LATE 20TH CENTURY TO PRESENT RESERVOIR SEDIMENTATION IN A SMALL, UPLAND WATERSHED IN EASTERN CONNECTICUT

20th-century dams and reservoirs were built for a variety of purposes around the northeast US, including flood management, water resources and recreation. Regardless of why they were built, these dams block the rivers where they occur and lead to increased sediment accumulation. In this study, we investigated sedimentation in Bicentennial Pond, an anthropogenically formed water body in a small upland stream in eastern Connecticut (in the Town of Mansfield). The current large, 14 ft high dam and upstream pond was formed in 1974; at one point the site had a smaller, historic dam and pond (from ~1850-1930s), but this dam had failed and the site was forested by the time the 1974’s dam was built. Today, the 1970s to present pond has had sediment buildup in the upstream end and now suffers from the presence of invasive plant species. We collected 4 sediment cores in a ~80 m longitudinal transect extending extending into the pond from the upstream tributary inlet. We did not core the downstream end, where the older historic dam existed. Laboratory methods on the cores included: LOI to quantify organic content, pXRF for elemental analysis, sieves to measure grain size; and gamma spectroscopy to determine a 210Pb and 137Cs based age model. GPR was collected over the entire pond to determine sediment thicknesses and extents and supplement thickness measurements derived from the cores. Overall, the sedimentation rates in the pond ranged from 0.4-1.78 cm/yr and were dependent on location, with the highest rate in the upstream-most pond location. Rates also may be impacted by swimmers kicking up and moving sediment, as the site is currently used for recreation.