Investigation of Mercury Exchange between Forest Canopy Vegetation and the Atmosphere Using a New Dynamic Chamber

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• 作者：Jennifer A. Graydon ; Vincent L.St. Louis ; Steve E. Lindberg ; Holger Hintelmann ; David P.Krabbenhoft
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：August 1, 2006
• 年：2006
• 卷：40
• 期：15
• 页码：4680 - 4688
• 全文大小：522K
• 年卷期：v.40,no.15(August 1, 2006)
• ISSN：1520-5851

文摘

This paper presents the design of a dynamic chambersystem that allows full transmission of PAR and UV radiationand permits enclosed intact foliage to maintain normalphysiological function while Hg(0) flux rates are quantifiedin the field. Black spruce and jack pine foliage bothemitted and absorbed Hg(0), exhibiting compensation pointsnear atmospheric Hg(0) concentrations of ~2-3 ng m^-3.Using enriched stable Hg isotope spikes, patterns of spikeHg(II) retention on foliage were investigated. Hg(0)evasion rates from foliage were simultaneously measuredusing the chamber to determine if the decline of foliarspike Hg(II) concentrations over time could be explainedby the photoreduction and re-emission of spike Hg to theatmosphere. This mass balance approach suggestedthat spike Hg(0) fluxes alone could not account for themeasured decrease in spike Hg(II) on foliage followingapplication, implying that either the chamber underestimatesthe true photoreduction of Hg(II) to Hg(0) on foliage, orother mechanisms of Hg(II) loss from foliage, such as cuticleweathering, are in effect. The radiation spectrumresponsible for the photoreduction of newly depositedHg(II) on foliage was also investigated. Our spike experimentssuggest that some of the Hg(II) in wet deposition retainedby the forest canopy may be rapidly photoreduced toHg(0) and re-emitted back to the atmosphere, while anotherportion may be retained by foliage at the end of thegrowing season, with some being deposited in litterfall.This finding has implications for the estimation of Hg drydeposition based on throughfall and litterfall fluxes.