Microbial and environmental regulation of greenhouse gas fluxes from marine ranching sediments under seasonal hypoxia.

Seasonal hypoxia presents a growing challenge in coastal ecosystems, especially in marine ranching zones characterized by intensive aquaculture and limited water exchange. This study assessed the impact of summer hypoxia on sedimentary greenhouse gas (GHG) emissions, focusing on carbon dioxide (CO2) and methane (CH4), in a northern Yellow Sea marine ranching area. By combining vertical water column profiling, sediment geochemical analysis, and microbial community characterization, the investigation documented spatial and temporal variations in gas concentrations and fluxes at the sediment-water interface under hypoxic and normoxic conditions. The results demonstrated that hypoxia significantly increased CO2 and CH4 concentrations in both water and sediment layers. These peaks coincided with elevated temperatures and reduced dissolved oxygen. CH4 fluxes were notably higher in hypoxic risk areas, associated with increased methanogen abundance and decreased aerobic methanotrophic activity. Redundancy analysis and correlation modeling identified bottom-water oxygen levels, sedimentary organic carbon, and nutrient concentrations as key regulators of greenhouse gas fluxes. The findings underscore the amplification of microbially mediated greenhouse gas emissions under hypoxic stress and emphasize the environmental risks associated with unmanaged sediment processes in marine aquaculture systems.