Modelling methane fluxes along the thawing gradient of Boreal-Arctic peatland ecosystems with CoupModel

Northern peatlands are key carbon reservoirs and natural sources of methane. The northern peatland soils have various mechanisms controlling water, energy and carbon cycles (soil freeze-thaw) which further make modeling the emissions a challenge. In this study, we developed the CoupModel with respect to more comprehensive representation of gas processes in soil and plants, and used it to simulate O₂, CO₂, CH₄ as well as energy and water fluxes in three pristine northern peatlands across the thawing gradient (seasonal frost – degraded permafrost – continuous permafrost). These sites have 10-15 years of CO₂ flux and CH₄ flux measurement data. CoupModel reproduced the measured hourly CH₄ fluxes with R² (coefficient of determination) values of 0.60±0.02, 0.32±0.02 and 0.18±0.005 in Degerö Stormyr, Stordalen and Zackenberg, respectively. Our model simulation showed CH₄ emissions from three sites along the Boreal-Arctic gradient have diverse sensitivities to temperature and WTD. Higher temperature sensitivity of CH₄ was found in continuous permafrost zone (Zackenberg), and a turning point for WTD (-0.15~-0.1 m) found over three sites. Hysteresis exists in CH₄ fluxes responding to water table, temperature and freezing-thawing cycles. We conclude that the newly developed CoupModel can adequately simulate the CH₄ emission and its controls for northern peatlands. Our study revealed the response trajectories of peatland ecosystems across the permafrost region to environmental controls and highlighted the need for future peatland models to better simulate and predict the future CH₄ dynamics in a changing climate.