Abstract
An oxygen-deficient water mass is formed every summer in the northern part of Hiroshima Bay, giving a serious damage to benthic organisms. Primary data analysis showed no relationships between land load and the intensity of the oxygen-deficient water mass, despite the intensive measures for the reduction in land load. Thus, the purpose of this study is to elucidate the mechanisms determining the intensity of the oxygen-deficient water mass using a pelagic-benthic coupled ecosystem model. It was clarified that not only the biological oxygen consumption by the decomposition of organic matter but also the chemical oxygen consumption by reduced compounds formed in the anoxic layer of the sediment is important. However, the former process is more important than the latter process in terms of the yearly variation in the intensity of oxygen-deficient water mass formation. In addition, estuarine circulation prevents the expansion of the oxygen-deficient water mass by supplying dissolved oxygen from outside the bay. Therefore, it is concluded that the yearly variation in the intensity of oxygen-deficient water mass formation is governed by the balance between oxygen consumption by the decomposition of organic matter and oxygen supply by estuarine circulation.
