures created preferential flow paths for acetate delivery that enhanced local zones of TEAP reactivity and subsidiary reactions. Conversely, smaller transport rates associated with the lower permeability lithofacies (e.g., fine) and vadose zone were shown to limit acetate access and reaction. Once accessed by acetate, however, these same zones limited subsequent acetate dilution and provided longer residence times that resulted in higher concentrations of TEAP reaction products when terminal electron donors and acceptors were not limiting. Finally, facies-based porosity and reactive surface area variations were shown to affect aqueous uranium concentration distributions with localized effects of the fine lithofacies having the largest impact on U(VI) surface complexation. The ability to model the comprehensive biogeochemical reaction network, and spatially and temporally variable processes, properties, and conditions controlling uranium behavior during engineered bioremediation in the naturally complex Rifle IFRC subsurface system required a subsurface simulator that could use the large memory and computational performance of a massively parallel computer. In this case, the eSTOMP simulator, operating on 128 processor cores for 12 h, was used to simulate the 110-day field experiment and 50 days of post-biostimulation behavior.

Yabusaki, Steven B.; Fang, Yilin; Williams, Kenneth H.; Murray, Christopher J.; Ward, Andy L.; Dayvault, Richard D.; Waichler, Scott R.; Newcomer, Darrell R.; Spane, Frank A.; Long, Philip E.

2011-11-01

151

Effects of solar UV radiation and climate change on biogeochemical cycling: Interactions and feedbacks  

SciTech Connect

Solar UV radiation, climate and other drivers of global change are undergoing significant changes and models forecast that these changes will continue for the remainder of this century. Here we assess the effects of solar UV radiation on biogeochemical cycles and the interactions of these effects with climate change, including feedbacks on climate. Such interactions occur in both terrestrial and aquatic ecosystems. While there is significant uncertainty in the quantification of these effects, they could accelerate the rate of atmospheric CO{sub 2} increase and subsequent climate change beyond current predictions. The effects of predicted changes in climate and solar UV radiation on carbon cycling in terrestrial and aquatic ecosystems are expected to vary significantly between regions. The balance of positive and negative effects on terrestrial carbon cycling remains uncertain, but the interactions between UV radiation and climate change are likely to contribute to decreasing sink strength in many oceanic regions. Interactions between climate and solar UV radiation will affect cycling of elements other than carbon, and so will influence the concentration of greenhouse and ozone-depleting gases. For example, increases in oxygen-deficient regions of the ocean caused by climate change are projected to enhance the emissions of nitrous oxide, an important greenhouse and ozone-depleting gas. Future changes in UV-induced transformations of aquatic and terrestrial contaminants could have both beneficial and adverse effects. Taken in total, it is clear that the future changes in UV radiation coupled with human-caused global change will have large impacts on biogeochemical cycles at local, regional and global scales.

Erickson III, David J [ORNL

2011-01-01

152

IBIRYS: a Regional High Resolution Reanalysis (physical and biogeochemical) over the European North East Shelf  

NASA Astrophysics Data System (ADS)

Mercator-Ocean has developed a regional forecasting system at 1/12° resolution over the North East Atlantic (IBI: Iberia, Biscay and Irish), taking advantage of the recent developments in NEMO. A reanalysis, called IBIRYS, was performed with the IBI system on the 2002-2012 period. The physical model was coupled on-line with the biogeochemical component of NEMO based on the PISCES model. The model was forced by ERA-interim products (every 3 hours) including the atmospheric pressure. In addition to atmospheric forcing, the model included astronomical tidal forcing. This regional forecasting system used boundary conditions from the Mercator-Ocean global reanalysis (GLORYS: GLobal Ocean ReanalYses and Simulations).The assimilation component SAM2 (Mercator Ocean assimilation system), was based on a reduced-order Kalman filter (the SEEK or Singular Extended Evolutive Kalman filter). An IAU method (Incremental Analysis Updates) was used to apply the increments in the system. The error statistics were represented in a sub-space spanned by a small number of dominant 3D error directions. A 3D-Var scheme corrected for the slowly evolving large-scale biases in temperature and salinity. The data assimilation system allowed to constrain the model in a multivariate way with Sea Surface Temperature (AVHRR + Multi-satellite High resolution), together with all available satellite Sea Level Anomalies, and with in situ observations from the CORA-03 data base, including ARGO floats temperature and salinity measurements. In this presentation, the results obtained with IBIRYS are compared to GLORYS results. The consistency of the IBIRYS and GLORYS results at large scales is demonstrated. The capacity of IBIRYS to provide useful information at high frequencies in the North East Atlantic is shown. The biogeochemical results of IBIRYS are evaluated.

Levier, Bruno; Benkiran, Mounir; Reffray, Guillaume; García Sottilo, Marcos

2014-05-01

153

Modeling the influence of oxygenated inflows on the biogeochemical structure of the Gotland Sea, central Baltic Sea: Changes in the distribution of manganese  

NASA Astrophysics Data System (ADS)

A coupled hydrodynamic-biogeochemical one-dimensional O-N-S-P-Mn-Fe-model based on the RedOx Layer Model, (ROLM) and the General Ocean Turbulence Model (GOTM) is used to simulate basic changes in the biogeochemical water column structure in transition phases between oxic and anoxic conditions in a marginal sea. Organic matter (OM) formation and decay, the reduction and oxidation of species of nitrogen, sulfur, manganese, iron, and the transformation of phosphorus species are parameterized in the model. The influence of oxygenated intrusions on the vertical biogeochemical structure of the central Gotland Basin of the Baltic Sea is modeled. The model-produced simulations demonstrate that a complete ventilation of the Gotland Deep bottom water caused by massive inflows of oxygenated North Sea water has led to substantial changes in the vertical biogeochemical structure of the basin. During the inflow events large amounts of iron and manganese precipitate and vanish from the water column. In addition redox reactions are accelerated and bacterial growth leads to an increase of particulate matter content and consequent sedimentation of particles. During reestablishment of anoxic conditions, the structure of the water column is unbalanced. This is partly due to the absence of Mn species that play a dominant role in the oxidation-reduction reactions at the pelagic redox interfaces. This unbalanced structure can serve as a biotope for the development of untypical microbial redox-cline reactions (i.e. anammox). According to our model simulations, the reestablishment of steady state biogeochemical conditions following a complete flushing takes ˜1.5 years.

Yakushev, E. V.; Kuznetsov, I. S.; Podymov, O. I.; Burchard, H.; Neumann, T.; Pollehne, F.

2011-04-01

154

Introduction to Special Section: Global Analysis, Interpretation and Modelling—Toward the Integration of Global Biogeochemical Systems  

NASA Astrophysics Data System (ADS)

The following special section consists of papers that were presented at the First Science Conference of the Global Analysis, Interpretation and Modelling Task Force (GAIM) that was held September 24-29, 1995, in Garmisch-Partenkirchen, Germany. The goal of GAIM is to advance the study of the coupled dynamics of the Earth system using as tools both data and models. The goal of the science conference was to provide a venue for the dissemination of scientific findings that would be steps toward developing prognostic biogeochemical models which could, in time, be coupled to models of the physical climate system. The science conference focused on papers in the areas of global data analysis and assessment, modeling of biogeochemical systems and their relationship to physical climate and hydrologic systems, and interpretation of current trends as indicated by global databases and model results for extrapolation with regard to future global change. Oral and poster session topics were grouped by time periods, including "Paleo" (<20 kyr), "Historical" (<2 kyr), "Contemporary" (<20 years), and "Future," with an additional session concerned with global systems integration. The new and continued research directions stemming from these contributions should eventually lead to answers regarding the measurement, causes, and consequences of natural and anthropogenic global change.

Sahagian, Dork L.; Moore, Berrien

1996-12-01

155

BIOGEOCHEMICAL ECOLOGY OF AQUACULTURE PONDS A DISSERTATION SUBMITIED TO THE GRADUATE DIVISION OF THE  

E-print Network

BIOGEOCHEMICAL ECOLOGY OF AQUACULTURE PONDS A DISSERTATION SUBMITIED TO THE GRADUATE DIVISION production and consumption were applied in shrimp aquaculture ponds which served as convenient model systems

Luther, Douglas S.

156

Impacts of mountain pine beetle outbreak on biogeochemical cycling in a high elevation whitebark pine ecosystem.  

E-print Network

??Ecological disturbances can significantly impact biogeochemical cycles in terrestrial ecosystems, but the effects of the current widespread mountain pine beetle outbreak on ecosystem processes like… (more)

Keville, Megan

2012-01-01

157

Enhanced biogeochemical cycling and subsequent reduction of hydraulic conductivity associated with soil-layer interfaces in the vadose zone.  

PubMed

Biogeochemical dynamics in the vadose zone are poorly understood due to the transient nature of chemical and hydrologic conditions but are nonetheless critical to understanding chemical fate and transport. This study explored the effects of a soil layer on linked geochemical, hydrological, and microbiological processes. Three laboratory soil columns were constructed: a homogenized medium-grained sand, a homogenized organic-rich loam, and a sand-over-loam layered column. Upward and downward infiltration of water was evaluated during experiments to simulate rising water table and rainfall events, respectively. In situ collocated probes measured soil water content, matric potential, and Eh. Water samples collected from the same locations were analyzed for Br, Cl, NO, SO, NH, Fe, and total sulfide. Compared with homogeneous columns, the presence of a soil layer altered the biogeochemistry and water flow of the system considerably. Enhanced biogeochemical cycling was observed in the layered column over the texturally homogeneous soil columns. Enumerations of iron- and sulfate-reducing bacteria showed 1 to 2 orders of magnitude greater community numbers in the layered column. Mineral and soil aggregate composites were most abundant near the soil-layer interface, the presence of which likely contributed to an observed order-of-magnitude decrease in hydraulic conductivity. These findings show that quantifying coupled hydrologic-biogeochemical processes occurring at small-scale soil interfaces is critical to accurately describing and predicting chemical changes at the larger system scale. These findings also provide justification for considering soil layering in contaminant fate and transport models because of its potential to increase biodegradation or to slow the rate of transport of contaminants. PMID:22031578

Hansen, David J; McGuire, Jennifer T; Mohanty, Binayak P

2011-01-01

158

Global changes in biogeochemical cycles in response to human activities  

NASA Technical Reports Server (NTRS)

The main objective of our research was to characterize biogeochemical cycles at continental and global scales in both terrestrial and aquatic ecosystems. This characterization applied to both natural ecosystems and those disturbed by human activity. The primary elements of interest were carbon and nitrogen and the analysis sought to quantify standing stocks and dynamic cycling processes. The translocation of major nutrients from the terrestrial landscape to the atmosphere (via trace gases) and to fluvial systems (via leaching, erosional losses, and point source pollution) were of particular importance to this study. Our aim was to develop the first generation of Earth System Models. Our research was organized around the construction and testing of component biogeochemical models which treated terrestrial ecosystem processes, aquatic nutrient transport through drainage basins, and trace gas exchanges at the continental and global scale. A suite of three complementary models were defined within this construct. The models were organized to operate at a 1/2 degree latitude by longitude level of spatial resolution and to execute at a monthly time step. This discretization afforded us the opportunity to understand the dynamics of the biosphere down to subregional scales, while simultaneously placing these dynamics into a global context.

Moore, Berrien, III; Melillo, Jerry

1994-01-01

159

Subsurface Biogeochemical Research FY11 Second Quarter Performance Measure  

SciTech Connect

The Subsurface Biogeochemical Research (SBR) Long Term Measure for 2011 under the Performance Assessment Rating Tool (PART) measure is to "Refine subsurface transport models by developing computational methods to link important processes impacting contaminant transport at smaller scales to the field scale." The second quarter performance measure is to "Provide a report on computational methods linking genome-enabled understanding of microbial metabolism with reactive transport models to describe processes impacting contaminant transport in the subsurface." Microorganisms such as bacteria are by definition small (typically on the order of a micron in size), and their behavior is controlled by their local biogeochemical environment (typically within a single pore or a biofilm on a grain surface, on the order of tens of microns in size). However, their metabolic activity exerts strong influence on the transport and fate of groundwater contaminants of significant concern at DOE sites, in contaminant plumes with spatial extents of meters to kilometers. This report describes progress and key findings from research aimed at integrating models of microbial metabolism based on genomic information (small scale) with models of contaminant fate and transport in aquifers (field scale).

Scheibe, Timothy D.

2011-03-31

160

Hydro-biogeochemical Controls on Geophysical Signatures (Invited)  

NASA Astrophysics Data System (ADS)

Geophysical techniques such as seismic, magnetic and electrical techniques have historically played a major role in oil exploration. Their main use has been for delineation basin geometry, structures and hydrocarbon traps and for understanding the subsurface stratigraphy. Their use for investigating microbial processes has only recently been recognized over the last decade resulting in the development of biogeophysics as a frontier research area which bridges the fields of environmental microbiology, biogeochemistry, geomicrobiology. Recent biogeophysical studies have demonstrated the potential of geophysical technologies to (1) probe the presence of microbial cells and biofilms in subsurface geologic media, (2) investigate the interactions between microorganisms and subsurface geologic media, (3) assess biogeochemical transformations, biomineralization, and biogeochemical reaction rates, and (4) investigate the alteration of physical properties of subsurface geologic media induced by microorganisms. The unique properties of geophysical datasets (e.g. non-invasive data acquisition, spatially continuous properties retrieved) make them attractive for probing microbial processes affecting fate and transport of contaminants. This presentation will provide an updated understanding of major controls on geophysical signatures by highlighting some of the important advancements in biogeophysical studies at hydrocarbon contaminated environments. Important challenges that provide an opportunity for further research in this new field will also be examined.

Atekwana, E. A.

2013-12-01

161

Aqueous complexation reactions governing the rate and extent of biogeochemical U(VI) reduction  

SciTech Connect

The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments.

Kemner, K.M.; Kelly, S.D.; Brooks, Scott C.; Dong, Wenming; Carroll, Sue; Fredrickson, James K.

2006-06-01

162

Natural biogeochemical cycle of mercury in a global three-dimensional ocean tracer model  

E-print Network

Natural biogeochemical cycle of mercury in a global three-dimensional ocean tracer model Yanxu enhancement in Hg concentrations. 1. Introduction The ocean plays a central role in the biogeochemical cycling, USA Abstract We implement mercury (Hg) biogeochemistry in the offline global 3-D ocean tracer model

Lyatt Jaeglé

163

Evaluation of an integrated biogeochemical model (PnET-BGC) at a northern hardwood forest ecosystem  

Microsoft Academic Search

An integrated biogeochemical model (PnET-BGC) was formulated to simulate chemical transformations of vegetation, soil, and drainage water in northern forest ecosystems. The model operates on a monthly time step and depicts the major biogeochemical processes, such as forest canopy element transformations, hydrology, soil organic matter dynamics, nitrogen cycling, geochemical weathering, and chemical equilibrium reactions involving solid and solution phases. The

Solomon S. Gbondo-Tugbawa; Charles T. Driscoll; John D. Aber; Gene E. Likens

2001-01-01

164

Biogeochemical responses of the carbon cycle to natural and human perturbations: Past, present, and future  

SciTech Connect

In the past three centuries, human perturbations of the environment have affected the biogeochemical behavior of the global carbon cycle and that of the other three nutrient elements closely coupled to carbon: nitrogen, phosphorus, and sulfur. The partitioning of anthropogenic CO{sub 2} among its various sinks in the past, for the present, and for projections into the near future is controlled by the interactions of these four elemental cycles within the major environmental domains of the land, atmosphere, coastal oceanic zone, and open ocean. The authors analyze the past, present, and future behavior of the global carbon cycle using the Terrestrial-Ocean-aTmosphere Ecosystem Model (TOTEM), a unique process-based model of the four global coupled biogeochemical cycles of carbon, nitrogen, phosphorus, and sulfur. They find that during the past 300 yrs, anthropogenic CO{sub 2} was mainly stored in the atmosphere and in the open ocean. Human activities on land caused an enhanced loss of mass from the terrestrial organic matter reservoirs (phytomass and humus) mainly through deforestation and consequently increased humus remineralization, erosion, and transport to the coastal margins by rivers and runoff. Photosynthetic uptake by the terrestrial phytomass was enhanced owing to fertilization by increasing atmospheric CO{sub 2} concentrations and supported by nutrients remineralized from organic matter. TOTEM results indicate that through most of the past 300 yrs, the loss of C from deforestation and other land-use activities was greater than the gain from the enhanced photosynthetic uptake. Since pre-industrial time (since 1700), the net flux of CO{sub 2} from the coastal waters has decreased by 40%, from 0.20 Gt C/yr to 0.12 Gt C/yr. TOTEM analyses of atmospheric CO{sub 2} concentrations for the 21st century were based on the fossil-fuel emission projections of IPCC (business as usual scenario) and of the more restrictive UN 1997 Kyoto Protocol. By the mid-21st century, the projected atmospheric CO{sub 2} concentrations range from about 550 ppmv (TOTEM, based on IPCC projected emissions) to 510 ppmv (IPCC projection) and to 460 ppmv (TOTEM, based on the Kyoto Protocol reduced emissions).

Ver, L.M.B.; Mackenzie, F.T.; Lerman, A.

1999-07-01

165

Trimethylbenzoic acids as metabolite signatures in the biogeochemical evolution of an aquifer contaminated with jet fuel hydrocarbons.  

PubMed

Evolution of trimethylbenzoic acids in the KC-135 aquifer at the former Wurtsmith Air Force Base (WAFB), Oscoda, MI was examined to determine the functionality of trimethylbenzoic acids as key metabolite signatures in the biogeochemical evolution of an aquifer contaminated with JP-4 fuel hydrocarbons. Changes in the composition of trimethylbenzoic acids and the distribution and concentration profiles exhibited by 2,4,6- and 2,3,5-trimethylbenzoic acids temporally and between multilevel wells reflect processes indicative of an actively evolving contaminant plume. The concentration levels of trimethylbenzoic acids were 3-10 orders higher than their tetramethylbenzene precursors, a condition attributed to slow metabolite turnover under sulfidogenic conditions. The observed degradation of tetramethylbenzenes into trimethylbenzoic acids obviates the use of these alkylbenzenes as non-labile tracers for other degradable aromatic hydrocarbons, but provides rare field evidence on the range of high molecular weight alkylbenzenes and isomeric assemblages amenable to anaerobic degradation in situ. The coupling of actual tetramethylbenzene loss with trimethylbenzoic acid production and the general decline in the concentrations of these compounds demonstrate the role of microbially mediated processes in the natural attenuation of hydrocarbons and may be a key indicator in the overall rate of hydrocarbon degradation and the biogeochemical evolution of the KC-135 aquifer. PMID:14607476

Namocatcat, J A; Fang, J; Barcelona, M J; Quibuyen, A T O; Abrajano, T A

2003-12-01

166

Trimethylbenzoic acids as metabolite signatures in the biogeochemical evolution of an aquifer contaminated with jet fuel hydrocarbons  

NASA Astrophysics Data System (ADS)

Evolution of trimethylbenzoic acids in the KC-135 aquifer at the former Wurtsmith Air Force Base (WAFB), Oscoda, MI was examined to determine the functionality of trimethylbenzoic acids as key metabolite signatures in the biogeochemical evolution of an aquifer contaminated with JP-4 fuel hydrocarbons. Changes in the composition of trimethylbenzoic acids and the distribution and concentration profiles exhibited by 2,4,6- and 2,3,5-trimethylbenzoic acids temporally and between multilevel wells reflect processes indicative of an actively evolving contaminant plume. The concentration levels of trimethylbenzoic acids were 3-10 orders higher than their tetramethylbenzene precursors, a condition attributed to slow metabolite turnover under sulfidogenic conditions. The observed degradation of tetramethylbenzenes into trimethylbenzoic acids obviates the use of these alkylbenzenes as non-labile tracers for other degradable aromatic hydrocarbons, but provides rare field evidence on the range of high molecular weight alkylbenzenes and isomeric assemblages amenable to anaerobic degradation in situ. The coupling of actual tetramethylbenzene loss with trimethylbenzoic acid production and the general decline in the concentrations of these compounds demonstrate the role of microbially mediated processes in the natural attenuation of hydrocarbons and may be a key indicator in the overall rate of hydrocarbon degradation and the biogeochemical evolution of the KC-135 aquifer.

Namocatcat, J. A.; Fang, J.; Barcelona, M. J.; Quibuyen, A. T. O.; Abrajano, T. A.

2003-12-01

167

Natural biogeochemical cycle of mercury in a global three-dimensional ocean tracer model Yanxu Zhang1  

E-print Network

1 Natural biogeochemical cycle of mercury in a global three-dimensional ocean tracer model Yanxu plays a central role in the biogeochemical cycling of mercury (Hg). Sea-air exchange is a major source Corresponding author: Lyatt Jaeglé (jaegle@atmos.washington.edu) Submitted to Global Biogeochemical Cycles

Lyatt Jaeglé

168

Linking soil and sediment properties for research on biogeochemical cycles  

NASA Astrophysics Data System (ADS)

Conventional perspectives on soil erosion include the on-site damage to soil and reductions in crop yield, as well as the resulting off-site effects on water quality, runoff and sediment loads in rivers. Our evolving understanding of the Earth System has added a new dimension to the role of soil erosion within the global geochemical cycles. First, the relevance of soil as a nutrient and Carbon (C) pool was recognized. Initially, the role of soils in the global C cycle was largely considered to be limited to a vertical exchange of greenhouse house gases (GHG) between vegetation, soil and atmosphere and thus mostly studied by soil scientists, plant ecologists and climatologists. Even Critical Zone research focused mostly on weathering and regolith properties and ignored lateral fluxes of dissolved or particulate organic matter. Since the late 1990s, a wider role of soils in biogeochemical cycles has emerged. Recent estimates place the lateral movement of C between soil and sediment pools in terrestrial ecosystems (including rivers and lakes) at approximately 0.6 to 1.5 Gt per year. Some of the eroded C is replaced by photosynthesis from the atmosphere, but at a cost of additional emissions, for example due to fertilizer production. The long-term fate of the eroded and deposited soil organic matter is subject to an open debate and suffers from a lack of reliable spatial information on lateral C fluxes and its subsequent fate in terrestrial ecosystems. The connection between soil C pool, GHG emissions and erosion illustrates the relevance of surface processes for the C fluxes between Earth's spheres. Accordingly, soil is now considered as mobile system to make accurate predictions about the consequences of global change for terrestrial biogeochemical cycles and climate feedbacks. This expanded perspective on soils as dynamic pool of weathering regolith, sediment, nutrients and C at the interface between the geospheres requires the analysis of relevant soil properties, i.e. nutrient or C content, with regards to their mobility within local, regional and global biogeochemical cycles, including past, current and future rates of transfer. In this presentation, an initial framework illustrating a concept for linking soil properties and the mobility (lateral and vertical) of nutrients and organic matter critical for environmental conditions and services is developed.

Kuhn, Nikolaus J.

2013-04-01

169

Variably Saturated Flow and Multicomponent Biogeochemical Reactive Transport Modeling of a Uranium Bioremediation Field Experiment  

SciTech Connect

Field experiments at a former uranium mill tailings site have identified the potential for stimulating indigenous bacteria to catalyze the conversion of aqueous uranium in the +6 oxidation state to immobile solid-associated uranium in the +4 oxidation state. This effectively removes uranium from solution resulting in groundwater concentrations below actionable standards. Three-dimensional, coupled variably-saturated flow and biogeochemical reactive transport modeling of a 2008 in situ uranium bioremediation field experiment is used to better understand the interplay of transport rates and biogeochemical reaction rates that determine the location and magnitude of key reaction products. A comprehensive reaction network, developed largely through previous 1-D modeling studies, was used to simulate the impacts on uranium behavior of pulsed acetate amendment, seasonal water table variation, spatially-variable physical (hydraulic conductivity, porosity) and geochemical (reactive surface area) material properties. A principal challenge is the mechanistic representation of biologically-mediated terminal electron acceptor process (TEAP) reactions whose products significantly alter geochemical controls on uranium mobility through increases in pH, alkalinity, exchangeable cations, and highly reactive reduction products. In general, these simulations of the 2008 Big Rusty acetate biostimulation field experiment in Rifle, Colorado confirmed previously identified behaviors including (1) initial dominance by iron reducing bacteria that concomitantly reduce aqueous U(VI), (2) sulfate reducing bacteria that become dominant after {approx}30 days and outcompete iron reducers for the acetate electron donor, (3) continuing iron-reducer activity and U(VI) bioreduction during dominantly sulfate reducing conditions, and (4) lower apparent U(VI) removal from groundwater during dominantly sulfate reducing conditions. New knowledge on simultaneously active metal and sulfate reducers has been incorporated into the modeling. In this case, an initially small population of slow growing sulfate reducers is active from the initiation of biostimulation. Three-dimensional, variably saturated flow modeling was used to address impacts of a falling water table during acetate injection. These impacts included a significant reduction in aquifer saturated thickness and isolation of residual reactants and products, as well as unmitigated uranium, in the newly unsaturated vadose zone. High permeability sandy gravel structures resulted in locally high flow rates in the vicinity of injection wells that increased acetate dilution. In downgradient locations, these structures created preferential flow paths for acetate delivery that enhanced local zones of TEAP reactivity and subsidiary reactions. Conversely, smaller transport rates associated with the lower permeability lithofacies (e.g., fine) and vadose zone were shown to limit acetate access and reaction. Once accessed by acetate, however, these same zones limited subsequent acetate dilution and provided longer residence times that resulted in higher concentrations of TEAP products when terminal electron donors and acceptors were not limiting. Finally, facies-based porosity and reactive surface area variations were shown to affect aqueous uranium concentration distributions; however, the ranges were sufficiently small to preserve general trends. Large computer memory and high computational performance were required to simulate the detailed coupled process models for multiple biogeochemical components in highly resolved heterogeneous materials for the 110-day field experiment and 50 days of post-biostimulation behavior. In this case, a highly-scalable subsurface simulator operating on 128 processor cores for 12 hours was used to simulate each realization. An equivalent simulation without parallel processing would have taken 60 days, assuming sufficient memory was available.

Yabusaki, Steven B.; Fang, Yilin; Williams, Kenneth H.; Murray, Christopher J.; Ward, Anderson L.; Dayvault, Richard; Waichler, Scott R.; Newcomer, Darrell R.; Spane, Frank A.; Long, Philip E.

2011-11-01

170

Comparative study of infrared techniques for fast biogeochemical sediment analyses  

NASA Astrophysics Data System (ADS)

Analysis of sediment samples in the visible to mid infrared (IR) region requires small amounts of sample material and enables rapid and cost efficient geochemical analysis of mineral and organic sediment components. Here we use geochemical properties (total organic and inorganic carbon, biogenic silica, total nitrogen) from the ICDP deep drilling project PASADO to compare three different IR spectroscopy techniques: Diffuse Reflectance Fourier Transform IR Spectrometry (DRIFTS), Attenuated Total Reflectance Fourier Transform IR Spectroscopy (ATR-FTIRS) and Visible Near IR Spectroscopy (VNIRS). ATR-FTIRS and VNIRS are more rapid techniques compared to DRIFTS. Results show that calibration models developed using DRIFTS are most robust (correlation coefficient: R = 0.92 for TIC, R = 0.84 for BSi, R = 0.97 for TOC, R = 0.95 for TN). However, good statistical performance was also obtained by using ATR-FTIRS and VNIRS. When time and costs are limiting factors, these tools may be given preference for rapid biogeochemical screening.

Hahn, A.; RoséN, P.; Kliem, P.; Ohlendorf, C.; Zolitschka, B.

2011-10-01

171

Differential leaflet mortality may influence biogeochemical cycling following tropical cyclones.  

PubMed

Intensity of tropical cyclones is expected to increase in the coming century, and an improved understanding of their influence on biogeochemical cycles would benefit ecologists and conservationists. We studied the November 2013 Typhoon Haiyan damage to observe that numerous examples of partial leaf necrosis on intact leaves of trees in the Cycadaceae and Arecaceae families resulted, leaving behind a copious amount of arboreal dead leaf material attached to live leaves. The decay process of this form of arboreal litter has not been previously studied. When compared with decay of ground litter or detached litter suspended in the canopy, we predict the decay process of this form of arboreal litter will include increased photooxidation, leaching, and comminution by detritivorous insects and mites; but decreased catabolism of organic molecules by saprophytic organisms. PMID:25083171

Marler, Thomas E; Ferreras, Ulysses

2014-01-01

172

Isotopic constraints on biogeochemical cycling of copper in the ocean.  

PubMed

Trace elements and their isotopes are being actively studied as powerful tracers in the modern ocean and as proxies for the palaeocean. Although distributions and fractionations have been reported for stable isotopes of dissolved Fe, Cu, Zn and Cd in the ocean, the data remain limited and only preliminary explanations have been given. Copper is of great interest because it is either essential or toxic to organisms and because its distribution reflects both biological recycling and scavenging. Here we present new isotopic composition data for dissolved Cu (?(65)Cu) in seawater and rainwater. The Cu isotopic composition in surface seawater can be explained by the mixing of rain, river and deep seawater. In deep seawater, ?(65)Cu becomes heavier with oceanic circulation because of preferential scavenging of the lighter isotope ((63)Cu). In addition, we constrain the marine biogeochemical cycling of Cu using a new box model based on Cu concentrations and ?(65)Cu. PMID:25476795

Takano, Shotaro; Tanimizu, Masaharu; Hirata, Takafumi; Sohrin, Yoshiki

2014-01-01

173

A GIS approach to conducting biogeochemical research in wetlands  

NASA Technical Reports Server (NTRS)

A project was initiated to develop an environmental data base to address spatial aspects of both biogeochemical cycling and resource management in wetlands. Specific goals are to make regional methane flux estimates and site specific water level predictions based on man controlled water releases within a wetland study area. The project will contribute to the understanding of the Earth's biosphere through its examination of the spatial variability of methane emissions. Although wetlands are thought to be one of the primary sources for release of methane to the atmosphere, little is known about the spatial variability of methane flux. Only through a spatial analysis of methane flux rates and the environmental factors which influence such rates can reliable regional and global methane emissions be calculated. Data will be correlated and studied from Landsat 4 instruments, from a ground survey of water level recorders, precipitation recorders, evaporation pans, and supplemental gauges, and from flood gate water release; and regional methane flux estimates will be made.

Brannon, David P.; Irish, Gary J.

1985-01-01

174

Differential leaflet mortality may influence biogeochemical cycling following tropical cyclones  

PubMed Central

Intensity of tropical cyclones is expected to increase in the coming century, and an improved understanding of their influence on biogeochemical cycles would benefit ecologists and conservationists. We studied the November 2013 Typhoon Haiyan damage to observe that numerous examples of partial leaf necrosis on intact leaves of trees in the Cycadaceae and Arecaceae families resulted, leaving behind a copious amount of arboreal dead leaf material attached to live leaves. The decay process of this form of arboreal litter has not been previously studied. When compared with decay of ground litter or detached litter suspended in the canopy, we predict the decay process of this form of arboreal litter will include increased photooxidation, leaching, and comminution by detritivorous insects and mites; but decreased catabolism of organic molecules by saprophytic organisms. PMID:25083171

Marler, Thomas E; Ferreras, Ulysses

2014-01-01

175

Biogeochemical evolution of a landfill leachate plume, Norman, Oklahoma  

USGS Publications Warehouse

Leachate from municipal landfills can create groundwater contaminant plumes that may last for decades to centuries. The fate of reactive contaminants in leachate-affected aquifers depends on the sustainability of biogeochemical processes affecting contaminant transport. Temporal variations in the configuration of redox zones downgradient from the Norman Landfill were studied for more than a decade. The leachate plume contained elevated concentrations of nonvolatile dissolved organic carbon (NVDOC) (up to 300 mg/L), methane (16 mg/L), ammonium (650 mg/L as N), iron (23 mg/L), chloride (1030 mg/L), and bicarbonate (4270 mg/L). Chemical and isotopic investigations along a 2D plume transect revealed consumption of solid and aqueous electron acceptors in the aquifer, depleting the natural attenuation capacity. Despite the relative recalcitrance of NVDOC to biodegradation, the center of the plume was depleted in sulfate, which reduces the long-term oxidation capacity of the leachate-affected aquifer. Ammonium and methane were attenuated in the aquifer relative to chloride by different processes: ammonium transport was retarded mainly by physical interaction with aquifer solids, whereas the methane plume was truncated largely by oxidation. Studies near plume boundaries revealed temporal variability in constituent concentrations related in part to hydrologic changes at various time scales. The upper boundary of the plume was a particularly active location where redox reactions responded to recharge events and seasonal water-table fluctuations. Accurately describing the biogeochemical processes that affect the transport of contaminants in this landfill-leachate-affected aquifer required understanding the aquifer's geologic and hydrodynamic framework.

Cozzarelli, Isabelle M.; Bohlke, Johnkarl F.; Masoner, Jason R.; Breit, George N.; Lorah, Michelle M.; Tuttle, Michele L.; Jaeschke, Jeanne B.

2011-01-01

176

Biogeochemical consequences of an oxygenated intrusion into an anoxic fjord  

PubMed Central

Background This paper is based on the studies of the biogeochemical structure of the water column in the anoxic Fjord Hunnbunn (south-eastern Norway) performed in 2009, 2011 and 2012. This Fjord is an enclosed basin of brackish water separated by a narrow and shallow outlet to the sea with a permanently anoxic layer. We show how an oxygenated intrusion could lead to both positive and negative effects on the ecosystem state in Hunnbunn due to a change in the biogeochemical structure. Results During the stratified periods in 2009 and 2012 the anoxic layer amounted to approximately 10% of the total water volume in the Fjord, while dissolved oxygen (DO) was present in 80-90% of the water. In the autumn of 2011 the water chemistry structure observed in Fjord Hunnbunn was clearly affected by a recent oxygenated intrusion defined by abnormal salinity patterns. This led to a shift of the DO boundary position to shallower depths, resulting in a thicker anoxic layer comprising approximately 40% of the total water volume, with DO present only in approximately 60% of the water. The oxygenated water intrusions led to a twofold decrease of the concentrations of hydrogen sulphide, ammonia, phosphate and silicate in the deep layers with a simultaneous increase of these nutrients and a decrease of the pH level in the surface layers. The concentrations of manganese, iron, and mercury species changed dramatically and in particular revealed a significant supply of iron and methylmercury to the water column. Conclusions Oxic water intrusions into anoxic fjords could lead not only to the flushing of the bottom anoxia, but to a dispersal of sulphidic and low oxygen conditions to the larger bottom area. The elevation of the hydrogen sulphide to the shallower layers (that can be rapidly oxidized) is accompanied by the appearance in the subsurface water of methylmercury, which is easily accumulated by organisms and can be transported to the surrounding waters, affecting the ecosystem over a larger area. PMID:24872727

2014-01-01

177

Watershed Management and Mercury Biogeochemical Cycling in Lake Zapotlan, Mexico  

NASA Astrophysics Data System (ADS)

Lake Zapotlan is an endorheic subtropical eutrophic lake located in Jalisco State, Mexico. The lake supports a small but important local fishery for carp (Cyprinus sp.) and tilapia (Oreochromis sp.) and is an internationally recognized RAMSAR site. Very little research exists in these regions regarding mercury biogeochemical cycling. The lake receives considerable untreated municipal wastewater discharge that is elevated in inorganic total mercury (250-800 ng Hg/L) and organic methylmercury (3-10 ng CH3Hg+/L). The lake is also located on an active fault zone near an active volcano which may cause natural mercury enrichment. To assess a mercury risk to the commercial fishery we investigated the distribution of total inorganic mercury and organic methylmercury in waters, sediments, and fish tissues of the lake, surrounding wetlands, and incoming waters. Although there were high concentrations of inorganic mercury entering the lake in wastewater and seasonal tributary stream flow inputs, average concentrations in lake surface waters (3 ng Hg/L) and sediments (50 ng Hg/gdw) were relatively low. Average concentrations of total inorganic mercury were an order of magnitude higher in water (70 ng Hg/L) and sediment (245 ng Hg/gdw) in wetlands receiving the wastewater discharges. Mercury loading to the main body of the lake is likely reduced by these wetland buffer zones which allow mercury bound to particulate matter to settle out. A similar pattern was seen with respect to methylmercury concentrations. Average concentrations of methylmercury in lake surface water (below detect) and sediment (0.1 ng/gdw) were lower than in impounded wetlands (1 ng CH3Hg+/L, 0.7 ng CH3Hg+/gdw). Mercury concentrations in tilapia (3.5 ng/g) and carp (8 ng/g) from the commercial catch were found to be low in mercury; likely due to a combination of physiological, biogeochemical, and ecological factors.

Malczyk, E. A.; Branfireun, B. A.

