The effects of beaver engineering on downstream fluxes in Colorado mountain streams
Date
2019
Authors
Laurel, DeAnna J., author
Wohl, Ellen, advisor
Rathburn, Sara, committee member
Covino, Tim, committee member
Kelly, Eugene, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Beaver meadows compose only a small fraction of catchment area in mountain watersheds, but they provide a potentially large role in retaining fluxes of water, sediment, and organic carbon (OC) in mountain meadows. Beaver (Castor canadensis) build dams and ponds that encourage overbank flows and deposition of fine sediment along with particulate OC that create an anastomosing stream channel and a geomorphically heterogeneous floodplain with high biodiversity. I combined geomorphic surveys, soil depth probing by rebar, and soil cores analyzed for carbon content to investigate the influence of beaver activity, geomorphic unit, soil depth, soil moisture, and drainage area on fluxes of fine sediment and organic carbon storage in 7 active and abandoned beaver meadows in Rocky Mountain National Park. I found that surface spatial heterogeneity and mean soil moisture differed significantly only between active and long abandoned meadows, indicating a nonlinear change through time. Soil depth and OC stock did not differ significantly between different levels of beaver activity, indicating that larger-scale geologic controls on valley sediment depth contribute to long-term storage of OC after beaver abandon a meadow. I examined the seasonal hydrologic flux between the inflow and outflow of 19 active and abandoned beaver meadows to determine the influence of beaver activity, valley geometry, elevation, drainage area, and meadow size relative to drainage area on the reduction of peak flow, enhancement of base flow, and lag of the recession curve of the meadow hydrographs during the Spring and Summer. I found that beaver activity, along with meadow size relative to drainage area, and valley geometry, influence peak flow attenuation. Predicting the flow attenuation is complicated by these additional factors, as well as the difficulty of quantifying subsurface processes that contribute to the lateral flow, storage, and release of water from the meadows. These results indicate that relatively wide meadows located in the upper reaches of channel networks are the best candidates among abandoned beaver meadows in mountain environments to store more organic carbon and attenuate peak flows if beaver are successfully reintroduced.