Methane flux: Water table relations in northern wetlands

Water table position, through the creation of aerobic and anaerobic conditions in the soil profile, plays an important role in controlling CH 4 flux from wetlands. A laboratory study of peat columns revealed that CH 4 emission rates initially increased and then decreased as the water table was lowered from the peat surface to a depth of 50 cm, with the release of CH 4 trapped in pores. There was a strong hysteresis between CH 4 flux on the falling and rising water table limbs (falling > rising). When expressed as seasonal average values, there was a strong relationship (r² 0.08 – 0.74) between log CH 4 flux and water table position for sites within 5 wetland regions in boreal‐subarctic Canada. The regression coefficients were similar among regions (0.022 – 0.037), but there were differences in the regression constants (0.47 – 1.89). CH 4 flux from drained, forested peatland soils decreased as the water table depth increased, and several sites were transformed from sources to sinks of CH 4 . Global CH 4 emissions to the atmosphere may have been reduced by ≈ 1 Tg yr −1 by peatland drainage during the last 100 yr.