GRAIN-SIZE CHARACTERISTICS AND THEIR ENVIRONMENTAL SIGNIFICANCE OF WANGHU LAKE SEDIMENTS IN THE MIDDLE REACH OF YANGTZE RIVER
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摘要: 通过放射性核素137Cs和210Pb精确计年,建立了长江中游原通江湖泊网湖近代沉积物年代序列。运用沉积物粒度指标分析了近100年来网湖沉积记录的环境特征,结果表明,近100多年来网湖沉积速率较大,平均约为0.56 cm/a;沉积物粒度指标变化与流域降雨量、人类活动以及长江洪水密切相关,降水大的年份和大洪水时期沉积物粒径增大,分选性变差,峰态变宽。根据沉积物粒度指标特征,近100年来网湖沉积环境大致可分为两个阶段:(1)20世纪50年代以前,湖泊沉积主要受降水和洪水等自然因素控制,沉积物粒度组合变化相对较小,在湖泊水动力条件变化时沉积物粒度指标出现明显的波动,反映了流域降水及长江洪水对湖泊沉积环境的影响。(2)20世纪50年代以后,湖泊沉积物平均粒径较大且分选性差,与流域强烈的人类活动所引起的大量陆源碎屑进入湖泊有关,湖泊沉积粒度指标主要反映了流域工农业生产的快速发展、人口的持续增长以及水利工程建设等人类活动对湖泊沉积环境的影响。Abstract: 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.
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Key words:
- grain-size of lake sediment /
- flood /
- precipitation /
- human activity /
- Wanghu Lake
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