Application of Controlled Mesocosms for Understanding Mercury Air−Soil−Plant Exchange

Ms, Gustin; Ja, Ericksen; De, Schorran; Dw, Johnson; Se, Lindberg; Js, Coleman

doi:10.1021/es0487933

Cited by 81 publications

(60 citation statements)

References 31 publications

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“…Friedli et al (2009) estimate larger biomass burning emissions of 675 ± 240 Mg a −1 based on satellite-derived fire area and biome-specific emission factors, but our results here are not sensitive to this difference because these emissions are relatively small in any case. The model no longer includes emissions through plant transpiration because of field evidence that this process is unimportant (Gustin et al, 2004).…”

Section: Emissionsmentioning

confidence: 99%

Global atmospheric model for mercury including oxidation by bromine atoms

et al. 2010

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Abstract. Global models of atmospheric mercury generally assume that gas-phase OH and ozone are the main oxidants converting Hg 0 to Hg II and thus driving mercury deposition to ecosystems. However, thermodynamic considerations argue against the importance of these reactions. We demonstrate here the viability of atomic bromine (Br) as an alternative Hg 0 oxidant. We conduct a global 3-D simulation with the GEOS-Chem model assuming gas-phase Br to be the sole Hg 0 oxidant (Hg + Br model) and compare to the previous version of the model with OH and ozone as the sole oxidants (Hg + OH/O 3 model). We specify global 3-D Br concentration fields based on our best understanding of tropospheric and stratospheric Br chemistry. In both the Hg + Br and Hg + OH/O 3 models, we add an aqueous photochemical reduction of Hg II in cloud to impose a tropospheric lifetime for mercury of 6.5 months against deposition, as needed to reconcile observed total gaseous mercury (TGM) concentrations with current estimates of anthropogenic emissions. This added reduction would not be necessary in the Hg + Br model if we adjusted the Br oxidation kinetics downward within their range of uncertainty. We find that the Hg + Br and Hg + OH/O 3 models are equally capable of reproducing the spatial distribution of TGM and its seasonal cycle at northern mid-latitudes. The Hg + Br model shows a steeper decline of TGM concentrations from the tropics to southern mid-latitudes. Only the Hg + Br model can reproduce the springtime depletion and summer rebound of TGM observed at polar sites; the snowpack component of GEOS-Chem suggests that 40% of Hg II deposited to snow in the Arctic is transferred to the ocean and land reservoirs, amounting to aCorrespondence to: C. D. Holmes (cdholmes@post.harvard.edu) net deposition flux to the Arctic of 60 Mg a −1 . Summertime events of depleted Hg 0 at Antarctic sites due to subsidence are much better simulated by the Hg + Br model. Model comparisons to observed wet deposition fluxes of mercury in the US and Europe show general consistency. However the Hg + Br model does not capture the summer maximum over the southeast US because of low subtropical Br concentrations while the Hg + OH/O 3 model does. Vertical profiles measured from aircraft show a decline of Hg 0 above the tropopause that can be captured by both the Hg + Br and Hg + OH/O 3 models, except in Arctic spring where the observed decline is much steeper than simulated by either model; we speculate that oxidation by Cl species might be responsible. The Hg + Br and Hg + OH/O 3 models yield similar global budgets for the cycling of mercury between the atmosphere and surface reservoirs, but the Hg + Br model results in a much larger fraction of mercury deposited to the Southern Hemisphere oceans.

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Section: Emissionsmentioning

confidence: 99%

Global atmospheric model for mercury including oxidation by bromine atoms

et al. 2010

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“…The temporal variation of vegetation growth plays an important role in the forest GEM emission because of the vital function of vegetation to Hg cycle in forest ecosystem through changing environmental variables at ground surfaces (e.g., reducing solar radiation, temperature and friction velocity) (Gustin et al, 2004) and providing active surfaces for Hg uptake. Recent measurements have suggested that airsurface exchange of GEM is largely bidirectional between air and plant, and that growing plants act as a net sink (Ericksen et al, 2003;Stamenkovic et al, 2008;Hartman et al, 2009).…”

Section: Factors Influencing Gem Fluxmentioning

confidence: 99%

Gaseous elemental mercury (GEM) fluxes over canopy of two typical subtropical forests in south China

Luo

Wang

et al. 2018

Atmos. Chem. Phys.

