title: Comparison of surficial CO2 efflux to other measures of subsurface crude oil degradation.
abstract: At a spill site near Bemidji, Minnesota, crude oil at the water table has been undergoing anaerobic biodegradation for over 30years. Previous work at this site has shown that methane produced from biodegradation of the oil migrates upward and is oxidized in a methanotrophic zone midway between the water table and the surface. To compare microbial activity measurement methods from multiple locations in the oil body, surficial carbon dioxide efflux, methanogen and methanotroph concentrations, and oil degradation state were collected. Carbon dioxide effluxes over the oil body averaged more than four times those at the background site. Methanotrophic bacteria concentrations measured using pmoA were over 10(5) times higher above the oil-contaminated sediments compared with the background site. Methanogenic archaea measured using mcrA ranged from 10(5) to over 10(7) in the oil and were below detection in the background. Methanogens correlated very well with methanotroph concentrations (r=0.99), n-alkylcyclohexane losses as a proxy for degradation state (r=-0.96), and somewhat less well with carbon dioxide efflux (r=0.92). Carbon dioxide efflux similarly correlated to methanotroph concentrations (r=0.90) and n-alkylcyclohexane losses (r=-0.91).
authors.affiliation: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States. Electronic address: ewarren@usgs.gov.
authors.forename: Ean
authors.initials: E
authors.lastname: Warren
authors.affiliation: Department of Earth, Ocean and Atmospheric Sciences, The University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada. Electronic address: nsihota@eos.ubc.ca.
authors.forename: Natasha J
authors.initials: NJ
authors.lastname: Sihota
authors.affiliation: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States. Electronic address: fdhostet@usgs.gov.
authors.forename: Frances D
authors.initials: FD
authors.lastname: Hostettler
authors.affiliation: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States. Electronic address: babekins@usgs.gov.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Bekins
mesh_terms: D000693:Anaerobiosis; D001105:Archaea / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D008697:Methane / Q000096:biosynthesis* / Q000737:chemistry; D008910:Minnesota; D010578:Petroleum / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism*
chemical_list: D010578:Petroleum; D014874:Water Pollutants, Chemical; D002245:Carbon Dioxide; D008697:Methane
keywords: Alkylcyclohexane biodegradation; Carbon dioxide efflux; Crude oil; Microbial concentration; Pearson correlation