Assessment of hydrologic alteration induced by the Three Gorges Dam in Dongting Lake, China

Water-level variations are an internal aspect of lake ecosystems that play a key role in structuring aquatic diversity and providing ecosystem services. In this study, the hydrologic alteration of Dongting Lake induced by the Three Gorges Dam (TGD) was assessed using indicators of hydrologic alteration and range of variability approach. The results demonstrate a declining trend in autumn water level (0.52-2.26m) and 5-35days' advancement for date of minimum annual water level because of the impound of water by the TGD in early autumn. The spatial patterns in the degree of the indicators of hydrologic alteration were different among the sub-lake regions. Annual minimum water level and timing of annual extreme water level suffered a high degree of alteration in the eastern part of the lake, whereas autumn water level, date of minimum water level, and number of reversals in the western part of the lake showed a high degree of alteration. The average integrated degree of hydrologic alteration (D-0) for Dongting Lake was 50.40%, indicating that the hydrologic regime suffered a moderate alteration. The most ecologically relevant hydrologic indicators are critical for understanding eco-hydrology. On the basis of principal component analysis, the five selected ecologically relevant hydrologic indicators were 90-day minimum, date of minimum, high pulse duration, date of maximum, and May water level. Further studies are required to understand the impact of the TGD on water conditions in Dongting Lake, especially related to the response of the aquatic ecosystem.