Evaluation of Water Purification System of an Urban Park Pond with Cyanobacterial Blooms by Using the Enclosure Method

The purpose of this study was to evaluate the effect of inhibiting the growth of Microcystis spp. by water purification system （coagulating sedimentation and air flotation） applied to an urban park pond where cyanobacterial blooms occurs. By using enclosures installed in an urban park pond, the water quality of test area to which the purification system applied and that of control area were compared for 2.5 years. We removed suspended solid and improved to full transparency （1 m） by operating the water treatment system for three and a half days before Microcystis blooms occurred. The following results were obtained: in control area, Microcystis blooms were occurred in the summer for three years. On the other hand, in test area, the total density of Microcystis spp. in the first summer （2 colonies/mL） was significantly low compared to that in control area （13,700 colonies/mL）. Furthermore, in test area, the total density of Microcystis spp. in the second summer （2,890 colonies/mL） was relatively low compared to that in control area （6,170 colonies/mL）. However, in test area, the total density of Microcystis spp. in the third summer （4,800 colonies/mL） was higher than that in control area （3,120 colonies/mL）.