黒部川出し平ダムおよび富山湾における堆積物の特性: 懸濁粒子が魚類に与える影響の検討

1991年12月,排砂ゲートを設けた出し平ダム(富山県黒部川水系1985年設立)から,初の直接排砂が行われ,その際,多量のヘドロが排出された.その後も1999年までに計8回の排砂が行われた.本研究において,出し平ダム湖および富山湾堆積物の特性について分析を行った.その結果,特に芦野沖にヘドロが堆積していること,そして,富山湾堆積物は他の湾堆積物と比べカオリン鉱物,スメクタイトが多く,出し平ダム湖堆積物と類似した粘土鉱物組成を持つことが明らかとなった.実験より,ニジマスのエラにスメクタイトが吸着することで,エラの変形や脱水を引き起こすことが明らかとなり,また,富山湾で採取されたヒラメのエラ表面が,微細粒子で覆われているのが観察された.以上の結果と1991年から1999年の出し平ダム排砂量とヒラメの漁獲量の変遷には密接な関係が認められ,ダム湖や富山湾底質の経時変化を観察することの重要性が示された.

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In 1985, a dam with a discharge gate was built at Dashidaira at Kurobe River, Toyama Prefecture for the first time in Japan. The dam sediments were first flushed out in December, 1991. The sediments with bad smell, such as sludge, spread all over the downstream of Kurobe River. After the first discharge of the dam sediments, benthic fishes decreased year by year in Toyama Bay. In this study, the sediments in Dashidaira Dam Reservoir and Toyama Bay were collected in 1997, 2000 and 2001. The Toyama Bay sediments which were considered to have been affected by discharged dam sediments were collected on July 20, 2000, November 19, 2000, and March 3, 2001. The sediments in the dam reservoir and the bay were studied chemically, physically and mineralogically for comparative study. The quantity of clay minerals, mainly smectite, increase toward the discharge gate at Dashidaira Dam. The distribution of clay minerals approximately corresponded to distribution of the N, C, and S concentration in Toyama Bay. XRD data show similar clay mineral components and patterns between dam sediments and suspended particles from the seabed at the offing of Kurobe River mouth. The sediments in Dashidaira Dam Reservoir and Toyama Bay contain relatively high content of kaolin minerals associated with chlorite, vermiculite, smectite, and mica clay minerals compared with sediments of the other bays. Rainbow trouts in water with smectite suspension result clearly indicated the damage to the fish. In the highest concentration of smectite (lOg/l), all 7 rainbow trouts died in five hours. The fish's gills were deformed and dehydrated, suggesting influence of smectite particles adhered to the surface of the gills. Furthermore, SEM observation and EDX analysis of the flat fish's gill in Toyama Bay clearly showed the presence of particle-like thin films with organic materials sticking on the surface. The volume of discharged sediments from Dashidaira Dam Reservoir is clearly related to the decrease of annual haul of benthic fishes in Toyama Bay within the past nine years (1991-1999).

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http://purl.org/coar/version/c_970fb48d4fbd8a85

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2023-07-27 15:10:58.419651

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