GRAIN-SIZE CHARACTERISTICS AND THEIR ENVIRONMENTAL SIGNIFICANCE OF WANGHU LAKE SEDIMENTS IN THE MIDDLE REACH OF YANGTZE RIVER

Sediment cores were collected in November 2007 from Wanghu Lake, a river-connecting lake before 1960s, in the middle reach of the Yangtze River.Grain sizes of sediment samples were analyzed using Mastersizer 2000 and the grain-size parameters were calculated by moment method. Sedimentation rates were determined with high-resolution radionuclide timing (¹³⁷Cs and ²¹⁰Pb-date to age-depth profile translation). The results show that the average sedimentation rate of Wanghu Lake is about 0.56 a/cm and the grain size parameters occur obviously fluctuating due to annual precipitation variation and flood. The average grain size is increasing, the coefficient of sorting is worse, and the feature of kurtosis is wider during heavy rainfalls and flood. After 1950s,human activities, such as the hydraulic engineering construction, the development of industry and agriculture, reclaiming land from the lake, resulted in remarkable increase of erosion and more terrestrial materiells were carried into Wanghu Lake. Therefore, the average grain size of deposit gradually increased.