Numerical Investigation of Land Reclamation Effects on Hydrodynamics and Mangroves in Shacheng Bay for the Last 36 Years

Since the 1980s, the robust economic growth of China has prompted extensive land reclamation projects along its coastline, notably affecting local hydrodynamics and resulting in ecological repercussions. Using a nearshore finite volume ocean model, we constructed a hydrodynamic model for Shacheng Bay, a southeastern coastal region with a winding and narrow entrance. We examined the hydrodynamic changes and mangrove dynamics over the past 36 years and the relationship between hydrodynamic alterations and mangrove degradation. Simulation results reveal that extensive reclamation projects between 1984 and 2000 weakened the current in Shacheng Bay, leading to decreased water exchange capacity and a significant reduction in mangrove area from 0.3 to 0.06 km². During this period, over 37% of mangrove degradation was ascribed to time-changing hydrodynamic variables without the direct influence of land reclamation. The results also highlight the changes in local hydrodynamics and water exchange patterns that adversely influenced mangrove growth. From 2000 to 2020, there were minimal coastline changes in Shacheng Bay, demonstrating reduced land reclamation activities. This stopped the further weakening trend of the currents, with a slight increase during ebb tides, while the residual current continued to weaken due to the decreasing tidal prism and water exchange capacity. The mangrove area partially recovered during this period, expanding from 0.06 to 0.11 km², predominantly in new areas instead of where mangroves disappeared from 1984 to 2000. This work underlines the intricate relationship between land reclamation, hydrodynamics, and mangrove ecosystems, underscoring the need for sustainable coastal development strategies.