Dynamics and spatial variability of near-bottom sediment exchange in the Yangtze Estuary, China
Dynamics and spatial variability of near-bottom sediment exchange in the Yangtze Estuary, China
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DOI：
10.1016/j.ecss.2009.04.020
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发表时间：
2010-02
影响因子：
2.8
通讯作者：
Hong Liu;Qing He;Z. Wang;G. Weltje;Jing Zhang
中科院分区：
文献类型：
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作者：
Hong Liu;Qing He;Z. Wang;G. Weltje;Jing Zhang
研究了长江口及邻近海域近底悬浮物与海底沉积物交换的空间变化特征，并探讨了研究区悬浮物的去向。沉积物的砂，粉砂，粘土含量之间的关系进行了分析，对数比分析，这揭示了一个非线性函数的选择性沉积和广泛的粒度分布在河口。这一发现不符合世界各地其他潮汐盆地的粘土/粉砂比几乎恒定的报告，由于复杂的水动力条件下的非线性沉积物混合。根据物质平衡原理，对长江口沉积物交换过程进行了定量分析。河口近底悬浮物的平均粒度分布表明，约49%的河流沉积物聚集在河口拦门沙区，而其余的，这主要是由细粒沉积物组成，被转移到河口外，并以絮凝体的形式沉积。沉积物交换比的空间分布表明，河口上游的细颗粒悬浮泥沙在落潮主导的潮流作用下被输送到河口拦门沙区，从而使少量的悬浮泥沙沉积到河口的海底（交换比<0.1）。由于近海洋流阻止了河流沉积物进一步向海扩散，外河口的沉积物交换率也显示出非常低的值（<0.1）。在双向潮流控制下，河口内沙泥混合，发生强烈的泥沙交换。此外，河口向海泥质区的泥沙交换率较高（>0.8），是现今长江泥质的沉积中心。将无因次交换率和整体沉积物累积率结合起来得到的沉积物交换率，在延伸至河口以南（经度122° E至123° E，纬度31° N）的泥泞沉积中心为2-3cm/年。
This study was conducted to examine the spatial variations in the exchange between near-bottom suspended and sea-bottom sediments in the Yangtze Estuary and adjacent region, as well as to explore the fate of suspended sediments in the study area. The relationship between the sand, silt, and clay contents of the sediments was analyzed by log-ratio analysis, which revealed a non-linear function for selective deposition and a wide range of grain-size distributions in the estuary. This finding does not conform to the nearly constant clay/silt ratios reported for other tidal basins around the world, due to non-linear sediment mixing under complex hydrodynamic conditions. The sediment exchange processes in the Yangtze Estuary were quantified based on the principle of mass balance. The average grain-size distribution of near-bottom suspended sediments from the estuary showed that approximately 49% of the riverine sediments accumulated in the mouth bar area, while the rest, which is primarily composed of fine-grained sediments, is transferred to the outer estuary and deposited in the form of flocs. The spatial distribution of the sediment exchange ratios demonstrated that small amounts of suspended sediment were deposited onto the seabed of the upper estuary (exchange ratio<0.1), because the fine-grained suspended sediments in this region were transported to the mouth bar area by the ebb-dominated tidal flow. The sediment exchange ratios in the outer estuary also showed very low values (<0.1) due to the oceanic currents offshore that prevented the diffusion of riverine sediments further seaward. Intensive sediment exchange occurred in the inner estuary due to the sand-mud mixing which was controlled by bidirectional tidal flows. In addition, a high sediment exchange ratio occurred in the muddy area (>0.8) seaward of the river mouth, which implies that this is the present-day depocenter of Yangtze mud. The sediment exchange rates obtained by combining the dimensionless exchange ratios and bulk sediment accumulation rates, were found to be 2–3cm/yr in the muddy depocenter, which extends to the south of the river mouth (from 122° E to 123° E longitude, at 31° N latitude).