Date of Award:

5-2012

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Charles P. Hawkins

Committee

Charles P. Hawkins

Committee

Peter T. Kolesar

Committee

Matthew E. Baker

Committee

Helga Van Miegroet

Committee

Michelle A. Baker

Abstract

Determining if a stream has been degraded by human activities requires knowing what that stream’s natural water quality and freshwater species composition would likely be without any alteration. However stream natural conditions vary greatly from stream to stream, making predicting natural conditions difficult. To determine natural stream conditions, I developed models to predict natural stream water chemistry at individual streams across the western USA. Specifically, the models predict a stream’s electrical conductivity (a measure of the amount of solids dissolved in water), acid neutralization capacity, and concentrations of calcium, magnesium, sulfate, total phosphorus, and total nitrogen. These models predict chemistry expected under natural conditions because they are based on measurements of watershed characteristics not influenced by human activities, such as geology, climate, soils and topography. Model predictions allow comparison of current water chemistry with the water chemistry expected under natural conditions. These comparisons can then used to determine if protection or restoration efforts are needed.

To better understand how natural differences in water chemistry could affect freshwater species, I also ran two experiments in which I exposed a range of animals to waters with different amounts of dissolved solids. I found that low amounts of dissolved solids in streams affect the survival of some invertebrates, but not others. These differences in survival occurred because some animals living in dilute freshwater are better at maintaining the required balance between water and salts (i.e., osmoregulating) than other species. Those animals with poorer survival when exposed to water with low dissolved solids in my experiments also did not occur in streams with low dissolved solids in nature.

Combining models and experimental results showed that streams underlain by granite or similar rocks have low dissolved solids, causing some invertebrates to be restricted from these streams. These combined results explain why invertebrate distributions in nature are related to geology and provides insight into the basic ecological question of why animals live where they do. This research increases our understanding of both how geology influences water chemistry and how different invertebrates respond to water chemistry, improving our ability to predict the chemical and biological conditions of streams.

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

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