Multi-indicator assessment of an artificial ecological island for mitigating coastal hypoxia in Shenzhen Bay, China

Coastal hypoxia poses a severe threat to marine ecosystem health. Shenzhen Bay, a highly urbanized embayment in China, has experienced prolonged low dissolved oxygen (DO) conditions. An artificial ecological island (AEI) scheme has been proposed in the local management plan to improve hydrodynamics and reduce siltation. In this study, a hydrodynamic-ecological coupled model was used to conduct a multi-indicator assessment of the AEI's effects on hypoxia in critical areas of the bay. Model results indicated that diel and periodic hypoxia were the primary drivers of persistent low DO conditions. Construction of the AEI and associated topographic optimization permanently submerged former tidal flats and enhanced DO exchange with external waters and sediments, thereby reducing the frequency and severity of both diel and periodic hypoxia under the modeled conditions. Consequently, the proportion of waters with DO >4 mg/L in the channels around the AEI exceeded 90%, and more than 75% of the area outside the Dasha Estuary maintained annual minimum DO levels above 3 mg/L. The scheme was further evaluated under a high-emission stress-test scenario (SSP5–8.5) for 2100. Results suggested that the AEI could continue to alleviate simulated diel hypoxia and provide an additional increase of approximately 0.51 mg/L in annual average DO relative to the climate-change baseline. Overall, the multi-indicator assessment indicates that the AEI may offer a promising topography-based option for mitigating hypoxia in Shenzhen Bay under the conditions examined, while the assessment framework itself provides transferable insights for similar urbanized coastal systems. Further field validation, ecological trade-off analysis, and comparison with alternative measures are required before broader application.