Pesticides have been routinely detected in the Delta waterways, with concentrations exceeding the benchmark for the protection of aquatic species. Pesticide loadings into the Delta are partially attributed to the San Joaquin watershed, a highly productive agricultural region located upstream. Therefore, this study aims to simulate pesticide loadings from the San Joaquin watershed to the Delta by applying the Soil and Water Assessment Tool (SWAT). Pesticide use patterns in the San Joaquin watershed were characterized by combining the California Pesticide Use Reporting (PUR) database and GIS analysis. SUFI-2 algorithm in SWAT-CUP was applied to perform global sensitivity analysis, multi-site calibration, and uncertainty analysis in the simulation of streamflow, sediment discharge, and pesticide loads along the San Joaquin River. Model performance was evaluated using a combination of graphic and quantitative measures (P-factor, R-factor, NSE, and PBIAS). Preliminary results indicated that the most sensitive parameters to stream flow were surface response parameters (CN2, SOL_AWC, HRU_SLP, SLSOIL), subsurface response parameters (ALPHA_BF, GWQMN, RCHRG_DP), and basin response parameters (CH_N2, CH_K2, and CH_L2). Streamflow was satisfactorily simulated along the San Joaquin River and the major eastern streams, whereas streamflow was less accurately simulated in the western tributaries, which are ephemeral creeks that peak during winter storm events and are mainly fed by irrigation return flow during the growing season. The automatic irrigation operation routine in SWAT was able to reasonably estimate irrigation water use by major crop type, in comparison with the values reported by the California Department of Water Resources. Anticipated results will include (1) pesticide use pattern analysis, (2) calibration and validation of streamflow, sediment discharge, and pesticide loads, and (3) characterization of spatial patterns and temporal trends of pesticide yield.

Modeling pesticide loadings from the San Joaquin watershed using SWAT

253rd National Meeting (2017)

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