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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 3
Biogeosciences, 15, 937-951, 2018
https://doi.org/10.5194/bg-15-937-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 937-951, 2018
https://doi.org/10.5194/bg-15-937-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Technical note 15 Feb 2018

Technical note | 15 Feb 2018

Technical note: Comparison of methane ebullition modelling approaches used in terrestrial wetland models

Olli Peltola1, Maarit Raivonen1, Xuefei Li1, and Timo Vesala1,2 Olli Peltola et al.
  • 1Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, P.O. Box 68, 00014 Helsinki, Finland
  • 2Institute for Atmospheric and Earth System Research/Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki, P.O. Box 27, 00014 Helsinki, Finland

Abstract. Emission via bubbling, i.e. ebullition, is one of the main methane (CH4) emission pathways from wetlands to the atmosphere. Direct measurement of gas bubble formation, growth and release in the peat–water matrix is challenging and in consequence these processes are relatively unknown and are coarsely represented in current wetland CH4 emission models. In this study we aimed to evaluate three ebullition modelling approaches and their effect on model performance. This was achieved by implementing the three approaches in one process-based CH4 emission model. All the approaches were based on some kind of threshold: either on CH4 pore water concentration (ECT), pressure (EPT) or free-phase gas volume (EBG) threshold. The model was run using 4 years of data from a boreal sedge fen and the results were compared with eddy covariance measurements of CH4 fluxes.

Modelled annual CH4 emissions were largely unaffected by the different ebullition modelling approaches; however, temporal variability in CH4 emissions varied an order of magnitude between the approaches. Hence the ebullition modelling approach drives the temporal variability in modelled CH4 emissions and therefore significantly impacts, for instance, high-frequency (daily scale) model comparison and calibration against measurements. The modelling approach based on the most recent knowledge of the ebullition process (volume threshold, EBG) agreed the best with the measured fluxes (R2 = 0.63) and hence produced the most reasonable results, although there was a scale mismatch between the measurements (ecosystem scale with heterogeneous ebullition locations) and model results (single horizontally homogeneous peat column). The approach should be favoured over the two other more widely used ebullition modelling approaches and researchers are encouraged to implement it into their CH4 emission models.

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Emission via bubbling, i.e. ebullition, is one of the main CH4 emission pathways from wetlands to the atmosphere, yet it is still coarsely represented in wetland CH4 models. In this study three ebullition modelling approaches are evaluated. Modeled annual CH4 emissions were similar, whereas temporal variability in CH4 emissions varied an order of magnitude between the approaches. Hence realistic description of ebullition is needed when models are compared to and calibrated against measurements.
Emission via bubbling, i.e. ebullition, is one of the main CH4 emission pathways from wetlands...
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