Date of Award:

5-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Charles P. Hawkins

Committee

Charles P. Hawkins

Committee

D. Richard Cutler

Committee

David G. Tarboton

Committee

Sarah E. Null

Committee

Jiming Jin

Abstract

Stream temperature in one of the most biologically important aspects of water quality, but we lack temperature information for the vast majority of streams within the USA. Stream temperature can be influenced by several types of landscape and waterway alteration including upstream urbanization, agriculture, and reservoir releases. Stream temperatures are also expected to be affected by climate change over the next
century. We need to know how stream temperatures vary naturally, how they are influenced by human activity, and how they will respond to climate changes to effectively manage stream ecosystems. I used data from several thousand streams within the conterminous USA to build models that predict mean summer, mean winter, and mean annual stream temperature. These models predict temperatures at unmeasured streams as a function of both natural features and upstream watershed alteration. I then used these models to identify those streams with minimal thermal modification and built models to predict natural stream temperatures. These models were both accurate and precise. I then used these models to explore the degree to which watershed alteration affects stream temperatures.

To be useful, stream temperature models must represent the thermal environments of streams in a biologically realistic way. I therefore compared how well
modeled and measured summer stream temperatures predicted stream invertebrate distributions across 92 streams within the USA. Modeled and measured stream
temperatures performed identically and were the most important predictors associated with the distributions of stream invertebrate species. Predicted and measure stream temperatures also produced very similar estimates of temperature preference for individual stream species.

There is great concern that climate change will alter stream temperatures over the next century. I assessed how well my models could predict climate-related
alterations to stream temperature by examining how predicted and measured changes in stream temperature responded to changes in air temperature between the 1970s and the present. The response of predicted stream temperatures to climate variation was similar to that of observed stream temperatures. I then used climate projections to predict potential shifts in stream temperature by the end of the 21st century. My models predicted that stream temperatures will warm by about 1.7°C, on average by 2099.

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