Sabine Sauvage

PhD
French National Centre for Sci... · Functional Ecology and Environment lab, ECOLAB, University of Toulouse, France

Publications

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    ABSTRACT: The MAELIA project develops an agent-based modeling and simulation platform to study the environmental, economic and social impacts of various regulations regarding water use and water management in combination with climate change. An integrated modelling approach has been used to model the investigated social-ecological system. MAELIA combines spatiotemporal models of ecologic (e.g. water flow and plant growth) and human decision-making processes (e.g. cropping plan), socio-economic dynamics (e.g. land cover changes). Due to the diversity and the interweaving of the processes considered, the calibration and evaluation of such a multi-agent platform is a scientific challenge. Indeed, many parameters can reveal to be influential on the model outputs, with a high level of interactions between parameters impacts. In order to get an overview of the model behaviour and to screen influential parameters, multiple sensitivity analyses were performed, while considering some sub-sets of processes or not. This step-by-step sensitivity analyses enabled to disentangle the different influences and interactions, and was a preliminary step to the calibration process. In our case, the calibration, which is a multi-objective (e.g. reproducing water flows and anthropic dynamics, traduced by different numerical criteria such as joint use of L2-norm with variance-covariance matrix and indices of squared errors on water crisis temporality) optimization problem, was achieved thanks to metamodels built on an appropriated design of experiments.
    7th Intl. Congress on Env. Modelling and Software, San Diego, CA, USA,; 06/2014
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    ABSTRACT: society/index.php/iemss-2014-proceedings Abstract: Sustainable water resource management is typical of environmental management problems emerging from complex social-ecological systems. It deeply depends upon water user strategies, land use management and water governance systems. MAELIA, a "policy issue" modelling platform, allows performing integrated assessment at watershed level of a wide range of scenarios regarding water and land use management strategies in combination with global changes. It has been developed through a strong analysis of different French water management situations and an inductive modelling process. It allows representing dynamic interactions between human activities (farming practices), ecological processes (hydrology and crop growth), and governance systems (water regulations and releases from dams) at fine spatiotemporal resolutions in order to handle actual problems of water managers and issues of the main water users (farmers). MAELIA includes original farmer, dam manager and state services (software) agents.
    IEMSS 2014; 06/2014
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    ABSTRACT: 1. This model of stream epilithic biofilm biomass dynamics is based on the system of equations from Uehlinger et al. (1996) and the term for autogenic detachment of biofilm from Boulêtreau et al. (2006). Its new features are: (1) a mathematical term based on estimated feeding activity of biofilm-dwelling invertebrates, (2) local hydrodynamics considered as the principal factor governing algal traits and biofilm structure, and (3) a variable parameterisation that was adjusted to biofilm biomass conditions. 2. Biofilm biomass was monitored over a one-year period in the Garonne river in France (September 2008–2009). An allometric approach was used to estimate the feeding activity of biofilm-dwelling invertebrates based on their energetic requirements. Diatom functional diversity was also monitored to find how it varied with overall biofilm growth patterns. The one-year biofilm monitoring period was divided into six biofilm biomass cycles, with each cycle consisting of a phase of biofilm growth as the main process, followed by detachment. 3. This model reproduced the observed data as a complex of biofilm growth/detachment cycles using different sets of empirical parameters which allowed: (1) the dominant processes involved in each biofilm cycle to be evaluated, and (2) the six cycles of biofilm growth/detachment observed during the study period to be reproduced. This accounted for the observed patterns more effectively than a parameterisation using a single set of empirical parameters. 4. High flow had a severe effect on biofilm dynamics through chronic and catastrophic detachment. Presumably as a result, assemblages of diatoms shifted towards species that were firmly attached and protected by mucilage. 5. During low flow (and when temperature was high), biofilm dynamics was mainly affected by autogenic detachment and grazer activity. The grazing pressure of the dominant biofilm-dwelling invertebrates (Nematoda and larvae of Chironomidae and Trichoptera) was fairly low (a maximum of 6% of biofilm biomass ingested daily); nevertheless their presence in the biofilm seemed to favour biofilm autogenic detachment.
