抄録
Time series survey of water column and sediments was conducted to clarify the cause of hypoxia at the northwestern part of Ariake Bay in summer. A freshet of the Chikugo River facilitated the stratification in water and phytoplankton bloom, and the phytoplankton was buried deep in the sediment down to ca. 20 cm at the neap tide after a strong mixing by the spring tide and the freshet. The large amount of buried phytoplankton cells rapidly consumed oxygen through the decomposition under the strong stratification which inhibits oxygen supply in water, resulted in the thick reducing condition of the sediment and the hypoxia in bottom water. Strong wind by the typhoon eliminated a hypoxia rapidly. On the other hand, a recovery from the reducing condition of the sediment occurred gradually by the usual tidal mixing.
