长江口悬浮体粒度特征及其季节性差异

PARTICLE-SIZE CHARACTERISTICS AND SEASONAL VARIABILITY OF SUSPENDED PARTICULATE MATTERS IN THE CHANGJIANG RIVER ESTUARY

1998年 1 1月和 1 999年 5月长江口悬浮体样品的激光粒度仪分析结果表明 ,长江口悬浮体粒度较细 ,分选较差 ,偏态和峰态偏小 ,粒度组成以粉砂为主 ;粘土含量次之 ,基本不含砂或砂含量很小 ,由陆向海平均粒径有由粗到细的变化趋势。粒度分布呈典型的非正态分布 ,存在“双峰”和“三峰”两种形式 ,表层样品以“双峰”分布为主 ,底层“三峰”或“双峰”并存。标准偏差 -粒度曲线上多峰出现 ,反映了长江口悬浮体组成的复杂性。长江口悬浮体粒度特征有较大的季节变化。悬浮体粒度变化的影响因素包括泥沙来源、底质再悬浮、生物作用和絮凝作用 ,粒度特征的季节差异是这些因素综合作用的结果。

Grain size compositions of 78 samples of suspended particulate matter collected from the Changjiang River estuary during November 1998 and May 1999 were analyzed with a Cilas-940L Laser Grain-size Analyzer.The results show that the suspended sediment consists mainly of fine-grained (silt) materials,relatively poorly sorted,with small skewness and kurtosis values; the grain size decreases in the seaward direction.The particle-size distribution curves show bimodal or multi-modal patterns,and several peaks are present in the curves of the standard deviation versus particle size.The correlation between the SPM concentration and the median particle-size is poor,but it is high between the inorganic particle content and D 50,indicating that the terrigenous detritus content of SPM is an important factor controlling the particle size of the SPM.Further,there is significant seasonal variability of the particle-size characteristics.The main factors affecting the variability include sediment sources,tidally-induced resuspension of bottom sediment,biological activity,and flocculation of fine-grained particles.