    Freshwater Biology 06/2014; in press. · 3.93 Impact Factor
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    ABSTRACT: Direct numerical simulations of a turbulent boundary layer flow over a bed of hemispheres of height h are performed using an immersed boundary method for comparison with river biofilm growth experiments performed in a hydraulic flume. Flow statistics above the substrates are shown to be in agreement with measurements performed by laser Doppler velocimetry and particle image velocimetry in the experiments. Numerical simulations give access to flow components inside the roughness sublayer, and biofilm colonization patterns found in the experiments are shown to be associated with low shear stress regions on the hemisphere surface. Two bed configurations, namely staggered and aligned configurations, lead to different colonization patterns because of differences in the local flow topology. Dependence with the Reynolds number of the biofilm distribution and accrual 7 days after inoculum is shown to be associated to local flow topology change and shear stress intensity. In particular, the shear stress τ on the surface of the hemispheres is found to scale as , where Ret = u∗h/ν, with u* as the log law friction velocity and ν as the fluid kinematic viscosity. This scaling is due to the development of boundary layers along the hemisphere surface. Associated with a critical shear stress for colonization and early growth, it explains the increasing delay in biomass accrual for increasing flow velocities in the experiments. Copyright © 2014 John Wiley & Sons, Ltd.
    River Research and Applications 03/2014; · 2.43 Impact Factor
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    ABSTRACT: The study area (Alegria watershed, Basque Country, Northern Spain) considered here is influenced by an important alluvial aquifer that plays a significant role in nitrate pollution from agricultural land use and management practices. Nitrates are transported primarily from the soil to the river through the alluvial aquifer. The agricultural activity covers 75% of the watershed and is located in a nitrate-vulnerable zone. The main objective of the study was to find land management options for water pollution abatement by using model systems. In a first step, the SWAT model was applied to simulate discharge and nitrate load in stream flow at the outlet of the catchment for the period between October 2009 and June 2011. The LOADEST program was used to estimate the daily nitrate load from measured nitrate concentration. We achieved satisfactory simulation results for discharge and nitrate loads at monthly and daily time steps. The results revealed clear variations in the seasons: higher nitrate loads were achieved for winter (20,000 kg mo −1 NO 3 –N), and lower nitrate loads were simulated for the summer (<1000 kg mo -1 NO 3 –N) period. In a second step, the calibrated model was used to evaluate the long-term effects of best management practices (BMPs) for a 50-yr period by maintaining actual agricultural practices, reducing fertilizer application by 20%, splitting applications (same total N but applied over the growing period), and reducing 20% of the applied fertilizer amount and splitting the fertilizer doses. The BMPs were evaluated on the basis of local experience and farmer interaction. Results showed that reducing fertilizer amounts by 20% could lead to a reduction of 50% of the number of days exceeding the nitrate concentration limit value (50 mg L -1) set by the European Water Framework Directive. I n regions with intense agricultural management, sur-face and groundwater are subjected to contamination by inputs of fertilizers and pesticides. Nitrate leaching from agricultural land is a common problem in many European countries with intensive agricultural production (Rode et al., 2008; Volk et al., 2009). Hence, regulations such as the European Water Framework Directive (WFD) aim to achieve a good ecological status for water bodies. The first challenging deadline for achieving the environ-mental objectives of the WFD is 2015. The WFD requires a focus on river basins and surface water bodies as reference units as well as the use of reliable modeling tools to evaluate the contribution of nitrogen sources to water pollution, to quantify loads, and to evaluate alternative water management policies, all of which pose significant new challenges to water managers, planning authorities, researchers, and stakeholders (Dørge and Windolf, 2003; Wasson et al., 2003; Rekolainen et al., 2003; Volk et al., 2008). This study focuses on the Alegria watershed (Basque Country, Spain), which is a flat lowland area with low hydraulic gradients and a high groundwater table. Such catchments are especially vulnerable to groundwater pollution (Lam et al., 2010; Schmalz et al., 2007; Muller et al., 2004). In such lowland watersheds, groundwater transport plays a key role in the transport of pollutants from the soils into the water system (Wriedt and Rode, 2006). The hydrological processes of the Alegria watershed are dominated by an important alluvial aquifer. The water quality of the aquifer is strongly impaired by farming activities in the watershed (García-Linares et al., 2003; Sánchez-Pérez et al., 2003b; Martinez, 2011). From the beginning of the 1980s to the early 1990s, nitrate concentration increased dramatically up to 200 mg L -1 in the East Sector of the aquifer (Arrate et al., 1997; Sánchez-Pérez et al., 2003b). These values significantly exceed the limit value for nitrates (50 mg L −1 NO 3) as set the Nitrate Directive of the European Commission (91/676/CEE), which forms part of a comprehensive framework of EU legislation to protect the environment. Due to this situation, Abbreviations: BMP, best management practice; NVZ, nitrate-vulnerable zone; WFD, Water Framework Directive.
