CHANGES OF SUSPENDED PARTICLE MATTER IN THE WATER MIXING ZONE OF THE YANGTZE RIVER ESTUARY AND THEIR SEDIMENTARY IMPLICATION

Abstract: The Yangtze River estuary where is a strong interaction area of land and ocean, experiences dramatically changes in sedimentary environment conditions and suspended particle matter. The changes in suspended particle matter would contain crucial information to the deposition processes in the area. Suspended particle samples alone the water mixing zone of the Yangtze River Estuary were collected in December 2016. The suspended particles were identified by a scanning electron microscope with an energy dispersive X-ray spectrometer, and their grain size distribution patterns were analyzed by a laser particle size analyzer. The suspended particles include terrigenous detritus, biogenic clast, organic film, authigenic mineral, and floc. Typical authigenic minerals include iron oxides, pyrite, and barite. They originated from the water mixing process or from re-work of the surface sediment. The average particle size of suspended matter in the mixing zone ranges from 5.73 Ф to 7.98 Ф. Suspended particle sizes have significant changes within the water mixing zone: in the freshwater dominating area, the suspended particles were mainly composed of fine particles and had small mean grain size; in the weak mixing zone, they included large amount of loose combined flocs and had relative large mean grain size; in the strong mixing zone, they contented some amount of solid combined flocs and had small mean grain size. The changes of suspended particle matter in the estuarine water mixing zone would promote the settling of suspended matter in there, which has important influence on the formation of the maximum turbidity zone and sedimentation process in the estuary.