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

Peatland forests play a significant, yet highly variable, role in atmospheric methane (CH 4 ) and nitrous oxide (N 2 O) emissions. Drainage reduces CH 4 but increases N 2 O 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. 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. Soil water‑table depth was the primary control on annual CH 4 exchange; DF sites acted as CH 4 sinks (–4.6 kg ha –1 y –1 ), whereas UF sites were net sources (38.2 kg ha –1 y –1 ). In contrast, N 2 O 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 N 2 O 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. Our findings reveal significantly lower CH 4 and moderately higher N 2 O 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 CH 4 and N 2 O emissions showed no significant difference across the three countries.