2009-05-01

178

Rn as a geochemical tool for estimating residence times in the hyporheic zone and its application to biogeochemical processes  

NASA Astrophysics Data System (ADS)

The hyporheic zone is at the interface between groundwater and surface water systems. It is also often a geochemical and redox boundary between typically reduced groundwater and oxic surface water. It experiences dynamic physical and chemical conditions as both groundwater fluxes and surface water levels vary in time and space. This can be particularly important for processes such as biogeochemical processing of nutrients and carbon. There has recently been an increasing focus on coupling residence times of surface water in the hyporheic zone with biogeochemical reactions. While geochemical profiles can be readily measured using established geochemical sampling techniques (e.g. peepers), quantifying surface water residence times and flow paths within the hyporheic zone is more elusive. The nobel gas radon offers a method for quantification of surface water residence times in the hyporheic zone. Radon activities are typically low in surface waters due to degassing to the atmosphere and decay. However once the surface water flows into the hyporheic zone radon accumulates along the flow path due to emanation from the sediments. Using simple analytical equations the water residence time can be calculated based on the difference between measured 222Rn activities and 222Rn activities at secular equilibrium, with a maximum limit of about 20 days (depending on measurement precision). Rn is particularly suited to residence time measurements in the hyporheic zone since it does not require addition of tracers to the stream nor does it require complex simulations and assumptions (such as 1D vertical flow) as for temperature measurements. As part of the biogeochemistry course at the University of Bayreuth, we have investigated the coupling of redox processes and water residence times in the hyporheic zone using 222Rn as a tracer for residence time. Of particular interest were nitrate and sulfate reduction and methane and CO2 production. Measurements were made in a sandy section of the Mistelbach, a second order stream running through agricultural land near the city of Bayreuth. Radon was measured at 1-3 locations on two occasions and at 5 different depths (-5 to-25 cm). Geochemical parameters NO3-, NO2-, SO4-, Fe2+, CO2 and CH4 was measured in peepers with a vertical resolution of 1-2 cm to a depth of 50 cm as well as in the same samples as the Rn. Groundwater activities were measured in incubation experiments and by the deepest sampling point in the hyporheic zone. The results showed that there was a clear dependence of biogeochemical processes on the residence time. Nitrate was reduced within 2 days, while sulfate reduction began after 5 days while Fe2+ was produced after 10 days. CH4 production occurred at >20 days, which is above the upper limit of residence time detection using Rn. Obviously, biogeochemical processes are controlled by the balance between reaction rates and advection rates in the hyporheic zone, and that the ratio of these rates (i.e. the Damköhler number) will control the efficiency of material processing. The uncertainty in the method increases towards longer residence times, as secular equilibrium activities and measured activities converge. It is also influenced by the heterogeneity of emanation in the sediments. However, research within the hyporheic zone is usually focused on residence times shorter than two weeks, and emanation can be quantified in the laboratory. Thus Rn appears well suited to the study of time scales over which biogeochemical processes occur in the hyporheic zone.

Gilfedder, Benjamin; Dörner, Sebastian; Ebertshäuser, Marlene Esther; Glaser, Barbara; Klug, Maria; Pittroff, Marco; Pieruschka, Ines; Waldemer, Carolin

2014-05-01

179

Incorporating urban infrastructure into biogeochemical assessment of urban tropical streams in Puerto Rico  

NASA Astrophysics Data System (ADS)

Urban development alters catchment hydrology and the subsequent delivery of solutes to streams and downstream ecosystems. The extent to which the impacts of urban development vary by biome is uncertain, and the impacts are poorly understood in tropical catchments. In a previous study (Helton et al. 2011), downstream changes in nitrogen (N) in the highly urbanized Rio Piedras catchment in Puerto Rico (42% urban land use) were found to be greater than predicted (23%) in a simple river network model that uses land use and in-stream N loss to predict spatial patterns in N fluxes. Here we evaluate the deviations of the biogeochemical patterns in this urban catchment through synoptic sampling of hydrology and water quality collected annually at approximately 40 sites over 8 years (2004 - 2011) coupled with spatial analysis of the urban infrastructure in the catchment. Results indicate that urbanization leads to an increase in most solute concentrations measured (DOC, DON, NH4, PO4), but not NO3. The lack of urban influence on NO3 is inconsistent with findings in other biomes, but consistent with previous studies in Puerto Rico. Conservative tracers (Cl and F) indicate that the source of the organic solutes increase is likely from sewage inputs. We suggest that stream nutrient cycling models that assume topographically driven flow accumulation need to be changed in urban catchments to include different delivery mechanisms such as sewer and water lines, especially in tropical regions where this infrastructure is often inadequate.

Potter, J.; McDowell, W. H.; Daley, M. L.; Helton, A. M.

2012-12-01

180

Past, present and future state of the biogeochemical Si cycle in the Baltic Sea  

NASA Astrophysics Data System (ADS)

The Baltic Sea is one of many aquatic ecosystems that show long-term declines in dissolved silicate (DSi) concentrations due to anthropogenic alteration of the biogeochemical Si cycle. Reductions in DSi in aquatic ecosystems have been coupled to hydrological regulation reducing inputs, but also with eutrophication, although the relative significance of both processes remains unknown for the observed reductions in DSi concentrations. Here we combine present and historical data on water column DSi concentrations, together with estimates of present river DSi loads to the Baltic, the load prior to damming together with estimates of the long-term accumulation of BSi in sediments. In addition, a model has been used to evaluate the past, present and future state of the biogeochemical Si cycle in the Baltic Sea. The present day DSi load to the Baltic Sea is 855 ktons y - 1 . Hydrological regulation and eutrophication of inland waters can account for a reduction of 420 ktons y - 1 less riverine DSi entering the Baltic Sea today. Using published data on basin-wide accumulation rates we estimate that 1074 ktons y - 1 of biogenic silica (BSi) is accumulating in the sediments, which is 36% higher than earlier estimates from the literature (791 ktons y - 1 ). The difference is largely due to the high reported sedimentation rates in the Bothnian Sea and the Bothnian Bay. Using river DSi loads and estimated BSi accumulation, our model was not able to estimate water column DSi concentrations as burial estimates exceeded DSi inputs. The model was then used to estimate the BSi burial from measured DSi concentrations and DSi load. The model estimate for the total burial of BSi in all three basins was 620 ktons y - 1 , 74% less than estimated from sedimentation rates and sediment BSi concentrations. The model predicted 20% less BSi accumulation in the Baltic Proper and 10% less in the Bothnian Bay than estimated, but with significantly less BSi accumulation in the Bothnian Sea by a factor of 3. The model suggests there is an overestimation of basin-wide sedimentation rates in the Bothnian Bay and the Bothnian Sea. In the Baltic Proper, modelling shows that historical DSi concentrations were 2.6 times higher at the turn of the last century (ca. 1900) than at present. Although the DSi decrease has leveled out and at present there are only restricted areas of the Baltic Sea with limiting DSi concentrations, further declines in DSi concentrations will lead to widespread DSi limitation of diatoms with severe implications for the food web.

Conley, Daniel J.; Humborg, Christoph; Smedberg, Erik; Rahm, Lars; Papush, Liana; Danielsson, Åsa; Clarke, Annemarie; Pastuszak, Marianna; Aigars, Juris; Ciuffa, Daniele; Mörth, Carl-Magnus

2008-10-01

181

Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction  

SciTech Connect

The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. ? Elucidate the controls on the rate and extent of contaminant reactivity. (2) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

Scott C. Brooks; Wenming Dong; Sue Carroll; Jim Fredrickson; Ken Kemner; Shelly Kelly

2006-06-01

182

Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction  

SciTech Connect

The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. (2) Elucidate the controls on the rate and extent of contaminant reactivity. (3) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

Scott C. Brooks; Wenming Dong; Sue Carroll; James K. Fredrickson; Kenneth M. Kemner; Shelly D. Kelly

2006-06-01

183

A positive and multi-element conserving time stepping scheme for biogeochemical processes in marine ecosystem models  

NASA Astrophysics Data System (ADS)

In this paper, an unconditionally positive and multi-element conserving time stepping scheme for systems of non-linearly coupled ODE's is presented. These systems of ODE's are used to describe biogeochemical transformation processes in marine ecosystem models. The numerical scheme is a positive-definite modification of the Runge-Kutta method, it can have arbitrarily high order of accuracy and does not require time step adaption. If the scheme is combined with a modified Patankar-Runge-Kutta method from Burchard et al. (2003), it also gets the ability to solve a certain class of stiff numerical problems, but the accuracy is restricted to second-order then. The performance of the new scheme on two test case problems is shown.

Radtke, H.; Burchard, H.

2015-01-01

184

A model of biogeochemical cycles of carbon, nitrogen and phosphorus including symbiotic nitrogen fixation and phosphatase production.  

NASA Astrophysics Data System (ADS)

Global climate models have not yet considered the effects of nutrient cycles and limitation when forecasting carbon uptake by the terrestrial biosphere into the future. Using the principle of resource optimization, we here develop a new theory by which C, N and P cycles interact. Our model is able to replicate the observed responses of net primary production to nutrient additions in N-limited, N and P co-limited, and P-limited environments. Our framework identifies a new pathway by which N2 fixers can alter P availability: by investing in N-rich phosphorus liberation enzymes (phosphatases), fixers can greatly accelerate soil P availability and its cycling rates. This is critical for the successive invasion and establishment of N2 fixers into an N limited environment. We conclude that our model can be used to examine nutrient limitation broadly, and thus offers promise for coupling the biogeochemical system of C, N, and P to broader climate-system models.

Wang, Y.; Houlton, B.; Field, C. B.

2006-12-01

185

Biogeochemical and hydrological controls on fate and distribution of trace metals in oiled Gulf salt marshes  

NASA Astrophysics Data System (ADS)

On April 20, 2010, the drilling rig Deepwater Horizon exploded in the Gulf of Mexico, resulting in the release of approximately 5 million barrels of crude oil into the environment. Oil and its associated trace metals have been demonstrated to have a detrimental effect on coastal wetland ecosystems. Wetlands are particularly susceptible to oil contamination because they are composed largely of fine-grained sediments, which have a high capacity to adsorb organic matter and metals. The biogeochemical cycling of trace metals can be strongly influenced by microbial activity, specifically those of sulfate- and iron-reducing bacteria. Microbial activity may be enhanced by an increase in amounts of organic matter such as oil. This research incorporates an assessment of levels of trace metals and associated biogeochemical changes from ten coastal marshes in Alabama, Mississippi, and Louisiana. These sampling sites range in their pollution levels from pristine to highly contaminated. A total digestion analysis of wetland sediments shows higher concentrations of certain trace metals (e.g., Ni, Cu, Pb, Zn, Sr, Co, V, Ba, Hg, As) in heavily-oiled areas compared to less-affected and pristine sites. Due to chemical complexation among organic compounds and metals, crude oils often contain elevated levels (up to hundreds of mg/kg) of trace metals At the heavily-oiled Louisiana sites (e.g., Bay Jimmy, Bayou Dulac, Bay Batiste), elevated levels of metals and total organic carbon have been found in sediments down to depths of 30 cm. Clearly the contamination is not limited to shallow sediments and oil, along with various associated metals, may be invading into deeper (pre-industrial) portions of the marsh sediments. Pore-waters extracted from contaminated sediments are characterized by very high levels of reduced sulfur (up to 80 mg/kg), in contrast to fairly low ferrous iron concentrations (<0.02 mg/kg). The influx of oil into the wetlands might provide the initial substrate and carbon source for stimulating sulfate-reducing bacteria. The high sulfur levels, coupled with the low levels of iron, indicate that iron-reducing bacteria are outcompeted by sulfate reducers in oiled salt marshes. Moreover, pore-water pH values show a general increasing trend (ranging from 6.6 to 8.0) with depth, possibly reflecting the combined effects of bacterial sulfate reduction and saltwater intrusion at depth. Despite high levels of trace metals in bulk sediments, concentrations of trace metals dissolved in pore-waters are generally low. It is very likely that high organic matter content and bacterially-mediated sulfate reduction promote metal retention through the formation of sulfide solids. Framboidal pyrites, as well as other sulfides, have been identified, and are currently undergoing XRD, SEM, and EDAX analyses. Continued research is needed to monitor possible re-mobilization of trace metals in changing redox and biogeochemical conditions.

Keevan, J.; Natter, M.; Lee, M.; Keimowitz, A.; Okeke, B.; Savrda, C.; Saunders, J.

2011-12-01

186

Connections between physical, optical and biogeochemical processes in the Pacific Ocean  

NASA Astrophysics Data System (ADS)

A new biogeochemical model has been developed and coupled to a three-dimensional physical model in the Pacific Ocean. With the explicitly represented dissolved organic pools, this new model is able to link key biogeochemical processes with optical processes. Model validation against satellite and in situ data indicates the model is robust in reproducing general biogeochemical and optical features. Colored dissolved organic matter (CDOM) has been suggested to play an important role in regulating underwater light field. With the coupled model, physical and biological regulations of CDOM in the euphotic zone are analyzed. Model results indicate seasonal variability of CDOM is mostly determined by biological processes, while the importance of physical regulation manifests in the annual mean terms. Without CDOM attenuating light, modeled depth-integrated primary production is about 10% higher than the control run when averaged over the entire basin, while this discrepancy is highly variable in space with magnitudes reaching higher than 100% in some locations. With CDOM dynamics integrated in physical-biological interactions, a new mechanism by which physical processes affect biological processes is suggested, namely, physical transport of CDOM changes water optical properties, which can further modify underwater light field and subsequently affect the distribution of phytoplankton chlorophyll. This mechanism tends to occur in the entire Pacific basin but with strong spatial variability, implying the importance of including optical processes in the coupled physical-biogeochemical model. If ammonium uptake is sufficient to permit utilization of DOM, that is, UB??-U{U}/{U}-{(1-r_b)}/{RB}, then bacteria uptake of DOM has the form of FB=(1-r_b){U}/{RB}, bacteria respiration, SB=r_b×U, remineralization by bacteria, EB=UC{UN}/{UC}-{(1-r_b)}/{RB}. If EB > 0, then UB = 0; otherwise, UB = -EB. If there is insufficient ammonium, that is, UB?<-U{U}/{U}-{(1-r_b)}/{RB}, then bacteria uptake of ammonia is obtained by, UB=UB?, bacteria uptake of DOM, FB=U+UB, bacteria respiration, SB=RBFB{r_b}/{1-r_b}, remineralization by bacteria, EB=-UB. CDOM photolysis (Bissett et al., 1999a): UVLDOC=a(410)×RtUVLDOC×{PAR(0)}/{410}×exp?z0Kd(300)dz, UVSDOC=a(410)×RtUVSDOC×{PAR(0)}/{410}×exp?z0Kd(300)dz, UVLDIC=a(410)×RtUVLDIC×{PAR(0)}/{410}×exp?z0Kd(300)dz, UVSDIC=a(410)×RtUVSDIC×{PAR(0)}/{410}×exp?z0Kd(300)dz, a(410)=acdoc?×CLDOC, a(410)=acdoc?×CSDOC, Kd(300)=[a(410)+a(410)]×exp[0.0145×(410-300)]+0.154. The dissolution rate for biogenic silica (Jiang et al., 2003): D=(0.19T/25+0.01)×exp(0.069(T-25)). The air-sea flux of CO2 is calculated using the transfer velocity-wind speed relationships from Wanninkhof (1992): air-sea CO flux=0.31U2(660S{()sea-()air}, where U is the wind speed at sea surface and Sc is the Schmidt number for CO2 that can be calculated as: Sc=2073.1-125.62T+3.6276T2-0.043219T3, S is the solubility of CO2 and (pCO2)air is the partial pressure of CO2 in the air. In the model, we set a spatially uniform distribution of (pCO2)air observed at the Mauna Loa Observatory (Keeling et al., 1976).Dissolved oxygen (DO) is modeled using constant oxygen-to-nitrate and oxygen-to-ammonium ratios. At the surface, air-sea exchange of O2 is calculated as: O flux=0.31U2(660(DOsat-DO), where DOsat is the saturation concentration of DO calculated from temperature and salinity. So2 is the Schmidt number for O2 that can be calculated as follows: So2=1638.0-81.83T+1.483T2-0.008004T3.

Xiu, Peng; Chai, Fei

2014-03-01

187

BRIE: The Penn State Biogeochemical Research Initiative for Education  

NASA Astrophysics Data System (ADS)

Few scientists are prepared to address the interdisciplinary challenges of biogeochemical research due to disciplinary differences in vocabulary, technique, and scientific paradigm. Thus scientists and engineers trained in traditional disciplines bring a restricted view to the study of environmental systems, which can limit their ability to exploit new techniques and opportunities for scientific advancement. Although the literature is effusive with enthusiasm for interdisciplinary approaches to biogeochemistry, there remains the basic difficulty of cross-training geological and biological scientists. The NSF-IGERT funded Biogeochemical Research Initiative for Education (BRIE) program at Penn State is specifically designed to break down both disciplinary and institutional barriers and it has fostered cross-disciplinary collaboration and training since 1999. Students and faculty are drawn from environmental engineering, geochemistry, soil science, chemistry and microbiology, and the program is regarded on the Penn State campus as a successful example of how interdisciplinary science can best be promoted. There are currently 23 Ph.D. students funded by the program, with an additional 7 affiliated students. At present, a total of 6 students have completed doctoral degrees, and they have done so within normal timeframes. The program is "discipline-plus," whereby students enroll in traditional disciplinary degree programs, and undertake broad training via 12 credits of graduate coursework in other departments. Students are co-advised by faculty from different disciplines, and engage in interdisciplinary research facilitated by research "credit cards." Funding is available for international research experiences, travel to meetings, and other opportunities for professional development. Students help institutionalize interdisciplinary training by designing and conducting a teaching module that shares their expertise with a class in another department or discipline. Community building through social activities and scientific forums is a priority in both the undergraduate and graduate programs. In addition, entering Ph.D. students build cohort identity by taking a course that introduces them to BRIE faculty and research facilities through hands-on laboratory and field-based research activities. The BRIE undergraduate summer internship program has provided interdisciplinary research opportunities for a total of 35 students over the past five summers. This program aims to recruit students to the Ph.D. program, and at present, two Ph.D. students have entered this way. Our efforts have focused on attracting students from under-represented groups. Diversity in this program has been above national norms: and summer students have include 10 (29 %) African-American or Hispanic-American students, and 25 (over 70 %) females. The Ph.D. students and graduates are 50% female, with three students from minority populations.

Freeman, K. H.; Brantley, S. L.; Brenchley, J.

2003-12-01

188

Spatial heterogeneity in biogeochemical transport on Arctic hill slopes  

NASA Astrophysics Data System (ADS)

Water tracks, saturated regions of the hill slope in permafrosted Arctic catchments, likely deliver the majority of water entering streams in these regions, and may play a central role in delivery of nutrients. Fate of dissolved nutrients and carbon as they are transported in water tracks has a substantial effect on stream ecosystems, as water tracks may cover up to 35% of the catchment land area. Water tracks are distinguished from adjacent areas of the hillslope by higher rates of hydrologic transport, greater woody biomass, and increased pools of nutrients. Substantial spatial heterogeneity within and between water tracks may influence their role in transfer of materials between the terrestrial and aquatic landscape. We examined spatial variability of hydrologic and chemical characteristics within and between water tracks in the Kuparuk Basin of northern Alaska to increase understanding of the factors influencing nutrient export from arctic catchments. We studied a sedge-dominated water track with perennial surface water flow with shrub-dominated water tracks containing intermittent surface flow. Nominal transit times of water in the perennial site was 5 hours, compared to 15.5 h in an ephemeral track over a 50 meter reach, indicating substantial variation in water residence time and opportunity for biogeochemical reaction across sites. We evaluated spatial heterogeneity in biogeochemical characteristics within 25-m reaches at each site with a grain size of 10 m. Dissolved CH4 concentration was elevated above atmospheric equilibrium only at the perennial water track, where CH4 concentration varied by more than 15-fold within the water track, indicating hot spots of anaerobic microbial activity. Dissolved CO2 concentration was 9 times greater on average at the perennial water track, compared to the ephemeral site, suggesting that continuous water flow supports more rapid microbial activity. CO2 concentration was also more variable in the perennial water track, with a CV of 64% compared to 11% in an ephemeral water track. Despite spatial heterogeneity in dissolved gas concentrations within the perennial site, NH4+ concentration in surface and soil water was less variable, with a CV of 38%. In contrast, NH4+ concentration was more variable (CV=41%) than dissolved gases within the ephemeral site, and mean concentration was 2 times greater than at the perennial site, suggesting less active biological retention of nitrogen at the ephemeral site. These differences in dissolved gases and nutrient concentrations among water tracks indicate that nutrient processing during hydrologic transport on hill slopes varies across the catchment, which will likely result in spatially heterogeneous responses of elemental cycles in response to permafrost loss.

Risser, R.; Harms, T.; Jones, J.

2013-12-01

189

Biogeochemical value of managed realignment, Humber estuary, UK.  

PubMed

We outline a plausible, albeit extreme, managed realignment scenario ('Extended Deep Green' scenario) for a large UK estuary to demonstrate the maximum possible biogeochemical effects and economic outcomes of estuarine management decisions. Our interdisciplinary approach aims to better inform the policy process, by combining biogeochemical and socioeconomic components of managed realignment schemes. Adding 7494 ha of new intertidal area to the UK Humber estuary through managed realignment leads to the annual accumulation of a 1.2 x 10(5) t of 'new' sediment and increases the current annual sink of organic C and N, and particle reactive P in the estuary by 150%, 83% and 50%, respectively. The increase in intertidal area should also increase denitrification. However, this positive outcome is offset by the negative effect of enhanced greenhouse gas emissions in new marshes in the low salinity region of the estuary. Short-term microbial reactions decrease the potential benefits of CO(2) sequestration through gross organic carbon burial by at least 50%. Net carbon storage is thus most effective where oxidation and denitrification reactions are reduced. In the Humber this translates to wet, saline marshes at the seaward end of estuaries. Cost-benefit analysis (CBA) was used to determine the economic efficiency of the Extended Deep Green managed realignment. When compared to a 'Hold-the-Line' future scenario, i.e. the present state/extent of sea defences in the estuary, the CBA shows that managed realignment is cost effective when viewed on >25 year timescales. This is because capital costs are incurred in the first years, whereas the benefits from habitat creation, carbon sequestration and reduced maintenance costs build up over time. Over 50- and 100-year timescales, the Extended Deep Green managed realignment scenario is superior in efficiency terms. The increased sediment accumulation is also likely to enhance storage of contaminant metals. In the case of Cu, a metal that currently causes significant water quality issues, Cu removal due to burial of suspended sediment in realigned areas translates to a value of approximately pounds sterling 1000 a(-1) (avoided clean up costs). Although this is not formally included in the CBA it illustrates another likely positive economic outcome of managed realignment. Although we focus on the Humber, the history of reclamation and its biogeochemistry is common to many estuaries in northern Europe. PMID:16996577

Andrews, J E; Burgess, D; Cave, R R; Coombes, E G; Jickells, T D; Parkes, D J; Turner, R K

2006-12-01

190

Quantifying biogeochemical feedbacks on global climate using a simple Earth system model  

NASA Astrophysics Data System (ADS)

A simple Earth system model is used to evaluate the effects of various biogeochemical feedbacks on the evolution of the Earth system to 2200 under a range of anthropogenic forcings. The model includes a 2D atmosphere, latitudinally resolved ocean and land surfaces, and a range of biogeochemical processes such as primary production, decomposition, methane emissions, and N2O fluxes from agricultural soils and the ocean. Biogeochemical fluxes influence radiative forcing, with consequences for climate and hence biological processes. The model is forced with three RCPs, and the effects of different biogeochemical feedbacks, and parameterizations therein, on compatible emissions are calculated. Implications for the consistency of land use scenarios with RCPs and future pathways of global agricultural production in relation to expected human population growth are assessed.

Friend, A. D.

2013-12-01

191

Understanding Biogeochemical Transformations Of Trace Elements In Multi Metal-Rich Geomaterials Under Stimulated Redox Conditions  

EPA Science Inventory

Natural and anthropogenic influences on hydrological conditions can induce periodic or long-term reduced conditions in geologic materials. Such conditions can cause significant impacts on biogeochemical processes of trace elements in subsurface or near surface environments. The...

192

CALIBRATION OF SUBSURFACE BATCH AND REACTIVE-TRANSPORT MODELS INVOLVING COMPLEX BIOGEOCHEMICAL PROCESSES  

EPA Science Inventory

In this study, the calibration of subsurface batch and reactive-transport models involving complex biogeochemical processes was systematically evaluated. Two hypothetical nitrate biodegradation scenarios were developed and simulated in numerical experiments to evaluate the perfor...

193

Quantifying the effects of mountain pine beetle infestation on water and biogeochemical cycles at multiple spatial and temporal scales  

NASA Astrophysics Data System (ADS)

Unprecedented levels of bark beetle infestation over the last decade have radically altered forest structure across millions of hectares of Western U.S. montane environments. The widespread extent of this disturbance presents a major challenge for governments and resource managers who lack a predictive understanding of how water and biogeochemical cycles will respond to this disturbance over various temporal and spatial scales. There is a widespread perception, largely based on hydrological responses to fire or logging, that a reduction in both transpiration and interception following tree death will increase soil water availability and catchment water yield. However, few studies have directly addressed the effects of insect-induced forest decline on water and biogeochemical cycling. We address this knowledge gap using observations and modeling at scales from 100 to 109 m2 across study sites in CO and WY that vary in the intensity and timing of beetle infestation and tree death. Our focus on multiple sites with different levels of impact allows us to address two broad, organizing questions: How do changes in vegetation structure associated with MPB alter the partitioning of energy and water? And How do these changes in energy and water availability affect local to regional scale water and biogeochemical cycles? This presentation will focus primarily on energy balance and water partitioning, providing context for ongoing biogeochemical work. During the growing season, stand-scale transpiration declines rapidly and soil moisture increases following infestation, consistent with streamflow data from regional catchments that shows an increase in baseflow following widespread attack. During the winter and spring, stand scale snow surveys and continuous snow depth sensors suggested that the variability in snow cover decreased as the severity of beetle impact increases, but there were no significant stand-scale differences in snow depth among levels of impact. This is due both to an increase in snow under the canopies of dead trees and a decrease in snow cover in canopy gaps. For example, mean snow depth under the canopy was 86cm (CV 0.02) in unimpacted sites and 95cm (CV 0.05) in heavily impacted sites. In canopy gaps however, mean snow depth was 117cm (CV 0.11) in unimpacted sites but only 93cm (CV 0.07) in heavily impacted sites. At the watershed scale, bark beetle infestation was more likely to decrease the amount of both snowmelt and annual runoff, suggesting that the opening of the canopy increases sublimation and evaporation of the snow cover. These data suggest that the disturbance due to bark beetle infestation is both quantitatively and qualitatively different than either fire or logging. Using these observations, we develop a conceptual model for evaluating how biotic and abiotic processes couple water and biogeochemical cycles in forest ecosystems.

Brooks, P. D.; Harpold, A. A.; Somor, A. J.; Troch, P. A.; Gochis, D. J.; Ewers, B. E.; Pendall, E.; Biederman, J. A.; Reed, D.; Barnard, H. R.; Whitehouse, F.; Aston, T.; Borkhuu, B.

2010-12-01

194

Diel biogeochemical processes and their effect on the aqueous chemistry of streams: A review  

USGS Publications Warehouse

This review summarizes biogeochemical processes that operate on diel, or 24-h, time scales in streams and the changes in aqueous chemistry that are associated with these processes. Some biogeochemical processes, such as those producing diel cycles of dissolved O2 and pH, were the first to be studied, whereas processes producing diel concentration cycles of a broader spectrum of chemical species including dissolved gases, dissolved inorganic and organic carbon, trace elements, nutrients, stable isotopes, and suspended particles have received attention only more recently. Diel biogeochemical cycles are interrelated because the cyclical variations produced by one biogeochemical process commonly affect another. Thus, understanding biogeochemical cycling is essential not only for guiding collection and interpretation of water-quality data but also for geochemical and ecological studies of streams. Expanded knowledge of diel biogeochemical cycling will improve understanding of how natural aquatic environments function and thus lead to better predictions of how stream ecosystems might react to changing conditions of contaminant loading, eutrophication, climate change, drought, industrialization, development, and other factors.

Nimick, David A.; Gammons, Christopher H.; Parker, Stephen R.

2011-01-01

195

Biogeochemical responses following coral mass spawning on the Great Barrier Reef: pelagic-benthic coupling  

NASA Astrophysics Data System (ADS)

This study quantified how the pulse of organic matter from the release of coral gametes triggered a chain of pelagic and benthic processes during an annual mass spawning event on the Australian Great Barrier Reef. Particulate organic matter (POM) concentrations in reef waters increased by threefold to 11-fold the day after spawning and resulted in a stimulation of pelagic oxygen consumption rates that lasted for at least 1 week. Water column microbial communities degraded the organic carbon of gametes of the broadcast-spawning coral Acropora millepora at a rate of >15% h-1, which is about three times faster than the degradation rate measured for larvae of the brooding coral Stylophora pistillata. Stable isotope signatures of POM in the water column reflected the fast transfer of organic matter from coral gametes into higher levels of the food chain, and the amount of POM reaching the seafloor immediately increased after coral spawning and then tailed-off in the next 2 weeks. Short-lasting phytoplankton blooms developed within a few days after the spawning event, indicating a prompt recycling of nutrients released through the degradation of spawning products. These data show the profound effects of coral mass spawning on the reef community and demonstrate the tight recycling of nutrients in this oligotrophic ecosystem.

Wild, C.; Jantzen, C.; Struck, U.; Hoegh-Guldberg, O.; Huettel, M.

2008-03-01

196

Biogeochemical responses following coral mass spawning on the Great Barrier Reef: pelagic–benthic coupling  

Microsoft Academic Search

This study quantified how the pulse of organic matter from the release of coral gametes triggered a chain of pelagic and benthic\\u000a processes during an annual mass spawning event on the Australian Great Barrier Reef. Particulate organic matter (POM) concentrations\\u000a in reef waters increased by threefold to 11-fold the day after spawning and resulted in a stimulation of pelagic oxygen

C. Wild; C. Jantzen; U. Struck; O. Hoegh-Guldberg; M. Huettel

2008-01-01

197

Hydro-biogeochemical coupling beneath a large polythermal Arctic glacier: Implications for subice sheet biogeochemistry  

Microsoft Academic Search

We analyze the interannual chemical and isotopic composition of runoff from a large, high Arctic valley glacier over a 5 year period, during which drainage evolved from a long-residence-time drainage system feeding an artesian subglacial upwelling (SGU) at the glacier terminus to a shorter-residence-time drainage system feeding an ice-marginal channel (IMC). Increased icemelt inputs to the SGU are thought to

J. L. Wadham; M. Tranter; A. J. Hodson; R. Hodgkins; S. Bottrell; R. Cooper; R. Raiswell

2010-01-01

198

Coupled biogeochemical and hydrological responses of streams and rivers to drought  

Microsoft Academic Search

SUMMARY 1. Severe or extreme droughts occurred about 10% of the time over a 105-year record from central New Mexico, U.S.A., based on the Palmer Drought Severity Index. 2. Drought lowers water tables, creating extensive areas of groundwater recharge and fragmenting reaches of streams and rivers. Deeper groundwater inputs predominate as sources of surface flows during drought. Nutrient inputs to

CLIFFORD N. D AHM; M ICHELLE A. B AKER; DOUGLAS I. M OORE; J AMES R. T HIBAULT

2003-01-01

199

Coupled Hydrological and Biogeochemical Controls on Methylmercury Production and Export from a Boreal Wetland  

Microsoft Academic Search

Through long-term addition of a mercury (Hg) stable isotope to a wetland, we have begun to unravel the complexity of Hg and methylmercury (MeHg) cycling in a Boreal wetland. As part of the METAALICUS project being conducted at the Experimental Lakes Area, the lake 658 wetland was annually amended from 2001-2006 with a mercury isotope at a level approximately 5

A. Heyes; D. P. Krabbenhoft; B. A. Branfireun; C. C. Gilmour; C. P. Mitchell; M. T. Tate; M. Richardson

2007-01-01

200

COUPLED REACTIVE TRANSPORT MODELING BASED ON THE NEW BIOGEOCHEMICAL CODE HP1  

Technology Transfer Automated Retrieval System (TEKTRAN)

The migration of many naturally occurring elements and contaminants in the subsurface is affected by a multitude of complex, interactive physical, chemical, mineralogical, geological, and biological processes. Recently, a new comprehensive simulation tool HP1 (HYDRUS1D-PHREEQC) was developed by cou...

201

Biogeochemical controls on nitrogen fixers in the global ocean  

NASA Astrophysics Data System (ADS)

We explore the biogeochemical controls on the nitrogen fixers (or diazotrophs) in a global ocean model. Diazotrophs are essential organisms in the ocean, as they provide most of the new nitrogen to the global ocean. We employ a three-dimensional global ocean model with a self-organizing phytoplanktonic community, which successfully accounts for diverse marine autotrophic diazotrophs (Trichodesmium, unicellular cyanobacteria and diatom-diazotroph associations). We examine in the model how temperature, nitrogen, iron and phosphate limitations influence the global distribution of marine diazotrophs. In the observations and model, total diazotroph population is distributed over most of the oligotrophic warm sub-and-tropical waters. We find that this global diazotroph distribution is restricted to the low fixed-nitrogen regions which have sufficient supplies in dissolved iron and phosphate. We use resource competition theory to illustrate the intertwined response of marine nutrients, dust input and ecosystem, and map out regions of iron and phosphate regulations of marine diazotroph distribution. The theory suggests that diazotroph distribution is largely regulated by iron availability, in particular in the South Atlantic, Pacific and Indian Oceans. This result demonstrates how important it is to understand the iron dust sources to the marine biological community in relation to the oceanic nitrogen cycle.

Monteiro, Fanny; Dutkiewicz, Stephanie; Follows, Michael

2010-05-01

202

[Research the biogeochemical processes of nutrients in Minjiang Estuary].  

PubMed

The variations in the concentration and distribution of nutrients and influencing factors in the Minjiang Estuary with a tidal cycle were investigated based on the data obtained during field observations in May 2007. The results showed the suspended sediment, dissolved inorganic nitrogen and silicate were opposite to the change of tidal, while the water level and salinity were consistent with tidal. The buffer mechanism of phosphate was controlled by suspended sand and water. The concentrations of silicate, phosphate and inorganic nitrogen were ranged 0.63-9.00 mg/L, 0.013-0.075 mg/L, 0.33-4.24 mg/L respectively. The contents of dissolved inorganic nitrogen in water mass increased remarkably comparing 1980s because of agriculture, industry and living. The research indicated that the nitrate and silicate were conservative, but phosphate was non-conservative in the biogeochemical processes of nutrients in Minjiang Estuary. The diluted water carried abundant inorganic nitrogen, silicate nutrients to Minjiang Estuary and thus phosphate was similar between diluted water and sea water. Based on the results of nutrient ratios, it was suggested that phosphate was a limiting factor for phytoplankton growth in the Minjiang Estuary. PMID:21528557

Ye, Xiang; Chen, Jian; Ji, Wei-Dong; Li, Dong-Yi

2011-02-01

203

Biogeochemical effects of seawater restoration to diked salt marshes  

USGS Publications Warehouse

We conducted greenhouse microcosm experiments to examine the biogeochemical effects of restoring seawater to historically diked Cape Cod salt marshes. Peat cores from both seasonally flooded and drained diked marshes were waterlogged with seawater, and porewater chemistry was subsequently monitored for 21 mo. The addition of seawater to highly organic, seasonally flooded peat caused the death of freshwater wetland plants, 6-8 cm of sediment subsidence, and increased N and P mineralization. Also, sulfides and alkalinity increased 10-fold, suggesting accelerated decomposition by sulfate reduction. Addition of seawater to the low-organic-content acidic peat from the drained marsh increased porewater pH, alkalinity, PO4-P, and Fe(II), which we attribute to the reestablishment of SO4 and Fe(III) mineral reduction. Increased cation exchange contributed to 6-fold increases in dissolved Fe(II) and Al and 60-fold increases in NH4-N within 6 mo of sail-nation. Seawater reintroductions to seasonally flooded diked marshes will cause porewater sulfides to increase, likely reducing the success of revegetation efforts. Sulfide toxicity is of less concern in resalinated drained peats because of the abundance of Fe(II) to precipitate sulfides, and of NH4-N to offset sulfide inhibition of N uptake. Restoration of either seasonally flooded or drained diked marshes could stimulate potentially large nutrient and Fe(II) releases, which could in turn increase primary production and lower oxygen in receiving waters. These findings suggest that tidal restoration be gradual and carefully monitored.

Portnoy, J.W.; Giblin, A.E.

1997-01-01

204

The genomic potential of Marinobacter aquaeolei - A biogeochemical opportunotroph  

NASA Astrophysics Data System (ADS)

The family of Marinobacter is one of the most ubiquitous in the ocean. Members of this genus are found throughout the water column, in the deep sea, and are often associated with hydrothermal plume particles and marine snow. They are known to degrade hydrocarbons and show some extremophilic lifestyles, such as pyschrophily, oligotrophy and halotolerance. This study has determined the genomic potential of one particular strain - Marinobacter aquaeolei VT8, which relies on a very large set of survival strategies. Isolated from an oil well in Southern Vietnam, M. aquaeolei was known to be a facultative anaerobe with the ability to utilize various carbon sources. Fitting with these observations, genome annotation has revealed: four variations of the TCA cycle, complete pathways of glycolysis and the degradation of more complex hydrocarbons (including octane oxidation and cyclohexanol degradation), alternative phosphorous and nitrogen sources, genes for the use of nitrate and sulfate as electron acceptors as well as complete pathways for sulfite oxidation, denitrification and iron oxidation. The versatility and interrelatedness of these metabolic potentials coin the opportunistic character of M. aquaeolei and help to more completely define the biogeochemical niche of the genus.