    Journal of Environmental Quality 01/2014; 43:67-74. · 2.35 Impact Factor
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    ABSTRACT: High nitrate concentrations in streams have become a widespread problem throughout Europe in recent decades, damaging surface water and groundwater quality. The European Nitrate Directive fixed a potability threshold of 50 mg L−1 for European rivers. The performance of the Soil and Water Assessment Tool model was assessed in the 1110-km2 Save catchment in southwestern France for predicting water discharge and nitrate loads and concentrations at the catchment outlet, considering observed data set uncertainty. Simulated values were compared with intensive and extensive measurement data sets. Daily discharge fitted observations (Nash- Sutcliffe efficiency coefficient = 0.61, R2 = 0.7, and PBIAS = -22%). Nitrate simulation (1998–2010) was within the observed range (PBIAS = 10–21%, considering observed data set uncertainty). Annual nitrate load at the catchment outlet was correlated to the annual water yield at the outlet (R2 = 0.63). Simulated annual catchment nitrate exportation ranged from 21 to 49 kg ha−1 depending on annual hydrological conditions (average, 36 kg ha-1). Exportation rates ranged from 3 to 8% of nitrogen inputs. During floods, 34% of the nitrate load was exported, which represented 18% of the 1998–2010 period. Average daily nitrate concentration at the outlet was 29 mg L-1 (1998–2010), ranging from 0 to 270 mg L−1. Nitrate concentration exceeded the European 50 mg L−1 potability threshold during 244 d between 1998 and 2010. A 20% reduction of nitrogen input reduced crop yield by between 5 and 9% and reduced by 62% the days when the 50 mg L−1 threshold was exceeded.
    Journal of Environmental Quality 01/2014; 43(1):46-54. · 2.35 Impact Factor
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    ABSTRACT: In agricultural watersheds, pesticide contamination in surface water mostly occurs during stormflow events. When modelling pesticide fate for risks assessment, the application timing input is one of the main uncertainty sources among all the parameters involved in the river network contaminations process. We therefore aimed to assess the sensitivity of the river network pesticide concentration patterns to application timing shifts within a plausible range of application dates, considering two pre-emergence herbicides (metolachlor and aclonifen) characterised by two different octanol/water partition coefficients (Kow). The Soil and Water Assessment Tool (SWAT) was applied in the 1110 km2 agricultural watershed of the river Save (south-western France), where wheat, maize, sorghum and sunflower are intensively grown. The pesticide application date was changed within a one-month interval and the pesticide concentration at catchment outlet was simulated from March to June 2010. Total metolachlor concentration prediction could be improved by an application timing shift to 3 days later (Daily R2 = 0.22 and PBIAS = − 57%). By testing the behaviour of the two molecules, it was shown that sorption processes were influencing the control of application timing on the transfer to surface water:metolachlor concentration in the channel depended on both discharge and delay between application date and first stormflow event whereas the transfer of aclonifen depended on rainfall intensity for exportation with suspended sediments through surface runoff. At last, the study discusses the potential implications of the sensitivity in terms of regional agricultural management practice design.
    CATENA. 01/2014; 119:97–103.
