[A-CG31] Nutrient footprint of primary production in the coastal and marginal seas of East and Southeast Asia

[ACG31-09] Roles of riverine nutrients from different sources in the Harima-Nada and their contributions to primary production

*Siraporn Tong-u-dom¹, Akihiko Morimoto¹, Qian Leng¹, Xinyu Guo¹, Naoki Yoshie¹, Kuninao Tada², Kazuhiko Ichimi², Hitomi Yamaguchi², Masatoshi Nakakuni² (1.Ehime university, 2.Kagawa university)

Keywords:Numerical model, A Physical-Biogeochemical coupled model, lower trophic ecosystem , primary production, contribution ratio, Harima-Nada

The Harima-Nada is a shallow, semi-enclosed coastal system in the eastern part of the Seto Inland Sea (SIS), connected to the Bigo-Nada, Osaka Bays, and the Kii Channel in the Pacific Ocean through narrow straits; namely, the Bisan, Akashi, and Naruto Straits, respectively. This area is influenced by local winds, air-sea heat flux, and river discharge, which affect water exchange, accumulation of pollutants, and biogeochemical processes. Harima-Nada was one of the most seriously impacted areas by eutrophication in the SIS during rapid economic growth in the 1960s-70s, but since the enactment of the Interim Measures Law for Conservation of the Environment of the SIS (later the Special Measures Law), nutrient loads have gradually decreased and Harima-Nada has become an oligotrophic coastal system. Changes in nutrient concentrations are associated with primary production and fluctuation of the lower trophic ecosystem in the coastal area. Understanding these processes is essential for managing and protecting the ecosystems in this region. Therefore, we investigated the roles of riverine nutrients from different sources and their contributions to primary production using a Three-dimensional physical model coupled with the lower-trophic level ecosystem model in Harima-Nada. The different sources of nutrients, including oceanic, riverine, and benthic nutrients were applied as major sources of nutrients in this study. However, several rivers supply fresh water into Harima-Nada, especially the Yodo river in Osaka Bay, which is the largest river in the SIS. In order to evaluate the contribution of each source of riverine nutrients to the nutrient inventory and primary production of the lower-trophic level over the Harima-Nada, we applied a tracking technique to all the state variables in a biogeochemical model. Our study will present the contribution ratio of each source of riverine nutrients and their roles in primary production in Harima-Nada. In addition, we will examine the sensitivity experiment to investigate the nutrient response to nutrient supply from the river.