Singer, E.; Webb, E.; Nelson, W.; Heidelberg, J.; Edwards, K. J.

2009-12-01

205

Genomic Potential of Marinobacter aquaeolei, a Biogeochemical “Opportunitroph”?†  

PubMed Central

The genus of Marinobacter is one of the most ubiquitous in the global oceans and assumed to significantly impact various biogeochemical cycles. The genome structure and content of Marinobacter aquaeolei VT8 was analyzed and compared with those from other organisms with diverse adaptive strategies. Here, we report the many “opportunitrophic” genetic characteristics and strategies that M. aquaeolei has adopted to promote survival under various environmental conditions. Genome analysis revealed its metabolic potential to utilize oxygen and nitrate as terminal electron acceptors, iron as an electron donor, and urea, phosphonate, and various hydrocarbons as alternative N, P, and C sources, respectively. Miscellaneous sensory and defense mechanisms, apparently acquired via horizontal gene transfer, are involved in the perception of environmental fluctuations and antibiotic, phage, toxin, and heavy metal resistance, enabling survival under adverse conditions, such as oil-polluted water. Multiple putative integrases, transposases, and plasmids appear to have introduced additional metabolic potential, such as phosphonate degradation. The genomic potential of M. aquaeolei and its similarity to other opportunitrophs are consistent with its cosmopolitan occurrence in diverse environments and highly variable lifestyles. PMID:21335390

Singer, Esther; Webb, Eric A.; Nelson, William C.; Heidelberg, John F.; Ivanova, Natalia; Pati, Amrita; Edwards, Katrina J.

2011-01-01

206

Biogeochemical budgets and processes in Bandon Bay, Suratthani, Thailand  

NASA Astrophysics Data System (ADS)

Water, salt, dissolved nitrogen, and dissolved phosphorus budgets have been constructed for Bandon Bay for the wet and dry periods of 1997 and 1998. The two-box model shows that while most of the dissolved N and P loading is taken up in the estuarine section of Tapi River and Bandon Bay, a significant portion is exported to the Gulf of Thailand. In general, the export fluxes are higher during the wet season than in the dry season. The export flux of DIN is normally dominated by NH 4, and generally greater than the export flux of DON, while DIP is exported at about the same rate as that of DOP. Bandon Bay appears to be in balance metabolically ( p- r=0), suggesting a very high efficiency within the Bay for recycling organic material. The system consumes about 3% more organic matter than it produces in the dry season and produces about 4% more organic matter than it consumes in the wet season. Tapi Estuary is a net denitrifying system while Bandon Bay is slightly net nitrogen fixing. The presence of benthic algae on the mud flats and the mangrove fringe around the bay could account for nitrogen fixation in the bay. Seasonal variations in biogeochemical rates were attributable to differences in magnitude of freshwater inputs. Under conditions of high river flow, overall rates of net production were enhanced by increased nutrient delivery.

Wattayakorn, Gullaya; Prapong, Panyanee; Noichareon, Damrongsak

2001-09-01

207

A quantitative model of the biogeochemical transport of iodine  

NASA Astrophysics Data System (ADS)

Iodine deficiency disorders (IDD) are among the world’s most prevalent public health problems yet preventable by dietary iodine supplements. To better understand the biogeochemical behavior of iodine and to explore safer and more efficient ways of iodine supplementation as alternatives to iodized salt, we studied the behavior of iodine as it is absorbed, accumulated and released by plants. Using Chinese cabbage as a model system and the 125I tracing technique, we established that plants uptake exogenous iodine from soil, most of which are transported to the stem and leaf tissue. The level of absorption of iodine by plants is dependent on the iodine concentration in soil, as well as the soil types that have different iodine-adsorption capacity. The leaching experiment showed that the remainder soil content of iodine after leaching is determined by the iodine-adsorption ability of the soil and the pH of the leaching solution, but not the volume of leaching solution. Iodine in soil and plants can also be released to the air via vaporization in a concentration-dependent manner. This study provides a scientific basis for developing new methods to prevent IDD through iodized vegetable production.

Weng, H.; Ji, Z.; Weng, J.

2010-12-01

208

Feedbacks between hydrological heterogeneity and bioremediation induced biogeochemical transformations  

SciTech Connect

For guiding optimal design and interpretation of in-situ treatments that strongly perturb subsurface systems, knowledge about the spatial and temporal patterns of mass transport and reaction intensities are important. Here, a procedure was developed and applied to time-lapse concentrations of a conservative tracer (bromide), an injected amendment (acetate) and reactive species (iron(II), uranium(VI) and sulfate) associated with two field scale biostimulation experiments, which were conducted successively at the same field location over two years. The procedure is based on a temporal moment analysis approach that relies on a streamtube approximation. The study shows that biostimulated reactions can be considerably influenced by subsurface hydrological and geochemical heterogeneities: the delivery of bromide and acetate and the intensity of the sulfate reduction is interpreted to be predominantly driven by the hydrological heterogeneity, while the intensity of the iron reduction is interpreted to be primarily controlled by the geochemical heterogeneity. The intensity of the uranium(VI) reduction appears to be impacted by both the hydrological and geochemical heterogeneity. Finally, the study documents the existence of feedbacks between hydrological heterogeneity and remediation-induced biogeochemical transformations at the field scale, particularly the development of precipitates that may cause clogging and flow rerouting.

Englert, A.; Hubbard, S.S.; Williams, K.H.; Li, L.; Steefel, C.I.

2009-04-15

209

Catchment Legacies and Trajectories: Understanding Time Lags in Catchment Response as a Function of Hydrologic and Biogeochemical Controls  

NASA Astrophysics Data System (ADS)

Increased nutrient loads delivered from watersheds due to agricultural intensification, industrialization, and urbanization have contributed globally to the persistence of large hypoxic zones in inland and coastal waters. Watershed management practices targeting these non-point source pollutants often lead to little or no improvement in water quality, even after extensive implementation of conservation measures or Best Management Practices (BMPs). The lag time between implementation of a conservation measure and resultant water quality benefits has recently been recognized as an important factor in the "apparent" failure of these BMPs. When conservation measures are implemented without explicit consideration of the lag time and with expectations that they will lead to immediate benefits, the resulting failure to meet such expectations can discourage vital restoration efforts. It is therefore important to quantify the lag times associated with watershed management efforts a priori and to implement restoration strategies targeted specifically at minimizing lag times and maximizing restoration benefits. The focus of this research is to develop a framework for understanding the time lags between land-use changes and stream water quality benefits. We hypothesize that such time lags arise from nutrient legacies building over decades of fertilizer application. For nitrogen (N), one can conceptualize this as either hydrologic legacy, in the form of dissolved nitrate that is delayed due to slow groundwater transport, or as biogeochemical legacy, in the form of organic N, possibly in dissolved or readily mineralizable forms. Indeed, mass-balance studies across the Mississippi and Thames river basins indicate the possibility of missing N mass in these landscapes, with inputs being consistently greater than the outputs even when accounting for all possible pathways of nitrogen transformation. Historical soil data within the upper Mississippi River Basin (MRB) indicate that agriculture depletes organic N in surface soil, but leads to N accumulations deeper in the profile. Nitrogen accumulation estimates (approximately 2 million Mt/yr) based on the historical data are startlingly close to the deficit suggested by mass-balance studies of the MRB (3 million Mt/yr). Understanding the lag times associated with such biogeochemical legacies requires quantification of this accumulation as a function of landscape attributes, climate, and management controls, as well as the rate of mineralization of accumulated N after implementation of management practices. Understanding hydrologic legacy requires a partitioning of flow along various pathways (e.g., overland flow, tile flow, or groundwater pathways), and the distribution of travel times along the pathways. Based on this framework, we developed a coupled hydrologic and biogeochemical model to quantify these legacies and predict landscape recovery times as a function of natural and anthropogenic controls.

Basu, N. B.; Van Meter, K. J.

2012-12-01

210

High-resolution mineralogical characterization and biogeochemical modeling of uranium reaction pathways at the FRC  

SciTech Connect

High-Resolution Mineralogical Characterization and Biogeochemical Modeling of Uranium Reduction Pathways at the Oak Ridge Field-Research Center (FRC) Chen Zhu, Indiana University, David R. Veblen, Johns Hopkins University We have successfully completed a proof-of-concept, one-year grant on a three-year proposal from the former NABIR program, and here we seek additional two-year funding to complete and publish the research. Using a state-of-the-art 300-kV, atomic resolution, Field Emission Gun Transmission Electron Microscope (TEM), we have successfully identified three categories of mineral hosts for uranium in contaminated soils: (1) iron oxides; (2) mixed manganese-iron oxides; and (3) uranium phosphates. Method development using parallel electron energy loss spectroscopy (EELS) associated with the TEM shows great promise for characterizing the valence states of immobilized U during bioremediation. We have also collected 27 groundwater samples from two push-pull field biostimulation tests, which form two time series from zero to approximately 600 hours. The temporal evolution in major cations, anions, trace elements, and the stable isotopes 34S, 18O in sulfate, 15N in nitrate, and 13C in dissolved inorganic carbon (DIC) clearly show that biostimulation resulted in reduction of nitrate, Mn(IV), Fe(III), U(VI), sulfate, and Tc(VII), and these reduction reactions were intimately coupled with a complex network of inorganic reactions evident from alkalinity, pH, Na, K, Mg, and Ca concentrations. From these temporal trends, apparent zero order rates were regressed. However, our extensive suite of chemical and isotopic data sets, perhaps the first and only comprehensive data set available at the FRC, show that the derived rates from these field biostimulation experiments are composite and lump-sum rates. There were several reactions that were occurring at the same time but were masked by these pseudo-zero order rates. A reaction-path model comprising a total of nine redox couples (NO3–/NH4+, MnO2(s)/Mn2+, Fe(OH)3(s) /Fe2+, TcO4–/TcO2(s), UO22+/UO2(s), SO42–/HS–, CO2/CH4, ethanol/acetate, and H+/H2.) is used to simulate the temporal biogeochemical evolution observed in the field tests. Preliminary results show that the models based on thermodynamics and more complex rate laws can generate the apparent zero order rates when several concurrent or competing reactions occur. Professor Alex Halliday of Oxford University, UK, and his postdoctoral associates are measuring the uranium isotopes in our groundwater samples. Newly developed state-of-the-art analytical techniques in measuring variability in 235U/238U offer the potential to distinguish biotic and abiotic uranium reductive mechanisms.

Chen Zhu

2006-06-15

211

Hotspots and hot moments of aquifer river exchange and biogeochemical cyclinbg in the streambed of lowland rivers  

NASA Astrophysics Data System (ADS)

Exchange fluxes across aquifer-river interfaces can have a major impact on the biogeochemical cycling in streambed environments. This paper presents integrated experimental and model-based investigations of physical drivers and chemical controls on streambed biogeochemcial cycling at two UK lowland rivers. It combines in-stream geophysical surveys, multi-level mini-piezometer networks and active and passive heat tracing methods for identifying spatial patterns and temporal dynamics of aquifer-river exchange fluxes with multi-scale hyporheic pore-water sampling and applications of reactive "smart-tracers". Hyporheic pore water analysis from nested multi-level piezometers and passive gel probe samplers revealed significant spatial variability in streambed nitrogen cycling in dependence of redox-conditions, dissolved oxygen and bio-available organic carbon concentrations. Hot spots of increased nitrate attenuation and anaerobic respiration were associated with semi-confining streambed peat lenses. The intensity of concentration changes underneath the confining peat layers correlated with the state of anoxia in the pore water as well as the supply of organic carbon and hyporheic residence times. In contrast, at locations where flow inhibiting peat layers were absent or disrupted - fast exchange between aquifer and river caused a break-through of nitrate without significant concentration changes along the hyporheic flow path. Fibre-optic Distributed Temperature Sensing was applied for identifying groundwater - surface water exchange flow patterns in dependency of streambed structural heterogeneity and support the identification of the location and extend of flow inhibiting structures as indicators of streambed reactivity hot spots. Coupled groundwater-surface water model simulations supported the experimental results, indicating that hotspots of exchange fluxes and biogeochemical activity were predominantly controlled by the spatial heterogeneous impact of streambed conductivity patterns on groundwater up-welling while surface driven processes as advective pumping had only marginal impacts.

Krause, Stefan; Munz, Mathias; Tecklenburg, Christina; Blume, Theresa; Binley, Andrew

2013-04-01

212

Biogeochemical indicators of elevated nitrogen deposition in semiarid Mediterranean ecosystems.  

PubMed

Nitrogen (N) deposition has doubled the natural N inputs received by ecosystems through biological N fixation and is currently a global problem that is affecting the Mediterranean regions. We evaluated the existing relationships between increased atmospheric N deposition and biogeochemical indicators related to soil chemical factors and cryptogam species across semiarid central, southern, and eastern Spain. The cryptogam species studied were the biocrust-forming species Pleurochaete squarrosa (moss) and Cladonia foliacea (lichen). Sampling sites were chosen in Quercus coccifera (kermes oak) shrublands and Pinus halepensis (Aleppo pine) forests to cover a range of inorganic N deposition representative of the levels found in the Iberian Peninsula (between 4.4 and 8.1 kg N ha(-1) year(-1)). We extended the ambient N deposition gradient by including experimental plots to which N had been added for 3 years at rates of 10, 20, and 50 kg N ha(-1) year(-1). Overall, N deposition (extant plus simulated) increased soil inorganic N availability and caused soil acidification. Nitrogen deposition increased phosphomonoesterase (PME) enzyme activity and PME/nitrate reductase (NR) ratio in both species, whereas the NR activity was reduced only in the moss. Responses of PME and NR activities were attributed to an induced N to phosphorus imbalance and to N saturation, respectively. When only considering the ambient N deposition, soil organic C and N contents were positively related to N deposition, a response driven by pine forests. The PME/NR ratios of the moss were better predictors of N deposition rates than PME or NR activities alone in shrublands, whereas no correlation between N deposition and the lichen physiology was observed. We conclude that integrative physiological measurements, such as PME/NR ratios, measured on sensitive species such as P. squarrosa, can provide useful data for national-scale biomonitoring programs, whereas soil acidification and soil C and N storage could be useful as additional corroborating ecosystem indicators of chronic N pollution. PMID:24894911

Ochoa-Hueso, Raúl; Arróniz-Crespo, María; Bowker, Matthew A; Maestre, Fernando T; Pérez-Corona, M Esther; Theobald, Mark R; Vivanco, Marta G; Manrique, Esteban

2014-09-01

213

Biogeochemical controls on hexavalent chromium formation in estuarine sediments.  

PubMed

Predicting the aquatic and human health impacts of chromium (Cr) necessitates one to determine its speciation as either relatively nontoxic Cr(III) or toxic Cr(VI) and elucidate the influence of biogeochemical changes on its behavior and fate. In the Baltimore Harbor, Cr predominantly exists as Cr(III) associated with sediments. While reduction of Cr(VI) to Cr(III) is dominant in these anoxic sediments, the potential of Cr(III) oxidation and Cr(VI) reoccurrence during sediment resuspension and oxygenation resulting from dredging, bioturbation, and flood events poses a serious concern. In batch experiments, aqueous Cr(VI) spiked into continuously mixed anoxic suspensions was reduced to product Cr(III) under anaerobic conditions. No Cr(VI) reoccurrence was observed when conditions remained anaerobic. Aeration caused Cr(VI) reoccurrence from the abiotic oxidation of product Cr(III). Rates of aeration-driven Cr(VI) reoccurrence increased with pH, and Cr(VI) reoccurrence positively correlated with dissolved manganese (Mn) decline at pH ? 7. Aeration-driven oxidation of Mn(II) to Mn(III,IV)(hydr)oxides was the underlying mechanism causing product Cr(III) oxidation. Cr(VI) reoccurrence decreased with sediment loading and negatively correlated with the acid volatile sulfide (AVS) concentration. Although sediment resuspension and oxygenation may create temporary conditions conducive to Cr(VI) formation, long-term Cr(VI) persistence is unlikely in the presence of sediment reductants. While such natural attenuation in reducing environments mitigates the risk associated with Cr toxicity, this risk may still persist in Mn-rich and reductant-deficient environments. PMID:23802856

Wadhawan, Amar R; Stone, Alan T; Bouwer, Edward J

2013-08-01

214

Stoichiometric vs hydroclimatic controls on soil biogeochemical processes  

NASA Astrophysics Data System (ADS)

Soil nutrient cycles are controlled by both stoichiometric constraints (e.g., carbon to nutrient ratios) and hydroclimatic conditions (e.g., soil moisture and temperature). Both controls tend to act in a nonlinear manner and give rise to complex dynamics in soil biogeochemistry at different space-time scales. We first review the theoretical basis of soil biogeochemical models, looking for the general principles underlying these models across space-time scales and scientific disciplines. By comparing more than 250 models, we show that similar kinetic and stoichiometric laws, formulated to mechanistically represent the complex biochemical constraints to decomposition, are common to most models, providing a basis for their classification. Moreover, a historic analysis reveals that the complexity (e.g., phase space dimension, model architecture) and degree and number of nonlinearities generally increased with date, while they decreased with increasing spatial and temporal scale of interest. Soil biogeochmical dynamics may be suitable conceptualized using a number of compartments (e.g., decomposers, organic substrates, inorganic ions) interacting among each other at rates that depend (nonlinearly) on climatic drivers. As a consequence, hydroclimatic-induced fluctuations at the daily scale propagate through the various soil compartments leading to cascading effects ranging from short-term fluctuations in the smaller pools to long-lasting changes in the larger ones. Such cascading effects are known to occur in dryland ecosystems, and are increasingly being recongnized to control the long-term carbon and nutrient balances in more mesic ecosystems. We also show that separating biochemical from climatic impacts on organic matter decomposition results in universal curves describing data of plant residue decomposition and nutrient mineralization across the globe. Future extensions to larger spatial scales and managed ecosystems are also briefly outlined. It is critical that future modeling efforts carefully account for the scale-dependence of their mathematical formulations, especially when applied to a wide range of scales.

Manzoni, Stefano; Porporato, Amilcare

2010-05-01

215

Biogeochemical characterisation of a coal tar distillate plume.  

PubMed

The distillation of acidified coal tars for up to 50 years has given rise to a phenol plume approximately 500 m long, 50 m deep and containing up to 15 g l(-1) dissolved organic carbon (DOC) in the Triassic Sandstones aquifer. A conceptual biogeochemical model based on chemical and microbiological analysis of groundwater samples has been developed as a preliminary to more detailed studies of the controls on natural attenuation. While the development of redox zones and the production of methane and carbon dioxide provide evidence of natural attenuation, it appears that degradation is slow. The existence of sulphate in the plume indicates that this electron acceptor has not been depleted and that consequently methanogenesis is probably limited. Based on a simple estimate of sulphate input concentration, a half-life of about 15 years has been estimated for sulphate reduction. Geochemical modelling predicts that increased alkalinity within the plume has not led to carbonate precipitation, and thus within the limits of accuracy of the measurement, alkalinity may reflect the degree of biodegradation. This implies a loss of around 18% of the DOC over a 30-year period. Despite limited degradation, microbial studies show that there are diverse microbial communities in the aquifer with the potential for both anaerobic and aerobic biodegradation. Microbial activity was found to be greatest at the leading edge of the plume where DOC concentrations are 60 mg l(-1) or less, but activity could still be observed in more contaminated samples even though cells could not be cultured. The study suggests that degradation may be limited by the high phenol concentrations within the core of the plume, but that once diluted by dispersion, natural attenuation may proceed. More detailed studies to confirm these initial findings are identified and form the basis of associated papers. PMID:11820470

Williams, G M; Pickup, R W; Thornton, S F; Lerner, D N; Mallinson, H E; Moore, Y; White, C

2001-12-15

216

Assessment of a global eddy-permitting biogeochemical hindcast of the ocean colour era.  

NASA Astrophysics Data System (ADS)

The combination of climate change and various anthropogenic drivers, such as e.g. changes in external nutrient inputs and exploitation of marine resources drive important changes in marine ecosystems. These changes occur against the background of natural variability. The retrospective analysis of global ocean biogeochemical state holds promise for identifying the response of marine ecosystems and biogeochemical fluxes to natural climate variability and, potentially, allows to detect trends driven by global climate change. Ideally, such a biogeochemical hindcast simulation should resolve the mesoscale and span multiple decades. Here, we present a biogeochemical simulation at 1/4° resolution for the period between 1994 to 2010 with NEMO/PISCES. The biogeochemical model PISCES was forced off-line by weekly fields provided by a physical simulation at 1/4° resolution (orca025) over the same period. The model was initialized with global climatologies. The spin-up involved 20 years of biogeochemical off-line simulation forced by a climatology of ocean physics. The inter-annual simulation (1994-2010) followed on the spin-up. The analysis of our spin-up strategy is presented with focus on the adjustment of model fields. The inter-annual simulation is evaluated by systematically comparing model fields to observations at global and regional scales. We draw on EOF (Empirical Orthogonal Functions) analysis to evaluate spatial/temporal variability. We focus on links between biogeochemical and physical variables in order to identify underlying common modes of variability for multiple variables. Finally, to complete the assessment, we compare EOF modes for Globcolour chlorophyll estimates (a merged Seawifs-Meris-Modis product) and model output over the period of observations.

Perruche, Coralie; Gehlen, Marion; Daudin, Anne; El Moussaoui, Abdelali; Greiner, Eric; Ethe, Christian

2013-04-01

217

Nutrient biogeochemical cycles in the Gulf of Riga: scaling up field studies with a mathematical model  

NASA Astrophysics Data System (ADS)

A box model has been implemented to understand the large-scale biogeochemical cycles of nitrogen, phosphorus, and silicon in the Gulf of Riga. The large data sets collected within the international Gulf of Riga Project in 1993/1995 were used to validate the model. The comparison to data was useful in scaling up to the gulf-wide level and scrutinizing the conclusions based on short-term field surveys and experimental studies. The simulations indicate that the limiting role was passing from silicon to phosphorus to nitrogen over the seasons of organic production. However, on an annual scale, nutrient limitation was close to the "Redfield equilibrium". Mass balance considerations, based on modeled coupled fluxes, disagree with the conclusions on low sediment denitrification and high phosphorus retention in the pelagic system, which were derived from isolated measurements. Nutrient budgets constructed with the model revealed the high buffer capacity of the Gulf of Riga. The nutrient residence times span a range from 6 years for N to 70 years for Si. The buffering arises from intensive internal recycling in the water body and by the bottom sediments. The budgets indicate that the Gulf retains about two-thirds of external nitrogen and silicon inputs, while phosphorus retention is only 10%. A slow response to external perturbations is demonstrated with numerical experiments run for 15 years under 50% reductions of terrestrial nutrient inputs. These experiments imply that the most effective is the N+P reduction scenario, which resulted in a 20% decrease of primary production after 12 years. A reduction of P resulted in only a 6% decrease of primary production; however, it yielded an 80% drop in the amount of nitrogen fixation.

Savchuk, Oleg P.

2002-05-01

218

Development of Arsenic and Iron Biogeochemical Gradients upon Anaerobiosis at Soil Aggregate Scale  

NASA Astrophysics Data System (ADS)

In aerated soils, As release is limited due to the strong interaction between As(V) and soil minerals. However, under anaerobic conditions, As desorption is stimulated by As(V) reduction to As(III) and reductive dissolution/transformation of Fe (hydr)oxides, common hosts of As. The effect of As(V) and Fe(III) reduction on As release has been extensively studied in laboratory batch and column systems; correlation of apparent Fe and As reduction, with concomitant release to pore water, has also been noted under field conditions. What remains unresolved is the coupling of biogeochemical and physical processes that ultimately control As transport within structured media such as soils. Soils are heterogeneous porous media that are comprised of individual aggregates having pores that are dominated by diffusive (aggregate interiors) or advective (aggregate exteriors) transport. As a consequence of physical and chemical differences in the interior and the exterior of aggregates, As(III,V) and Fe(II,III) chemical gradients develop. Here, we examine As release from constructed aggregates exposed to fluctuating redox conditions. Artificial aggregates were made with As(V) adsorbed ferrihydrite-coated sand homogeneously inoculated with Shewanella sp. ANA-3 (model As(V) and Fe(III) reducer) and then fused using an agarose binder into spheres. Aggregates were placed in a flow reactor and saturated flow of aerobic or anaerobic artificial groundwater media was initiated. Redox fluctuated in select systems to examine changes in chemical gradient under changing aeration status. Our results show that within aerated solutions, oxidized aggregate exteriors provide a "gprotective barrier"h against As release despite anoxia within diffusively constrained aggregate interiors. During a transition to anaerobic conditions in advective zones, however, As is released and transport is promoted. Our study illustrates the microscale variation in biogeoechemical processes within soils and the importance of appreciating the spatial connection between reaction and transport fronts.

Masue-Slowey, Y.; Pallud, C.; Bedore, P.; Tufano, K.; Fendorf, S.

2008-12-01

219

The effect of tidal forcing on biogeochemical processes in intertidal salt marsh sediments  

PubMed Central

Background Early diagenetic processes involved in natural organic matter (NOM) oxidation in marine sediments have been for the most part characterized after collecting sediment cores and extracting porewaters. These techniques have proven useful for deep-sea sediments where biogeochemical processes are limited to aerobic respiration, denitrification, and manganese reduction and span over several centimeters. In coastal marine sediments, however, the concentration of NOM is so high that the spatial resolution needed to characterize these processes cannot be achieved with conventional sampling techniques. In addition, coastal sediments are influenced by tidal forcing that likely affects the processes involved in carbon oxidation. Results In this study, we used in situ voltammetry to determine the role of tidal forcing on early diagenetic processes in intertidal salt marsh sediments. We compare ex situ measurements collected seasonally, in situ profiling measurements, and in situ time series collected at several depths in the sediment during tidal cycles at two distinct stations, a small perennial creek and a mud flat. Our results indicate that the tides coupled to the salt marsh topography drastically influence the distribution of redox geochemical species and may be responsible for local differences noted year-round in the same sediments. Monitoring wells deployed to observe the effects of the tides on the vertical component of porewater transport reveal that creek sediments, because of their confinements, are exposed to much higher hydrostatic pressure gradients than mud flats. Conclusion Our study indicates that iron reduction can be sustained in intertidal creek sediments by a combination of physical forcing and chemical oxidation, while intertidal mud flat sediments are mainly subject to sulfate reduction. These processes likely allow microbial iron reduction to be an important terminal electron accepting process in intertidal coastal sediments. PMID:17567893

Taillefert, Martial; Neuhuber, Stephanie; Bristow, Gwendolyn

2007-01-01

220

Biogeochemical control of marine productivity in the Mediterranean Sea during the last 50 years  

NASA Astrophysics Data System (ADS)

temporal dynamics of biogeochemical variables derived from a coupled 3-D model of the Mediterranean Sea are evaluated for the last 50 years (1960-2010) against independent data on fisheries catch per unit effort (CPUE) for the same time period. Concordant patterns are found in the time series of all of the biological variables (from the model and from fisheries statistics), with low values at the beginning of the series, a later increase, with maximum levels reached at the end of the 1990s, and a posterior stabilization. Spectral analysis of the annual biological time series reveals coincident low-frequency signals in all of them. The first, more energetic signal peaks around the year 2000, while the second, less energetic signal peaks near 1982. Almost identical low-frequency signals are found in the nutrient loads of the rivers and in the integrated nutrient levels in the surface marine ecosystem. Nitrate concentration shows a maximum level in 1998, with a later stabilization to present-day values, coincident with the first low-frequency signal found in the biological series. Phosphate shows maximum concentrations around 1982 and a posterior sharp decline, in concordance with the second low-frequency signal observed in the biological series. That result seems to indicate that the control of marine productivity (plankton to fish) in the Mediterranean is principally mediated through bottom-up processes that could be traced back to the characteristics of riverine discharges. The high sensitivity of CPUE time series to environmental conditions might be another indicator of the overexploitation of this marine ecosystem.

Macias, Diego; Garcia-Gorriz, Elisa; Piroddi, Chiara; Stips, Adolf

2014-08-01

221

Consequences of ecological, evolutionary and biogeochemical uncertainty for coral reef responses to climatic stress.  

PubMed

Coral reefs are highly sensitive to the stress associated with greenhouse gas emissions, in particular ocean warming and acidification. While experiments show negative responses of most reef organisms to ocean warming, some autotrophs benefit from ocean acidification. Yet, we are uncertain of the response of coral reefs as systems. We begin by reviewing sources of uncertainty and complexity including the translation of physiological effects into demographic processes, indirect ecological interactions among species, the ability of coral reefs to modify their own chemistry, adaptation and trans-generational plasticity. We then incorporate these uncertainties into two simple qualitative models of a coral reef system under climate change. Some sources of uncertainty are far more problematic than others. Climate change is predicted to have an unambiguous negative effect on corals that is robust to several sources of uncertainty but sensitive to the degree of biogeochemical coupling between benthos and seawater. Macroalgal, zoanthid, and herbivorous fish populations are generally predicted to increase, but the ambiguity (confidence) of such predictions are sensitive to the source of uncertainty. For example, reversing the effect of climate-related stress on macroalgae from being positive to negative had no influence on system behaviour. By contrast, the system was highly sensitive to a change in the stress upon herbivorous fishes. Minor changes in competitive interactions had profound impacts on system behaviour, implying that the outcomes of mesocosm studies could be highly sensitive to the choice of taxa. We use our analysis to identify new hypotheses and suggest that the effects of climatic stress on coral reefs provide an exceptional opportunity to test emerging theories of ecological inheritance. PMID:24845674

Mumby, Peter J; van Woesik, Robert

2014-05-19

222

Aquifer/aquitard interfaces: mixing zones that enhance biogeochemical reactions  

NASA Astrophysics Data System (ADS)

Several important biogeochemical reactions are known to occur near the interface between aquifer and aquitard sediments. These reactions include O2 reduction; denitrification; and Fe3+, SO42-, and CO2 (methanogenesis) reduction. In some settings, these reactions occur on the aquitard side of the interface as electron acceptors move from the aquifer into the electron-donor-enriched aquitard. In other settings, these reactions occur on the aquifer side of the interface as electron donors move from the aquitard into the electron-acceptor-enriched, or microorganism-enriched, aquifer. Thus, the aquifer/aquitard interface represents a mixing zone capable of supporting greater microbial activity than either hydrogeologic unit alone. The extent to which biogeochemical reactions proceed in the mixing zone and the width of the mixing zone depend on several factors, including the abundance and solubility of electron acceptors and donors on either side of the interface and the rate at which electron acceptors and donors react and move across the interface. Biogeochemical reactions near the aquifer/aquitard interface can have a substantial influence on the chemistry of water in aquifers and on the chemistry of sediments near the interface. Résumé. Il se produit au voisinage de l'interface entre les aquifères et les imperméables plusieurs réactions biogéochimiques importantes. Il s'agit des réactions de réduction de l'oxygène, de la dénitrification et de la réduction de Fe3+, SO42- et CO2 (méthanogenèse). Dans certaines situations, ces réactions se produisent du côté imperméable de l'interface, avec des accepteurs d'électrons qui vont de l'aquifère vers l'imperméable riche en donneurs d'électrons. Dans d'autres situations, ces réactions se produisent du côté aquifère de l'interface, avec des donneurs d'électrons qui se déplacent de l'imperméable vers l'aquifère riche en accepteurs d'électrons ou en microorganismes. Ainsi, l'interface aquifère/imperméable constitue une zone de mélange capable de supporter une plus grande activité microbienne que chacune des deux unités hydrogéologiques seules. L'extension des réactions biogéochimiques dans la zone de mélange et la largeur de cette zone dépendent de plusieurs facteurs, dont l'abondance et la solubilité des accepteurs et des donneurs d'électrons de chaque côté de l'interface, et le taux de réaction et de déplacement des accepteurs et des donneurs d'électrons au travers de cette interface. Les réactions biogéochimiques au voisinage de l'interface aquifère/imperméable peuvent avoir une influence appréciable sur le chimisme de l'eau des aquifères et sur celui des sédiments au niveau de l'interface. Resúmen. Es conocido que varias reacciones biogeoquímicas de importancia pueden tener lugar cerca de la interfaz entre los sedimentos de un acuífero y de un acuitardo. Entre ellas, destaca la reducción del O2, la denitrificación, y la reducción del Fe+3, SO4-2 y CO2 (metanogénesis). En algunos casos, estas reacciones se producen en la región cercana al acuitardo, ya que los dadores de electrones se mueven desde éste hacia el acuífero, el cual está enriquecido en aceptores de electrones o en microorganismos. Así, la interfaz acuífero/acuitardo constituye una zona de mezcla que es capaz de sustentar una actividad microbiana mayor que cualquier unidad hidrogeológica por sí misma. El alcance de las reacciones biogeoquímicas en la zona de mezcla y el ancho de esta zona de mezcla depende de varios factores, como la abundancia y la solubilidad de los aceptores y dadores de electrones en ambas caras de la interfaz y la velocidad a la que los aceptores y dadores de electrones reaccionan y se mueven a través de la interfaz. Las reacciones biogeoquímicas cerca de la interfaz acuífero/acuitardo pueden tener una influencia substancial en la hidroquímica de los acuíferos y en la química de los sedimentos cerca de la superficie.

McMahon, P. B.

2001-01-01

223

Terrestrial biogeochemical cycles - Global interactions with the atmosphere and hydrology  

NASA Technical Reports Server (NTRS)

A review is presented of developments in ecosystem theory, remote sensing, and geographic information systems that support new endeavors in spatial modeling. A paradigm has emerged to predict ecosystem behavior based on understanding responses to multiple resources. Ecosystem models couple primary production to decomposition and nutrient availability utilizing this paradigm. It is indicated that coupling of transport and ecosystem processes alters the behavior of earth system components (terrestrial ecosystems, hydrology, and the atmosphere) from that of an uncoupled model.

Schimel, David S.; Parton, William J.; Kittel, Timothy G. F.

1991-01-01

224

Biogeochemical features of aquatic plants in the Selenga River delta  

NASA Astrophysics Data System (ADS)

The Selenga River system provides more than a half of the Lake Baikal total inflow. The river collects a significant amount of pollutants (e.g. heavy metals) from the whole basin. These substances are partially deposited within the Selenga delta, and partially are transported further to the lake. A generous amount of aquatic plants grow in the delta area according to its favorable conditions. This vegetation works as a specific biofilter. It accumulates suspended particles and sorbs some heavy metals from the water. The study aimed to reveal the species of macrophytes which could be mostly important for biomonitoring according to their chemical composition. The field campaign took place in the Selenga River delta in July-August of 2011 (high water period) and in June of 2012 (low water period). 14 species of aquatic plants were collected: water starwort Callitriche hermaphroditica, small yellow pond lily Nuphar pumila, pondweeds Potamogeton crispus, P. pectinatus, P. friesii, broadleaf cattail Typha latifolia, hornwort or coontail Ceratophyllum demersum, arrowhead Sagittaria natans, flowering rush (or grass rush) Butomus umbellatus, reed Phragmites australis, parrot's feather Myriophyllum spicatum, the common mare's tail Hippuris vulgaris, Batrachium trichophyllum, canadian waterweed Elodea canadensis. The samples were dried, grinded up and digested in a mixture of HNO3 and H2O2. The chemical composition of the plant material was defined using ICP-MS and ICP-AES methods. Concentrations of Fe, Mn, Cr, Ni, Cu, B, Zn, V, Co, As, Mo, Pb, and U were considered. The study revealed that Potamogeton pectinatus and Myriophyllum spicatum concentrate elements during both high and low water periods. Conversely the Butomus umbellatus and Phragmites australis contain small amount of heavy metals. The reed as true grasses usually accumulates fewer amounts of elements than other macrophytes. To compare biogeochemical specialization of different species we suggest to use concentration ratio relatively Phragmites australis as a background content. This factor showed that Nuphar pumila and Ceratophyllum demersum are acting like concentrators in comparison with the reed. According to this ratio, the mostly accumulated elements in aquatic plants in 2011 were V, Co, As, U, and in 2012 - Cu, As, Bi. Differences in chemical composition are due to different water periods. During the high water period in 2011 a large amount of soil particles after the heavy rains were taken into the flow from the river banks and then deposited within the delta. The transportation of suspended particles during the low water period of 2012 was significantly less.

Shinkareva, Galina; Lychagin, Mikhail

2014-05-01

225

Significant differences in biogeochemical processes between a glaciated and a permafrost dominated catchment  

NASA Astrophysics Data System (ADS)

It is increasingly recognised that microbially mediated processes have a significant impact on chemical fluxes from glaciated catchments. One important reaction is the oxidation of pyrite since the production of sulphuric acid facilitates the dissolution of minerals without the need for acidity generated by dissolved atmospheric CO2. Thus weathering processes can still continue even when isolated from the atmosphere, as is thought to occur under large ice masses. However, as a glacier melts, it is expected that the microbial community will change with knock-on effects on the stream water chemistry. Understanding the difference in solute generation processes between glaciated and un-glaciated terrain is key to understanding how glacial-interglacial cycles affect atmospheric CO2 consumption by chemical weathering. In order to investigate whether biogeochemical processes differ between glaciated and un-glaciated terrain we collected stream water samples from two small catchments (each approximately 3 km2) in Svalbard. One catchment is glaciated and the other catchment is un-glaciated but is affected by permafrost and a seasonal snow-pack. The two catchments are situated next to each other with identical bedrock (shale with minor siltstone and sandstone). The proximity of the catchments to each other ensures that meteorological variables such as temperature and precipitation are very similar. Sampling was conducted early in the melt-season when there was still significant snow-cover and in mid-summer when most of the seasonal snow-pack had melted. The water samples were analysed for ?34S-SO4, ?18O-SO4, ?18O-H2O, ?13C-DIC and ?13C-DOC, together with major anions and cations. Despite the nominally identical lithology, there were significant differences in the stream water chemistry between the two catchments. For example, sulphate was the dominant anion in the un-glaciated catchment whereas bicarbonate was the dominant anion in the glaciated catchment. Pyrite oxidation under anoxic conditions and microbially mediated sulphate reduction occur in both catchments. However, in the glaciated catchment pyrite oxidation is mainly coupled to carbonate dissolution and in the un-glaciated catchment it is mainly coupled to silicate dissolution. These significant differences in weathering processes will be discussed with reference to the microbial communities found in the two catchments.