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    ABSTRACT: Pesticides applied on crops are leached with rainfall to groundwater and surface water. They threat the aquatic environment and may render water unfit for human consumption. Pesticide partitioning is one of the pesticide fate processes in the environment that should be properly formalised in pesticide fate models. Based on the analysis of 7 pesticide molecules (alachlor, atrazine, atrazine's transformation product deethylatrazine or DEA, isoproturon, tebuconazole and trifluralin) sampled from July 2009 to October 2010 at the outlet of the river Save (south-western France), the objectives of this study were (1) to check which of the environmental factors (discharge, pH, concentrations of total suspended matter (TSM), dissolved organic carbon (DOC) and particulate organic carbon (POC) could control the pesticide sorption dynamic, and (2) to establish a relationship between environmental factors, the partition coefficient Kd and the octanol/water distribution coefficient Kow. The comparison of physico-chemical parameters values during low flow and high flow shows that discharge, TSM and POC are the factors most likely controlling the pesticide sorption processes in the Save river network, especially for lower values of TSM (below 13mgL(-1)). We therefore express Kd depending on the widely literature-related variable Kow and on the commonly simulated variable TSM concentration. The equation can be implemented in any model describing the fluvial transport and fate of pesticides in both dissolved and sorbed phases, thus, Kd becomes a variable in time and space. The Kd calculation method can be applied to a wide range of catchments and organic contaminants.
    Chemosphere 01/2014; 99C:134-142. · 3.14 Impact Factor
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    ABSTRACT: Pesticides used for crop protection are leached with rainfall events to groundwater and surface water. The bioavailable dissolved fraction threatens the fluvial ecosystems. Pesticide partitioning in the environment is therefore one of the key pesticide fate processes that should be properly formalized for risk assessment. In modelling approaches, the partition coefficient Kd is usually estimated from different empirical models based on laboratory batch studies, such as Karickhoff equation. We first showed that the partition parameter in SWAT was more sensitive in the river network than in the soil. Therefore we sought a new relationship for Kd in rivers, relating Kd to the octanol/water distribution coefficient Kow and to the Total Suspended Matter (TSM) concentration. This relationship was obtained from in-stream measurements of TSM and of Particulate Organic Carbon (POC) sampled from 2007 to 2010 at the outlet of the 1110 km² Save catchment. We also calculated the Kd values of 7 pesticide molecules for both high flow and low flow periods (2009- 2010). We sought a relationship between TSM and the percentage of POC in TSM. We related the organic carbon normalized partition coefficient Koc to Kow. We showed a bias of 0.5 between instream observed Koc average values and Koc values calculated with Karickhoff’s equation. Thus, we expressed Kd depending on the widely literature-related variable Kow and on the commonly observed and simulated TSM concentration: Kd became a variable in time and space depending on simulated TSM concentration. The novel equation can be implemented in the SWAT model.
    2013 International SWAT Conference, Toulouse, France; 07/2013
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    ABSTRACT: Interactions between epilithic biofilm and local hydrodynamics were investigated in an experimental flume. Epilithic biofilm from a natural river was grown over a 41-day period in three sections with different flow velocities (0.10, 0.25 and 0.40 m s-1 noted LV, IV and HV respectively). Friction velocities u* and boundary layer parameters were inferred from PIV measurement in the three sections and related to the biofilm structure. The results show that there were no significant differences in Dry Mass and Ash-Free Dry Mass (g m-2) at the end of experiment, but velocity is a selective factor in algal composition and the biofilms' morphology differed according to differences in water velocity. A hierarchical agglomerative cluster analysis (Bray-Curtis distances) and an Indicator Species Analysis (IndVal) showed that the indicator taxa were Fragilaria capucina var. mesolepta in the low-velocity (u*. = 0.010-0.012 m s-1), Navicula atomus, Navicula capitatoradiata and Nitzschia frustulum in the intermediate-velocity (u*. = 0.023-0.030 m s-1) and Amphora pediculus, Cymbella proxima, Fragilaria capucina var. vaucheriae and Surirella angusta in the high-velocity (u*. = 0.033-0.050 m s-1) sections. A sloughing test was performed on 40-day-old biofilms in order to study the resistance of epilithic biofilms to higher hydrodynamic regimes. The results showed an inverse relationship between the proportion of detached biomass and the average value of friction velocity during growth. Therefore, water velocity during epilithic biofilm growth conditioned the structure and algal composition of biofilm, as well as its response (ability to resist) to higher shear stresses. This result should be considered in modelling epilithic biofilm dynamics in streams subject to a variable hydrodynamics regime.
