Dissolved oxygen-driven transformations of inorganic sulfur and heavy metals during mariculture sediment aging.

Dissolved oxygen (DO) critically regulates biogeochemical processes in mariculture sediments, yet its integrated effects on sulfur-metal interactions during sediment aging remain poorly understood. This study investigated the migration and transformation of reduced inorganic sulfur (RIS) and heavy metals in mariculture sediments under varying DO levels. Lower DO accelerated the dominance of acid-volatile sulfide (AVS) within the reduced inorganic sulfur pool (AVS/RIS = 56.11% under DO-1 vs. 41.18% under DO-3) and shortened the time required for AVS to become the dominant component by 16.67% (compared to DO-3). DO variations minimally affected overall metal mobility (coefficient of variation, CV < 12%), but Cu exhibited exceptional sensitivity. The influence of DO concentration was particularly significant on the oxidizable (F3) and residual (F4) fractions of Cu, and the F4 fraction of Pb. The F4 fraction of both Cu and Pb increased under low DO, likely due to reductive activation and lattice diffusion. The differing impacts of DO on RIS (significant) versus heavy metal speciation (relatively minor) resulted in significant variations in the correlations between sulfur species and heavy metal fractions across DO treatments. Sediment microbial richness and diversity declined with decreasing DO, significantly altering the relative abundance of bacterial phyla and the genus Desulfuromonas. DO primarily regulated sediment carbon, sulfur, and iron cycling, exerting its most pronounced impacts on sulfur transformations. Depleted DO intensifies the environmental hazards of inorganic sulfides through enhanced mobilization. Proactive control strategies are therefore imperative during hypoxic episodes to mitigate sulfide-driven ecological risks. This study provides new insights for managing sediment redox conditions in mariculture systems.