Thermal Regimes of Beaver Impacted Streams

Thank you for supporting this research on the thermal regimes of beaver-impacted streams in the Tualatin River Basin. This project sought to explore three primary questions: (1) how thermal sensitivity—defined as the relationship between air and water temperatures—varies across different monitored subbasins; (2) how thermal regimes differ between reach and beaver dam scales; and (3) how specific site variables, such as stream depth, vegetation, and dam characteristics, influence thermal regimes within beaver-impacted areas.

Thermal Sensitivity: Our results show that thermal sensitivity varies significantly between subbasins. For example, Chicken Creek exhibited the highest thermal sensitivity, with stream temperatures more responsive to air temperature changes than Fanno and Springville Creeks. This indicates that recently restored, shallower streams with limited canopy cover (like Chicken Creek) may be more vulnerable to atmospheric changes than more established, deeper streams with greater shading.

Scale-Based Thermal Variability: By analyzing both reach-scale and beaver dam-scale temperatures, we observed that beaver dams contribute to distinct temperature patterns. These dams create microhabitats where temperatures can vary greatly, depending on factors like dam location, stream morphology, and proximity to downstream or upstream sites. Notably, downstream temperatures tend to be warmer during the day and cooler at night, highlighting the role of beaver dams in creating diurnal temperature fluctuations that can support biodiversity.

Site-Specific Influences on Thermal Regimes: Site characteristics, including dam morphology, stream depth, and vegetation cover, strongly influenced thermal impacts at each study site. Shallow areas downstream of dams often warmed during the day and cooled at night, while deeper areas retained cooler temperatures. This variability underscores the need to consider specific ecological objectives when using beaver dams for restoration, as their effects on temperature are not uniform but rather contribute to a mosaic of thermal conditions that enhance habitat complexity.

These findings underscore the importance of multi-scale approaches in restoration planning, particularly in urbanized watersheds where vegetation, depth, and geomorphology vary widely. This research will inform sustainable watershed management strategies and guide future projects to enhance stream complexity, resilience, and biodiversity through tailored restoration practices.