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Significant Seasonal Variations in Isotopic Composition of Atmospheric Total Gaseous Mercury at Forest Sites in China Caused by Vegetation and Mercury Sources.

07:00 EST 13th November 2019 | BioPortfolio

Summary of "Significant Seasonal Variations in Isotopic Composition of Atmospheric Total Gaseous Mercury at Forest Sites in China Caused by Vegetation and Mercury Sources."

In this study, isotopic compositions of atmospheric total gaseous mercury (TGM) were measured in the Mt. Changbai (MCB) temperate deciduous forest and the Mt. Ailao (MAL) subtropical evergreen forest over a 1-year period. Higher δHg values were observed under the forest canopy than above the forest canopy in the MCB forest. The vertical gradients in δHg and ΔHg are positively correlated with the satellite-based normalized difference vegetation index (NDVI, representing the vegetation photosynthetic activity), suggesting that a strong vegetation activity (high NDVI) induces both mass-dependent and mass-independent fractionation of TGM isotopes. The observed δHg and ΔHg showed seasonal variations. Mean δHg and ΔHg in summer were 0.35-0.99‰ and 0.06-0.09‰ higher than those in other seasons in the MCB forest. In contrast, the highest seasonal δHg in the MAL forest was observed in winter at 0.07-0.40‰ higher than the values found in other seasons. The variability of δHg and ΔHg in MCB was attributed to vegetation activities, whereas the seasonal δHg in the MAL forest was driven by the exposure of air masses to anthropogenic emissions. Using the data in this study and in the literature, we concluded that vegetation activity and anthropogenic Hg release are the main drivers for the spatial variations in TGM isotopic compositions in the northern hemisphere.

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Name: Environmental science & technology
ISSN: 1520-5851
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