Implications of long-chain anteiso compounds in acidic freshwater lake environments: Inawashiro-ko in Fukushima Prefecture, Japan

A series of long-chain (⩾C23) monomethyl-branched alkanes, alk-1-enes, alkanoic acids and alkanols were identified in settling particles and surface sediments from some acidic freshwater lakes in Japan by Fukushima et al. [Verh. Int. Verein. Limnol. 25 (1993) 835; Geochem. J. 30 (1996) 111]. Mass spectra of those branched compounds showed that the methyl side-chain is present at the C-3 position of alkanes, and at the ω-2 position in the functionalized compounds, i.e., the anteiso position. The present work was undertaken to evaluate the source of the anteiso compounds and to assess their utility as molecular markers of lake water acidity. The lake system examined is Inawashiro-ko, the third largest freshwater lake in Japan, where the pH is 5.0-5.5. The anteiso compounds are present in the sediments, as well as in suspended material in the lake water. In the water column, the majority of the anteiso compounds occur in the fine particulate matter (0.6 ≪ 40 μm). Analysis of the suspended materials in the inflowing river waters proves that the anteiso compounds are not transported from outside of the lake via any rivers, including the Nagase-gawa that acidifies the lake water. The results indicate that the anteiso compounds are produced within the lake by planktonic microbes and might be useful molecular markers for lake acidity.