Award Date

8-1-2016

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Committee Member

Brian P. Hedlund

Second Committee Member

Duane P. Moser

Third Committee Member

Dennis A. Bazylinski

Fourth Committee Member

Elisabeth Hausrath

Number of Pages

170

Abstract

Walker Lake is a saline, alkaline, terminal lake ecosystem located in west-central Nevada. For over one hundred years, anthropogenic streamflow diversions within the Walker River Basin have ultimately led to little or no water reaching Walker Lake, the basin’s terminus for water flow. These diversions have resulted in a >46 meter decrease in the lake surface altitude and increases in salinity and dissolved salt constituents that have caused the elimination of native fish species. This study examines how the lack of freshwater inflow has altered the physical, chemical, and microbiological structure of Walker Lake during the lake’s ongoing desiccation.

Between 2007 and 2015, water and sediment samples were collected from a central lake location of Walker Lake, coinciding with the historical timing of late summer thermal stratification. Physical parameters and chemical constituent measurements show Walker Lake to have shifted from a monomictic to a polymictic system sometime after 2008, with salinity increasing conservatively to values over 21 g L-1 in 2015. Illumina sequencing of the V4 region of the 16S rRNA gene was completed on all environmental filter and sediment samples to observe trends and changes in the microbial populations of the water column and sediment as a result of the changing lake dynamics. Over time, distinct differences in overall community composition and diversity were observed between sampling dates. The sediment communities were found to be highly dissimilar from the overlying pelagic microbial communities and showed more similarity to microbial communities from anoxic hypolimnion water samples from the 2008 sampling event when lake stratification was observed.

The anthropogenic and climatic factors that Walker Lake has faced over the past century have dramatically altered the ecosystem. This study aims to contribute to the overall understanding of the Walker River Basin and to other terminal lake basins throughout the world. By examining the microbial communities of Walker Lake and documenting the limnological shift of this transitioning ecosystem, we gain insights into the physiological aspects of Walker Lake and possible ways to manage and restore this unique environment to the thriving ecosystem it once was.

Disciplines

Fresh Water Studies | Microbiology

Language

English


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