Comparing the sources of sediment retained by beaver dams and beaver dam analogues

Beavers modify stream channels and their floodplains by building dams that alter downstream fluxes of water and sediment. Where beavers have been lost and stream channels degraded, beaver dam analogues (BDAs) are being used to mimic the effects of beaver engineering. Central to the success of these structures in accelerating stream recovery is creating similar channel responses as beaver dams. Unknown is the importance of beaver actions versus erosion in the catchment in generating the retained sediment. This study tested the viability of sediment fingerprinting to determine the source of sediment retained by beaver dams and BDAs at a watershed in Alberta, Canada. Elemental concentrations were determined in potential sediment sources (forest, grassland, floodplain, stream bank, and beaver canal) and sediment collected from the upstream face of beaver dams and BDAs. Of the 29 elements evaluated, only Se and Ti could discriminate potential sediment sources in this watershed. Mixing models showed that about 55% of the sediment retained by the beaver dams originated from floodplains, 23% from upland sources, and 13% from beaver canals whereas about 89% of sediment retained by the BDAs originated from eroding stream banks. Our findings indicate that sediment fingerprinting is a viable technique for identifying sources of sediment retained by beaver ponds and BDAs. The actions of beavers, a known geomorphic agent, are important in actively eroding the sediment that becomes retained by their dams. The study has implications for determining the processes by which BDAs cause channel aggradation.