The research of exchange processes between the suspended sediment near the bottom and the depositions in the Changjiang (Yangtze) Estuary
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摘要:
大河河口的动力沉积过程一直是陆海相互作用研究的核心内容，其中水体泥沙的垂向交换是河口动力-沉积机制分析中的关键环节。基于2011年12月对长江河口及其邻近海湾采集的大范围、高密度的近底层悬沙、海床表层1~2 cm（表层沉积物）和垂向向下约2~10 cm的沉积物（次表层沉积物）同步3组303个样品，利用经验正交函数方法，对河口地区的悬沙和沉积物交换过程进行研究。结果表明：近底层水体悬沙的空间分布模式主要以粉砂粒级为主，空间分布差异性不大；表层及次表层沉积物的空间分布模式相似，但较近底层水体悬沙的分布复杂，存在明显的区域性特征，其中南汇边滩水域中部辐散区的沉积物表现为粗粉砂-细砂模式，其他区域由粉砂组分模式组成。近底层水体悬沙、表层和次表层沉积物的第一模态主要反映了粒径较细的泥沙运动，第二模态主要反映了粒径较粗的泥沙运动。在近底层水体悬沙与表层沉积物的垂向交换中，主要交换粒级为粉砂组分粒级。在表层沉积物与次表层沉积物的垂向交换中，南汇边滩中部辐散区的主要交换粒级为粗粉砂-细砂组分粒级，其他区域主要为粉砂组分粒级。
Abstract:The large estuarine sediment dynamic process has been the core content of the land ocean interactions in the coastal zone research. The vertical exchange for sediments in the different water depth of the estuary is a key in the analysis of estuarine dynamics and deposition mechanism. Here,a large-scale and dense sediment samples cruise of the Changjiang (Yangtze) Estuary was carried out in December 2011,where three sets with 303 sediment samples including suspended sediment near the bottom,surface deposition with a vertical thickness of 1 to 2 cm,and subsurface deposition with a vertical thickness of 2 to 10 cm were simultaneously taken by grabber instrument. Thereafter,based on the collected sediment samples,the empirical orthogonal function method was applied to discuss the exchange process of the suspended load near the bottom and bed sediments. The results are shown as follows: the spatial distribution patterns of the suspended load near the bottom of the Changjiang Estuary are mainly composed of silt with a small difference in spatial distributions. The spatial distribution patterns of surface bed sediments and subsurface bed sediments are similar with regional characteristics. Their spatial distributions are more complex than that of the suspended load near the bottom. In the central district of Nanhui Shoal,sediments were characterized by coarse silt and fine sand,and the sediments distributed in other areas were characterized by silt. Furthermore,the first mode of the sediments by EOF could mainly reflect the sediments movement of fine particle size,and the second mode mainly reflects the sediments movement of coarse particle size. The vertical exchange between the suspended load and the surface bed sediments with main grain size is silt components. However,during the exchange process between the surface bed sediments and subsurface bed sediments in the central district of Nanhui Shoal,the dominant exchange component is coarse silt,and fine sand exchange occurred in other regions. Taken altogether,grain size with silt components of the Changjiang Estuary should play a dominant role in bed sediments exchange process.
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