The response of fish to human alterations of habitat conditions is of critical management and policy importance. For example, withdrawal of groundwater from stream ecosystems can result in altered thermal regimes, and changes in fish populations. Many streams are fed groundwater inputs that help maintain in-stream hydraulic conditions by stabilizing discharge as well as stream temperature. However, groundwater withdrawal through high-capacity wells is also important to the agricultural industry. Withdrawal can cause reductions in streamflow and typically results in increased stream temperature, and can initiate shifts in aquatic community assemblage. In Michigan, the Water Withdrawal Assessment Tool (WWAT) is used to estimate ecological impacts associated with water withdrawal. The model uses flow-fish response relationships to estimate the effects of flow reduction on downstream warming for Michigan streams, and subsequently estimates the degree of impact of on stream fish communities. The chapters of this thesis investigate potential improvements to the mechanisms of Michigan's WWAT used to set policy regarding water withdrawal throughout the state. In the first chapter, I investigate the use of several benchmark detection methods for setting thermal benchmarks for stream fishes. The second chapter includes the development and analysis of several models which attempt to predict downstream warming rates within 24 streams located throughout Michigan's Upper and Lower Peninsulas.
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