    Water Research 01/2013; · 4.66 Impact Factor
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    ABSTRACT: Periphyton communities, which are native to river beds, serve as a functional indicator of river health but remain one of the least-studied communities despite the significant increase in the examination of aquatic microbial communities in recent years. In this study, we tested the relevance of three formulations of the chronic detachment term in a simple model for the biomass dynamics of periphyton. Numerical simulations of the periphyton biomass dynamics were performed by using three different descriptors for the flow conditions: the discharge Q, the friction velocity u∗, and the roughness Reynolds number k = u∗ks/ν (where ν is water kinetic viscosity and ks is the Nikuradse equivalent sand roughness). Comparisons of numerical simulation results with experimental data from literature revealed chronic detachment to be better simulated by taking the roughness Reynolds number as the external variable of detachment. These results support the idea that transport phenomena that occur in the near-bed layer, e.g. chronic detachment of periphyton matter or vertical transport of nutrients and pollutants in submerged aquatic canopies, are not related to a single turbulence descriptor such as the friction velocity u∗. Its description requires at least two descriptors, here the friction velocity u∗ and the Nikuradse equivalent sand roughness ks, which depend on the initial form and dimensions of the colonized substratum, and its changes owing to the thickness, resistance, and composition of the epilithic matter.
    Desalination and Water Treatment - DESALIN WATER TREAT. 01/2012; 41:79-87.
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    ABSTRACT: Fifty years after the hyporheic zone was first defined (Orghidan, 1959), there are still gaps in the knowledge regarding the role of biodiversity in hyporheic processes. First, some methodological questions remained unanswered regarding the interactions between biodiversity and physical processes, both for the study of habitat characteristics and interactions at different scales. Furthermore, many questions remain to be addressed to help inform our understanding of invertebrate community dynamics, especially regarding the trophic niches of organisms, the functional groups present within sediment, and their temporal changes. Understanding microbial community dynamics would require investigations about their relationship with the physical characteristics of the sediment, their diversity, their relationship with metabolic pathways, their inter-actions with invertebrates, and their response to environmental stress. Another fundamental research question is that of the importance of the hyporheic zone in the global metabolism of the river, which must be explored in relation to organic matter recycling, the effects of disturbances, and the degradation of contaminants. Finally, the application of this knowledge requires the development of methods for the estimation of hydro-logical exchanges, especially for the management of sediment clogging, the optimization of self-purification, and the integration of climate change in environmental policies. The development of descriptors of hyporheic zone health and of new metrology is also crucial to include specific targets in water policies for the long-term management of the system and a clear evaluation of restoration strategies.
    Annales de Limnologie - International Journal of Limnology 01/2012; 48:253-266. · 0.74 Impact Factor
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    ABSTRACT: Rising pesticide levels in streams draining intensively managed agricultural land have a detrimental effect on aquatic ecosystems and render water unfit for human consumption. The Soil and Water Assessment Tool (SWAT) was applied to simulate daily pesticide transfer at the outlet from an agriculturally intensive catchment of 1110 km(2) (Save river, south-western France). SWAT reliably simulated both dissolved and sorbed metolachlor and trifluralin loads and concentrations at the catchment outlet from 1998 to 2009. On average, 17 kg of metolachlor and 1 kg of trifluralin were exported at outlet each year, with annual rainfall variations considered. Surface runoff was identified as the preferred pathway for pesticide transfer, related to the good correlation between suspended sediment exportation and pesticide, in both soluble and sorbed phases. Pesticide exportation rates at catchment outlet were less than 0.1% of the applied amount. At outlet, SWAT hindcasted that (i) 61% of metolachlor and 52% of trifluralin were exported during high flows and (ii) metolachlor and trifluralin concentrations exceeded European drinking water standards of 0.1 μg L(-1) for individual pesticides during 149 (3.6%) and 17 (0.4%) days of the 1998-2009 period respectively. SWAT was shown to be a promising tool for assessing large catchment river network pesticide contamination in the event of floods but further useful developments of pesticide transfers and partition coefficient processes would need to be investigated.
