東部瀬戸内海における栄養塩の動態とノリ養殖などのための栄養塩管理

摘要

In recent years, production of Nori (Pyropia) in the Seto Inland Sea is getting lower because of discoloration of Nori which is caused by nutrient (dissolved inorganic nitrogen; DIN) deficiency in the sea water. For contributing to promote nutrient level management, we examined nutrient dynamics and elucidated nutrient budget by using a lower trophic level ecosystem model. The nutrient budget indicated that DIN consumption by phytoplankton was large and caused nutrient deficiency in the Nori cultivating season. The proportion of DIN discharge from land was very high in Osaka Bay. In southern Harima-Nada, on the contrast, the land discharge was very low and benthic flux of DIN from the sediment was much important. The model simulation also indicated that increase of the land discharge resulted in increase of DIN in the sea water and reduction of damage from discoloring of Nori. It is suggested that nutrient level management is necessary for the sustainable production of Nori.