Formation of Concentrated Benthic Suspension in a Time-Dependent Salt Wedge Estuary
Formation of Concentrated Benthic Suspension in a Time-Dependent Salt Wedge Estuary
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随时间变化的盐楔河口浓底栖悬浮液的形成
DOI：
10.1029/2018jc013876
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发表时间：
2018-11
影响因子：
3.6
通讯作者：
Gu Jinghua
中科院分区：
文献类型：
--
作者：
Ge Jianzhong;Zhou Zaiyang;Yang Wanlun;Ding Pingxing;Chen Changsheng;Wang Zheng Bing;Gu Jinghua
泥沙浓缩底泥悬浮物(CBS)作为河口最大浑浊带泥沙输移的主要贡献者，其形成机理尚不清楚，难以通过现场测量准确监测。利用配备多台仪器的三脚架系统对长江口北槽近床水动力和泥沙进行了测量，以确定CBS的形成机制。近床层1m处泥沙含量明显偏高，南部约20g/L，北部约47g/L。强CBS发生在弱潮汐混合条件下，与沉积物对湍动能的抑制以及咸水入侵和泥沙悬浮引起的水层结增强有直接关系。在弱混合小潮期间，CBS的典型厚度约为0.2-0.3m，寿命约为2.83小时(悬浮泥沙浓度>；15.0g/L)。增强的水层结减少了垂向混合，限制了从近床层到上层的泥沙夹带。这一增强是由于枯水期间近底柱中的泥沙积累抑制了湍动能，也是由于靠近底部的咸水入侵在垂直方向上出现了两层盐度结构。这些物理过程在CBS的形成过程中起到了正反馈回路的作用，可以用面向过程的一维垂直CBS模型来模拟。在浑浊度最大时，浓缩型底栖生物悬浮物(CBS)常常主导着近床面泥沙的输移，然而，这很难被正确观测到，尤其是在层化条件下。由于沉积物和水动力的相互作用，CBS的形成机制复杂。在长江口潮汐分层航道中，研制了一套综合的三脚架系统，集成了许多尖端仪器，用于测量CBS和确定其形成过程。该系统在近海床下部1-m层中检测到CBS的存在，南部为~20g/L，北部为~47g/L，平均厚度为20~30 cm。相应的盐度、潮汐速度、波浪和湍动能也被记录下来。在CBS形成过程中，潮汐混合作用较弱。盐度/泥沙引起的层结极大地限制了垂直混合，抑制了湍动能的产生。咸水入侵造成了盐度的双层结构，导致分层，减少了混合。这些物理效应就像一个正反馈循环。建立了一个一维垂直模式，成功地模拟了CBS的形成过程，表明CBS在弱潮混合小潮循环期间是稳定的。
The concentrated benthic suspension (CBS) of mud, as a major contributor of sediment transport in the turbidity maximum of the estuary, is of great challenge to be correctly monitored through field measurements, and its formation mechanism is not well understood. A tripod system equipped with multiple instruments was deployed to measure the near-bed hydrodynamics and sediments in the North Passage of the Changjiang Estuary, with the aim at determining the formation mechanisms of CBS. The measurements detected a significant dominance of high sediment concentration in the near-bed 1-m layer: ~20 g/L at the southern site and ~47 g/L at the northern site. Strong CBS occurred under weak tidal mixing condition and was directly relevant to the sediment-induced suppression of turbulent kinetic energy and the enhanced water stratification due to saltwater intrusion and sediment suspension. During the weak-mixing neap period, the typical thickness of CBS was about 0.2–0.3 m, with a life time of ~2.83 hr (suspended-sediment concentration > 15.0 g/L). Enhanced water stratification reduced vertical mixing and confined the sediment entrainment from the near-bed layer to the upper column. This enhancement was due to the suppression of turbulent kinetic energy as a result of the sediment accumulation in the near-bottom column during the slack waterand also due to the appearance of a two-layer salinity structure in the vertical as a result of saltwater intrusion near the bottom. These physical processes worked as a positive feedback loop during the formation of CBS and can be simulated with a process-oriented, one-dimensional vertical CBS model. Plain Language Summary In the turbidity maximum, concentrated benthic suspension (CBS) frequently dominates the near-bed sediment transport, which, however, is difficult to be correctly observed, especially in the stratified condition. And the formation mechanism of CBS is complex due to the interaction of sediment and hydrodynamics. In a stratified tide channel of the Changjiang Estuary, China, a comprehensive tripod system, integrated with many cutting-edge instruments, is developed and deployed tomeasure the CBS and to determine the formation process. This system detected the existence of CBS in the lower near-bed 1-m layer, ~20 g/L at the southern site and ~47 g/L at the northern site, with the mean thickness of 20–30 cm. The corresponding salinity, tidal velocities, wave, and turbulent kinetic energy were also recorded. During the formation of CBS, tidal mixing is weak. And the salinity/sediment-induced stratification greatly limits the vertical mixing and suppresses the turbulent kinetic energy production. The saltwater intrusion creates a two-layer structure of salinity, leading to stratification and decreasing the mixing. These physical effects work like a positive feedback loop. A one-dimensional vertical model had been developed to successfully simulate the formation process of CBS, indicating the stable CBS during weak-tidal-mixing neap cycle.
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影响因子：
2.3
作者：
P. Traykovski;P. Wiberg;W. Geyer
通讯作者：
P. Traykovski;P. Wiberg;W. Geyer
影响因子：
4.4
作者：
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通讯作者：
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利用原位声学反演算法估算中国高浊度长江口泥沙输运
影响因子：
1.6
作者：
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通讯作者：
Kong Ya-zhen
影响因子：
4.4
作者：
Pawlowicz, R;Beardsley, B;Lentz, S
通讯作者：
Lentz, S
影响因子：
2.3
作者：
A. Sottolichio;D. Hurther;N. Gratiot;P. Bretel
通讯作者：
A. Sottolichio;D. Hurther;N. Gratiot;P. Bretel