Changes and Current State of Nutrient loads in the Osaka Bay Basin

Abstract

 Although Osaka Bay was heavily eutrophicated during the period of high economic growth, water qualities in Osaka Bay has been improved by measures for conservation of water environment, such as an introduction of total load control and development of sewerage systems. In the bay head, however red tide and blue tide has occurred frequently to the present day. To obtain a closer estimate of a amount of inflow loads, field surveys including rainy day surveys were carried out in rivers and sewerage treatment plants, and the impacts of flood and the combined sewer overflow (CSO) on the inflow of nutrient loads were clarified. The inflow load from the Neya River sub-basin showed largest amount, about 40 % of total inflow load for nutrients. Inflow load due to floods and CSOs, especially NH₄-N load, has a significant impact on nutrient cycle in Osaka Bay.