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 pro files where water table had not varied, the water-saturated layers showed s ignificant potentials while the unsaturated layers did not. The production potentials in the saturated layers below water level ranged from 0.1 to 2.4 mu g 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 v aried only a little, production potentials slightly increased towards the a utumn. After a water level draw-down, in the profiles from the dry microsit es, production and oxidation potentials were detected in layers that had be en unsaturated up to 6 weeks. The maximal oxidation zone was shifted downwa rds during low water periods. In a wet microsite, a 2 week period of unsatu ration eliminated the production potentials and decreased the oxidation pot entials. After a rise in the water level, the potentials were reactivated m ore rapidly in the wet than in the dry microsites. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.