[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we discuss the importance of developing integrated assessment models to support the design and implementation of policies to address water quality problems associated with agricultural pollution. We describe a new modelling system, LUMI-NATE, which links land use decisions made at the field scale in the Upper Mississippi, Ohio and Tennessee Basins through both environmental and hydrological components to downstream water quality effects and hypoxia in the Gulf of Mexico. This modelling system can be used to analyse detailed policy scenarios identifying the costs of the pol-icies and their resulting benefits for improved local and regional water quality. We dem-onstrate the model's capabilities with a simple scenario where cover crops are incentivised with green payments over a large expanse of the watershed.
European Review of Agricultural Economics 06/2014; 41(3):431-459. · 1.85 Impact Factor
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] ABSTRACT: There is increasing concern about the ongoing reduction in water supplies in the tropical Andes due to climate change effects such as glacier/snow melting resulting from rising air temperatures. In addition, extreme events and population growth are already directly affecting life and water renewability in the country. A countrywide integrated national plan for improving basin-scale water management in Bolivia is needed to assure water availability for agriculture, industry, mining, and human consumption. This study aims to provide a modeling tool to assess Bolivia’s past, current, and future water availability and identify basins at risk of water deficits. The Soil Water Assessment Tool was used to simulate the monthly water balance from 1997 to 2008, as well as the water balance projected to 2050 for the entire country. It considers possible changes in air temperatures and precipitation proposed by 17 Global Circulation Models as well as carbon dioxide projections derived from the Special Report Emission Scenario. Overall, model results were close to satisfactory compared to observations, with some exceptions due to lack of information for expanding the timeline and improving calibration. Based on the calculation of three hydrologic indicators, the study identifies basins that would be the most susceptible to water deficits for a baseline from 1997 to 2008, and in the event of the projected climate change, to 2050.
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] ABSTRACT: Climate change is one of the most compelling modern issues and has important implications for almost every aspect of natural and human systems. The Soil and Water Assessment Tool (SWAT) model has been applied worldwide to support sustainable land and water management in a changing climate. However, the inadequacies of the existing carbon algorithm in SWAT limit its application in assessing impacts of human activities on CO2 emission, one important source of greenhouse gasses (GHGs) that traps heat in the earth system and results in global warming. In this research, we incorporate a revised version of the CENTURY carbon model into SWAT to describe dynamics of soil organic matter (SOM)-residue and simulate land-atmosphere carbon exchange. We test this new SWAT-C model with daily eddy covariance (EC) observations of net ecosystem exchange (NEE) and evapotranspiration (ET) and annual crop yield at six sites across the U.S. Midwest. Results show that SWAT-C simulates well multi-year average NEE and ET across the spatially distributed sites and capture the majority of temporal variation of these two variables at a daily time scale at each site. Our analyses also reveal that performance of SWAT-C is influenced by multiple factors, such as crop management practices (irrigated vs. rainfed), completeness and accuracy of input data, crop species, and initialization of state variables. Overall, the new SWAT-C demonstrates favorable performance for simulating land-atmosphere carbon exchange across agricultural sites with different soils, climate, and management practices. SWAT-C is expected to serve as a useful tool for including carbon flux into consideration in sustainable watershed management under a changing climate. We also note that extensive assessment of SWAT-C with field observations is required for further improving the model and understanding potential uncertainties of applying it across large regions with complex landscapes.
Science of The Total Environment 07/2013; 463-464C:810-822. · 3.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Highlights
► The effect of climate change on freshwater availability in Africa was analyzed. ► The ensembles of the future climate projections were fed into SWAT hydrologic model. ► In Africa as a whole, the mean total quantity of water resources is likely to increase. ► For individual subbasins and countries, variations were substantial. ► Prolonged droughts in dry regions, entails an additional challenge to food production.
