Date of Award:

5-2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Sarah E. Null

Committee

Sarah E. Null

Committee

Nancy Mesner

Committee

Michelle Baker

Abstract

Degraded water quality has reduced aquatic species abundance and survivability in Nevada’s Walker River. Low instream flows and increased nutrients affect native fish populations through high daily stream temperatures and low nightly dissolved oxygen concentrations. Increasing streamflow, through environmental water purchases, may improve water quality and enhance habitat for native fish species, such as Lahontan cutthroat trout. This study uses River Modeling System, a computer model, to estimate streamflows, stream temperatures, and dissolved oxygen concentrations in the Walker River. Streamflow increases are simulated to determine potential improvements to high water temperatures and low dissolved oxygen concentrations, enabling the prioritization of time periods and locations that water purchases most improve habitat for native species. Environmental water purchases ranged from 0.03 cms to 1.41 cms average daily increases. Modeling results show that increased streamflow generally affects dissolved oxygen concentrations in two ways. First, more streamflow keeps stream temperatures cooler during the day but also allows temperatures to stay warmer at night. This prevents conditions that cause the lowest nightly dissolved oxygen concentrations but increases the overall length of time that dissolved oxygen concentrations remain under preferred levels. This effect is due to the inverse relationship between dissolved oxygen concentrations and stream temperature. Second, dissolved oxygen concentrations are affected by upstream environmental conditions. High water quality upstream improves poor downstream water quality conditions, but the reverse is also true wherein poor upstream water quality can worsen water quality downstream.

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