Impact of drainage on soil CH4 and N2O fluxes in nutrient-rich hemiboreal peatland forests of Europe

Background and aims: Peatland forests play a significant, yet highly variable, role in atmospheric methane (CH4) and nitrous oxide (N2O) emissions. Drainage reduces CH4 but increases N2O fluxes from nutrient-rich soils, creating complex climate trade-offs. To refine regional climate strategies, a clearer understanding of soil fluxes and influencing factors across forest types in the hemiboreal zone is needed. Methods: This study presents two years of soil flux and environmental data collected from 2020 to 2023 using manual chambers at 18 drained (DF) and 7 undrained (UF) sites, with different tree species, in Estonia, Latvia, and Lithuania. Results: Soil water‑table depth was the primary control on annual CH4 exchange; DF sites acted as CH4 sinks (–4.6 kg ha–1 y–1), whereas UF sites were net sources (38.2 kg ha–1 y–1). In contrast, N2O emissions occurred at all sites, averaging 5.9 kg ha–1 y–1 in DF and 1.4 kg ha–1 y–1 in UF soils. Within DF sites, Myrtillus‑type pine stands exhibited the lowest N2O fluxes, while alder stands showed the highest, followed by birch- and spruce-dominated stands, reflecting differences in hydrology, pH, and C/N ratios of the soil. Conclusions: Our findings reveal significantly lower CH4 and moderately higher N2O emissions from DF soils than the IPCC Tier 1 temperate zone emission factor (EF), which has thus far been used for the hemiboreal zone. This study can improve national GHG inventories using specific information. We recommend applying Baltic region-specific EFs, as the mean annual CH4 and N2O emissions showed no significant difference across the three countries.