Depletion of atmospheric gaseous elemental mercury by plant uptake at

Abstract

There exists observational evidence that GEM can be readily removed from the 13 atmosphere via chemical oxidation followed by deposition in the polar and sub-polar regions, 14 free troposphere, lower stratosphere, and marine boundary layer under specific environmental 15 conditions. Here we report GEM depletions in a temperate mixed forest at Mt. Changbai, 16 Northeast China. The depletion occurred exclusively at night during leaf-growing season and in 17 the absence of GOM enrichment (GOM < 3 pg m -3). Vertical gradients of decreasing GEM 18 concentrations from layers above to under forest canopy suggest in situ loss of GEM to forest 19 canopy at Mt. Changbai. Foliar GEM flux measurements showed that the foliage of two 20 predominant tree species is a net sink of GEM at night, with a mean deposition flux of -1.8 ± 0.3 21 ng m 2 h -1 over Fraxinus mandshurica (deciduous tree species) and -0.1 ± 0.2 ng m 2 h -1 over 22 Pinus Koraiensis (evergreen tree species). Daily integrated GEM δ 202 Hg, Δ 199 Hg, and Δ 200 Hg at 23 Mt. Changbai ranged from -0.34 to 0.91‰, from -0.11 to -0.04‰ and from -0.06 to 0.01‰, 24 respectively. A large positive shift of GEM δ 202 Hg occurred during the GEM depletion events, 25 whereas Δ 199 Hg and Δ 200 Hg remained essentially unchanged. The observational findings and box 26 model results show that uptake of GEM by forest canopy plays a predominant role in the GEM 27 depletion at Mt. Changbai forest. Such depletion events of GEM are likely to be a widespread 28 phenomenon, suggesting that the forest ecosystem represents one of the largest sinks (~1930 Mg) 29 of atmospheric Hg at global scale. 30 31 32 Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-391, 2016 Manuscript under review for journal Atmos. Chem. Phys. Published: 1 July 2016 c Author(s) 2016. CC-BY 3.0 License.