METHANE METABOLISM IN A TEMPERATE SWAMP

Comparisons between in situ CH4 concentration and potential factors controlling its net production were made in a temperate swamp. Seasonal measurements of water table level and depth profiles of pH, dissolved CN4, CO2, O-2, SO42-, NO3-, formate, acetate, propionate, and butyrate were made at two adjacent sites 1.5 to 2 m apart. Dissolved CH4 was inversely correlated to O-2 and, in general, to NO3- and SO42-, potential inhibitors of methanogenesis. At low water table levels (August 1992), maximal CH4 (2 to 4 mu M) occurred below 30 cm, whereas at high water table levels (October 1992) or under flooded conditions (May 1993), CH4 maxima (4 to 55 mu M) occurred in the top 10 to 20 cm. Higher CH4 concentrations were likely supported by inputs of fresh organic matter from decaying leaf litter, as suggested by high acetate and propionate concentrations (25 to 100 mu M) in one of the sites in fall and spring. Measurements of potential CH4 production (and consumption) showed that the highest rates generally occurred in the top 10 cm of soil. Soil slurry incubations confirmed the importance of organic matter to CH4 production but also showed that competition for substrates by nonmethanogenic microorganisms could greatly attenuate its effect.