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https://doi.org/10.5194/bg-2020-263
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-263
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  10 Sep 2020

10 Sep 2020

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This preprint is currently under review for the journal BG.

Topography-based modelling reveals high spatial variability and seasonal emission patches in forest floor methane flux

Elisa Vainio1,2, Olli Peltola3, Ville Kasurinen4, Antti-Jussi Kieloaho5, Eeva-Stiina Tuittila6, and Mari Pihlatie1,2,7 Elisa Vainio et al.
  • 1Environmental Soil Sciences, Department of Agricultural Sciences, University of Helsinki, Finland
  • 2Institute for Atmospheric and Earth System Research (INAR) / Forest Science, University of Helsinki, Finland
  • 3Climate Research Programme, Finnish Meteorological Institute, Helsinki, Finland
  • 4Integrated Carbon Observation System (ICOS), Helsinki, Finland
  • 5Natural Resources Institute Finland(LUKE),Helsinki, Finland
  • 6School of Forest Sciences, University of Eastern Finland, Joensuu, Finland
  • 7Viikki Plant Science Centre (ViPS), University of Helsinki, Finland

Abstract. Boreal forest soils are globally an important sink for methane (CH4), while these soils are also capable to emit CH4 under favourable conditions. Soil wetness is a well-known driver of CH4 flux, and the wetness can be estimated with several terrain indices developed for the purpose. The aim of this study was to quantify the spatial variability of the forest floor CH4 flux with a topography-based upscaling method connecting the flux with its driving factors. We conducted spatially extensive forest floor CH4 flux and soil moisture measurements, complemented with ground vegetation classification, in a boreal pine forest. We then modelled the soil moisture with a Random Forest model using topography, based on which we upscaled the forest floor CH4 flux – this was performed for two seasons: May–July and August–October. Our results demonstrate high spatial heterogeneity in the forest floor CH4 flux, resulting from the soil moisture variability, as well as on the related ground vegetation. The spatial variability in the soil moisture and consequently in the CH4 flux was higher in the early summer compared to the autumn period, and overall the CH4 uptake rate was higher in autumn compared to early summer. In the early summer there were patches emitting high amounts of CH4, however, these wet patches got drier and smaller in size towards the autumn, which was enough for changing their dynamics to CH4 uptake. The results highlight the small-scale spatial variability of the boreal forest floor CH4 flux, and the importance of soil chamber placement in order to obtain spatially representative CH4 flux results. We recommend that a site of similar size and topographical variation would require 15–20 sample points in order to achieve accurate forest floor CH4 flux.

Elisa Vainio et al.

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Elisa Vainio et al.

Elisa Vainio et al.

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Short summary
We studied forest floor methane exchange over an area of ten hectares in a boreal pine forest. The results demonstrate high spatial variability in soil moisture and consequently in the methane flux. We detected wet patches emitting high amounts of methane in the early summer, however, these patches turned to methane uptake in the autumn. We concluded that the small-scale spatial variability of the boreal forest methane flux highlights the importance of soil chamber placement in similar studies.
We studied forest floor methane exchange over an area of ten hectares in a boreal pine forest....
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