西南地区树线高山湖泊枝角类记录与生态环境变化

Global warming and atmospheric deposition have significantly impacted catchment environment and lake systems in alpine regions. There exists strong difference in catchment features and surface processes between zones above and below treeline. This can affect key environmental process of alpine lakes, and therefore alter long-term patterns of lake response. Cladocerans are important primary consumers in lakes and their sediment remains can reliable track the changes of lake environment. Two alpine lakes with different vegetation zonation (i.e. above and below tree lines, respectively) in southwest China are selected in this study. Firstly, seasonal variation of cladocerans and their relationship with limnological factors will be identified through monitoring surveys. With the construction of chronological sequence and high-resolution sediment cladoceran analyses, sedimentary analyses on diatoms and geochemical proxies will be conducted for the sediment core of each lake, to reconstruct the history of lake biological and environmental changes in the past 200 years. Furthermore, the heterogeneity of cladoceran community succession will be evaluated through lake comparison. With the application of multivariate analyses, key driving factors of cladoceran community structure and production will be identified and their relationship with catchment processes will also be assessed. Combining with previous data from this study region, this research will reveal the regional patterns and mechanisms of lake response to climate and environmental changes in this alpine region. Therefore, this study will not only contribute to the theoretical exploration of paleoecological research in alpine regions, but also provide basis for ecological evaluation and prediction of future trend for alpine lakes.

全球变暖与大气沉降过程已经对高山地区的流域环境与湖泊系统产生了重要的影响。高山地区的流域特征和地表过程在树线上下存在差异，可以影响湖泊关键环境特征及其生态响应的长期模式。湖泊枝角类是重要的初级消费者，其遗存记录能有效反映水体环境的变化特征。本研究采用古今结合的方法，选取西南地区不同植被带（如树线以上和以下）中的高山湖泊为研究对象，首先开展现代过程监测，识别枝角类群落的季节变化特征及其与生态环境要素的关系。通过沉积物测年与高分辨率的枝角类钻孔分析，结合硅藻和环境代用指标，重建近两百年来湖泊生态环境变化历史。对比分析树线上下湖泊枝角类古生态变化的异同特征，利用多元统计分析，甄别驱动枝角类群落结构和生产量变化的关键因子及其与流域过程的关系。结合已有资料，揭示高山湖泊响应气候与环境变化的区域模式与影响机制。本研究将丰富高山湖泊古生态研究的理论探讨，可为高山湖泊生态评价与变化趋势预测提供依据。

对比分析树线上下高山湖泊环境变化过程和沉积物枝角类群落演化过程，利用多元统计分析，甄别驱动枝角类群落结构和生产量变化的关键因子及其与流域过程的关系，可以揭示高山湖泊响应气候与环境变化的区域模式与影响机制，为高山湖泊生态评价与变化趋势预测提供依据。本项目利用捕获器对高山湖泊枝角类群落进行季节监测和影响因子分析，并结合50个湖泊表层沉积物样品的分析获取了云南地区湖泊枝角类时空变化特征和主要环境影响因子；在此基础上，通过对滇西北高山湖泊沃迪错和丁公娘错及丁公错3个湖泊沉积物短钻孔的详细的铅铯测年、AMS14C测年、沉积物理化指标分析及枝角类亚化石鉴定等，重建了过去近两百年区域树线上下湖泊环境和枝角类群落演化序列，并与重建的区域气候数据、区域及格陵兰地区的大气氮沉降记录进行对比分析，获得了以下几个认识：1）云南地区湖泊枝角类在空间分布上具有明显差异，主要受海拔和湖泊水深梯度影响，而对营养盐指标变化不敏感；2）滇西北高山湖泊在过去近200多年经历了明显的气候波动，湖泊营养水平呈上升趋势，可能反映了流域过程（放牧、植被调节）的影响；3）三个高山湖泊沉积钻孔中δ15N均从1800年代呈下明显下降趋势，与中国西南地区沉积记录和格陵兰冰芯记录有较好的一致性，指示大气似氮沉降过程；4）湖泊营养水平变化和气候变暖是高山湖泊枝角类群落发生变化的主要影响因子，值得注意的是树线上湖泊丁公娘错枝角类群落变化节点早于树线下湖泊沃迪错，可能指示了树线上下湖泊理化环境（营养水平、水温）差异对枝角类群落变化的影响。