| Project/Area Number |
14340247
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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 |
生態
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| Research Institution | Prefectural University of Kumamoto |
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Principal Investigator |
TSUTSUMI Hiroaki Prefectural University of Kumamoto, Faculty of Enviromental and Symbiotic Sciences, Professor, 環境共生学部, 教授 (50197737)
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| Co-Investigator(Kenkyū-buntansha) |
OHWADA Koichi Prefectural University of Kumamoto, Faculty of Enviromental and Symbiotic Sciences, Professor, 環境共生学部, 教授 (30013585)
KOGA Minoru Prefectural University of Kumamoto, Faculty of Enviromental and Symbiotic Sciences, Professor, 環境共生学部, 教授 (40131916)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥14,600,000 (Direct Cost: ¥14,600,000)
Fiscal Year 2004: ¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 2003: ¥5,600,000 (Direct Cost: ¥5,600,000)
Fiscal Year 2002: ¥7,200,000 (Direct Cost: ¥7,200,000)
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| Keywords | Ariake Bay / Red tide / Tidal flat / Clam / Water quality / Eutrophication / Sediment / 諌早湾 / 貧酸素化現象 / 成層構造 / 諫早湾 / 貧酸素 |
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| Research Abstract |
In Ariake Bay, large scale red tides have repeatedly occurred from autumn to early winter in recent years, and seriously damaged the nori (a red alga, Porphyra) culture. According to the previous records on the occurrence of red tide in Ariake Bay between October and December since 1981, the scale of red tide markedly increased from 1998. However, the amounts of nutrients loaded on Ariake Bay from the coastal lands through the major rivers have increased little in the past two decades. In this study, we monitored the water conditions at 24 sampling stations in Ariake Bay monthly from April 2002 to April 2003. The large scale red tides occurred in the inner part of the bay in July and October to December, 2002. In these two periods, the inflow of the river water diluted the surface layer of the sea water in the inner part of the bay, caused the stratification of the water and highly eutrophicated conditions in the surface layer, and resulted in the occurrence of large scales of red tides in the inner part of the bay. The marked increase of the scale of red tide from 1998 indicates that the gradual decrease of the tidal amplitude and current since 1980 i s not one of the main causes of the frequent occurrence of the large red tides. The results of this study suggest that the estuary circulation of the inner part of Ariake Bay was changed by the closure of the gates of the dike in Isahaya Bay in 1997, and the surface water with lowered salinity and eutrophic conditions formed by the inflow of the river water became more stagnant than before the closure of the gates. It is very likely that the marked increase in the scale of the red tide in the inner part of Ariake Bay from 1998 is one of the results of a series of phenomena originated from the closure of the gates in Isahaya Bay.
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