Vertical profile of microbiological decomposition rate for organic matter in lake sediments from the viewpoint of methane fermentation

Abstract

Core samples were collected from Lake Suwa and Lake Kizaki in Nagano Prefecture, Japan. They were divided into several pieces at 2 or 15 cm intervals. Each of them was taken in a soil injector and incubated at 26-27°0 for about 40 days. The production of CH4 in the surface sediments amounts to about 200 ml/100 g of dry sediment and markedly decreases toward 20 cm core depth to about 20 ml/100g. In sediments deeper than 20 cm, 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 100 cm, 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. © 1976, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.