长白山和哀牢山偏远山地森林系统与大气间汞的交换通量研究

汞污染可在全球传输，2013年签署的水俣公约旨在控制汞排放以减少汞在生物体积累及暴露风险。东亚和东南亚地区人为源汞排放占全球份额的40%，其中我国排放占全球年排放总量的1/3。汞的化学转化及迁移受气候变化影响，生态系统对汞减排的响应可能更为复杂。大气中汞主要是单质态，汞减排将直接影响地表和大气间汞沉降和释放的平衡进而影响汞进入土壤、水体和生物体。精确、高时空分辨率的观测地表与大气间Hg0的交换通量是定量这一过程的关键。生态系统尺度通量观测的微气象方法已广泛应用于多种微量气体，而在Hg0通量上的研究还较少。植被加强了大气汞的沉降，植物与大气间汞交换的过程在汞地球化学循环中尤为重要。本研究拟在我国长白山落叶阔叶林和哀牢山亚热带常绿林森林系统采用弛豫涡旋积累技术结合林冠内梯度的同步测定开展长期、分季节、高分辨率（40min）的观测，以定量偏远山地森林系统汞交换通量和厘清林冠内Hg0的动力学过程。

Recognition of the global dimensions of the human-caused mercury pollution in the 1970's has set in motion decades of research and policy development that have culminated last year in the UN's legally binding Minimata Convention. The treaty will restrain the rate of increases in Hg use and emissions to the atmosphere in the hopes of reducing Hg accumulation in biota and therefore human exposure to this neurotoxic contaminant. East and Southeast Asia are currently responsible for about 40% of global anthropogenic emissions. About 75% of the mercury from this region comes from China, which is about one-third of the global total. Global climate change may complicate the response of global ecosystems to mercury emission reductions, through its profound effects on many aspects of the movement and chemical transformations of mercury in the environment. Since Hg can exist as a gas (primarily Hg0) though, the balance of Hg deposition and re-emission between land and atmosphere influences the rate at which Hg emission controls will influence Hg in soils, water and ultimately the biota. A key barrier to defining this balance is the precision, temporal resolution and spatial scale with which land-atmosphere Hg0 exchange (flux) is measured. Ecosystem-level flux sampling approaches - i. e. micro-meteorological (MM) techniques already implemented for a broad range of trace gases should also be utilized for Hg0, which has previously received very little attention in Hg research community. SKLEG has taken the lead in China to advance experimental field techniques to measure such Hg0 fluxes. The exchange of Hg between plants and the atmosphere is an important process of the biogeochemical cycle of Hg, particularly as canopy processes enhance atmospheric deposition to terrestrial ecosystems. Here, we propose to use relaxed eddy accumulation-technique in conjunction with continuous in-canopy gradient measurements to for the first time quantify net ecosystem Hg0 vapor exchange for forest ecosystems and address the fine-scale source/sink distribution of Hg0 in the canopy of two contrasting remote upland forests of China. The proposed work will be a long-term study with a high time-resolution (40 min) covering a broad seasonal record in an old-growth subtropical evergreen forest (Mt. Ailao) and the period of spectacular surface layer airborne mercury depletion episodes (June - August) in a deciduous broad-leaf forest (Mt. Changbai).