Contrasted effects of simulated drought on the production and oxidation of methane in a mid-Wales wetland

Wetlands are a major contributor to the global CH4 budget. Currently, there is a consensus view that drought restrains CH4 emissions from wetlands, and that this arises due to a suppression of CH4 production and stimulation of CH4 oxidation under the more aerobic conditions that accompany lower water table levels. Our data confirm that under drought conditions, CH4 production is lower (−73%, P<0.05) largely because it is confined to the deeper, more anaerobic, depths. Lower production rates were found to persist at least 1 month beyond the end of the drought (−89%, P<0.01). However, we found no evidence of increased rates of CH4 oxidation during the drought, and in contrast, at the end of the simulation observed significantly less CH4 oxidation in the drought treated system (P<0.05). These findings suggest that under drought conditions, the regulation of wetland methane flux occurs primarily through changes in methane production, with methane oxidation playing only a secondary role.