Methane production and oxidation potentials in relation to water table fluctuations in two boreal mires

We studied the response of methane production and oxidation potentials in a minerotrophic and an ombrotrophic mire to water table fluctuations. In profiles where water table had not varied, the water-saturated layers showed significant potentials while the unsaturated layers did not. The production potentials in the saturated layers below water level ranged from 0.1 to 2.4 μg CH4 h−1 (g d.w.)− 1 and oxidation potentials (first order reaction rate constants) between −0.010 and −0.120 h−1 (g d.w.)− 1. In profiles with constant water level, the maximal production potential occurred 20 cm and maximal oxidation potential 10 cm below water level. When water table varied only a little, production potentials slightly increased towards the autumn. After a water level draw-down, in the profiles from the dry microsites, production and oxidation potentials were detected in layers that had been unsaturated up to 6 weeks. The maximal oxidation zone was shifted downwards during low water periods. In a wet microsite, a 2 week period of unsaturation eliminated the production potentials and decreased the oxidation potentials. After a rise in the water level, the potentials were reactivated more rapidly in the wet than in the dry microsites.