Characterization of nutrient and suspended sediment concentrations in stormwater runoff in the Lake Tahoe basin

The clarity of Lake Tahoe has declined about one foot per year since 1968. One element in the Lake Tahoe basin that contributes to the lake's water clarity decline is stormwater runoff. Nineteen monitoring sites have been established throughout the basin, from which two years of discharge measurements and nutrient and sediment concentrations have been collected. These data were compared to concentrations reported in national stormwater databases and found to be significantly different. Discharge-weighted concentrations for each monitoring site were related to watershed characteristics and land use through multiple linear regression analysis. Particulate species of nitrogen and phosphorus were the most abundant sources of nutrients in stormwater, and they were especially high in commercial land uses. The concentrations of all nutrients and sediment were enhanced significantly by localized summer thunderstorms. Population density and residential yard maintenance play a key role in nutrient and sediment concentrations for residential land uses.