WATER QUALITY AND COMPOSITIONS OF THE PHYTOPLANKTON AND ZOOPLANKTON BEFORE AND AFTER BUILDING CONSTRUCTION IN LAKE FUKAMI-IKE, JAPAN

Abstract

Lake Fukami-ike is a small monomictic and eutrophic lake, located in southern Nagano
Prefecture in central Japan. Water quality improvement was expected from maintenance of farm village
drainage and waterfront function was carried out for town activation in 1992. However, no blue-green algal
bloom outbreak had occurred before. We studied the water quality and compositions of the zooplankton and
phytoplankton before and after building a bulkhead maintenance construction. Large decreased values for
NO3-N, NH4-N and NO2-N were 1.87→0.50 gNm-2
(26.7%), 1.49→0.78 gNm-2
(52.3%) and 0.085→0.030
gNm-2
(35.3%), respectively. Aphanizomenon flos-aquae (Cyanophyceae) were dominant in the summer;
some species of the genus Fragilaria were dominant among phytoplankton during study periods. The
dominant species of zooplankton during study periods were Keratella cochlearis (Rotatoria); smaller than
Cyclops vicinus (Crustaceae) were dominant species of zooplankton before the construction.