Hindshaw, Ruth; Heaton, Tim; Boyd, Eric; Lang, Susan; Tipper, Ed

2014-05-01

226

Decadal variability in biogeochemical models: Comparison with a 50-year ocean colour dataset  

NASA Astrophysics Data System (ADS)

Assessing the skill of biogeochemical models to hindcast past variability is challenging, yet vital in order to assess their ability to predict biogeochemical change. However, the validation of decadal variability is limited by the sparsity of consistent, long-term biological datasets. The Phytoplankton Colour Index (PCI) product from the Continuous Plankton Recorder survey, which has been sampling the North Atlantic since 1948, is an example of such a dataset. Converting the PCI to chlorophyll values using SeaWiFS data allows a direct comparison with model output. Here we validate decadal variability in chlorophyll from the GFDL TOPAZ model. The model demonstrates skill at reproducing interannual variability, but cannot simulate the regime shifts evident in the PCI data. Comparison of the model output, data and climate indices highlights under-represented processes that it may be necessary to include in future biogeochemical models in order to accurately simulate decadal variability in ocean ecosystems.

Henson, Stephanie A.; Raitsos, Dionysios; Dunne, John P.; McQuatters-Gollop, Abigail

2009-11-01

227

Radionuclide release from simulated waste material after biogeochemical leaching of uraniferous mineral samples.  

PubMed

Biogeochemical mineral dissolution is a promising method for the released of metals in low-grade host mineralization that contain sulphidic minerals. The application of biogeochemical mineral dissolution to engineered leach heap piles in the Elliot Lake region may be considered as a promising passive technology for the economic recovery of low grade Uranium-bearing ores. In the current investigation, the decrease of radiological activity of uraniferous mineral material after biogeochemical mineral dissolution is quantified by gamma spectroscopy and compared to the results from digestion/ICP-MS analysis of the ore materials to determine if gamma spectroscopy is a simple, viable alternative quantification method for heavy nuclides. The potential release of Uranium (U) and Radium-226 ((226)Ra) to the aqueous environment from samples that have been treated to represent various stages of leaching and passive closure processes are assessed. Dissolution of U from the solid phase has occurred during biogeochemical mineral dissolution in the presence of Acidithiobacillus ferrooxidans, with gamma spectroscopy indicating an 84% decrease in Uranium-235 ((235)U) content, a value in accordance with the data obtained by dissolution chemistry. Gamma spectroscopy data indicate that only 30% of the (226)Ra was removed during the biogeochemical mineral dissolution. Chemical inhibition and passivation treatments of waste materials following the biogeochemical mineral dissolution offer greater protection against residual U and (226)Ra leaching. Pacified samples resist the release of (226)Ra contained in the mineral phase and may offer more protection to the aqueous environment for the long term, compared to untreated or inhibited residues, and should be taken into account for future decommissioning. PMID:24726552

Williamson, Aimee Lynn; Caron, François; Spiers, Graeme

2014-12-01

228

The interplay of microbially mediated and abiotic reactions in the biogeochemical Fe cycle.  

PubMed

Many iron (Fe) redox processes that were previously assumed to be purely abiotic, such as photochemical Fe reactions, are now known to also be microbially mediated. Owing to this overlap, discerning whether biotic or abiotic processes control Fe redox chemistry is a major challenge for geomicrobiologists and biogeochemists alike. Therefore, to understand the network of reactions within the biogeochemical Fe cycle, it is necessary to determine which abiotic or microbially mediated reactions are dominant under various environmental conditions. In this Review, we discuss the major microbially mediated and abiotic reactions in the biogeochemical Fe cycle and provide an integrated overview of biotic and chemically mediated redox transformations. PMID:25329406

Melton, Emily D; Swanner, Elizabeth D; Behrens, Sebastian; Schmidt, Caroline; Kappler, Andreas

2014-12-01

229

GLOBAL BIOGEOCHEMICAL CYCLES, VOL. ???, XXXX, DOI:10.1029/, Global Dry Deposition of Nitrogen Dioxide and1  

E-print Network

GLOBAL BIOGEOCHEMICAL CYCLES, VOL. ???, XXXX, DOI:10.1029/, Global Dry Deposition of Nitrogen central roles in biogeochemical24 cycles. Nitrogen oxides (NOx=NO+NO2) and SO2 are emitted, annual dry deposition to land estimated from OMI as NO2 contributes12 1.5 ± 0.5 Tg of nitrogen and as SO2

Martin, Randall

230

Biogeochemical dynamics of pollutants in Insitu groundwater remediation systems  

NASA Astrophysics Data System (ADS)

Insitu (bio) remediation of groundwater contaminants has been area of potential research interest in last few decades as the nature of contaminant encountered has also changed drastically. This gives tough challenge to researchers in finding a common solution for all contaminants together in one plume. Redox processes play significant role in pollutant dynamics and mobility in such systems. Arsenic particularly in reduced environments can get transformed into its reduced form (As3+), which is apparently more mobile and highly toxic. Also parallel sulfate reduction can lead to sulfide production and formation of thioarsenic species. On the other hand heavy metals (Zn, Fe, and Cd) in similar conditions will favour more stable metal sulfide precipitation. In the present work, we tested Zero Valent Iron (ZVI) in handling such issues and found promising results. Although it has been well known for contaminants like arsenic and chlorinated compounds but not much explored for heavy metals. Its high available surface area supports precipitation and co -precipitation of contaminants and its highly oxidizing nature and water born hydrogen production helps in stimulation of microbial activities in sediment and groundwater. These sulfate and Iron reducing bacteria can further fix heavy metals as stable metal sulfides by using hydrogen as potential electron donor. In the present study flow through columns (biotic and control) were set up in laboratory to understand the behaviour of contaminants in subsurface environments, also the impact of microbiology on performance of ZVI was studied. These glass columns (30 x 4cm) with intermediate sampling points were monitored over constant temperature (20°C) and continuous groundwater (up)flow at ~1ml/hr throughout the experiment. Simulated groundwater was prepared in laboratory containing sulfate, metals (Zn,Cd) and arsenic (AsV). While chemical and microbial parameters were followed regularly over time, solid phase has been characterized at the end of experiment using synchrotron and other microscopic techniques (SEM, µXRF). Stable isotope signatures have been proved as a critical tool in understanding the redox and microbial processes. We monitored ?34S, ?66Zn and ?56Fe isotope evolution with time to understand the relationship between biogeochemical process and isotope fractionation. We observed ?34S biotic - abiotic ~6‰ and ?56Fe variation up to 1.5‰ in our study. ZVI was very efficient in metal removal and also in enhancing sulfate reduction in column sediment. Arsenic reduction and thiarsenic species were also detected in biotic columns showing a positive correlation with sulfide production and Fe speciation. Latest results will be presented with integration of different processes. This multidisciplinary approach will help in deep understanding of contaminants behaviour and also to constrain the efficiency and longitivity of treatment system for different contaminants. “This is contribution of the AquaTrain MRTN (Contract No. MRTN-CT-2006-035420) funded under the European Commission sixth framework programme (2002-2006) Marie Curie Actions, Human Resources & Mobility Activity Area- Research Training Networks”

Kumar, N.; Millot, R.; Rose, J.; Négrel, P.; Battaglia-Brunnet, F.; Diels, L.

2010-12-01

231

The Neoproterozoic oxygenation event: Environmental perturbations and biogeochemical cycling  

NASA Astrophysics Data System (ADS)

The oxygen content of the Earth's surface environment is thought to have increased in two broad steps: the Great Oxygenation Event (GOE) around the Archean-Proterozoic boundary and the Neoproterozoic Oxygenation Event (NOE), during which oxygen possibly accumulated to the levels required to support animal life and ventilate the deep oceans. Although the concept of the GOE is widely accepted, the NOE is less well constrained and its timing and extent remain the subjects of debate. We review available evidence for the NOE against the background of major climatic perturbations, tectonic upheaval related to the break-up of the supercontinent Rodinia and reassembly into Gondwana, and, most importantly, major biological innovations exemplified by the Ediacarian Biota and the Cambrian 'Explosion'. Geochemical lines of evidence for the NOE include perturbations to the biogeochemical cycling of carbon. Generally high ? 13C values are possibly indicative of increased organic carbon burial and the release of oxidative power to the Earth's surface environment after c. 800 Ma. A demonstrably global and primary record of extremely negative ? 13C values after about 580 Ma strongly suggests the oxidation of a large dissolved organic carbon pool (DOC), the culmination of which around c. 550 Ma coincided with an abrupt diversification of Ediacaran macrobiota. Increasing 87Sr/ 86Sr ratios toward the Neoproterozoic-Cambrian transition indicates enhanced continental weathering which may have fuelled higher organic production and burial during the later Neoproterozoic. Evidence for enhanced oxidative recycling is given by the increase in sulfur isotope fractionation between sulfide and sulfate, exceeding the range usually attained by sulfate reduction alone, reflecting an increasing importance of the oxidative part in the sulfur cycle. S/C ratios attained a maximum during the Precambrian-Cambrian transition, further indicating higher sulfate concentrations in the ocean and a transition from dominantly pyrite burial to sulfate burial after the Neoproterozoic. Strong evidence for the oxygenation of the deep marine environment has emerged through elemental approaches over the past few years which were able to show significant increases in redox-sensitive trace-metal (notably Mo) enrichment in marine sediments not only during the GOE but even more pronounced during the inferred NOE. In addition to past studies involving Mo enrichment, which has been extended and further substantiated in the current review, we present new compilations of V and U concentrations in black shales throughout Earth history that confirm such a rise and further support the NOE. With regard to ocean ventilation, we also review other sedimentary redox indicators, such as iron speciation, molybdenum isotopes and the more ambiguous REE patterns. Although the timing and extent of the NOE remain the subjects of debate and speculation, we consider the record of redox-sensitive trace-metals and C and S contents in black shales to indicate delayed ocean ventilation later in the Cambrian on a global scale with regard to rising oxygen levels in the atmosphere which likely rose during the Late Neoproterozoic.

Och, Lawrence M.; Shields-Zhou, Graham A.

2012-01-01

232

Hydrogen and carbon isotope geochemistry of freshwater aquifers at the Mizunami Underground Research Laboratory: Implications for ongoing biogeochemical processes in deep granitic rocks  

NASA Astrophysics Data System (ADS)

Granite is one of major plutonic rocks and widely distributed in the terrestrial deep subsurface. Although many studies of biogeochemical processes have been carried out for granitic aquifers associated with seawater in Scandinavian countries, there is not much knowledge of biogeochemical processes mediated in those associated with freshwater. The Mizunami Underground Research Laboratory (MIU), which is located in Central Japan, provides us opportunities to investigate freshwater aquifers in granitic rocks. We collected groundwater samples from 200-m to 1150-m depths below ground level. We measured the concentration of methane, ethane, total inorganic carbon (TIC), molecular hydrogen, acetate, sulfate and ammonium, and the carbon and hydrogen isotopic compositions of methane and TIC. The concentration of methane increased with depth from 127 to 1164 ?M, and TIC decreased from 1300 to 50 ?M, respectively. The C1/C2+C3 ratios of >~800 indicated that methane might be biogenic. In contrast, the carbon and hydrogen isotopic composition of methane ranged from -42.6 to -26.9 ‰ and from -157 to -111 ‰, respectively, and the carbon isotopic composition of TIC ranged from -2.5 to -14.7 ‰. As the higher isotopic composition of methane and the difference in carbon isotopic composition between methane and TIC were around 30 ‰, the origin of main methane pool could be abiogenic. The concentration of hydrogen is the most sensitive indicator of ongoing biogeochemical processes. The higher level of hydrogen was consistent with acetogenesis at a depth of 300-m (~100 nM), while the lower level was indicative of sulfate reduction at a depth of 200-m (~1.5 nM). The depletion of sulfate and the enrichment of acetate in the 300-m deep groundwater agreed with the hydrogen profile. Interestingly, this redox shift was associated with an increase in ammonia concentration. The depth profiles of sulfate and methane in which sulfate reduction is coupled to methane oxidation have been obtained from the seawater granitic aquifers in Olkiluoto, Finland. Apparent lack of the profiles characterized by anaerobic methane oxidation in Mizunami groundwater might be attributed to the low level of sulfate. From our results, it is suggested that dominant biogeochemical processes mediated in the deep granitic rocks differ significantly between freshwater and seawater aquifer systems. This study was supported by grants from the Nuclear and Industrial Safety Agency (NISA).

Konno, U.; Fukuda, A.; Kouduka, M.; Komatsu, D. D.; Tsunogai, U.; Aosai, D.; Mizuno, T.; Suzuki, Y.

2010-12-01

233

Distribution of barium in the Weddell Gyre: Impact of circulation and biogeochemical processes  

E-print Network

of barium in the Weddell Gyre: Impact of circulation and biogeochemical processes M. Hoppemaa,1 , F@vub.ac.be Key words : Barium; silicate; geochemical cycle; (Southern Ocean, Weddell Sea) Manuscript Click here barium (Bad) has been augmented significantly with two sections across the Weddell Gyre sampled

Paris-Sud XI, Université de

234

Biogeochemical cycling of phosphorus: Insights from oxygen isotope effects of phosphoenzymes  

Microsoft Academic Search

Geochemical cycling of phosphorus (P) in aquatic environments is carried out almost exclusively by biota and involves reactions that are catalyzed by enzymes. Oxygen isotope effects accompanying phosphoenzymatic reactions have been determined in controlled laboratory experiments in order to elucidate processes underlying biogeochemical cycling of P, and to identify possible reaction pathways for P-compounds in nature. Phosphate oxygen isotope effects

RUTH E. BLAKE; JAMES R. O'NEIL; ALEKSANDR V. SURKOV

2005-01-01

235

ForPeerReview Biogeochemical reduction processes in a hyper-alkaline  

E-print Network

ForPeerReview Only Biogeochemical reduction processes in a hyper-alkaline affected leachate soil processes in a hyper-alkaline affected leachate soil profile1 2 Ian T. Burke1* , Robert J.G. Mortimer1 in a buried, saturated, organic­16 rich soil layer at pH 12.3. The soil has been trapped beneath calcite

Burke, Ian

236

Marine Biogeochemical Cycles of Trace Metals; from molecules to ecosystems M. T. Maldonado  

E-print Network

Marine Biogeochemical Cycles of Trace Metals; from molecules to ecosystems M. T. Maldonado Earth, Ocean & Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada Marine phytoplankton half of the total C fixation on Earth. About 20% of the organic carbon produced in marine surface

Simon, Emmanuel

237

Biogeochemical changes at early stage after the closure of radioactive waste geological repository in South Korea  

E-print Network

Biogeochemical changes at early stage after the closure of radioactive waste geological repository e Korea Radioactive Waste Agency (KORAD), 111, Daedeok-daero 989 beon-gil, Yuseong-gu, Daejeon 305 Organic waste a b s t r a c t Permanent disposal of low- and intermediate-level radioactive wastes

Ohta, Shigemi

238

Biocomplexity associated with biogeochemical cycles in arctic frost-boil ecosystems  

E-print Network

i Biocomplexity associated with biogeochemical cycles in arctic frost-boil ecosystems Principal CYCLES IN ARCTIC FROST-BOIL ECOSYSTEMS A PROJECT SUMMARY The central goal of this project to changing climate. We focus on frost-boils because: (1) The processes that are involved in the self

Wagner, Diane

239

DAAC for Biogeochemical Dynamics PI: Suresh K.S. Vannan (ORNL DAAC Manager)  

E-print Network

://webmap.ornl.gov/wcsdown/ index.jsp ) and using a browser-based Geospatial Information Systems (GIS) tool (http:// webmapDAAC for Biogeochemical Dynamics PI: Suresh K.S. Vannan (ORNL DAAC Manager) PARTICIPATING STAFF Observing System Data and Information System (EOSDIS). Project Website: http://daac.ornl.gov PROJECT

240

NUTRIENT STOICHIOMETRIC RELATIONS AND BIOGEOCHEMICAL NICHE IN COEXISTING PLANT SPECIES: EFFECT OF SIMULATED CLIMATE CHANGE  

Microsoft Academic Search

ABSTRACT: Here ,we define ,a “biogeo- chemical niche” characterized by the,species po- sition in the ,multivariate space generated ,by its content not only of macronutrients like N, P or K, but also of micronutrients such as Mo, Mg and Ca, and trace toxic elements such as Pb and As. We then ,hypothesize ,that the flexibility of the species “biogeochemical niche”

Josep Peñuelas; Jordi Sardans; Romà Ogaya; Marc Estiarte

241

Nitrate reduction in streambed sediments: Effects of flow and biogeochemical kinetics  

E-print Network

Nitrate reduction in streambed sediments: Effects of flow and biogeochemical kinetics Chuanhui Gu,1. The calibrated model successfully replicated the spatial profiles of nitrate under both steady and transient). At the study site, the Peclet number and the Damkohler numbers for both oxygen and nitrate are high (Pe = 25

Virginia, University of

242

INTERACTIVE EFFECTS OF OZONE DEPLETION AND CLIMATE CHANGE ON BIOGEOCHEMICAL CYCLES  

EPA Science Inventory

The effects of ozone depletion on global biogeochemical cycles, via increased UV-B radiation at the Earth's surface, have continued to be documented over the past 4 years. In this report we also document various effects of UV-B that interact with global climate change because the...

243

Winter flooding in Dutch stream valley floodplains: biogeochemical effects and vegetation consequences  

Microsoft Academic Search

Winter flooding in Dutch stream valley floodplains: biogeochemical effects and vegetation consequences Victor Beumer Climatic change has great impacts on stream catchments and their ecology. Expectations are that more extreme climate events will result in undesired flooding in stream catchments. In the Netherlands, former floodplains with a history of agricultural or semi natural land use are put into use again

V. Beumer

2009-01-01

244

Assessment of skill and portability in regional marine biogeochemical models: Role of multiple planktonic groups  

Microsoft Academic Search

Application of biogeochemical models to the study of marine ecosystems is pervasive, yet objective quantification of these models' performance is rare. Here, 12 lower trophic level models of varying complexity are objectively assessed in two distinct regions (equatorial Pacific and Arabian Sea). Each model was run within an identical one-dimensional physical framework. A consistent variational adjoint implementation assimilating chlorophyll-a, nitrate,

Marjorie A. M. Friedrichs; Jeffrey A. Dusenberry; Laurence A. Anderson; Robert A. Armstrong; Fei Chai; James R. Christian; Scott C. Doney; John Dunne; Masahiko Fujii; Raleigh Hood; Dennis J. McGillicuddy Jr; J. Keith Moore; Markus Schartau; Yvette H. Spitz; Jerry D. Wiggert

2007-01-01

245

Effects of Solar UV Radiation and Climate Change on Biogeochemical Cycling: Interactions and Feedbacks  

EPA Science Inventory

Solar UV radiation, climate and other drivers of global change are undergoing significant changes and models forecast that these changes will continue for the remainder of this century. Here we assess the effects of solar UV radiation on biogeochemical cycles and the interactions...

246

Overview of the Water, Energy, Biogeochemical Budgets Program of the U.S. Geological Survey  

Microsoft Academic Search

Small watershed studies serve as an important mechanism to understand changes in a broad range of hydrologic environments at a scale where multiple processes can be understood. The U. S. Geological Survey's (USGS) Water, Energy, and Biogeochemical Budgets (WEBB) program was designed to understand processes in small watersheds located in geographically diverse environments that represent a range of hydrologic, ecologic,

Mary Jo Baedecker

247

BENTIDC-BIOGEOCHEMICAL RESPONSES TO PARTICLE FLUX: THE MINERALS AND MICROBIOTA OF CROSS SEAMOUNT  

E-print Network

ofmanganese deposition during the 4- month experiment is remarkable, given the expectedaccumulation rate the deposition of pelagic particles. Most ofthe bariteparticles originated in the water column, however otherBENTIDC-BIOGEOCHEMICAL RESPONSES TO PARTICLE FLUX: THE MINERALS AND MICROBIOTA OF CROSS SEAMOUNT

Luther, Douglas S.

248

The role of slackwater areas for biogeochemical processes in rehabilitated river corridors: examples  

E-print Network

The role of slackwater areas for biogeochemical processes in rehabilitated river corridors production are key eco- system functions and are related to areas of higher retention in the river corridor rivers where both retention and hydrologic connections between the main channel and its slackwater areas

Thorp, James H.

249

Sensitivity analysis of simple global marine biogeochemical models I. Kriest,1  

E-print Network

Sensitivity analysis of simple global marine biogeochemical models I. Kriest,1 A. Oschlies,1 and S] This study presents results from 46 sensitivity experiments carried out with three structurally simple (2, 3 with respect to observed phosphate and oxygen distributions is found to be particularly sensitive to changes

Khatiwala, Samar

250

A tubular-coring device for use in biogeochemical sampling of succulent and pulpy plants  

USGS Publications Warehouse

A hand-operated, tubular-coring device developed for use in biogeochemical sampling of succulent and pulpy plants is described. The sampler weighs about 500 g (1.1 lb); and if 25 ?? 175 mm (1 ?? 7 in) screw-top test tubes are used as sample containers, the complete sampling equipment kit is easily portable, having both moderate bulk and weight. ?? 1986.

Campbell, W.L.

1986-01-01

251

Gene-centric approach to integrating environmental genomics and biogeochemical models  

PubMed Central

Rapid advances in molecular microbial ecology have yielded an unprecedented amount of data about the evolutionary relationships and functional traits of microbial communities that regulate global geochemical cycles. Biogeochemical models, however, are trailing in the wake of the environmental genomics revolution, and such models rarely incorporate explicit representations of bacteria and archaea, nor are they compatible with nucleic acid or protein sequence data. Here, we present a functional gene-based framework for describing microbial communities in biogeochemical models by incorporating genomics data to provide predictions that are readily testable. To demonstrate the approach in practice, nitrogen cycling in the Arabian Sea oxygen minimum zone (OMZ) was modeled to examine key questions about cryptic sulfur cycling and dinitrogen production pathways in OMZs. Simulations support previous assertions that denitrification dominates over anammox in the central Arabian Sea, which has important implications for the loss of fixed nitrogen from the oceans. Furthermore, cryptic sulfur cycling was shown to attenuate the secondary nitrite maximum often observed in OMZs owing to changes in the composition of the chemolithoautotrophic community and dominant metabolic pathways. Results underscore the need to explicitly integrate microbes into biogeochemical models rather than just the metabolisms they mediate. By directly linking geochemical dynamics to the genetic composition of microbial communities, the method provides a framework for achieving mechanistic insights into patterns and biogeochemical consequences of marine microbes. Such an approach is critical for informing our understanding of the key role microbes play in modulating Earth’s biogeochemistry. PMID:24449851

Reed, Daniel C.; Algar, Christopher K.; Huber, Julie A.; Dick, Gregory J.

2014-01-01

252

Global Biogeochemical Fluxes Program for the Ocean Observatories Initiative: A Proposal. (Invited)  

Microsoft Academic Search

The overarching emphasis of the Global Biogeochemical Flux Ocean Observatories Initiative is to assess the role of oceanic carbon, both living and non-, in the Earth climate system. Modulation of atmospheric CO2 and its influence on global climate is a function of the quantitative capacity of the oceans to sequester organic carbon into deep waters. Critical to our understanding of

K. M. Ulmer; C. Taylor

2010-01-01

253

Biogeochemical cycles of Fe and Mn in the southwestern East Sea (Sea of Japan)  

Microsoft Academic Search

Biogeochemical cycles of Fe and Mn were studied for the southwestern East Sea (Sea of Japan) with a particular emphasis on the early diagenetic processes occurring in the upper part of sediments. In a cruise on October, 1995, we obtained 6 box core sediments from the southwestern part of the East Sea. The sampling sites cover continental slope areas and

H. Cha; C. Lee; B. Kim

2003-01-01

254

Catchment hydro-biogeochemical response to forest harvest intensity and spatial pattern  

EPA Science Inventory

We apply a new model, Visualizing Ecosystems for Land Management Assessment (VELMA), to Watershed 10 (WS10) in the H.J. Andrews Experimental Forest to simulate the effects of harvest intensity and spatial pattern on catchment hydrological and biogeochemical processes. Specificall...

255

A 15-year global biogeochemical reanalysis with ocean colour data assimilation  

NASA Astrophysics Data System (ADS)

A continuous global time-series of remotely sensed ocean colour observations is available from 1997 to the present day. However coverage is incomplete, and limited to the sea surface. Models are therefore required to provide full spatial coverage, and to investigate the relationships between physical and biological variables and the carbon cycle. Data assimilation can then be used to constrain models to fit the observations, thereby combining the advantages of both sources of information. As part of the European Space Agency's Climate Change Initiative (ESA-CCI), we assimilate chlorophyll concentration derived from ocean colour observations into a coupled physical-biogeochemical model. The data assimilation scheme (Hemmings et al., 2008, J. Mar. Res.; Ford et al., 2012, Ocean Sci.) uses the information from the observations to update all biological and carbon cycle state variables within the model. Global daily reanalyses have been produced, with and without assimilation of merged ocean colour data provided by GlobColour, for the period September 1997 to August 2012. The assimilation has been shown to significantly improve the model's representation of chlorophyll concentration, at the surface and at depth. Furthermore, there is evidence of improvement to the representation of pCO2, nutrients and zooplankton concentration compared to in situ observations. We use the results to quantify recent seasonal and inter-annual variability in variables including chlorophyll concentration, air-sea CO2 flux and alkalinity. In particular, we explore the impact of physical drivers such as the El Niño Southern Oscillation (ENSO) on the model's representation of chlorophyll and the carbon cycle, and the pros and cons of the model reanalyses compared to observation-based climatologies. Furthermore, we perform a comparison between the GlobColour product and an initial version of a new merged product being developed as part of the ESA-CCI. Equivalent year-long hindcasts are performed with assimilation of each data set, and compared to a control run. Differences in the products are discussed, along with their impact on model accuracy compared to in situ observations, and the representation of the carbon cycle in each hindcast.

Ford, David; Barciela, Rosa

2013-04-01

256

Implications of variance in biogeochemical proxy records spanning Mesozoic Oceanic Anoxic Events  

NASA Astrophysics Data System (ADS)

The cycling of key elements through the ocean and atmosphere varied widely in the Mesozoic in response to changes in primary productivity and organic carbon burial, volcanism, weathering, and evaporite burial. Many of these processes have been proposed as triggers for the discreet periods of widespread organic carbon production and/or preservation termed Ocean Anoxic Events or OAE's. Thus, it might be expected that similar patterns of elemental cycling would characterize most major OAE intervals and could be used to help elucidate the controls on initiation and/or termination of these events. Yet this is not the case. In this study we compare the variability of a series of geochemical proxies, focusing on sulfur (S) isotopes of marine sulfate and sulfide minerals, through a series of Mesozoic OAE's. The data set includes our own results from OAE1a (ca. 125Ma) and OAE2 (ca. 94Ma), as well as published data from other events. The results indicate that S cycling varied significantly among the events, despite many similarities in the behavior of carbon isotopes and geochemical indicators of oxygen deficiency. Specifically, S isotope compositions of seawater sulfate and pyrite are quite variable during OAE2 suggesting that a short-term increase in sulfate levels upon a low background occurred at the onset due to enhanced volcanism and/or weathering. In contrast, S isotope compositions of seawater sulfate and pyrite decrease dramatically through the OAE1a and are completely decoupled from the carbon cycle. We evaluate these trends using coupled sulfur and carbon box models and show that patterns of S cycling during OAE1a were predominantly controlled by volcanism, whereas S cycling during OAE2 represents a stronger interplay between volcanic processes and linkage with the carbon cycle. An analysis of the differences in S cycling among events provides improved insight into the suite of processes that interacted to drive large-scale changes in environmental conditions during the Mesozoic. Major changes in biogeochemical systems from one event to another likely contributed to low ecosystem resilience, which helped lay the foundation for significant levels of species turnover during Mesozoic OAE's.

Gomes, M. L.; Mills, J. V.; Hurtgen, M. T.; Sageman, B. B.

2013-12-01

257

MODELING COUPLED HYDROLOGICAL AND CHEMICAL PROCESSES: LONG-TERM URANIUM TRANSPORT FOLLOWING PHOSPHOROUS-FERTILIZATION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Contaminants in the vadose zone are affected by the physical processes of water flow, heat movement and multicomponent transport, as well as generally by a range of interacting biogeochemical processes. Coupling these various processes within one integrated numerical simulator provides a process-ba...

258

Modeling the Natural Biogeochemical Cycle of Mercury in the Global Ocean  

NASA Astrophysics Data System (ADS)

The ocean plays an important role in the biogeochemical cycling of mercury (Hg) because of its large reservoir mass and re-emission flux via evasion. The currently available Hg models, including 2D slab, 1D column and 0D box model cannot fully resolve the marine Hg cycle because of the lack of the proper spatial resolution. In this work, we have implemented Hg biogeochemistry in a state-of-the-art 3D offline ocean tracer model (OFFTRAC). OFFTRAC simulates the evolution of three Hg species (Hg0aq, HgIIaq and HgPaq), which are diffused and advected in the ocean. Hg0aq and HgII aq are interconverted in the surface ocean via parameterized photochemical and biological redox processes. The partitioning between HgIIaq and HgPaq depends on the local levels of particulate organic carbon (POC). The sinking of HgPaq is parameterized by coupling with the nutrient phosphorous cycle simulated in OFFTRAC. The reduction of HgIIaq to Hg0aq in the anaerobic subsurface water is proportional to the remineralizaiton of POC. OFFTRAC is coupled to a global simulation of the natural atmospheric Hg cycle in the GEOS-Chem chemical transport model. The GEOS-Chem simulation includes a geogenic source and provides the atmospheric deposition flux of HgII to the ocean and atmospheric Hg0 concentrations. The riverine input of Hg is calculated based on the climatological monthly mean fresh water discharge from continental to ocean and the average soil concentrations near the river mouth. The results show that the riverine input enhances Hg concentrations at surface by a factor of 2-3 near large river mouths and nearby coastal regions. The riverine input approximately doubles surface Hg concentration over the Arctic because of the small basin volume. In the deep ocean, which is not influenced by anthropogenic emissions, the model results (1.1±0.3 pM) generally agree with the observed present-day total Hg concentration profiles (1.4±0.9 pM). In the surface ocean, observations show average total Hg concentrations of 1.0±0.6 pM, while our natural ocean model shows an average concentration of 0.17±0.1 pM, indicating enrichment between present-day and natural condition by a factor of 5-6. The results show that Hg accumulates in the tropical ocean basins at depth due to the stronger particle sinking flux. Higher levels of surface concentration are also modeled in the upwelling regions in the subarctic North Pacific, subpolar North Atlantic and in the Southern Ocean. The modeled HgIIaq concentration in the deep North Pacific is approximately twice of that of the deep North Atlantic because of the accumulated source from particles removing Hg from the surface waters. The Hg0aq concentrations are highest in the Pacific equatorial intermediate ocean (1000 - 2000 m), where the remineralization rate is largest and oxygen concentrations are low. We will present preliminary results from a 560 year (1450 - 2008) coupled atmosphere-ocean Hg simulation with increasing anthropogenic input.

Zhang, Y.; Jaegle, L.; Thompson, L.; Emerson, S. R.; Deutsch, C. A.; Trossman, D. S.; Shao, A.

2012-12-01

259

Realistic primary and new productions in a 3D global biogeochemical model: biological complexity or physical forcing?  

NASA Astrophysics Data System (ADS)

A nitrogen-based, five compartment biological model has been coupled to a one degree OCCAM (Ocean Circulation and Climate Advanced Modelling Project) model with a KPP ("K profile parameterisation") of the vertical mixing. The biological model state variables are Phytoplankton, Zooplankton, Detritus, Nitrate, and Ammonium. A comparison of the solution with global satellite ocean colour shows that the model is capable of a realistic description of the main seasonal and regional patterns of the surface chlorophyll. Agreement is also good for satellite derived estimates of primary production. In situ data available from local study sites (such as BATS, NABE, India, Papa) are used for the detailed comparison of the model output with the observed ecosystem dynamics in different biological provinces. We discuss performance of the physical and biological model in contrasting areas of the World Ocean. In spite of the biological model being a very simple one, we are able to reproduce the major differences between ecosystem dynamics of these areas. We believe that the success of any global biogeochemical model is dependent first of all on the correct representation of the upper mixed layer (UML) dynamics. Without being able to reproduce contrasting UML regimes in different areas of the World Ocean (such as difference between the North Atlantic and Southern Ocean, or North Atlantic and North Pacific), increased complexity biological models are in danger of producing the right results by the wrong reason.

Popova, E. E.; Coward, A. C.

2003-04-01

260

Biogeochemical signatures and microbial activity of different cold-seep habitats along the Gulf of Mexico deep slope  

NASA Astrophysics Data System (ADS)

Microorganisms and the processes they mediate serve as the metabolic foundation of cold seeps. We characterized a suite of biogeochemical constituents and quantified rates of two key microbial processes, Sulfate Reduction (SR) and Anaerobic Oxidation of Methane (AOM), to assess variability between habitats at water depths exceeding 1000 m in the northern Gulf of Mexico. Rates of SR were highest in sediments beneath microbial mats, lower in brine-influenced and oil-influenced sediments, and lowest in animal habitats. Sediments collected near tubeworms had the highest SR rates for animal habitats. Rates of AOM generally were low, but higher rates were associated with brine-influenced, oil-influenced, tubeworm- and urchin-inhabited sediments. Rates of both SR and AOM were orders of magnitude lower at deep-slope sites compared to upper-slope sites examined previously. As observed at upper-slope sites, SR and AOM rates were often loosely coupled. At one site, AOM rates exceeded SR rates, suggesting that an alternate electron acceptor for AOM is possible. Extremely depleted ?13C values in methane illustrated the broad significance of biogenic methane production at deep-slope sites. Brine-influenced habitats were characterized by extremely high concentrations of ammonium and dissolved organic carbon, serving as important focused sources of these chemicals to adjacent environments.

Joye, Samantha B.; Bowles, Marshall W.; Samarkin, Vladimir A.; Hunter, Kimberley S.; Niemann, Helge

2010-11-01

261

A model of biogeochemical cycles of carbon, nitrogen, and phosphorus including symbiotic nitrogen fixation and phosphatase production  

NASA Astrophysics Data System (ADS)

Global climate models have not yet considered the effects of nutrient cycles and limitation when forecasting carbon uptake by the terrestrial biosphere into the future. Using the principle of resource optimization, we here develop a new theory by which C, N, and P cycles interact. Our model is able to replicate the observed responses of net primary production to nutrient additions in N-limited, N- and P-colimited, and P-limited terrestrial environments. Our framework identifies a new pathway by which N2 fixers can alter P availability: By investing in N-rich, phosphorus liberation enzymes (phosphatases), fixers can greatly accelerate soil P availability and P cycling rates. This interaction is critical for the successful invasion and establishment of N2 fixers in an N-limited environment. We conclude that our model can be used to examine nutrient limitation broadly, and thus offers promise for coupling the biogeochemical system of C, N, and P to broader climate-system models.

Wang, Y.-P.; Houlton, B. Z.; Field, C. B.

2007-03-01

262

Integrated Biogeochemical and Hydrologic Processes Driving Arsenic Release from Shallow Sediments to Groundwaters of the Mekong Delta  

SciTech Connect

Arsenic is contaminating the groundwater of Holocene aquifers throughout South and Southeast Asia. To examine the biogeochemical and hydrological processes influencing dissolved concentrations and transport of As within soils/sediments in the Mekong River delta, a ~50 km? field site was established near Phnom Penh, Cambodia, where aqueous As concentrations are dangerously high and where groundwater retrieval for irrigation is minimal. Dissolved As concentrations vary spatially, ranging up to 1300 µg/L in aquifer groundwater and up to 600 µg/L in surficial clay pore water. Groundwaters with high As concentrations are reducing with negligible dissolved O? and high concentrations of Fe(II), NH?? , and dissolved organic C. Within near-surface environments, these conditions are most pronounced in sediments underlying permanent wetlands, often found within oxbow channels near the Mekong River. There, labile C, co-deposited with As-bearing Fe (hydr)oxides under reducing conditions, drives the reductive mobilization (inclusive of Fe and As reduction) of As. Here, conditions are described under which As is mobilized from these sediments, and near-surface As release is linked to aquifer contamination over long time periods (100s to 1000s of years). Site biogeochemistry is coupled with extensive hydrologic measurements, and, accordingly, a comprehensive interpretation of spatial As release and transport within a calibrated hydraulic flow-field is provided of an As-contaminated aquifer that is representative of those found throughout South and Southeast Asia.

