[A-OS22] 沿岸域の海洋循環と物質循環

[AOS22-04] 西部瀬戸内海における栄養塩の時空間変動と供給機構に関する研究

*吉江 直樹¹、小川 颯兵¹、大西 秀次郎¹ (1.愛媛大学沿岸環境科学研究センター)

キーワード：栄養塩、貧栄養化、瀬戸内海

In recent years, the decrease of nutrient concentration with strong and long-term regulation of nutrient discharge by act on special measures concerning the conservation of the environmental of the Seto Inland Sea (SIS) is significant and may affect marine ecosystem and fish resources in the eastern SIS. The special measure law was just revised for the bountiful SIS from the poor SIS due to the oligotrophication on June 3^rd in 2021, and individual administrations for each region were needed on the basis of scientific knowledge. In the western SIS, the spatio-temporal variations and supply mechanisms of nutrient were not still clear. To clarify them, we investigated the relationship time variations of nutrient concentration from 2004 to 2021 at the Cape Sada-misaki, where is representative monitoring station in the western SIS including the Iyo-Nada and Bungo Channel, and the nutrient supplies from terrestrial and offshore regions. As a result, there is no significant decreasing trend of nutrient concentrations from 2004 to 2021. The seasonal variations of nutrient had the minimum values in April, which were different form typical variations in the mid-latitude offshore regions with the minimum values in the summer. This is because the nutrient supplies mainly from the terrestrial region from May to September associated with the rainy and typhoon seasons in Japan. In the autumn, the interannual variations of nutrient were significantly controlled by the bottom intrusion of the Kuroshio subsurface water from the offshore region. These results suggest that special administration such as the artificial increase of nutrient discharge from sewage treatment plant does not need in the western SIS.