ANALYSIS OF ANTHROPOGENIC HEAVY METALS IN HISTORIC MILL DAM SEDIMENTS: A CASE STUDY FROM MILL BROOK, COVENTRY, CONNECTICUT (USA)

Reservoirs behind historic mill dams can store legacy sediment and record increased concentrations of heavy metals associated with late 19th to early 20th century industrial activity. The northeast U.S. has a well-documented history of land use changes including mill dam construction for industrial activity along rivers during the 18-20th centuries. In this study, we present an analysis of sediment cores taken from a wetland along Mill Brook in Coventry, Connecticut (~13.6 km2) that was formerly a reservoir behind a historic dam built ca. 1809 to reconstruct anthropogenic sedimentation at the site. In the 1800s, the channel upstream was populated with ~15 mills for industries including paper, hatting, ammunition, and lumber production. Historic maps and aerial imagery show a reservoir at the site from the 19th century until 2021, when heavy storms destroyed the dam; the reservoir area now has a small channel flowing through the wetland. Three vibracores were collected in a transect along the length of the former reservoir, each getting deep enough to include gravel and sand layers assumed to be associated with the stream sediment and floodplain that predated the dam. Loss on ignition (LOI), portable X-ray fluorescence (pXRF), radiocarbon dating, and grain size analyses were performed on core subsamples to better understand sedimentation and geochemistry expressed in the cores. High concentrations of Pb, As, Hg, Zn, and Cu were detected using pXRF and peak near the surface (0-80 cm) within each core, serving as a record of industrial activity within the reservoir sediment. A radiocarbon date obtained below the interpreted reservoir sediment and former channel bed provides a calibrated age of 880 cal yrs BP. High concentrations of heavy metals in our cores show that historic land use is directly tied to contamination of the sediments, and recent breaching of the dam may have released highly contaminated sediments downstream. These findings have implications for sediment release associated with dam removal or future restoration at this site.