Application of oyster shells for environmental remediation of sewage-affected coastal sediments in Masan Bay, Korea.

Coastal sediments in semi-enclosed bays are particularly susceptible to contamination due to limited water circulation and ongoing contaminant input. In Masan Bay, a heavily impacted coastal area in Korea, sediment remediation is essential to alleviate the effects of organic enrichment and hypoxia. This study investigated the effectiveness of oyster shell capping as an in-situ remediation technique by assessing its impact on sediment environment, microbial communities, and macrobenthic fauna. Field experiments were conducted using two capping thicknesses: OS5 (5 cm) and OS10 (10 cm), with uncapped sediments serving as a control. In OS10, the dissolved inorganic phosphorus (DIP) concentration in porewater was consistently lower than that of the control, with DIP decreasing from 2.89 mg-P/L to 0.04 mg-P/L over the monitoring period. The microbial community structure showed a decrease in the abundance of sulfur-reducing bacteria belonging to the phylum Thermodesulfobacteriota, whereas aerobic Actinomycetes and Alphaproteobacteria increased. Macrobenthic abundance rose to 10,190 ind. m in OS10 by May 2024, compared to 2358 ind. m in the control site. However, all sites exhibited seasonal declines during summer, likely driven by recurring hypoxia. Among the two treatments, OS10 showed more favorable trends in sediment quality and indications of biological recovery. These findings suggest that oyster shell capping, particularly at greater thicknesses, may serve as a supportive strategy for coastal sediment remediation, although the results remain preliminary and site-specific.