Kocar, Benjamin D.; Polizzotto, Matthew L.; Benner, Shawn G.; Ying, Samantha C.; Ung, Mengieng; Ouch, Kagna; Samreth, Sopheap; Suy, Bunseang; Phan, Kongkea; Sampson, Michael; Fendorf, Scott

2008-11-01

263

Vadose zone attenuation of organic compounds at a crude oil spill site - Interactions between biogeochemical reactions and multicomponent gas transport  

USGS Publications Warehouse

Contaminant attenuation processes in the vadose zone of a crude oil spill site near Bemidji, MN have been simulated with a reactive transport model that includes multicomponent gas transport, solute transport, and the most relevant biogeochemical reactions. Dissolution and volatilization of oil components, their aerobic and anaerobic degradation coupled with sequential electron acceptor consumption, ingress of atmospheric O2, and the release of CH4 and CO2 from the smear zone generated by the floating oil were considered. The focus of the simulations was to assess the dynamics between biodegradation and gas transport processes in the vadose zone, to evaluate the rates and contributions of different electron accepting processes towards vadose zone natural attenuation, and to provide an estimate of the historical mass loss. Concentration distributions of reactive (O2, CH4, and CO2) and non-reactive (Ar and N2) gases served as key constraints for the model calibration. Simulation results confirm that as of 2007, the main degradation pathway can be attributed to methanogenic degradation of organic compounds in the smear zone and the vadose zone resulting in a contaminant plume dominated by high CH4 concentrations. In accordance with field observations, zones of volatilization and CH4 generation are correlated to slightly elevated total gas pressures and low partial pressures of N2 and Ar, while zones of aerobic CH4 oxidation are characterized by slightly reduced gas pressures and elevated concentrations of N2 and Ar. Diffusion is the most significant transport mechanism for gases in the vadose zone; however, the simulations also indicate that, despite very small pressure gradients, advection contributes up to 15% towards the net flux of CH4, and to a more limited extent to O2 ingress. Model calibration strongly suggests that transfer of biogenically generated gases from the smear zone provides a major control on vadose zone gas distributions and vadose zone carbon balance. Overall, the model was successful in capturing the complex interactions between biogeochemical reactions and multicomponent gas transport processes. However, despite employing a process-based modeling approach, honoring observed parameter ranges, and generally obtaining good agreement between field observations and model simulations, accurate quantification of natural attenuation rates remains difficult. The modeling results are affected by uncertainties regarding gas phase saturations, tortuosities, and the magnitude of CH4 and CO2 flux from the smear zone. These findings highlight the need to better delineate gas fluxes at the model boundaries, which will help constrain contaminant degradation rates, and ultimately source zone longevity. ?? 2009 Elsevier B.V.

Molins, S.; Mayer, K.U.; Amos, R.T.; Bekins, B.A.

2010-01-01

264

Vadose zone attenuation of organic compounds at a crude oil spill site — Interactions between biogeochemical reactions and multicomponent gas transport  

NASA Astrophysics Data System (ADS)

Contaminant attenuation processes in the vadose zone of a crude oil spill site near Bemidji, MN have been simulated with a reactive transport model that includes multicomponent gas transport, solute transport, and the most relevant biogeochemical reactions. Dissolution and volatilization of oil components, their aerobic and anaerobic degradation coupled with sequential electron acceptor consumption, ingress of atmospheric O 2, and the release of CH 4 and CO 2 from the smear zone generated by the floating oil were considered. The focus of the simulations was to assess the dynamics between biodegradation and gas transport processes in the vadose zone, to evaluate the rates and contributions of different electron accepting processes towards vadose zone natural attenuation, and to provide an estimate of the historical mass loss. Concentration distributions of reactive (O 2, CH 4, and CO 2) and non-reactive (Ar and N 2) gases served as key constraints for the model calibration. Simulation results confirm that as of 2007, the main degradation pathway can be attributed to methanogenic degradation of organic compounds in the smear zone and the vadose zone resulting in a contaminant plume dominated by high CH 4 concentrations. In accordance with field observations, zones of volatilization and CH 4 generation are correlated to slightly elevated total gas pressures and low partial pressures of N 2 and Ar, while zones of aerobic CH 4 oxidation are characterized by slightly reduced gas pressures and elevated concentrations of N 2 and Ar. Diffusion is the most significant transport mechanism for gases in the vadose zone; however, the simulations also indicate that, despite very small pressure gradients, advection contributes up to 15% towards the net flux of CH 4, and to a more limited extent to O 2 ingress. Model calibration strongly suggests that transfer of biogenically generated gases from the smear zone provides a major control on vadose zone gas distributions and vadose zone carbon balance. Overall, the model was successful in capturing the complex interactions between biogeochemical reactions and multicomponent gas transport processes. However, despite employing a process-based modeling approach, honoring observed parameter ranges, and generally obtaining good agreement between field observations and model simulations, accurate quantification of natural attenuation rates remains difficult. The modeling results are affected by uncertainties regarding gas phase saturations, tortuosities, and the magnitude of CH 4 and CO 2 flux from the smear zone. These findings highlight the need to better delineate gas fluxes at the model boundaries, which will help constrain contaminant degradation rates, and ultimately source zone longevity.

Molins, S.; Mayer, K. U.; Amos, R. T.; Bekins, B. A.

2010-03-01

265

Hybrid Numerical Methods for Multiscale Simulations of Subsurface Biogeochemical Processes  

SciTech Connect

Many subsurface flow and transport problems of importance today involve coupled non-linear flow, transport, and reaction in media exhibiting complex heterogeneity. In particular, problems involving biological mediation of reactions fall into this class of problems. Recent experimental research has revealed important details about the physical, chemical, and biological mechanisms involved in these processes at a variety of scales ranging from molecular to laboratory scales. However, it has not been practical or possible to translate detailed knowledge at small scales into reliable predictions of field-scale phenomena important for environmental management applications. A large assortment of numerical simulation tools have been developed, each with its own characteristic scale including molecular (e.g., molecular dynamics), microbial (e.g., cellular automata or particle individual-based models), pore (e.g., lattice-Boltzmann, pore network models, and discrete particle methods such as smoothed particle hydrodynamics) and continuum scales (e.g., traditional partial differential equations solved by finite difference or finite element methods). While many problems can be effectively addressed by one of these models at a single scale, some problems may require explicit integration of models across multiple scales. We are developing a hybrid multi-scale subsurface reactive transport modeling framework that integrates models with diverse representations of physics, chemistry and biology at different scales (sub-pore, pore and continuum). The modeling framework is being designed to take advantage of advanced computational technologies including parallel code components using the Common Component Architecture, parallel solvers, gridding, data and workflow management, and visualization. This paper describes the specific methods/codes being used at each scale, techniques used to directly and adaptively couple across model scales, and preliminary results of application to a multi-scale model of mineral precipitation at a solute mixing interface.

Scheibe, Timothy D.; Tartakovsky, Alexandre M.; Tartakovsky, Daniel M.; Redden, George D.; Meakin, Paul

2007-08-01

266

Investigation of CO2 induced biogeochemical reactions and active microorganisms of two German gas fields  

NASA Astrophysics Data System (ADS)

The BMBF-Geotechnologien project "RECOBIO 2" continues the investigation of the long-term biogeochemical transformation of stored CO2. In addition to the Upper Carboniferous gas reservoir Schneeren (Westphalian C) the almost depleted Altmark gas field (Permian - Upper Rotliegend) is also investigated. Both sandstone reservoirs belong to the North German Basin and are operated by the GDF SUEZ E&P Germany (GDF SUEZ). The reservoirs differ in depth, initial and current fluid pressure as well as reservoir temperature, which is a biogeochemical important parameter. While the uplifted horst structure of Schneeren (approx. depth 2700 m) has a temperature level of 80 - 90 °C, the Altmark gas field (approx. depth 3300 m) shows temperatures around 120 °C. The Altmark site is known to be favourable for underground CO2-storage by enhanced gas recovery (EGR). This EGR process is operated by GDF SUEZ at the small and hydraulic isolated reservoir block "Altensalzwedel". This pilot test is accompanied by the scientific large-scale project CLEAN. In addition the RECOBIO2 project characterises the biogeochemical situation of the both large reservoir blocks of the Altmark gas field - „Salzwedel/ Peckensen" and „Heidberg/ Mellin". The produced formation waters of these reservoir blocks were sampled on different wellheads. The redox potentials are partly very low (Eh up to -300 mV) with slightly acidic pH-values (5,5 to 6). The high saline and (nearly) sulphate free formation waters of Na/Ca-Cl type have very high loads of Zn, Pb, Hg and As. In combination to the analysed DOC levels the talk discusses the importance of metal organic complexes. Also results of fluid geochemical calculations will be presented. Furthermore the diversity of bacteria and archaea of the formation waters as well as the potentials of CH4-, CO2-formation and sulphate reduction will be shown. Therefore the cultivation experiments were carried out with different substrates (H2/CO2, acetate, methanol). It can be summarised, that mainly the differences between wells treated with chemical foams (to enhance the gas lift) and such without this treatment have to take into account. The autoclave experiments for the Schneeren site show the importance of biogeochemical reactions for the long-term pressure behaviour of the storage unit. During autotrophic (CO2 consuming) metabolic activities a CO2 turnover into the liquid and solid phase takes place (DOC increase, carbonate phase formation). Without the knowledge of these biogeochemical induced processes the accompanied decreasing pressure can be interpreted wrongly as a leaky storage unit. That's why a well-founded biogeochemical process understanding is important.

Hoth, N.; Kassahun, A.; Seifert, J.; Krüger, M.; Bretschneider, H.; Gniese, C.; Frerichs, J.; Simon, A.; Simon, E.; Muschalle, T.

2009-04-01

267

Dynamics of sinuosity-driven hyporheic zones: the effects of hydraulic and biogeochemical timescales  

NASA Astrophysics Data System (ADS)

Groundwater-surface water interactions take place across a range of spatio-temporal scales. Sinuosity-driven hyporheic exchange, a ubiquitous example of these interactions, occurs over spatial scales of the order of 1-1000 m and over time scales from hours to years. This exchange is modulated by event, diurnal, and seasonal dynamic forcing that modifies the hyporheic zone's geometry, flow field, and residence time distributions (RTDs), and, at the same time, influences timing-sensitive biogeochemical reactions. This work explores the role of dynamic forcing on the flow field and RTDs for the case of channel sinuousity-driven lateral hyporheic exchange. A two-dimensional, transient, numerical flow and transport model is used to illustrate the effect that dynamics, caused by deterministically and stochastically generated flood events, has on flow fields and RTDs, and therefore on the character of the hyporheic zone as a biogeochemical reactor. In particular, the characteristic hydraulic time scale, expressed as a function of sediment hydraulic diffusivity and the system geometry, plays a key role in determining the memory that the hyporheic zone has of previous flood events. For example, the rising limb of flood events causes accumulation of fresh water into the system and diminishes the flux of hyporheic water with long RTs into the stream. Water with longer RTD is then released during the falling limb at time scales dictated by the hydraulic characteristic time of the system; however, if the characteristic hydraulic time scale is of the order of the time between flood events, long-RT water is accumulated, increasing the water RTs inside the system. Additionally, a simple analytical model is used to estimate the characteristic biogeochemical time scales associated to the degradation of dissolved organic carbon in these hydrologic systems, which are compared to numerically-modeled RTDs and used to estimate the biogeochemical zonation within the HZ and its net biogeochemical response. This parsimonious approach can be used as a predictive tool to quantify the potential of meanders as biogeochemical reactors at the watershed scale with the aid of historic discharge data, remote sensing data, and GIS processing techniques.

Gomez, J. D.; Wilson, J. L.; Cardenas, M. B.

2012-12-01

268

Dimensionless Numbers For Morphological, Thermal And Biogeochemical Controls Of Hyporheic Processes  

NASA Astrophysics Data System (ADS)

Transport of solutes and heat within the hyporheic zone are interface processes that gained growing attention in the last decade, when several modelling strategies have been proposed, mainly at the local or reach scale. We propose to upscale local hyporheic biogeochemical processes to reach and network scales by means of a Lagrangian modelling framework, which allows to consider the impact of the flow structure on the processes modelled. This analysis shows that geochemical processes can be parametrized through two new Damköhler numbers, DaO, and DaT. DaO = ?up,50-?lim is defined as the ratio between the median hyporheic residence time, ?up,50 and the time of consuming dissolved oxygen to a prescribed threshold concentration, ?lim, below which reductive reactions are activated. It quantifies the biogeochemical status of the hyporheic zone and could be a metric for upscaling local hyporheic biogeochemical processes to reach and river-network scale processes. In addition, ?up,50 is the time scale of hyporheic advection; while ?lim is the representative time scale of biogeochemical reactions and indicates the distance along the streamline, measured as the time needed to travel that distance, that a particle of water travels before the dissolved oxygen concentration declines to [DO]lim, the value at which denitrification is activated. We show that DaO is representative of the redox status and indicates whether the hyporheic zone is a source or a sink of nitrate. Values of DaO larger than 1 indicate prevailing anaerobic conditions, whereas values smaller than 1 prevailing aerobic conditions. Similarly, DaT quantifies the importance of the temperature daily oscillations of the stream water on the hyporheic environment. It is defined as the ratio between ?up,50, and the time limit at which the ratio between the amplitude of the temperature oscillation within the hyporheic zone (evaluated along the streamline) and in the stream water is smaller than e-1. We show that values of DaT > 1 indicate a thermally stable hyporheic zone, where organism metabolism is not influenced by surface water thermal oscillations and biogeochemical reaction rates depend on the mean daily stream water temperature. Values smaller than 1 suggest that organisms need to adapt to the daily thermal variations and biogeochemical reaction rates will depend on the daily fluctuations induced by stream water.

Bellin, Alberto; Marzadri, Alessandra; Tonina, Daniele

2013-04-01

269

Coupling TOUGH2 with CLM3: Developing a Coupled Land Surface andSubsurface Model  

SciTech Connect

An understanding of the hydrologic interactions among atmosphere, land surface, and subsurface is one of the keys to understanding the water cycling system that supports life on earth. The inherent coupled processes and complex feedback structures among subsystems make such interactions difficult to simulate. In this paper, we present a model that simulates the land surface and subsurface hydrologic response to meteorological forcing. This model combines a state-of-the-art land-surface model, the NCAR Community Land Model version 3 (CLM3), with a variably saturated groundwater model, TOUGH2, through an internal interface that includes flux and state variables shared by the two submodels. Specifically, TOUGH2 uses infiltration, evaporation, and root-uptake rates, calculated by CLM3, as source/sink terms in its simulation; CLM3 uses saturation and capillary pressure profiles, calculated by TOUGH2, as state variables in its simulation. This new model, CLMT2, preserves the best aspects of both submodels: the state-of-the-art modeling capability of surface energy and hydrologic processes (including snow, runoff, freezing/melting, evapotranspiration, radiation, and biophysiological processes) from CLM3 and the more realistic physical-process-based modeling capability of subsurface hydrologic processes (including heterogeneity, three-dimensional flow, seamless combining of unsaturated and saturated zone, and water table) from TOUGH2. The preliminary simulation results show that the coupled model greatly improved the predictions of the groundwater table, evapotranspiration, and surface temperature at a real watershed, as evaluated using 18 years of observed data. The new model is also ready to be coupled with an atmospheric simulation model, to form one of the first top of the atmosphere to deep groundwater atmosphere-land-surface-subsurface models.

Pan, Lehua; Jin, Jiming; Miller, Norman; Wu, Yu-Shu; Bodvarsson,Gudmundur

2006-05-19

270

EFFECT OF NUTRIENT LOADING ON BIOGEOCHEMICAL AND MICROBIAL PROCESSES IN A NEW ENGLAND HIGH SALT MARSH, SPARTINA PATNES, (AITON MUHL)  

EPA Science Inventory

Coastal marshes represent an important transitional zone between uplands and estuaries and can assimilate nutrient inputs from uplands. We examined the effects of nitrogen (N) and phosphorus (P) fertilization on biogeochemical and microbial processes during the summer growing sea...

271

Dynamic Landscape Connectivity, Threshold Behavior, and Scaling Frameworks for Hydrologic and Bio-geochemical Fluxes  

NASA Astrophysics Data System (ADS)

The hydrologic connectivity of landscapes (the surface fluvial and non-fluvial flowpaths and the flowpaths in the sub-surface) is temporally and spatially changing as dictated by landscape features and precipitation. Developing simple conceptual frameworks for quantifying the response of a basin (hydrologic, sedimentologic, and bio-geochemical) based on theories of network dynamics is still an open problem with slow progress. In this talk two issues will be addressed: (1) scaling of peak flows in response to space-time variable rainfall of duration smaller than the time of concentration of the basin, and (2) predictive modeling and scaling of bio-geochemical fluxes using a spatially explicit model of light and nutrient availability, streamflow, and temperature on the connected network. Data from the Walnut Gulch watershed and the Eel river at Angelo Coast Range Reserve are used for model development and testing.

Foufoula, E.; Zanardo, S.; Danesh-Yazdi, M.; Zaliapin, I.; Power, M.; Dietrich, W.

2012-12-01

272

Novel imaging techniques, integrated with mineralogical, geochemical and microbiological characterizations to determine the biogeochemical controls on technetium mobility in FRC sediments  

SciTech Connect

The objective of this research program was to take a highly multidisciplinary approach to define the biogeochemical factors that control technetium (Tc) mobility in FRC sediments. The aim was to use batch and column studies to probe the biogeochemical conditions that control the mobility of Tc at the FRC. Background sediment samples from Area 2 (pH 6.5, low nitrate, low {sup 99}Tc) and Area 3 (pH 3.5, high nitrate, relatively high {sup 99}Tc) of the FRC were selected (http://www.esd.ornl.gov/nabirfrc). For the batch experiments, sediments were mixed with simulated groundwater, modeled on chemical constituents of FRC waters and supplemented with {sup 99}Tc(VII), both with and without added electron donor (acetate). The solubility of the Tc was monitored, alongside other biogeochemical markers (nitrate, nitrite, Fe(II), sulfate, acetate, pH, Eh) as the 'microcosms' aged. At key points, the microbial communities were also profiled using both cultivation-dependent and molecular techniques, and results correlated with the geochemical conditions in the sediments. The mineral phases present in the sediments were also characterized, and the solid phase associations of the Tc determined using sequential extraction and synchrotron techniques. In addition to the batch sediment experiments, where discrete microbial communities with the potential to reduce and precipitate {sup 99}Tc will be separated in time, we also developed column experiments where biogeochemical processes were spatially separated. Experiments were conducted both with and without amendments proposed to stimulate radionuclide immobilization (e.g. the addition of acetate as an electron donor for metal reduction), and were also planned with and without competing anions at high concentration (e.g. nitrate, with columns containing Area 3 sediments). When the columns had stabilized, as determined by chemical analysis of the effluents, we used a spike of the short-lived gamma emitter {sup 99m}Tc (50-200 MBq; half life 6 hours) and its mobility was monitored using a {gamma}-camera. Incorporation of low concentrations of the long-lived 99Tc gave a tracer that can be followed by scintillation counting, should the metastable form of the radionuclide decay to below detection limits before the end of the experiment (complete immobilization or loss of the Tc from the column). After the Tc was reduced and immobilized, or passed through the system, the columns were dismantled carefully in an anaerobic cabinet and the pore water geochemistry and mineralogy of the columns profiled. Microbial community analysis was determined, again using molecular and culture-dependent techniques. Experimental results were also modeled using an established coupled speciation and transport code, to develop a predictive tool for the mobility of Tc in FRC sediments. From this multidisciplinary approach, we hoped to obtain detailed information on the microorganisms that control the biogeochemical cycling of key elements at the FRC, and we would also be able to determine the key factors that control the mobility of Tc at environmentally relevant concentrations at this site.

Jonathan R. Lloyd

2009-02-03

273

A bottom-up approach: using residence time distributions and characteristic biogeochemical timescales to upscale multiphysics models of hyporheic exchange  

NASA Astrophysics Data System (ADS)

Residence time distributions (RTDs) and characteristic biogeochemical time scales (CBTSs) are integrated metrics that can be used to describe the biogeochemical evolution of water within hydrologic systems. RTDs describe the time that water and solutes are in contact with the system and strongly depend on the forcing and geomorphic features driving exchange and the system's hydraulic properties. On the other hand, CBTSs describe the time necessary for a biogeochemical transformation to take place and depend on the reaction type, solute concentrations entering the system, and chemical kinetics (or thermodynamics). Comparing RTDs and CBTSs allow us to evaluate the potential for transformation within the hydrologic system. In this work, we illustrate this approach with sinuosity-driven hyporheic zones; however, these concepts can be applied to other hydrologic systems. A two-dimensional, transient, numerical flow and transport model is used to illustrate the effect that dynamics, caused by deterministically generated flood events, has on flow fields and RTDs, and therefore on the character of the hyporheic zone as a biogeochemical reactor. A simple analytical model is used to estimate the CBTSs associated to the degradation of dissolved organic carbon in these hydrologic systems, which are compared to numerically-modeled RTDs and used to estimate the biogeochemical zonation within the HZ and its net biogeochemical response. Additionally, we use a multispecies, reactive transport model to assess this approach, paying special attention to those portions of the system with intermittent hyporheic contributions. In particular, transient flow results in time-varying hot-spot for biogeochemical reactions and induces the emergence of new modes on the dynamic RTDs, which are observed within the system and at the outlet. This parsimonious approach can be used as a predictive tool to quantify the potential of meanders as biogeochemical reactors at the watershed scale with the aid of historic discharge data, remote sensing data, and GIS processing techniques.

Gomez, Jesus D.; Wilson, John L.

2013-04-01

274

A biogeochemical study of the coccolithophore, Emiliania huxleyi, in the North Atlantic  

Microsoft Academic Search

The biogeochemical properties of an extensive bloom (~250,000 km2) of the coccolithophore, EMiliania huxleyi, in the north east Atlantic Ocean were investigated in June 1991. Satellite (NOAA-AVHRR) imagery showed that the bloom was centered initially at 60°-63°N by 13°-28°W and lasted approximately 3 weeks. Spatial variations in satellite-measured reflectance were well correlated with surface measurements of the beam attenuation coefficient,

Patrick M. Holligan; Emilio Fernández; James Aiken; William M. Balch; Philip Boyd; Peter H. Burkill; Miles Finch; Stephen B. Groom; Gillian Malin; Kerstin Muller; Charles C. Trees; Suzanne M. Turner; Paul van der Wal

1993-01-01

275

Experimental study and steady-state simulation of biogeochemical processes in laboratory columns with aquifer material  

Microsoft Academic Search

Packed bed laboratory column experiments were performed to simulate the biogeochemical processes resulting from microbially catalyzed oxidation of organic matter. These included aerobic respiration, denitrification, and Mn(IV), Fe(III) and SO4 reduction processes. The effects of these reactions on the aqueous- and solid-phase geochemistry of the aquifer material were closely examined. The data were used to model the development of alkalinity

Aria Amirbahman; René Schönenberger; Gerhard Furrer; Jürg Zobrist

2003-01-01

276

Toward a dynamic biogeochemical division of the Mediterranean Sea in a context of global climate change  

NASA Astrophysics Data System (ADS)

In recent decades, it has been found useful to ecoregionalise the pelagic environment assuming that within each partition environmental conditions are distinguishable and unique. Indeed, each partition of the ocean that is proposed aimed to delineate the main oceanographical and ecological patterns to provide a geographical framework of marine ecosystems for ecological studies and management purposes. The aim of the present work is to integrate and process existing data on the pelagic environment of the Mediterranean Sea in order to define biogeochemical regions. Open access databases including remote sensing observations, oceanographic campaign data and physical modeling simulations are used. These various dataset allow the multidisciplinary view required to understand the interactions between climate and Mediterranean marine ecosystems. The first step of our study has consisted in a statistical selection of a set of crucial environmental factors to propose the most parsimonious biogeographical approach that allows detecting the main oceanographic structure of the Mediterranean Sea. Second, based on the identified set of environmental parameters, both non-hierarchical and hierarchical clustering algorithms have been tested. Outputs from each methodology are then inter-compared to propose a robust map of the biotopes (unique range of environmental parameters) of the area. Each biotope was then modeled using a non parametric environmental niche method to infer a dynamic biogeochemical partition. Last, the seasonal, inter annual and long term spatial changes of each biogeochemical regions were investigated. The future of this work will be to perform a second partition to subdivide the biogeochemical regions according to biotic features of the Mediterranean Sea (ecoregions). This second level of division will thus be used as a geographical framework to identify ecosystems that have been altered by human activities (i.e. pollution, fishery, invasive species) for the European project PERSEUS (Protecting EuRopean Seas and borders through the intelligence US of surveillance) and the French program MERMEX (Marine Ecosystems Response in the Mediterranean Experiment).

Reygondeau, Gabriel; Olivier Irisson, Jean; Guieu, Cecile; Gasparini, Stephane; Ayata, Sakina; Koubbi, Philippe

2013-04-01

277

Effect of nutrient loading on biogeochemical processes in tropical tidal creeks  

Microsoft Academic Search

The effect of increased nutrient loads on biogeochemical processes in macrotidal, mangrove-lined creeks was studied in tropical\\u000a Darwin Harbour, Australia. This study uses an integrative approach involving multiple benthic and pelagic processes as measures\\u000a of ecosystem function, and provides a comparison of these processes in three tidal creeks receiving different loads of treated\\u000a sewage effluent. There were significant differences in

Jodie SmithMichele; Michele A. Burford; Andrew T. Revill; Ralf R. Haese; Julia Fortune

278

Introduction to special section: Transport and transformation of biogeochemically important materials in coastal waters  

NASA Astrophysics Data System (ADS)

Two projects in the Laurentian Great Lakes were funded under the Coastal Ocean Processes Program. In Lake Superior the Keweenaw Interdisciplinary Transport Experiment in Superior (KITES) focused on a region dominated by a strong coastal jet, and a sister project in Lake Michigan, Episodic Events—Great Lakes Experiment (EEGLE), concentrated on the biogeochemical effects of a major plume of resuspended sediment that occurs annually in the southern portion of the lake.

Green, Sarah A.; Eadie, Brian J.

2004-10-01

279

Climate-quality Ocean Biogeochemical Research Data From Satellite Ocean Color Observations  

Microsoft Academic Search

The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectroradiometer (MODIS)\\/Aqua missions are providing global climate research-quality time series of several important marine biogeochemical quantities such as chlorophyll-a, net primary production, calcite, and particulate organic carbon. The accuracies of these data sets rely on precise sensor calibrations and estimates of water-leaving radiances. While SeaWiFS and MODIS\\/Aqua have been

C. R. McClain

2008-01-01

280

Principal Biogeochemical Factors Affecting the Speciation And Transport of Mercury through the terrestrial environment  

Microsoft Academic Search

It is increasingly becoming known that mercury transport and speciation in the terrestrial environment play major roles in methyl-mercury bioaccumulation potential in surface water. This review discusses the principal biogeochemical reactions affecting the transport and speciation of mercury in the terrestrial watershed. The issues presented are mercury-ligand formation, mercury adsorption\\/desorption, and elemental mercury reduction and volatilization. In terrestrial environments, OH–,

Mark C. Gabriel; Derek G. Williamson

2004-01-01

281

Comparing soil biogeochemical processes in novel and natural boreal forest ecosystems  

NASA Astrophysics Data System (ADS)

Emulating the variability that exists in the natural landscape prior to disturbance should be a goal of soil reconstruction and land reclamation efforts following resource extraction. Long-term ecosystem sustainability within reclaimed landscapes can only be achieved with the re-establishment of biogeochemical processes between reconstructed soils and plants. In this study, we assessed key soil biogeochemical attributes (nutrient availability, organic matter composition, and microbial communities) in reconstructed, novel, anthropogenic ecosystems, covering different reclamation treatments following open-cast mining for oil extraction. We compared the attributes to those present in a range of natural soils representative of mature boreal forest ecosystems in the same area of Northern Alberta. Soil nutrient availability was determined in situ with resin probes, organic matter composition was described with 13C nuclear magnetic resonance spectroscopy and soil microbial community structure was characterized using phospholipid fatty acid analysis. Significant differences among natural ecosystems were apparent in nutrient availability and seemed more related to the dominant tree cover than to soil type. When analyzed together, all natural forests differed significantly from the novel ecosystems, in particular with respect to soil organic matter composition. However, there was some overlap between the reconstructed soils and some of the natural ecosystems in nutrient availability and microbial communities, but not in organic matter characteristics. Hence, our results illustrate the importance of considering the range of natural landscape variability and including several soil biogeochemical attributes when comparing novel, anthropogenic ecosystems to the mature ecosystems that constitute ecological targets.

Quideau, S. A.; Swallow, M. J. B.; Prescott, C. E.; Grayston, S. J.; Oh, S.-W.

2013-08-01

282

Comparing soil biogeochemical processes in novel and natural boreal forest ecosystems  

NASA Astrophysics Data System (ADS)

Emulating the variability that exists in the natural landscape prior to disturbance should be a goal of soil reconstruction and land reclamation efforts following resource extraction. Long-term ecosystem sustainability within reclaimed landscapes can only be achieved with the re-establishment of biogeochemical processes between reconstructed soils and plants. In this study, we assessed key soil biogeochemical attributes (nutrient availability, organic matter composition, and microbial communities) in reconstructed, novel, anthropogenic ecosystems covering different reclamation treatments following open-cast mining for oil extraction. We compared the attributes to those present in a range of natural soils representative of mature boreal forest ecosystems in the same area of northern Alberta. Soil nutrient availability was determined in situ with resin probes, organic matter composition was described with 13C nuclear magnetic resonance spectroscopy and soil microbial community structure was characterized using phospholipid fatty acid analysis. Significant differences among natural ecosystems were apparent in nutrient availability and seemed more related to the dominant tree cover than to soil type. When analyzed together, all natural forests differed significantly from the novel ecosystems, in particular with respect to soil organic matter composition. However, there was some overlap between the reconstructed soils and some of the natural ecosystems in nutrient availability and microbial communities, but not in organic matter characteristics. Hence, our results illustrate the importance of considering the range of natural landscape variability, and including several soil biogeochemical attributes when comparing novel, anthropogenic ecosystems to the mature ecosystems that constitute ecological targets.

Quideau, S. A.; Swallow, M. J. B.; Prescott, C. E.; Grayston, S. J.; Oh, S.-W.

2013-04-01

283

Integrating remotely sensed land cover observations and a biogeochemical model for estimating forest ecosystem carbon dynamics  

USGS Publications Warehouse

Land cover change is one of the key driving forces for ecosystem carbon (C) dynamics. We present an approach for using sequential remotely sensed land cover observations and a biogeochemical model to estimate contemporary and future ecosystem carbon trends. We applied the General Ensemble Biogeochemical Modelling System (GEMS) for the Laurentian Plains and Hills ecoregion in the northeastern United States for the period of 1975-2025. The land cover changes, especially forest stand-replacing events, were detected on 30 randomly located 10-km by 10-km sample blocks, and were assimilated by GEMS for biogeochemical simulations. In GEMS, each unique combination of major controlling variables (including land cover change history) forms a geo-referenced simulation unit. For a forest simulation unit, a Monte Carlo process is used to determine forest type, forest age, forest biomass, and soil C, based on the Forest Inventory and Analysis (FIA) data and the U.S. General Soil Map (STATSGO) data. Ensemble simulations are performed for each simulation unit to incorporate input data uncertainty. Results show that on average forests of the Laurentian Plains and Hills ecoregion have been sequestrating 4.2 Tg C (1 teragram = 1012 gram) per year, including 1.9 Tg C removed from the ecosystem as the consequences of land cover change. ?? 2008 Elsevier B.V.

Liu, J.; Liu, S.; Loveland, T.R.; Tieszen, L.L.

2008-01-01

284

Biogeochemical processes on tree islands in the greater everglades: Initiating a new paradigm  

USGS Publications Warehouse

Scientists' understanding of the role of tree islands in the Everglades has evolved from a plant community of minor biogeochemical importance to a plant community recognized as the driving force for localized phosphorus accumulation within the landscape. Results from this review suggest that tree transpiration, nutrient infiltration from the soil surface, and groundwater flow create a soil zone of confluence where nutrients and salts accumulate under the head of a tree island during dry periods. Results also suggest accumulated salts and nutrients are flushed downstream by regional water flows during wet periods. That trees modulate their environment to create biogeochemical hot spots and strong nutrient gradients is a significant ecological paradigm shift in the understanding of the biogeochemical processes in the Everglades. In terms of island sustainability, this new paradigm suggests the need for distinct dry-wet cycles as well as a hydrologic regime that supports tree survival. Restoration of historic tree islands needs further investigation but the creation of functional tree islands is promising. Copyright ?? 2011 Taylor & Francis Group, LLC.

Wetzel, P.R.; Sklar, F.H.; Coronado, C.A.; Troxler, T.G.; Krupa, S.L.; Sullivan, P.L.; Ewe, S.; Price, R.M.; Newman, S.; Orem, W.H.

2011-01-01

285

Integrating Environmental Genomics and Biogeochemical Models: a Gene-centric Approach  

NASA Astrophysics Data System (ADS)

Rapid advances in molecular microbial ecology have yielded an unprecedented amount of data about the evolutionary relationships and functional traits of microbial communities that regulate global geochemical cycles. Biogeochemical models, however, are trailing in the wake of the environmental genomics revolution and such models rarely incorporate explicit representations of bacteria and archaea, nor are they compatible with nucleic acid or protein sequence data. Here, we present a functional gene-based framework for describing microbial communities in biogeochemical models that uses genomics data and provides predictions that are readily testable using cutting-edge molecular tools. To demonstrate the approach in practice, nitrogen cycling in the Arabian Sea oxygen minimum zone (OMZ) was modelled to examine key questions about cryptic sulphur cycling and dinitrogen production pathways in OMZs. By directly linking geochemical dynamics to the genetic composition of microbial communities, the method provides mechanistic insights into patterns and biogeochemical consequences of marine microbes. Such an approach is critical for informing our understanding of the key role microbes play in modulating Earth's biogeochemistry.

Reed, D. C.; Algar, C. K.; Huber, J. A.; Dick, G.

2013-12-01

286

Integrating Microbial Community Composition With Biogeochemical Carbon and Nitrogen Dynamics: Examples From Lignin and Polyphenol Decomposition  

NASA Astrophysics Data System (ADS)

Biogeochemical models conceptually utilize box and arrow diagrams to explain the rates of carbon cycling in soil. Within these models, labile, intermediate, and recalcitrant pools of carbon are linked to each other, to respiration, and dissolved organic carbon (DOC) flux using parameterized rate functions. These models have often been successful at predicting carbon cycling rates, but they often have to be parameterized to new environmental conditions. This may occur in part because biogeochemical models do not explicitly include the underlying biological mechanisms controlling decomposition. Biogeochemical models may be improved by advances in our understanding the distribution, biomass, and activity of decomposer functional groups. It is especially useful to understand the dynamics of decomposer functional groups and enzyme systems that breakdown recalcitrant soil carbon such as lignin and condensed polyphenolics. Quantitative PCR (QPCR) is an advance in molecular biology that can target decomposer functional groups and functional genes that holds promise for understanding the landscape-level variability in microbial communities controlling the flow and fate of carbon. Here we provide examples of how the abundance and distribution of soil fungi in grassland, temperate and boreal forests predicts the enzymatic capacity of the soil community to decompose recalcitrant soil C. Moreover, the abundance of soil fungi has important implications for the response of decomposers to soil N availability.

Waldrop, M.; Zak, D. R.; Blackwood, C.; Harden, J.

2005-12-01

287

Invasive Fishes Generate Biogeochemical Hotspots in a Nutrient-Limited System  

PubMed Central

Fishes can play important functional roles in the nutrient dynamics of freshwater systems. Aggregating fishes have the potential to generate areas of increased biogeochemical activity, or hotspots, in streams and rivers. Many of the studies documenting the functional role of fishes in nutrient dynamics have focused on native fish species; however, introduced fishes may restructure nutrient storage and cycling freshwater systems as they can attain high population densities in novel environments. The purpose of this study was to examine the impact of a non-native catfish (Loricariidae: Pterygoplichthys) on nitrogen and phosphorus remineralization and estimate whether large aggregations of these fish generate measurable biogeochemical hotspots within nutrient-limited ecosystems. Loricariids formed large aggregations during daylight hours and dispersed throughout the stream during evening hours to graze benthic habitats. Excretion rates of phosphorus were twice as great during nighttime hours when fishes were actively feeding; however, there was no diel pattern in nitrogen excretion rates. Our results indicate that spatially heterogeneous aggregations of loricariids can significantly elevate dissolved nutrient concentrations via excretion relative to ambient nitrogen and phosphorus concentrations during daylight hours, creating biogeochemical hotspots and potentially altering nutrient dynamics in invaded systems. PMID:23342083

Capps, Krista A.; Flecker, Alexander S.

