Mercury Accumulation in Foliage over Time in Two Northern Mixed-Hardwood Forests

Abstract

Concentrations of mercury (Hg) in live foliage increased ten-fold from spring bud break (mean ± std. dev. from bothsites: 3.5±1.3 ng g -1 ) to autumn litterfall(36±8 ng g -1 ). Mercury in foliage did not behavesimilarly to eight other elements with known soil or aerosolsources (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 onmeasured and modeled data, uptake of only 25% of the availableambient dry deposited Hg 0 could explain all of the Hgmeasured in foliage throughout the growing season. Estimates ofgaseous elemental Hg (Hg 0 ) uptake from soil water accountedfor 3–14%% of the Hg in litterfall. Mercury deposition toforested sites in the Lake Champlain and Lake Huron basins washighest in litterfall (40%), followed by total throughfall(33%), and precipitation (27%). The Hg flux in litterfall was15.8±1.9~μg m -2 yr -1 to the Lake ChamplainWatershed in 1995 and was 11.4±2.8~μg 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~μg m -2 yr -1 in the Lake Champlain Watershed (1995), and 8.7±0.5 and 10.5±1.0~μg m -2 yr -1 in the Lake Huron Watershed (1996).