From a boreal bog to an abandoned peatland pasture: the effect of agricultural management and abandonment on the greenhouse gas fluxes, carbon balance and radiative forcing of a boreal bog in western Newfoundland, Canada

Undisturbed peatlands generally act as a long-term carbon (C) sink and climate cooling. Agriculturally managed peatlands have been identified as hotspots for C and greenhouse gases (GHGs) emissions. However, the increased magnitude of C and GHGs emissions following agriculture management was found to be significantly variable, dependent on the management intensity, peatland initial conditions, cultivation species, time for plant regeneration and fertilization amount. Moreover, the knowledge of how agricultural management and abandonment affects GHGs fluxes is limited by insufficient direct comparisons of GHGs fluxes between undisturbed peatlands and agriculturally managed ones and failure to consider all three GHGs species. To bridge this gap, I conducted a study measuring the landscape-scale carbon dioxide (CO₂) and methane (CH₄) fluxes by eddy covariance and plot-scale N2O fluxes using static chamber technique in a boreal bog and an adjacent abandoned peatland pasture to determine and compare the controls on the temporal patterns of all GHGs fluxes and the effect of agricultural conversion and abandonment on the GHGs fluxes, the C balance and radiative forcing of a boreal bog in western Newfoundland, Canada. This study showed that the gross primary productivity (GPP) and ecosystem respiration (ER) of the abandoned peatland pasture was significantly higher than the counterparts at the bog. The between-site difference in GPP was mainly related to their different vegetation conditions, and the between-site ER difference was linked to different conditions of water table, substrate availability and autotrophic respiration. Overall, the abandoned peatland pasture was a stronger CO₂ sink than the bog. The abandoned peatland pasture was a smaller CH₄ source than the bog. CH₄ flux showed distinct diel and seasonal patterns at the bog but not at the abandoned peatland pasture. Subsurface soil temperature was the main control on CH₄ flux during the growing season but friction velocity became important in the non-growing season at the bog, while no variable was found to be significantly related to the seasonal variation in CH₄ flux at the abandoned peatland pasture. N₂O flux did not show any significant temporal and spatial pattern and the fluxes were very low at both the bog and abandoned peatland pasture. The C and GHGs balance were mainly determined by the magnitude and direction of CO₂ at the pasture, but the GHGs balance was determined by CH₄ flux at the bog. The abandoned peatland pasture acted as a stronger C and GHGs sink than the bog. Therefore, results in this study suggest that the C sequestration capacity and climate cooling function of agriculturally managed peatlands can become stronger than the undisturbed peatlands after long-term abandonment. Research in the thesis contributes new understanding of how agricultural management and abandonment affects the controls on GHGs fluxes and the C balance and climate regulation of peatlands. The work also shows the controls on C fluxes vary over different time-scales and different periods and pose difficulty for incorporation into ecosystem models.