Abstract
There are many inorganically acidic freshwater lakes in Japan. In some of those moderately acidic (pH=3-5) lake sediments (e.g., Lakes Kussharo, Tazawa, Usori and Inawashiro), significant amounts of long-chain anteiso-compound series (3-methylalkanes, (ω-2)-methylalcan-1-ol and (ω-2)-methyl-alkanoic acids) have been identified. Based on the analysis of the particulate matter collected both from the river water which makes the lake water acidic, and from the lake water, it was concluded that the source organism(s) of theanteiso-compounds is aquatic biota inhabiting the moderately acidic lake water (Miki and Fukushima, 1996). But the source organisms were not specified. The purpose of this study is to provide further evidences on the origin of the anteiso-compounds. The particulate matter (0.6-40μm) and planktons (>40μm and >100μm) were separately collected by using plankton nets and a glass fiber filter from L. Tazawa (pH=4.8-5.2) and L. Inawashiro (pH=4.4-5.0) water and analyzed for lipid compounds. In both lakes, the quantity of theanteiso-compounds in the fine particulate matter (0.6-40μm) was obviously larger than those in the planktons (>40μm), indicating that the true source may be finer bacteria dispersed in the lake water.
