Effects of Water Regimes on Methane Emissions in Peatland and Gley Marsh

Core Ideas Large pulses of CH 4 can be emitted during short‐duration drying–wetting episodes. Peatland soils had higher CH 4 emissions than gley marsh soils under a steady water table. Accurate CH 4 estimates should include weather events that cause rapid changes in soil moisture regimes. The increasing frequency of extreme drought and intense precipitation events with global warming may affect CH 4 emissions from different types of wetlands by regulating drying–wetting cycles. To determine the effects of different water regimes on CH 4 emissions, a mesocosm experiment was conducted. Soil cores sampled from peatland and gley marsh were subjected to two drying–wetting cycles (i.e., fluctuating between −10 and 10 cm for 7 and 15 d, respectively) and three steady water table treatments (10, 0, and −10 cm). Alternation between drying and wetting stimulated CH 4 emissions ( F = 16.03 for 7 d and F = 31.85 for 15 d, P < 0.01). The highest emission pulses were observed between 4 and 9 d after the water table increased according to the models. Peak pulse emissions significantly increased by 41% in peatland and 109% in gley marsh after rewetting compared with that in the steady 0‐cm water table treatment. Peatland soils had higher CH 4 emissions than gley marsh soils under steady water table treatments ( P < 0.01). This study shows that large pulses of CH 4 can be emitted during short‐duration drying–wetting episodes. If these pulses are not accounted for in budgets, CH 4 emissions may be incorrectly assessed when comparing with field measurements during regularly spaced sampling intervals over only a few days or weeks by the static opaque chamber technique. Accurate estimates of CH 4 budgets not only depend on increased measurement frequency but by necessity should incorporate weather events that cause rapid changes in the soil moisture regime.