Depletion of atmospheric gaseous elemental mercury by plant uptake at Mt. Changbai, Northeast China

Abstract

There exists observational evidence that gaseous elemental mercury (GEM) can be readily removed from the atmosphere via chemical oxidation followed by deposition in the polar and sub-polar regions, free troposphere, lower stratosphere, and marine boundary layer under specific environmental conditions. Here we report GEM depletions in a temperate mixed forest at Mt. Changbai, Northeast China. The strong depletions occurred predominantly at night during the leaf-growing season and in the absence of gaseous oxidized mercury (GOM) enrichment (GOM ĝ€‰ (deciduous tree species) and 0.1 ± 0.2 ng m2 h-1 over Pinus Koraiensis (evergreen tree species). Daily integrated GEM δ 202Hg, Δ199Hg, and Δ200Hg at Mt. Changbai during 8-18 July 2013 ranged from 0.34 to 0.91 ĝ€°, from 0.11 to 0.04 ĝ€° and from 0.06 to 0.01 ĝ€°, respectively. A large positive shift in GEM δ 202Hg occurred during the strong GEM depletion events, whereas Δ199Hg and Δ200Hg remained essentially unchanged. The observational findings and box model results show that uptake of GEM by forest canopy plays a predominant role in the GEM depletion at Mt. Changbai forest. Such depletion events of GEM are likely to be a widespread phenomenon, suggesting that the forest ecosystem represents one of the largest sinks (∼ 1930 Mg) of atmospheric Hg on a global scale.