Abstract
The formation of water blooms with blue-green algae Microcystis spp. has been observed in Lake Koyamaike (Tottori Prefecture) every year, and the changes of the water quality for the worse is of concern. An algal growth potential assay using Microcystis aeruginosa isolated from the lake and water quality examination of the lake and four inflowing rivers were carried out in order to determine the mechanism of the heavy algal growth. Both examinations were continued every month from April 1995 until August 1998.
The substance limiting the algal growth was estimated to be chelate compounds. This proved true throughout the year except during the summer. The chelate compounds were found not only in the lake water but also inflowing river water in June. This was attributed to be basal fertilizer which contains molasses used in paddy fields. The algal growth under the elimination of the effects of nitrogen and phosphorus showed good correlation with the copper complexing capacity.
