Mercury accumulation in foliage over time in two northern mixed-hardwood forests

Concentrations of mercury (Hg) in live foliage increased ten-fold from spring bud break (mean +/- std. dev. from both sites: 3.5 +/-1.3 ng g(-1)) to autumn litterfall (36 +/-8 ng g(-1)). Mercury in foliage did not behave similarly to eight other elements with known soil or aerosol sources (Aluminum (Al), Vanadium (V), Strontium (Sr), Rubidium (Rb), Copper (Cu), Zinc (Zn), Barium (Ba), and lead (Pb)), suggesting that Hg originated from a distinct pathway. Based on measured and modeled data, uptake of only 25% of the available ambient dry deposited Hg(0) could explain all of the Hg measured in foliage throughout the growing season. Estimates of gaseous elemental Hg (Hg(0)) uptake from soil water accounted for 3-14%% of the Hg in litterfall. Mercury deposition to forested sites in the Lake Champlain and Lake Huron basins was highest in litterfall (40%), followed by total throughfall (33%), and precipitation (27%). The Hg flux in litterfall was 15.8 +/-1.9 mug m(-2) yr(-1) to the Lake Champlain Watershed in 1995 and was 11.4 +/-2.8 mug m(-2) yr(-1) to the Lake Huron Watershed in 1996. In comparison, the Hg fluxes in precipitation and total throughfall were 9.0 +/-0.6 and 11.6 +/-0.7 mug m(-2) yr(-1) in the Lake Champlain Watershed (1995), and 8.7 +/-0.5 and 10.5 +/-1.0 mug m(-2) yr(-1) in the Lake Huron Watershed (1996).