The vertical changes of suspended sediment in the turbidity maximum zone along the South Passage of the Changjiang River Estuary
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摘要: 最大浑浊带水体悬沙时空变化过程是河口沉积动力学研究的核心内容之一。利用2013年6月16—24日在长江口南槽最大浑浊带自小潮至大潮连续9天的逐时定点水文及悬沙观测资料，分析南槽最大浑浊带悬沙垂向变化特征及影响机制，由此加深对长江口最大浑浊带形成及变化的理解。主要结果包括：(1) 南槽最大浑浊带悬沙平均粒径为3.52～18.84 μm。从小潮到大潮、从表层水体到底层水体，悬沙粒径逐渐增大，水体含沙量逐渐增大，含沙量为0.12～2.29 g/L。(2)水体流速呈现自下而上、自小潮到大潮逐渐增大的态势，与悬沙粒径的关联度较好；而水体盐度呈现自上而下、自小潮到大潮逐渐增大的态势，与悬沙含量的关联度较好。(3)南槽最大浑浊带水体悬沙垂向变化涵括两种控制机制：涨落潮作用引起的底沙再悬浮控制水体悬沙约7 h的周期性变化；涨潮流挟带的口外泥沙絮凝形成的絮团在涨潮流和重力作用的影响下引起水体悬沙出现约14 h的周期性变化特征。Abstract: Temporal and spatial variation processes of suspended sediment in the estuary turbidity maximum zone (TMZ) is one of the crucial issues of estuarine sedimentation dynamics. Based on hourly hydrological data and suspended sediment samples collected on June 16—24, 2013 covering a complete neap-spring tide cycle, the vertical changing characteristics and related dominant mechanism of suspended sediments in the TMZ in the South Passage (SP) were analyzed to deepen the understanding of TMZ formation and evolution in the Changjiang River estuary. Results show that: (1) the average grain size of the suspended sediment ranged 3.52～18.84 μm while the suspended sediment concentration (SSC) fluctuated between 0.12 ～2.29 g/L. The SSC was increased from neap tide to spring tide in temporal scale, and from surface to bottom in spatial scale. (2) The current velocity increased from bottom to surface and from neap tide to spring tide, and correlated closely with the average grain size of suspended sediment. The salinity decreased from bottom to surface and from spring tide to neap tide and correlated closely with the SSC. (3) The vertical changes of the suspended sediment exhibited two types of controlling mechanisms: the bed sediment resuspension under flood and ebb tidal forces, which generated a periodical change of 7 hours, and the sediment flocculation under the forces of flood tide and gravity, which generated a periodical change of 14 hours.
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图 3 不同潮周期悬沙平均粒径垂向变化
a. 小潮涨潮，b. 中潮涨潮，c. 大潮涨潮，d. 小潮落潮，e. 中潮落潮，f. 大潮落潮。
Figure 3. The vertical changes of average particle size in different tide cycles
a: Rising tide in neap tide, b: rising tide in middle tide, c: rising tide in spring tide, d: ebb tide in neap tide, e: ebb tide in middle tide, f: ebb tide in spring tide.
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图 4 小中大潮悬沙组分垂向变化
Figure 4. The vertical changes in suspended sediment component in different tide cycles
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图 5 不同潮周期含沙量垂向变化
a. 小潮涨潮，b. 中潮涨潮，c. 大潮涨潮，d. 小潮落潮，e. 中潮落潮，f. 大潮落潮。
Figure 5. Vertical changes of sediment in different tide cycles
a: Rising tide in neap tide, b: rising tide in middle tide, c: rising tide in spring tide, d: ebb tide in neap tide, e: ebb tide in middle tide, f: ebb tide in spring tide.
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图 6 小波周期性变化
a. 含沙量小波功率谱，b. 含沙量小波周期性，c. 平均粒径小波功率谱，d. 平均粒径小波周期性。
Figure 6. Wavelet periodical change
a: Wavelet coefficient of sediment, b: wavelet cyclicity of sediment, c: wavelet coefficient of average particle size, d: wavelet cyclicity of average particle size.
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图 7 流速及盐度与每层水体悬沙平均粒径的关联度
a. 表层平均粒径与各要素灰色关联分析，b. 0.2H平均粒径与各要素灰色关联分析，c. 0.4H平均粒径与各要素灰色关联分析，d. 0.6H平均粒径与各要素灰色关联分析，e. 0.8H平均粒径与各要素灰色关联分析，f. 底层平均粒径与各要素灰色关联分析。
Figure 7. Correlation of average particle size vs current velocity and salinity in different water layers
a: Surface layer, b: 0.2H layer, c: 0.4H layer, d: 0.6H layer, e: 0.8H layer, f: bottom layer.
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图 8 不同潮周期水动力垂向变化
a. 小潮涨潮，b. 中潮涨潮，c. 大潮涨潮，d. 小潮落潮，e. 中潮落潮，f. 大潮落潮。
Figure 8. Hydrodynamic vertical changes in different tide cycles
a: Rising tide in neap tide, b: rising tide in middle tide, c: rising tide in spring tide, d: ebb tide in neap tide, e: ebb tide in middle tide, f：ebb tide in spring tide.
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图 9 不同潮周期盐度垂向变化
a. 小潮涨潮，b. 中潮涨潮，c. 大潮涨潮，d. 小潮落潮，e. 中潮落潮，f. 大潮落潮。
Figure 9. The vertical changes of salinity in different tide cycles
a: Rising tide in neap tide, b: rising tide in middle tide, c: rising tide in spring tide, d: ebb tide in neap tide, e: ebb tide in middle tide, f: ebb tide in spring tide.
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图 10 流速及盐度对每层水体含沙量关联度
a. 表层含沙量与各要素灰色关联分析，b. 0.2H含沙量与各要素灰色关联分析，c. 0.4H含沙量与各要素灰色关联分析，d. 0.6H含沙量与各要素灰色关联分析，e. 0.8H含沙量与各要素灰色关联分析，f. 底层含沙量与各要素灰色关联分析。
Figure 10. Correlation of turbidity vs current velocity and salinity
a: Rurface layer, b: 0.2H layer, c: 0.4H layer, d: 0.6H layer, e: 0.8H layer, f: bottom layer.
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