Effect of the 2018 drought on methane and carbon dioxide exchange of northern mire ecosystems

In 2018, North-Western Europe experienced very dry and warm summer. These conditions can have considerable effects on the functioning and greenhouse gas exchange of terrestrial ecosystems. Peat-forming wetlands, or mires, are a characteristic component of the North-European boreal landscape, and crucial for long-term carbon storage as well as for methane emission. We have analyzed the effect of the drought on greenhouse gas (GHG) exchange of five North European mire ecosystems in Sweden and Finland in 2018. The low precipitation and high summer temperatures in Fennoscandia led to a lowered water table in majority of the mires. This lowered both carbon dioxide (CO₂) uptake and methane (CH₄) emission during 2018, turning many of the mires from CO₂sinks to sources during this year. The changes in methane emission and total GHG exchange, expressed as CO₂equivalent, were significantly correlated with change in water table position. The calculated time-evolving radiative forcing due to the changes in GHG fluxes in 2018 showed that the drought-induced changes in GHG fluxes first resulted in a cooling effect lasting 15-50 years, due to the lowered CH₄emission, which was followed by longer-term warming phase due to the lower CO₂ uptake in 2018.