Institute of Agricultural and Forest Engineering, University of Tsukuba, Tsukuba, 305 - 8572, Japan

^*Corresponding author: Tel: 81-298-534715; fax: 81-298-534715. Email address: cyasugi@sakura.cc.tsukuba.ac.jp

Abstract

  To study the response pattern of phytoplankton to eutrophication, the long-term water chemistry and biological data spanning three phytoplankton phyla and 19 genera were investigated in Lake Kasumigaura, a eutrophic lake in Japan. Fisher's linear discrimination functions in combination with ecological indexes and a similarity index were used to analyze the relationship between the eutrophic levels (representing with dissolved inorganic nitrogen and total dissolved phosphorus) and the response of the inter-phylum phytoplankton diversity. The algal similarity index was found to characterize the change of eutrophication levels well. Almost 80 percent of eutrophic lake water samples can be correctly discriminated based on the logarithmic cells of phytoplankton genera. However, the ecological indices (number of genera, Margalef's index, Menhinick's index, McNaughton's index, as well as the Shannon's index and evenness index) failed to predict the change of eutrophic state.