Analysis of suspended sediment concentration characteristics under erosion-deposition condition changes in the Yangtze River Estuary.

In recent years, as river-borne sediment transport has decreased, land loss in estuarine areas has become increasingly severe. Particularly from 2009 to 2022, due to the reduced sediment load from the upper reaches of the Yangtze River, significant changes in the erosion-deposition conditions at the Yangtze River Estuary have become a critical concern. The suspended sediment concentration (SSC) in the estuary is closely linked to sediment content, and against this backdrop, this study aims to thoroughly explore the response mechanisms of the Yangtze River Estuary's SSC to changes in erosion-deposition conditions, with the goal of providing scientific bases and strategic recommendations for erosion-deposition management. To this end, this research collected historical water depth data for the Yangtze River Estuary, measured vertical distribution of SSC in September 2022, surface suspended sediment concentration (SSSC) data from 2021 to 2023, and 25 factors influencing SSSC, to analyze in detail the changes in the erosion-deposition conditions at the Yangtze River Estuary and the response mechanisms of SSC to these changes. The analysis showed that between 2009 and 2022, the mouth bar area of the Yangtze River Estuary experienced net erosion for the first time since 1958, with an annual erosion rate reaching 63.2 × 10^6 m/yr, and the highest erosion rate occurring in the North Passage area, reaching 83.3 mm/yr. This phenomenon is likely caused by human-induced changes in underwater topography, with the Yangtze River Estuary shifting from deposition to erosion. Between 2021 and 2023, the turbidity maximum zone (TMZ) of the Yangtze River Estuary did not show regular changes in SSSC, which may be related to the frequent occurrence of typhoons and changes in sediment supply in the submerged delta of the Yangtze River Estuary.