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Introduced Species in Water Quality Treatment Basins and Pollutant Loading Estimates from a Small Watershed at Lake Tahoe
AuthorRios, David Thomas
Natural Resources and Environmental Science
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Watersheds are an important component of the natural landscape, yet can be negatively affected by humans. Humans affect watersheds by altering land cover, changing flow paths, and contributing pollution. Lake Tahoe, California-Nevada (USA), is a world renowned destination known for its crystal clear water and scenic subalpine environment. However, a variety of natural resource issues have been identified in Lake Tahoe, both at the large watershed-scale and small catchment-scale. Over the past forty years, urbanization has trigged the enhanced delivery of nonpoint source pollutants into Lake Tahoe. Dissolved nutrients and fine-sediment have been identified as the principal factors contributing to an observed decline in clarity and doubling in primary productivity. These chemical changes are addressed by implementing improvement projects within Lake Tahoe watersheds. Water quality treatment basins capture and treat stormwater from small catchments before discharging into the lake; however, these treatment basins may promote the establishment of introduced plant species. In Chapter 1, nonpoint source nutrient and sediment pollution were characterized for Barton Creek, a small subalpine urbanized Lake Tahoe watershed. A simple constant concentration water quality model was developed to identify and quantify pre-restoration pollutant loads. Our results suggest Barton Creek contributes significant pollutant loads compared with estimates previously reported for 10 primary stream monitoring stations. A Geographical Information System (GIS) was used to characterize impervious area in the 11 watersheds using a contemporary land use raster dataset. Simple linear regression analysis revealed significant relationships between watershed percent impervious area and nonpoint source pollutant loads for Barton Creek and the 10 primary monitoring stations. Our findings suggest small urbanized watersheds are significant pollutant contributors and raise concern over other impervious areas in the basin. In chapter 2, baseline botanical surveys document the native and introduced species in water quality treatment basins. Previously collected botanical survey data and revegetation specifications were the basis for comparisons with current surveys. In a greenhouse experiment, we examined how inoculating soil with arbuscular mycorrhizal fungi (AMF) influenced plant performance for a common upland seed mix. At three treatment basins, the number of native and introduced species declined during a12-year period from baseline surveys in 1997 to current surveys in 2009. Soil inoculation with AMF did not influence above and belowground biomass for a seed mix consisting of thirteen upland species. Our results suggest water quality treatment basins are dominated by native, mostly seeded species, while introduced terrestrials make up a small component.