CHANGES OF CHLOROPHYLL-A, BACTERIOCHLOROPHYLL-C AND DOC BEFORE AND AFTER REVETMENT WORK IN LAKE FUKAMI-IKE, JAPAN

Abstract

Lake Fukami-ike is a small eutrophic lake of 2.1 ha with a maximum depth of 7.70 m in central
Japan and water stratified from March to October. Anoxic conditions prevailed below 4-5 m depth from April
to October and a photosynthetic green sulfur bacteria (BChl.c) accumulated in the hypolimnion. In Lake
Fukami-ike, the revetment work was environment maintenance for activation of the town in 1992, and the
water quality of this lake was considered to be clean. However, fluctuation in the transparency became larger
than before. Data before and after revetment work (1992) was studied. The DOC amount of stagnation period
was increased after revetment work more than before it, and the difference between maximum and minimum
values also increased. Chl.a was increased in both water concentration and the water column. BChl.c had been
confirmed to increase concentration and biomass. The inflow of domestic wastewater did not stop; nutrients
increased and Chl.a, BChl.c and the DOC also increased. Such a phenomenon is considered to be one of the
factors in the variation in the transparency increase.