Patterns of stream temperature and the influence of groundwater in northern Rocky Mountain watersheds
Creators: Fitzpatrick, John
Publisher: name: University of Alberta Library
Year: 2023

<p>Stream temperature is an important water quality parameter linked to biotic and abiotic processes that influence the abundance and distribution of aquatic organisms. Stream temperatures can be highly variable through space and time and are determined by energy flux processes. Key energy flux processes that influence stream temperature can be categorized into climatic controls (e.g., solar radiation, air temperature, precipitation) and hydrologic controls (e.g., groundwater inputs, tributary inflows). Generally, groundwater inputs into streams have a cooling effect on stream thermal regimes in the summer, and a warming effect in the winter, relative to air temperatures. Fish species that require relatively cold stream temperatures in summer are susceptible to habitat loss due to shifting stream thermal regimes. The objective of this thesis is to explore the importance of groundwater on moderating summer stream thermal regimes in the Canadian Rocky Mountains and foothills. In particular, this work examines the comparative influence of climatic controls versus hydrologic controls and attempts to identify spatial and temporal patterns of summer stream temperature at the watershed scale. A long-term (2005-2018) comparison of climatic versus hydrologic controls in seven headwater sub-catchments identified that groundwater inputs to streamflow explain 1.3-6.9 times more of the variation in stream temperature than climatic controls. Although inputs of groundwater consistently decreased summer stream temperature, there was noteworthy variability in the effects of groundwater inputs across the sub-catchments suggesting there is variability in temperature of different groundwater inputs. Spatiotemporal patterns of stream temperature were identified across a study area (28648 km2) that included Rocky Mountains and foothills in Alberta. An empirical spatiotemporal model (adjusted r2=0.93) derived from continuous summer data (2019-2021) from 16 watersheds identified that: 1) groundwater inputs cooled stream temperatures (p&lt;0.001), however generalized across a larger, more diverse study area, groundwater inputs were less predictive of stream temperature than climatic controls; 2) an anomalous weather event (“Heat Dome”) in 2021 elevated mean stream temperatures 0.78 ⁰C and disrupted patterns of cooling groundwater inputs observed in 2019 and 2020; 3) variability in stream thermal regimes across the different watersheds was highly correlated with terrain complexity metrics (p&lt;0.001, r2=79-81%). These results emphasize the importance of considering both climatic and hydrologic controls (particularly groundwater inputs) on stream temperature in order to understand thermal regimes and their susceptibility to natural and anthropogenic disturbances and changing climates. In addition, the identification of terrain complexity metrics as predictors of thermal regimes may become a useful tool for identifying watersheds with streams that are relatively warmer/cooler and enable resource managers to more effectively prioritize conservation efforts.</p>