Sulfate‐ and iron‐dependent anaerobic methane oxidation occurring side‐by‐side in freshwater lake sediment

Abstract

AbstractAnaerobic oxidation of methane (AOM) is a potentially important methane sink in lake sediments, but the biogeochemistry and microbial ecology of this process are understudied. Potential electron acceptors for AOM include Fe(III) and sulfate; however, it is not clear to which extent low sulfate concentrations constrain the coupling of AOM to sulfate reduction, nor if Fe(III) reduction drives AOM directly or via a cryptic sulfur cycle. We investigated AOM pathways in the sediment of iron‐rich Danish Lake Ørn through anoxic sediment slurry incubations with additions of 13C‐labeled methane as a substrate, sulfate and Fe(III) as potential electron acceptors, and molybdate as an inhibitor of sulfate reduction. The experiments demonstrated the co‐occurrence of sulfate‐ and iron‐dependent modes of AOM, with the former supported by recycling of sulfate coupled to iron reduction. Quantitative PCR analysis demonstrated the abundance of archaea of the ANME‐2d clade (Ca. Methanoperedenaceae) as likely drivers of AOM. Our study demonstrates that sulfate‐dependent AOM can consume methane at sulfate concentrations typical for freshwater systems and emphasizes the importance of sulfur and iron cycling in the regulation of methane emission from freshwater sediments.