Soil and Water Assessment Tool model predictions of annual maximum pesticide concentrations in high vulnerability watersheds

Abstract

Recent national regulatory assessments of potential pesticide exposure of threatened and endangered species in aquatic habitats have led to increased need for watershed-scale predictions of pesticide concentrations in flowing water bodies. This study was conducted to assess the ability of the uncalibrated Soil and Water Assessment Tool (SWAT) to predict annual maximum pesticide concentrations in the flowing water bodies of highly vulnerable small-to medium-sized watersheds. The SWAT was applied to 27 watersheds, largely within the midwest corn belt of the United States, ranging from 20 to 386 km 2 , and evaluated using consistent input data sets and an uncalibrated parameterization approach. The watersheds were selected from the Atrazine Ecological Exposure Monitoring Program and the Heidelberg Tributary Loading Program, both of which contain high temporal resolution atrazine sampling data from watersheds with exceptionally high vulnerability to atrazine exposure. The model performance was assessed based upon predictions of annual maximum atrazine concentrations in 1-d and 60-d durations, predictions critical in pesticide-threatened and endangered species risk assessments when evaluating potential acute and chronic exposure to aquatic organisms. The simulation results showed that for nearly half of the watersheds simulated, the uncalibrated SWAT model was able to predict annual maximum pesticide concentrations within a narrow range of uncertainty resulting from atrazine application timing patterns. An uncalibrated model's predictive performance is essential for the assessment of pesticide exposure in flowing water bodies, the majority of which have insufficient monitoring data for direct calibration, even in data-rich countries. In situations in which SWAT over-or underpredicted the annual maximum concentrations, the magnitude of the over-or underprediction was commonly less than a factor of 2, indicating that the model and uncalibrated parameterization approach provide a capable method for predicting the aquatic exposure required to support pesticide regulatory decision making.

A Systems Approach to Modeling Watershed Ecohydrology and Pesticide Transport

“…Fields simulated as tiled were selected using a weighed approach based on the percentage of Hydrologic Group C and D soils, assuming fields with higher percentages of these soil types are more likely to be tiled. For the selected fields, tile drain parameters were edited for each of the associated HRUs to reflect general values outlined in the Winchell et al (2018). All other SWAT model parameters were the same as described in Scenario D.…”

“…To evaluate transport, initial atrazine distribution in the watershed must be characterized (Boithias et al, 2014). Given the absence of field specific application data, probabilistic methods similar to Winchell et al (2018) were used estimate spatial and temporal distributions of atrazine applications, with boundary conditions based on local knowledge. Potential atrazine use on crops in the watershed was first characterized using the Pesticide Information Center Online (PICOL) pesticide label database for Oregon and Washington (Daniels and Boyer, 2013) to identify 16 atrazine uses for crops grown in the Zollner Creek watershed in 2010 and 2011.…”

Modeling Pesticide and Sediment Transport in the Malewa River Basin (Kenya) Using SWAT

“…It is a physically based semidistributed model implemented in ArcGIS that aims to predict the impact of land practices on water and of sediment and agrochemical production in watersheds for diverse soil types and varying land use and management conditions [9]. This model has been used in different studies for simulating discharge, sediment yield and agrochemicals transport [6,[10][11][12][13][14][15][16][17][18] and in most of them the capability of this model has been confirmed.…”

Land use and water quality in watersheds in the State of São Paulo, based on GIS and SWAT data

“…The lack of continuous monitoring data on flow and sediment in watersheds has been a limiting factor for the validation of the results obtained and for their use in the formal processes of water resource management in the watersheds. Nevertheless, the SWAT has been considered an important tool for the prediction of maximum annual concentrations of pollutants even in unmonitored basins and without modeling calibration (Winchell et al, 2018).…”