长江水下三角洲邻近海域^(210)Pb分布特征及沉积动力学指示意义

Distribution of ^(210)Pb in the sediments of subaqueous Changjiang(Yangtze) Delta and its implications for the sediment dynamics

为了研究长江水下三角洲及邻近海域沉积动力环境对长江入海输沙量减少的响应,进行了野外采样以及论文数据收集工作,利用^(210)Pb放射性同位素的测量和分析,分别比较表层和柱状沉积物的^(210)Pb活度在2003年前后的变化。结果显示,在2003年后,表层沉积物^(210)Pb活度分布特征由原来的明显梯度变化变为均一分布,同时活度值普遍降低;而柱状沉积物的^(210)Pb垂向分布曲线也由原来的稳定沉积曲线变为混合强烈的均匀分布。这说明了,在长江入海输沙量减小的背景下,研究区内的沉积动力环境随之发生改变,河口过程主导的沉积作用在不断减弱,而陆架过程主导的混合作用却在不断加强。

In order to ascertain the response of sediment dynamics of the subaqueous Changjiang Delta to the Changjiang River catchment changes, the ^210Pb was selected as the tracer, and the ^210Pb activity distribution in both surface sediments and sediment cores were investigated. The results indicate that, after 2003, the distribution pattern of ^210pb in the surface sediment became more uniform than that before 2003, and the ^210Pb activity greatly reduced. In addition, the vertical distribution of ^210pb also shows that, after 2003, the sedimentary environment of this area converted from continuous deposition to intensive mixing. Above phenomenon demonstrates that, after the impoundment of the TGD （Three Gorges Dam） in 2003, the intensity of sediment mixing became intensified, due to the sediment load reduction of Changjiang River catchment.