Deconstruction of historic mercury accumulation in lake sediments, northeastern United States

Total atmospheric contribution of mercury (Hg_T) 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 Hg_T. Factors addressed include: lake-specific background accumulation rates of Hg (Hg_B), variability of sediment accumulation rates that caused variation in Hg accumulation during the last 100-150 years (Hg_V), and variable flux of anthropogenic Hg from the atmosphere (Hg_A). These fluxes were normalized for sediment focusing using a regional, unsupported ²¹⁰Pb correction factor to yield Hg_A,F. Time series maps of Hg_A,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. Hg_A,F started to increase near the end of the 19th century to a maximum between 1970 and 1990, depending on the lake. Maximum Hg_T across the region ranges from 27.1 to 175 μg/m² year. Maximum Hg_A,F ranged from 10.4 to 66.3 μg/m² year. The timing of Hg_A,F declines in response to decreased atmospheric deposition may be controlled by in-lake and in-watershed storage and transport of Hg-bearing sediment.