基于湖泊沉积记录的我国西南地区大气重金属污染历史过程研究

Heavy metals pollution is one of the most prominent environmental problems all around the world. Heavy metals from the mining and metallurgical industry and the fossil fuel consumption are the major anthropogenic sources, which could be transported in the atmosphere on the regional and even hemispherical scales and induced the pollution of earth surface environment. The southwest China is facing heavy atmospheric heavy metals pollution, where has been the center of mining and metallurgical industry in China with a long history. However, there had little knowledge about the historical variations in atmospheric heavy metals pollution especially in the remote area with the mining and metallurgical activities, fossil fuel consumption and rapid industrial development in recent decades,and the impact on the regional environment. The sedimentary records from the highland lakes make its feasible to trace the historical variations in atmospheric heavy metals pollution in southwest China. Concentrations of heavy metals, Pb isotope composition will be analyzed in the sediment cores from the Lakes Tianchi, Mubang, Shengmu and Heilongtan distributed in northeast and west regions of Yunnan Province. The geochemical proxies will also be analyzed for the rock and parent soil in the catchment of the lakes and the atmospheric dust, moss samples. We aims to differentiate the proportions of heavy metals from the natural detritus/dust and that from anthropogenic sources, which accumulated in the sediment of the lakes, combining the methods of isotope mixing model and geochemical normalization. The historical variations in heavy metals pollution will be reconstructed referencing to the chronology of the sediment cores, and its correlations with human activities such as mining and metallurgical activities, fossil fuel consumption and the rapid industrial development in recent decades will be revealed. Our research is helpful for further understanding of regional atmospheric heavy metals pollution in historical perspective, provides scientific basis for the prevention and control of regional atmospheric pollution and will also facilitate the understanding and comparison of historical atmospheric heavy metals pollution between different regions with long history of mining and metallurgical industries.

重金属污染是全球面临的主要环境问题之一，作为主要污染源，矿冶业及化石燃料使用释放的重金属通过大气输移与沉降可导致区域甚至半球尺度地表环境污染。我国西南地区矿冶业历史悠久，目前大气重金属污染较重；早期矿冶业及近代工业发展导致的区域大气重金属污染历史变化过程及对地表环境的影响如何，尚缺乏深入研究；该地区广泛分布的高山湖泊为开展上述研究提供了良好的载体。本项目选择云南不同地区典型湖泊，通过对沉积岩芯重金属、铅同位素等地球化学指标分析，耦合流域基岩/土壤、大气污染监测等分析结果，采用同位素混合模型、参比元素校正等技术，建立湖泊沉积物重金属自然来源与人为污染大气沉降贡献的判识方法；结合沉积岩芯年代标尺，重建Pb、Zn、Cu、Cd等重金属大气污染历史变化过程，揭示重金属污染的变化特征及其与矿冶业发展、化石燃料使用等人类活动的关系，为区域大气重金属污染防治及区域间大气重金属污染演化对比研究提供参考。

西南地区矿冶业历史悠久，也是我国目前大气重金属污染较重的地区之一。本项目针对我国西南地区在重金属污染历史过程、早期矿冶业及近代工业发展时期区域大气重金属污染研究方面的不足，选择不同类型湖泊，开展了百年-千年尺度重金属污染沉积记录的对比研究。完善了基于流域基岩、历史沉积物为背景，以Pb同位素模型、参比元素校正等技术的人为重金属定量辨识方法；揭示了高海拔地区目前大气Pb等重金属污染程度、来源与空间规律，阐明了Hg、Pb、Cd、Sb、Zn与As等重金属污染的历史过程、不同重金属污染的时空差异及其与区域有色金属冶炼等人类活动的关系。研究发现，早期矿冶业发展（铜银等有色金属冶炼）导致的Pb等重金属污染仅限于局地，其中滇中地区（开始于15世纪中期）早于滇西地区（开始于19世纪中期-20世纪初期）；西南地区区域性的大气Pb、Cd等重金属污染开始于上世纪50-80年代，反映了区域经济发展对西南地区大气重金属污染的主导贡献。阐明了西南高海拔地区大气Hg沉降的自然背景（2.4±0.7ug/m2/a），与全球平均值相当；区域性的大气Hg污染开始于16世纪，上世纪中期以来污染加重。人类活动强度差异导致的Hg污染具有显著的逆“山地汞诱捕”海拔效应，即受人类活动强烈影响的低海拔地区Hg污染明显高于高海拔地区，20世纪80年代以来，大气Hg沉降通量低海拔地区平均为高于高海拔地区的4.5倍，区域/局地人为污染排放对大气Hg污染占主导贡献。结合苔藓/地衣生物监测结果，认为西南地区大气Pb污染主要来自区域有色金属冶炼释放，同时还受到缅甸等南亚国家含铅汽油源的影响。总之，通过西南地区湖泊沉积记录与苔藓与地衣等监测载体重金属研究，回答了典型重金属污染的现状、历史过程、增量与来源等问题，弥补了高海拔与偏远地区重金属污染研究的不足，为区域/全球大气污染及其对地表生态环境影响的对比研究提供了参考，为区域大气重金属减排政策的制定提供了科学依据。