HR: 15:15h
AN: NS43A-05    [Abstracts]
TI: Resistivity-based geophysical monitoring of biogenic gas dynamics in a large peat block
AU: * Slater, L
EM: lslater@andromeda.rutgers.edu
AF: Rutgers-Newark, 101 Warren St., Newark, NJ 07102, United States
AU: Roy Maillok, M
EM: maitryr@andromeda.rutgers.edu
AF: Rutgers-Newark, 101 Warren St., Newark, NJ 07102, United States
AU: Comas, X
EM: xcomas@pegasus.rutgers.edu
AF: University of Maine, Bryand Global Sciences Center, Orono, ME 04469, United States
AU: Ntarlagiannis, D
EM: dimntar@pegasus.rutgers.edu
AF: Rutgers-Newark, 101 Warren St., Newark, NJ 07102, United States
AB: Northern peatlands are an important component of the global carbon (C) cycle, estimated to account for 10 percent of annual methane flux to the atmosphere. Yet considerable uncertainty exists regarding the spatial and temporal character of free phase gas (FPG) build up and release in peat soils. We describe here an experiment on a large peat block (dimensions .28 m x 0.2 m x 0.2 m) whereby electrical resistivity measurements were made over a 66-day period of biogenic gas build up and release. Vertical profiles of resistivity were obtained using five vertical resistivity arrays (20 electrodes at 0.01 m spacing per array) distributed throughout the block. In addition to the geophysical measurements, methane release was quantified with a portable gas detector and surface deformation (due to peat expansion as a result of gas build up) recorded using 30 rods distributed equally across the block surface. Pore fluid conductivity was also recorded at three depths (0.05, 0.09 and 0.15 m below the peat surface). The geophysical measurements, after correction for increases in pore fluid conductivity apparently driven by methanogenesis, exhibit a distinct pattern of resistivity variation that we interpret as a result of repeated build up and release of a resistive gas phase. This interpretation is supported by the significant correlation between resistivity change and associated surface deformation due to expansion, as well as periods of maximum resistivity change generally occurring during maximum gas emission as estimated with the portable gas detector. Inversion of the resistivity datasets obtained from the five arrays yielded clear images of the spatial distribution of gas accumulation within the block. The inversion clearly shows that the FPG build up is non- uniform within the block and primarily concentrated in (a) a zone about 5 cm below the peat surface, and (b) a zone below 0.16 m towards the base of the peat block. The images of predicted gas build up are remarkably consistent with previously published vertical profiles of methane concentration produced/accumulated in peat soils and support the concept that production is focused within a higher porosity zone of more rapid organic matter decomposition just below the water table.
DE: 0428 Carbon cycling (4806)
DE: 0694 Instruments and techniques
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1835 Hydrogeophysics
DE: 1890 Wetlands (0497)
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly