Effect of biogenic gas bubbles on water flow through poorly decomposed blanket peat

Abstract

Abstract. A laboratory investigation was used to determine whether biogenic gas bubbles accumulate and block water-conducting pores below the water table in poorly decomposed Sphagnum peat. We found that biogenic gas bubbles did accumulate under realistic incubation temperatures. At the end of incubations at 10.5øC, volumetric water contents in two peat samples decreased to between 0.8 and 0.85 (porosity of the samples ranged from 0.96 to 0.97), indicating that the peat was considerably undersaturated with respect to water. Methane was found to be an important constituent of the gas bubbles. The presence of gas bubbles appeared to have a major effect on hydraulic conductivity (K). In control incubations, prior to which the peat had been irradiated and dosed with a biocide, biogenic gas bubbles did not accumulate, and K was 5-8 times higher than at the end of the microbially active incubations. Our results suggest that biogenic gas bubbles have a potentially significant effect on seepage in peat soils.

Ebullition of methane from peat with falling atmospheric pressure

“…The initial volumetric gas content (V g1 ) was assumed to be 12%, which is the median of the existing typical data of the gas content in waterlogged peat. Calculations of DV g under different assumptions of V g1 , with the maximum literature value of 16% [Beckwith and Baird, 2001;Baird et al, 2004] and the minimum of 8% [Tokida et al, 2005], were also made.…”

“…In this study, we tried to isolate the effect of air pressure change alone from other potential factors, among which the trapped gas-phase volume in the peat can be the most important regulator of CH 4 ebullition [Baird et al, 2004]. Because reported peat incubation experiments suggested that an increase in the volume of trapped gas would level off in less than 100 days of incubation [Beckwith and Baird, 2001;Baird et al, 2004], it can be said that the amount of the stored gas have already plateaued and had little effect on the difference in the CH 4 flux. The duration of each flux measuring period was approximately 60 hours, in which an intensive sampling scheme (at intervals of 1 -3 hours) was adopted with the chamber placement time of 20 minutes in order to identify the expected episodic, short-time bubbling of CH 4 from the peat matrix to the atmosphere.…”

Intense methane ebullition from open water area of a shallow peatland lake on the eastern Tibetan Plateau

“…Since methane is continuously produced in lake sediment and is relatively insoluble in water, methane-containing bubbles are formed in pore water (Boudreau et al, 2005;Laing et al, 2008). Release of such methanecontaining bubbles due to buoyancy presumably occurs when the stored gas volume exceeds some critical value (Beckwith and Baird, 2001). Methane release via bubbles (ebullition) results in direct flux of methane from the sediment to the atmosphere, with limited impact of methane oxidation in the water column, therefore ebullition is often the dominant pathway of methane release from lakes, particularly from the shallow area of lakes (Bastviken et al, 2004(Bastviken et al, , 2008.…”

Monitoring microbe-induced physical property changes using high-frequency acoustic waveform data: Toward the development of a microbial megascope

“…al., 1998;Reynolds et. al., 1992;Beckwith and Baird, 2001]. In particular, efforts have been made to establish a connection between microbial gases produced within pore spaces and the obstruction of fluid flow pathways.…”

“…The resulting decrease in Κ s is often attributed to the blocking of pore throats by accumulated gas bubbles with the available data suggesting that Κ s may be lowered by as much as an order of magnitude [Reynolds et. al., 1992;Beckwith and Baird, 2001]. …”