Spatio-Temporal Characteristics of Suitable Ecological Water Levels in Dongting Lake, China

Dongting Lake, the second largest freshwater lake in China, has recently attracted increasing global attention for its water level alterations and subsequent ecological issues. Anomalous water level changes could cause advanced exposure or area reduction of wetlands in dry season, consequently leading to the reduction of migratory birds and aquatic species. Suitable ecological water level (SEWL) in Dongting Lake is thus of primary concern for ecological conservation and management. Based on field data collected over 50 years, moving T-test, Mann-Kendall test, moving F-test and Ratio Flow Deviation methods were applied to detect abrupt changes of water levels at six stations in Dongting Lake, namely, Chenglingji and Lujiao stations (in East Dongting), Yangliutan and Yingtian stations (in South Dongting), Nanzui and Xiaohezui stations (in West Dongting). The lognormal distribution, generalized extreme value distribution were employed for curve fitting of the water level sequence before variation and the Kolmogorov-Smirnov statistic were employed to test the goodness of fit. The water level at the highest probability density of the best distribution function is selected as the s SEWL. Results indicated that the distribution of SEWL in Dongting Lake varies temporally and spatially due to complex climate change and anthropogenic activities. For the whole Dongting Lake, the spatial average of monthly SEWLs for the six stations increases to the maximum (31.13 m) in July, and decreases to the minimum (24.38 m) in January. The difference of SEWL between three lake regions generally reaches the maximum in dry season while reduces to the minimum in wet season. The spatial distribution of SEWL shows a gradual increasing trend from East Dongting to West Dongting, ranging from 24.67 m to 30.30 m. In contrast, the intra-annual fluctuations of SEWL is 10.21 m in the eastern region but 3.88 m in the western region. The spatio-temporal characteristics of SEWL in Dongting Lake demonstrated in this study provides a useful reference for ecological lake level management in this region.