Stable lead isotopes, contaminant metals and radionuclides in upper Hudson River sediment cores: implications for improved time stratigraphy and transport processes

Abstract

Radionuclide, stable lead isotope and trace metal analyses on fine-grained sediment cores collected along a 24-mile reach of the upper Hudson River were used to establish temporal trends of contaminant loadings, to establish stable lead isotopes as an additional stratigraphic tool, and as tracers for resolving particle transport fluxes over periods of decades. Very large contaminant inputs of Cd, Sb, Pb and Cr were evident in the sediment record. One potential large source for these metals was from a pigment manufacturing facility in Glens Falls, NY. The total range in stable lead isotope ratios observed in well-dated cores from about 15 miles downstream of the potential metal inputs was large (e.g., maximum difference in 206Pb/ 207Pb is 10%) and characterized by four major shifts occurring in the 1950s, 1960s, 1970s and 1980s. The temporal trend in 206Pb/ 207Pb has been used to establish precise dating of a sediment core from 24 miles further downstream. The large magnitude and abrupt shifts in stable lead isotope ratios preserved in upper Hudson sediment cores provide a way to significantly improve dating models, based only on radionuclide analyses. Cadmium, lead and antimony were identified as quite sensitive tracers of upper Hudson sediments due to the magnitude of contamination and the lack of significant additional downstream sources of these contaminant metals. Metal measurements in a pair of sediment cores located 24 miles apart were used to constrain relative fluxes of sediment entering the river between the two coring locations, with sediment sections deposited between the early 1960s and the late 1970s in these two cores suggesting that 3–4 times more sediment entered the river between the two coring sites than was transported from upstream. These dilution factors agree very well with estimates based on suspended sediment measurements during a flood event in April 1994 and with estimates based on mechanistic model of suspended sediment transport between 1977 and 1992.