抄録
Recently, it has been shown that the sediments of some acid lakes in Japan (pH=3-5), for example, sediments from Lakes Tazawa-ko and Kussharo-ko, are containing characteristic lipids which include series of long-chain anteiso compounds. This study was undertaken to extend the organic geochemical research to a similar inorganically acid (pH=5) Lake Inawashiro-ko in Fukushima Prefecture, Japan. Analytical results revealed that the anteiso hydrocarbons were certainly detected in the upper layers above 10-12cm section of the sediment core taken from near the northwest coast (Core 3; length: 24cm; water depth 5m). However they were absent below the 14-16cm section. In the sediment core, relative proportion of diatom verbs of Cyclotella genis which favor neutral or alkaline water condition increased as the core depth increased. Hence the results were interpreted to indicate a pH decrease in the past to the present state of lake water.
