Date of Award:

5-2012

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Charles Hawkins

Committee

Charles Hawkins

Committee

Patrick Belmont

Committee

Richard Cutler

Abstract

To protect and restore stream biota, managers need to be able to both detect biological degradation and infer likely causes of impairment. Managers commonly develop indices based on stream biota to assess the biological condition of streams. However, the performance of these indices dictates the ability to detect degradation, and although index performance varies widely, the sources of this variation are often unclear. In addition, bioassessments do not identify causes of impairment. My thesis research had two general goals: 1) develop indices to measure biological condition in Nevada streams and 2) quantify relationships between land uses, stressors, and biological condition to infer likely causes of degradation.

I developed two types of biological indices based on stream invertebrates to measure biological condition and detect degradation in Nevada streams: (1) an index of taxonomic completeness, and (2) a multimetric index (MMI) that aggregates several attributes of invertebrate assemblages. The Nevada index of taxonomic completeness was relatively imprecise compared with indices developed for other regions, which I argue is a consequence of the spatial isolation of aquatic habitats in arid regions. In contrast, the Nevada MMI was more precise than most previously developed indices, likely the result of using models to reduce variation in assemblage attributes along natural environmental gradients. Index values were positively related to how evenly individuals were distributed among taxa in a sample. Adjustments of index scores for sample evenness increased index precision and also altered inferences of biological impairment for specific sites.

I also developed models to relate measures of biological condition, instream stressors, and human land uses. Coupled with known causal mechanisms, associations between stressors and biological degradation can be used to infer likely causes of impairment. Total dissolved solids and metal contamination were the stressors most strongly associated with biological impairment. Stressors associated with degraded biological condition were also associated with land uses like agriculture, urbanization, and mining. The tools I developed to detect biological degradation and identify important stressors and their potential sources should help managers target conservation and restoration efforts and improve their ability to protect freshwater resources.

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2487beb8d09f1bfaddc11229d3db4adb

Comments

This work made publicly available electronically on September 20, 2012.

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