EVOLUTION OF BIOGENIC GASSES IN PEAT SOILS USING GROUND PENETRATING RADAR (GPR)

Peatlands generate significant amounts of free-phase biogenic gases (e.g. methane and carbon dioxide), but the mechanisms of formation and spatial distribution of these gases within the soil matrix still remain uncertain. In this work we investigate the utility of ground penetrating radar (GPR) as a geophysical tool to image the evolution and spatial location of gas accumulation both at the laboratory and field scale. In the laboratory, EM measurements were performed in a peat block (0.22m x 0.32m x 0.31m) extracted from a large freshwater peatland in Maine (Caribou Bog), as temperature was increased from 5°C to 21°C and then held constant. Methane emissions and surface peat deformation were monitored concurrently by using a portable methane detector and elevation rods, respectively. In the field, EM measurements were performed in a larger section (approximately 4m x 4m x 6m) of Caribou Bog (Central Unit). Methane emissions and surface peat deformation were also monitored. All field measurements were performed along a platform built to avoid disturbance of the peat surface. Changes in EM travel time (using GPR) revealed shifts in gas content. These results demonstrate that GPR measurements are a totally non-invasive way of investigating gas evolution without risking alteration of gas dynamics (e.g. by insertion of probes), and provide unique information on spatial distribution of biogenic gasses in peat soils. These findings also have implications for the monitoring of changes in biogenic gas emissions to the atmosphere from peatlands and its impact on global warming.