Blooming of blue-green algae (Microcystis sp.) that produce toxic substances,microcystins, in the reservoir of the reclaimed land in Isahaya Bay (Kyushu Japan) and accumulation of the toxic substance in the sediment and aquatic animals I. Blooming of blue

摘要

Isahaya Bay is located in the western coast of Ariake Bay in Kyushu, Japan. A dike was constructed across the bay to develop farmlands (about 1,000 ha), and created a reservoir (about 2,600 ha) in the reclamation project of Isahaya Bay, and the drainage gates of the dike were closed in April 1997. Recently, blue-green algae including Microcystis sp. that produces a highly toxic substance (microcystins, MCs) have bloomed in the reservoir, and the water containing high concentrations of MCs has been discharged outside the reservoir. It is likely that a large amount of MCs is dispersing outside the reservoir. The purposes of this study are to examine the seasonal fluctuations of the quality of water and sediment and abundance of the microalgae in the reservoir to clarify the water conditions suitable for blooming of Microcystis, and to follow the dispersion of MCs outside the reservoir. In this symposium, we report that the toxic blue-green algae bloomed in the reservoir twice in a year (April to May, and August to September), producing large amounts of MCs, when the water was in high temperature (17.5 to 33.0℃) and low DIN/DIP ratio (< 4). The water contained 34.5 kg of MCs in the reservoir in mean of 2009, and 64.5 kg of MCs was discharged to the bay in the year. These results predict the possibility of bioaccumulation of MCs by the suspension-feeding animals in the reservoir and the bay since most of it is suspended in the water.