Journal of Hydrology 02/2013; 480:85–101. · 2.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Lake Cocibolca watershed is a globally unique cradle of biodiversity with major importance not only to the global and local environment, but also to the 750,000 people living within its boundaries. Several fish species are endemic to the lake, and the watershed’s location within the Mesoamerican Biological Corridor has made it a meeting ground for fish, bird and mammal species from North and South America. Apart from its importance for fishing and recreation industries, the lake is beginning to be used as a source of water supply for some coastal towns; its role as a source of drinking water may grow in the future. Lake Cocibolca and its watershed are under pressure from multiple sources but, in the absence of reliable monitoring information, the extent of the environmental degradation is unclear. Environmental deterioration in the watershed is high on the government’s agenda. This study has assessed the sources and the magnitude of the pressures that threaten Lake Cocibolca. It was accomplished by applying a hydrological and land use model (SWAT) to the lake’s watershed and by conducting additional estimates of nutrients generated from wastewater sources and tilapia farming. The study has confirmed that sediment loads are very high, and has estimated their magnitude in each sub-watershed. The key results of the study are the estimation of sedimentation levels in the watershed and the identification of erosion hotspots. At about 13.3 tons/ha per year on average for the watershed, sediment yields are high and comparable to watersheds with well-documented sedimentation problems such as Lake Victoria, which is more than ten times the size of the Lake Cocibolca watershed but has similar elevations, rainfall patterns and deforestation problems. The load of sediments and nutrients can be greatly reduced through programs that combine such measures as reforestation in areas with the steepest slopes, the adoption of conservation tillage, and improved pasture management. The study also shows that climate change could significantly affect the water balance and severity of the sedimentation problem for the lake.
[Show abstract][Hide abstract] ABSTRACT: Riebschleager, K.J., R. Karthikeyan, R. Srinivasan, and K. McKee, 2012. Estimating Potential E. coli Sources in a Watershed Using Spatially Explicit Modeling Techniques. Journal of the American Water Resources Association (JAWRA) 48(4): 745-761. DOI: 10.1111/j.1752-1688.2012.00649.xAbstract: The Spatially Explicit Load Enrichment Calculation Tool (SELECT) was automated to characterize waste and the associated pathogens from various sources within a mixed land use watershed. Potential Escherichia coli loads in Lake Granbury watershed were estimated using spatially variable governing factors, such as land use, soil condition, and distance to streams. A new approach for characterizing E. coli loads resulting from malfunctioning on-site wastewater treatment systems (OWTSs) was incorporated into SELECT along with the Pollutant Connectivity Factor (PCF) module. The PCF component was applied to identify areas contributing E. coli loads during runoff events by incorporating the influence of potential E. coli loading, runoff potential, and travel distance to waterbodies. Simulation results indicated livestock and wildlife are potential E. coli contributing sources in the watershed. The areas in which these sources are potentially contributing are not currently monitored for E. coli. The bacterial water quality violations seen around Lake Granbury are most likely the result of malfunctioning OWTSs and pet wastes. SELECT results demonstrate the need to evaluate each contributing source separately to effectively allocate site specific best management practices (BMPs) utilizing stakeholder inputs. It also serves as a powerful screening tool for determining areas where detailed investigation is merited.
JAWRA Journal of the American Water Resources Association 08/2012; 48(4). · 1.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Large-scale hydrologic models are being used more and more in watershed management and decision making. Sometimes rapid modeling and analysis is needed to deal with emergency environmental disasters. However, time is often a major impediment in the calibration and application of these models. To overcome this, most projects are run with fewer simulations, resulting in less-than-optimum solutions. In recent years, running time-consuming projects on gridded networks or clouds in Linux systems has become more and more prevalent. But this technology, aside from being tedious to use, has not yet become fully available for common usage in research, teaching, and small to medium-size applications. In this paper we explain a methodology where a parallel processing scheme is constructed to work in the Windows platform. We have parallelized the calibration of the SWAT (Soil and Water Assessment Tool) hydrological model, where one could submit many simultaneous jobs taking advantage of the capabilities of modern PC and laptops. This offers a powerful alternative to the use of grid or cloud computing. Parallel processing is implemented in SWAT-CUP (SWAT Calibration and Uncertainty Procedures) using the optimization program SUFI2 (Sequential Uncertainty FItting ver. 2). We tested the program with large, medium, and small-size hydrologic models on several computer systems, including PCs, laptops, and servers with up to 24 CPUs. The performance was judged by calculating speedup, efficiency, and CPU usage. In each case, the parallelized version performed much faster than the non-parallelized version, resulting in substantial time saving in model calibration.
