Year of Award

2016

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Systems Ecology

Department or School/College

College of Forestry and Conservation

Committee Co-chair

Erin Landguth, Clint Muhlfield

Commitee Members

Lucy Marshall, Ashley Ballantyne, John Kimball

Abstract

Changes in seasonal climate patterns are altering thermal distributions of freshwater ecosystems worldwide. The Crown of the Continent Ecosystem is one of the most biologically diverse ecosystems in North America, spanning northwestern Montana, USA, Alberta and British Columbia, Canada. The fluvial landscape consists of pristine freshwater habitats that provide strongholds for many aquatic species. My dissertation work provides the first broad scale analysis of seasonal climate effects on spatiotemporal patterns of stream temperature in the Crown of the Continent, and a multi-scalar analysis of potential impacts to bull trout (Salvelinius confluentus) populations, the most stenothermic cold-water fish in the northern Rocky Mountains.

Seasonal stream temperature models were developed to predict monthly temperatures under current and future climate scenarios. Future climate simulations forecast increasing stream temperatures during spring, summer, and fall, with the largest absolute increases predicted for July, August, and September and the largest increases relative to historic temperatures predicted for April and November. Results portend a temporal shift in seasonal stream temperatures, including an earlier onset and extended duration of warm summer stream temperatures. Stream temperature warming was most pronounced in high-elevation montane and alpine streams, where glacial-fed streams were predicted to experience the largest magnitude (>50%) of change due to the loss of alpine glaciers.

Thermal riverscapes were used to assess spatiotemporal shifts in habitat distributions of bull trout. Models predicted thermal preferences for juvenile bull trout within tributary habitats during the summer months < 12°C, while preferred temperatures for sub-adult and adult bull trout within river habitats were < 15°C. Future stream temperature warming is likely to result in a contraction of thermally optimal habitats, suggesting a shift in the distributional range of bull trout further north in latitudes and higher in elevation. Thermal sensitivities during the summer months are likely to be highest in the southern periphery of their distributional range, while model simulations under extreme climate scenarios predict headwater tributaries within the Oldman, Flathead, and South Fork Flathead basins to provide cold-water refugia into the future. My dissertation work provides a decision support framework for predicting climate-induced stream temperature impacts on freshwater riverscapes and sensitive aquatic species to prioritize climate adaptation strategies in the Crown of the Continent.

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© Copyright 2016 Leslie Anne Jones