諏訪湖におけるアオコの発生とＤＯＮ：ＤＩＮ比等との関係

Abstract

In 1992, Microcystis and Anabaena blooms occurred in Lake Suwa from 10 June to 10 October, and the first and second peaks of TN (total nitrogen): DIN (dissolved inorganic nitrogen) and DON (dissolved organic nitrogen): DIN ratios in the water were found at near 10 July and 10 September. Microcystis viridis and Microcystis aeruginosa occurred with high cell densities near the first peak, and M. viridis and Anabaena flos-aquae occurred with high cell densities near the second peak. With regard to TP (total phosphorus): DIP (dissolved inorganic phosphorus) and DOP (dissolved organic phosphorus): DIP ratios, the positive peaks of these ratios were found near 10 July and the negative peaks near 10 September. These results suggest that TN:DIN and DON:DIN ratios are important factors which control the occurrence of Microcystis and Anabaena blooms, and TP:DIP and DOP:DIP ratios affect the constituent species of these blooms. From these results, the relative increase of DON in water and inorganization of DON due to the symbiotic bacteria might have supplied DIN to Microcystis, as many bacteria with the same form were similarly found at the middle layer of mucilage slime of colonies of 3 species of genus Microcystis.