炭素·窒素安定同位体比とメイオベントス相から見た瀬戸内海の底質環境の変遷  [in Japanese] Changes in Sediment Environment of Seto Inland Sea Estimated from Carbon and Nitrogen Stable Isotope Ratios and Meiobenthos Communities  [in Japanese]

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Abstract

瀬戸内海の底質環境の変遷を調べるため,播磨灘,大阪湾,周防灘において堆積物コアを採取し,<SUP>137</SUP>Cs法による堆積年代の推定とδ<SUP>13</SUP>Cとδ<SUP>15</SUP>Nの鉛直分布,および貝形虫·有孔虫群集の種数や個体数等との関係について解析した。播磨灘と大阪湾ではδ<SUP>13</SUP>Cの微増とδ<SUP>15</SUP>Nの増加,および貝形虫群集の貧酸素耐性種の優占率の増加から,1950年代以降には表層域の植物プランクトンの増殖または底層域での貧酸素水塊の発生が推察された。周防灘のδ<SUP>13</SUP>C-δ<SUP>15</SUP>N図は非常に狭い範囲に分布し,貝形虫群集の種数は著しく多く多様性に富んでいることから,今日まで底層域に貧酸素水塊は一部の海域を除いて発生していないことが示唆された。本研究の手法は,瀬戸内海の底層域における貧酸素水塊の発生と底生生物に対する影響を明らかにし,瀬戸内海の各海域の富栄養化による汚染の歴史を解明する上で有効な手段であることを示した。

The purpose of this study is to clarify the transition of the sediment environment of the Seto Inland Sea. To estimate the sedimentation rate and deposition year in Harima-nada, Osaka Bay, and Suo-nada, the vertical distribution of <SUP>137</SUP>Cs was determined for sediment cores. The carbon and nitrogen stable isotope ratios (δ<SUP>13</SUP>C, δ<SUP>15</SUP>N) of sediment core layers in Harima-nada and Osaka Bay were measured and plotted in a δ<SUP>13</SUP>C vs δ<SUP>15</SUP>N diagram. The plots were distributed in a very narrow range during 1865 to 1948, but an increase in δ<SUP>15</SUP>N and a slight increase in δ<SUP>13</SUP>C were simultaneously observed during 1954 to 2000. Since 1950, the frequency of occurrence of an ostracode and a foraminiferal species resistant to oxygen-deficient environments has increased. From 1950, hypoxia was occurred in the bottom layer, or phytoplankton in the surface layer thrived. Consequently, the δ<SUP>15</SUP>N of phytoplankton increased, thereby increasing the δ<SUP>15</SUP>N of sediment core samples. The plots for Suo-nada, from 1825 to 2008 were distributed only in a very narrow range of the δ<SUP>13</SUP>C vs δ<SUP>15</SUP>N diagram. Ostracode assemblages were significantly rich in diversity. It was estimated that δ<SUP>15</SUP>N of phytoplankton did not vary because denitrification did not occur and hypoxia did not occur in the bottom layer.

Journal

  • Journal of Japan Society on Water Environment

    Journal of Japan Society on Water Environment 38(2), 39-47, 2015

    Japan Society on Water Environment

Codes

  • NII Article ID (NAID)
    130004923019
  • NII NACSIS-CAT ID (NCID)
    AN10372439
  • Text Lang
    JPN
  • ISSN
    0916-8958
  • NDL Article ID
    026999095
  • NDL Call No.
    Z16-1045
  • Data Source
    NDL  J-STAGE 
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