Atmospheric mercury deposition to sediments of New Jersey and southern New York state: Interpretations from dated sediment cores

Analyses of radionuclide-dated sediment samples from coring sites were used to derive geographical and temporal trends for mercury and other trace metal inputs to sediments of New Jersey and southern New York. Sediment cores were collected at six sites throughout New Jersey and one site in southern New York in order to characterize regional atmospheric mercury deposition to the area. The timing of deposition was established through analysis of Cs-137 and Pb-210 activity with depth in the cores. Sediment focusing was accounted for by normalizing Hg fluxes to the whole core inventories of these nuclides.; Peak calculated mercury fluxes occurred several decades ago, between the 1930s and 1960s at all of the sites. All sites also show a steady decline in fluxes from periods of peak deposition through recent years. Fluxes varied considerably among sites. At Wawayanda Lake in north central New Jersey, the average yearly Hg flux calculated over the past half-century was 25 μg/m 2/yr, about twice that reported for remote regions. At Woodcliff Lake in northeastern New Jersey, the average flux (1700 μg/m2/yr) was about seventy times larger. Similar elevated Hg fluxes (1500 μg/m 2/yr) have been observed at Central Park Lake in Manhattan, NY. Woodcliff Lake soil data suggests some level of enhanced atmospheric Hg deposition, but doesn't eliminate the possibility of significant non-atmospheric Hg. Further study is in progress to determine the possibility of a significant “localized northeastern NJ” Hg atmospheric deposition signal. At the other four sites, average Hg fluxes ranged from about 50 to 250 μg/m2/yr, comparable to those reported for atmospheric deposition to the Great Lakes, and indicative of a broad regional industrial signal. Deposition rates of other trace metals (Pb, Zn, Cu and others) generally decreased with distance away from the population and industrialization of the New York City Metropolitan area. Modeling of core Cs-137 profiles for drainage basin holdup and post-depositional mixing is proposed as a useful constraint on the flux estimates provided by sediment core analysis.