A FIELD OBSERVATION ON THE ECOSYSTEM AND WATER QUALITY AND THEIR SEASONAL VARIATIONS IN AN IRRIGATION POND WITH A FLOATING-LEAVED PLANT (NYMPHOIDES INDICA) COMMUNITY

MARUYAMA JIRO (Graduate school of Civil Engineering, Tokyo Denki University) ;
NAKAI MASANORI (Department of Civil and Environmental Engineering, Tokyo Denki University) ;
MURATA TOMOYA (Grauate school of Civil Engineering, Tokyo Denki University) ;
ARITA MASAMITSU (Department of Civil and Environmental Engineering, Tokyo Denki University)