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Alan C. Heyvaert, John E. Reuter and Scott Hackley University of California at Davis, Tahoe Research Group Previous studies by the UCD Tahoe Research Group (TRG) have shown significant nutrient and sediment loading to Lake Tahoe from stormwater runoff that drains directly into the lake (Reuter et al. 2000). Much of this direct runoff is conveyed from urbanized areas that occupy lower gradient slopes around the lake. These areas once served as marsh or forested buffer zones that slowed runoff velocities and scavenged nutrients and sediments before stormwater reached the shoreline. However, this function has been lost as impervious surface areas from housing, roads and commercial districts have replaced natural surface coverage over the last several decades of urbanization. Resource management agencies in the Tahoe Basin are attempting to mitigate impacts from direct stormwater runoff by building artificial wetlands, detention basins and infiltration systems. Preliminary results from monitoring over the last year at an artificial wetland system in Tahoe City (TCWQIP) indicate significant improvements in nutrient and sediment concentrations of outflow water compared to inflow concentrations (Heyvaert et al. 2001). On average, over the period of this study, wetland functions decreased nutrient and sediment concentrations by approximately 80% compared to inflow concentrations. Median values for the outflow water approached nutrient and sediment concentrations typically found in stormwater runoff at more pristine, undisturbed sites.  Reuter, Heyvaert and Hackley. Preliminary analysis of sediment and phosphorus in surface runoff from selected intervening zones in the Tahoe Basin. Technical report to the LRWQCB, South Lake Tahoe, California. December 15, 2000. Heyvaert, Reuter and Hackley. Progress report and preliminary results from monitoring and evaluation of selected stormwater treatment projects. Technical report to the California Tahoe Conservancy, South Lake Tahoe, California. June 30, 2001. |