    Journal of hazardous materials 09/2011; 196:210-9. · 4.14 Impact Factor
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    ABSTRACT: The SWAT model was tested at a daily time step to assess the fate of pesticides of a wide range of solubility. SWAT was applied on an 1100km² intensive agricultural catchment (Save river, southwestern France). Simulated pesticide concentrations were compared to data collected at the catchment outlet from July 2009 to June 2010, with weekly measurements during low flow and daily or sub-daily measurements during flood events. SWAT was able to accurately reproduce measured pesticides concentrations during base flow and flood events, especially concentrations of pesticide in the soluble phase. During the simulation period, simulated preferred pathway for pesticide transport from land area to stream network was surface runoff. Flood events were responsible for most pesticide transfer. The SWAT model hindcasted daily pesticide concentrations back to 1998 and possible water quality policy thresholds exceeding depending on climate.
    2011 International SWAT Conference, Toledo, Splain; 05/2011
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    ABSTRACT: The main objective of this study was to measure the impact of benthic invertebrate diversity on river sediment processes. We quantified the effects of interactions between three taxa (asellids, chironomid larvae, and tubificid worms). The impacts of different taxa richness treatments were measured on sediment reworking, O2 concentrations, bacterial abundances, and numbers of active bacteria in slow filtration sand–gravel columns. The coefficients of sediment reworking measured in multitaxa treatments were lower than those predicted from one-taxon treatments. The interactions among invertebrates also significantly reduced O2 concentrations in sediments. These results were probably due to interactions between the different sediment structures produced by each taxon (tubes, macropores, and fecal pellets) that modified water flow and associated microbial activities in the interstitial habitat. The stimulation of aerobic microbial processes with two- and three-taxa treatments, whereas one-taxon treatments could increase or decrease O2 consumption in columns, indicates that interactions among invertebrates limited the variability of the system functioning. We suggest that, beyond a small number of detritivorous taxa, a threshold effect on bioturbation process and microbial activities was produced by animals in the experimental system. Finally, the interactions between taxa played a significant role in microbial processes in the system studied.
    Canadian Journal of Fisheries and Aquatic Sciences 04/2011; 61(10):1817-1831. · 2.32 Impact Factor
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    ABSTRACT: Water draining from a large agricultural catchment of 1 110 km2 in southwest France was sampled over an 18-month period to determine the temporal variability in suspended sediment (SS) and dissolved (DOC) and particulate organic carbon (POC) transport during flood events, with quantification of fluxes and controlling factors, and to analyze the relationships between discharge and SS, DOC and POC. A total of 15 flood events were analyzed, providing extensive data on SS, POC and DOC during floods. There was high variability in SS, POC and DOC transport during different seasonal floods, with SS varying by event from 513 to 41 750 t; POC from 12 to 748 t and DOC from 9 to 218 t. Overall, 76 and 62% of total fluxes of POC and DOC occurred within 22% of the study period. POC and DOC export from the Save catchment amounted to 3090 t and 1240 t, equivalent to 1·8 t km−2 y−1 and 0·7 t km−2 y−1, respectively. Statistical analyses showed that total precipitation, flood discharge and total water yield were the major factors controlling SS, POC and DOC transport from the catchment. The relationships between SS, POC and DOC and discharge over temporal flood events resulted in different hysteresis patterns, which were used to deduce dissolved and particulate origins. In both clockwise and anticlockwise hysteresis, POC mainly followed the same patterns as discharge and SS. The DOC-discharge relationship was mainly characterized by alternating clockwise and anticlockwise hysteresis due to dilution effects of water originating from different sources in the whole catchment. Copyright © 2011 John Wiley & Sons, Ltd.
