ABSTRACT

Core samples were collected from Lake Suwa and Lake Kizaki in Nagano Prefecture, Japan. They were divided into several pieces at 2 or 15cm intervals. Each of them was taken in a soil injector and incubated at 26-27°C for about 40 days. The production of CH₄ in the surface sediments amounts to about 200ml/100g of dry sediment and markedly decreases toward 20cm core depth to about 20ml/100g. In sediments deeper than 20cm, the production of CH₄ gradually decreases to nearly zero at a depth of about 60cm. The vertical profile of the CH₄ production is similar to those of various organic components. The methane production in the core samples from 50 to 100cm, mixed with sodium acetate corresponds to about 70% of what is theoretically expected from the amount of sodium acetate added. For samples from 100 to 140cm, however, it decreases on a straight line to zero. This seems to reveal that the decrease in CH₄ production for deeper parts of the core samples is not only caused by the decrease in the substrates for methane fermentation but also by the decrease in microbiological activities for methane fermentation resulting in gradual disappearance from 100cm toward 140cm core depth.