Investigation of mercury exchange between forest canopy vegetation and the atmosphere using a new dynamic chamber
Investigation of mercury exchange between forest canopy vegetation and the atmosphere using a new dynamic chamber
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DOI：
10.1021/es0604616
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发表时间：
2006-08-01
影响因子：
11.4
通讯作者：
Krabbenhoft, David P.
中科院分区：
文献类型：
--
作者：
Graydon, Jennifer A.;St. Louis, Vincent L.;Krabbenhoft, David P.
本文介绍了动态室系统的设计，该系统允许 PAR 和 UV 辐射完全传输，并允许封闭的完整叶子保持正常的生理功能，同时在现场量化 Hg(0) 通量率。黑云杉和短叶松叶子均排放和吸收Hg(0)，在大气中Hg(0)浓度附近表现出类似于2-3 ng m(-3)的补偿点。使用富集的稳定汞同位素尖峰，研究了尖峰汞 (II) 在叶子上的保留模式。使用该室同时测量叶子的 Hg(0) 逃逸率，以确定叶尖 Hg(II) 浓度随时间的下降是否可以通过光还原和尖峰汞重新排放到大气中来解释。这种质量平衡方法表明，单独的峰值 Hg(0) 通量无法解释施用后测量到的叶子上峰值 Hg(II) 的减少，这意味着该室低估了叶子上 Hg(II) 到 Hg(0) 的真实光还原，或者叶子中 Hg(II) 损失的其他机制（例如角质层风化）正在发挥作用。还研究了导致叶子上新沉积的 Hg(II) 光还原的辐射光谱。我们的尖峰实验表明，森林冠层保留的湿沉积中的一些 Hg(II) 可能会迅速光还原为 Hg(0) 并重新排放回大气中，而另一部分可能会在生长季节结束时被树叶保留，其中一些沉积在凋落物中。这一发现对于根据径流和凋落物通量估算汞干沉降具有重要意义。
This paper presents the design of a dynamic chamber system that allows full transmission of PAR and UV radiation and permits enclosed intact foliage to maintain normal physiological function while Hg(0) flux rates are quantified in the field. Black spruce and jack pine foliage both emitted and absorbed Hg(0), exhibiting compensation points near atmospheric Hg(0) concentrations of similar to 2-3 ng m(-3). Using enriched stable Hg isotope spikes, patterns of spike Hg(II) retention on foliage were investigated. Hg(0) evasion rates from foliage were simultaneously measured using the chamber to determine if the decline of foliar spike Hg(II) concentrations over time could be explained by the photoreduction and re-emission of spike Hg to the atmosphere. This mass balance approach suggested that spike Hg(0) fluxes alone could not account for the measured decrease in spike Hg(II) on foliage following application, implying that either the chamber underestimates the true photoreduction of Hg(II) to Hg( 0) on foliage, or other mechanisms of Hg(II) loss from foliage, such as cuticle weathering, are in effect. The radiation spectrum responsible for the photoreduction of newly deposited Hg(II) on foliage was also investigated. Our spike experiments suggest that some of the Hg(II) in wet deposition retained by the forest canopy may be rapidly photoreduced to Hg(0) and re-emitted back to the atmosphere, while another portion may be retained by foliage at the end of the growing season, with some being deposited in litterfall. This finding has implications for the estimation of Hg dry deposition based on throughfall and litterfall fluxes.