Current 　Water　Environment　of 　Ariake　Bay 　Observed 　from　Routine 　Surveys

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Other Title
  • 広域定期観測 に よる有明海水環境 の 現状
  • コウイキ テイキ カンソク ニ ヨル アリアケ カイスイ カンキョウ ノ ゲンジョウ

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Description

Since 1998, large scale red tides have occurred in autumn and early winter. We established 13 sampling stations at intervals of approximately 3km on a longitudinal line in Ariake Bay, and surveyed the vertical profile of water quality at each station ten times from April, 2002 to April, 2003. In this study, we twice July and November, 2003 observed a large scale red tide that extended for over 600km^2 from the coast of Saga Prefecture, at the innermost areas of Ariake Bay, to Fukuoka and Kumamoto Prefectures. From the results of this study, the process of red tide blooms in these areas can be described as follows. First, the water in the innermost areas of Ariake Bay was stratified due to a decrease of salinity in the surface layer of water loaded from rivers. A large amount of nutrient was transported from the rivers to the innermost areas of the bay, and concentrated in the surface layer of the stratified water. The concentration of the nutrients rapidly increased, but only at the surface layer of the water, and temporarily became extremely eutrophicated at over 40μmol L^<-1> in DIN and 2μmol L^<-1> in DIP; resulting in the occurrence of a red tide in just this surface layer. Therefore, the occurrence of the large scale of red tide in the inner areas of Ariake Bay started from the occurrence of the halocline conditions of a well-defined vertical salinity gradient.

Journal

  • Bulletin on Coastal Oceanography

    Bulletin on Coastal Oceanography 42 (1), 35-42, 2004

    Coastal Oceanography Research Committee, the Oceanographic Society of Japan

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