    Hydrological Processes 02/2011; 25(15):2365 - 2378. · 2.50 Impact Factor
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    ABSTRACT: A combined modelling and field study approach was used to examine biogeochemical functioning of the hyporheic zone in two gravel bars in an N-rich fourth-order stream (River Hers, south-west France).Surface water and interstitial water were sampled monthly (August 1994–January 1995), the latter in a network of 29 piezometers in the first gravel bar and 17 in the second. In both gravel bars, the hyporheic zone was created only by advected channel water without any connection with groundwater. Longitudinal chemical profiles of Dissolved Organic Carbon (DOC), nitrate (NO3–N), ammonium (NH4–N) and Dissolved Oxygen (DO) were established for both gravel bars. Ambient and potential denitrification were measured in the laboratory during the same period using the acetylene inhibition technique. Factors limiting denitrification were also examined by testing the separate effects of nitrate or nitrate+carbon additions.A 1D reactive-transport model was used to simulate longitudinal transformation of nitrogen in the hyporheic zone, and to estimate the role of organic matter (DOC and POC) in the biogeochemical functioning of the hyporheic zone.Denitrification measurements with nitrate and nitrate+carbon additions both showed increased denitrification, suggesting that denitrification might not be C-limited at this site. Observations and model results showed the hyporheic zone to be a sink of DOC and nitrate, but DOC consumption appeared insufficient to explain nitrate depletion measured in the two gravel bars. Field data were better modelled when an additional DOC source from the POC fraction degraded by anaerobic respiration was included in the model.
    Physics and Chemistry of The Earth - PHYS CHEM EARTH. 01/2011; 36(12):599-611.
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    ABSTRACT: The Soil and Water Assessment Tool (SWAT, 2005) was used to simulate discharge and sediment transport at daily time steps within the intensively farmed Save catchment in south-west France (1110 km2). The SWAT model was applied to evaluate catchment hydrology and sediment and associated particulate organic carbon yield using historical flow and meteorological data for a 10-years (January 1999–March 2009). Daily data on sediment (27 months, January 2007–March 2009) and particular organic carbon (15 months, January 2008–March 2009) were used to calibrate the model. Data on management practices (crop rotation, planting date, fertiliser quantity and irrigation) were included in the model during the simulation period of 10 years.Simulated daily discharge, sediment and particulate carbon values matched the observed values satisfactorily. The model predicted that mean annual catchment precipitation for the total study period (726 mm) was partitioned into evapotranspiration (78.3%), percolation/groundwater recharge (14.1%) and abstraction losses (0.5%), yielding 7.1% surface runoff. Simulated mean total water yield for the whole simulation period amounted to 138 mm, comparable to the observed value of 136 mm. Simulated annual sediment yield ranged from 4.3 t km−2 y−1 to 110 t km−2 y−1 (annual mean of 48 t km−2 y−1). Annual yield of particulate organic carbon ranged from 0.1 t km−2 y−1 to 2.8 t km−2 y−1 (annual mean of 1.2 t km−2 y−1). Thus, the highest annual sediment and particulate carbon yield represented 25 times the minimum annual yield. However, the highest annual water yield represented five times the minimum (222 mm and 51 mm, respectively). An empirical correlation between annual water yield and annual sediment and organic carbon yield was developed for this agricultural catchment. Potential source areas of erosion were also identified with the model. The range of the annual contributing erosive zones varied spatially from 0.1 to 6 t ha−1 according to the slope and agricultural practices at the catchment scale.Research highlights► Annual sediment yield ranged from 4.3 t km2 y−1 to 110 t km2 y−1. ► Particulate organic carbon ranged from 0.1 t km2 y−1 to 2.8 t km2 y−1. ► Highest annual sediment yield represented 25 times the minimum annual yield. ► Highest annual particulate carbon yield represented 25 times the minimum one. ► Contributing erosive zones varied spatially from 0.1 to 6 t ha−1.
    Journal of Hydrology 01/2011; 401:145-153. · 2.96 Impact Factor

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