ANALYZING SEDIMENTATION AND CHANNEL CHANGES SINCE THE REEMERGENCE OF BEAVERS IN UPLAND CONNECTICUT RIVER CORRIDORS

The North American beaver, once trapped near to extinction upon European settlement, has reoccupied much of its former range. Beavers alter the hydrology of stream corridors by building dams of woody debris, stones and mud, creating discontinuities that alter patterns of sediment transport patterns and channel morphology, and increasing heterogeneity that improves many ecological services, including hyporheic groundwater exchange, nutrient cycling and juvenile fish habitat. While the details how beaver dams impact stream hydrology has been extensively studied, there has been less research into how these changes are reflected in sediment transport patterns and sediment accumulation. Here we investigate multiple sites in Connecticut where aerial imagery indicates beavers have had maintained beaver dams for the 50+ years, providing excellent conditions to capture multidecadal changes in a river corridor due to beaver activity. At each site we employ a three-pronged approach to study beaver impact and sedimentation at the site: 1) historical aerial imagery analysis, 2) Ground Penetrating Radar (GPR) surveys, and 3) sediment coring. Aerial imagery analysis is used to map and identify sites with long term evidence of beaver occupation from their first reestablishment in the 1960s to 2019 (the most recent imagery). GPR surveys allow for the depth to sediment/water interface and depth to refusal (bedrock/glacial till) in beaver ponds to be mapped spatially, which allows us to estimate the amount of fine-grained sediment stored behind the dam and to determine the best location for sediment coring. Sediment cores serve two purposes: 1) they verify GPR interpretations; 2) they allow for detailed analysis of sediment characteristics and timing of recent beaver related sedimentation using Cs-137, which peaks in 1963 and is a convenient geochemical marker for studying sediment accumulation since 1960s. Preliminary results show a relative increase in fine grained organic rich sediment on paleo-floodplains, but less sediment accumulation in the old channel indicating continued scour. This could also indicate that on decadal time scales beavers have more of an impact on water storage and ecosystem services than dictating changes to sediment budgets and geomorphology.