Study on control of phytoplankton growth by flow condition.

Research Project

Project/Area Number	11650561
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Single-year Grants
Section	一般
Research Field	Civil and environmental engineering
Research Institution	OKAYAMA UNIVERSITY
Principal Investigator	KAWARA Osami Okayama Univ, Faculty of Environmental Science & Technology, Professor, 環境理工学部, 教授 (90093228)
Co-Investigator(Kenkyū-buntansha)	ONO Yoshiro Okayama Univ, Faculty of Environmental Science & Technology, Accoc. Professor, 環境理工学部, 助教授 (50152541)
Project Period (FY)	1999 – 2001
Project Status	Completed (Fiscal Year 2001)
Budget Amount *help	¥3,600,000 (Direct Cost: ¥3,600,000) Fiscal Year 2001: ¥600,000 (Direct Cost: ¥600,000) Fiscal Year 2000: ¥1,200,000 (Direct Cost: ¥1,200,000) Fiscal Year 1999: ¥1,800,000 (Direct Cost: ¥1,800,000)
Keywords	phytoplankton / current velocity / growth rate / field observation / laboratory experiment / eutrophication / 流速 / 増殖抑制効果 / 増殖抑制 / 水質浄化
Research Abstract	The research purpose: In the eutrophication, influence of phytoplankton increase on water use is the most severe. Therefore, it is the most important to control the increase of phytoplankton in order to improve the water quality in eutrophic waters. The purpose of this study is to clarify the inhibition effect of current velocity on increase of phytoplankton, and to obtain the guideline for the water purification using this effect. Laboratory experiments using circular channels and field observations in the Asahi River were carried out. In addition, the former experimental results for the eutrophic pond were investigated. Main results: (1) The laboratory experiments of mixed culture using phytoplankton in the pond and pure culture for chlorella were carried out. It was confirmed by these experiments that current velocity suppresses the growth of the phytoplankton. The degree of inhibition effect of phytoplankton growth by current velocity is different in both cases. (2) On the basis of the result of the experiment, the growth rate equations were formulated, and the constants in the equation were estimated. Cyanobacteria became dominant species in case of the mixed culture experiments. Cyanobacteria tend to decay at night. In chlorella, such tendency was not found. Therefore, the kinetic equations for both species are different a little. (3) Based on the observations in the Asahi River, the concentrations of phytoplankton increase only in the reaches with current velocities less than 10 cm/s and decrease in the reaches with current velocities more than 25 cm/s. (4) The field experiments for the pond showed that the species of the phytoplankton changed by the current condition.