Greenhouse gas emissions from two rewetted peatlands previously managed for forestry

The aim of this study was to investigate the controls on carbon dioxide (CO ₂ ), methane (CH ₄ ) and nitrous oxide (N ₂ O) dynamics on a blanket bog (at Pollagoona) and a raised bog (at Scohaboy) in Ireland after felling of plantation forestry and rewetting, and to produce annual balances for each gas at both sites. Gas fluxes were measured during a twelve-month period using the chamber method. Microsite types reflecting the dominant plant species at the chamber plots were identified and classified as Eriophorum-Sphagnum, Cladonia-Calluna and Molinia at Pollagoona and Eriophorum-Sphagnum, Cladonia-mosses, Eriophorum and brash (logging residues) at Scohaboy. The relationships between gas fluxes and environmental variables were assessed, and regression models were used to estimate annual CO ₂ and CH ₄ gas balances for each microsite type. Annual estimates of N ₂ O exchange were calculated using seasonal means. Over the course of the study both sites acted as CO ₂ and CH ₄ sources. Although Pollagoona was an overall net source of CO ₂ -C (131.6 ± 298.3 g m ^-2 yr ^-1 ), one microsite type (Cladonia-Calluna) acted as a strong sink for CO ₂ -C (-142.8 g m ^-2 yr ^-1 ). Molinia microsites exhibited the highest CH ₄ -C emissions (2.53 ± 1.01 g m ^-2 yr ^-1 ). Nitrous oxide emissions at Pollagoona were calculated as 12 μg m ^-2 yr ^-1 . Scohaboy acted as a large CO ₂ -C source (585.3 ± 241.5 g m ^-2 yr ^-1 ) (all microsite types) despite re-vegetation of non-brash plots, due to the availability of fresh organic matter across the site. Scohaboy was also a CH ₄ -C source, emitting 3.25 ± 0.58 g m ^-2 yr ^-1 . Emissions of both CO ₂ -C (819.31 ± 57.7 g m ^-2 yr ^-1 ) and CH ₄ -C (4.76 ± 0.98 g m ^-2 yr ^-1 ) were highest from the brash plots. Annual N ₂ O-N emissions were small over the study period (72 µg m ^-2 yr ^-1 ). Our results indicate that, despite remedial work being conducted on both peatlands to raise the water table, the C sink function has not yet been restored at either site.