Abstract: In recent years, with the continuous expansion of reclamation projects in coastal areas, seawater intrusion has become a significant ecological risk for sustainable development in coastal regions. This study focused on the eastern Guanghai Bay, an area within the Guangdong-Hong Kong-Macao Greater Bay Area, and analyzed the physicochemical indicators of nearshore seawater, surface water, and groundwater based on monitoring data from April 2016 to January 2020. The study systematically investigated the impact mechanism of reclamation projects on seawater intrusion in groundwater and its temporal and spatial variations. The findings revealed: (1) The monitoring wells in the reclamation area, J1, J2, and J3, exhibited varying degrees of seawater intrusion, with J3 showing the most severe intrusion, while J0 experienced no intrusion; (2) The variations in groundwater TDS and water level demonstrated significant time dependency, with seawater intrusion being particularly severe during the non-flood season (October to March of the following year); (3) The synergistic response between groundwater and surrounding water bodies exhibited complex lagging effects, with the standard deviation of both salinity and water level lags being the highest for J3, indicating heterogeneous responsiveness; (4) Tidal upwelling and uneven distribution of precipitation were identified as the primary drivers of seawater intrusion. The results provide scientific support for environmental risk assessment of reclamation projects, the development of seawater intrusion prevention measures, and regional ecological environmental protection.

Key words: Reclamation Project, Groundwater, Seawater Intrusion, Synergistic Response, Lagging Effect, Guanghai Bay