Summary: A gas chromatograph–gas proportional counting procedure has been developed to measure the rates of metabolism of short-chain fatty acids in anaerobic saltmarsh sediment. The technique was used to determine the turnover rates of acetate, propionate and butyrate in sediment cores injected with C-labelled tracers and incubated at field temperature. Experiments showed that all three fatty acids were metabolized by micro-organisms present in the sediment, although an initial fast rate of disappearance of C from the injected [C]propionate and [C]butyrate was partly due to exchange of the tracer between an extractable pool of fatty acids and a tightly bound fatty acid pool which was not extracted. Measurement of the rates of metabolism of acetate, propionate and butyrate in intact cores of sediment from the surface layer (0–4 cm) of a saltmarsh pan showed that carbon flow through the acetate pool was far greater than that through either propionate or butyrate. Only about 14% of the acetate could have been derived from propionate and butyrate, 86% being from other precursors. The rate of acetate turnover decreased markedly with increased depth, and at 20 cm was negligible. The turnover of propionate and butyrate was totally inhibited by the presence of 20 mM-sodium molybdate, and their metabolism was attributed to the activity of sulphate-reducing bacteria.


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