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

A field observation was carried out to examine the effects of a floating-leaved plant (Nymphoides indica) community on the ecosystem and water quality in an irrigation pond. The appearance of the plant community and the values of various water quality items were monitored through a year (2003). The plant community suppressed multiplication of phytoplankton in the upper layer and generation of oxygen-deficient water masses in the lower layer and absorb a lot of nutrients from the water body and bottom mud in summer. In contrast, withering of the plant community leads temporary multiplication of phytoplankton and slightly gives negative influence on the ecosystem and water quality in fall and winter.