Spatial variability in biogenic gas accumulations in peat soils is revealed by ground penetrating radar (GPR)

Abstract

We performed surface and borehole ground penetrating radar (GPR) tests, together with moisture probe measurements and direct gas sampling to detect areas of biogenic gas accumulation in a northern peatland. The main findings are: (1) shadow zones (signal scattering) observed in surface GPR correlate with areas of elevated CH4 and CO2 concentration; (2) high velocities in zero offset profiles and lower water content inferred from moisture probes correlate with surface GPR shadow zones; (3) zero offset profiles depict depth variable gas accumulation from 0–10% by volume; (4) strong reflectors may represent confining layers restricting upward gas migration. Our results have implications for defining the spatial distribution, volume and movement of biogenic gas in peatlands at multiple scales.

The hydrology of northern peatlands as affected by biogenic gas: current developments and research needs

“…Episodic ebullition events occur when an accumulation of gas at some depth in the peat column is released suddenly to the peat surface. Indirect evidence of releases of trapped gas includes will-o'-the-wisp nighttime light sources (Glaser et al, 2004), vigorous bubbling following extraction of peat cores Siegel et al, 2001;Comas et al, 2005), and rapid temporal changes in peat-column chemical profiles .…”

Ground-penetrating radar study of the Cena Bog, Latvia: linkage of reflections with peat moisture content

“…where θ -volumetric water content; ϕ -porosity; ε s -dielectric permittivity of the solid phase (set to a a a a 2; Comas et al, 2005b); ε w -dielectric permittivity of water; ε g -dielectric permittivity of air. In the course of calculations α was set to 0.35 as commonly used for peat (Strack & Mierau, 2010), ε w was set to 83.83 (selected for in the field measured average temperature of peat 10 °C) and it was assumed that gas content is negligible (ϕ = θ).…”

Deep CO<sub>2</sub> soil inhalation / exhalation induced by synoptic pressure changes and atmospheric tides in a carbonated semiarid steppe

“…Advection has been detected using isotopic methods (Bowling and Massman, 2011), buried p sensors (Maier et al, 2010;Takle et al, 2004), 222 Rn concentrations (Clemets and Wilkening, 1974;Fujiyoshi et al, 2010), ground-penetrating radar (Comas et al, 2005) or variations in CO 2 and other gases (Seok et al, 2009;Hirsch et al, 2004;Reicosky et al, 2008). Even in volcanoes the atmospheric p has a strong influence on both CO 2 degassing (Rogie et al, 2001) and the CO 2 soil efflux (Granieri et al, 2003), as well as on their combination as measured by eddy covariance (Lewicki et al, 2008;Lewicki et al, 2007).…”

“…Ventilation (gas advection through porous media) can decouple the soil CO 2 source from emissions to the atmosphere with changes in pressure, wind or friction velocity. Scientists have confirmed subterranean advective transport in laboratories (Nachshon et al, 2012;Maier et al, 2012), soils (Clemets and Wilkening, 1974;Maier et al, 2010;Subke et al, 2003;Weisbrod et al, 2009), peatlands (Comas et al, 2005;Comas et al, 2007;Comas et al, 2011), and snow (Bowling and Massman, 2011;Fujiyoshi et al, 2010;Seok et al, 2009;Massman et al, 1997). Some have applied the gradient method -based on Fick's law for molecular diffusion -to model exchange with the atmosphere during calm conditions, but highlight the importance of advective transport in exchanges at other times.…”