2013-01-01

288

Global response of the terrestrial biosphere to CO2 and climate change using a coupled climate-carbon cycle model  

E-print Network

feedback in the climate-carbon cycle system. INDEX TERMS: 0315 Atmospheric Composition and Structure: Impact phenomena; KEYWORDS: climate change impact, terrestrial carbon cycle Citation: Berthelot, M., P of the terrestrial biosphere to CO2 and climate change using a coupled climate-carbon cycle model, Global Biogeochem

Dufresne, Jean-Louis

289

Simulating the early Holocene eastern Mediterranean sapropel formation using an ocean biogeochemical model  

NASA Astrophysics Data System (ADS)

The early Holocene sapropel S1 is an organic-rich sediment layer deposited under oxygen depleted conditions below 1800 m between 10 to 6.5 kyr BP in the eastern Mediterranean Sea. Whereas this silled ocean basin is well-ventilated and has a low biological productivity today, the S1 formation indicates drastic changes in the deep water circulation and/or productivity. Commonly, both of these processes are attributed to an enhanced humidity over the broader Mediterranean area. In particular, an increase in the strength of the African monsoon during the African humid period (AHP) is thought to have provided enhanced Nile runoff and nutrient load. However, the exact mechanisms leading to S1 formation are still being debated. Here we apply a regional ocean general circulation model coupled to a marine biogeochemical model covering the entire Mediterranean Sea to explore some of the many published hypotheses on sapropel formation. With a set of simulations we show that S1 formation cannot be explained by either enhanced biological productivity fueled by increased riverine nutrient input, or by an AHP climatic induced stagnating deep water circulation combined with enhanced biological productivity. The main reasons are: (i) Enhanced biological productivity cannot overcome the effect of a continuous deep ventilation, so that a stagnating deep water circulation is a prerequisite for S1 formation. (ii) The pre-sapropel period is characterized by low particulate organic carbon (POC) sediment burial fluxes, implying that river induced eutrophication is not a viable scenario. (iii) The time span required for complete oxygen depletion within the stagnating deep water circulation exceeds the time span between the beginning of the AHP and the onset of the S1 oxygen deficiency, so that the enhanced Nile runoff fueled by the AHP climate is an unlikely trigger for deep water isolation that caused S1 formation. Available data suggest substantial freshening and warming of the Mediterranean upper ocean during the last glacial-interglacial transition that stabilized stratification and prevented deep water ventilation. Imposing the climatic signals of the last glacial-interglacial transition triggers a persistent (> 4 kyr) deep water stagnation in this simulation. The productivity regime in this simulation was assumed similar to the present-day oligotrophic regime, and the simulated POC burial fluxes agree with observed pre-sapropel burial fluxes in sediments. No deep water anoxia evolves in the short time frame of this simulation (4 kyr) relative to the temporal extent of the deglaciation period, which started at ~17.5 kyr BP. The trend of the modeled oxygen consumption suggests that it takes at least 6.5 kyr until deep water anoxia is established. The simulation also suggests that addition of freshwater is required to maintain the stratification in order to meet the reconstructed spatial extent and duration of the S1 deposition. An examination of records of epibenthic deep-sea foraminifera ?18O supports our findings, and indicates that the stagnation of the deep circulation started ~6 kyr before the onset of the S1 deposition.

Grimm, Rosina; Maier-Reimer, Ernst; Mikolajewicz, Uwe; Schmiedl, Gerhard; Adloff, Fanny; Emeis, Kay

2013-04-01

290

Nitrous oxide emissions from cropland: a procedure for calibrating the DayCent biogeochemical model using inverse modelling  

USGS Publications Warehouse

DayCent is a biogeochemical model of intermediate complexity widely used to simulate greenhouse gases (GHG), soil organic carbon and nutrients in crop, grassland, forest and savannah ecosystems. Although this model has been applied to a wide range of ecosystems, it is still typically parameterized through a traditional “trial and error” approach and has not been calibrated using statistical inverse modelling (i.e. algorithmic parameter estimation). The aim of this study is to establish and demonstrate a procedure for calibration of DayCent to improve estimation of GHG emissions. We coupled DayCent with the parameter estimation (PEST) software for inverse modelling. The PEST software can be used for calibration through regularized inversion as well as model sensitivity and uncertainty analysis. The DayCent model was analysed and calibrated using N2O flux data collected over 2 years at the Iowa State University Agronomy and Agricultural Engineering Research Farms, Boone, IA. Crop year 2003 data were used for model calibration and 2004 data were used for validation. The optimization of DayCent model parameters using PEST significantly reduced model residuals relative to the default DayCent parameter values. Parameter estimation improved the model performance by reducing the sum of weighted squared residual difference between measured and modelled outputs by up to 67 %. For the calibration period, simulation with the default model parameter values underestimated mean daily N2O flux by 98 %. After parameter estimation, the model underestimated the mean daily fluxes by 35 %. During the validation period, the calibrated model reduced sum of weighted squared residuals by 20 % relative to the default simulation. Sensitivity analysis performed provides important insights into the model structure providing guidance for model improvement.

Rafique, Rashad; Fienen, Michael N.; Parkin, Timothy B.; Anex, Robert P.

2013-01-01

291

Seasonal ITCZ migration dynamically controls the location of the (sub)tropical Atlantic biogeochemical divide.  

PubMed

Inorganic nitrogen depletion restricts productivity in much of the low-latitude oceans, generating a selective advantage for diazotrophic organisms capable of fixing atmospheric dinitrogen (N2). However, the abundance and activity of diazotrophs can in turn be controlled by the availability of other potentially limiting nutrients, including phosphorus (P) and iron (Fe). Here we present high-resolution data (?0.3°) for dissolved iron, aluminum, and inorganic phosphorus that confirm the existence of a sharp north-south biogeochemical boundary in the surface nutrient concentrations of the (sub)tropical Atlantic Ocean. Combining satellite-based precipitation data with results from a previous study, we here demonstrate that wet deposition in the region of the intertropical convergence zone acts as the major dissolved iron source to surface waters. Moreover, corresponding observations of N2 fixation and the distribution of diazotrophic Trichodesmium spp. indicate that movement in the region of elevated dissolved iron as a result of the seasonal migration of the intertropical convergence zone drives a shift in the latitudinal distribution of diazotrophy and corresponding dissolved inorganic phosphorus depletion. These conclusions are consistent with the results of an idealized numerical model of the system. The boundary between the distinct biogeochemical systems of the (sub)tropical Atlantic thus appears to be defined by the diazotrophic response to spatial-temporal variability in external Fe inputs. Consequently, in addition to demonstrating a unique seasonal cycle forced by atmospheric nutrient inputs, we suggest that the underlying biogeochemical mechanisms would likely characterize the response of oligotrophic systems to altered environmental forcing over longer timescales. PMID:24367112

Schlosser, Christian; Klar, Jessica K; Wake, Bronwyn D; Snow, Joseph T; Honey, David J; Woodward, E Malcolm S; Lohan, Maeve C; Achterberg, Eric P; Moore, C Mark

2014-01-28

292

Morphological, hydrological, biogeochemical and ecological changes and challenges in river restoration - the Thur River case study  

NASA Astrophysics Data System (ADS)

River restoration can enhance river dynamics, environmental heterogeneity and biodiversity, but the underlying processes governing the dynamic changes need to be understood to ensure that restoration projects meet their goals, and adverse effects are prevented. In particular, we need to comprehend how hydromorphological variability quantitatively relates to ecosystem functioning and services, biodiversity as well as ground- and surface water quality in restored river corridors. This involves (i) physical processes and structural properties, determining erosion and sedimentation, as well as solute and heat transport behavior in surface water and within the subsurface; (ii) biogeochemical processes and characteristics, including the turnover of nutrients and natural water constituents; and (iii) ecological processes and indicators related to biodiversity and ecological functioning. All these aspects are interlinked, requiring an interdisciplinary investigation approach. Here, we present an overview of the recently completed RECORD (REstored CORridor Dynamics) project in which we combined physical, chemical, and biological observations with modeling at a restored river corridor of the perialpine Thur River in Switzerland. Our results show that river restoration, beyond inducing morphologic changes that reshape the river bed and banks, triggered complex spatial patterns of bank infiltration, and affected habitat type, biotic communities and biogeochemical processes. We adopted an interdisciplinary approach of monitoring the continuing changes due to restoration measures to address the following questions: How stable is the morphological variability established by restoration? Does morphological variability guarantee an improvement in biodiversity? How does morphological variability affect biogeochemical transformations in the river corridor? What are some potential adverse effects of river restoration? How is river restoration influenced by catchment-scale hydraulics and which feedbacks exist on the large scale? Beyond summarizing the major results of individual studies within the project, we show that these overarching questions could only be addressed in an interdisciplinary framework.

Schirmer, M.; Luster, J.; Linde, N.; Perona, P.; Mitchell, E. A. D.; Barry, D. A.; Hollender, J.; Cirpka, O. A.; Schneider, P.; Vogt, T.; Radny, D.; Durisch-Kaiser, E.

2014-06-01

293

Afforestation alters the composition of functional genes in soil and biogeochemical processes in South American grasslands.  

PubMed

Soil microbes are highly diverse and control most soil biogeochemical reactions. We examined how microbial functional genes and biogeochemical pools responded to the altered chemical inputs accompanying land use change. We examined paired native grasslands and adjacent Eucalyptus plantations (previously grassland) in Uruguay, a region that lacked forests before European settlement. Along with measurements of soil carbon, nitrogen, and bacterial diversity, we analyzed functional genes using the GeoChip 2.0 microarray, which simultaneously quantified several thousand genes involved in soil carbon and nitrogen cycling. Plantations and grassland differed significantly in functional gene profiles, bacterial diversity, and biogeochemical pool sizes. Most grassland profiles were similar, but plantation profiles generally differed from those of grasslands due to differences in functional gene abundance across diverse taxa. Eucalypts decreased ammonification and N fixation functional genes by 11% and 7.9% (P < 0.01), which correlated with decreased microbial biomass N and more NH(4)(+) in plantation soils. Chitinase abundance decreased 7.8% in plantations compared to levels in grassland (P = 0.017), and C polymer-degrading genes decreased by 1.5% overall (P < 0.05), which likely contributed to 54% (P < 0.05) more C in undecomposed extractable soil pools and 27% less microbial C (P < 0.01) in plantation soils. In general, afforestation altered the abundance of many microbial functional genes, corresponding with changes in soil biogeochemistry, in part through altered abundance of overall functional gene types rather than simply through changes in specific taxa. Such changes in microbial functional genes correspond with altered C and N storage and have implications for long-term productivity in these soils. PMID:19700539

Berthrong, Sean T; Schadt, Christopher W; Piñeiro, Gervasio; Jackson, Robert B

2009-10-01

294

Global patterns of nitrogen limitation: confronting two global biogeochemical models with observations.  

PubMed

Projections of future changes in land carbon (C) storage using biogeochemical models depend on accurately modeling the interactions between the C and nitrogen (N) cycles. Here, we present a framework for analyzing N limitation in global biogeochemical models to explore how C-N interactions of current models compare to field observations, identify the processes causing model divergence, and identify future observation and experiment needs. We used a set of N-fertilization simulations from two global biogeochemical models (CLM-CN and O-CN) that use different approaches to modeling C-N interactions. On the global scale, net primary productivity (NPP) in the CLM-CN model was substantially more responsive to N fertilization than in the O-CN model. The most striking difference between the two models occurred for humid tropical forests, where the CLM-CN simulated a 62% increase in NPP at high N addition levels (30 g N m(-2) yr(-1)), while the O-CN predicted a 2% decrease in NPP due to N fertilization increasing plant respiration more than photosynthesis. Across 35 temperate and boreal forest sites with field N-fertilization experiments, we show that the CLM-CN simulated a 46% increase in aboveground NPP in response to N, which exceeded the observed increase of 25%. In contrast, the O-CN only simulated a 6% increase in aboveground NPP at the N-fertilization sites. Despite the small response of NPP to N fertilization, the O-CN model accurately simulated ecosystem retention of N and the fate of added N to vegetation when compared to empirical (15) N tracer application studies. In contrast, the CLM-CN predicted lower total ecosystem N retention and partitioned more losses to volatilization than estimated from observed N budgets of small catchments. These results point to the need for model improvements in both models in order to enhance the accuracy with which global C-N cycle feedbacks are simulated. PMID:23744637

Thomas, R Quinn; Zaehle, Sönke; Templer, Pamela H; Goodale, Christine L

2013-10-01

295

Afforestation alters the composition of functional genes in soil and biogeochemical processes in South American grasslands  

SciTech Connect

Soil microbes are highly diverse and control most soil biogeochemical reactions. We examined how microbial functional genes and biogeochemical pools responded to the altered chemical inputs accompanying land use change. We examined paired native grasslands and adjacent Eucalyptus plantations (previously grassland) in Uruguay, a region that lacked forests before European settlement. Along with measurements of soil carbon, nitrogen, and bacterial diversity, we analyzed functional genes using the GeoChip 2.0 microarray, which simultaneously quantified several thousand genes involved in soil carbon and nitrogen cycling. Plantations and grassland differed significantly in functional gene profiles, bacterial diversity, and biogeochemical pool sizes. Most grassland profiles were similar, but plantation profiles generally differed from those of grasslands due to differences in functional gene abundance across diverse taxa. Eucalypts decreased ammonification and N fixation functional genes by 11% and 7.9% (P < 0.01), which correlated with decreased microbial biomass N and more NH{sub 4}{sup +} in plantation soils. Chitinase abundance decreased 7.8% in plantations compared to levels in grassland (P = 0.017), and C polymer-degrading genes decreased by 1.5% overall (P < 0.05), which likely contributed to 54% (P < 0.05) more C in undecomposed extractable soil pools and 27% less microbial C (P < 0.01) in plantation soils. In general, afforestation altered the abundance of many microbial functional genes, corresponding with changes in soil biogeochemistry, in part through altered abundance of overall functional gene types rather than simply through changes in specific taxa. Such changes in microbial functional genes correspond with altered C and N storage and have implications for long-term productivity in these soils.

Berthrong, Sean T [ORNL; Schadt, Christopher Warren [ORNL; Pineiro, Gervasio [Duke University; Jackson, Robert B [Duke University

2009-01-01

296

Validating a Biogeochemical Watershed Disturbance and Climate Change Proxy: Tampa Bay. FL  

NASA Astrophysics Data System (ADS)

The Tampa Bay estuary and watershed have been impacted in the past century by residential and industrial development activities that have resulted in pollutant release via runoff and wastewater discharges. Mangrove forest loss, mining activities, accidental spills and nutrient loading have also decreased water quality in this aquatic environment. The primary goal of this project is to provide historical water quality and climate information by determining biogeochemical properties of oyster shells and sediments collected from various locations throughout the Tampa Bay region including ancient Native American shell mounds. Biogeochemical properties of shells collected from these middens will provide insight regarding historical water quality of Tampa Bay. It is expected that a pristine, pre-Columbian baseline may be revealed from the midden shells, and changes in the biogeochemical record may be demonstrated over the recent past from the industrial age to modern day on a seasonal and yearly scale. In order to achieve the goal of this project, midden shells and sediments will be collected and compared from three stations in Tampa Bay that range from undisturbed to severely impacted; Emerson Point, Weedon Island, and Bayboro Harbor, respectively. Water and sediment samples have also been examined to provide additional information regarding radiogeochemical properties of the three study sites. Sediments will be dated using gamma spectrometry techniques (U/Th series). Standard ICP-OES methods are being utilized to determine concentrations of trace, minor and major elements in the oyster and sediment samples. This project is part of a larger on-going investigation. If successful, this investigation will ultimately yield a high-resolution tool for establishing the history of terrestrial land use and climate change.

Schwing, P. T.; Martinez, E.; Pyrtle, A. J.; Haynes, S.

2007-12-01

297

Biogeochemical study of areas of sulphide mineralisation in eastern Thrace, Greece.  

PubMed

The uptake of copper, lead and zinc by plants in several areas of sulphide mineralisation in eastern Thrace, Greece, has been studied. Two indicator plants for sulphide deposits in central Macedonia,Rumex acetosella L. andMinuartia verna (L.) Hiern, have not been found on Thracian soils high in sulphides. However, the widespread speciesHypericum perforatum L. andScleranthus perennis L. are tolerant of the elevated metal levels in these soils. AlthoughH. perforatum is not useful as a biogeochemical indicator, the levels of Cu, Pb and Zn inS. perennis were found to be strongly correlated with the corresponding concentrations in the soil. PMID:24202203

Kelepertsis, A E; Reeves, R D

1989-03-01

298

Tracing biogeochemical processes in stream water and groundwater using non-linear statistics  

NASA Astrophysics Data System (ADS)

SummaryStream water and groundwater solute concentration are subject to a multitude of biogeochemical processes that act at different scales and are often characterized by non-linear relationships and feedback loops. Different multivariate statistical methods were applied to investigate the interplay of different processes. The data set from the Lehstenbach catchment in South Germany comprised 2641 stream water and groundwater samples from 38 different sites in the catchment, where 13 different solutes had been determined. According to the correlation dimension analysis, the number of dominant processes was four. The first four components determined via principal component analysis comprised 88% of the total variance, whereas the non-linear isometric feature mapping explained 92% with the first four components. These components were ascribed to prevailing biogeochemical processes and were used to investigate spatial and temporal patterns. Redox processes and contamination by road salt explained 35% of the variance each. Another 13% were ascribed to near-surface runoff in the acidified topsoil, and 9% to the impact of contaminated filter gravel in some of the groundwater wells. The redox component exhibited clear seasonal patterns at most stream water and groundwater sampling sites, with the most reduced conditions in late summer, immediately before the onset of re-wetting. There was clear evidence that redox processes, especially denitrification, play an important role even in the oxic aquifer. During discharge peaks, stream water exhibited higher values of the near-surface runoff component. However, the associated lower values of the redox component pointed to near-surface runoff in the riparian wetlands as the predominating runoff generation process rather than to a contribution of upslope soil water. A series of major rain storms in fall 1998 altered groundwater and stream water solute concentration for months: stream water and groundwater became more oxic and more acidified, and showed a higher impact of road salt contamination at some sites. Overall, the spatial and temporal patterns of the predominating components gave a consistent picture and helped considerably to better understand the interplay between biogeochemical and hydrological processes. The chosen approach is a promising tool for investigating apparently complex hydrological and biogeochemical systems.

Lischeid, Gunnar; Bittersohl, Jochen

2008-07-01

299

The biogeochemical cycle of the adsorbed template. I - formation of the template  

NASA Technical Reports Server (NTRS)

Experimental results are presented for the verification of the first adsorption step of the 'adsorbed template' biogeochemical cycle, a simple model for a primitive prebiotic replication system. The adsorption of Poly-C, Poly-U, Poly-A, Poly-G, and 5'-AMP, 5'-GMP, 5'-CMP and 5'-UMP onto gypsum was studied. It was found that under the conditions of the experiment, the polymers have a very high affinity for the mineral surface, while the monomers adsorb much less efficiently.

Lazard, Daniel; Lahav, Noam; Orenberg, J. B.

1987-01-01

300

The biogeochemical cycle of the adsorbed template. II - Selective adsorption of mononucleotides on adsorbed polynucleotide templates  

NASA Technical Reports Server (NTRS)

Experimental results are presented for the verification of the specific interaction step of the 'adsorbed template' biogeochemical cycle, a simple model for a primitive prebiotic replication system. The experimental system consisted of gypsum as the mineral to which an oligonucleotide template attaches (Poly-C or Poly-U) and (5-prime)-AMP, (5-prime)-GMP, (5-prime)-CMP and (5-prime)-UMP as the interacting biomonomers. When Poly-C or Poly-U were used as adsorbed templates, (5-prime)-GMP and (5-prime)-AMP, respectively, were observed to be the most strongly adsorbed species.

Lazard, Daniel; Lahav, Noam; Orenberg, James B.

1988-01-01

301

Desert dust and anthropogenic aerosol interactions in the Community Climate System Model coupled-carbon-climate model  

Microsoft Academic Search

Coupled-carbon-climate simulations are an essential tool for predicting the impact of human activity onto the climate and biogeochemistry. Here we incorporate prognostic desert dust and anthropogenic aerosols into the CCSM3.1 coupled carbon-climate model and explore the resulting interactions with climate and biogeochemical dynamics through a series of transient anthropogenic simulations (20th and 21st centuries) and sensitivity studies. The inclusion of

N. Mahowald; K. Lindsay; D. Rothenberg; S. C. Doney; J. K. Moore; P. Thornton; J. T. Randerson; C. D. Jones

2010-01-01

302

Desert dust and anthropogenic aerosol interactions in the Community Climate System Model coupled-carbon-climate model  

Microsoft Academic Search

Coupled-carbon-climate simulations are an essential tool for predicting the impact of human activity onto the climate and biogeochemistry. Here we incorporate prognostic desert dust and anthropogenic aerosols into the CCSM3.1 coupled carbon-climate model and explore the resulting interactions with climate and biogeochemical dynamics through a series of transient anthropogenic simulations (20th and 21st centuries) and sensitivity studies. The inclusion of

Natalie Mahowald; K. Lindsay; D. Rothenberg; Scott C. Doney; Jefferson Keith Moore; P. Thornton; J. T. Randerson; C. D. Jones

2011-01-01

303

The coupling of mercury and organic matter in the biogeochemical cycle — towards a mechanistic model for the boreal forest zone  

Microsoft Academic Search

In boreal forest lakes, high Hg concentrations in fish are common, even in remote areas. In this paper, the effects of atmospheric\\u000a Hg pollution in Sweden are synthesized and related to a concept based on the strong interaction of Hg with biogenic matter\\u000a (Hg\\/B). Based on this concept, a compartment model is developed to predict concentrations, pool sizes, flux rates

Markus Meili

1991-01-01

304

Predicting skipjack tuna forage distributions in the equatorial Pacific using a coupled dynamical bio-geochemical model  

Microsoft Academic Search

ABSTRACT Skipjack tuna (Katsuwonus ,pelamis) contributes ~70% of the ,total tuna catch in the Pacific Ocean. This species ,occurs ,in the ,upper ,mixed-layer throughout the equatorial region, but the largest catches are taken from the warmpool,in the western equatorial Pacific. Analysis of catch,and effort data for U.S. purse seine fisheries in the western Pacific has demonstrated ,that one of the

PATRICK LEHODEY; JEAN-MICHEL ANDRE; MICHEL BERTIGNAC; JOHN HAMPTON; ANNE STOENS; CHRISTOPHE MENKES; LAURENT MEMERY; NICOLAS GRIMA

1998-01-01

305

A coupled geochemical and biogeochemical approach to characterize the bioreactivity of dissolved organic matter from a headwater stream  

NASA Astrophysics Data System (ADS)

bioreactivity or susceptibility of dissolved organic matter (DOM) to microbial degradation in streams and rivers is of critical importance to global change studies, but a comprehensive understanding of DOM bioreactivity has been elusive due, in part, to the stunningly diverse assemblages of organic molecules within DOM. We approach this problem by employing a range of techniques to characterize DOM as it flows through biofilm reactors: dissolved organic carbon (DOC) concentrations, excitation emission matrix spectroscopy (EEMs), and ultrahigh resolution mass spectrometry. The EEMs and mass spectral data were analyzed using a combination of multivariate statistical approaches. We found that 45% of stream water DOC was biodegraded by microorganisms, including 31-45% of the humic DOC. This bioreactive DOM separated into two different groups: (1) H/C centered at 1.5 with O/C 0.1-0.5 or (2) low H/C of 0.5-1.0 spanning O/C 0.2-0.7 that were positively correlated (Spearman ranking) with chromophoric and fluorescent DOM (CDOM and FDOM, respectively). DOM that was more recalcitrant and resistant to microbial degradation aligned tightly in the center of the van Krevelen space (H/C 1.0-1.5, O/C 0.25-0.6) and negatively correlated (Spearman ranking) with CDOM and FDOM. These findings were supported further by principal component analysis and 2-D correlation analysis of the relative magnitudes of the mass spectral peaks assigned to molecular formulas. This study demonstrates that our approach of processing stream water through bioreactors followed by EEMs and FTICR-MS analyses, in combination with multivariate statistical analysis, allows for precise, robust characterization of compound bioreactivity and associated molecular level composition.

Sleighter, Rachel L.; Cory, Rose M.; Kaplan, Louis A.; Abdulla, Hussain A. N.; Hatcher, Patrick G.

2014-08-01

306

Biogeochemical processes governing natural pyrite oxidation and release of acid metalliferous drainage.  

PubMed

The oxidative dissolution of sulfide minerals (principally pyrite) is responsible for the majority of acid metalliferous drainage from mine sites, which represents a significant environmental problem worldwide. Understanding the complex biogeochemical processes governing natural pyrite oxidation is critical not only for solving this problem but also for understanding the industrial bioleaching of sulfide minerals. To this end, we conducted a simulated experiment of natural pyrite oxidative dissolution. Pyrosequencing analysis of the microbial community revealed a distinct succession across three stages. At the early stage, a newly proposed genus, Tumebacillus (which can use sodium thiosulfate and sulfite as the sole electron donors), dominated the microbial community. At the midstage, Alicyclobacillus (the fifth most abundant genus at the early stage) became the most dominant genus, whereas Tumebacillus was still ranked as the second most abundant. At the final stage, the microbial community was dominated by Ferroplasma (the tenth most abundant genus at the early stage). Our geochemical and mineralogical analyses indicated that exchangeable heavy metals increased as the oxidation progressed and that some secondary sulfate minerals (including jarosite and magnesiocopiapite) were formed at the final stage of the oxidation sequence. Additionally, we propose a comprehensive model of biogeochemical processes governing the oxidation of sulfide minerals. PMID:24730689

Chen, Ya-ting; Li, Jin-tian; Chen, Lin-xing; Hua, Zheng-shuang; Huang, Li-nan; Liu, Jun; Xu, Bi-bo; Liao, Bin; Shu, Wen-sheng

2014-05-20

307

Biogeochemical implications of the ubiquitous colonization of marine habitats and redox gradients by Marinobacter species  

PubMed Central

The Marinobacter genus comprises widespread marine bacteria, found in localities as diverse as the deep ocean, coastal seawater and sediment, hydrothermal settings, oceanic basalt, sea-ice, sand, solar salterns, and oil fields. Terrestrial sources include saline soil and wine-barrel-decalcification wastewater. The genus was designated in 1992 for the Gram-negative, hydrocarbon-degrading bacterium Marinobacter hydrocarbonoclasticus. Since then, a further 31 type strains have been designated. Nonetheless, the metabolic range of many Marinobacter species remains largely unexplored. Most species have been classified as aerobic heterotrophs, and assessed for limited anaerobic pathways (fermentation or nitrate reduction), whereas studies of low-temperature hydrothermal sediments, basalt at oceanic spreading centers, and phytoplankton have identified species that possess a respiratory repertoire with significant biogeochemical implications. Notable physiological traits include nitrate-dependent Fe(II)-oxidation, arsenic and fumarate redox cycling, and Mn(II) oxidation. There is also evidence for Fe(III) reduction, and metal(loid) detoxification. Considering the ubiquity and metabolic capabilities of the genus, Marinobacter species may perform an important and underestimated role in the biogeochemical cycling of organics and metals in varied marine habitats, and spanning aerobic-to-anoxic redox gradients. PMID:23734151

Handley, Kim M.; Lloyd, Jonathan R.

2013-01-01

308

Biogeochemical Changes at Early Stage After the Closure of Radioactive Waste Geological Repository in South Korea  

SciTech Connect

Permanent disposal of low- and intermediate-level radioactive wastes in the subterranean environment has been the preferred method of many countries, including Korea. A safety issue after the closure of a geological repository is that biodegradation of organic materials due to microbial activities generates gases that lead to overpressure of the waste containers in the repository and its disintegration with the release of radionuclides. As part of an ongoing large-scale in situ experiment using organic wastes and groundwater to simulate geological radioactive waste repository conditions, we investigated the geochemical alteration and microbial activities at an early stage (~63 days) intended to be representative of the initial period after repository closure. The increased numbers of both aerobes and facultative anaerobes in waste effluents indicate that oxygen content could be the most significant parameter to control biogeochemical conditions at very early periods of reaction (<35 days). Accordingly, the values of dissolved oxygen and redox potential were decreased. The activation of anaerobes after 35 days was supported by the increased concentration to ~50 mg L-1 of ethanol. These results suggest that the biogeochemical conditions were rapidly altered to more reducing and anaerobic conditions within the initial 2 months after repository closure. Although no gases were detected during the study, activated anaerobic microbes will play more important role in gas generation over the long term.

Choung, Sungwook [Pohang Univ. of Science and Technology (Korea, Republic of); Um, Wooyong [Pohang Univ. of Science and Technology (Korea, Republic of); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Choi, Seho [Pohang Univ. of Science and Technology (Korea, Republic of); Francis, Arokiasamy J. [Pohang Univ. of Science and Technology (Korea, Republic of); Brookhaven National Laboratory (BNL), Upton, NY (United States); Kim, Sungpyo [Korea Univ., Sejong (Korea, Republic of); Park, Jin beak [Korea Radioactive Waste Agency (KORAD), Daejeon (Korea, Republic of); Kim, Suk-Hoon [FNC Technology Co., Seoul National University (Korea, Republic of)

2014-03-18

309

Environmental and biogeochemical changes following a decade's reclamation in the Dapeng (Tapong) Bay, southwestern Taiwan  

NASA Astrophysics Data System (ADS)

This study examines the environmental and biogeochemical changes in Dapeng (formerly spelled Tapong) Bay, a semi-enclosed coastal lagoon in southwestern Taiwan, after two major reclamation works performed between 1999 and 2010. The lagoon was largely occupied by oyster culture racks and fish farming cages before December, 2002. Substantial external inputs of nutrients and organic carbon and the fairly long water exchange time (?) (10 ± 2 days) caused the lagoon to enter a eutrophic state, particularly at the inner lagoon, which directly received nutrient inputs. However, the entire lagoon showed autotrophic, and the estimated net ecosystem production (NEP) during the first stage was 5.8 mol C m-2 yr-1. After January, 2003, the aquaculture structures were completely removed, and the ? decreased to 6 ± 2 days. The annual mean concentrations of dissolved oxygen increased, and nutrients decreased substantially, likely due to improved water exchange, absence of feeding and increased biological utilization. The NEP increased 37% to 7.7 mol C m-2 yr-1 after structure removal. The second reclamation work beginning from July, 2006, focused on establishing artificial wetlands for wastewater treatment and on dredging bottom sediment. Although the ? did not change significantly (8 ± 3 days), substantial decreases in nutrient concentrations and dissolved organic matter continued. The NEP (14.3 mol C m-2 yr-1) increased 85% compared to that in the second stage. The data suggest that the reclamations substantially improved water quality, carbon and nutrient biogeochemical processes and budgets in this semi-enclosed ecosystem.

Hung, J.-J.; Huang, W.-C.; Yu, C.-S.

2013-09-01

310

Biogeochemical impacts of wildfires over four millennia in a Rocky Mountain subalpine watershed.  

PubMed

Wildfires can significantly alter forest carbon (C) storage and nitrogen (N) availability, but the long-term biogeochemical legacy of wildfires is poorly understood. We obtained a lake-sediment record of fire and biogeochemistry from a subalpine forest in Colorado, USA, to examine the nature, magnitude, and duration of decadal-scale, fire-induced ecosystem change over the past c. 4250 yr. The high-resolution record contained 34 fires, including 13 high-severity events within the watershed. High-severity fires were followed by increased sedimentary N stable isotope ratios (?15N) and bulk density, and decreased C and N concentrations--reflecting forest floor destruction, terrestrial C and N losses, and erosion. Sustained low sediment C : N c. 20-50 yr post-fire indicates reduced terrestrial organic matter subsidies to the lake. Low sedimentary ?15N c. 50-70 yr post-fire, coincident with C and N recovery, suggests diminishing terrestrial N availability during stand development. The magnitude of post-fire changes generally scaled directly with inferred fire severity. Our results support modern studies of forest successional C and N accumulation and indicate pronounced, long-lasting biogeochemical impacts of wildfires in subalpine forests. However, even repeated high-severity fires over millennia probably did not deplete C or N stocks, because centuries between high-severity fires allowed for sufficient biomass recovery. PMID:24803372

Dunnette, Paul V; Higuera, Philip E; McLauchlan, Kendra K; Derr, Kelly M; Briles, Christy E; Keefe, Margaret H

2014-08-01

311

Novel Imaging Techniques, Integrated with Mineralogical, Geochemical and Microbiological Characterization to Determine the Biogeochemical Controls....  

SciTech Connect

Aims and objectives Technetium-99 is a priority pollutant at numerous DOE sites, due to a combination of its long half life (2.1 x 105 years), high mobility as Tc(VII) (TcO4-; pertechnetate anion) in oxic waters, and bioavailability as a sulfate analog. Under anaerobic conditions, however, the radionuclide is far less mobile, forming insoluble Tc(IV) precipitates. As anaerobic microorganisms can reduce soluble Tc(VII) to insoluble Tc(IV), microbial metabolism may have the potential to treat sediments and waters contaminated with Tc. In previous studies we have focused on the fundamental mechanisms of Tc(VII) bioreduction and precipitation, and we have identified direct enzymatic (hydrogenase-mediated) mechanisms, and a range of potentially important indirect transformations catalyzed by biogenic Fe(II), U(IV) or sulfide. These baseline studies have generally used pure cultures of metal-reducing bacteria, in order to develop conceptual models for the biogeochemical cycling of Tc. There is, however, comparatively little known about interactions of metal-reducing bacteria with environmentally relevant trace concentrations of Tc, against a more complex biogeochemical background provided by mixed microbial communities in the subsurface.

Lloyd, Jonathan R.

2004-06-01

312

Contrasting biogeochemical characteristics of the Oubangui River and tributaries (Congo River basin).  

PubMed

The Oubangui is a major tributary of the Congo River. We describe the biogeochemistry of contrasting tributaries within its central catchment, with watershed vegetation ranging from wooded savannahs to humid rainforest. Compared to a 2-year monitoring record on the mainstem Oubangui, these tributaries show a wide range of biogeochemical signatures, from highly diluted blackwaters (low turbidity, pH, conductivity, and total alkalinity) in rainforests to those more typical for savannah systems. Spectral analyses of chromophoric dissolved organic matter showed wide temporal variations in the Oubangui compared to spatio-temporal variations in the tributaries, and confirm that different pools of dissolved organic carbon are mobilized during different hydrological stages. ?(13)C of dissolved inorganic carbon ranged between -28.1‰ and -5.8‰, and was strongly correlated to both partial pressure of CO2 and to the estimated contribution of carbonate weathering to total alkalinity, suggesting an important control of the weathering regime on CO2 fluxes. All tributaries were oversaturated in dissolved greenhouse gases (CH4, N2O, CO2), with highest levels in rivers draining rainforest. The high diversity observed underscores the importance of sampling that covers the variability in subcatchment characteristics, to improve our understanding of biogeochemical cycling in the Congo Basin. PMID:24954525

Bouillon, Steven; Yambélé, Athanase; Gillikin, David P; Teodoru, Cristian; Darchambeau, François; Lambert, Thibault; Borges, Alberto V

2014-01-01

313

Contrasting biogeochemical characteristics of the Oubangui River and tributaries (Congo River basin)  

NASA Astrophysics Data System (ADS)

The Oubangui is a major tributary of the Congo River. We describe the biogeochemistry of contrasting tributaries within its central catchment, with watershed vegetation ranging from wooded savannahs to humid rainforest. Compared to a 2-year monitoring record on the mainstem Oubangui, these tributaries show a wide range of biogeochemical signatures, from highly diluted blackwaters (low turbidity, pH, conductivity, and total alkalinity) in rainforests to those more typical for savannah systems. Spectral analyses of chromophoric dissolved organic matter showed wide temporal variations in the Oubangui compared to spatio-temporal variations in the tributaries, and confirm that different pools of dissolved organic carbon are mobilized during different hydrological stages. ?13C of dissolved inorganic carbon ranged between -28.1‰ and -5.8‰, and was strongly correlated to both partial pressure of CO2 and to the estimated contribution of carbonate weathering to total alkalinity, suggesting an important control of the weathering regime on CO2 fluxes. All tributaries were oversaturated in dissolved greenhouse gases (CH4, N2O, CO2), with highest levels in rivers draining rainforest. The high diversity observed underscores the importance of sampling that covers the variability in subcatchment characteristics, to improve our understanding of biogeochemical cycling in the Congo Basin.

Bouillon, Steven; Yambélé, Athanase; Gillikin, David P.; Teodoru, Cristian; Darchambeau, François; Lambert, Thibault; Borges, Alberto V.

2014-06-01

314

Impacts of Bark Beetle Outbreaks in the Western US on Biogeochemical Cycling  

NASA Astrophysics Data System (ADS)

Insect outbreaks are major forest disturbances, altering carbon and nitrogen fluxes through growth reductions and/or tree mortality. In western North America, bark beetles have killed trees over millions of hectares. Here we report on several studies that increase our understanding of the biogeochemical impacts of bark beetle epidemics. We modified the Community Land Model to simulate these disturbances, then ran the model for a range of hypothetical, realistic outbreak conditions to explore variability in impacts. We find significant differences in the responses of carbon and nitrogen based on the severity of the outbreak, the timing of snagfall, and the time since attack. Given the importance of identifying the number of trees killed within a study region for accurately quantifying impacts, we have developed a database of mortality in the western US and British Columbia for 1997-2009. We combined this database with spatially explicit maps of carbon stocks to estimate the amount of carbon in killed trees. We also used this database to drive CLM to quantify changes in biogeochemical stocks and fluxes. We find that in some regions, bark beetle-killed trees accounted for over 30% of the carbon stocks, whereas in other areas, the number of killed trees was low. Effects on net carbon fluxes in outbreak regions were significant, with fluxes switching from sinks to sources.

