Evidence for anaerobic CH4 oxidation in freshwater peatlands

This study involved in vitro assays of peat soil to investigate the occurrence, importance and potential mechanism(s) of anaerobic methane oxidation (AOM) in several northern peatlands ranging from ombrotrophic bog to minerotrophic fen. Although strong evidence suggests that AOM is linked to sulfate reduction in marine sediments, very little is known about AOM in freshwater systems such as northern peatlands, which have large methane (CH4) production and are a significant source of atmospheric CH4. Our results showed a mean net AOM rate of 17 +/- 2.6 nmol kg(-1) s(-1) with a maximum rate of 17 +/- 2.6 nmol kg(-1) s(-1) for a minerotrophic fen in central New York. AOM was demonstrated with three independent methods to verify our results: (a) additions of methanogenic inhibitors, (b) stable isotope enrichment (C-13-CH4), and (c) natural abundance stable isotope analysis (C-13-CH4). These experiments confirmed that AOM occurs simultaneously with methanogenesis, consumes a significant portion of gross CH4 production, and significantly fractionates C isotopes (similar to -12%). Experiments using a variety of potential electron acceptors demonstrated that Fe( III) and SO42- are not quantitatively important, while the role of NO3- is uncertain and deserves more attention. The exact mechanism(s) for AOM in peat soils remains unclear; however the AOM rates reported in this study are similar to those reported for CH4 production and aerobic CH4 oxidation in northern peatlands, suggesting that AOM may be an important control on CH4 fluxes in northern peatland ecosystems.