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

Rewetting agricultural peatland abates carbon dioxide (CO) emission, but the resulting waterlogged anaerobic soil condition may create hotspots of methane (CH) emissions. In this study, we measured CH 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 CH m yr in Year 1 and 2, respectively, which were significantly higher than the emissions from semi-flooded plots (35 and 69 g CH m yr in Year 1 and 2, respectively) and from control plots (3 and 9 g CH m yr 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 CH emissions.