Determination of Volatile Fatty Acid Turnover Rates in Organic-rich Marine Sediments

Sansone, F.J. and Martens, C.S., 1981. Determination of volatile fatty acid turnover rates in organic-rich marine sediments. Mar. Chern., 10: 233-247. 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 ,umoll;l , respectively, for 600 ml samples. Rate con­ stants for acetate and propionate were determined by anaerobically incubating samples at in-situ temperatures with tracer levels of 14C-labelled VFAs. Metabolized label was re­ covered as CO 2 , CH4 , 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,umoll;1 h-1 for acetate and 0.7-7.0 ,umoll;l h-1 for propionate.