Ecosystem-scale floodplain forest methane exchange

Floodplain forests as wetlands are characterized by methane (CH₄) emission. Methane, after carbon dioxide (CO₂) is the second main driver of global climate change. The magnitude of CH₄ emission is site specific and depends on environmental factors like water table level and soil temperature. The standard method to quantify ecosystem-scale CH₄ exchange is the eddy covariance (EC) method. Gap-filling procedures, however, are manifold and not standardized yet.

The main aim of our study was to quantify the CH₄ emission on the floodplain forest ecosystem level using the EC method, with special emphasis on environmental conditions, turbulence development and footprint. Furthermore, the ecosystem-scale CH₄ fluxes shall be analysed with regards to the CH₄ emissions of water bodies within the EC footprint.

The studied floodplain forest represents nowadays relatively dry conditions. Consequently, we initially hypothesized that ecosystem-scale CH₄ exchange will be negligible.

First results, however, showed, that the whole ecosystem is a small but constant CH₄ source as we observed an average emission flux of 11.7 mg CH₄ m^-2 day^-1 over the period June to December 2021.  In parallel, CH₄ fluxes from a stream located within the footprint of the EC tower were measured using the floating chambers and bubble traps. Stream was substantial source of CH₄ with mean CH₄ fluxes of 260 ± 107 mg CH₄ m^-2 day^-1, respectively, over the period from April to December 2021. Both, the EC and floating chamber measurements of CH₄ were conducted also in 2022 and results will be presented.

In the future, the ecosystem-scale CH₄ measurements shall be connected not only with the CH₄ measurements from the water bodies, but also with stem CH₄ efflux measurements conducted at the study site. Finally, an overview of all relevant CH₄ sources in the studied ecosystem shall evolve including their relative importance for ecosystem CH₄ exchange.