Abstract
Volatile fatty acid (VFA) apparent turnover rates in organic-rich marine sediments were determined by measuring whole sediment VFA concentration and the corresponding first-order reaction rate constants. In order to measure VFA concentrations, bulk wet sediment samples were basified, freeze-dried, extracted with methanol, derivatized to form methyl esters of the VFAs, and analyzed by packed-column gas chromatography using hexanoic acid as an internal standard. The detection limits for acetate, propionate, iso-butyrate and butyrate were 1.0, 0.4, 0.2 and 0.2 μmol l −1 s, respectively, for 600 ml samples. Rate constants for acetate and propionate were determined by anaerobically incubating samples at in-situ temperatures with tracer levels of 14C-labelled VFAs. Metabolized label was recovered as CO 2, CH 4, cellular material, water-soluble material, and VFA (ether-soluble) fractions. Apparent turnover rates measured during summer and winter in anoxic Cape Lookout Bight, North Carolina (U.S.A.) sediments were in the range of 19–330 μmol l −1 s h −1 for acetate and 0.7–7.0 μmol l −1 s h −1 for propionate.
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