Interannual variability of carbon dioxide (CO₂) and methane (CH₄) fluxes in a temperate bog over a 5-year period

Peatland rewetting, which is a management effort to restore water levels in previously drained peatlands, is important for re-establishing the role of peatlands as carbon (C) sinks. Since rewetted peatlands often have a highly variable response to year-to-year changes in climatic conditions and to functional changes, long term studies of C fluxes are needed in these ecosystems. Here, we evaluated the impact of climate variability and functional change on the interannual variability of CO₂ and CH₄ fluxes at Burns Bog, a rewetted temperate bog in Canada, based on five years of continuous eddy-covariance measurements. We found that the study site alternated between being an annual-scale net CO₂ sink and source, ranging from -32.6 ± 21.5 (± 95% CI) to 11.9 ± 15.1 g CO₂-C mˉ² yearˉ¹, respectively, while consistently being a CH₄ source, ranging from 11.6 ± 0.7 to 18.0 ± 1.6 g CH₄-C mˉ² yearˉ¹. On a five-year average, CH₄ emissions (13.7 ± 2.5 g CH₄-C mˉ² yearˉ¹; ± SD across years) completely offset the CO₂ sink (-12.3 ± 20.4 g CO₂-C mˉ² yearˉ¹; ± SD across years) on a carbon equivalent basis, resulting in the site losing an average of 1.3 ± 23.9 g C mˉ² yearˉ¹ (± SD across years). This finding indicates that excluding CH₄ fluxes from the net ecosystem C budget results in a significant overestimation of the net C uptake at this peatland site. The bog was the greatest annual CO₂ source in the year with a dry and warm summer, emphasizing the importance of temperature and water table depth at the bog. Regardless of the GHG metrics (i.e., global warming potential or sustained global warming potential) used in calculating the annual CO₂-eq GHG balance, the bog consistently had a positive radiative balance during each year of the study period. Despite mainly acting as a GHG source, the rewetted bog will likely have cooling effect on climate over long timescales compared to drained bogs that are large CO₂ sources.Arts, Faculty ofGeography, Department ofGraduat