Accelerating sea‐level rise and decreasing riverine sediment supply are widely considered to lead to global losses of deltaic marshes and their valuable ecosystem services. However, little is known about the degree to which the related erosion of the seaward delta front can provide sediments to sustain salt marshes. Here, we present data from the mesomacrotidal Yangtze Delta demonstrating that marshes have continued to accrete vertically and laterally, despite rapid relative sea‐level rise (∼10 mm yr⁻¹) and a > 70% decrease in the Yangtze River sediment supply. Marsh progradation has decelerated at a lower rate than fluvial sediment reduction, suggesting an additional source of sediment. We find that under favorable conditions (e.g., a mesomacrotidal range, strong tidal flow, flood dominance, sedimentary settling lag/scour lag effects, and increasing high‐tide level), delta‐front erosion can actually supply sediment to marshes, thereby maintaining marsh accretion rates in balance with relative sea‐level rise. Comparison of global deltas illustrates that the ability of sediment remobilization to sustain marshes depends on coastal processes and varies by more than an order of magnitude among the world's major deltas.

A sharp decline in the Sediment load at the seaward most Datong station (DTS) of the Yangtze River occurred at an average rate of 7.22 × 10⁶ t/yr since 1956, and this drop had a staircase pattern that can be divided into five distinct periods (1956–1968, 1969–1991, 1992–2002, 2003–2012, and 2013–2017). In this study, a new holistic basin‐wide Sediment Budget Method (SBM) was developed using sediment data from a total of 74 gauging stations (arguably the largest datasets so far) to estimate the sediment contributions to DTS from tributaries and mainstream. Our results show that the Jinsha River in upper basin between Panzhihua and Xiangjiaba used to be one of the largest contributors to DTS in 1956–2002 (16%–33%), but its contribution decreased sharply after 2003 due to the impoundment of Three Gorges Dam (TGD) and decreased further to nearly nil in 2013–2017 due to the impoundment of new cascade dams (CDs) which were upstream of TGD. In contrast, the mainstream between Yichang and Datong contributed 50%–64% of the DTS in 2003–2017, owing to the active channel erosion downstream of TGD. Before 2003 about 66%–84% of the DTS was contributed by the upper reach, but 72%–91% of the DTS was from the middle‐lower reaches after 2003, reflecting a drastic shift in sediment suppliers from upper to middle‐lower reaches. On average, the drop of DTS was 128.37 × 10⁶ t/yr due to TGD impoundment in 2003–2012 and 27.28 × 10⁶ t/yr due to CDs impoundment in 2013–2017 because of the reservoir trapping and the inhibition of historically eroding channels in the reservoir area. This new SBM can be applied to other large and small rivers around the world to track sediment sources/sinks and provide valuable results for sediment resource management.

Benthic animal populations inhabiting intertidal flats provide important ecosystem functions and services that may be disrupted by physical disturbances such as tropical cyclones, which are predicted to increase in frequency and intensity under future climate change. However, the spatial reach at which tropical cyclones impact macrobenthos populations in intertidal flats remains poorly understood. We examined whether a typhoon with a center that remained more than 1400 km away from the study site could trigger severe erosion of intertidal flats and adversely affect macrobenthos populations. We undertook simultaneous measurements of hydrodynamics (waves, currents), morphodynamics (erosion, accretion) and density and biomass of the macrobenthic bivalve Meretrix meretrix during the passage of this typhoon, on an intertidal flat on the Chinese coast. Our results showed that, in spite of the considerable distance from the storm center, the bed shear stress greatly exceeded the critical value for erosion, resulting in rapid erosion of approximately 10 cm and a nearly 50% reduction in both the density and the biomass of the clam species. Our findings suggest that if storms become more frequent and more intense in a future warmer climate, they may increase physical disturbances to intertidal flats and their benthic animal populations, even at great distances from storm centers.