PRODUCTION AND EMISSION OF METHANE IN A BRACKISH AND A FRESH-WATER WETLAND

There is no clear consensus on how environmental and biotic factors control microbially-mediated methane production in wetlands, as well as emission of this important 'greenhouse gas' from wetlands into the atmosphere. To provide insight, I studied rates of methane production and emission into the atmosphere, as well as factors controlling those rates, along a toposequence from non-flooded to seasonally flooded in a coastal meadow and in a fen in Denmark. Methane production was estimated from anaerobic soil slurries while emission was estimated from static dux chambers. Methane emission into the atmosphere averaged 0.04 mu g C-CH, dm(-2) h(-1) in the coastal meadow and 1.9 mu g C-CH4 dm(-2) h(-1) in the fen. A comparison of potential CH4 production and CH4 emission into the atmosphere showed that in the coastal meadow, but not in the fen, emission increased when production increased during summer. Relationships between potential CH4 production and soil water content as well as soil temperature are discussed. Arrhenius plots indicated strikingly similar temperature responses of CH4 production in the two wetlands. Also, both wetlands showed different temperature responses in saturated soils (Q(10) = 3.1 and 3.6; E(h) = 79 and 84 kJ mol(-1)) compared to unsaturated soils (Q(10) = 8.1 and 8.7; E(h) = 138 and 142 kJ mol(-1)). My results suggest that different types of methanogens inhabit saturated and unsaturated soils in both a coastal meadow and a fen. Overall, the study indicates that CH4 production in wetlands and CH4 emission into the atmosphere from wetlands are controlled by a complex set of environmental and biotic factors which differ between wetlands.