Turnover of14C-labelled acetate in marine sediments

✍ Scribed by D. Christensen; T. H. Blackburn

• Publisher: Springer-Verlag
• Year: 1982
• Tongue: English
• Weight: 613 KB
• Volume: 71
• Category: Article
• ISSN: 0025-3162
• DOI: 10.1007/bf00394618

✦ Synopsis

A method for the determination of volatile fatty acids (VFA) in coastal marine sediments is presented. Acidified porewater was vacuum distilled to extract the VFA and the distillate was analysed by gas chromatography (Porapak QS column and flame ionization detection). The limit of detection was 2/zM in the samples, but was increased tenfold by lyophilization. In the upper 10 cm of the sediments 2-70 nmol acetate cm -3 sediment was found. Uniformly labelled ~4C-acetate (0.02 nmol, 10 -3/~ ci) was injected at 1-to 2-cm intervals through silicone-stoppered holes in the tubing of undisturbed sediment cores. Turnover rate constants were determined from semilogarithmic plots of the ~4C-acetate radioactivity versus the incubation time. The 14C-acetate was shown to be distributed in at least three sediment pools: a porewater pool, an adsorbed pool which was displaced by excess acetate, and an adsorbed pool which was not displaced by excess acetate. The rate constants ranged from 1.5-13 h -1 in the investigated sediments. The turnover rates of acetate were calculated from the turnover rate constants and the acetate concentrations in the porewater. The rate of acetate turnover calculated from the NH~-turnover and the N:C ratio of the sediment organic matter was only 16% of the measured rate of acetate turnover. The apparent overestimation of the acetate turnover was most likely due to an overestimation of the degradable acetate pool. A gel filtration of ~4C-acetatecontaining porewater showed that the fractions which contained the tracer had only 25% of the total acetate. This implied that a large fraction of the acetate in the porewater was unavailable to the microbes. This was also indicated by the fact that the measured acetate pool in porewater incubated with 14C-acetate did not decrease, when the added 14C-acetate was oxidized.