Evaluating non-point nutrient pollution in Steamboat Creek, Nevada

Steamboat Creek in western Nevada is the largest contributor of non-point pollution to the Truckee River. Steamboat Creek is a complex system due to the presence of numerous irrigation diversions, geothermal activity, and the emergence of rapid urbanization of agricultural and undeveloped lands. Historic water quality data was analyzed to identify trends associated with different land uses adjacent to the creek, seasonal flows, and irrigation regimes. Three Lagrangian-style water quality surveys were performed---one each during high flow with irrigation, medium flow with irrigation, and low flow with minimal irrigation. Hydrodynamics, nutrient flux, and diel variation of dissolved oxygen concentrations associated with periphyton productivity were simulated using the Water Quality Analysis Simulation Program Version 5 (WASP5). Information from one survey was used in model calibration leaving the remaining two for verification. Finally, the calibrated and verified model was used to estimate the magnitude of non-point nutrient loading from septic systems, shallow groundwater, and flood irrigation. During all surveys, model results indicate that non-point nitrate loading occurred. Model results suggest that non-point nitrate loads entered Steamboat Creek in reaches where households built adjacent to the channel use septic systems for disposal of domestic waste. During the high flow regime with irrigation, model results demonstrate non-point loading of organic phosphorous from an agricultural reach where cattle were not restricted from entering the channel.