Impacts Of Natural Processes And Human Activities On The River Sediment Flux Into The Sea And Its Environmental Significance, China

This paper mainly deals with the characteristic of the sediment supply to the sea of the main rivers in China, in view of the impacts of natural process and human activities, with the special emphasis on the Yangtze River. The results and conclusions are:1 In the past five decades, the averaged sediment supply to the sea of the main rivers in China is 13 × 10~8 t/a, with a significant decreasing trend. The resent (1994-2003a) averaged sediment load (6.6× 10~8 t/a) is only 37% of that of the 1954-1973a. Northern rivers observe more sharp decrease than the southern rivers do. Precipitation in drainage basin the main rivers in China slightly decreased in the past five decades, which is one of the causes that induced the decrease of the sediment load in the northern rivers. Periodical analysis showed that abrupt change of sediment load happened in 1968 and 1984, which divided the variation process of river sediment load into three stages. The main cause of the periodical variation patterns is the human activities. According to the spectrum analysis, the sediment load also fluctuated at the periodicity of 3a and 10a. Human activities have overwhelming impacts on the river sediment yield and transportation process. Though human activities induced the increasing trend of sediment load of some small rivers, such as Jiulongjiang River, but rapid dam construction induced the sharp decrease of the total sediment supply to the sea. Though climate change has contribution to the sediment decrease in the northern rivers, but generally, is not fundamental Influencing factors. Dam causes the decrease of the sediment supply to sea of the main rivers in China.2 Spectrum analysis showed that consistency exist among the periodicity of precipitation, water and sediment discharge of each tributary of Yangtze River. This demonstrated that the fluctuation of sediment load is governed by the periodical variation of climate change. Apart from the Jinshajiang River, all the sediment discharge of the tributaries show decreasing trend. While precipitation and water discharge of Jinshajiang River, Lake Dongting and Lake Poyang drainage basin show...