A Possibility of Control and Prevenhon of Excessive Phytoplankton Growth by Photochromism

摘要

In the past few decades, eutrophication in closed water areas has been becoming a serious problem on the use of water for drinking, agriculture, recreation, and other purposes. Especially, excessive phytoplankton growth seriously degrades the environment and aquatic ecosystems; algal blooms, lose of oxygen, fish kills, loss of biodiversity, and other problems. This paper intends to investigate control and prevention of the excessive phytoplankton growth by reducing light levels below those necessary for photosynthesis. To shield sunlight, photochromic (PC) films, which show photo- chromism such as colorless forms turn to colored forms by ultraviolet irradiation, were prepared. The PC films containing Spironaphthoxazine as a photochromi c compound showed excellent photocoloration (75 to 80 absorbance at 600nm) under sunlight irradiation, and they maintained the photocoloration ability, at least longer than a month. However the results of algal growth potential tests with the PC films were the oppsite to what we had expected. While the growth of mixed algal cultures was controlled with the PC films under sunlight irradiation, the application of the PC films was not successful for the prevention of pure cultures M. aeruginosa growth. It was probably attributable to the difference between the wavelength for the PC films' maximum absorbance (approximately 600nm) and the available wavelength for photosynthesis (approximately 680nm). The absorbance at 680nm by PC films was approximately 20.