Nitrate Runoff Contributing from the Agriculturally Intensive San Joaquin River Watershed to Bay-Delta in California

摘要: Nitrogen loading from agricultural landscapes can trigger a cascade of detrimental effects on aquatic ecosystems. Recently, the spread weed infestations (Eichhornia crassipes, Egeria densa, Ludwigia spp., and Onagraceae) in Sacramento-San Joaquin Delta northern California has raised concerns, nitrogen California’s intensive farming regions is considered as one major contributors. In this study, we employed Soil Water Assessment Tool (SWAT) to simulate exports agriculturally San River watershed Delta. The alternate tile drainage routine SWAT was tested against monitoring data tile-drained area examine suitability new for nitrate simulation. We found that physically based Hooghoudt Kirkham drain improved model performance representing runoff, which contributed 40% River. Calibration results show simulated riverine loads matched observed fairly well. According simulation, plays critical role exporting by 3135 tons nitrate-nitrogen annually, strong ecological implication supporting growth weeds, impeded water flow, impairs commercial navigation recreational activities, degrades quality Bay-Delta waterways. Since loadings upstream runoff are an important nutrient facilitate development, our study should be seen prerequisite evaluate potential impact weeds scientific evidence area-wide control decisions.