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Mercury isotopes in a forested ecosystem: Implications for air-surface exchange dynamics and the global mercury cycle

Global biogeochemical cycles, 2013-03, Vol.27 (1), p.222-238 [Peer Reviewed Journal]

2013. American Geophysical Union. All Rights Reserved. ;2014 INIST-CNRS ;ISSN: 0886-6236 ;EISSN: 1944-9224 ;DOI: 10.1002/gbc.20021 ;CODEN: GBCYEP

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  • Title:
    Mercury isotopes in a forested ecosystem: Implications for air-surface exchange dynamics and the global mercury cycle
  • Author: Demers, Jason D. ; Blum, Joel D. ; Zak, Donald R.
  • Subjects: Air-Surface Exchange ; Animal and plant ecology ; Animal, plant and microbial ecology ; Atmosphere ; Biological and medical sciences ; Earth sciences ; Earth, ocean, space ; Ecosystems ; Exact sciences and technology ; Forested Ecosystems ; Forests ; Fundamental and applied biological sciences. Psychology ; General aspects ; Geochemistry ; Isotopes ; Leaves ; Mercury Biogeochemistry ; Mercury Stable Isotopes ; Synecology
  • Is Part Of: Global biogeochemical cycles, 2013-03, Vol.27 (1), p.222-238
  • Description: Forests mediate the biogeochemical cycling of mercury (Hg) between the atmosphere and terrestrial ecosystems; however, there remain many gaps in our understanding of these processes. Our objectives in this study were to characterize Hg isotopic composition within forests, and use natural abundance stable Hg isotopes to track sources and reveal mechanisms underlying the cycling of Hg. We quantified the stable Hg isotopic composition of foliage, forest floor, mineral soil, precipitation, and total gaseous mercury (THg(g)) in the atmosphere and in evasion from soil, in 10‐year‐old aspen forests at the Rhinelander FACE experiment in northeastern Wisconsin, USA. The effect of increased atmospheric CO2 and O3 concentrations on Hg isotopic composition was small relative to differences among forest ecosystem components. Precipitation samples had δ202Hg values of −0.74 to 0.06‰ and ∆199Hg values of 0.16 to 0.82‰. Atmospheric THg(g) had δ202Hg values of 0.48 to 0.93‰ and ∆199Hg values of −0.21 to −0.15‰. Uptake of THg(g) by foliage resulted in a large (−2.89‰) shift in δ202Hg values; foliage displayed δ202Hg values of −2.53 to −1.89‰ and ∆199Hg values of −0.37 to −0.23‰. Forest floor samples had δ202Hg values of −1.88 to −1.22‰ and ∆199Hg values of −0.22 to −0.14‰. Mercury isotopes distinguished geogenic sources of Hg and atmospheric derived sources of Hg in soil, and showed that precipitation Hg only accounted for ~16% of atmospheric Hg inputs. The isotopic composition of Hg evasion from the forest floor was similar to atmospheric THg(g); however, there were systematic differences in δ202Hg values and MIF of even isotopes (∆200Hg and ∆204Hg). Mercury evasion from the forest floor may have arisen from air‐surface exchange of atmospheric THg(g), but was not the emission of legacy Hg from soils, nor re‐emission of wet‐deposition. This implies that there was net atmospheric THg(g) deposition to the forest soils. Furthermore, MDF of Hg isotopes during foliar uptake and air‐surface exchange of atmospheric THg(g) resulted in the release of Hg with very positive δ202Hg values to the atmosphere, which is key information for modeling the isotopic balance of the global mercury cycle, and may indicate a shorter residence time than previously recognized for the atmospheric mercury pool. Key pointsAtmospheric Hg was fractionated during uptake by foliage (‐2.89 permil δ202Hg)Hg evading from soil was from atmospheric Hg interaction with soil environmentAir‐surface exchange of Hg releases Hg with positive δ202Hg to global reservoir
  • Publisher: Washington, DC: Blackwell Publishing Ltd
  • Language: English
  • Identifier: ISSN: 0886-6236
    EISSN: 1944-9224
    DOI: 10.1002/gbc.20021
    CODEN: GBCYEP
  • Source: Wiley Blackwell AGU Digital Library
    Alma/SFX Local Collection
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