祁连山疏勒河上游雪冰中汞甲基化微生物群落及其在甲基汞生成中的作用

The glaciers in Qinghai-Tibet Plateau glaciers are an important carrier of mercury. With global warming, mercury enters into the downstream ecosystem accompany by the melting water of glaciers, which threatens human health and ecosystem security in the region. In this process, a portion of inorganic mercury is converted to methylmercury that is more biohazardous. Methylmercury in nature is mostly converted by microbial catalysis of inorganic mercury. Recent studies showed that abundance and diversity of mercury methylated microorganisms in cold environments were higher. Therefore, it is necessary that the study of mercury methylation microbial communities and its role of methylmercury production in snow and ice on the Tibetan Plateau. This project is planned to research snow，ice and melt water in the surface of the 4 glaciers in the upper reaches of the Shule River, Qilian Mountains. Through analysis of the methylmercury content and the characteristics of the mercury methylation microbial community structure, the results obtained aim to reveal the temporal and spatial variation rule of the methylmercury and mercury methylated microbial communities. Meanwhile, combining with the analysis on the physicochemical properties of the samples and the environmental factors, the contribution of mercury-methylated microorganisms in snow and ice to the formation of methylmercury can be clarified. It will provide a scientific basis for predicting the concentration and bioavailability of methylmercury in the downstream ecological environment as well.

青藏高原冰川是汞的一个重要载体。随着全球变暖，汞随着冰川融水加速进入到下游生态系统，对区域的人类健康和生态系统安全造成威胁。在这一过程中，一部分无机汞转化为对生物危害更大的甲基汞。自然界甲基汞大多由微生物催化无机汞而来，最近的研究表明冷环境汞甲基化微生物种类和丰度更高。因此，研究青藏高原雪冰中汞甲基化微生物群落及其在甲基汞生成中的作用很有必要。以祁连山疏勒河上游老虎沟4条典型冰川表层雪冰和融水为研究对象，通过分析其中甲基汞含量、汞甲基化微生物群落结构特征，揭示甲基汞和汞甲基化微生物群落的时空变化规律，同时结合样品理化性质和环境要素分析，阐明雪冰中汞甲基化微生物对甲基汞生成的贡献。为预测下游生态环境中甲基汞浓度和生物有效性提供科学依据。

甲基汞是一种生物毒性远大于无机汞的化合物，环境中的甲基汞主要为微生物催化无机汞而来。冰川作为汞的一个重要载体，其雪冰中汞甲基化微生物群落及其在甲基汞生成中的作用尚不清楚。本项目通过对祁连山疏勒河上游典型冰川表层雪冰和融水中汞和微生物的研究，揭示了山地冰川表层雪冰中总汞、甲基汞、微生物群落和汞甲基化微生物群落的时空变化规律，阐明了雪冰中汞甲基化微生物对甲基汞生成的贡献。为预测下游生态环境中甲基汞浓度和生物有效性提供科学依据。主要研究结果如下:.1）冰川中总汞和甲基汞分布规律较为相似，同时受到样品类型、海拔、季节等的影响。冰川中的尘埃颗粒是影响汞分布的关键因素；在海拔4900米以下的表层雪冰中，总汞、甲基汞与海拔正相关，但整体上并未表现出相关性；表层雪冰中的汞浓度夏季>秋季>春季。.2）冰川中存在较高比例的未知微生物，已知的微生物多样性受样品类型、海拔等的影响。冰川消融区中主要类群为变形菌门和拟杆菌门，其中新降雪的微生物多样性最低，融水的最高；冰川表面不同海拔区域雪冰中优势门是蓝细菌门、变形菌门和放线菌门，其中蓝细菌门相对丰度与海拔呈负相关，变形菌门随海拔变化较小；冰川的积累区和消融区雪冰中微生物群落差异较大。.3）冰川中汞甲基化微生物多样性较高，具有很多新的类群，广泛存在于冰川表面和内部，受环境类型影响较大，对冰川表面雪冰中甲基汞的生成起重要贡献。冰川末端融水中汞甲基化微生物数量和种类远高于其他类型和区域，具有威胁冰川下游区域人类健康的潜在风险。