ESTIMATE OF LONG-TERM VARIATION OF INFLOW LOADS, AND THE EFFECT OF INFLOW DISCHARGE ON RED TIDE IN THE ARIAKE SEA

It is necessary to grasp a long term inflow load for the study of enclosed bay. The Ariake Sea is one of such bay and there are some missing data of river discharge flowing into this bay. In this study, our developed method to estimate the missing discharge data is applied to all major rivers flowing into this bay. Amounts of inflow loads are calculated using L-Q curves and pollutant load factors. Long term changes of the river discharges and loads into the bay are estimated from 1981 to 2010. A characteristic of inflow discharge's change and a relationship between red tide occurrences and the inflow discharges are also discussed. The inflow discharge and loads of COD, T-N and T-P are found not to be changing in the Ariake Sea from 1981 to 2010. An increase of the inflow discharge is considered to be a trigger for a red tide occurrence not in winter but in the season between spring to autumn in the Ariake Sea.