The southeastern portion of the Yangtze River Estuary (or Yangtze Estuary) was considered to be the deposition center and the mudbank of the Yangtze River Delta. As the fluvial sediment supply began to decline in the 1980s and the reduction accelerated after the completion of the Three Gorge Dam in 2003, more fluvial sediment was trapped decreasing the suspended sediment concentration (SSC) environment in the river mouth area. Moreover, the accretion rate of the mudbank has slowed down in recent decades. In fact, the mudbank shrank and has faced a regime shift from sediment sink to source. A better understanding of the tidal-scale dynamics and spatial variability of the system is essential to explore the conversion of the sediment sources and sinks in the Yangtze Estuary affected by natural variations and human activities. Flow velocity, salinity, and suspended-sediment concentration during spring and neap tides were measured at three sites on the mudbank in July 1982 and July 2013. The variation in flow was not significant at all the sites measured in the study area from 1982 to 2013. However, the sediment dynamics changed remarkably over these three decades. The temporal distribution of the SSC increased in the bottom layer. The SSC was much larger during the early flood tide period in 2013. The tidal range increased by nearly 10% and the flood dominance increased in the study area from 1982 to 2013. The salinity dynamics underwent a transition from a stratified system in 1982 to a well-mixed system in 2013. The landward sediment budget increased remarkably from 1982 to 2013. The decreased fluvial sediment supply, increased flood dominance, well-mixed salinity, and increased tidal range were directly responsible for the larger landward sediment budget and more severe erosion in the mudbank in 2013. The current results reveal the flow and sediment dynamics during the conversion of the sediment sink to source. Furthermore, it was determined that the sediment-starved process in the estuarine environment, which occurred due to the reduction in the fluvial sediment, leads to an increased landward transport of sediment. The current study provides a clear understanding of the mechanisms governing the delta system transition in the mudbank of the Yangtze Estuary, which is useful for delta protection in the future.

长江口东南部（或长江口）被认为是长江三角洲的沉积中心和泥滩。随着1980年代河流泥沙供应量开始下降，2003年三峡大坝建成后，河流泥沙供应量开始减少，更多的河流泥沙被截留，降低了河口地区的悬浮泥沙浓度（SSC）环境。此外，近几十年来泥滩的吸积速度有所放缓。事实上，泥滩缩小了，并面临着从沉积物汇到源的制度转变。更好地了解系统的潮汐尺度动力学和空间变异性对于探索长江口受自然变化和人类活动影响的沉积物源汇转换至关重要。流速、盐度、1982 年 7 月和 2013 年 7 月在泥滩上的 3 个站点测量了春季和小潮期间的悬浮泥沙浓度。1982 年至 2013 年研究区测量的所有站点的流量变化不显着。在这三个十年中，动态发生了显着变化。SSC 的时间分布在底层增加。2013年前期大潮期SSC较大，1982—2013年研究区潮差增加近10%，洪水优势度增加。盐度动态经历了从1982年分层系统向2013 年良好混合系统。1982 年至 2013 年，陆上泥沙收支显着增加。河流泥沙供应减少，洪水优势增加，盐度混合良好，2013 年泥滩向陆沉积物收支增加和侵蚀更严重直接导致了潮差和潮差增加。目前的结果揭示了沉积物汇转换为源过程中的水流和沉积动力学。此外，已确定由于河流沉积物减少而发生的河口环境中的沉积物匮乏过程导致沉积物向陆运移增加。本研究对长江口泥滩三角洲系统转型机制有了清晰的认识，对今后的三角洲保护工作具有重要意义。目前的结果揭示了沉积物汇转化为源过程中的流动和沉积物动力学。此外，已确定由于河流沉积物减少而发生的河口环境中的沉积物匮乏过程导致沉积物向陆运移增加。本研究对长江口泥滩三角洲系统转型机制有了清晰的认识，对今后的三角洲保护工作具有重要意义。目前的结果揭示了沉积物汇转化为源过程中的流动和沉积物动力学。此外，已确定由于河流沉积物减少而发生的河口环境中的沉积物匮乏过程导致沉积物向陆运移增加。本研究对长江口泥滩三角洲系统转型机制有了清晰的认识，对今后的三角洲保护工作具有重要意义。