Hydrological Regime Alteration and Ecological Effects of Dongting Lake During the Past 60 Years

In order to quantitatively evaluate the dynamic changes of the Dongting Lake hydrological situation in the past 60 years, based on the daily average water level sequence of the Dongting Lake Chenglingji, Nanzui and Yangliutan hydrological stations from 1959 to 2016.The Mann-Kendall method and the cumulative anomaly method were used to analyze the trend and sudden change of the Dongting Lake water level, and the IHA-RVA method was used to comprehensively evaluate the changes in the hydrological indicators of Dongting Lake before and after the hydrological variation.The cumulant slope change rate method is used to quantitatively evaluate the contribution rate of human activities and climate change to the changes in the hydrological regime of Dongting Lake under the changing environment.The results showed that:(1) The annual average water level of the Nanzui hydrological station showed a downward trend, while Chenglingji and Yangliutan hydrological station showed an upward trend.The abrupt years of water level in Dongting Lake were 1979 and 2003.(2) Taking the hydrological situation of Dongting Lake from 1959 to 1978 as the natural hydrological stage, the hydrological variation stage I (1979~2002) of the hydrological stations in Chenglingji, Nanzui and Yangliutan is 39%, 26% and 26% respectively.27%, the overall hydrological change of Dongting Lake is a low-degree change;the hydrological variation stage II (2003~2016) in the Chenglingji, Nanzui and Yangliutan hydrological stations is 60%, 41% and 31% respectively.The hydrological changes of the lake are generally moderate changes.Generally, the hydrological changes of East Dongting Lake is the largest, and the hydrological changes of West Dongting Lake and South Dongting Lake are small.(3) West Dongting Lake and South Dongting Lake were greatly affected by human activities during 1979~2002, and were greatly affected by climate precipitation changes from 2003 to 2016;East Dongting Lake was greatly affected by climate precipitation during 1979~2002, human activities are relatively small, but after 2003, the impact of human activities, especially the Three Gorges Project, has increased.(4) The impoundment of the Three Gorges Project has changed the relationship between the Yangtze River and Dongting Lake to a certain extent, resulting in changes in the water level of Dongting Lake, especially in East Dongting Lake, which in turn changed the succession of vegetation communities in the lake wetland and the number of fish and birds, which will adversely affect the safety of the lake and wetland ecosystem.This research can provide references for water resources protection and ecological restoration of Dongting Lake.