浴仙湖沉积物记录的云南极端干旱事件与生态响应评价

SEDIMENT RECORDS OF EXTREME DROUGHTS AND ECOLOGICAL CONSEQUENCES IN YUXIAN LAKE, SOUTHEAST YUNNAN

为评价湖库生态环境对极端气候的响应特征,以经历水位明显降低的云南浴仙湖为研究对象,通过沉积物多指标分析并结合多变量统计方法,识别了2009—2013年极端干旱事件驱动湖泊生态环境变化的模式。其中沉积物粒度显示近百年来湖泊水文条件总体稳定,但在2011年左右粗颗粒物质和中值粒径增大,同期沉积物元素、同位素记录表明水体营养水平没有明显变化。硅藻群落近百年来以湖泊底栖物种占绝对优势,约2011年开始优势种属Fragilaria被Nitzschia、Navicula等河流水体中常见的物种所替代,且硅藻多样性指标总体增加,而指示水位变化的PCA主轴一解释了硅藻群落结构的主要变化(约55.8%)。总之,极端干旱事件的发生与持续明显改变了湖泊生物群落结构与多样性特征,已成为影响该气候敏感区水资源安全与生态环境功能的重要挑战之一。

The increased intensity and frequency of extreme droughts due to global warming have led to the dedine ofwater levels and significant shortage of water resources in many lakes and reservoirs, which could severely threaten thesocio-economic development and ecological security. To date the ecological evaluation of extreme droughts have beenmainly focused on terrestrial ecosystems in China. This study aim to assess the impact of extreme droughts on diatomassemblages and diversity patterns through multi-proxy sediment analyses in Yuxian Lake, which has experienced sig-nificant water level change during the period of 2009 to 2013. The grain size records showed an increase in sedimentparticles starting from about 2011, which corresponded to the occurrence of the most recent drought event. The isotopic and elementary records indicated that the trophic state remained oligotrophic over the past century. Diatom assemblages were dominated by benthic and limnetic diatoms （i.e. Fragilaria construens/pinnata）, but these taxa werethere after replaced by fluvial and riverine taxa （i.e. Nitzschia and Navicula） with the most recent decline of lake levels.Our results demonstrated that the diatom PCA axis was strongly associated with extreme climate, which accounted for55.8% of the total variance for diatom assemblages. Our study provided sediment evidence for the role of extremedroughts in regulating freshwater environment and biota and highlighted the urgency of climate mitigation actions inmaintaining water security and ecosystem functioning for this climatesensitive region.