ZOOPLANKTON COMMUNITY BEFORE AND AFTER NUTRIENT DIVERSION AND REVETMENT CONSTRUCTION IN LAKE FUKAMI-IKE, JAPAN

Abstract

Lake Fukami-ike is a small eutrophic lake, to improve the water quality of the lake, a lake
management project was carried out in 1992. This project involved nutrient diversion and revetment
construction along the lake shore. A biotope was built near the lake in 2000. As a result, although the inorganic
nitrogen in the lake decreased considerably, chlorophyll-a (phytoplankton) increased slightly. The zooplankton
community in the lake before the project in 1978-1979 predominantly comprised large-sized species (about 1.8
mm), however, small-sized species (about 0.1-0.2 mm) were dominant after in 2013-2015. The reason for the
decrease of the large-sized zooplankton was thought to be the possibility of losing habitat space because aquatic
macrophytes of the littoral zone were filled up when revetment construction built in 1992. We compared the
body length and composition of zooplankton community between the lake (nearly emergent plants on the lake
shore) and the biotope (emergent and floating-leaved plant cover). Large-sized zooplankton (about 0.9-1.2
mm) were dominant in the biotope, and size distribution did not differ in 1978-1979. The presence of developed
aquatic macrophytes was suggested to promote the survival of large zooplankton.