青藏高原热融湖汞的生物地球化学循环研究

The thermokarst lake is one of common geomorphic units in the permafrost zone of high-latitude and high-altitude region. The formation and variation of the thermokarst is important for the climate and trace elemental cycle in the region and global scale. Climate change and human activities have induced the significant variation of number and area of thermokarst lake in the cold ecosystem. The formation and expand of thermokarst lake alters the Hg behavior in local scale and further alters the Hg cycling in regional and global scale. However, the issue of Hg biogeochemical cycle in thermokarst lake system does not receive enough attentions. The wide distribution of thermokarst lake in Qinghai-Tibet Plateau (QTP) in China provide the valuable opportunity to explore this issue. In this study, we use the combination of field measurement, isotopic tracer method, laboratory experiment, regional survey and remote sensing to investigate the Hg distribution, transportation and transformation in various environmental medium of the thermokarst lake system. We focus on the Hg input to the thermokarst lake via thawing palsa mire and its transformation in the lake. Furthermore, we combine the previous study to estimate the Hg(0) emission flux from the thermokarst lake to the atmosphere in QTP and further explore the influence of thermokarst lake on the regional Hg cycle. This study will increase the knowledge of cold ecosystem on the Hg cycling and further promote the understanding of the effect of climate change and human activity on the global Hg biogeochemistry.

热融湖是高纬度和高海拔多年冻土区常见的地貌单元，其演变对区域乃至全球的气候和痕量物质循环有着重要的影响。气候变化和人为活动导致许多寒带陆地生态系统中热融湖的数量和面积持续增加。热融湖的形成和发展改变了汞的局地行为，进而影响区域乃至全球汞的循环。然而，热融湖系统汞的生物地球化学循环研究尚未受到关注。本研究利用我国青藏高原热融湖广泛分布的独特地理优势，综合运用现场观测、同位素示踪、实验室模拟、区域调查和遥感技术，系统认识汞在青藏高原典型热融湖多种环境介质中的形态、时空分布及其迁移转化规律，重点关注热融坍塌向热融湖中输送汞的通量及其后续迁移转化行为，估算青藏高原地区热融湖气态汞的排放通量，初步揭示热融湖的形成与发展对区域汞循环的影响，进而推进对寒带生态系统在全球汞循环中作用的认识，加深气候变化和人为活动对全球汞循环影响的理解。

高纬度和高海拔多年冻土区是气候变化的敏感区域。热融湖是该区域常见的地貌单元之一，其演变对区域乃至全球痕量物质循环和气候变化有着十分重要的影响。然而，热融湖系统汞的生物地球化学循环研究尚未受到关注。本项目以青藏公路及青藏高原东北部冻土区为主要研究对象，并依托青藏高原腹地北麓河站深入开展热融湖汞的生物地球化学循环的系统研究。基于区域调查，系统认识了汞在青藏高原典型热融湖系统多种环境介质中的浓度、形态和时空分布特征。基于现场观测数据和其他辅助信息，建立了北麓河站附近三个典型热融湖湖水可光致还原汞的质量平衡模型，发现湖面气态汞的排放是湖水可光致还原汞主要的汇，冻土融水即是热融湖湖水可光致还原汞的主要来源，同时也是湖水气态汞排放的限制因素。利用观测数据和遥感影像，评估了北麓河盆地热融湖气态汞的排放通量的变化趋势。保守估计，在过去半个世纪，北麓河盆地热融湖气态汞的排放量以每10年3%的速度增长。本研究表明，气候变化导致的冻土区地貌的改变（如热融湖的扩张）及水文地球化学过程的改变将快速驱动冻土中的汞释放至大气。综上所述，本研究较为深入地揭示了热融湖的形成与发展对区域汞循环的影响，推进对寒带生态系统在全球汞循环中作用的认识，加深气候变化和人为活动对全球汞循环影响的理解。现已在Environmental Science & Technology, Atmospheric Chemistry and Physics、Environmental Pollution等国际知名期刊发表SCI论文6篇，尚在撰写的SCI论文4篇。