Hicke, J. A.; Edburg, S. L.; Meddens, A. J.

2011-12-01

315

Effects of bark beetle-caused tree mortality on biogeochemical and biogeophysical MODIS products  

NASA Astrophysics Data System (ADS)

affect forest-atmosphere exchanges of carbon, water, and energy, thereby influencing weather and climate. Bark beetle outbreaks are one such disturbance type that alters biogeochemical and biogeophysical processes in forests. Few studies have documented bark beetle impacts to leaf area index (LAI), gross primary productivity (GPP), evapotranspiration (ET), land surface temperature (LST), and surface albedo with satellite observations. Our objective was to use Landsat-derived estimates of bark beetle-caused tree mortality and Moderate Resolution Imaging Spectroradiometer (MODIS) land surface products to estimate beetle-caused changes in LAI, GPP, ET, LST, and surface albedo in northern Colorado. Following bark beetle-caused tree mortality, decreases occurred in LAI (0.02-0.80 m2m-2, 1-40%), annual GPP (50-248 gC m-2 yr-1, (5-26%), and daily summer ET (0.20-0.70 mm day-1, 13-44%), whereas increases occurred in August LST (1-3.9 K) and February albedo (0.03-0.09, 19-52%). We found greater responses of these variables in areas of greater mortality severity. The extent and severity of tree mortality in northern Colorado caused substantial changes in land surface variables (9-23%) when averaged across all forested areas of our study area. Our results demonstrate that land surface variables are sensitive to bark beetle-caused tree mortality and that bark beetle outbreaks can significantly impact biogeochemical and biogeophysical processes.

Bright, Benjamin C.; Hicke, Jeffrey A.; Meddens, Arjan J. H.

2013-07-01

316

Spatio-temporal evolution of biogeochemical processes at a landfill site  

NASA Astrophysics Data System (ADS)

Predictions of fate and transport of contaminants are strongly dependent on spatio-temporal variability of soil hydraulic and geochemical properties. This study focuses on time-series signatures of hydrological and geochemical properties at different locations within the Norman landfill site. Norman Landfill is a closed municipal landfill site with prevalent organic contamination. Monthly data at the site include specific conductance, ?18O, ?2H, dissolved organic carbon (DOC) and anions (chloride, sulfate, nitrate) from 1998-2006. Column scale data on chemical concentrations, redox gradients, and flow parameters are also available on daily and hydrological event (infiltration, drainage, etc.) scales. Since high-resolution datasets of contaminant concentrations are usually unavailable, Wavelet and Fourier analyses were used to infer the dominance of different biogeochemical processes at different spatio-temporal scales and to extract linkages between transport and reaction processes. Results indicate that time variability controls the progression of reactions affecting biodegradation of contaminants. Wavelet analysis suggests that iron-sulfide reduction reactions had high seasonal variability at the site, while fermentation processes dominated at the annual time scale. Findings also suggest the dominance of small spatial features such as layered interfaces and clay lenses in driving biogeochemical reactions at both column and landfill scales. A conceptual model that caters to increased understanding and remediating structurally heterogeneous variably-saturated media is developed from the study.

Arora, B.; Mohanty, B. P.; McGuire, J. T.

2011-12-01

317

Biogeochemical implications of the ubiquitous colonization of marine habitats and redox gradients by Marinobacter species.  

PubMed

The Marinobacter genus comprises widespread marine bacteria, found in localities as diverse as the deep ocean, coastal seawater and sediment, hydrothermal settings, oceanic basalt, sea-ice, sand, solar salterns, and oil fields. Terrestrial sources include saline soil and wine-barrel-decalcification wastewater. The genus was designated in 1992 for the Gram-negative, hydrocarbon-degrading bacterium Marinobacter hydrocarbonoclasticus. Since then, a further 31 type strains have been designated. Nonetheless, the metabolic range of many Marinobacter species remains largely unexplored. Most species have been classified as aerobic heterotrophs, and assessed for limited anaerobic pathways (fermentation or nitrate reduction), whereas studies of low-temperature hydrothermal sediments, basalt at oceanic spreading centers, and phytoplankton have identified species that possess a respiratory repertoire with significant biogeochemical implications. Notable physiological traits include nitrate-dependent Fe(II)-oxidation, arsenic and fumarate redox cycling, and Mn(II) oxidation. There is also evidence for Fe(III) reduction, and metal(loid) detoxification. Considering the ubiquity and metabolic capabilities of the genus, Marinobacter species may perform an important and underestimated role in the biogeochemical cycling of organics and metals in varied marine habitats, and spanning aerobic-to-anoxic redox gradients. PMID:23734151

Handley, Kim M; Lloyd, Jonathan R

2013-01-01

318

Biophysical and Biogeochemical Responses to Climate Change Depend on Dispersal and Migration  

NSDL National Science Digital Library

This peer- reviewed article from BioScience looks at the effects of dispersal and migration on biophysical and biogeochemical responses to climate change. Different species, populations, and individuals disperse and migrate at different rates. The rate of movement that occurs in response to changes in climate, whether fast or slow, will shape the distribution of natural ecosystems in the decades to come. Moreover, land-use patterns associated with urban, suburban, rural, and agricultural development will complicate ecosystem adaptation to climate change by hindering migration. Here we examine how vegetation's capacity to disperse and migrate may affect the biophysical and biogeochemical characteristics of the land surface under anthropogenic climate change. We demonstrate that the effectiveness of plant migration strongly influences carbon storage, evapotranspiration, and the absorption of solar radiation by the land surface. As a result, plant migration affects the magnitude, and in some cases the sign, of feedbacks from the land surface to the climate system. We conclude that future climate projections depend on much better understanding of and accounting for dispersal and migration.

PAUL A. T. HIGGINS and JOHN HARTE (;)

2006-05-01

319

Biogeochemical processes governing exposure and uptake of organic pollutant compounds in aquatic organisms.  

PubMed Central

This paper reviews current knowledge of biogeochemical cycles of pollutant organic chemicals in aquatic ecosystems with a focus on coastal ecosystems. There is a bias toward discussing chemical and geochemical aspects of biogeochemical cycles and an emphasis on hydrophobic organic compounds such as polynuclear aromatic hydrocarbons, polychlorinated biphenyls, and chlorinated organic compounds used as pesticides. The complexity of mixtures of pollutant organic compounds, their various modes of entering ecosystems, and their physical chemical forms are discussed. Important factors that influence bioavailability and disposition (e.g., organism-water partitioning, uptake via food, food web transfer) are reviewed. These factors include solubilities of chemicals; partitioning of chemicals between solid surfaces, colloids, and soluble phases; variables rates of sorption, desorption; and physiological status of organism. It appears that more emphasis on considering food as a source of uptake and bioaccumulation is important in benthic and epibenthic ecosystems when sediment-associated pollutants are a significant source of input to an aquatic ecosystem. Progress with mathematical models for exposure and uptake of contaminant chemicals is discussed briefly. PMID:1904812

Farrington, J W

1991-01-01

320

Biogeochemical cycling of C, N, and water in paddy rice agriculture in Monsoon Asia  

NASA Astrophysics Data System (ADS)

We report latest results of an ongoing project to evaluate the biogeochemical cycling of C, N, and water in paddy rice agriculture in Monsoon Asia. The core project focus is application of the DNDC biogeochemical model to estimate greenhouse gas emissions from paddy rice, and possible impacts of changes in agricultural management on those emissions. Simulations are done at the scale of sub-national political units (county equivalents and/or provinces/states). One effort has been to develop geospatial input data sets of agricultural land use and management, including crop rotations, cropping intensity, water management (irrigated or rainfed), fertilizer use. We have worked with both statistical census data and MODIS space-borne remote sensing data to map paddy rice across the domain. A second effort has been model development for application to rainfed paddy agriculture, and model testing against field data from paddy sites in India. The final thrust is model application across the domain to estimate water use, crop yield, net C-sequestration in soils, and emissions of methane and nitrous oxide.

Frolking, S.; Li, C.; Xiao, X.; Babu, J. Y.; Boles, S.; Salas, W.

2006-05-01

321

Global Biogeochemical Fluxes Program for the Ocean Observatories Initiative: A Proposal. (Invited)  

NASA Astrophysics Data System (ADS)

The overarching emphasis of the Global Biogeochemical Flux Ocean Observatories Initiative is to assess the role of oceanic carbon, both living and non-, in the Earth climate system. Modulation of atmospheric CO2 and its influence on global climate is a function of the quantitative capacity of the oceans to sequester organic carbon into deep waters. Critical to our understanding of the role of the oceans in the global cycling of carbon are the quantitative dynamics in both time and space of the fixation of CO2 into organic matter by surface ocean primary production and removal of this carbon to deep waters via the “biological pump”. To take the next major step forward in advancing our understanding of the oceanic biological pump, a global observation program is required that: (i) greatly improves constraints on estimates of global marine primary production (PP), a critical factor in understanding the global CO2 cycle and for developing accurate estimates of export production (EP); (ii) explores the spatiotemporal links between PP, EP and the biogeochemical processes that attenuate particulate organic carbon (POC) flux; (iii) characterizes microbial community structure and dynamics both in the surface and deep ocean; (iv) develops a comprehensive picture of the chemical and biological processes that take place from the surface ocean to the sea floor; (v) provides unique time-series samples for detailed laboratory-based chemical and biological characterization and tracer studies that will enable connections to be made between the operation of the biological pump at present and in the geologic past. The primary goal is to provide high quality biological and biogeochemical observational data for the modeling and prediction efforts of the global CO2 cycle research community. Crucial to the realization of the GBF-OOI is the development of reliable, long-term, time-series ocean observation platforms capable of precise and controlled placement of sophisticated biogeochemical sensors/samplers, and in situ experimental systems at a wide range of depths, including close proximity to the sea surface. Significant opportunities exist to exploit sensor miniaturization in combination with recent exponential improvements in “omics” technologies for measurement of nucleic acids, proteins and metabolites with unprecedented throughput and resolution. We will discuss the goals, philosophy, principal experimental and technical approaches and operational challenges. We will outline proposed mooring systems as well as means for accurate, spatiotemporal assessment of: (i) primary production, (ii) constraint of POC export flux with season and depth, (iii) assessment of microbial and zooplankton community structure/function throughout the water column, and (iv) collection and preservation of particulate and water samples for land-based examination of temporal and vertical variability of specific tracers, isotopes, nutrients, DOC and related substances for even more precise measurements of environmental biogeochemical properties. The GBF-OOI will become our Hubble for the sea.

Ulmer, K. M.; Taylor, C.

2010-12-01

322

The role of the vertical fluxes of particulate organic matter and calcite in the oceanic carbon cycle: Studies using an ocean biogeochemical general circulation model  

Microsoft Academic Search

Distributions of chemical tracers in the world ocean are well reproduced in an ocean general circulation model which includes biogeochemical processes (biogeochemical general circulation model, B-GCM). The difference in concentration of tracers between the surface and the deep water depends not only on the export production but also on the remineralization depth. Case studies changing the vertical profile of particulate

Yasuhiro Yamanaka; Eiichi Tajika

1996-01-01

323

Helix coupling  

DOEpatents

A coupling for connecting helix members in series, which consists of a pair of U-shaped elements, one of which is attached to each helix end with the "U" sections of the elements interlocked. The coupling is particularly beneficial for interconnecting helical Nitinol elements utilized in thermal actuators or engines. Each coupling half is attached to the associated helix at two points, thereby providing axial load while being easily removed from the helix, and reusable.

Ginell, W.S.

1989-04-25

324

Interannuality and CO 2 sensitivity of the SECHIBA-BGC coupled SVAT-BGC model  

Microsoft Academic Search

SECHIBA-BGC is a coupled Soil Vegetation Atmosphere Transfer (SVAT)\\/ Biogeochemical Cycle (BGC) biosphere model based on the SECHIBA land surface scheme. In this paper, SECHIBA-BGC was used: (1) to simulate the interannual variability of net CO2 fluxes during the 1990–1992 period, (2) to simulate the changes of water fluxes and carbon fluxes due to a doubling of atmospheric CO2. Differences

N. Viovy

1996-01-01

325

Coupling of the Perturbed C–N–P Cycles in Industrial Time  

Microsoft Academic Search

Coupling of the C–N–P biogeochemical cycles is effected by the dependence of the land and aquatic primary producers on the availability of N and P. In general, the Redfield ratios C:P and N:P in the reservoirs supplying nutrients for primary production on land, in the oceanic coastal zone, and in the surface ocean differ from these ratios in the land

Abraham Lerman; Fred T. Mackenzie; L. May Ver

2004-01-01

326

Novel biogeochemical fingerprinting approaches to sediment source apportionment in catchments (Invited)  

NASA Astrophysics Data System (ADS)

Apportioning the source of organic carbon in eroding sediments is important to constrain the scale of transport processes and to assess the impact of anthropogenic activity on environmental quality. Established biogeochemical techniques are used to trace organic inputs typically derived directly or indirectly from plants into soils, sediments and water using lipid biomarkers. Recently, advances in bulk and compound specific stable 13C isotope analyses have provided novel ways of exploring the source and residence times of organic matter in soils using the natural abundance stable 13C isotope signature of C3 and C4 plant end member values. However, the application of biogeochemical source tracing technologies at the molecular level at field to catchment scales has been slow to develop because of perceived problems with dilution of molecular-scale signals. This paper describes the results of recent experiments in natural and agricultural environments in the UK (Collins et al., 2013; Dungait et al., 2013) and United States (Puttock et al., 2012; Beniston et al., submitted) that have successfully applied new biogeochemical fingerprinting techniques using stable 13C isotope approaches and complementary modelling approaches to explore the transport of particulate and sediment-bound organic carbon at a range of scales from the small plot (m2) to field (ha) and small catchment (10's ha). References Beniston et al (submitted) The effects of crop residue removal on soil erosion and macronutrient dynamics on soils under no till for 42 years. Biogeosciences Collins et al (2013) Catchment source contributions to the sediment-bound organic matter degrading salmonid spawning gravels in a lowland river, southern England. Science of the Total Environment 456-457, 181-195. Dungait et al (2013) Microbial responses to the erosional redistribution of soil organic carbon in arable fields. Soil Biology and Biochemistry 60, 195-201. Puttock et al (2012) Stable carbon isotope analysis of fluvial sediment fluxes over two contrasting C4-C3 semi-arid vegetation transitions. Rapid Communications in Mass Spectrometry 26, 2386-2392

Dungait, J.; Puttock, A.; Beniston, J. W.; Brazier, R. E.; Lal, R.; Collins, A.

2013-12-01

327

Biogeochemical cycling of cadmium isotopes along a high-resolution section through the North Atlantic Ocean  

NASA Astrophysics Data System (ADS)

Cadmium (Cd) is a bioactive trace element in the oceans, with a nutrient-like distribution that closely matches dissolved phosphate. Seawater-dissolved stable Cd isotope ratios (?114Cd) are a relatively new parameter, which show much promise for furthering our understanding of the biogeochemical cycling of Cd in the oceans. Here we present a high-resolution paired section of dissolved Cd concentrations and dissolved ?114Cd from 21 open-ocean stations along the US GEOTRACES GA03 transect through the North Atlantic Ocean. Dissolved Cd concentrations along the section are strongly influenced by water-mass distribution and the cycling of Cd. The highest dissolved Cd concentrations (400-540 pmol kg-1) are associated with Antarctic-sourced water masses, whilst biological uptake in the surface ocean results in a strong vertical gradient in dissolved Cd towards the surface, reaching as low as 0.03 pmol kg-1 in western surface waters. Dissolved ?114Cd is also characterized by a vertical gradient from ?+0.2‰ in the deep ocean to +2‰ to +5‰ in the Cd-depleted surface ocean (relative to NIST SRM 3108). This variability in ?114Cd can be ascribed to mixing of Antarctic and North Atlantic water masses, together with fractionation due to in situ biological uptake of light Cd in the very surface ocean. Subtle deviations from this overall pattern of dissolved Cd concentration and dissolved ?114Cd are observed within low-oxygen waters off North Africa, where a dissolved Cd deficit relative to phosphate is associated with higher dissolved ?114Cd values. Together with elevated particulate Cd and Ba, this suggests that Cd sulfide precipitation is occurring within the water column of the North Atlantic, constituting a potentially important sink for isotopically light Cd. Additionally, the first measurements of dissolved ?114Cd within a hydrothermal plume at the Mid-Atlantic Ridge show that Cd is scavenged from the dissolved phase, leaving the remnant dissolved Cd isotopically heavier. Constraining the significance of these marine sinks for dissolved Cd is important, not only for our understanding of the marine biogeochemical cycling of Cd in the modern oceans, but also for the successful application of the microfossil Cd/Ca proxy and the development of ?114Cd as a tracer for past-ocean biogeochemical cycling.

Conway, Tim M.; John, Seth G.

2015-01-01

328

Evidence of linked biogeochemical and hydrological processes in homogeneous and layered vadose zone systems  

NASA Astrophysics Data System (ADS)

Understanding chemical fate and transport in the vadose zone is critical to protect groundwater resources and preserve ecosystem health. However, prediction can be challenging due to the dynamic hydrologic and biogeochemical nature of the vadose zone. Additional controls on hydrobiogeochemical processes are added by subsurface structural heterogeneity. This study uses repacked soil column experiments to quantify linkages between microbial activity, geochemical cycling and hydrologic flow. Three “short” laboratory soil columns were constructed to evaluate the effects of soil layering: a homogenized medium-grained sand, homogenized organic-rich loam, and a sand-over-loam layered column. In addition, two “long” columns were constructed using either gamma-irradiated (sterilized) or untreated sediments to evaluate the effects of both soil layers and the presence of microorganisms. The long columns were packed identically; a medium-grained sand matrix with two vertically separated and horizontally offset lenses of organic-rich loam. In all 5 columns, downward and upward infiltration of water was evaluated to simulate rainfall and rising water table events respectively. In-situ colocated probes were used to measure soil water content, matric potential, Eh, major anions, ammonium, Fe2+, and total sulfide. Enhanced biogeochemical cycling was observed in the short layered column versus the short, homogeneous columns, and enumerations of iron and sulfate reducing bacteria were 1-2 orders of magnitude greater. In the long columns, microbial activity caused mineral bands and produced insoluble gases that impeded water flow through the pores of the sediment. Capillary barriers, formed around the lenses due to soil textural differences, retarded water flow rates through the lenses. This allowed reducing conditions to develop, evidenced by the production of Fe2+ and S2-. At the fringes of the lenses, Fe2+ oxidized to form Fe(III)-oxide bands that further retarded water flux. No such mineral bands developed in the sterilized column. As a consequence, water content in the lenses of the sterilized column was half that of the other column and flow rates through the lenses were an order of magnitude lower. This flow impedance limited the interaction and mixing of groundwater with infiltrating vadose zone water and led to the formation of geochemically distinct water masses residing in relatively close proximity to one another. Results provide a specific examples of the direct impact of biogeochemical cycling on water flow in the vadose zone and vice versa. In addition, these demonstrate that the presence of layers in vadose zone environments may be an important control on overall chemical fate and transport in subsurface systems.

McGuire, J. T.; Hansen, D. J.; Mohanty, B. P.

2010-12-01

329

Influence of Biogeochemical Conditions on the Stability and Remobilization of Biogenic U(IV)  

NASA Astrophysics Data System (ADS)

Uranium (U) is a common contaminant at the US Department of Energy (DOE) sites resulting from its central role in nuclear fuel cycle, and at U mine tailing sites associated with its production. U is present in the environment primarily as the hexavalent U(VI) and tetravalent U(IV). U(IV) is typically contained in insoluble precipitates, such as uraninite [UO2(s)], whereas U(VI) exists as uranyl ion, UO22+, and its complexes with various ligands. The mobility of U(VI) is a major concern in the subsurface environments. Under anoxic conditions, U(VI) can be reduced into U(IV) by some metal reducing bacteria, thus immobilizing U from groundwater. The reductive immobilization of U has been proposed as a remediation technology and under active studies at many US DOE sites. A key to the success of such immobilization technology is the maintenance of long term stability of the immobilized U when remediation completes and subsurface environments return to oxic conditions. This study investigated the influence of biogeochemical conditions on the stability and remobilization of biogenic U(IV). The experiments were conducted in a batch system using sediments collected from the US DOE Field Research Center at Oak Ridge National Laboratory. Both sediments and U(VI) were first reduced by a dissimilatory metal reducing bacterium, Shewanella putrefaciens strain CN32, and then mixed in a solution containing 0.1 mM bicarbonate and 0.1 M NaNO3 in contact with atmospheric O2. Aqueous U(VI) in the suspensions were monitored as a function of time to determine the rates of U remobilization. The influence of biogeochemical conditions in the initial suspensions including Fe(II) concentration, pH, and the aging of bio-reduced U was evaluated. The results demonstrated that the Fe(II) concentration and pH had significant effects on the rate of U remobilization, while aging had only minor influence. The immobilized U was the most stable under neutral pH condition and its stability increased with increasing Fe(II) concentration. The armoring of U(IV) by Fe(III) oxides precipitated from Fe(II) oxidation and strong U(VI) adsorption to iron oxides are two mechanisms potentially responsible for the decreased rate of U remobilization. Overall, this study demonstrated that the U remobilization rate may be controlled by manipulating biogeochemical conditions

Zhong, L.; Liu, C.; Szecsody, J. E.; Zachara, J. M.

2004-05-01

330

Two decades and counting: 24-years of sustained open ocean biogeochemical measurements in the Sargasso Sea  

NASA Astrophysics Data System (ADS)

The Bermuda Atlantic Time-series Study (BATS) program has sampled the northwestern Sargasso Sea on a biweekly (January to April) to monthly basis since October 1988. The primary objective of the core BATS program continues to be an improved understanding of the time-variable processes and mechanisms that control the biogeochemical cycling of carbon and related elements in the surface ocean. With 24 years of measurements for most chemical, physical and biological variables, we have moved beyond descriptions of seasonal and interannual variability to examination of multi-year trends and potential controls, however there remain substantial gaps in our knowledge of the ecosystem mechanisms related to organic matter production, export and remineralization. While earlier BATS overviews have focused on describing seasonal and year-to-year variability, this overview provides new information on three long-standing biogeochemical questions in Sargasso Sea biogeochemistry. First, why is there a discrepancy between biological (i.e., sediment trap) and geochemical estimates of carbon export production? Winter storms and mesoscale eddies have now been clearly shown to contribute to annual nutrient budgets and carbon export production. Recent information on phytoplankton natural isotopic nitrogen composition, and data from profiling floats suggests that small phytoplankton are important contributors to new production in summer despite the apparent absence of a mechanism to entrain nitrate into the euphotic zone. These findings aid in closing the gap between these two different estimates of carbon export production. Second, what supports the seasonal drawdown of carbon dioxide in the absence of detectable nutrients? The zooplankton timeseries at BATS highlights the importance of zooplankton as a conduit for carbon removal due to grazing and vertical migration. Although increases in cellular elemental stoichiometry to values greater than the canonical Redfield Ratio, and the seasonal (and interannual) accumulation of euphotic zone dissolved organic carbon (DOC) without accumulation of DON in the surface ocean are also important explanations. Lastly, what are the sources of the elevated nitrate to phosphate ratio in the seasonal thermocline (N:P>30 on average)? While generally accepted that nitrogen fixation is the source of the additional nitrogen, new research suggests that export and remineralization of non-diazotroph particulate matter enriched in nitrogen (alternatively viewed as depleted in phosphorus) may also make substantial contributions. In addition, the ratio of particulate nitrogen to phosphorus captured in sediment traps has decreased from 50-75 to <50, possibly due to enhanced nitrogen remineralization. These and other findings from the core BATS observational program contribute to our improved understanding of biogeochemical cycles and ecosystem mechanisms in the subtropical North Atlantic Ocean and how they are changing over time.

Lomas, M. W.; Bates, N. R.; Johnson, R. J.; Knap, A. H.; Steinberg, D. K.; Carlson, C. A.

2013-09-01

331

Oceanic biogeochemical characteristic maps identified with holistic use of satellite, model and data  

NASA Astrophysics Data System (ADS)

Ocean province level plankton community exhibit heterogeneity across Arctic, Nordic, Atlantic Gyre and Southern Ocean provinces. GreenSeas research is an international FP7 consortium that includes Arctic, Atlantic and Southern Ocean based research teams who are analysing the planktonic ecosystem. We are looking at how the planktonic ecosystem responds to environmental and climate change. Using Earth Observation monitoring data we report new results on identifying generic plankton characteristics observable at a province level, and also touch on spatial and temporal trends that are evident using a holistic analysis framework. Using advanced statistical methods this framework compares and combines Earth Observation information together with an in-situ Oceanic plankton Analytical Database and up to 40 year ocean general circulation biogeochemical model (OGCBM) time series of the equivalent plankton and sea-state measures of this system. Specifically, we outline the use of the GreenSeas Analytical Database, which is a harmonised set of Oceanic in-situ plankton and sea-state measures covering different cruises and time periods. The Analytical Database information ranges from plankton community,primary production, nutrient cycling to physical sea state temperature and salinity measures. The combined analysis utilises current, 10 year+ Earth Observations of ocean colour and sea surface temperature metrics and interprets these together with biogeochemical model outputs from PELAGOS, ERSEM & NORWECOM model runs to help identify planktonic based biomes. Generic planktonic characteristic maps that are equivalently observable in both the Earth Observations and numerical models are reported on. Both ocean surface and sub-surface signals are analysed together with relevant Analytical Database biome extracts. We present the current results of this inter-comparison & discuss challenges of identifying the province level plankton dominance with the satellite, model and data. In particular we discuss the strategic importance of systematically analysing the knowledge present in the existing key long term Oceanic observation platforms through such holistic analysis frameworks. These maps help to enhance and improve current biogeochemical models, our understanding of the plankton community structure and predictions used for future assessment of climate change.

Bruun, John; Allen, Icarus; Vichi, Marcello; Somerfield, Paul; Samuelsen, Annette; Racault, Marie-Fanny; Waldron, Howard; Monteiro, Pedro; McKiver, William; Bellerby, Richard; Thomalla, Sandy; Lygre, Kjetil; Moiseev, Denis; Johannessen, Johnny; Brewin, Robert; Butenschön, Momme; Jeansson, Emil; Vines, Aleksander; Heard, Jessica

2014-05-01

332

Role of sea ice in global biogeochemical cycles: emerging views and challenges  

NASA Astrophysics Data System (ADS)

Observations from the last decade suggest an important role of sea ice in the global biogeochemical cycles, promoted by (i) active biological and chemical processes within the sea ice; (ii) fluid and gas exchanges at the sea ice interface through an often permeable sea ice cover; and (iii) tight physical, biological and chemical interactions between the sea ice, the ocean and the atmosphere. Photosynthetic micro-organisms in sea ice thrive in liquid brine inclusions encased in a pure ice matrix, where they find suitable light and nutrient levels. They extend the production season, provide a winter and early spring food source, and contribute to organic carbon export to depth. Under-ice and ice edge phytoplankton blooms occur when ice retreats, favoured by increasing light, stratification, and by the release of material into the water column. In particular, the release of iron - highly concentrated in sea ice - could have large effects in the iron-limited Southern Ocean. The export of inorganic carbon transport by brine sinking below the mixed layer, calcium carbonate precipitation in sea ice, as well as active ice-atmosphere carbon dioxide (CO2) fluxes, could play a central role in the marine carbon cycle. Sea ice processes could also significantly contribute to the sulphur cycle through the large production by ice algae of dimethylsulfoniopropionate (DMSP), the precursor of sulphate aerosols, which as cloud condensation nuclei have a potential cooling effect on the planet. Finally, the sea ice zone supports significant ocean-atmosphere methane (CH4) fluxes, while saline ice surfaces activate springtime atmospheric bromine chemistry, setting ground for tropospheric ozone depletion events observed near both poles. All these mechanisms are generally known, but neither precisely understood nor quantified at large scales. As polar regions are rapidly changing, understanding the large-scale polar marine biogeochemical processes and their future evolution is of high priority. Earth system models should in this context prove essential, but they currently represent sea ice as biologically and chemically inert. Palaeoclimatic proxies are also relevant, in particular the sea ice proxies, inferring past sea ice conditions from glacial and marine sediment core records and providing analogues for future changes. Being highly constrained by marine biogeochemistry, sea ice proxies would not only contribute to but also benefit from a better understanding of polar marine biogeochemical cycles.

Vancoppenolle, Martin; Meiners, Klaus M.; Michel, Christine; Bopp, Laurent; Brabant, Frédéric; Carnat, Gauthier; Delille, Bruno; Lannuzel, Delphine; Madec, Gurvan; Moreau, Sébastien; Tison, Jean-Louis; van der Merwe, Pier

2013-11-01

333

Biogeochemical Modeling of In Situ U(VI) Reduction and Immobilization with Emulsified Vegetable Oil as the Electron Donor at a Field Site in Oak Ridge, Tennessee  

NASA Astrophysics Data System (ADS)

A comprehensive biogeochemical model was developed to quantitatively describe the coupled hydrologic, geochemical and microbiological processes that occurred following injection of emulsified vegetable oil (EVO) as the electron donor to immobilize U(VI) at the Oak Ridge Integrated Field Research Challenge site (ORIFRC) in Tennessee. The model couples the degradation of EVO, production and oxidation of long-chain fatty acids (LCFA), glycerol, hydrogen and acetate, reduction of nitrate, manganese, ferrous iron, sulfate and uranium, and methanoganesis with growth of multiple microbial groups. The model describes the evolution of geochemistry and microbial populations not only in the aqueous phase as typically observed, but also in the mineral phase and therefore enables us to evaluate the applicability of rates from the literature for field scale assessment, estimate the retention and degradation rates of EVO and LCFA, and assess the influence of the coupled processes on fate and transport of U(VI). Our results suggested that syntrophic bacteria or metal reducers might catalyze LCFA oxidation in the downstream locations when sulfate was consumed, and competition between methanogens and others for electron donors and slow growth of methanogen might contribute to the sustained reducing condition. Among the large amount of hydrologic, geochemical and microbiological parameter values, the initial biomass, and the interactions (e.g., inhibition) of the microbial functional groups, and the rate and extent of Mn and Fe oxide reduction appear as the major sources of uncertainty. Our model provides a platform to conduct numerical experiments to study these interactions, and could be useful for further iterative experimental and modeling investigations into the bioreductive immobiliztion of radionuclide and metal contaminants in the subsurface.

Tang, G.; Parker, J.; Wu, W.; Schadt, C. W.; Watson, D. B.; Brooks, S. C.; Orifrc Team

2011-12-01

334

Anthropogenic influences on the input and biogeochemical cycling of nutrients and mercury in Great Salt Lake, Utah, USA  

Microsoft Academic Search

Despite the ecological and economic importance of Great Salt Lake (GSL), little is known about the input and biogeochemical cycling of nutrients and trace elements in the lake. In response to increasing public concern regarding anthropogenic inputs to the GSL ecosystem, the US Geological Survey (USGS) and US Fish and Wildlife Service (USFWS) initiated coordinated studies to quantify and evaluate

David Naftz; Cory Angeroth; Terry Kenney; Bruce Waddell; Nathan Darnall; Steven Silva; Clay Perschon; John Whitehead

2008-01-01

335

Plants growing in abandoned mines of Portugal are useful for biogeochemical exploration of arsenic, antimony, tungsten and mine reclamation  

Microsoft Academic Search

Several plants across taxonomic hierarchy have evolved heavy metal tolerance strategies and detoxification mechanisms that enable them to survive, grow and reproduce in metal contaminated and polluted sites. Plants growing on the abandoned Portuguese mines, highly contaminated with arsenic (As), antimony (Sb) and tungsten (W), have been studied for their biogeochemical prospecting and mine stabilization potential. The results of soil

J. Pratas; M. N. V. Prasad; H. Freitas; L. Conde

2005-01-01

336

Physical and biogeochemical properties in landfast sea ice (Barrow, Alaska): Insights on brine and gas dynamics across seasons  

NASA Astrophysics Data System (ADS)

The impacts of the seasonal evolution of sea-ice physical properties on ice-ocean biogeochemical exchanges were investigated in landfast ice at Barrow (Alaska) from January through June 2009. Three stages of brine dynamics across the annual cycle have been identified based on brine salinity, brine volume fraction, and porous medium Rayleigh number (Ra). These are sea-ice bottom-layer convection, full-depth convection, and brine stratification. We further discuss the impact of brine dynamics on biogeochemical compounds in sea ice: stable isotopes of water (?D, ?18O), nutrients (NO3-, PO43-, NH4+), microalgae (chlorophyll-a), and inert gas (argon). In general, full-depth convection events favor exchanges between sea ice and seawater, while brine stratification limits these exchanges. However, argon responds differently to brine dynamics than the other biogeochemical compounds analyzed in this study. This contrast is attributed to the impact of bubble nucleation on inert gas transport compared to the other biogeochemical compounds. We present a scenario for argon bubble formation and evolution in sea ice and suggest that a brine volume fraction approaching 7.5-10% is required for inert gas bubbles to escape from sea ice to the atmosphere.

Zhou, Jiayun; Delille, Bruno; Eicken, Hajo; Vancoppenolle, Martin; Brabant, FréDéRic; Carnat, Gauthier; Geilfus, Nicolas-Xavier; Papakyriakou, Tim; Heinesch, Bernard; Tison, Jean-Louis

2013-06-01

337

U.S. Department of Energy (DOE)Surface Biogeochemical Research (SBR) 6th Annual PI Meeting: Abstracts  

Microsoft Academic Search

On behalf of the Subsurface Biogeochemical Research (SBR) program managers in the Climate and Environmental Sciences Division (CESD), Office of Biological and Environmental Research (BER), welcome to the 2011 SBR Principal Investigators meeting. Thank you in advance for your attendance and your presentations at this year's meeting. As the events in Japan continue to unfold, we are all reminded that

Hazen Ed

2011-01-01

338

ELSEVIER Journal of Hydrology 199 (1997) 88-120 Linking the hydrologic and biogeochemical controls of nitrogen  

E-print Network

and biogeochemical controls of nitrogen transport in near-stream zones of temperate-forested catchments: a review towpaths and the biogeochemicai environment controlling Nitrogen cycling and transport in near critical for elucidating controls of N transport and transformation. We review published studies concerning

McDonnell, Jeffrey J.

339

The Influence of Hurricanes and Other Biogeochemical Factors on Net Mercury Methylation and Mercury Cycling in the Gulf of Mexico  

Microsoft Academic Search

Methylation of mercury (Hg) in coastal region sediments is a potentially important source of methylmercury (MeHg) to ocean food webs. Sediment Hg studies in the coastal zone have focused mostly on biogeochemical relationships but have not studied in detail the impact of extreme events, such as hurricanes, on Hg dynamics. As a result of two funded studies, samples were collected

R. Mason; M. Bank; T. Hollweg; B. Liu; N. Rabalais; L. Schaider; D. Senn; J. Shine; P. Swarzenski

2007-01-01

340

Biogeochemical evolution of a sulfur-iron rich aquatic system in a reflooded wetland environment (Lake Agmon, northern Israel)  

Microsoft Academic Search

Major biogeochemical processes in the newly created, shallow Lake Agmon (Hula Valley, northern Israel) were investigated from 1994 to 1996. Sediment cores, lake water and porewater were analyzed for chemical composition and spatial distribution. Sediment analyses revealed that Lake Agmon has two different sediment types: peat sediments in the northern and central parts, and marls in the southern part. The

D. Markel; E. Sass; B. Lazar; A. Bein

1998-01-01

341

FeCycle: Attempting an iron biogeochemical budget from a mesoscale SF6 tracer experiment in unperturbed low iron waters  

E-print Network

FeCycle: Attempting an iron biogeochemical budget from a mesoscale SF6 tracer experiment in unperturbed low iron waters P. W. Boyd,1 C. S. Law,2 D. A. Hutchins,3 E. R. Abraham,2 P. L. Croot,4 M. Ellwood December 2005. [1] An improved knowledge of iron biogeochemistry is needed to better understand key

Wilhelm, Steven W.

342

BIOGEOCHEMICAL CONTROLS ON REACTION OF SEDIMENTARY ORGANIC MATTER AND AQUEOUS SULFIDES IN HOLOCENE SEDIMENTS OF MUD LAKE FLORIDA: JOURNAL ARTICLE  

EPA Science Inventory

JOURNAL NRMRL-ADA-00133 Filley,T.R., Freeman, K.H., Wilkin*, R.T., and Hatcher, P.G. Biogeochemical Controls on Reaction of Sedimentary Organic Matter and Aqueous Sulfides in Holocene Sediments of Mud Lake Florida. Geochimica et Cosmochimica Acta 66 (6):937-954...

