Deconstruction of Historic Mercury Accumulation in Lake Sediments, Northeastern United States
Total atmospheric contribution of mercury (HgT) to lake sediment was estimated using 210Pb-dated sediment cores. Algorithms based on estimates of lake and watershed processes were applied to more accurately assess anthropogenic contributions of Hg to the environment and HgT. Factors addressed include: lake-specific background accumulation rates of Hg (HgB), variability of sediment accumulation rates that caused variation in Hg accumulation during the last 100–150 years (HgV), and variable flux of anthropogenic Hg from the atmosphere (HgA). These fluxes were normalized for sediment focusing using a regional, unsupported 210Pb correction factor to yield HgA,F. Time series maps of HgA,F allow for comparison across time and space, and are provided for 1900, 1950, 1975 and 1990 across eastern New York and New England, USA. Deconstruction algorithms reduce inter-/intra-lake variability in Hg accumulation rates and improve temporal coherence. HgA,F started to increase near the end of the 19th century to a maximum between 1970 and 1990, depending on the lake. Maximum HgT across the region ranges from 27.1 to 175 g/m2 year. Maximum HgA,F ranged from 10.4 to 66.3 g/m2 year. The timing of HgA,F declines in response to decreased atmospheric deposition may be controlled by in-lake and in-watershed storage and transport of Hg-bearing sediment.