Hydrocarbon and fatty acid distributions in Rostherne lake sediment (England)

Hydrocarbon and carboxylic acid distributions in the top 30-cm section of a contemporary lacustrine sediment (Rostherne Mere, Cheshire, England), of age 0–150 yr. present variations which can be correlated with changes in input of organic material as well as the effects of early diagenesis. Thus, the higher proportions of short-chain and branched lipids in the top (0–7 cm) sediment section are as expected on the basis of the relatively greater contribution of algal and other microbial matter to the surface sediment layer. Similarly, the increase in the ratio of saturated to unsaturated straight-chain acids with depth is in accord with the more facile diagenesis of the unsaturated components. Acid hydrolysis of solvent-extracted sediment afforded lipid fractions featuring a more significant microbial contribution than pre-hydrolysis extracts, as denoted by the greater abundance of C 15 and C 17 iso- and anteiso-branched acids. Also, no trend with depth in the ratio of saturated to unsaturated acids was observed for post-hydrolysis extracts indicating that bound compounds may be somewhat protected relative to soluble lipids. A contribution from petroleum-derived hydrocarbons to the sediment, apparent from the complex branched/cyclic (B/C) alkane distributions, decreases with depth and is virtually absent from the 18–30-cm sediment section.