| Changes in land use and land cover are known to be important factors causing thermal alterations in small streams. The heating of coldwater and coolwater streams influences aquatic communities that inhabit such environments. We recorded continuous stream temperature data at 50 sites during July--September of 2008 to better understand thermal controls on small streams (1st--3rd order) within Minnesota's Lake Superior watershed, with specific interest in determining the role of water storage capacity and impervious surface cover. Local and landscape variables were used to predict in-stream temperature using multiple regression analyses. These analyses identify those variables most correlated with stream temperature, and therefore, most likely to influence thermal characteristics. Sites were selected to represent natural gradients of water storage capacity (0--86%) and impervious surface cover (0--26%) within each catchment. Stream habitat data were collected to explain natural temperature variation among sites due to local conditions. Results indicate that geomorphic (stream width and depth), atmospheric (air temperature), and local landscape (riparian shading) variables are all strongly correlated with stream temperature. Thermal characteristics are also influenced by regional landscape variables such as hydraulic conductivity and percent land cover classified as open water or emergent herbaceous wetlands. In contrast, neither impervious surface cover nor water storage capacity were good predictors of the stream temperature metrics summarized in this study. Land cover variables were selected more frequently in best-fit models when they were weighted by distance from the sampling location, indicating that position in the watershed may be an important factor. These trends suggest that changes in land use and land cover have great potential to either mitigate or exacerbate the impacts on stream temperature from climate change, and stress the importance of effective land management. |
