Prediction of the Occurrence of an Oxygen-deficient Water Body in the Closed Sectin of Hakata Bay

• Published in: ENVIRONMENTAL ENGINEERING RESEARCH Vol. 42; pp. 277 - 285
• Main Authors: KUMGAI Hiroshi, SUSHIMOTO Kenji
• Format: Journal Article
• Language: Japanese
• Published: Japan Society of Civil Engineers 2005; 公益社団法人 土木学会
• Subjects: density stratification; oxygen consumption rate; Oxygen-deficient water body
• ISSN: 1341-5115; 1884-829X
• DOI: 10.11532/proes1992.42.277

In this study, on the basis of survey data, we present the major incidents responsible for the formation of an oxygen-deficient water body in the closed section of Hakata bay. Further, we propose a method to predict the occurrence of the oxygen-deficient water body. Observations with regard to the oxygen-deficient water body in the closed section of Hakata Bay were noted in the summer seasons of both 2001 and 2002. In that area, oxygen deficiency occurred in 2001; moreover, it was not identified in 2002. By comparing these observed data, it was found that the major contributing factors for generating oxygendeficient water in the summer season are (a) salinity stratification caused by the input of freshwater after rainfall and (b) an increased consumption rate of oxygen due to the degradation of sedimented organic matter of terrestrial and primary production origins. On the basis of these findings, we formulated a prediction relation expressed as a function of the effective accumulated precipitation. Furthermore, the following results were obtained.(1) The concentration of dissolved oxygen in the bottom layer of that area decreased with the effective accumulated precipitation.(2) An oxygen-deficient water body is generated when the effective accumulated precipitation exceeds 150 mm.