SOLUTE RUNOFF SYSTEM AND RUNOFF LOAD FROM THE FORESTED BASIN ADJACENT TO HIKETA BAY

Hiketa bay is located in southwest of Harima-Nada where the red tide happens frequently. For estimating the solute runoff system to Hiketa bay from a surrounding forested basin, water quality observation was executed in Umayado river basin adjacent to the bay. The following findings were obtained. (1) The seasonal change of the stream water quality was not seen, as for the solute like NO3-. It is thought that the paucity of precipitation caused it. (2) Rain that exceeds 100mm influences the stream water quality system of about one month after the rainfall event. (3) The dam in the upstream decreases the concentration of NO3- and SO42-. However the concentration of SiO2 and T-Fe were not influenced. (4) The amount of SiO2 supplied from the forested basin in a year equals the amount of SiO2 that always exits in Hiketa Bay. (5) The heavy rain caused by the seasonal rain front and the typhoon is the key role of SiO2 and T-Fe runoff system in the basin.