Methane Metabolism in a Temperate Swamp

Abstract

Comparisons between in situ CH 4 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 CH 4 , CO 2 , O 2 , SO 4 2- , NO 3 - , formate, acetate, propionate, and butyrate were made at two adjacent sites 1.5 to 2 m apart. Dissolved CH 4 was inversely correlated to O 2 and, in general, to NO 3 - and SO 4 2- , potential inhibitors of methanogenesis. At low water table levels (August 1992), maximal CH 4 (2 to 4 μM) occurred below 30 cm, whereas at high water table levels (October 1992) or under flooded conditions (May 1993), CH 4 maxima (4 to 55 μM) occurred in the top 10 to 20 cm. Higher CH 4 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 μM) in one of the sites in fall and spring. Measurements of potential CH 4 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 CH 4 production but also showed that competition for substrates by nonmethanogenic microorganisms could greatly attenuate its effect.