Behavior of low salinity water and its implication for the water quality after freshets at the head of the Ariake Sea

• Published in: Bulletin on coastal oceanography Vol. 46; no. 2; pp. 161 - 173
• Main Authors: Yamaguchi, Soichi, Hayami, Yuichi
• Format: Journal Article
• Language: Japanese
• Published: 01.01.2009
• Subjects: Marine; INW, Japan, Kyushu, Ariake Sea; Japan, Kyushu, Chikugo River; Japan, Kyushu, Chikugo R
• ISSN: 1342-2758

This study documents the behavior of low salinity water formed by the increase in fresh water discharge from the Chikugo River at the head of the Ariake Sea (Japan) based on monthly monitoring data obtained during spring tide by the Saga Prefectural Ariake Fisheries Research and Development Center, and Fukuoka Fisheries and Marine Technology Research Center, Ariake-kai Laboratory. The effects of the increase in fresh water discharge on stratification, concentrations of nutrients and the bottom DO were also documented. When the increase in fresh water discharge finished within a few days, the low salinity water mass propagated cyclonically looking at the coast to the north and passes away from the head of the Ariake Sea within one week. When the high discharge continued for more than a few days, the low salinity water spread widely so that density stratification was intensified. In such cases, the hypoxia was frequently formed in the western area of the head. As the freshets persisted longer, the concentration of DIN and DSi increased but there was a small change in the concentration of DIP in the surface layer. This would be due to the phosphate buffer mechanism caused by suspended sediments in the turbid water at the mouth of the Chikugo River. The DIP concentration in the bottom layer increased when the freshet was prolonged. This would be caused by the release of DIP from the sediments under hypoxic conditions.