EVALUATING POTENTIAL SOURCES OF MERCURY ACCUMULATION IN CAYUGA LAKE, NY (USA) OVER THE PAST TWO CENTURIES

The history of mercury (Hg) deposition in Cayuga Lake, NY was reconstructed using ²¹⁰Pb- and ¹³⁷Cs-dated sediment box cores to determine the relative contributions of local, regional, and global sources of Hg. Cayuga Lake, which is located in a rural, agriculturally dominated setting, has undergone significant changes in land use and point source discharges of Hg over the last two hundred years. The core site was selected due to its proximity to a local Hg emission source, a coal-fired electric generating station that has been in operation for more than 50 years. An 80-cm core was collected and subsampled every 1 cm. Samples were homogenized, freeze-dried, and analyzed for total Hg (THg) by thermal decomposition amalgamation and atomic absorption spectrophotometry using a Milestone DMA-80 direct mercury analyzer. THg fluxes (mg/m²y) were estimated by multiplying the average mercury concentration (ng/g) by the average sediment accumulation rate. The THg concentration in the core ranged from 43.0 to 179 ng/g. The concentration of THg gradually increased with decreasing sediment depth until 42 cm (~1920) where THg concentration then decreased upcore. A smaller, superimposed peak in THg occurred between 1940 and 1980, similar to THg records in other lakes within the Great Lakes airshed. THg concentrations are not correlated with organic matter or terrigenous content, suggesting that the major source of Hg contamination is not from the watershed but from atmospheric sources. The peak in THg predates the operation of the coal-fired electric generating station. During the late-1800s and early 1900s, the most likely sources of contamination appear to be from residential and commercial coal-burning stoves and then during the mid-late 1900s, electric utilities.