Ground-penetrating radar (GPR) is a promising technology for investigating methane cycling in peatlands over a wide range of spatial scales. Unlike most commonly applied techniques that seek to ascertain information on the vertical distribution of peat structure and/or gas content, GPR can be employed entirely noninvasively with minimal disruption to the in situ gas regime. We discuss the following applications of the GPR method in peatlands research: (1) imaging the lateral continuity of confining layers that may permit free-phase gas (FPG) accumulation and regulate methane emissions; (2) estimation of vertical profiles of FPG content using surface and cross-hole measurements; and (3) noninvasive temporal monitoring of FPG production and emissions from a peat column. We present new GPR results that demonstrate how 1-D velocity profiles from the glacial Lake Agassiz peatland (GLAP) complex support the suggestion of accumulation of FPG below confining layers at 3-4 m depth. Using cross-borehole GPR data collected from a peatland in Maine, we show how GPR tomography (previously unapplied in peatlands) can image the spatial distribution of FPG content in Caribou Bog, with minimal invasiveness. We also present results of 3-D surface reflection amplitude analysis, suggesting that reflection amplitudes, in addition to travel times, may yield insights into changes in methane production and emissions (e.g., via ebullition) from peat soils. We finish by discussing limitations of the technique (e.g., petrophysical conversion) and recommendations for further research to improve the application of this technology in studies of methane cycling in northern peatlands.
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