Impact of changing groundwater flow paths on CO2 and CH4 dynamics in the groundwater of temperate-to-arctic mires

Mires are one of the systems, which are highly affected by climate change. At the same time, they are main sources of greenhouse gases (GHG) such as methane (CH₄) and carbon dioxide (CO₂). Considering that hydrological patterns remain major factors affecting these emissions and they are likely to be affected by climate change, GHG fluxes may be altered as well. Whereas majority of the studies focused on direct GHG emissions from the peat or mire surface waters, less in known about the processes of groundwater flow especially in relation to transfer of GHG-rich groundwater to the mire ecosystems.

The main objective of this study was to assess how dynamics of CO₂ and CH₄ in groundwater of mires is likely to be affected due to changed paths of groundwater flow.

The study was conducted from May 2023 till October 2023 in four mires located along latitudinal gradient from subarctic Norway to temperate areas in Poland, which serve as examples of systems exposed to abrupt climate change. They include Nordic permafrost and bog-like systems in Norway through bog-lake system in Poland. The study used the set of gas piezometers (gas-equilibrators) located towards-to-lake transect, where concentrations of CO₂ and CH₄ were measured in vertical profiles (2 m, 1m, 0.1m). Simultaneously, water levels were measured with automatic pressure transducers in a 3-h interval. We also documented electric conductivity of groundwater along the transects in which the dynamics of CO₂ and CH₄ were assessed.

We determined the amounts of CO₂ and CH₄ transported by groundwater to the mires. Our results demonstrate high vertical and temporal variability of GHG concentrations in groundwater of mires, which has implications for determination of future carbon balance in such areas.  Additionally, our findings imply that groundwater is an important GHG source to the mire and need to be considered in the light of climate change as increasing sources of GHG into the atmosphere. Changes in groundwater flow caused by global warming (e.g., palsa mires decomposition, increase of evapotranspiration in temperate mires) can have significant influence on emissions of GHG in the future.