Approaches to Control Nitrate Pollution in the San Joaquin Watershed

Modeling of the San Joaquin valley using SWAT can give a comprehensive overview of hydrologic traits of the San Joaquin River and its tributaries, specifically for nutrients like nitrate. The San Joaquin valley is a site of intense modeling interest and policy making, as the San Joaquin River joins the Sacramento River to feed into the Delta. The environmental impact of dissolved oxygen on aquatic life on the Delta is a particularly key concern (Quinn 2000). The San Joaquin watershed also represents considerable investment in agriculture on the valley floor and has been studied for nitrate, sediment, and salinity concerns particularly with regard to agricultural runoff. Evaluation of model accuracy and utility are important for any future studies on the San Joaquin River for hydrology and nutrients, especially in regards to policy making. Criteria for model evaluation are based on model accuracy and reliable conclusions on the watershed traits. The accuracy of the model is summarized by the goodness-of-fit (e.g., Nash- Sutcliffe efficiency, mean of sum of square residuals), as well as the ability of the model to reproduce trustworthy results. Reliable conclusions concerning the hydrological simulation of the San Joaquin are based on recognizable hydrology trends in surface flow and nutrient origin and transport, particularly nitrates