Abstract
Since September 1984 when a large amount of foam was first found in lake Chuzenji, we have measured the concentrations of carbohydrate and protein in lake waters. The foam was present from late summer to autumn. The carbohydrate concentration was relatively high, while the protein concentration was almost below 0.1 mg·l-1. Therefore, carbohydrate seemed to be one of the main causes of the foam while protein did not. We have thus investigated the origin of carbohydrate in the lake.
Because the primary production in the lake was much lower than the carbohydrate concentration during the foam was observed, carbohydrate from phytoplankton cannot be the main source for the foam. The concentration of carbohydrate having molecular weight above 100, 000, which seemed to be leached from fallen leaves and aquatic macrophytes, increased in autumn.
These results suggest that carbohydrate in the lake mainly originates from fallen leaves and aquatic macrophytes. The foam which was observed in autumn seems to be due to an increase in the concentration of high molecular weight carbohydrate.
