Modelling the responses of the salt marsh and its adjacent tidal mudflat to the tidal dyke and different supplied sediments in Laizhou Bay, China

Intertidal salt marsh degradation due to natural and anthropogenic pressures poses a significant threat to coastal ecosystems. This degradation largely depends on the expansion of salt marsh, and our current understanding and ability to predict how salt marshes respond to varying sediment supplies, especially in relation to tidal dykes, are still limited. This study developed a model by coupling tide movement, plant growth, and sedimentation to simulate the expansion processes of the Suaeda salsa salt marsh and its adjacent tidal mudflat, while also predicting potential future expansion trends. The results revealed that net sediment height was negative in the tidal mudflat but positive in the salt marsh. When suspended matter concentration in tidewater ranged from 10 to 25 g m⁻³, tide mudflat areas would increase and reach a stable maximum, while salt marsh areas would continuously decline. Higher sediment supplies delayed maximum mudflat expansion, suggesting that enhancing sediment availability could mitigate salt marsh loss. However, even with increased sediment, rising sea levels and sediment undersupply over extended periods (decades to centuries) may still result in salt marsh drowning, disappearance, and transformation into tidal mudflats. Our findings highlighted that (i) Pioneer plant survival is crucial for determining salt marsh migration inland or seaward; (ii) Tidal dykes stabilize mudflat areas at the expense of salt marsh loss; (iii) Removing dykes or enhancing sediment supply could help conserve and restore intertidal salt marshes. These insights offer valuable strategies for coastal ecosystem management.