Relationship between Multiplication of Phytoplankton and Water Quality in the Agricultural Region on the Coast of Ariake Bay

Abstract

Some relationships between the multiplication of phytoplankton and water environment were investigated from the observation in the eutrophicated agricultural water region on the coast of Ariake bay. Similarity of phytoplankton flora estimated by Kimoto's similarity index can be roughly explained by the water use conditions. The similarity index appears high in the case when the first dominant species of both stations are the same, so the first dominant species is important. The diversity index (DI) of phytoplankton decreases as water pollution progresses, and then Chlamydomonas globosa mainly dominates. It is assumed that Chl. globosa is one of the species that can grow easily and dominantly in a eutrophicated condition. To estimate the proportion of individual phytoplankton from the water quality of primarily grown species, regression analysis was applied. Both the proportion of Trachelomonas scabra and Tribonema sp. are in direct proportion to the Cl_- concentration, and Dictyoashaerium pulchellum is to the TN: TP ratio. From the relation between the proportion and water quality of eutrophication, the species could be grouped into two categories, one composed of Chlamydomonas and Trachelomonas and the other composed of Melosira and Dictyoashaerium. Significant regression equations with the proportion of phytoplankton as a target variable, and water quality as explanation variables were carried out for six species.