Methane fluxes from a rewetted agricultural fen during two initial years of paludiculture

Rewetting agricultural peatland abates carbon dioxide (CO₂) emission, but the resulting waterlogged anaerobic soil condition may create hotspots of methane (CH₄) emissions. In this study, we measured CH₄ emissions from side-by-side replicated plots in an agricultural fen cultivated with reed canary grass under a control and two experimental rewetting (i.e., paludiculture) conditions as either continuously flooded to soil surface or semi-flooded where water from the flooded plots intruded from sub-surface. Fluxes were measured for two successive years at 1-2 week intervals (total 59 measurement dates) using static chambers. Annual emissions were estimated by trapezoidal linear interpolation of the measured fluxes between the measurement dates. Two-year time-weighted average ground water tables (GWT) in the flooded, semi-flooded and control plots were 1, 3 and 9 cm below soil surface, respectively. The annual average emissions from flooded plots were 82 and 116 g CH₄ m^-2 yr^-1 in Year 1 and 2, respectively, which were significantly higher than the emissions from semi-flooded plots (35 and 69 g CH₄ m^-2 yr^-1 in Year 1 and 2, respectively) and from control plots (3 and 9 g CH₄ m^-2 yr^-1 in Year 1 and 2, respectively). Overall, the results showed that the GWT in paludiculture should be maintained few cm below soil surface during high temperature periods to prevent risks of high CH₄ emissions.