HISTORIC MERCURY DEPOSITION IN TWO NEW YORK FINGER LAKES

Previous studies of mercury (Hg) fluxes to many lakes in the Northern Hemisphere document a peak in Hg accumulation during the mid- to late 20^th century and decline in recent decades. Here, we reconstructed historical Hg accumulation to the profundal sediment of Seneca Lake and Owasco Lake, two New York Finger Lakes, using ²¹⁰Pb dated box cores. In Seneca Lake, total Hg (HgT) fluxes were low (197 μgm-2y-1) in 1770, peaked between 1890 and 1910 (583 μgm-2y-1) and gradually returned to background levels (127 μgm-2y-1) by 1977. HgT fluxes in Owasco Lake were lowest in 1919 (606 μgm-2y-1), peaked between 1967 and 1972 (828 μgm-2y-1) and declined to almost 1919 levels (629 μgm-2y-1) by 2008. While trends in Hg accumulation in Owasco Lake are similar to many other Finger Lakes and Great Lakes, the HgT peak recorded by Seneca Lake sediments predates those observed in local and regional lakes by approximately 60 years. Both the timing and magnitude of change in the sediment record suggest that point sources, not atmospheric deposition, was responsible for the pre-20^th century HgT peak in Seneca Lake and large subsequent declines. Pre-20^th century industry, including tanneries, hatteries, and paper mills, along a major inlet are possible sources of Hg in the lake sediment. In contrast, the record from Owasco Lake indicates primarily an atmospheric signal resulting from Hg emissions in the Great Lakes region. In both lakes, the HgT fluxes show episodic accumulation events superimposed on a more general, long-term trend. Hg stored in legacy sediment that accumulated over decades of anthropogenic deposition behind mill dams was released episodically to streams during major storm events. For example, the HgT flux increased significantly in both lakes as a result of Hurricane Agnes in 1972. Historic local and regional sources of Hg still play an important role in observed HgT concentrations in the lake sediment.