2004–2018 年の夏季における大阪湾の水質特性の変遷 : 河川負荷と COD 濃度に焦点を当てて

抄録

Using data collected from 2004 to 2018, the relationships between fluctuation in water quality and river loads were analyzed in eight areas within Osaka Bay, comprising the A-, B-, and C-type areas as designated by the chemical oxygen demand（COD）environmental quality standards. Different trends were confirmed in each area, related to their location in the bay. Decreasing COD concentrations were observed around the Muko River mouth, while concentrations near the Yodo River mouth, near the Yamato River mouth, and in areas at the center of the bay remained unchanged. These stable trends might be attributable to the high COD concentrations in the inflow water at the inner part of the bay, as well as the in situ COD production in the center of the bay. In summary, changes in water quality reflecting river loads were observed in the inner part of the bay, but the effect decreased toward the center of the bay where in situ production might be greater. Therefore, for the future restoration plan in Osaka Bay, different approaches will be required, depending on the characteristics of the individual sea areas.