2008 Volume 45 Pages 103-112
Both of the field and the literature survey have been carried out to investigatethe mechanism of the water-bloom production in Urushizawa dam reservoir. From the literature examination, the average value of the tempreture of the surface water was 22.3°C in the year in which the water-bloom was generated, 17.4°C in the year in which that was not. The cyanobacteria occupied larger than the greenalgae and the diatom when the tempreture of the surface water, TN, TP and TN/TP ratio was relatively high. This tendency was same in both of the field and the literature survey. It was indicated that the production of the cyanobacteria was derived by the vanish of PO4-P in the surface water. It was suggested that the vanish of PO4-P in the surface water was derived by the production of diatoms in spring, the discharge of diatoms to the outside of resouvoir and sedimentation. The increase of inflow due to the flash of the river promoted the production of the green algae, because of the disturbance of the aquatic environments in the dam reservoir and the supply of the phosphrus.
