Nature-based solutions to mitigate early marsh-edge erosion in a coastal wetland

Protecting coastal wetlands and preventing the erosion of tidal flats are major challenges in the most coastal regions of China because of strong anthropogenic influence and ongoing sediment reduction from upstream sources. The Jiuduansha Wetland holds both national and international value. However, there has been a decrease in the accretion rate, leading to the occurrence of marsh and bank erosion along the southern bank section of the wetland. In this study, we examined the effects of various nature-based solutions (Nbs) on the marsh-edge erosion belt, including fencing (F) with environmentally friendly bamboo piles; vegetation planting (V) using native species; fencing and vegetation planting (FV); fencing and sediment addition (FS) using dredged soil; and fencing, vegetation planting, and sediment addition (FSV). The results show that the flat elevation in the early erosion belt continuously declined without any treatment, and the mitigation functions of the different approaches were comparable. The F treatments with single wave barriers could not protect the bank and could even aggravate the degree of erosion over one year. Although exogenetic sediments filled the FS experimental plots, the flat elevation level did not notably increase. When the marsh vegetation was established in the experimental plots (V treatment), notable elevation accretion occurred (2.4 cm year⁻¹), and the FV and FSV treatments further enhanced sedimentary accretion (4.5 cm and 6.4 cm year⁻¹, respectively) and vegetation growth (based on density and biomass), showing positive feedback of hydro-sedimentary and biological processes. The synthesized approach to utilize environmentally friendly wave barriers, establish native vegetation and replenish dredged sediment is recommended to be used in the Nbs that aim at preserving the biogeomorphology of coastal salt marshes in the early erosion stage.