2005 Fiscal Year Final Research Report Summary
Biological and chemical estimation for environments of the sea bed of Ariake Sea and its activation
| Project/Area Number |
15360268
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
水工水理学
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
MATSUNAGA Nobuhiro Kyushu University, Dept.Earth System Science and Technology, Professor, 大学院・総合理工学研究院, 教授 (50157335)
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| Co-Investigator(Kenkyū-buntansha) |
YASUDA Hidekazu National Fisheries University, Dept.of Fisheries Information and Management, Professor, 水産情報経営学科, 教授 (10399628)
SUGIHARA Yuji Kyushu University, Dept.Earth System Science and Technology, Associate professor, 大学院・総合理工学研究院, 助教授 (70243970)
ONITSUKA Go National Fisheries University, Dept.of Fisheries Information and Management, Research associate, 水産情報経営学科, 助手 (40399647)
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| Project Period (FY) |
2003 – 2005
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| Keywords | Ariake Sea / Sea bed environments / Oxygen consumption / Adsorption of nutrients / Desorption of nutrients |
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| Research Abstract |
Field observations were made in September 22 to 13, 2002 in order to investigate the formation mechanism of oxygen-deficient water mass in the western area of Ariake Sea in Kyushu Island of Japan. A high turbidity layer was formed near the bottom by strong tidal currents. When the concentration of dissolved oxygen (DO) was kept enough high over the whole depth, a good negative high correlation was seen between the turbidity and the DO concentration near the bottom. Therefore, the oxygen consumption seems to be closely related to the formation of a high turbidity layer. It is found through the laboratory experiments that the oxygen consumption rate due to suspended solids (SS) takes 13 times the value of sediment oxygen demand (SOD). It suggests that the oxygen consumption due to SS is important for the formation of oxygen-deficient water mass in the western area of Ariake Sea.
The seabed environments were investigated at 20 stations located in the northern area of Ariake Sea in July 200
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4. The spatial distributions of sediment characteristics and nutrients in porewater were obtained. It is found that the area where the acid volatile sulfides (AVS) content exceeds 0.2mg/gdry spreads along the west coast, and the seabed conditions in the area are bad. The concentrations of dissolved inorganic nitrogen (DIN) in porewater increase from the southwest to the northeast, and the concentration of phosphate (PO_4-P) takes the reverse distribution. The spatial distributions of nutrients seem to depend strongly on the process of adsorption and desorption of PO_4-P and the process of nitrification and denitrification of DIN.
On the basis of the idea the low release of ammonium (NH_4-N) observed in the seabed surface off Takesaki of Ariake Sea may be caused by the nutrient adsorption due to the bed materials, mud cores were sampled off Takesaki and the quantities of water were investigated through laboratory experiments. The oxygen consumption and the concentrations of NH_4-N and phosphate PO_4-P measured through the experiments of mud resuspension. Though the concentrations of NH_4-N and (PO_4-P) were also increased with the depth from the surface of the mud core, they began to decrease after taking maximum values at some depths. The vertical profiles were very different from those seen in ordinary mud. The experiments of mud resuspension showed that the concentrations of NH_4-N and PO_4-P were kept constant though DO was consumed. These experimental results support the possibility that the high nutrient adsorption by the bottom mud occurs off Takesaki of Ariake Sea. Less
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