Date of Award:

2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Department name when degree awarded

Aquatic Ecology

Advisor/Chair:

Sarah Null

Abstract

Human impacts from land and water development have degraded water quality and altered the physical, chemical, and biological integrity of Nevada's Walker River. Reduced instream flows and increased nutrient concentrations affect native fish populations through warm daily stream temperatures and low nightly dissolved oxygen concentrations. Environmental water purchases are being considered to maintain instream flows, improve water quality, and enhance habitat for native fish species, such as Lahontan cutthroat trout. This study uses the River Modeling System (RMSv4), an hourly, physically-based hydrodynamic and water quality model, to estimate streamflows, temperatures, and dissolved oxygen concentrations in the Walker River. Stream temperature and dissolved oxygen changes were simulated from potential environmental water purchases to prioritize the time periods and locations that water purchases most enhance stream temperatures and dissolved oxygen concentrations for aquatic habitat. Environmental water purchases ranged from 0.03 cms to 1.41 cms average daily increases. Modeling results indicate that increased water purchases generally affect dissolved oxygen in two ways. First, environmental water purchases increase the thermal mass of the river, cooling daily stream temperatures and warming nightly temperatures. This prevents conditions that cause the lowest nightly dissolved oxygen concentrations (moderate production impairment thresholds are

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