HR: 1330h
AN: NB33C-16    [Abstracts]
TI: Estimation of Biogenic Gas Distribution in a Northern Peatland Using Surface and Borehole Ground Penetrating Radar
AU: * Comas, X
EM: xcomas@pegasus.rutgers.edu
AF: Rutgers University, Dept. Earth & Env. Sciences 101 Warren St., Newark, NJ 07102 United States
AU: Slater, L
EM: lslater@andromeda.rutgers.edu
AF: Rutgers University, Dept. Earth & Env. Sciences 101 Warren St., Newark, NJ 07102 United States
AU: Reeve, A
EM: asreeve@maine.edu
AF: University of Maine, Dept. Earth Sciences Bryand Global Sciences Center, Orono, ME 04401 United States
AB: A combination of borehole and surface ground penetrating radar (GPR), time domain reflectometry (TDR) and direct gas sampling was performed to detect biogenic gas accumulation areas in Caribou Bog, a multi-unit peatland in central Maine (Orono). Areas of electromagnetic (EM) signal scattering (or shadow zones, similar to those reported with the seismic reflection method) observed in the surface GPR coincide with sampled zones of high CH4 and CO2 concentration. Shadow zones also correlate with areas of high EM wave velocity detected in zero offset profiles (ZOP) conducted with the borehole GPR, and with areas of low water content inferred with TDR. Application of the Complex Refractive Index Model (CRIM) to the EM wave velocities implies that the anomalous high velocity zones results from a volumetric gas content of 7% and 10% for a peat soil porosity of 91% and 94% respectively. In the absence of gas, the CRIM model predicts a porosity value of only 84% to reach the maximum EM wave velocity recorded, a value not supported by our peat porosity measurements in the laboratory and inconsistent with the high porosity of peat recorded by others. Strong reflectors detected with the surface GPR are interpreted as confining layers acting as biogenic gas traps and inducing overpressurized biogenic gas pockets as postulated by others. Spatial gas distribution and volumetric gas content can be roughly estimated considering the areas affected by EM wave blanking. These findings also have implications for the monitoring of temporal behavior of biogenic gas emissions to the atmosphere from peatlands.
DE: 0900 EXPLORATION GEOPHYSICS
DE: 1890 Wetlands
DE: 4805 Biogeochemical cycles (1615)
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly