Stable Isotope Evidence Shows Re-emission of Elemental Mercury Vapor Occurring after Reductive Loss from Foliage

Yuan, Wei; Sommar, Jonas; Lin, Che‐Jen; Wang, Xun; Li, Kai; Liu, Yi; Zhang, Hui; Lü, Zifeng; Wu, Chuansheng; Feng, Xinbin

doi:10.1021/acs.est.8b04865

Cited by 126 publications

(230 citation statements)

References 54 publications

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“…This discrepancy can be explained by the fact that δ 202 Hg signatures measured in vegetation not only reflect the isotopic fractionation during foliar uptake, but also contain a re-emission component. Hg(II) reduction is expected to lead to more positive δ 202 Hg values in the residual, foliar Hg(II) fraction, irrespective of the reduction mechanism (Bergquist and Blum, 2007;Zheng and Hintelmann, 2010;Kritee et al, 2007;Jiskra et al, 2015). Re-emission of foliar Hg is supported by the observed negative shifts in odd-mass isotope MIF ( 199 Hg) in vegetation relative to 199 Hg of atmospheric Hg(0), which have been observed at Toolik Field Station (Olson et al, 2019) and elsewhere (Enrico et al, 2016;Demers et al, 2013).…”

Section: Hg Isotope Fractionation During Foliar Uptake Ofmentioning

confidence: 80%

Insights from mercury stable isotopes on terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra

et al. 2019

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Abstract. The tundra plays a pivotal role in the Arctic mercury (Hg) cycle by storing atmospheric Hg deposition and shuttling it to the Arctic Ocean. A recent study revealed that 70 % of the atmospheric Hg deposition to the tundra occurs through gaseous elemental mercury (GEM or Hg(0)) uptake by vegetation and soils. Processes controlling land–atmosphere exchange of Hg(0) in the Arctic tundra are central, but remain understudied. Here, we combine Hg stable isotope analysis of Hg(0) in the atmosphere, interstitial snow air, and soil pore air, with Hg(0) flux measurements in a tundra ecosystem at Toolik Field Station in northern Alaska (USA). In the dark winter months, planetary boundary layer (PBL) conditions and Hg(0) concentrations were generally stable throughout the day and small Hg(0) net deposition occurred. In spring, halogen-induced atmospheric mercury depletion events (AMDEs) occurred, with the fast re-emission of Hg(0) after AMDEs resulting in net emission fluxes of Hg(0). During the short snow-free growing season in summer, vegetation uptake of atmospheric Hg(0) enhanced atmospheric Hg(0) net deposition to the Arctic tundra. At night, when PBL conditions were stable, ecosystem uptake of atmospheric Hg(0) led to a depletion of atmospheric Hg(0). The night-time decline of atmospheric Hg(0) was concomitant with a depletion of lighter Hg(0) isotopes in the atmospheric Hg pool. The enrichment factor, ε202Hgvegetationuptake=-4.2 ‰ (±1.0 ‰) was consistent with the preferential uptake of light Hg(0) isotopes by vegetation. Hg(0) flux measurements indicated a partial re-emission of Hg(0) during daytime, when solar radiation was strongest. Hg(0) concentrations in soil pore air were depleted relative to atmospheric Hg(0) concentrations, concomitant with an enrichment of lighter Hg(0) isotopes in the soil pore air, ε202Hgsoilair-atmosphere=-1.00 ‰ (±0.25 ‰) and E199Hgsoilair-atmosphere=0.07 ‰ (±0.04 ‰). These first Hg stable isotope measurements of Hg(0) in soil pore air are consistent with the fractionation previously observed during Hg(0) oxidation by natural humic acids, suggesting abiotic oxidation as a cause for observed soil Hg(0) uptake. The combination of Hg stable isotope fingerprints with Hg(0) flux measurements and PBL stability assessment confirmed a dominant role of Hg(0) uptake by vegetation in the terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra.

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Section: Hg Isotope Fractionation During Foliar Uptake Ofmentioning

confidence: 80%

Insights from mercury stable isotopes on terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra

et al. 2019

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“…In a recent study that employed stable Hg isotopes to measure exchange uxes for the rst time, the potential re-emission ux of Hg 0 from leaves was measured to be 30% in a forest canopy. 48 However, that study also reported a large uncertainty range (29-83%). Because of the current uncertainty in the re-emission ux and its temporal variation, we did not implement an immediate re-emission ux of Hg 0 from canopies in our model evaluation.…”

