中文摘要：

三峡工程是长江中游干流最大的骨干工程，蓄水后下游水文情势发生明显改变。分析水库运行后下游水文情势的改变情况，将为了解大型水利工程对河流健康状况的影响程度和开展生态保护提供有意义的信息和帮助。本文选择宜昌站作为研究对象，并以中华鲟和四大家鱼为典型代表物种，研究三峡工程初期蓄水对下游生态系统的影响。结果表明，三峡工程蓄水运行后，坝下宜昌站生态水文条件发生明显变化，主要表现为多年平均水温上升，多年平均流量、水位和含沙量下降；非汛期的水温以及汛期的流量、水位和含沙量月径流过程明显改变；下游生态水文条件的改变，导致中华鲟鲟卵孵化适宜度和四大家鱼产卵适宜度明显降低；栖息地内生态水文条件的变化是影响中华鲟鲟卵孵化和四大家鱼产卵行为的关键因素，而不是影响中华鲟产卵和四大家鱼鱼卵孵化的关键因素。

英文摘要：

The Three Gorges Reservoir is the largest key project in the middle reach of the Yangtze River. Downstream hydrological regime has been changing significantly after the impoundment of the reservoir. To analyze the changing situation of the downstream eeo-hydrological conditions, the basic information for river restoration could be provided. The Yiehang Hydrolgieal Station is taken in the study to assess the impact of the Three Gorges Reservoir impoundment on Chinese sturgeon and four major Chinese carps as the typical species of the downstream ecosystem. The results show that after water filling of the reservoir, （1） eco-hy- drological conditions in Yiehang Hydrological Station change significantly, including average annual water temperature rise, and a decrease in runoff, water level and suspended sediment concentration; （2） water temperature in non-flood season, and runoff, water level and suspended sediment concentration in flood sea- son have changed obviously; （3） the change of downstream eeo-hydrological conditions results in the suit- ability of sturgeon eggs hatching and carps spawning reduced distinctly; （4） the variation of eco-hydrologi- eal conditions within the habitat is a key factor for sturgeon eggs hatching and carps spawning, but that is not the key factor for sturgeon spawning and carps eggs hatching.