Methane emission from tidal freshwater marshes

In two tidal freshwater marshes, methane emission, production and accumulation in the pore-water have been studied. The two sites differ in their dominant vegetation, i.e., reed and bulrush, and in their heights above sea level. The reed site was elevated in relation to the bulrush site and had higher rates of methane emission and production. It is argued that this difference in methane emission between sites was primarily due to a different effect of reed and bulrush plants on methane dynamics rather than methane oxidation related to tidal elevation. Methane emission showed strong seasonality related primarily to plant physiology and only secondarily to temperature. Two control sites at which vegetation was removed systematically had lower emission rates indicating an overall stimulating effect of plants on methane emission from tidal marshes. Flooding reduced methane emission, probably by blocking the primary sites of methane release in the lower part of the plant stems.