Trace metals and radionuclides reveal sediment sources and accumulation rates in Jordan Cove, Connecticut

Many small estuaries are influenced by flow restrictions resulting from transportation rights-of-way and other causes. The biogeochemical functioning and history of such systems can be evaluated through study of their sediments. Ten long and six short cores were collected from the length of Jordan Cove, Connecticut, a Long Island Sound subestuary, and analyzed for stratigraphy, radionuclides (C-14, Pb-210, Ra-226, Cs-137, and Co-60), and metals (Ag, Cd, Cu, ph, Zn, Fe, and Al). For at least 3,800 yr, rising sea level has gradually inundated Jordan Cove, filling it with mud similar to that currently being deposited there. Long-term sediment accumulation in the cove averaged close to 0.1 cm yr(-1) over the last three millennia. Recent sediment accumulation rates decrease inland from 0.84 cm yr(-1) to 0.40 cm yr(-1), and are slightly faster than relative sea-level rise at this site (0.3 cm yr(-1)). Similarity of depth distributions of trace metals was used to confirm relative sediment accumulation rates. Co-60 and Ag are derived from sources outside the cove and its watershed, presumably the Millstone nuclear power plant and regional contaminated sediments, respectively. The combined data suggest that Long Island Sound is an important source of sediment to the cove; a minor part of total sediment is supplied from the local watershed. Trace metal levels are strongly correlated with Fe but not with either organic matter or Al. Sediment quality has declined in the cove over the past 60 yr, but only slightly. Cu, Pb, and Zn data correlate strongly with Fe but not with either organic matter or aluminum. Ratios of Ag to Fe and to trace metals suggest that Ag in the cove is derived almost entirely from Long Island Sound. This result supports the notion that Fe-normalized Ag can serve as a better tracer of some kinds of contamination than more common and abundant metals, like Cu, Pb, and Zn.