Sulfate availability affect sulfate reduction pathways and methane consumption in freshwater wetland sediments

Methane (CH₄) emissions from wetlands significantly contribute to global greenhouse gas fluxes, yet the mechanisms regulating CH₄ production and oxidation in freshwater wetlands remain underexplored, particularly in the role of sulfate in the anaerobic oxidation of CH₄. This study investigated the production, consumption, and release of CH₄ in the sediments of the Qilihai wetland, focusing on the roles of hydrogenotrophic methanogenesis and sulfate dynamics across different seasons. CH₄ concentrations ranged from 2.42 to 2290.52 μmol L⁻¹, and δ¹³C–CH₄ values became progressively more negative with depth, ranging from −87.37‰ to −57.18‰. Results indicate that hydrogenotrophic methanogenesis is the dominant pathway for CH₄ production, particularly in sulfate-depleted environments, with CH₄ concentrations in the sulfate-methane transition zone (SMTZ) strongly correlated with sulfate availability. Sulfate consumption through Sulfate Anaerobic Oxidation of Methane (SAOM) and Organoclastic Sulfate Reduction (OSR) demonstrated significant seasonal variation, with OSR accounting for up to 73% of sulfate consumption in the SMTZ. The SMTZ exhibited variations ranging from 2 to 40 cm in October, narrowing to 2–4 cm in July. These findings emphasize the complex interactions between sulfate availability, methanogenic pathways, and CH₄ emissions in freshwater wetlands, highlighting the need for further research on sulfate dynamics and their implications for greenhouse gas emissions in the context of global climate change.