Collaborative Research: Magnitude and Pathway of Gaseous Atmospheric Mercury Deposition in Forests

汞（Hg）的释放来自自然来源和人类活动。该项目的目标是在两个截然不同的森林地点进行为期一整年的汞测量。这一丰富的数据集将用于更好地了解汞如何在树木、土壤和大气中移动。了解汞的分布很重要，因为它是一种有毒物质，会对人类的神经系统产生负面影响，并与其他大气气体发生反应。该项目的知识将有助于评估汞的全球分布，从而实现国际公认的减少汞污染的目标。此外，该项目每年将为一名博士后研究员、两名研究生和一名本科生提供部分支持。降雨）沉积过程，包括植物对气态汞的吸收。当植物死亡或落叶时，植物中的汞转移到土壤中，占土壤中汞的54-94%。在没有直接测量的情况下，气态元素汞（Hg[0]）沉积是从凋落物和被动膜推断的，但这些都不是理想的代理净汞（0）沉积，因为他们不？无法解释再排放。因此，本项目的第一个目标是量化两种具有不同季节性的森林（落叶温带森林和万年青亚热带雨林）中的净气态干Hg（0）沉积（总沉积量减去排放量的总和）的幅度和时间动态。汞（0）的净沉积将通过在大型塔上进行微气象测量来测量，这是在生态系统一级（包括所有底层汇和源）直接、非侵入性和长时间测量汞（0）净交换的唯一可用方法。第二个目标是通过部署两个相应的通量系统将Hg（0）通量划分为林冠和土壤贡献--一个在森林林冠上方测量生态系统水平的Hg（0）交换，另一个在林冠下方量化土壤贡献。冠层Hg（0）通量将通过差分计算。通量划分将提供年度、季节和昼夜Hg（0）汇（例如，到檐篷）和来源优势（例如，在全球和区域化学迁移模型中限制Hg（0）沉积所需要的。最后，这项工作的第三个目标是通过比较Hg（0）通量与二氧化碳、臭氧、水蒸气和硫化羰的通量来阐明沉积的途径。所有这些微量气体在生态系统中有不同的汇和源，它们在冠层、气孔、叶肉和土壤中对通量的贡献程度也各不相同。通量之间的比较，包括季节性，昼夜性和组分通量将使我们能够量化Hg（0）交换与光合作用活性，气孔导度，叶片内的酶活性，外部表皮吸收和土壤交换的耦合程度。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Mercury (Hg) is released from both natural sources and human activities. The goal of this project is to make measurements of mercury for an entire year in two contrasting forest locations. This rich dataset will be used to better understand how Hg moves through trees, soil, and the atmosphere. Understanding the distribution of mercury is important because it is a toxic substance, which can cause negative neurological effects in humans and react with other atmospheric gases. The knowledge from this project will be useful for assessing the global distribution of a mercury so that international recognized goals for reducing Hg pollution can be achieved. Additionally, the project will provide partial support for a postdoctoral researcher, two graduate students, and one undergraduate student per year.Atmospheric mercury deposits via various dry and wet (e.g., rainfall) deposition processes, including gaseous mercury uptake by plants. Mercury in vegetation is transferred to soils when plants die off or shed leaves, contributing 54-94% of mercury in soil. In the absence of direct measurements, gaseous elemental mercury (Hg[0]) deposition is inferred from litterfall and passive membranes, yet these are not ideal proxies for net Hg(0) deposition as they don?t account for re-emission. Consequently, first objective of this project is to quantify the magnitude and temporal dynamics of net gaseous dry Hg(0) deposition (sum of gross deposition minus emission) in two forests with different seasonalities, a deciduous temperate forest and an evergreen subtropical rain forest. Net Hg(0) deposition will be measured using micrometeorological measurements on large towers, the only available method for direct, non-intrusive and time-extended measurements of net Hg(0) exchange at the ecosystem level encompassing all underlying sinks and sources. The second objective is to partition Hg(0) fluxes into canopy and soil contributions via deployment of two corresponding flux systems - one above the forest canopy to measure ecosystem-level Hg(0) exchange and a second system below the canopy to quantify soil contributions. Canopy Hg(0) fluxes will be calculated by difference. Flux partitioning will provide annual, seasonal and diurnal Hg(0) sink (e.g., to canopies) and source strengths (e.g., from soils) needed to constraint Hg(0) deposition in global and regional chemical transport models. Finally, the third goal of this work is to elucidate pathways of deposition by comparing Hg(0) fluxes to those of carbon dioxide, ozone, water vapor, and carbonyl sulfide. All these trace gases have different sinks and sources in ecosystems and vary in their degree of canopy, stomatal, mesophyll and soil contributions to fluxes. Comparison among fluxes, including seasonality, diurnality and component fluxes will allow us to quantify the degree to which Hg(0) exchange is coupled to photosynthetic activity, stomatal conductance, enzymatic activity within leaves, external cuticular uptake and soil exchange.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.