中文摘要：

首先阐述了土壤侵蚀可分为自然侵蚀和人为加速侵蚀，自然侵蚀是自地球形成以来就普遍存在的一种自然现象；继而从夷平面、河流阶地、沉积盆地等侵蚀和堆积地貌形迹论述了第四纪以来长江中上游土壤自然侵蚀存在的佐证事实；在此基础上，依据侵蚀沉积相关原理，利用沉积物的厚度、面积和沉积时段分别计算了洞庭湖流域、鄱阳湖流域和古云梦泽流域全新世以来的自然侵蚀量，它们分别为264．2t／km^2·a、312．5t／km^2·a和297．0t／km^2·a；同时，本文还辅以川西和三峡地区的对比实验小区资料，现代自然侵蚀量分别为342．0t／km^2·a、75-270t／km^2·a佐证历史自然侵蚀量。长江上中游区域的自然侵蚀量介于264．0t／km^2·a～342．0t／km^2·a之间。流域平均自然侵蚀量是现代侵蚀量的50％～60％之间；本研究成果有助于对长江中上游现代土壤侵蚀的属性、演变过程有一个科学的认识；同时可为生态保护、环境友好建设目标提供背景参照物。

英文摘要：

In this study, soil erosion is divided into natural soil erosion and anthropogenic soil erosion. The natural soil erosion is ubiquitous on the earth since the earth came into being. Erosive and accumulative topographic features, such as peneplain, river terrace, sedimentary basin, etc., have disclosed the existence of natural soil erosion in the upper and middle Yangtze River since the early Quaternary. Using the thickness, dating and area of sediment deposited in the Dongting Lake, Poyang Lake and the ancient Yunmeng Lake, the specific sediment yield of the watersheds draining into these lakes is found to be 264. 2t/km^2·a, 312. 5t/km^2·a and 297.0t/km^2·a, respectively. Moreover, the natural sediment yield from some experimental plots located in west Sichuan and the Three Gorge areas is estimated to be about 342.0t/km^2·a and 75-270t/km^2·a, respectively. Thus, the natural sediment yield ranges from 264.0t/km^2·a to 342.0t/km^2·a in the upper and middle Yangtze River, which is about 50%- 60% of the modern sediment yield in the area. The results of this study will help us to understand the characteristics and tendency of the modern soil erosion in the upper and middle Yangtze River, and will be a sound background for realizing the goal of conserving eco-systems and building an environmental management in the area.