LONG-TERM MERCURY DYNAMICS IN A LAKE-WATERSHED IN THE ADIRONDACK REGION OF NEW YORK STATE

Though there has been a significant decline in US mercury emissions, wet deposition of mercury in the Adirondack Park of New York State has remained relatively constant while fish mercury concentrations have exhibited mixed effects. We examined long-term trends and seasonal patterns of methylmercury, total mercury, and dissolved organic carbon concentrations and fluxes in the Arbutus Lake watershed and the lake in the Adirondacks from 2004 to 2014 to better understand watershed and lake mercury dynamics. Total mercury deposition has decreased over the study, due to decreases in litter mercury inputs (17.9 μg/ m²-yr in 2004,10.8 μg/ m²-yr in 2014). Seasonal patterns in dissolved organic carbon, methylmercury, and total mercury were observed, with higher values found in the warmer summer months. Watershed areal total mercury flux inputs were 6.9 μg/ m²-yr, and the outlet flux was 2.7 μg/ m²-yr at the outlet; watershed areal methylmercury flux inputs were 0.13 μg/ m²-yr, and the outlet flux was 0.05 μg/ m²-yr; watershed areal dissolved organic carbon flux inputs were 1.01 g/m²-yr at the inlet, and the outlet flux was 0.76 g/m²-yr. The lake was found to be a net sink, with retentions of 61% for total mercury, 64% for methylmercury, and 24% for dissolved organic carbon. Total mercury and methylmercury fluxes were found to decrease over time, while dissolved organic carbon flux increased over time; concurrently, total mercury/dissolved organic carbon ratios at the outlet and methylmercury/dissolved organic carbon ratios at the inlet and outlet decreased over time, suggesting that decreases in atmospheric mercury deposition drive decreases in stream and lake total mercury and methylmercury concentrations and fluxes.