EGU23-9590, updated on 26 Feb 2023
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Temporal and vertical variation of in-situ methane turnover from stable isotope studies at a boreal peatland

Xuefei Li1, Maxim Dorodnikov2, Lukas Kohl3, and Timo Vesala1,4
Xuefei Li et al.
  • 1Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, Helsinki, Finland
  • 2Institute for Landscape Ecology, University of Münster, Münster, Germany
  • 3School of Forest Sciences, University of Eastern Finland, Kuopio, Finland
  • 4Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Helsinki, Finland

Boreal peatlands emit a substantial amount of CH4, a potent greenhouse gas, to the atmosphere. Despite decades of effort made on studying CH4 efflux to the atmosphere, understanding the dynamics of the different co-occurring processes underlying CH4 emission remains a challenge in peatland CH4 modeling, especially during the non-growing seasons. Stable isotope signatures of the soil pore water and emitted CH4 can provide information on these processes. To this end, we conducted a first systematic study using stable isotope methods on in-situ major CH4 turnover processes along a peat profile in a typical boreal peatland (Siikaneva fen) in Southern Finland.

We run a cavity ring-down spectrometer continuously in 2022 to capture the dynamics of belowground dissolved CH4 and CO2 concentrations and their δ13C natural abundance signatures at 10, 30 and 50cm. Same variables were measured at 40cm above peatland surface to estimate ecosystem-scale average δ13C value of the emitted CH4 using nocturnal boundary-layer accumulation approach. These data were used to indicate CH4 production pathways, in-situ CH4 oxidation and transport pathways on an annual basis. Additionally, 13C pulse labelling experiments targeting acetoclastic methanogenesis, hydrogenotrophic methanogenesis and methanotrophy were performed both in-situ and in the lab condition to trace all these processes which cannot be separated by the isotope natural abundance approach alone.

Preliminary results indicated a successful implementation of these novel methods. Continuous measurement of soil gas showed systematic differences in the vertical profile of soil pore water isotopes between winter and summer. δ13C-CH4 values were highest in the deepest layer during winter but they were the lowest in summer. As expected, CH4 production pathway moved towards acetoclastic methanogenesis through winter-summer transition. In winter, the δ13C-CH4 values from emitted CH4 was higher than those from the soil which indicating CH4 oxidation, while in summer the opposite was found due to CH4 diffusive plant transport. CH4 concentrations were higher in summer than in winter from all the depths, while at -30cm had the highest concentration. In-situ labelling experiments showed a higher rate of acetoclastic methanogenesis at -30cm than at -50cm, while hydrogenotrophic methanogenesis was similar at both depths. Experiments also demostrated that there was substantial methanotrophy in the soil as deep as 50cm belowground.


How to cite: Li, X., Dorodnikov, M., Kohl, L., and Vesala, T.: Temporal and vertical variation of in-situ methane turnover from stable isotope studies at a boreal peatland, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9590,, 2023.