Modeling pesticide fate and transport at watershed scale using the soil & water assessment tool: general applications and mitigation strategies

Authors: WANG, RUOYU - University Of California, Davis; CHEN, HUAJIN - University Of California, Davis; LUO, YUZHOU - California Department Of Pesticide Regulation; YEN, HAW - Texas A&M University; Arnold, Jeffrey; BUBENHEIM, DAVID - National Aeronautics Space Administration (NASA) - Jet Propulsion Laboratory; Moran, Patrick; ZHANG, MINGHUA - University Of California, Davis

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 12/1/2018
Publication Date: 3/26/2019
Citation: Wang, R., Chen, H., Luo, Y., Yen, H., Arnold, J.G., Bubenheim, D., Moran, P.J., Zhang, M. 2019. Modeling pesticide fate and transport at watershed scale using the soil & water assessment tool: general applications and mitigation strategies. In: Goh, K.S., Gan, J., Young, D.F., Luo, Y., editors. Pesticides in Surface Water: Monitoring, Modeling, Risk Assessment, and Management. Washington, DC: ACS Publications. p. 391-419. https://doi.org/10.1021/bk-2019-1308.ch020.
DOI: https://doi.org/10.1021/bk-2019-1308.ch020

Interpretive Summary: Management of agricultural pesticide runoff in water is of concern for protection of freshwater resources for conservation of native fish, insects, and other organisms. Scientists have developed advanced computer modeling tools to predict where, when and how much pesticide will run off after use of pesticides to protect crops from insect and fungal pests. Many factors are involved including time of year, rainfall, soil type, temperature of the soil, air, and water, chemical degradation properties of the specific pesticide used, and pesticide runoff management strategies (best management practices or BMPs) implemented by farmers, such as contoured cropping, intercropping and runoff retention ponds. A model developed by the USDA-Agricultural Research Service (USDA-ARS), has been used worldwide, especially in the U.S. Midwest and California, northern Europe, and southeastern Asia, to model and predict pesticide runoff. The model, called the Soil Water Assessment Tool, or SWAT, can be customized with parameters specific to each watershed and agricultural land use pattern to provide high-quality results to track and predict pesticide runoff. This review book chapter summarizes how these customized SWAT models have been constructed in past studies, and how their performance in simulating known runoff patterns has been assessed. Successful use of these SWAT models can lead to adoption of new BMPs to mitigate (reduce) pesticide runoff. Some challenges to successful use of SWAT models remain, including the integration of SWAT with new water quality models that are refined to track the benefits of specific BMPs; better incorporation of the benefits of settling ponds to remove pesticides in SWAT models; and integration of SWAT with a newadvanced hydrogeological mapping system developed by the U.S. Geological Survey (USGS). Still, the potential for SWAT-based models of pesticide runoff in water to improve water quality through wise management of pesticide applications is great.

Technical Abstract: Pesticide residue runoff to surface water is of great concern to local stakeholders who seek to preserve or achieve good water quality objectives. The Soil and Water Assessment Tool (SWAT) has been widely used to assess many environmental problems related to water resources and nonpoint-source pollution, including sediment/nutrient loads and pesticides. However, a comprehensive review of existing studies on SWAT-based pesticide modeling is still not available in the literature. Therefore, in this chapter, we present an overview summarizing all previous SWAT applications in studying the fate and transport of pesticides around the world, based on the peer-reviewed literature. We aim to 1) introduce the fundamental mechanisms for SWAT pesticide modeling; 2) summarize the required modeling inputs and associated parameterization processes; 3) provide an overview of global applications and evaluate model performance; 4) discuss SWAT representations of mitigation strategies to alleviate potential pollution; and finally, yet importantly 5) recommend future needs to address current modeling limitations to fill research gaps.