A large fraction of the methane that is biogenically produced in lake sediments is oxidized by methane oxidation near the sediment-water interface and/or in the water column. Oxygen appears as the prime electron acceptor in lacustrine methane oxidation (MOx). Methane oxidizing microorganisms seem to thrive even under micro-oxic conditions, i.e., they may be responsible for significant methane turnover at extremely low, or “cryptic”, oxygen concentrations, for example in stratified lakes. Under anoxic condition, they may also use electron acceptors other than oxygen, yet our understanding of the modes and microbial players of true anaerobic methane oxidation (AOM) in freshwater environments is still incomplete. Here we showcase different scenarios in meromictic lakes where the combined lacustrine “aerobic/anaerobic methane filter” works efficiently. We demonstrate that strong MOx potentials can be maintained across redox transition zones, below which bacterial AOM is additionally fueled by nitrite/nitrate or other oxidants. We also show that sulfate-dependent archaeal AOM in lake sediments can be stimulated in the presence of Fe and Mn oxides through oxidation of reduced sulfur compounds. We argue that S- and N-dependent AOM may play a greatly underappreciated role in lakes, yet, the AOM regime and the key microorganisms involved may strongly depend on lake characteristics (e.g., water column dynamics) and/or other environmental controls.

Primary Presenter: Moritz Lehmann, University of Basel (moritz.lehmann@unibas.ch)

Authors:

Moritz Lehmann, University of Basel, Department of Environmental Sciences  (moritz.lehmann@unibas.ch)

Guangyi Su, State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen, China  (guangyisu@xmu.edu.cn)

Maciej Bartosiewicz, Department of Polar and Marine Research, Geophysics Institute, Polish Academy of Science, Warsaw, Poland  (maciej.bartosiewicz@igf.edu.pl)

Helge Niemann, NIOZ Royal Netherlands Institute for Sea Research  (helge.niemann@nioz.nl)

Jakob Zopfi, University of Basel, Department of Environmental Sciences  (jakob.zopfi@unibas.ch)