STUDYING ANTHROPOCENE SEDIMENTATION BEHIND A 19TH-20TH CENTURY DAM IN WESTERN CONNECTICUT

18^th to early 20^th century dams are a common occurrence in New England. Made from compacted earth and rock, and later with stone and brick masonry and concrete, these river impoundments served a variety of functions from powering mills to cooling iron furnaces. Over time, the reservoirs behind these dams become infilled with a sedimentary and geochemical archive of the contributing watershed that potentially preserves land use changes such as the clearing and regrowth of forest as well as recording historic flood events. With dam removal becoming more common, the possibility of releasing contaminated sediment is also a growing concern in the region. Our study reconstructs and analyzes sedimentation behind the Hollenbeck dam in Canaan Connecticut, which was used to cool the Buena Vista iron furnace from ~1847-1893. We assess the volume, sedimentology and geochemistry of 19^th-20^th century sediment preserved at this site. We collected three vibracore cores (HPSC1, HPSC2 and HPSC3) behind the Hollenbeck dam, recovering 237 cm, 203 cm and 390 cm of compacted sediment, respectively. Intercalated wood at the bottom of our deepest core (HPSC3) yields a ¹⁴C age of 12,327+/-184 ka. We will use Cs-137 and Pb-210 dating to constrain the age of post-dam sediment in the upper portions of our cores and core samples will be analyzed for Hg and grain size. 30 probe-depth measurements were also collected from river and floodplain locations behind the dam. At each point, we measured depths of the first, second and third impenetrable sandy layer, which are hypothesized to reflect historic floods. Field data will be combined with a 2010 1m LIDAR DEM and air photos from 1934-present to analyze the extent of the upstream reservoir. Our objective is to use the cores, probe, LiDAR and sediment chemistry data to correlate layers and reconstruct the Hollenbeck Dam’s history of infilling associated with Anthropocene activities and land-use change.