WATER QUALITY RESTORATION BY CONTINUOUS INJECTION OF SURFACE WATER TO BOTTOM LAYER IN A RESERVIOR

The problem that oxygen depletion observed in eutrophic natural lakes and reservoirs damages natural benthonic organisms and induces nutrient release from sediment is becoming serious. For this problem, we proposed a method which transports surface water including a large amount of dissolved oxygen (DO) to a bottom layer in which DO is not usually enough in mesocosm. The effect of injection of surface water into hypolimnion on water quality restoration by this system has already been proved. In this study, we investigate the degree of water quality restoration in case of continuous injection of surface water into hypolimnion by field experiments in a reservoir having an area of 15, 000m2.From this field experiment, we find that our system reduces nutrient release from the sediment even when oxygen supplied by our system is depleted by sediment oxygen demand.