343

Influence of the human perturbation on carbon, nitrogen, and oxygen biogeochemical cycles in the global coastal ocean  

Microsoft Academic Search

The responses to human perturbations of the biogeochemical cycles of carbon (C), nitrogen (N), and oxygen (O) in the global coastal ocean were evaluated using a process-based model. In this model, the global coastal ocean is represented by two distinct zones: the proximal zone which includes large bays, the open water part of estuaries, deltas, inland seas, and salt marshes;

Christophe Rabouille; Fred T. Mackenzie; Leah May Ver

2001-01-01

344

A biogeochemical model for phosphorus and nitrogen cycling in the Eastern Mediterranean Sea. Part 1. Model development, initialization and sensitivity  

NASA Astrophysics Data System (ADS)

The Eastern Mediterranean Sea (EMS) is the largest marine basin whose annual primary productivity is limited by phosphorus (P) rather than nitrogen (N). The basin is nearly entirely land-locked and receives substantial external nutrient fluxes, comparable for instance to those of the Baltic Sea. The biological productivity of the EMS, however, is among the lowest observed in the oceans. The water column exhibits very low P and N concentrations with N:P ratios in excess of the Redfield value. These unique biogeochemical features are analyzed using a mass balance model of the coupled P and N cycles in the EMS. The present paper describes the conceptual basis, quantitative implementation and sensitivity of the model. The model is initialized for the year 1950, that is, prior to the large increase in anthropogenic nutrient loading experienced by the EMS during the second half of the 20th century. In the companion paper, the model is used to simulate the P and N cycles during the period 1950-2000. The 1950 model set-up and sensitivity analyses support the following conclusions. Inorganic molar N:P ratios in excess of the 16:1 Redfield value observed in the water column reflect higher-than-Redfield N:P ratios of the external inputs, combined with negligible denitrification. Model simulations imply that the denitrification flux would have to increase by at least a factor of 14, relative to the 1950 flux, in order for the inorganic N:P ratio of the deep waters to approach the Redfield value. The higher-than-Redfield N:P ratios of dissolved and particulate organic matter in the EMS further imply the preferential regeneration of P relative to N during organic matter decomposition.

Van Cappellen, P.; Powley, H. R.; Emeis, K.-C.; Krom, M. D.

2014-11-01

345

FORWARD AND INVERSE BIO-GEOCHEMICAL MODELING OF MICROBIALLY INDUCED PRECIPITATION IN 0.5M COLUMNAR EXPERIMENTS  

NASA Astrophysics Data System (ADS)

Subsurface contamination by metals and radionuclides threatens water supplies and ecosystem health at sites worldwide. One potential solution is immobilization in calcite where mineral precipitation is induced in situ by microbially-mediated ureolysis. Specifically, immobile aerobic biophases (cells or enzymes) mediate the conversion of urea to ammonium and carbonate, raising pH and promoting calcite precipitation. Divalent species such as strontium (including 90Sr, a common radionuclide contaminant) can co-precipitate, resulting in in situ immobilization. In waters that are saturated with respect to calcite, this represents a long-term sequestration mechanism. Calcite precipitation also enables control of mechanical properties of the medium through the cementation of particles thus increasing the shear strength and stiffness, while decreasing the permeability and compressibility. Challenges in application include design of the injectate aqueous chemistry (e.g., calcium, carbonate, urea, pH buffer, microbial nutrients) and selection of injection rates in order to control the timing and rate of calcite precipitation to generate the desired spatial distribution. Modeling ultimately requires incorporation of comprehensive reaction networks into transport simulators for non-uniform flow. To develop and validate the reaction network for use in both contaminant co-precipitation and subsurface structural modification applications, multicomponent biogeochemical modeling (TOUGHREACT v2) was applied in analyses of laboratory batch and column investigations of microbially-mediated calcite precipitation using Sporosarcina pasteurii. Column experiments included continuous and repeat pulse-flows, with cumulative flux equal in both cases. Aqueous chemistry and calcite distribution were monitored, as well as seismic shear waves that correlate to the stiffness of the column and thus to precipitation extent. TOUGHREACT was coupled with the inversion code UCODE to invert on observed pH and calcite abundance data to determine the effective urease concentrations and calcite precipitation rate (through the reactive calcite surface area). Simulations included both constant and spatially distributed urease concentrations to account for non-uniform distributions of bacteria in the column experiments. For the inversion of the model with constant distribution of urease, regression was initiated at several initial parameter values to test the uniqueness of the solution by searching the error surface for local minima. The calibrated model with distributed urease values shows a good agreement with the experimental calcite precipitation data, and will be used to predict the results of future pilot- and field-scale experiments with push-pull well configurations.

Barkouki, T. H.; Martinez, B.; Mortensen, B.; Dejong, J.; Weathers, T. S.; Spycher, N.; Ginn, T. R.; Fujita, Y.; Smith, R. W.

2009-12-01

346

Biogeochemical cycles of Chernobyl-born radionuclides in the contaminated forest ecosystems: long-term dynamics of the migration processes  

NASA Astrophysics Data System (ADS)

Biogeochemical migration is a dominant factor of the radionuclide transport through the biosphere. In the early XX century, V.I. Vernadskii, a Russian scientist known, noted about a special role living things play in transport and accumulation of natural radionuclide in various environments. The role of biogeochemical processes in migration and redistribution of technogenic radionuclides is not less important. In Russia, V. M. Klechkovskii and N.V. Timofeev-Ressovskii showed some important biogeochemical aspects of radionuclide migration by the example of global fallout and Kyshtym accident. Their followers, R.M. Alexakhin, M.A. Naryshkin, N.V. Kulikov, F.A. Tikhomirov, E.B. Tyuryukanova, and others also contributed a lot to biogeochemistry of radionuclides. In the post-Chernobyl period, this area of knowledge received a lot of data that allowed building the radioactive element balance and flux estimation in various biogeochemical cycles [Shcheglov et al., 1999]. Regrettably, many of recent radioecological studies are only focused on specific radionuclide fluxes or pursue some applied tasks, missing the holistic approach. Most of the studies consider biogeochemical fluxes of radioactive isotopes in terms of either dose estimation or radionuclide migration rates in various food chains. However, to get a comprehensive picture and develop a reliable forecast of environmental, ecological, and social consequences of radioactive pollution in a vast contaminated area, it is necessary to investigate all the radionuclide fluxes associated with the biogeochemical cycles in affected ecosystems. We believe such an integrated approach would be useful to study long-term environmental consequences of the Fukushima accident as well. In our long-term research, we tried to characterize the flux dynamics of the Chernobyl-born radionuclides in the contaminated forest ecosystems and landscapes as a part of the integrated biogeochemical process. Our field studies were started in June of 1986 (less than two months after the accident) and have been continued up to now, focused on the most common forest ecosystems scattered over the contaminated areas of Russian Federation and Ukraine. A comprehensive analysis of the 137Cs and 90Sr biogeochemical fluxes shows that downward radionuclide fluxes (those directed from tree crowns to the soil) dominated over the upward fluxes (from the soil to forest vegetation) in the first years after the accident. Currently, the biological cycle in the contaminated ecosystems is a main factor impeding further vertical migration of long-lived radionuclides from upper soil layers to the ground water. The role of biota as a retardation factor depends on landscape type as well. In accumulative landscapes (with positive material balance), biota plays leading role in radionuclide retardation, while in eluvial landscapes (with the negative balance) soil absorbing complex serves as the dominant barrier for radionuclides leaching down the soil profile. The manifestation of both soil- and biota-driven factors depends on the radionuclide chemical speciation in the initial fallout. The latter factor is most important for 137Cs, yet less manifested for 90Sr. Among the biota components, fungi and forest vegetation are of particular importance for 137Cs and 90Sr accumulation, respectively. In summary, biogeochemical cycles of 137Cs and 90Sr in the investigated forest ecosystems serve as main factors impeding the radionuclide migration from the fallout to ground water. Larger-scale landscape factors determine the radionuclide flux intensity in the biogeochemical cycles and affect the radionuclide spatial variability in the contaminated biota components.

Shcheglov, Alexey; Tsvetnova, Ol'ga; Klyashtorin, Alexey

2013-04-01

347

Biogeochemical evidence for subsurface hydrocarbon occurrence, Recluse oil field, Wyoming; preliminary results  

USGS Publications Warehouse

Anomalously high manganese-to-iron ratios occurring in pine needles and sage leaves over the Recluse oil field, Wyoming, suggest effects of petroleum microseepage on the plants. This conclusion is supported by iron and manganese concentrations in soils and carbon and oxygen isotope ratios in rock samples. Seeping hydrocarbons provided reducing conditions sufficient to enable divalent iron and manganese to be organically complexed or adsorbed on solids in the soils. These bound or adsorped elements in the divalent state are essential to plants, and the plants readily assimilate them. The magnitude of the plant anomalies, combined with the supportive isotopic and chemical evidence confirming petroleum leakage, makes a strong case for the use of plants as a biogeochemical prospecting tool.

Dalziel, Mary C.; Donovan, Terrence J.

1980-01-01

348

(Man-made radionuclides as tracers for biogeochemical and limnological processes)  

SciTech Connect

C.R. Olsen attended the 23rd SIL Congress and was asked to chair a session on man-made radionuclides as tracers for biogeochemical and limnological processes at the next Congress in Munich in 1989. The traveler presented his results on the use of radionuclides to quantify contaminant sorption kinetics and water-column removal rates at the IASW Symposium. Numerous discussions with several European scientists provided valuable information concerning the environmental fate of radionuclides released during the recent accident at Chernobyl. The traveler developed contacts with Swedish scientists involved in quantifying the effects of sediment resuspension on nutrient cycles. At the University of Melbourne, scientists have developed a new nuclear technique for reconstructing paleotemperatures and aiding in oil exploration.

Olsen, C.R.

1987-03-09

349

Biogeochemical Cycles of Carbon and Sulfur on Early Earth (and on Mars?)  

NASA Technical Reports Server (NTRS)

The physical and chemical interactions between the atmosphere, hydrosphere, geosphere and biosphere can be examined for elements such as carbon (C) and sulfur (S) that have played central roles for both life and the environment. The compounds of C are highly important, not only as organic matter, but also as atmospheric greenhouse gases, pH buffers in seawater, oxidation-reduction buffers virtually everywhere, and key magmatic constituents affecting plutonism and volcanism. S assumes important roles as an oxidation-reduction partner with C and Fe in biological systems, as a key constituent in magmas and volcanic gases, and as a major influence upon pH in certain environments. These multiple roles of C and S interact across a network of elemental reservoirs interconnected by physical, chemical and biological processes. These networks are termed biogeochemical C and S cycles.

DesMarais, D. J.

2004-01-01

350

Introduction to Indian Ocean biogeochemical processes and ecological variability: Current understanding and emerging perspectives  

NASA Astrophysics Data System (ADS)

Despite a history of exploration dating back to the classical era and its leading role as a pathway for trade and cultural exchange for the great civilizations of those times, the Indian Ocean has consistently been subject to less attention in the modern era in terms of oceanographic enquiry. The cornerstone of the Sustained Indian Ocean Biogeochemical and Ecosystem Research (SIBER) initiative has been to promote more frequent and persistent research activities that encompass the entire Indian Ocean basin and to facilitate international cooperation to realize these objectives. This volume's chapters are derived from the plenary talks given by the attendees of the first SIBER conference and are a blend of current knowledge reviews and new results. Thus this collection of papers represents an interdisciplinary contribution to the Indian Ocean literature by the leading members of the Indian Ocean research community.

Wiggert, Jerry D.; Hood, Raleigh R.; Naqvi, S. Wajih A.; Brink, Kenneth H.; Smith, Sharon L.

351

Synchrotron X-ray fluorescent analysis application in biogeochemical investigations in Yakutia  

NASA Astrophysics Data System (ADS)

Large possibilities of synchrotron X-ray fluorescent analysis (SR-XRFA), along with the simple preparation of biological samples, allowed us to carry out valuable biogeochemical investigations in Yakutia during the years 2002-2008. New data on the accumulation of macroelements K, Ca, Fe, Mn, biophilic microelements Cu, Zn, Mo, chalcophilous Ni, Pb, Ag, As, Sb, rare lithophilous Rb, Sr, Zr, Y, Nb, scattered chalcophilous Ga, Ge, Se, Cd, Te, Tl in the tissues of larch (Larix cajanderi Mayr.), mosses and lichens (Cladina genus, Dicranum genus, Hylocomium) were obtained. A connection between the elemental composition of larch tissues and the composition of bed rocks was revealed; a comparison with the elemental composition of mosses and lichens was carried out.

Artamonova, S. Yu.; Kolmogorov, Yu. P.

2009-05-01

352

Winter measurements of oceanic biogeochemical parameters in the Rockall Trough (2009-2012)  

NASA Astrophysics Data System (ADS)

This paper describes the sampling and analysis of biogeochemical parameters collected in the Rockall Trough in January/February of 2009, 2010, 2011 and 2012. Sampling was carried out along two transects, one southern and one northern transect each year. Samples for dissolved inorganic carbon (DIC) and total alkalinity (TA) were taken alongside salinity, dissolved oxygen and dissolved inorganic nutrients (total-oxidized nitrogen, nitrite, phosphate and silicate) to describe the chemical signatures of the various water masses in the region. These were taken at regular intervals through the water column. The data are available on the CDIAC database, http://cdiac.ornl.gov/ftp/oceans/Rockall_Trough/.

McGrath, T.; Kivimäe, C.; McGovern, E.; Cave, R. R.; Joyce, E.

2013-12-01

353

Ocean viruses and their effects on microbial communities and biogeochemical cycles  

PubMed Central

Viruses are the most abundant life forms on Earth, with an estimated 1031 total viruses globally. The majority of these viruses infect microbes, whether bacteria, archaea or microeukaryotes. Given the importance of microbes in driving global biogeochemical cycles, it would seem, based on numerical abundances alone, that viruses also play an important role in the global cycling of carbon and nutrients. However, the importance of viruses in controlling host populations and ecosystem functions, such as the regeneration, storage and export of carbon and other nutrients, remains unresolved. Here, we report on advances in the study of ecological effects of viruses of microbes. In doing so, we focus on an area of increasing importance: the role that ocean viruses play in shaping microbial population sizes as well as in regenerating carbon and other nutrients. PMID:22991582

Wilhelm, Steven W.

2012-01-01

354

Modeling the physical and biogeochemical response of a marine shelf system to a tropical cyclone  

NASA Astrophysics Data System (ADS)

We describe the first use of a fully integrated biogeochemical model to explore the response of a marine shelf system to a tropical cyclone. Ocean currents, nutrients, sediments and plankton dynamics were simulated under conditions representative of Tropical Cyclone Bobby, which traversed the Australian North West Shelf in February 1995. Results show strong upwelling of nutrients and a phytoplankton bloom. While chlorophyll changes were similar to those estimated from satellite data in other coastal systems exposed to cyclonic conditions, the overall phytoplankton response was limited by cyclone induced sediment resuspension and the net contribution to annual primary production on the shelf was relatively small. In contrast, sediment loads exported off the shelf during Bobby were found to be more than 50 times modeled annual loads in years with little cyclone exposure and equivalent to at least 20 years of annual river-loads to the North West Shelf.

Condie, S. A.; Herzfeld, M.; Margvelashvili, N.; Andrewartha, J. R.

2009-11-01

355

Holocene climate dynamics, biogeochemical cycles and ecosystem variability in the eastern Mediterranean Sea  

NASA Astrophysics Data System (ADS)

The past variability of biogeochemical processes and marine ecosystems of the eastern Mediterranean Sea (EMS) is documented in the form of organic-rich sapropels that occurred at northern hemisphere insolation maxima. In order to understand the processes leading from deglacial and Holocene climate variability to the formation of sapropel S1 via changed biogeochemical cycling in the EMS, we integrated results from global and regional Earth system model experiments with biogeochemical and micropaleontological proxy records. Our results suggest a high spatiotemporal variability of deep-water oxygenation and biogeochemical processes at the sea floor during the late glacial and early Holocene. Changes in trophic conditions of bathyal ecosystems along ocean margins are closely linked to the hydrology of the EMS borderlands; they reflect orbital and sub-orbital climate variations of the high northern latitudes and the African monsoon system. Local trophic conditions were particularly variable in the northern Aegean Sea as a response to changes in riverine runoff and Black Sea outflow. During the time of S1 deposition, average oxygen levels decreased exponentially with increasing water depth, suggesting a basin-wide shallowing of vertical convection superimposed by local signals. In the northernmost Aegean Sea, deep-water ventilation persisted during the early period of S1 formation, owing to temperature-driven local convection and the absence of low-salinity Black Sea outflow. At the same time, severe temporary dysoxia or even short anoxia occurred in the eastern Levantine basin at water depths as shallow as 900 m. This area was likely influenced by enhanced nutrient input of the Nile river that resulted in high organic matter fluxes and related high oxygen-consumption rates in the water column. In contrast, abyssal ecosystems of the Levantine and Ionian basins lack eutrophication during the early Holocene suggesting that enhanced productivity did not play a crucial role in basin-wide S1 formation. Instead, sapropel formation can be attributed to a long-term persistence of water column stratification. The modeled and observed trends of oxygen consumption rates and deep-water residence times date the initiation of stagnating deep-waters at the start of the deglacial period, thus several millennia prior to S1 deposition. Once oxygen levels fell below a critical threshold, bathyal and abyssal benthic ecosystems collapsed almost synchronously with onset of S1 deposition suggesting a rapid vertical propagation of the oxygen minimum layer. The recovery of bathyal deep-sea benthic ecosystems during the terminal phase of S1 formation is controlled by subsequently deeper convection and re-ventilation over a period of approximately 1500 years; the ultra-oligotrophic abyssal ecosystems reveal a considerably lower recovery potential. After the re-ventilation of the various sub-basins had been completed during the middle and late Holocene, deep-water renewal was more or less similar to recent rates. During that time, deep-sea ecosystem variability was driven by short-term changes in food quantity and quality as well as in seasonality, all of which are linked to millennial-scale changes in riverine runoff and associated nutrient input.

Schmiedl, Gerhard; Adloff, Fanny; Emeis, Kay; Grimm, Rosina; Maier-Reimer, Ernst; Mikolajewicz, Uwe; Möbius, Jürgen; Müller-Navarra, Katharina

2013-04-01

356

Interactive effects of solar UV radiation and climate change on biogeochemical cycling.  

PubMed

This report assesses research on the interactions of UV radiation (280-400 nm) and global climate change with global biogeochemical cycles at the Earth's surface. The effects of UV-B (280-315 nm), which are dependent on the stratospheric ozone layer, on biogeochemical cycles are often linked to concurrent exposure to UV-A radiation (315-400 nm), which is influenced by global climate change. These interactions involving UV radiation (the combination of UV-B and UV-A) are central to the prediction and evaluation of future Earth environmental conditions. There is increasing evidence that elevated UV-B radiation has significant effects on the terrestrial biosphere with implications for the cycling of carbon, nitrogen and other elements. The cycling of carbon and inorganic nutrients such as nitrogen can be affected by UV-B-mediated changes in communities of soil organisms, probably due to the effects of UV-B radiation on plant root exudation and/or the chemistry of dead plant material falling to the soil. In arid environments direct photodegradation can play a major role in the decay of plant litter, and UV-B radiation is responsible for a significant part of this photodegradation. UV-B radiation strongly influences aquatic carbon, nitrogen, sulfur and metals cycling that affect a wide range of life processes. UV-B radiation changes the biological availability of dissolved organic matter to microorganisms, and accelerates its transformation into dissolved inorganic carbon and nitrogen, including carbon dioxide and ammonium. The coloured part of dissolved organic matter (CDOM) controls the penetration of UV radiation into water bodies, but CDOM is also photodegraded by solar UV radiation. Changes in CDOM influence the penetration of UV radiation into water bodies with major consequences for aquatic biogeochemical processes. Changes in aquatic primary productivity and decomposition due to climate-related changes in circulation and nutrient supply occur concurrently with exposure to increased UV-B radiation, and have synergistic effects on the penetration of light into aquatic ecosystems. Future changes in climate will enhance stratification of lakes and the ocean, which will intensify photodegradation of CDOM by UV radiation. The resultant increase in the transparency of water bodies may increase UV-B effects on aquatic biogeochemistry in the surface layer. Changing solar UV radiation and climate also interact to influence exchanges of trace gases, such as halocarbons (e.g., methyl bromide) which influence ozone depletion, and sulfur gases (e.g., dimethylsulfide) that oxidize to produce sulfate aerosols that cool the marine atmosphere. UV radiation affects the biological availability of iron, copper and other trace metals in aquatic environments thus potentially affecting metal toxicity and the growth of phytoplankton and other microorganisms that are involved in carbon and nitrogen cycling. Future changes in ecosystem distribution due to alterations in the physical and chemical climate interact with ozone-modulated changes in UV-B radiation. These interactions between the effects of climate change and UV-B radiation on biogeochemical cycles in terrestrial and aquatic systems may partially offset the beneficial effects of an ozone recovery. PMID:17344963

Zepp, R G; Erickson, D J; Paul, N D; Sulzberger, B

2007-03-01

357

Sedimentary Biogeochemical Indicators for Assessing the Impacts of the Deepwater Horizon Blowout on Coastal Wetlands  

NASA Astrophysics Data System (ADS)

The impact of the Deepwater Horizon blowout on coastal wetlands can be understood through investigating carbon loading and microbial activity in salt marsh sediments. Carbon influx causes porewater sulfide to increase in wetland sediment, making it toxic and inhospitable to marsh vegetation. High sulfide levels due to increased microbial activity can lead to plant browning and mortality. Preliminary analyses at Marsh Point, MS indicated that sulfate reducing bacteria are more active in contaminated grass, producing sulfide concentrations 100x higher than in non-contaminated grass. Sediment electrode profiles, hydrocarbon contamination, and microbial community profiles were measured at three additional locations to capture the spatial sedimentary geochemical processes impacting salt marsh dieback. Findings indicate that response to contamination is variable due to physical and biogeochemical processes specific to each marsh. Temporal evaluation indicates that there is a lag in maximum response to contamination due to seasonal effects on microbial activity.

McNeal, K. S.; Guthrie, C. L.; Mishra, D.

2013-05-01

358

Biogeochemical and Physical Controls of Atmosphere-Ocean Ozone Fluxes During five Research Cruises  

NASA Astrophysics Data System (ADS)

A recently developed ship-based eddy covariance ozone flux system was deployed for investigating biogeochemical and physical controls of ozone surface fluxes over the open ocean. The relationship between ozone fluxes and chlorophyll were studied during the GOMECC 2007 cruise when large gradients in chlorophyll concentrations were observed along the cruise track in both the Gulf of Mexico and Northern Atlantic. The motivation for this study can be broken into two sections: a) evaluate the agreement between in- situ and satellite derived chlorophyll concentrations and b) establish if either method can represent the chlorophyll concentration at the surface where the reaction with ozone occurs. The two observation methods show good agreement in chlorophyll features but differ in the magnitude of observed concentrations The agreement between the two data sets and the postulated dependency of the oceanic ozone flux on chlorophyll levels opens up new opportunities for utilizing satellite-derived oceanic chlorophyll fields for description of the large scale oceanic ozone uptake.

Boylan, P.; Helmig, D.; Lang, E. K.; Bariteau, L.; Fairall, C. W.; Ganzeveld, L.; Hare, J. E.; Hueber, J.; Pallandt, M.

2012-03-01

359

Biogeochemical Cycling and Environmental Stability of Pu Relevant to Long-Term Stewardship of DOE Sites  

SciTech Connect

The overall objective of this proposed research is to understand the biogeochemical cycling of Pu in environments of interest to long-term DOE stewardship issues. Central to Pu cycling (transport initiation to immobilization) is the role of microorganisms. The hypothesis underlying this proposal is that microbial activity is the causative agent in initiating the mobilization of Pu in near-surface environments: through the transformation of Pu associated with solid phases, production of extracellular polymeric substances (EPS) carrier phases, and the creation of microenvironments. Also, microbial processes are central to the immobilization of Pu species, through the metabolism of organically complexed Pu species and Pu associated with extracellular carrier phases and the creation of environments favorable for Pu transport retardation.

Honeyman, Bruce D.

2006-06-01

360

Biogeochemical Cycling and Environmental Stability of Pu Relevant to Long-Term Stewardship of DOE Sites  

SciTech Connect

The overall objective of this proposed research is to understand the biogeochemical cycling of Pu in environments of interest to long-term DOE stewardship issues. Central to Pu cycling (transport initiation to immobilization) is the role of microorganisms. The hypothesis underlying this proposal is that microbial activity is the causative agent in initiating the mobilization of Pu in near-surface environments: through the transformation of Pu associated with solid phases, production of extracellular polymeric substances (EPS) carrier phases, and the creation of microenvironments. Also, microbial processes are central to the immobilization of Pu species, through the metabolism of organically complexed Pu species and Pu associated with extracellular carrier phases and the creation of environments favorable for Pu transport retardation.

Francis, Arokiasamy J.; Santschi, Peter H.; Honeyman, Bruce D.

2005-06-01

361

Biogeochemical Cycling and Environmental Stability of Pu Relevant to Long-Term Stewardship of DOE Sites  

SciTech Connect

The overall objective of this research is to understand the biogeochemical cycling of Pu in environments of interest to long-term DOE stewardship issues. Central to Pu cycling (transport initiation and immobilization) is the role of microorganisms. The hypothesis underlying this work is that microbial activity is the causative agent in initiating the mobilization of Pu in near-surface environments: through the transformation of Pu associated with solid phases, production of extracellular polymeric substances (EPS) carrier phases and the creation of microenvironments. Also, microbial processes are central to the immobilization of Pu species, through the metabolism of organically complexed Pu species and Pu associated with extracellular carrier phases and the creation of environments favorable for Pu transport retardation.

Honeyman, Bruce D.; Francis, A.J.; Gillow, Jeffrey B.; Dodge, Cleveland J.; Santschi, Peter H.; Chin-Chang Hung; Diaz, Angelique; Tinnacher, Ruth; Roberts, Kimberly; Schwehr, Kathy

2006-04-05

362

Biogeochemical cyclic activity of bacterial arsB in arsenic-contaminated mines.  

PubMed

Biogeochemical cyclic activity of the ars (arsenic resistance system) operon is arsB influx/efflux encoded by the ecological of Pseudomonas putida. This suggests that studying arsenite-oxidizing bacteria may lead to a better understanding of molecular geomicrobiology, which can be applied to the bioremediation of arsenic-contaminated mines. This is the first report in which multiple arsB-binding mechanisms have been used on indigenous bacteria. In ArsB (strains OS-5; ABB83931; OS-19; ABB04282 and RW-28; ABB88574), there are ten putative enzyme, Histidine (His) 131, His 133, His 137, Arginine (Arg) 135, Arg 137, Arg 161, Trptohan (Trp) 142, Trp 164, Trp 166, and Trp 171, which are each located in different regions of the partial sequence. The adenosine triphosphate (ATP)-binding cassette transports, binding affinities and associating ratable constants show that As-binding is comparatively insensitive to the location of the residues within the moderately stable alpha-helical structure. The alpha-helical structures in ArsB-permease and anion permease arsB have been shown to import/export arsenic in P. putida. We proposed that arsB residues, His 131, His 133, His 137, Arg 135, Arg 137, Arg 161, Trp 142, Trp 164, Trp 166, and Trp 171 are required for arsenic binding and activation of arsA/arsB or arsAB. This arsB influx/efflux pum-ping is important, and the effect in arsenic species change and mobility in mine soil has got a significantly ecological role because it allows arsenic oxidizing/reducing bacteria to control biogeochemical cycle of abandoned mines. PMID:19202875

Chang, Jin-Soo; Ren, Xianghao; Kim, Kyoung-Woong

2008-01-01

363

Biogeochemical Changes Associated With Conversion of Grazed Pastures to Plantation Forests in New Zealand  

NASA Astrophysics Data System (ADS)

Since the 1930s, large areas of marginally productive pasture and/or scrubland have been converted to plantation forests dominated by Pinus radiata. In the 1990s, up to 100,000 hectares of new plantings occurred each year, many into land used previously for pasture. Current plantation forest area is about 1.7 million hectares. This land-use change impacts many biogeochemical and hydrological processes, and plays an important role in several current environmental issues. Conversion of pasture to plantation forests increases evapotranspiration, and can reduce streamflow and regional water availability. However, afforestation also stabilizes pasture soils that would be highly erodible when covered with pasture vegetation. Soil temperatures are also lower in plantation forests than in pasture, influencing carbon and nitrogen cycling rates. Because of differences in plant litter quality and distribution of carbon inputs to the soil, afforestation often leads to a reduction in soil pH, lower soil carbon turnover rates, lower net N mineralization, lower total mineral soil N, and reduced numbers of soil invertebrates (particularly earthworms). At many sites, these changes can lead to a reduction in mineral soil C stocks, with the reduction sometimes greater than the C accumulated in the forest floor. High N availability associated with pastures can often lead to N leaching losses when tree seedlings are established and uptake of N by pasture grasses inhibited by e.g. herbicide application. We discuss the ability of ecosystem models to simulate these complex biogeochemical changes associated with afforestation, the potential importance of forest management on these changes, and the implications for key environmental issues such as the rate of carbon sequestration in Kyoto forests and decreased emissions of agricultural trace gases.

Scott, N. A.; Tate, K. R.; Ross, D. J.; Parfitt, R.; Parshotam, A.; Halliday, J.; McMurtrie, R.

2001-05-01

364

Saltwater intrusion into tidal freshwater marshes alters the biogeochemical processing of organic carbon  

NASA Astrophysics Data System (ADS)

Environmental perturbations in wetlands affect the integrated plant-microbial-soil system, causing biogeochemical responses that can manifest at local to global scales. The objective of this study was to determine how saltwater intrusion affects carbon mineralization and greenhouse gas production in coastal wetlands. Working with tidal freshwater marsh soils that had experienced roughly 3.5 yr of in situ saltwater additions, we quantified changes in soil properties, measured extracellular enzyme activity associated with organic matter breakdown, and determined potential rates of anaerobic carbon dioxide (CO2) and methane (CH4) production. Soils from the field plots treated with brackish water had lower carbon content and higher C : N ratios than soils from freshwater plots, indicating that saltwater intrusion reduced carbon availability and increased organic matter recalcitrance. This was reflected in reduced activities of enzymes associated with the hydrolysis of cellulose and the oxidation of lignin, leading to reduced rates of soil CO2 and CH4 production. The effects of long-term saltwater additions contrasted with the effects of short-term exposure to brackish water during three-day laboratory incubations, which increased rates of CO2 production but lowered rates of CH4 production. Collectively, our data suggest that the long-term effect of saltwater intrusion on soil CO2 production is indirect, mediated through the effects of elevated salinity on the quantity and quality of autochthonous organic matter inputs to the soil. In contrast, salinity, organic matter content, and enzyme activities directly influence CH4 production. Our analyses demonstrate that saltwater intrusion into tidal freshwater marshes affects the entire process of carbon mineralization, from the availability of organic carbon through its terminal metabolism to CO2 and/or CH4, and illustrate that long-term shifts in biogeochemical functioning are not necessarily consistent with short-term disturbance-type responses.

Neubauer, S. C.; Franklin, R. B.; Berrier, D. J.

2013-07-01

365

Saltwater intrusion into tidal freshwater marshes alters the biogeochemical processing of organic carbon  

NASA Astrophysics Data System (ADS)

Environmental perturbations in wetlands affect the integrated plant-microbial-soil system, causing biogeochemical responses that can manifest at local to global scales. The objective of this study was to determine how saltwater intrusion affects carbon mineralization and greenhouse gas production in coastal wetlands. Working with tidal freshwater marsh soils that had experienced ~ 3.5 yr of in situ saltwater additions, we quantified changes in soil properties, measured extracellular enzyme activity associated with organic matter breakdown, and determined potential rates of anaerobic carbon dioxide (CO2) and methane (CH4) production. Soils from the field plots treated with brackish water had lower carbon content and higher C : N ratios than soils from freshwater plots, indicating that saltwater intrusion reduced carbon availability and increased organic matter recalcitrance. This was reflected in reduced activities of enzymes associated with the hydrolysis of cellulose and the oxidation of lignin, leading to reduced rates of soil CO2 and CH4 production. The effects of long-term saltwater additions contrasted with the effects of short-term exposure to brackish water during three-day laboratory incubations, which increased rates of CO2 production but lowered rates of CH4 production. Collectively, our data suggest that the long-term effect of saltwater intrusion on soil CO2 production is indirect, mediated through the effects of elevated salinity on the quantity and quality of autochthonous organic matter inputs to the soil. In contrast, salinity, organic matter content, and enzyme activities directly influence CH4 production. Our analyses demonstrate that saltwater intrusion into tidal freshwater marshes affects the entire process of carbon mineralization, from the availability of organic carbon through its terminal metabolism to CO2 and/or CH4, and illustrate that long-term shifts in biogeochemical functioning are not necessarily consistent with short-term disturbance-type responses.

Neubauer, S. C.; Franklin, R. B.; Berrier, D. J.

2013-12-01

366

Interactive Effects of Urban Land Use and Climate Change on Biogeochemical Cycles (Invited)  

NASA Astrophysics Data System (ADS)

Urban land-use change can affect biogeochemical cycles through altered disturbance regimes, landscape management practices (e.g., irrigation and fertilization), built structures, and altered environments (heat island effect, pollution, introduction of non-native species, loss of native species). As a result, the conversion of native to urban ecological systems has been shown to significantly affect carbon, nitrogen, and water cycles at local, regional, and global scales. These changes have created novel habitats and ecosystems, which have no analogue in the history of life. Nonetheless, some of the environmental changes occurring in urban areas are analogous to the changes expected in climate by the end of the century, e.g. atmospheric increase in CO2 and an increase in air temperatures, which can be utilized as a “natural experiment” to investigate global change effects on large scale ecosystem processes. Moreover, as analogues of expected future environments, urban ecological systems may act as reservoirs of plant and animal species for adjoining landscapes that are expected to undergo relatively rapid climate changes in the next 100 years. Urban land-use change by itself may contribute to changes in regional weather patterns and long-term changes in global climate, which will depend on the net effect of converting native systems to urban systems and the comparison of per capita “footprints” between urban, suburban, and rural inhabitants. My objectives are to 1) assess the impact of changes in urban land-use on climate change and in turn how climate change may affect urban biogeochemical cycles and 2) discuss the potential for urban ecosystems to mitigate green house gas emissions.

Pouyat, R. V.

2009-12-01

367

Tracing biogeochemical and microbial variability over a complete oil sand mining and recultivation process.  

PubMed

Recultivation of disturbed oil sand mining areas is an issue of increasing importance. Nevertheless only little is known about the fate of organic matter, cell abundances and microbial community structures during oil sand processing, tailings management and initial soil development on reclamation sites. Thus the focus of this work is on biogeochemical changes of mined oil sands through the entire process chain until its use as substratum for newly developing soils on reclamation sites. Therefore, oil sand, mature fine tailings (MFTs) from tailings ponds and drying cells and tailings sand covered with peat-mineral mix (PMM) as part of land reclamation were analyzed. The sample set was selected to address the question whether changes in the above-mentioned biogeochemical parameters can be related to oil sand processing or biological processes and how these changes influence microbial activities and soil development. GC-MS analyses of oil-derived biomarkers reveal that these compounds remain unaffected by oil sand processing and biological activity. In contrast, changes in polycyclic aromatic hydrocarbon (PAH) abundance and pattern can be observed along the process chain. Especially naphthalenes, phenanthrenes and chrysenes are altered or absent on reclamation sites. Furthermore, root-bearing horizons on reclamation sites exhibit cell abundances at least ten times higher (10(8) to 10(9) cells g(-1)) than in oil sand and MFT samples (10(7) cells g(-1)) and show a higher diversity in their microbial community structure. Nitrate in the pore water and roots derived from the PMM seem to be the most important stimulants for microbial growth. The combined data show that the observed compositional changes are mostly related to biological activity and the addition of exogenous organic components (PMM), whereas oil extraction, tailings dewatering and compaction do not have significant influences on the evaluated compounds. Microbial community composition remains relatively stable through the entire process chain. PMID:25201817

Noah, Mareike; Lappé, Michael; Schneider, Beate; Vieth-Hillebrand, Andrea; Wilkes, Heinz; Kallmeyer, Jens

2014-11-15

368

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

USGS Publications Warehouse

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

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

2004-01-01

369

Sedimentological, biogeochemical and mineralogical facies of Northern and Central Western Adriatic Sea  

NASA Astrophysics Data System (ADS)

The aim of this work was to identify sedimentary facies, i.e. facies having similar biogeochemical, mineralogical and sedimentological properties, in present and recent fine sediments of the Northern and Central Adriatic Sea with their spatial and temporal variations. Further aims were to identify the transportation, dispersion and sedimentation processes and provenance areas of sediments belonging to the facies. A Q-mode factor analysis of mineralogical, granulometric, geochemical (major and trace elements) and biochemical (organic carbon and total nitrogen) properties of surficial and sub-surficial sediments sampled in the PRISMA 1 Project has been used to identify the sedimentary facies. On the whole, four facies were identified: 1) Padanic Facies, made up of fine siliciclastic sediments which reach the Adriatic Sea mainly from the Po River and are distributed by the Adriatic hydrodynamic in a parallel belt off the Italian coast. Southward, this facies gradually mixes with sediments from the Apennine rivers and with biogenic autochthonous particulate; 2) Dolomitic Facies, made up of dolomitic sediments coming from the eastern Alps. This facies is predominant north of the Po River outfalls and it mixes with Padanic Facies sediments in front of the Po River delta; 3) Mn-carbonate Facies, made up of very fine sediments, rich in coccolithophores and secondary Mn-oxy-hydroxides resulting from the reworking of surficial fine sediments in shallow areas and subsequent deposition in deeper areas; 4) Residual Facies, made up of coarse siliciclastic sediments and heavy m