30 May 2022
30 May 2022
Status: this preprint is open for discussion.

High-resolution vertical biogeochemical profiles in the hyporheic zone reveal insights into microbial methane cycling

Tamara Michaelis1, Anja Wunderlich1, Ömer K. Coskun2, William Orsi2,3, Thomas Baumann1, and Florian Einsiedl1 Tamara Michaelis et al.
  • 1Chair of Hydrogeology, School of Engineering and Design, Technical University Munich, Munich, Germany
  • 2Department of Earth and Environmental Sciences, Paleontology & Geobiology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
  • 3GeoBio-Center (LMU), Ludwig-Maximilians-Universität München, 80333 Munich, Germany

Abstract. Facing the challenges of climate change, policy making relies on sound greenhouse gas (GHG) budgets. Rivers and streams emit large quantities of the potent GHG methane (CH4), but their global impact on atmospheric CH4 concentrations is highly uncertain. In-situ data from the hyporheic zone (HZ), where most CH4 is produced and some of it can be oxidized to CO2, are lacking for an accurate description of CH4 production and consumption in streams. To address this, we recorded high-resolution depth-resolved geochemical profiles at five different locations in the stream bed of river Moosach, Southern Germany. Specifically, we measured pore-water concentrations and stable carbon isotopes (δ13C) of dissolved CH4 as well as relevant electron acceptors for oxidation with a 1 cm vertical depth-resolution. Findings were interpreted with the help of a numerical model, and 16S rRNA gene analyses added information on the microbial community at one of the locations. Our data confirms with pore-water CH4 concentrations of up to 1000 μmol L-1 that large quantities of CH4 are produced in the HZ. Stable isotope measurements of CH4 suggest that hydrogenotrophic methanogenesis represents a dominant pathway for CH4 production in the HZ of river Moosach, while a relatively high abundance of a novel group of methanogenic archaea, the Methanomethyliales (Phylum Verstraetearchaeota), indicate that CH4 production through H2 dependent methylotrophic methanogenesis might also be an important CH4 source. Combined isotopic and modeling results clearly implied CH4 oxidation processes at one of the sampled locations, but due to the steep chemical gradients and the close proximity of the oxygen and nitrate reduction zones no single electron acceptor for this process could be identified. Nevertheless, the numerical modeling results showed not only a potential for aerobic CH4 oxidation, but also for anaerobic oxidation of CH4 coupled to denitrification. In addition, the nitrate-methane transition zone was characterized by an increased relative abundance of microbial groups (Crenothrix, NC10) known to mediate nitrate and nitrite dependent methane oxidation in the hyporheic zone.

Tamara Michaelis et al.

Status: open (until 13 Jul 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-373', Carsten J. Schubert, 16 Jun 2022 reply
  • RC2: 'Comment on egusphere-2022-373', Anonymous Referee #2, 29 Jun 2022 reply

Tamara Michaelis et al.

Tamara Michaelis et al.


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Short summary
The greenhouse gas methane (CH4) drives climate change. Microorganisms in river sediments produce CH4 when degrading organic matter, but the contribution of rivers to atmospheric CH4 concentrations is uncertain. To better understand riverine CH4 cycling, we measured concentration profiles of CH4 and relevant reactants that might influence the CH4 cycle. We found substantial CH4 production, especially in fine, organic-rich sediments during summer and signs for microbial CH4 consumption.