Impacts of beaver dams on hydrologic and temperature regimes in a mountain stream

Abstract

Abstract. Beaver dams affect hydrologic processes, channel complexity, and stream temperature in part by inundating riparian areas, influencing groundwater–surface water interactions, and changing fluvial processes within stream systems. We explored the impacts of beaver dams on hydrologic and temperature regimes at different spatial and temporal scales within a mountain stream in northern Utah over a 3-year period spanning pre- and post-beaver colonization. Using continuous stream discharge, stream temperature, synoptic tracer experiments, and groundwater elevation measurements, we documented pre-beaver conditions in the first year of the study. In the second year, we captured the initial effects of three beaver dams, while the third year included the effects of ten dams. After beaver colonization, reach-scale (~ 750 m in length) discharge observations showed a shift from slightly losing to gaining. However, at the smaller sub-reach scale (ranging from 56 to 185 m in length), the discharge gains and losses increased in variability due to more complex flow pathways with beaver dams forcing overland flow, increasing surface and subsurface storage, and increasing groundwater elevations. At the reach scale, temperatures were found to increase by 0.38 °C (3.8 %), which in part is explained by a 230 % increase in mean reach residence time. At the smallest, beaver dam scale (including upstream ponded area, beaver dam structure, and immediate downstream section), there were notable increases in the thermal heterogeneity where warmer and cooler niches were created. Through the quantification of hydrologic and thermal changes at different spatial and temporal scales, we document increased variability during post-beaver colonization and highlight the need to understand the impacts of beaver dams on stream ecosystems and their potential role in stream restoration.

Ecosystem experiment reveals benefits of natural and simulated beaver dams to a threatened population of steelhead (Oncorhynchus mykiss)

“…The increase in groundwater elevation surrounding beaver ponds likely results in increased flow throughout the summer as water is slowly released2829. We also found that water temperatures stayed the same or decreased throughout reaches with beaver ponds, and that diel fluctuation was dampened.…”

“…Because dams slow water and often increase the area of solar input, a common assumption is that temperatures increase in impounded reaches30. However, quantitative evidence supporting3132 or refuting33 this claim suggests that the complex interaction of solar input, and exchange with the hyporheic or groundwater call into question this simple generality29. In Bridge Creek, increased residence time and the slowed release of potentially cooler water after the construction of BDAs also increases habitat quantity during times of very low discharge observed during hot summer conditions.…”

Beavers affect carbon biogeochemistry: both short‐term and long‐term processes are involved

“…The effects of beavers on water temperature have been studied quite extensively with varying results, but with the common conclusion that beaver damming increases water temperature (Majerova et al. ); at higher temperature, gas solubility decreases. The daily variation in CH 4 ebullition is also related to changes in atmospheric pressure, and bubble fluxes tend to be higher when the pressure is decreasing (Maeck et al.…”

Impacts of beaver dams on channel hydraulics and substrate characteristics in a mountain stream

“…There is a clear need for more detailed methods that assess the influence of beaver dams on channel hydraulics over different flow ranges as they relate to changes in stream ecosystems. Majerova et al () also highlighted the need for a better understanding of spatial and temporal variability of streamflow and temperature in beaver impacted reaches. They concluded that if beaver dam complexes are to be successfully used as a restoration tool, a better understanding of their influences on stream ecosystems needs to be reached through more quantitative field and modelling studies.…”