Influence of sulfate input on freshwater sediments: Insights from incubation experiments

Incubation experiments were carried out under high and low SO42- conditions to investigate the buffering capacity of lake sediments. Increased SO42- content in the water column enhanced microbial SO42- reduction, causing a continuous decrease of SO42- content from 1086 to 83 mg/L paralleled by an increase of pH in the water column from 3.76 to 7.20. These changes were accompanied by decreased methanogenesis in the incubated sediments. The results demonstrate that the buffering capacity resulted from a variety of biodegradation pathways controlled to a large extent by SO42- reduction, rather than by direct anaerobic oxidation of CH4. This is documented by distinctly lower δ13C values (from −73.99 to −65.24‰) of the CH4 generated under higher SO42- conditions compared to higher δ13C values (from −68.98 to −61.37‰) of the CH4 generated under lower SO42- conditions.