Long-term simulation of saltmarsh landscape based on hydro-sediment and vegetation Dynamics: Assessing future stability

Salt marshes play critical roles in coastal protection and ecosystem functioning but are increasingly threatened by sea level rise (SLR) and reduced sediment supply. These stressors disrupt the balance between vegetation dynamics and hydro-sediment dynamics, potentially leading to abrupt landscape transitions. In this study, we developed a vegetation dynamics model based on the life cycles of Spartina alterniflora, Phragmites australis, and Suaeda salsa, and coupled it with the hydrodynamic and morphodynamic modules of Delft3D Flexible Mesh. Using parameters representative of central Jiangsu's tidal flats, we conducted 50-year simulations under varying SLR and offshore suspended sediment scenarios. Results show species-specific resilience and feedbacks to environmental stress. Spartina exhibits strong tolerance to high SLR and low suspended sediment concentration (SSC), effectively stabilizing tidal flats through sediment trapping. In contrast, Suaeda and Phragmites are more sensitive, showing rapid decline or retreat under stress. Vegetation self-organization shapes elevation patterns, with dense vegetation promoting accretion and creek-edge zones remaining erosion-prone. Under moderate conditions, marsh zonation remains stable, but extreme scenarios lead to fragmentation and irreversible shifts. This study demonstrates that coupling vegetation dynamics with hydro-sediment modeling captures long-term biogeomorphic feedbacks critical to salt marsh evolution. Effective management should integrate ecological and engineering approaches, combining emission reduction with adaptive planning to enhance marsh resilience under future climate change.