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

The increased intensity and frequency of extreme droughts due to global warming have led to the dedine of water levels and significant shortage of water resources in many lakes and reservoirs, which could severely threaten the socio-economic development and ecological security. To date the ecological evaluation of extreme droughts have been mainly focused on terrestrial ecosystems in China. This study aim to assess the impact of extreme droughts on diatom assemblages and diversity patterns through multi-proxy sediment analyses in Yuxian Lake, which has experienced significant water level change during the period of 2009 to 2013. The grain size records showed an increase in sediment particles starting from about 2011, which corresponded to the occurrence of the most recent drought event. The isoto- pic 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 were there 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 for 55.8% of the total variance for diatom assemblages. Our study provided sediment evidence for the role of extreme droughts in regulating freshwater environment and biota and highlighted the urgency of climate mitigation actions in maintaining water security and ecosystem functioning for this climate-sensitive region.