Aquatic environmental changes and ecological implications from the combined effects of sea-level rise and land reclamation in Deep Bay, Pearl River Estuary, China

Rising sea levels due to climate change are altering the hydrodynamic and solute transport conditions in estuarine regions worldwide. At the same time, anthropogenic projects such as land reclamation could change the potential effects of sea-level rise (SLR). In this study, Deep Bay in the Pearl River Estuary of China was used as a case study to investigate the combined effects of SLR and reclamation. A numerical model was applied to simulate the changes of hydrodynamic and solute transport with 0.0, 0.3, and 0.5 m of SLR in two groups of scenarios (i.e., before and after land reclamation). SLR alone substantially affected the hydrodynamics and strengthened the tidal influence. SLR resulted in a loss of intertidal regions and an increased tidal prism in the bay. Reclamation further magnified SLR's effects on both the hydrodynamics and solute transport. The tidal energy entering the bay during each tidal phase increased by 39.2% and 66.4% with 0.3 and 0.5 m of SLR (respectively) before reclamation, versus 40.7% and 68.9% (respectively) after reclamation. The reclamation projects in the bay helped the saline sea water to intrude further upstream, and magnified the effects of SLR on variations in seasonal salinity. SLR also decreased the bay's ability to exchange water. However, the reclamation accelerated the solute circulation inside the bay, considerably reduced the water age, and offset the SLR's effects on the bay's ability to exchange water with the adjacent sea. The increase in salinity variation due to the combined effects of SLR and reclamation might exert stress on the ecological system of the inner bay, which contains a Ramsar wetland.