Ecosystem shifts and Cladocera responses in a freshwater lake in semi-arid regions: The successional synergistic effects of natural and human factors in the past 170 years

The data of cladocera subfossils in the sediment core of Hulun Lake, the largest freshwater lake in northern China's semi-arid region (48.55°~49.33°N, 116.97°~117.81°E). The results indicate that both internal factors (such as lake sedimentary environment, fish catches, lake water level, organic matter, and nutrients) within the lake and external factors (including population, urbanization rate, and livestock husbandry) in the surrounding basin have been key drivers influencing the structure of Cladocera in Hulun Lake over the past 170 years. The originally predominant littoral Cladocera species (Chydorus sphaericus. sl.) were replaced by planktonic (Bosminidae) since 1980s accompanied by a decline in diversity, which corresponds with the process of eutrophication and pollution in the lake.