Natural-abundance radiocarbon as a tracer of assimilation of petroleum carbon by bacteria in salt marsh sediments |
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Authors: | Stuart G Wakeham Ann P McNichol Tamara K Pease |
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Institution: | a Skidaway Institute of Oceanography, 10 Ocean Science Circle, Savannah, GA 31411, USA b National Ocean Science Accelerator Mass Spectrometry (NOSAMS) Facility, Woods Hole Oceanographic Institution, MS 8, Woods Hole, MA 02543, USA c Department of Oceanography, Florida State University, Tallahassee, FL 32306-4320, USA d Marine Science Institute, The University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX 78373-5015, USA |
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Abstract: | The natural abundance of radiocarbon (14C) provides unique insight into the source and cycling of sedimentary organic matter. Radiocarbon analysis of bacterial phospholipid lipid fatty acids (PLFAs) in salt-marsh sediments of southeast Georgia (USA)—one heavily contaminated by petroleum residues—was used to assess the fate of petroleum-derived carbon in sediments and incorporation of fossil carbon into microbial biomass. PLFAs that are common components of eubacterial cell membranes (e.g., branched C15 and C17, 10-methyl-C16) were depleted in 14C in the contaminated sediment (mean Δ14C value of +25 ± 19‰ for bacterial PLFAs) relative to PLFAs in uncontaminated “control” sediment (Δ14C = +101 ± 12‰). We suggest that the 14C-depletion in bacterial PLFAs at the contaminated site results from microbial metabolism of petroleum and subsequent incorporation of petroleum-derived carbon into bacterial membrane lipids. A mass balance calculation indicates that 6-10% of the carbon in bacterial PLFAs at the oiled site could derive from petroleum residues. These results demonstrate that even weathered petroleum may contain components of sufficient lability to be a carbon source for biomass production by marsh sediment microorganisms. Furthermore, a small but significant fraction of fossil carbon is assimilated even in the presence of a much larger pool of presumably more-labile and faster-cycling carbon substrates. |
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