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

Total atmospheric contribution of mercury (Hg-T) to lake sediment was estimated using Pb-210-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 Pb-210 correction factor to yield Hg-A,Hg-F. Time series maps of Hg-A,Hg-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,Hg-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 mu g/m(2) year. Maximum Hg-A,Hg-F ranged from 10.4 to 66.3 mu g/m(2) year. The timing of Hg-A,Hg-F declines in response to decreased atmospheric deposition may be controlled by in-lake and in-watershed storage and transport of Hg-bearing sediment.