中文摘要：

流域人类活动对长江中下游水沙态势变异产生重要影响,为了深入了解长江中下游水沙态势变异特征及主要影响因素,本文利用累积曲线法、M-K次序分析法和有序聚类法就长江中下游干流、主要支流和两湖（洞庭湖、鄱阳湖）湖口1950-2011年期间水沙态势变化特征进行研究,分析了流域人类活动的变化特征,指出长江中下游干流汉口站和大通站、主要支流汉江皇庄站及鄱阳湖湖口站年径流量没有明显的变化趋势,干流宜昌站和洞庭湖湖口城陵矶站的年径流量有显著减少的趋势;除鄱阳湖湖口站年输沙量变化不大外,干流、主要支流和洞庭湖水文站年输沙量显著减少.结合长江中下游水沙变化的特征,分析了水库拦沙、水土保持、两湖（洞庭湖、鄱阳湖）区域水沙变化、河道采砂等因素的影响,指出不同的影响因子对河道水沙态势变化的作用是不同的,特别是水库拦沙的影响更显著,三峡水库运用对中下游干流水沙态势变异的作用是非常重要的.

英文摘要：

Human activities in the basin severely affected flow and sediment in the Lower and Middle Yangtze River.In order to study the relationship between variations in flow and sediment and human activities,runoff and sediment during the period from 1950 to 2011 in the trunk stream,main tributaries and two lakes （the Dongting Lake and the Poyang Lake） of the Middle and Lower Yangtze River were investigated with the cumulative curve analysis method and the Mann-Kendall test method.Changes in human activities were also analyzed in this paper.Data analysis shows that there is no obvious changing trend for annual runoff in the Hankou station and the Datong station in the trunk steam,main tributaries and the Poyang Lake in the Middle and Lower Yangtze River.There is an obvious reducing trend in the Yichang station at the trunk and the Chenglingji station in the Dongting Lake.Annual sediment load reduced significantly in the main tributaries,the Dongting Lake and the trunk stations except for the Poyang Lake without obvious changing trends.The impacts of human activities such as sediment trapping by reservoirs,soil and water conservation,water and sediment changes in the both lakes and sand mining in river on water and sediment changes of the river are analyzed according to the characteristics of water and sediment variations in the Middle and Lower Yangtze River.The different human activity plays a different role in the changes of river runoff and sediment.The influence of the trapping sediment by reservoirs is more obvious than other factors,and the Three Gorges Reservoir takes a great role in the water and sediment variations in the trunk of the Middle and Lower Yangtze River.