Section: Modeling Re-emission Of Hgmentioning

confidence: 87%

“…Second, the modeled daytime Hg 0 uptake needs to be reduced substantially, because daytime deposition is over-predicted in the modeled F net by a factor of up to 5 (summer at the grassland site). This adjustment can be implemented either by increasing the stomatal resistance R st term in eqn (2) or by application of a Hg 0 re-emission factor of stomatal Hg 0 uptake, as suggested by Yuan et al 48 We selected the rst option, although both methods would lead to similar reductions in stomatal Hg 0 uptake. Third, further improvement in model vs. measurement agreement can be reached by adjusting the soil Hg 0 re-emission scheme.…”

Section: Model Response To Adjusted Deposition Parameterization In Sumentioning

confidence: 99%

Atmosphere-terrestrial exchange of gaseous elemental mercury: parameterization improvement through direct comparison with measured ecosystem fluxes

Khan

Obrist

Agnan

et al. 2019

Environ. Sci.: Processes Impacts

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“…In this study, NEE of Hg 0 and CO 2 was measured concurrently with two independent EC systems over the intensively managed grassland used for forage production. Details on grassland species composition, harvest, and fertilization practices are described in Zeeman et al (2010), Merbold et al (2014) and Fuchs et al (2018). The tower for long-term EC greenhouse gas measurements was located between two adjacent grassland parcels (Fig.…”

Section: Site Description and Instrumentationmentioning

confidence: 99%

“…From the 20 Hz IRGA measurements, 30 min flux averages were calculated using the LI-COR EddyPro ® software. The 30 min CO 2 flux has been recorded continuously since 2005 (Eugster and Zeeman, 2006;Zeeman et al, 2010). The measured meteorological variables included temperature and relative humidity (Hygroclip S3 sensor, Rotronic AG, Switzerland), net allwave radiation (CNR 1, Kipp & Zonen B.V., Delft, Netherlands), incoming and reflected photosynthetic active radiation (PAR lite, Kipp & Zonen B.V., Delft, Netherlands), and precipitation (height of 0.5 m; tipping bucket rain gauge from LAMBRECHT meteo GmbH, Göttingen, Germany).…”

Section: Site Description and Instrumentationmentioning

confidence: 99%

Eddy covariance flux measurements of gaseous elemental mercury over a grassland

et al. 2020

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Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg 0 ) are important to improve our understanding of global Hg cycling and, ultimately, human and wildlife Hg exposure. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg 0 flux estimates. It currently remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg 0 . Here, we show a detailed validation of direct Hg 0 flux measurements based on the eddy covariance technique (Eddy Mercury) using a Lumex RA-915 AM mercury monitor. The flux detection limit derived from a zero-flux experiment in the laboratory was 0.22 ng m −2 h −1 (maximum) with a 50 % cutoff at 0.074 ng m −2 h −1 . We present eddy covariance NEE measurements of Hg 0 over a low-Hg soil (41-75 ng Hg g −1 in the topsoil, referring to a depth of 0-10 cm), conducted in summer 2018 at a managed grassland at the Swiss FluxNet site in Chamau, Switzerland (CH-Cha). The statistical estimate of the Hg 0 flux detection limit under outdoor conditions at the site was 5.9 ng m −2 h −1 (50 % cutoff). We measured a net summertime emission over a period of 34 d with a median Hg 0 flux of 2.5 ng m −2 h −1 (with a −0.6 to 7.4 ng m −2 h −1 range between the 25th and 75th percentiles). We observed a distinct diel cycle with higher median daytime fluxes (8.4 ng m −2 h −1 ) than nighttime fluxes (1.0 ng m −2 h −1 ). Drought stress during the measurement campaign in summer 2018 induced partial stomata closure of vegetation. Partial stomata closure led to a midday depression in CO 2 uptake, which did not recover during the afternoon. The median CO 2 flux was only 24 % of the median CO 2 flux measured during the same period in the previous year (2017). We suggest that partial stomata closure also dampened Hg 0 uptake by vegetation, resulting in a NEE of Hg 0 that was dominated by soil emission. Finally, we provide suggestions to further improve the precision and handling of the "Eddy Mercury" system in order to assure its suitability for long-term NEE measurements of Hg 0 over natural background surfaces with low soil Hg concentrations (< 100 ng g −1 ). With these improvements, Eddy Mercury has the potential to be integrated into global networks of micrometeorological tower sites (FluxNet) and to provide the longterm observations on terrestrial atmosphere Hg 0 exchange necessary to validate regional and global mercury models.

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Stable Isotope Evidence Shows Re-emission of Elemental Mercury Vapor Occurring after Reductive Loss from Foliage

Cited by 126 publications

References 54 publications

Insights from mercury stable isotopes on terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra

Insights from mercury stable isotopes on terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra

Atmosphere-terrestrial exchange of gaseous elemental mercury: parameterization improvement through direct comparison with measured ecosystem fluxes

Eddy covariance flux measurements of gaseous elemental mercury over a grassland

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