| 摘要: |
| 2003年6月14日-22日,利用现场激光粒度仪LISST-100在不扰动颗粒物的情况下,于长江口徐六泾定点连续观测了洪季大、小潮表层粘性悬浮细颗粒泥沙絮凝体的实有粒径、体积浓度,配合OBS-3A现场测量的悬沙浓度计算了现场絮凝体的有效密度和静水沉速。观测结果显示,徐六泾大、小潮表层絮凝体体积浓度、粒径、有效密度和静水沉速的平均值分别为98.0 μl/L、39.8 μm、1173 kg/m3、1.14 mm/s和70.8 μl/L、64.4 μm、919 kg/m3、2.32 mm/s。研究表明:①长江口徐六泾表层絮凝体体积浓度主要受水流流速影响,再悬浮现象明显,体积浓度过程线滞后流速过程线,落潮期间滞后10-30 min,涨潮则滞后30-50 min;②小于一定流速时絮凝体平均粒径随流速增大而增大,大于一定流速时絮凝体平均粒径则随流速增大而减小,徐六泾大、小潮表层絮凝体在50 cm/s的垂线平均流速时出现平均粒径与垂线平均流速关系的转折;③徐六泾大、小潮表层絮凝体平均粒径在体积浓度75 μl/L时出现平均粒径与体积浓度关系的转折,体积浓度小于75 μl/L时粒径随体积浓度增加而增大,超过75 μl/L时粒径随体积浓度的增加变化不明显；4絮凝体有效密度由粒径大小控制，粒径大，有效密度小，反之亦然，粒径和有效密度共同决定絮凝体静水沉速，有效密度和沉速与平均粒径之间存在良好的幂指数关系。 |
| 关键词: LISST 絮凝体 粒径 有效密度 沉速 长江口 |
| DOI： |
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| 基金项目:国家重点基础研究发展规划“973”项目,2002CB412403、2004CB720505号;国家自然科学基金资助项目,50379014号 |
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| CHARACTERISTICS OF SUSPENDED FINE SEDIMENT FLOCS IN CHANGJIANG (YANGTZE) ESTUARY |
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CHENG Jiang1,2, HE Qing1, XIA Xiao-Ming3
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1.State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, 200062;2.Department of Environmental Science, East China Normal University, Shanghai, 200062;3.Second Institute of Oceanography, State Oceanic Administration, Hangzhou, 310012
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| Abstract: |
| Natural physical characteristics, such as mean diameter (Dm), effective density (Δρ) and settling
velocity (ωs) of fine suspended sediment flocs in Changjiang (Yangtze) Estuary are studied. Temporal changes in Dm and volume concentration (VC) of fine suspended sediment in surface water during spring and neap tides were measured in situ in June of 2003 in Xuliujing with a laser particle size analyzer (Laser In Situ Scattering and Transmissometry, LISST); and suspended sediment concentration (SSC) with an optical backscatter (OBS), from which mean Δρ and mean ωs of flocs were calculated in the field. The observation shows that average VC, Dm, Δρ and ωs at the surface water during spring tide are 98.0 μl/L, 39.8 μm, 1173 kg/m2 and 1.14 mm/s, whereas those during neap tide are 70.8 μl/L, 64.4 μm, 919 kg/m2 and 2.32 mm/s, respectively. Results show that flocs’ VC and Dm at the surface water were closely related to current velocity; and the peaks of VC lag those of the current velocity. The lag variation during ebb and flood tides is 10 - 30 min and 30 - 50 min, respectively. Current velocity at 50 cm/s is a turning point of Dm vs. vertical average current velocity, before the point, Dm increases with current velocity, and decreases after the point. Similarly, VC at 75 μl/L becomes a critical point in the surface water, below the point, Dm increases with VC, and above the point, Dm stabilizes. Δρ is Dm dependent, larger flocs have much lower Δρ than smaller flocs. Both Dm and Δρ of flocs affect ωs. In the surface water during spring tide and neap tide, a power exponent relationship exists between Δρ and Dm, and ωs and Dm. |
| Key words: LISST Flocs Grain size Effective density Settling velocity Changjiang (Yangtze) Estuary |
