Influence of the three Gorges Reservoir on the shrinkage of China's two largest freshwater lakes

摘要

The impoundment of the Three Gorges Reservoir (TGR), the largest hydropower project in the world, has altered the sediment deposition and erosion regime of downstream-linked rivers and lakes. The extent to which the TGR impoundment has changed the surface areas of the two largest freshwater lakes in China, Lake Dongting and Lake Poyang, remains largely unknown. Here, we compared the surface areas of the two lakes pre and post the TGR impoundment as well as with a modelled non-TGR scenario. We found that the mean surface areas of Lake Dongting and Lake Poyang during the post-TGR period (2003-2016) were significantly smaller than in the pre-TGR period (1956-2002) and in the modelled non-TGR scenario (2003-2016). The impoundment of TGR has led to a shift from a sediment deposition regime to an erosion-dominated regime of the downstream-linked rivers and the two lakes. The impoundment of TGR further changed the seasonal variabilities in discharge and water level in the downstream-linked rivers and the two lakes, especially in the flood season. Our results suggest that TGR resulted in a 5.1%, 16.2%, and 12.2% decrease of the surface area of Lake Dongting in June 2003-September 2006, October 2006-September 2008, and October 2008-December 2016, respectively, and a corresponding decrease of 12.4%, 19.6%, and 15.8% for Lake Poyang. These changes cannot be attributed to variations in rainfall as no significant differences were found in the annual or monthly mean rainfall in the watersheds upstream of Luoshan and Jiujiang + Hukou between the pre-TGR and the post-TGR period. Our results call for the development of a strong holistic management plan for cascading reservoirs, including TGR, to minimize the damage of downstream lake ecosystems.