津軽十二湖湖沼群の陸水生物学的研究(III) : 日暮の池における湖沼環境とアナベナを中心とした植物プランクトンの季節変化について

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Seasonal changes of phytoplankton and water environments were studied in LakeHigurashinoike in the Tsugaru-Jo.niko lake group from 1990 to 1992. The Tsugaru-Jo.nikolake group is situated in the beech forest at the western foot of the Shirakami mountainsin Aomori prefecture, northern Japan, and the Lake Higurashinoike is a small (11,500 m2)and eutrophic lake having a maximum depth of about 15m. In every year, Anabaenaincreased in summer to autumn. On the other hand, diatoms (Asterionella formosa andSynedra spp. dominated), green and golden algae occurred in other seasons. The Anabaenawas composed of three species in this lake, and the species composition and densities weredifferent by year. The most prevalent bloom was found in October 1990 by Anabaenasmithii, then the water surface was covered with Anabaena mat and Secchi disk transparencydecreased to O. Sm. The morphology of three Anabaena species were described andfigured, and some factors bringing Anabaena bloom were discussed.