Abstract: Xingyun Lake, a large and hypereutrophic lake in Southwest China, has experienced deterioration of water quality and degradation of ecosystem functioning during the past few decades. Despite the fact that this lake has suffered from multiple environmental stressors (i.e. eutrophication, fish invasion and hydrological regulation), few studies have examined their interactive roles in driving lake communities. Therefore, it is urgently needed to identify the pattern of multiple stressors in driving longterm ecosystem changes in Xingyun Lake. In combination with lake survey and historical data, we conducted multiproxy analyses of sediment records for Xingyun Lake with a focus on cladoceran community. We identified 10 genera and 16 species of cladocerans from sediments, with taxa such as Chydorus and Bosmina generally dominating through the sediment cores. The concentration of Chla pigments remained consistently low before 1890, but thereafter rose slowly and was concurrent with the increased proportion of sand particles (>63 μm). From 1980, the Chl-a level began to rise rapidly with increasing abundance of C. sphaericus which is known to tolerate high nutrient levels. Further analysis showed that total cladoceran production increased significantly with increased lake productivity (R²=0.753, P <0.001, n=33), and primary production was also a significant driver of cladoceran community change (R²=0.953, P<0.001, n=33). In addition, changes in predation pressure associated with fish introduction have led to an obvious reduction of Bosmina production. The gradual loss of macrophytes due to eutrophication and water level fluctuation may have caused the decline or even decimation of benthic cladocerans. In all, cladoceran community in Xingyun Lake has experienced longterm changes over the past century with nutrient enrichment identified as the key environmental driver. Furthermore, we found evidence for the impacts from fish introduction, hydrological fluctuation and change in macrophytes. Our sediment evidence of longterm ecological changes in Xingyun Lake can provide supplemental information for catchment management and lake restoration.

Key words: land use, loess hilly region, vertical variation, soil water storage characteristics, soil moisture, grey relational analysis