Soil CO₂ CH₄ and N₂O fluxes from an afforested lowland raised peatbog in Scotland: implications for drainage and restoration

Abstract. The effect of tree (lodgepole pine) planting with and without intensive drainage on soil greenhouse gas (GHG) fluxes was assessed after 45 yr at a raised peatbog in West Flanders Moss, central Scotland. Fluxes of CO₂ CH₄ and N₂O from the soil were monitored over a 2-yr period every 2 to 4 weeks using the static opaque chamber method in a randomised experimental block trial with the following treatments: drained and planted (DP), undrained and planted (uDP), undrained and unplanted (uDuP) and for reference also from an adjoining near-pristine area of bog at East Flanders Moss (n-pris). There was a strong seasonal pattern in both CO₂ and CH₄ effluxes which were significantly higher in late spring and summer months because of warmer temperatures. Effluxes of N₂O were low and no significant differences were observed between the treatments. Annual CH₄ emissions increased with the proximity of the water table to the soil surface across treatments in the order: DP < uDP < uDuP < n-pris with mean annual effluxes over the 2-yr monitoring period of 0.15, 0.64, 7.70 and 22.63 g CH₄ m⁻² yr⁻¹, respectively. For CO₂, effluxes increased in the order uDP < DP< n-pris < uDuP, with mean annual effluxes of 1.23, 1.66, 1.82 and 2.55 kg CO₂ m⁻² yr⁻¹, respectively. CO₂ effluxes dominated the total net GHG emission, calculated using the global warming potential (GWP) of the three GHGs for each treatment (76–98%), and only in the n-pris site was CH₄ a substantial contribution (23%). Based on soil effluxes only, the near pristine (n-pris) peatbog had 43% higher total net GHG emission compared with the DP treatment because of high CH₄ effluxes and the DP treatment had 33% higher total net emission compared with the uDP because drainage increased CO₂ effluxes. Restoration is likely to increase CH₄ emissions, but reduce CO₂ effluxes. Our study suggests that if estimates of CO₂ uptake by vegetation from similar peatbog sites were included, the total net GHG emission of restored peatbog would still be higher than that of the peatbog with trees.