EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Electron transfer to peat particulate organic matter in ombrotrophic bogs and implications for methane formation: a combined field and laboratory study

Nikola Obradović1, Saskia Läubli2, Rob Schmitz1, Martin Schroth1, and Michael Sander1
Nikola Obradović et al.
  • 1ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, Zürich, Switzerland
  • 2University of Basel, Department of Environmental Sciences, Basel, Switzerland

Ombrotrophic bogs are rainwater-fed, water-logged, anoxic, and carbon-rich ecosystems with low concentrations of dissolved inorganic terminal electron acceptors (TEAs), such as nitrate and sulfate. Consequently, methanogenesis is expected to dominate carbon turnover in many of these systems and to result in an approximatively equimolar formation of CO2 and CH4. Yet, numerous studies have reported elevated molar CO2:CH4 formation ratios in peat bog soil incubations, indicating that anaerobic respiration prevails over methanogenesis despite the apparent scarcity of inorganic TEAs. To explain anaerobic respiration, particulate organic matter (POM) was proposed to act as previously unrecognized TEA. Here, we present results from combined in situ field studies and laboratory peat soil incubations to assess electron transfer to oxidized POM (POMox) and its effects on CO2 and CH4 formation. In situ studies consisted of deploying litter mesh bags containing POMox in the anoxic, water saturated subsurface of three ombrotrophic bogs – Lungsmossen (LM), Storhultsmossen (SM), and Björsmossen (BM) – for one year. The electron accepting capacity (EAC) of the retrieved POM decreased by 0.16±0.02 mmol e-/g dry POM in LM, 0.15±0.02 in SM, and by 0.17±0.01 mmol e-/g dry POM in BM, as compared with the buried POMox, demonstrating extensive electron transfer to the buried POM over the course of one year. Extents of POMox reduction were similar for different depths, as tested in BM bog. Exposure of the reduced POM to air (i.e. O2)resulted in an increase in its EAC, supporting that POM acts as a reversible TEA at the oxic-anoxic interface of peat soils. We complemented these in situ field studies with laboratory incubations of reduced POM collected from the same three bogs. Methanogenic conditions were observed in BM peat soil incubations, which were used for further studies. Amending BM soils with POMox and glucose resulted in increases in CO2:CH4 formation ratios of several orders of magnitude. These findings pointed towards anaerobic respiration using POMox as TEA, thereby suppressing methanogenesis. Taken together, our work provides evidence for POMox reduction in situ and substantiates the important role of POM as TEA in controlling CH4 formation in ombrotrophic bogs.

How to cite: Obradović, N., Läubli, S., Schmitz, R., Schroth, M., and Sander, M.: Electron transfer to peat particulate organic matter in ombrotrophic bogs and implications for methane formation: a combined field and laboratory study, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12388,, 2023.