琵琶湖における優占植物プランクトンとＤＩＮ：ＤＩＰ比等との相互関係

Abstract

The relationships between the dominant phytoplankton and the factors of water quality were examined in Lake Biwa, referring to the Shiga Prefecture's data. In the lake, TN (total nitrogen): TP (total phosphorus) and DIN (dissolved inorganic nitrogen): DIP (dissolved inorganic phosphorus) ratios tended to be lower with increased WT (water temperature), and this was more remarkable for DIN: DIP ratios than TN: TP ratios. As one of the causes, it was suggested that TN: DIN ratios increased and DIN decreased with increased WT. The relationships between the dominant phytoplankton and the factors of water quality were considerably variable and complex. Uroglena americana and Asterionella formosa occurred in waters with low WT and TN: DIN ratios and with high DIN, TN: TP and DIN: DIP ratios. On the other hand, Microcystis aeruginosa and Anabaena affinis occurred in waters with high WT, TN: DIN, TP: DIP ratios and with low DIN, TN: TP and DIN: DIP ratios. These results suggest that the examination on the relationships between the dominant phytoplankton and the factors of water quality was one of the useful methods to clarify the distinctive features of phytoplankton and to forecast the occurrence of algal blooms.