Is situ monitoring of free-phase gas accumulation and release in peatlands using ground penetrating radar (GPR)

Abstract

We tested a set of surface common mid-point (CMP) ground penetrating radar (GPR) surveys combined with elevation rods (to monitor surface deformation) and gas flux measurements to investigate in-situ biogenic gas dynamics and ebullition events in a northern peatland (raised bog). The main findings are: (1) changes in the two-way travel time from the surface to prominent reflectors allow estimation of average gas contents and evolution of free-phase gas (FPG); (2) peat surface deformation and gas flux measurements are strongly consistent with GPR estimated changes in FPG content over time; (3) rapid decreases in atmospheric pressure are associated with increased gas flux; and (4) single ebullition events can induce releases of methane much larger (up to 192 g/m2) than fluxes reported by others. These results indicate that GPR is a useful tool for assessing the spatial distribution, temporal variation and volume of biogenic gas deposits in peatlands. Copyright 2007 by the American Geophysical Union.