Recent Decrease of Nutrients in Harima-Nada Sea and Its Relation to Variation of Nutrient Flux from River Basins

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We quantitatively show a large amount of river waters flow into the Harima-Nada Sea from Harima area(Honsyu Island side) as compared with the Shikoku and Awaji Islands sides. The river waters have strong influence on the nutrient concentration in the sea. Especially, a short-term river runoff during a flood has a large influence. It is clarified that the difference of river water spread in the north side of the Sea of Harima and the south side and the effects of short-term river flood inflow are important to understand the water environment in the Harima-Nada Sea. We suggest the possibility that the change and variation of river water chemistry and discharge is one of factor to the recent decrease of nutrients in Harima-Nada Sea.