EVALUATION OF MEASURES TO OLIGOTOROPHICATION IN HARIMA-NADA SEA BY AN ECOSYSTEM MODEL: EFFECT AND MECHANISMS OF MEASURES OF RIVER, OSAKA BAY, AND BIVALES

Abstract

 The effects of dissolved inorganic nitrogen (DIN) inflow from rivers, DIN concentrations in Osaka Bay, and bivalves on oligotrophication in Harima-nada Sea were analyzed over one year by using a benthic-pelagic coupled ecosystem model. The analysis showed that an increase in DIN inflow from rivers and an increase in DIN concentration in Osaka Bay increase the amount of DIN discharged out of Harima-nada Sea and the amount of DIN consumed in Harima-nada Sea in terms of the annual nitrogen budget. However, an increase in bivalves increase the amount of DIN discharged in Harima-nada Sea, and increased the amount of DIN produced within Harima-nada Sea. All three measures increased DIN throughout the four seasons, and an increase in DIN inflow from rivers increased DIN in the surface layer of the Hyogo Prefecture coast, especially in summer, while an increase in bivalves reduced red tide especially in summer and autumn.