Preprints
https://doi.org/10.5194/bg-2021-223
https://doi.org/10.5194/bg-2021-223

  24 Aug 2021

24 Aug 2021

Review status: this preprint is currently under review for the journal BG.

Modification of methane oxidation pathways during long-term incubations of methanic lake sediments

Hanni Vigderovich1, Werner Eckert2, Michal Elul1, Maxim Rubin-Blum3, Marcus Elvert4, and Orit Sivan1 Hanni Vigderovich et al.
  • 1Department of Earth and Environmental Science, Ben-Gurion University of the Negev, Beer Sheva, Israel
  • 2Israel Oceanographic & Limnological Research, The Yigal Allon Kinneret Limnological Laboratory, Migdal, Israel
  • 3Israel Limnology and Oceanography Research, Haifa, Israel
  • 4MARUM - Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen, Bremen, Germany

Abstract. Anaerobic oxidation of methane (AOM) is one of the major processes limiting the release of the greenhouse gas methane from natural environments. In Lake Kinneret sediments, iron-coupled AOM (Fe-AOM) was suggested to play a substantial role (10–15 % relative to methanogenesis) in the methanic zone (> 20 cm sediment depth), based on geochemical profiles and experiments on fresh sediments. Apparently, the oxidation of methane is mediated by a combination of mcr gene bearing archaea and aerobic bacterial methanotrophs. Here we aimed to investigate the survival of this complex microbial interplay under controlled conditions. We followed the AOM process during long-term (~18 months) anaerobic slurry experiments of these methanic sediments with two stages of incubations and additions of 13C-labeled methane, multiple electron acceptors and inhibitors. After these incubation stages carbon isotope measurements in the dissolved inorganic pool still showed considerable AOM (3–8 % relative to methanogenesis). Specific lipid carbon isotope measurements and metagenomic analyses indicate that after the prolonged incubation aerobic methanotrophic bacteria were no longer involved in the oxidation process, whereas mcr gene bearing archaea were most likely responsible for oxidizing the methane. Humic substances and iron oxides are likely electron acceptors to support this oxidation, whereas sulfate, manganese, nitrate, and nitrite did not support the AOM in these methanic sediments. Our results suggest in the natural lake sediments methanotrophic bacteria are responsible for part of the methane oxidation by the reduction of combined micro levels of oxygen and iron oxides in a cryptic cycle, while the rest of the methane is converted by reverse methanogenesis. After long-term incubation, the latter prevails without bacterial methanotropic activity and with a different iron reduction pathway.

Hanni Vigderovich et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on bg-2021-223', Edgardo I. Valenzuela, 26 Aug 2021
  • RC1: 'Comment on bg-2021-223', Anonymous Referee #1, 21 Sep 2021
    • CC2: 'Reply on RC1', Hanni Vigderovich, 04 Oct 2021
  • RC2: 'Comment on bg-2021-223', Anonymous Referee #2, 21 Sep 2021
    • CC3: 'Reply on RC2', Hanni Vigderovich, 04 Oct 2021
  • RC3: 'Comment on bg-2021-223', Anonymous Referee #3, 21 Sep 2021
    • CC4: 'Reply on RC3', Hanni Vigderovich, 04 Oct 2021
  • RC4: 'Comment on bg-2021-223', Anonymous Referee #4, 21 Sep 2021
    • CC5: 'Reply on RC4', Hanni Vigderovich, 04 Oct 2021

Hanni Vigderovich et al.

Hanni Vigderovich et al.

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Short summary
Anaerobic oxidation of methane (AOM) is one of the major processes limiting the release of the greenhouse gas methane from natural environments. Here we show that significant AOM exists in the methane zone of lake sediments in natural conditions and even after long-term (~18 months) anaerobic slurry incubations with two stages. Methanogens were most likely responsible for oxidizing the methane, and humic substances and iron oxides are likely electron acceptors to support this oxidation.
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