Environmental Modelling and Software 05/2012; 31:28–36. · 3.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: SWAT: Model Use, Calibration, and Validation SWAT: Model Use, Calibration, and Validation SWAT (Soil and Water Assessment Tool) is a comprehensive, semi-distributed river basin model that requires a large number of input parameters, which complicates model parameterization and calibration. Several calibration techniques have been developed for SWAT, including manual calibration procedures and automated procedures using the shuffled complex evolution method and other common methods. In addition, SWAT-CUP was recently developed and provides a decision-making framework that incorporates a semi-automated approach (SUFI2) using both manual and automated calibration and incorporating sensitivity and uncertainty analysis. In SWAT-CUP, users can manually adjust parameters and ranges iteratively between autocalibration runs. Parameter sensitivity analysis helps focus the calibration and uncertainty analysis and is used to provide statistics for goodness-of-fit. The user interaction or manual component of the SWAT-CUP calibration forces the user to obtain a better understanding of the overall hydrologic processes (e.g., baseflow ratios, ET, sediment sources and sinks, crop yields, and nutrient balances) and of parameter sensitivity. It is important for future calibration developments to spatially account for hydrologic processes; improve model run time efficiency; include the impact of uncertainty in the conceptual model, model parameters, and measured variables used in calibration; and assist users in checking for model errors. When calibrating a physically based model like SWAT, it is important to remember that all model input parameters must be kept within a realistic uncertainty range and that no automatic procedure can substitute for actual physical knowledge of the watershed.
[Show abstract][Hide abstract] ABSTRACT: One of the most important transboundary animal diseases (TADs) in the southern African region is foot-and-mouth disease (FMD). In this region, a pathway for spread of FMD virus is contacts between cattle and certain species of wildlife. The objective of this study was to evaluate contacts between cattle and wildlife in the Kruger National Park (KNP) and the adjacent Limpopo province for the time periods October 2006 to March 2007 and April to September 2007. In this study, 87 livestock owners and 57 KNP field rangers were interviewed. Fifteen (17%) livestock owners reported contacts between wildlife and cattle. More livestock owners reported observing contacts between cattle and all wildlife species during October-March than April-September (p=0.012). However, no difference was found between these periods for contacts between cattle and individual wildlife species. A total of 18 (32%) field rangers reported contacts between cattle and wildlife. The most common species-specific contacts were between cattle and buffalo (63/year), cattle and impala (17/year) and cattle and lion (10/year). There were no significant differences in rangers reporting observed contacts between cattle and wildlife during October-March versus April-September or between rangers reporting observed contacts outside versus within the KNP. Overall, there was no evidence of higher contact rates between cattle and wildlife in the study area during October-March compared to April-September. Contact data collected in this study can be used to better understand the transmission of FMD virus in this region.
Preventive Veterinary Medicine 09/2011; 103(1):16-21. · 2.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Simulating irrigation systems by accounting for various water loss rates is necessary while modeling the hydrology of cultivated canal-irrigated watersheds. The existing approaches to modeling canal irrigation use situation-specific optimization procedures. In addition, they are focused on a water management perspective rather than a hydrologic perspective. In this study, an approach is developed to model canal irrigation systems and irrigation best management practices (BMPs) to adequately simulate the water balance of irrigated watersheds. The approach is based on the water requirement of crops, number and frequency of irrigation, and critical crop water requirement stages. Two irrigation BMPs are modeled as water savers rather than physical changes in irrigation appurtenances. Land leveling is modeled by changing model parameters and water management by changes in frequency, timing, and magnitude of irrigation with respect to cumulative precipi-tation. The developed approach was tested with a 1;692 km 2 intensively cultivated, canal-irrigated watershed using the Soil and Water Assessment Tool (SWAT). Test results suggest that the approach captures water balance and observed runoff hydrograph of the study area adequately.
Journal of Hydrologic Engineering 09/2011; 16(9). · 1.38 Impact Factor
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] ABSTRACT: Soil erosion/sedimentation is an immense prob-lem that has threatened water resources development in the Nile river basin, particularly in the Eastern Nile (Ethiopia, Sudan and Egypt). An insight into soil erosion/sedimentation mechanisms and mitigation methods plays an imperative role for the sustainable water resources development in the re-gion. This paper presents daily sediment yield simulations in the Upper Blue Nile under different Best Management Prac-tice (BMP) scenarios. Scenarios applied in this paper are (i) maintaining existing conditions, (ii) introducing filter strips, (iii) applying stone bunds (parallel terraces), and (iv) refor-estation. The Soil and Water Assessment Tool (SWAT) was used to model soil erosion, identify soil erosion prone areas and assess the impact of BMPs on sediment reduction. For the existing conditions scenario, the model results showed a satisfactory agreement between daily observed and simu-lated sediment concentrations as indicated by Nash-Sutcliffe efficiency greater than 0.83. The simulation results showed that applying filter strips, stone bunds and reforestation sce-narios reduced the current sediment yields both at the sub-basins and the basin outlets. However, a precise interpre-tation of the quantitative results may not be appropriate be-cause some physical processes are not well represented in the SWAT model.
Hydrology and Earth System Sciences 03/2011; 15(3):807-818. · 3.59 Impact Factor