Impacts of cascade reservoirs on Yangtze River water temperature: Assessment and ecological implications

Abstract

The natural hydrological regime of the Yangtze River has been influenced by dam construction over past decades. More reservoirs are being built and have been planned in the upper reach of the Yangtze River (URYR). To investigate the effects of reservoirs in the URYR and the Three Gorges Reservoir (TGR) on the water temperature regime, a reservoir water heat model combined with the Soil and Water Assessment Tool is used to simulate the water temperature change under different scenarios. The results show that the water temperature regime has been dramatically altered by reservoir operation, especially in spring and autumn. Reservoir operations impose a noticeable hysteresis effect on water temperature rising and falling processes, thereby resulting in a delay of the suitable temperature date for the Chinese Sturgeon (Acipenser sinensis) and four famous major carps. When more reservoirs are put into use, the delays in the target spawning times of these fishes will be further exacerbated. Modifying operation modes of these reservoirs and depth of water release is necessary during fish spawning seasons, which could facilitate a better balance between ecological and socioeconomic demands. We hope the results of this study will be useful to the river ecosystem health and stability.