Nutrient Contribution of Nonpoint Source Runoff in the Las Vegas Valley
A Geographic Information System (GIS) based non-point source runoff model is developed for the Las Vegas Valley, Nevada, to estimate the nutrient loads during the years 2000 and 2001. The estimated non-point source loads are compared with current waste water treatment facilities loads to determine the non-point source contribution of total phosphorus (TP), total nitrogen (TN), and total suspended solids (TSS) on a monthly and annual time scale. An innovative calibration procedure is used to estimate the pollutant concentrations for different land uses based on available water quality data at the outlet. Results indicate that the pollutant concentrations are higher for the Las Vegas Valley than previous published values for semi-arid and arid regions. The total TP and TN loads from non-point sources are approximately 15 percent and 4 percent, respectively, of the total load to the receiving water body, Lake Mead. The TP loads during wet periods approach the permitted loads from the waste water treatment plants that discharge into Las Vegas Wash. In addition, the GIS model is used to track pollutant loads in the stream channels for one of the subwatersheds. This is useful for planning the location of Best Management Practices to control nonpoint pollutant loads.