Controls on methane production in a tidal freshwater estuary and a peatland: Methane production via acetate fermentation and CO2 reduction

Rates of total methane production, acetate fermentation and CO2 reduction were compared for two different wetland sites. On a per-liter basis, sediments from the White Oak River estuary, a tidal freshwater site in eastern North Carolina, had an annual methane production rate (53.3 mM yr-1) an order of magnitude higher than that of Buck Hollow Bog (5.5 mM yr-1), a peatland in Michigan. Methane was produced in the White Oak River site on an annual basis by both acetate fermentation (72%) and CO2 reduction (28%) in a ratio typical of freshwater methanogenic sites. Competition for acetate by non-methanogenic microorganisms in Buck Hollow peat limited methane production from acetate to only a few months a year, severely impacting annual methane production rates. However, when acetate was available to the methanogens in the peat during early spring, the percentage of methane production from acetate fermentation (84%) and CO2 reduction (16%) and rates of total methane production were similar to those of the White Oak River sediments at the same temperature. Rates of CO2 reduction and acetate fermentation conducted at both sites at various temperatures showed that Buck Hollow peat methane production was also limited by a colder temperature regime as well as differences in the response of the CO2 reducing and aceticlastic methanogens to temperature variations.