Trapped methane volume and potential effects on methane ebullition in a northern peatland, Limnol

A novel way of estimating the gas bubble volume in the floating mat sediment of a peatland was developed at Thoreau’s Bog in Concord, Massachusetts. Statistically significant relationships between the buoyancy of the floating Sphagnum mat and atmospheric pressure were observed, and these relationships were used to estimate the gas bubble volume. The mass of CH, stored in gas bubbles is estimated to be as much as 3 times the mass of dissolved CH,, depending on the time of year. The gas bubble volume is frequently large enough to serve as a significant buffer between microbial production of CH, and the release of CH, to the atmosphere. Changes in atmospheric pressure, temperature, and water-table elevation may result in mod-ulation of the ebullitive CH, flux. Periods of rapidly rising atmospheric pressure or equivalent pressure changes due to water-table elevation are capable of arresting bubble volume growth, thereby halting CH, ebullition. Periods of rapid cooling of the bog could also temporarily halt ebullition, as thermally induced contraction of bubbles and dissolution of CH, offset bubble volume growth due to methanogenesis. Methane is a greenhouse gas whose tropospheric con-centration is increasing at an annual rate of- 1 % (Khalil and Rasmussen 1990). A significant source of tropo-spheric CH4 is releases from northern peatlands (Asel-mann and Crutzen 1989; Fung et al. 199 1). Published estimates of the magnitude of CH, fluxes from northern peatlands vary considerably, most likely owing to the high spatial and temporal variability of peatland flux mea-surements (e.g. Roulet et al. 1994). Methane enters the atmosphere through several pro-cesses: diffusion, ebullition (Chanton and Martens 1988; Lansdown et al. 1992), and transport through plants (Morrissey and Livingston 1992). Ebullition, or bubbling, has been proposed as the dominant CH, transport process in many environments, including a temperate bog i