|Institution:||University of Nevada – Las Vegas|
|Keywords:||chlorophyll-a; lake mead; Microcystis; phytoplankton; quagga mussels; transparency; Aquaculture and Fisheries; Environmental Sciences; Public Health|
|Full text PDF:||http://digitalscholarship.unlv.edu/thesesdissertations/2751|
Quagga mussels (Dreissena rostriformis bugensis) are an invasive species that were discovered in Lake Mead in January of 2007, and rapidly spread throughout the lake. Quagga mussels are about the size of a fingernail, but are known to clog pipes, damage infrastructure and alter ecosystems. In large numbers, mussels can have a dramatic impact on an ecosystem by reducing the phytoplankton and potentially increasing toxin producing cyanobacteria. This research analyzed data collected from three separate basins in Lake Mead to determine if water quality characteristics that are commonly impacted by invasive mussels have changed. Transparency, chlorophyll-a, phytoplankton and zooplankton samples were collected before (2004-2006) and after (2009-2011) quagga mussel establishment and tested for differences using a Wilcoxon Signed Rank Test. The results indicate that Lake Mead has not had drastic lake wide changes similar to other ecosystems at these three locations. Transparency, chlorophyll-a, and phytoplankton biomass were significantly different in the Boulder Basin, but these results are confounded by long term reductions in phosphorus loading to the Boulder Basin. Although not significant at every location, there was a 23-26% reduction in phytoplankton cell numbers and a 17-68% reduction in phytoplankton biomass between means of the two time periods. Toxin producing cyanobacteria like Microcystis, Oscillatoria, Cylindrospermopsis and Anabaena did not have a significant change in frequency of detections or cell numbers at these locations. Quagga mussels may have less of an impact in Lake Mead due to some fundamental differences compared to water bodies in the Eastern United States. The large volume of water, deep depths, thermal stratification, and limited food supply may limit quagga mussel populations from changing water quality characteristics similar to other ecosystems. Additional monitoring will be required to understand the long term impacts of quagga mussels in Lake Mead. Advisors/Committee Members: Shawn Gerstenberger, Patricia Cruz, Guogen Shan, Steve Weber, Helen Neill.