Volatile fatty acid cycling in organic-rich marine sediments |
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| Authors: | Francis J Sansone Christopher S Martens |
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| Institution: | 1. Marine Sciences Program, University of North Carolina at Chapel Hill, 12-5 Venable Hall 045A, Chapel Hill, NC 27514, U.S.A.;2. Institute of Marine Sciences, University of North Carolina at Chapel Hill, Morehead City, NC 28557, U.S.A. |
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| Abstract: | Volatile fatty acid (VFA) apparent turnover rates were determined by measuring whole sediment VFA concentrations and the corresponding reaction rate constants. The following ranges of VFA concentrations were measured in Cape Lookout Bight, N.C. sediments (μmole·ls?1): acetate 54–660, propionate 1–24, butyrate <0.5–22, iso-butyrate <0.5–6. Apparent turnover rates measured over a one-year period ranged from 18–600 μmole·ls?1·h?1 for acetate and 0.7–7 μmole·ls?1·h?1 for the carboxyl carbon of propionate. Methane production was observed only with acetate and only in sulfatedepleted sediments; total acetate turnover attained approximately the same maximum value in both sulfate-reducing and sulfate-depleted sediments.Apparent turnover rates for acetate and propionate appeared to be controlled by similar factors: in sulfate-reducing (surface) sediments the turnover rates were stimulated by autumn storm-mediated deposition/resuspension events; in deeper sulfate-depleted sediments the turnover rates followed changes in the ambient temperature. Changes in VFA poolsizes were proportionally much larger than changes in corresponding rate constants. The ratio of CO2 to CH4 produced from acetate vs. depth suggested that non-methanogenic bacteria accounted for 60% of the acetate turnover in sulfate-depleted sediments.VFA concentrations were much lower in N.C. continental slope mud than in Cape Lookout sediments; acetate was the only VFA detectable throughout the top 40 cm of the slope sediments. The estimated production rate of CO2 from acetate decreased rapidly with depth. The surface rate was approximately 20 times less than that measured at similar temperatures in sulfate-reducing Cape Lookout sediments. |
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