Sediment dynamics and vegetation resilience: A case study on the tidal flats in the Yangtze Delta

Salt marshes are among the most resilient systems in coastal environments, playing a key role in resisting rising sea level through sediment accretion and mitigating the pressures of climate change. However, our understanding of the highly complex interactions between salt marsh vegetation resilience and sediment dynamics is limited. Hence this study collected data from three land-to-sea stations (interior salt marsh, salt marsh edge, mudflat) in the Yangtze Delta. Our findings revealed that waves were attenuated more heavily than currents in salt marshes, whereas both dissipated less intensely in mudflats. The tide-averaged, wave-current coupled bed shear stress was 0.25 N/m² at the mudflat, respectively 1.5 and 2.2 times greater than values at the edge of the salt marsh (0.17 N/m²) and in the marsh itself (0.12 N/m²). The dynamic intensity (bed-shear-stress impulse after accounting for inundation duration), was 2.1 and 3.2 times higher at the mudflat than at the other two stations. We identified two possible key interactive processes. First, long-term dynamic intensity could be a better representative indicator that affects the spatial distribution of vegetation, with plants becoming sparser seaward as the enhancement of dynamic intensity accelerates. Second, root length might be related to intratidal-scale sediment resuspension controlled by hydrodynamic forces, with roots becoming shorter shoreward as the thickness of intratidal erodible sediment decreases. In conclusion, we addressed the critical question of how environmental drivers affect spatial distribution and resilience of salt marsh vegetation. These findings have major implications for global efforts to restore natural coastal ecosystems and enhance resilience against marine disasters.