Japan Geoscience Union Meeting 2022

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[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-OS Ocean Sciences & Ocean Environment

[A-OS22] Ocean circulation and material cycle in coastal seas

Wed. May 25, 2022 1:45 PM - 3:15 PM Exhibition Hall Special Setting (2) (Exhibition Hall 8, Makuhari Messe)

convener:Daisuke Takahashi(Tokai University), convener:Naoki Furuichi(Fisheries Technology Institute, Japan Fisheries Research and Education Agency ), Hitomi Yamaguchi(Kagawa University), convener:Akihiko Morimoto(Ehime University), Chairperson:Daisuke Takahashi(Tokai University), Naoki Furuichi(Fisheries Technology Institute, Japan Fisheries Research and Education Agency), Hitomi Yamaguchi(Kagawa University), Akihiko Morimoto(Ehime University)

2:30 PM - 2:45 PM

[AOS22-04] Spatio-temporal variations and supply mechanisms of nutrient in the western Seto Inland Sea, Japan

*Naoki Yoshie1, Sohei Ogawa1, Hidejiro Onishi1 (1.Center for Marine Environmental Studies, Ehime University)

Keywords:nutrient, oligotrophication, Seto Inland Sea

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 3rd 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.