Characteristics of hypoxia in the inner western area of Ariake Bay

Abstract

To investigate and verify the mechanism of occurrence of hypoxia in the waters of the inner western part of Ariake Bay, field observations were performed in summer (July to September) 2008. During the observation period, bottom DO decreased at neap tides, especially at the shallow station, and recovered to higher levels during spring tides. The hypoxic waters in the inner western part of Ariake Bay were essentially generated at two points: around the subtidal (between stations T1 and T14) and in the deeper offshore zone (around station P6). In some cases, hypoxic waters were found from stations T1 to P6 along the submarine valley of the Shiota River, suggesting that that the two masses of hypoxia generated individually were unified because of long-term stratification and massive oxygen consumption by SPM and sediments.