Importance of chemical oxygen consumption to the formation of hypoxia was cleared by measuring the DO concentration at the 0.2 m above the bottom, analyzing the hydrogen sulfide profiles in the sediment and some field experiments of the fraction of oxygen consumption (biochemical and chemical oxygen consumption) in the inner western area of Ariake Bay. Contribution rate of the chemical oxygen consumption to the total oxygen consumption at the 0.2 m above the sediment were 99.6% on 1 August, others were low (18 and 31 August). High chemical oxygen consumption before the hypoxic condition implicated that the chemical oxygen consumption has an important role to the generation of hypoxia in the inner western area of Ariake Bay.
