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Magnetic Susceptibility as a Proxy for Investigating Microbial Mediated Iron Reduction
Citation:
Mewafy, F. M., E. A. Atekwana, D. D. WERKEMA, L. D. Slater, D. Ntarlagiannis, A. Revil, M. Skold, AND G. N. Delin. Magnetic Susceptibility as a Proxy for Investigating Microbial Mediated Iron Reduction. GEOPHYSICAL RESEARCH LETTERS. American Geophysical Union, Washington, DC, 38(0):1-5, (2012).
Impact/Purpose:
We investigated magnetic susceptibility (MS) variations in hydrocarbon contaminated sediments. Our objective was to determine if MS can be used as an intrinsic bioremediation indicator due to the activity of iron-reducing bacteria. A contaminated and an uncontaminated core were retrieved from a site contaminated with crude oil near Bemidji, MN and subsampled for MS measurements. The contaminated core revealed enriched MS zones within the hydrocarbon smear zone, which is related to iron-reduction coupled to oxidation of hydrocarbon, compounds and the vadose zone, which is coincident with a zone of methane depletion suggesting aerobic or anaerobic oxidation of methane is coupled to iron-reduction. The latter has significant implications for methane cycling. We conclude that MS can serve as a proxy for intrinsic bioremediation by iron-reducing bacteria and for the application of geophysics to iron cycling studies. monitoring, and remediating hydrocarbon contamination. Due to the relationship between magnetic minerals and redox reactions associated with hydrocarbon seeps, magnetic susceptibility (MS) has been used as a possible tool for oil exploration [e.g., Saunders et al., 1999]. In surficial sediments, MS traditionally is used for climate studies [e.g., Kukla et al., 1988], mapping heavy metal soil contamination [e.g., Hanesch and Scholger, 2002], and identifying sediment sources and transport trends [Ellwood et al., 2006]. MS has recently emerged as a tool for investigating iron cycling mediated by microbial activity [e.g., Porsch et al., 2010;Rijal et al., 2010].
Description:
We investigated magnetic susceptibility (MS) variations in hydrocarbon contaminated sediments. Our objective was to determine if MS can be used as an intrinsic bioremediation indicator due to the activity of iron-reducing bacteria. A contaminated and an uncontaminated core were retrieved from a site contaminated with crude oil near Bemidji, MN and subsampled for MS measurements. The contaminated core revealed enriched MS zones within the hydrocarbon smear zone, which is related to iron-reduction coupled to oxidation of hydrocarbon compounds and the vadose zone, which is coincident with a zone of methane depletion suggesting aerobic or anaerobic oxidation of methane is coupled to iron-reduction. The latter has significant implications for methane cycling. We conclude that MS can serve as a proxy for intrinsic bioremediation by iron-reducing bacteria and for the application of geophysics to iron cycling studies.