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Abstract. Mercury (Hg) exchange between forests and the atmosphere plays an important role in global Hg cycling. The present estimate of global emission of Hg from natural source has large uncertainty, partly due to the lack of chronical and valid field data, particularly for terrestrial surfaces in China, the most important contributor to global atmospheric Hg. In this study, the micrometeorological method (MM) was used to continuously observe gaseous elemental mercury (GEM) fluxes over forest canopy at a mildly polluted site (Qianyanzhou, QYZ) and a moderately polluted site (Huitong, HT, near a large Hg mine) in subtropical south China for a full year from January to December in 2014. The GEM flux measurements over forest canopy in QYZ and HT showed net emission with annual average values of 6.67 and 0.30 ng m −2 h −1 , respectively. Daily variations of GEM fluxes showed an increasing emission with the increasing air temperature and solar radiation in the daytime to a peak at 13:00, and decreasing emission thereafter, even as a GEM sink or balance at night. High temperature and low air Hg concentration resulted in the high Hg emission in summer. Low temperature in winter and Hg absorption by plant in spring resulted in low Hg emission, or even adsorption in the two seasons. GEM fluxes were positively correlated with air temperature, soil temperature, wind speed, and solar radiation, while it is negatively correlated with air humidity and atmospheric GEM concentration. The lower emission fluxes of GEM at the moderately polluted site (HT) when compared with that in the mildly polluted site (QYZ) may result from a much higher adsorption fluxes at night in spite of a similar or higher emission fluxes during daytime. This shows that the higher atmospheric GEM concentration at HT restricted the forest GEM emission. Great attention should be paid to forests as a crucial increasing Hg emission source with the decreasing atmospheric GEM concentration in polluted areas because of Hg emission abatement in the future.

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“…However, recent data have shown that Hg(0) fluxes from contaminated soils to the atmosphere are not related to the movement of Hg(0) in the transpiration stream (Greger et al, 2005), but rather to processes happening on the soil surface such as incident light, watering, and surface soil temperature and moisture content (Gustin et al, 2004). Comparison of the Hg(0) flux from unplanted and planted substrates using gasexchange mesocosmos have indicated reduced Hg(0) emissions from planted substrates in the presence of incident light (Gustin et al, 2004). The authors attributed this reduced effect to soil shading of the leaf canopy.…”

Section: Origin Of Plant-hg Emissions From Contaminated Substratesmentioning

confidence: 99%

Effect of Thioligands on Plant-Hg Accumulation and Volatilisation from Mercury-contaminated Mine Tailings

et al. 2005

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This study investigated the effect of thioligands on mercury (Hg) volatilisation and plant accumulation for Brassica juncea plants grown in mine tailings collected from artisanal gold mines in Brazil (the Serra Pelada mine) and China (the Gold Mountain mine). Plants were treated with either (NH 4 ) 2 S 2 O 3 or NH 4 SCN and enclosed in gas-tight volatilisation chambers. Elemental Hg released from substrates was captured in a two-trap system containing 5% KMnO 4 dissolved in 2N H 2 SO 4 . Mercury accumulation was enhanced in the presence of (NH 4 ) 2 S 2 O 3 for plants grown in GM tailings. There was no significant increase in the plant-Hg accumulation after application of NH 4 SCN to the SP tailings. Volatilisation from planted substrates was not affected by the application of thioligands to either GM or SP mine tailings. Mercury volatilisation from planted substrates was significantly higher than from control substrates. Abiotic (photoreduction) and biotic (microbial interactions) factors might be linked to the enhanced plant effect on Hg volatilisation. There was no significant correlation for the Hg mass released from substrates and the amount of Hg uptake by roots and translocated to shoots. Our results indicate that volatilisation and plant-Hg accumulation are two independent processes. Thiosulphate-induced plant-Hg accumulation may be a potential tool for the phytoextraction of Hg contaminated soils but there are risks of groundwater contamination by Hg-containing leachates.

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Application of Controlled Mesocosms for Understanding Mercury Air−Soil−Plant Exchange

Cited by 81 publications

References 31 publications

Global atmospheric model for mercury including oxidation by bromine atoms

Global atmospheric model for mercury including oxidation by bromine atoms

Gaseous elemental mercury (GEM) fluxes over canopy of two typical subtropical forests in south China

Effect of Thioligands on Plant-Hg Accumulation and Volatilisation from Mercury-contaminated Mine Tailings

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