通江湖泊是一种常见的自然生态系统类型，由于河流-湖泊系统的复杂连接关系，湖泊对气候变化和人类活动的响应极为敏感。洞庭湖是中国第二大淡水湖，拥有巨大的水沙通量，为研究气候变化和人类活动影响下通江湖泊的水沙演变提供了重要的研究背景。研究变化环境下通江湖泊的水沙变化和湖泊演变，对揭示新情势下湖泊演变规律、科学认识江湖关系，水资源的可持续利用、生态环境的综合整治具有重要的指导意义。本研究首先利用统计分析方法对1951-2017年洞庭湖出入湖水沙通量变化进行趋势分析，并分离出重大人类活动对水沙要素变化的定量影响。结果显示，1969年之前洞庭湖流域基本仅受气候变化影响，人类活动使径流在1969-1988年、1989-2002年和2003年后分别下降了17.8%、25.4%和30.5%，输沙量分别下降了47.5%、72.1%和90.8%。其中下荆江裁弯取直、葛洲坝水库建成、三峡水库运行对泥沙减少的贡献分别47.9%、39.9%、69.5%。通过构建了洞庭湖水沙数值模型，模拟了三峡水库运行后（2003-2016年）荆南三河和洞庭湖的冲淤时空变化，进而探讨引起冲淤变化的动力过程和机制。研究发现，荆南三河在三峡工程运行后整体保持冲刷态势，由上游至下游沿程冲刷强度减小。冲刷状态短期内不会变化，但冲刷强度逐渐下降。分沙量大幅降低是荆南三河冲淤状态改变的关键，口门采砂活动也有重要影响。洞庭湖持续淤积的形势得到缓解，净冲淤量大幅下降，冲刷主要集中在湖泊洪道附近区域，东洞庭湖漫滩逐渐开始冲刷。由于荆南三河的缓冲作用，洞庭湖尚未发生全湖性的大规模冲刷，但随着荆南三河的冲淤调整完成，洞庭湖将进入新一轮的湖泊冲淤平衡调整期。为了定量分析单一要素对洞庭湖水位的影响程度，本研究运用洞庭湖水沙模型，基于不同的模拟情景分析了三峡水库运行后（2008-2016年）水库流量调控、大坝泥沙拦截、四水来流变化和湖底地形变化的影响及差异。结果表明，2~4月，四河流量的减少在洞庭湖水位的下降中起主导作用；8~10月，三峡水库对洪水的拦截是导致水位下降的关键因素。其中，三峡水库汛期拦洪和汛末蓄水导致丰水期和退水期湖区水位大幅下降，补水调度主要通过升高长江干流水位抬高洞庭湖水位；四水来流变化对南洞庭湖水位直接影响最为明显，东洞庭湖受到影响较小；湖区地形变化对水位呈现“高水位时水位升高，低水位时水位降低”的规律。

Lake connected with rivers is a common type of natural ecosystem. Due to the complex connection of river-lake systems, lakes are extremely sensitive to climate change and human activities. Dongting Lake is the second largest freshwater lake in China and has a huge runoff and sediment flux, which provides an important research background for research on the evolution of water-sediment fluxes in the river-lake systems under the influence of climate change and human activities. Studies on the change of runoff and sediment fluxes and lake evolution in river-lake systems under the changing environment is of great significance for revealing the evolution of the lake under the new conditions, scientific understanding of river-lake relationship, sustainable utilization of water resources and comprehensive improvement of ecological environment.This study analyzed the trend of changes in runoff and sediment fluxes of Dongting Lake from 1951 to 2017 and identified the major quantitative effects of climate change and human activities on changes in water-sediment fluxes. The results show that the runoff and sediment fluxes of Dongting Lake basin were basically only affected by climate change before 1969. Human activities respectively reduced runoff by 17.8%, 25.4% and 30.5% between 1969 and 1988, 1989 and 2002 and after 2003。 Sediment fluxes decreased by 47.5%, 72.1% and 90.8%, among which the Lower Jingjiang River Interception Project, the completion of Gezhouba Reservoir and the operation of Three Gorges Reservoir correspondingly contributed 47.9%, 39.9% and 69.5% to the sediment flux reduction.A hydraulics and sediment transport model in Dongting Lake was constructed to simulate the spatial and temporal changes of erosion and siltation in the river system in the lake region and Dongting Lake after the operation of Three Gorges Reservoir, and then to explore the dynamic processes and mechanisms causing the changes of erosion and siltation. It is found that the river system in Dongting Lake overall maintains a scouring trend after the operation of Three Gorges Reservoir, and the scouring intensity decreases from upstream to downstream. The significant reduction of the amount of sediment distribution is the key to the change of the erosion state of the river system in Dongting Lake, and sand mining at the estuary also has an important influence on the activity. The situation of continuous siltation in Dongting Lake is relieved, the net erosion and siltation volume decreases significantly, the erosion is mainly concentrated in the area near the flood channel of the lake, and the East Dongting Lake floodplain gradually starts to erode. Because of the buffering effect of the river system in Dongting Lake, Dongting Lake has not yet undergone a large-scale erosion. However, with the completion of the adjustment of the erosion and siltation of the river system in Dongting Lake, Dongting Lake will enter a new round of lake erosion and deposition balance adjustment period.In order to quantitatively analyze the influence of a single factor on the water level of Dongting Lake, the impact and difference of reservoir flow regulation, sediment interception by the dam, changes in the incoming flow of the Four Rivers (Xiang River, Zi River, Yuan River and Li River) and changes in the topography of the lake bottom after the operation of Three Gorges Reservoir were analyzed based on different simulation scenarios using the hydraulics and sediment transport model. The results show that from February to April, the reduction of the flow of the Four Rivers played a leading role in the decrease of the water level in Dongting Lake; from August to October, the interception of flood by the Three Gorges Reservoir was the key factor leading to the decrease of the water level. The water level decreased significantly during the flooding and receding periods due to the interception of flood by the Three Gorges Reservoir and the storage of water at the end of the flooding period. The water replenishment scheduling mainly raised the water level of the Yangtze River to support the water level of Dongting Lake. The changes in the incoming flow of the Four Rivers had a greater direct impact on the water level of South Dongting Lake, while the East Dongting Lake is less affected. And the topographical changes of the lake area showed the rule of "the water level rises when the water level is high and falls when the water level is low" to the water level.