Impacts of Exotic Saltmarsh Vegetation Removal and Native Saltmarsh Vegetation Restoration on Bed Level Change and Surficial Sediment Distribution in an Estuary Wetland

Abstract

The invasion of exotic saltmarsh species precipitates the degradation of native estuarine wetlands. In response, saltmarsh restoration projects, which concentrate on removing exotic saltmarsh species and replanting native ones, have been widely adopted to protect wetland biodiversity and restore ecosystem services. However, the morphological and sedimentary responses of wetlands during the restoration process remain unclear. This study investigates the impacts of saltmarsh restoration on bed level changes and surficial sediment distribution in the Shanyutan Wetland, Southeast China. A biomorphodynamic model is developed that integrates a remote-sensing-informed vegetation module with hydrodynamics and sediment transport processes. This model is used to explore the drivers of these morphodynamic changes and to understand the underlying mechanisms. Model results indicate that the removal of exotic saltmarshes induces erosion along saltmarsh edges and within zones near tidal channels, accompanied by a reduction in mud content. Meanwhile, the interior saltmarsh areas experience a modest increase in mud accumulation. The influence of this removal extends beyond the initial removed site, leading to sand deposition seawards of the salt marsh. Replanting native species contributes to an average increase in bed elevation, though it shows limited efficacy in enhancing mud content. These findings suggest that while wetland elevation may recover from the initial erosion induced by vegetation removal to reach a pre-removal state within 1–3 years, restoring sediment distribution by native saltmarsh replanting remains challenging. Overall, this research deepens our understanding of morphodynamic responses during estuarine wetland restoration and offers critical insights for landscape reconstruction in wetland management.