The vertical changes of suspended sediment in the turbidity maximum zone along the South Passage of the Changjiang River Estuary

Temporal and spatial variation processes of suspended sediment in the estuary turbidity maximum zone (TMZ) is one of the crucial issues of estuarine sedimentation dynamics. Based on hourly hydrological data and suspended sediment samples collected on June 16—24, 2013 covering a complete neap-spring tide cycle, the vertical changing characteristics and related dominant mechanism of suspended sediments in the TMZ in the South Passage (SP) were analyzed to deepen the understanding of TMZ formation and evolution in the Changjiang River estuary. Results show that: (1) the average grain size of the suspended sediment ranged 3.52～18.84 μm while the suspended sediment concentration (SSC) fluctuated between 0.12 ～2.29 g/L. The SSC was increased from neap tide to spring tide in temporal scale, and from surface to bottom in spatial scale. (2) The current velocity increased from bottom to surface and from neap tide to spring tide, and correlated closely with the average grain size of suspended sediment. The salinity decreased from bottom to surface and from spring tide to neap tide and correlated closely with the SSC. (3) The vertical changes of the suspended sediment exhibited two types of controlling mechanisms: the bed sediment resuspension under flood and ebb tidal forces, which generated a periodical change of 7 hours, and the sediment flocculation under the forces of flood tide and gravity, which generated a periodical change of 14 hours.