利用LISST观测絮凝体粒径、有效密度和沉速的垂线分布

Using LISST-100 for in-situ estimates of floc size,density and settling velocity,Changjiang Estuary,China

2003年6月,利用B型现场激光粒度仪LISST_100在长江口徐六泾站定点连续观测了洪季大潮垂线细颗粒悬浮泥沙的实有粒径、体积浓度,利用OBS-3A测量现场悬沙浓度。计算了现场絮凝体有效密度和沉速。观测结果显示现场细颗粒泥沙絮凝体的平均粒径从表层到底层逐渐增大,表层为30～60μm,中层为50～80μm,底层超过90μm。絮凝体有效密度受水动力条件控制,从表层到底层逐渐减小,有效密度在532～1456kgm3之间;絮凝体的现场沉速从表层到底层逐渐加大,沉速变化范围在070～562cms之间。

In June of 2003,the Laser In Situ Scattering and Transmissometry-100(LISST-100) was used to measure mean grain size (D-m)and volume concentrarion (VC) of fine suspended sediment flocs during spring tide in Xuliujin of Changjiang Estuary.Based on the value of D-m,VC and suspended sediment concentration(SSC) which was measured by OBS,the in situ mean effective density(Δρ) and mean settling velocity(ω-s) of fine suspended sediment flocs can be calculated.The observation data showed that average D-m increases with water depth,the variety ranges of D-m in the upper layer and middle layer of the water are from 30μm to 60μm and from 50μm to 80μm,respectively,and D-m in the bottom layer is over 90μm.The analysis of Δρ showed that it decreases from the upper layer to the bottom layer of the water with a range from 532 kg·m^-3 to 1456 kg·m^-3 .Floc ω-s increases from the upper layer to the bottom layer of the water in the range of 0.70 cm·s^-1 to 5.62cm·s^-1 .