Elucidation of the nutrient transport processes and the primary production systems in Ariake Sea

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K06513
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Hydraulic engineering
• Research Institution: Kyushu University
• Principal Investigator: MATSUNAGA NOBUHIRO 九州大学, 総合理工学研究院, 教授 (50157335)
• Co-Investigator(Kenkyū-buntansha): 李 洪源 山口大学, 創成科学研究科, 助教 (10599236)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 沿岸海域 / 水質環境 / 赤潮 / 貧酸素水塊

Outline of Final Research Achievements

The secular variations of red tide and anoxic water mass in Isahaya Bay were investigated based on the water quality data which the Kyushu Regional Agricultural Administration Office has measured at six measuring stations since 2002. The concentration of Chl.a was analyzed as the index of red tide and the DO concentration near the sea bed as the index of anoxic water mass. In Isahaya Bay, the occurrence frequency of red tide is decreasing with age and its scale is approaching to a stable situation. The analysis of the DO concentration shows that the secular variations of anoxic water mass are stable in Isahaya Bay. The multiple linear regression analysis shows that the primary factor controlling the DO concentration is water temperature and a strong negative correlation is seen between the both. The second factor is the density difference between the water surface and the bottom layer. A negative correlation is also seen between the DO concentration and the density difference.

Free Research Field

沿岸海域環境学

Academic Significance and Societal Importance of the Research Achievements

有明海西部に位置する諫早湾では1997年にその奥部が締め切られ，約15km2の干潟を含む35.5km2の浅海域が消失した．2000年冬季には海苔の大凶作が発生し，諫早湾の干拓事業と海苔の大凶作との関係が社会問題となった．そのような社会背景において，九州農政局がこれまで蓄積してきた膨大な長期多点同時水質観測データを解析し，諫早湾内における赤潮ならびに貧酸素水塊の経年変化を明らかにした．その結果，諫早湾内における赤潮の発生頻度ならびに赤潮の規模は減少し，収束傾向にあることを明らかにした．また，貧酸素水塊の発生頻度ならびにその規模も減少し，収束傾向にあることを明らかにした．