Characteristics of grain size distributions of seabed and suspended sediment over the Dafeng tidalflat of Jiangsu Coast

Grain size distributions of seabed and suspended sediment samples from several sites on the Dafeng tidalflat,northern Jiangsu coast,collected in July and August of 2002 and 2003,were analyzed.The results show that the seabed-sediment can be divided into different types from lower to upper parts of the flat in terms of grain size parameters;the sources and mode of sediment movement of the seabed sediment(consisting of suspended material and/or bed-load) and the saltmarsh vegetation are the main factors to influence the spatial distributions of seabed sediment.Two types of grain size distributions of suspended sediment according to the temporal-spatial variations during the tidal cycle can be identified.One is the stability type with small variations;the other is the type associated with a double-peak characteristic in the grain size distribution curve,with remarkable variations.The main factors that affect the grain size distributions of suspended sediment include localized resuspension and settling process,suspended sediment transported onto tidal flats during the flood phase of the tide,and the spatial distribution pattern of seabed sediment.The difference in gain size distribution between the seabed and suspended sediments is significant.The relationship between the two distributions can be explained by resuspension and settling processes.