AN ANALYSIS OF EFFECTS OF AQUATIC MACROPHYTES ON WATER QUALITY IN A SHALLOW MARSH

Aquatic macrophytes function in several ways in aquatic environment. We have analyzed the effects of aquatic macrophytes focusing on the reduction of resuspension of bottom sediments. Aquatic macrophytes are known to suppress the development of wind wave in shallow waters. Reduced wave height leads to the reduction of the resuspension of bottom sediments. This function that aquatic macrophytes may have seem important in deciding the water quality of shallow water bodies. A numerical simulation model was developed to estimate the quantitative effects of aquatic macrophytes on the water quality of a shallow marsh. Simulation results showed good agreement with observed water quality data. A simulation case that assumed dense vegetation of which area was maximum in recent years resulted in less turbid and lower organic matter concentration. The degree of reduction in suspended solids presumed by the simulation agreed well with the previous records in Inba marsh, Chiba prefecture that experienced the decay of aquatic macrophytes. Restoration of native aquatic macrophytes is important to restore the marsh to a previous clear state.