Articles | Volume 19, issue 8
Research article
11 Aug 2015
Research article |  | 11 Aug 2015

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

M. Majerova, B. T. Neilson, N. M. Schmadel, J. M. Wheaton, and C. J. Snow

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.

Short summary
This study quantifies the impacts of beaver on hydrologic and temperature regimes, as well as highlights the importance of understanding the spatial and temporal scales of those impacts. Reach-scale discharge showed shift from losing to gaining. Temperature increased by 0.38°C (3.8%) and mean residence time by 230%. At the sub-reach scale, discharge gains and losses increased in variability. At the beaver dam scale, we observed increase in thermal heterogeneity with warmer and cooler niches.