冻融作用下冻土-大气界面汞的释放特征及活化机理

Mercury (Hg) is a highly toxic metal that can cause harm to the environment and human health. It is well established that Hg as a gas phase can travel for a long distance in the atmosphere so that aquatic systems in pristine and remote regions can be impacted by Hg pollution through wet and dry deposition from the atmosphere. Therefore, it is very urgent to conduct long-term continuous measurements of mercury emission from different land interfaces. The freeze-thaw actions which lead on mercury emissions from soil /atmospheric interface are really a very important part to precisely understand the global mercury cycling. Based on it, we are prepared to carry out a well-designed project about mercury releasing flux in permafrost- atmospheric interface in Bei Lu he station which aims at: 1) to understand the real mercury emission from the freeze-thaw actions; 2) to reveal the influence factors of mercury flux during freezing and thawing process. Combine the parameters such as atmospheric environmental indexes and microbial community structure, discuss the exchange of mercury emission characteristics and its influencing factors in the process of frozen soil which based on climate change. The result not only further confirm the role of qinghai-tibet plateau in the process of circulation under the background of global warming, but also help researchers assess the atmospheric mercury pollution characteristics accurately and provide a scientific basis for performing international mercury convention.

汞是一种强毒性的重金属元素，能够长距离传输造成全球汞污染。弄清楚不同类型陆地与大气界面汞的交换过程、特征以及影响其交换过程的因素，对认识全球汞循环，继而治理和减少汞污染起着至关重要的作用。青藏高原多年冻土区是我国境内非常重要的地貌单元，对其在退化过程中汞的活化及释放过程研究还很薄弱。本研究依托青藏高原北麓河多圈层综合观测研究站开展综合野外观测和验，以连续定位观测为基础认识气候变化过程中区域汞的污染特征和冻土-大气界面汞排放特征。 综合大气环境监测指标和微生物群落结构等参数，分析和探讨气候变化过程中冻土-大气界面汞的交换特征及其影响因素，准确认识研究区域内冻融作用下汞在土壤-大气交换过程中的净交换量以及规律，进一步阐明青藏高原在气候变化背景下大气汞循环过程中的重要作用，为准确评估我国大气汞的污染特征和履行国际汞公约提供科学依据。

在多年冻土融化过程中，大量的汞可能被迁移，因此了解多年冻土地区汞的生物地球化学循环至关重要。然而，在高寒永久冻土区，陆-气-汞动力学知识仍然贫乏。在青藏高原中部(冬可马底)的一个高寒草地上测量了整个植被期的汞通量。在植被期(0.92 g m-2)，高寒草地是大气总气态汞(TGM)的一个小来源，与之前显示TGM汇的温带和北极苔原草原形成对比。Hg通量在植物生长期呈对数下降趋势，我们认为植被对Hg通量大小和方向的影响是遮荫和植物吸汞共同作用的结果，但植物吸汞作用可能较小，因为该地区的生物量较低。TGM的时间模式表明了地气交换在调节TGM水平中的重要性。在苗期过程中，TGM的昼夜模式与Hg排放通量共同变化，夜间浓度较低，下午浓度较高。在所有其他植被阶段，TGM在黎明前和日出后不久的晨峰出现一个极小值，同时对应的Hg通量在黎明前出现一个沉降，日出后出现一个源。TGM浓度随植物生长呈下降趋势，进一步说明了植被通过调节陆-气Hg动态来驱动TGM季节变化的作用。在气候变暖的情况下，由于植被绿色化趋势和气温变暖的相反影响，TP上广大多年冻土区未来的汞排放强度仍不明确。