Historical and present fluxes of mercury to Vermont and New Hampshire lakes inferred from 210Pb dated sediment cores

Lakes across the Northern Hemisphere have experienced enhanced atmospheric deposition of anthropogenically derived Hg for over 100 years. In the present study, we quantified Hg fluxes to the sediments of ten small drainage lakes across Vermont and New Hampshire, USA, for the period 1800 to present. Dates were established by 210Pb. Total Hg (HgT) fluxes to sediments ranged from 5 to 17 μg m−2 yr−1 during pre-industrial times, and from 21 to 83 μg m−2 yr−1 presently. Present-day HgT fluxes are between 2.1 to 6.9 times greater than pre-1850 fluxes. Current-day direct atmospheric Hg deposition to the study region was estimated at 21 μg m−2 yr−1, which agrees well with measured HgT deposition, when re-evasion of Hg is accounted for. Our data suggest that Hg fluxes to lake sediments have declined in recent decades, owing to reductions in atmospheric Hg deposition to the lake surface. Watershed export of atmospherically deposited Hg remains elevated relative to present-day deposition rates, which contributes to the impression that Hg retention by watershed soils has declined.