Dynamics and controls of methane oxidation in a Danish wetland sediment*

Abstract

The patterns and controls of methane oxidation in a Danish wetland sediment have been determined using a combination of slurry and intact core techniques. Results from slurries indicated that methane oxidation was effectively inhibited by low concentrations of nitrapyrin (9 μM) and acetylene (0.5 μM) but that oxidation was relatively insensitive to pH between 6 and 8; in addition, high concentrations of ammonia (1 mM) decreased oxidation, especially at alkaline pH. Kinetic analyses of methane oxidation in slurries indicated that Vmax was high relative to values reported for other sediments, that Vmax changed seasonally, that Km was consistently low (2–4 μM) and that threshold values were low (3–5 nM) but insufficient to allow consumption of atmospheric methane. Analyses based on intact cores indicated that the extent of methane oxidation was highly dependent on oxygen availability, particularly as affected by benthic photosynthesis or the presence of algal mats. Methane emission and oxidation showed a light saturation response above 400 μEinsteins m−2 s−1. Both core and slurry analyses indicated that even short periods of anoxia resulted in losses of the capacity for methane oxidation after re-exposure to air. On the other hand, the presence of anoxia-insensitive organisms provided for a significant residual post-anoxia activity. Results from addition of nitrapyrin to the surface of intact cores indicated that shifts in methane emissions coincident with short-term changes in the availability of oxygen were the result of changes in methane oxidation, not methanogenesis.