土壤冻融及雪盖情况下气态汞的土（雪）/气交换过程研究

The gaseous mercury exchange between soil and air is one of the important parts of the global mercury cycle. As a unique and important component of the soil ecosystem, the role of permafrost in the trace element cycle and climate system has received much attention. The process of freeze-thaw cycle and snow cover in soil system will induce the significant changes of the physicochemical properties of soil. These changes have close connection with soil mercury cycle, especially the gaseous mercury exchange at soil (snow) and air interface. Then the permafrost system plays important and unique role in global mercury cycle. However, at present this issue does not receive enough attention. In this study, we will conduct the field measurements and experiments in laboratory based on the combination of the dynamic flux chambers and high-time resolution atmospheric mercury analyzer to investigate the mercury fate and transport between soil (snow) and air. The study will focus on the production and transport of gaseous mercury during the period of freeze-thaw cycle, snow cover and snow melting. Finally, based on the results of our study and previous studies and the need of global mercury modeling development, we will improve the present parametrization of mercury exchange between soil (snow) and air. This study will significantly promote the understanding the role of the soil system in the global mercury cycle.

气态汞在土壤与大气间的交换是全球汞循环的重要过程之一。作为土壤系统中独特而又十分重要的组成部分，冻土在痕量物质循环和气候变化中的作用已经受到了广泛关注。土壤冻融交替及雪盖（融雪）过程导致土壤物化性质发生急剧变化，而这些变化都同土壤中汞的迁移转化，特别是气态汞的土（雪）/气交换有着紧密的联系。因此，冻土在全球汞循环中扮有重要作用。但是，目前对于冻土系统在全球汞循环中的作用研究尚未受到重视。本项目拟选取我国季节冻土和雪盖现象普遍存在的背景区域,以动态通量箱法为基础，通过现场观测与实验室模拟, 深入认识土壤冻融及雪盖（融雪）条件下汞在土（雪）/气界面间的迁移转化规律及其影响因素，重点关注冻融交替、雪盖和融雪过程中气态汞的生成与迁移。最终，结合本研究与其他研究者的成果和汞模式发展的需求，进一步优化现有气态汞土（雪）/气间交换的参数化方案，为深入认识土壤系统在全球汞循环中的作用提供科学依据。

土壤生态系统在全球汞循环中具有重要作用，冻土是全球土壤系统的重要组成部分。然而，目前对于冻土系统在全球汞循环中的作用的研究尚未受到重视。本项目选取我国冻土和雪盖现象普遍存在的青藏高原背景区域，以动态通量箱法为基础，通过现场观测与控制实验相结合，深入认识土壤冻融及雪盖（融雪）条件下气态汞在土（雪）/气界面间的迁移转化规律及其影响因素，重点关注冻融交替、雪盖和融雪过程中气态汞的生成与迁移。并结合不同深度土壤空气中气态汞的观测，进一步揭示土壤理化性质的变化对冻土汞的生物地球化学循环的影响。针对气态汞在土（雪）/气界面间的观测结果表明，整个观测期间表层土壤是气态汞的排放源。在暖季，表层土壤是气态汞的排放源，冬季则是大气汞的汇。进一步的分析发现，在绝大多数的观测期间，太阳辐射是气态汞排放的最重要的驱动因子，表层土壤整体表现出白天是大气气态汞的源，夜间是大气气态汞的汇。现场观测和控制实验均表明，降水能够在短时间内促进气态汞的排放，但降雨和降雪对气态汞的排放有着不同的影响。现场控制实验发现，太阳辐射中的短波辐射在土壤表层气态汞的排放中占据主导作用。现场的模拟实验表明，降水中的部分的汞在有利的条件下能够转化成气态汞。针对不同深度土壤空气中的气态汞的观测表明，表层土壤中气态汞的浓度高于深层，且深层土壤中气态汞的浓度低于大气中的气态汞。本项目的结果将为深入认识冻土系统在全球汞循环中的作用提供科学依据。