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Clay Minerals; June 2003; v. 38; no. 2; p. 243-253; DOI: 10.1180/0009855033820093
© 2003 Mineralogical Society of Great Britain and Ireland
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Effects of clay-rich river-dam sediments on downstream fish and plant life

K. TAZAKI1,*, M. SATO2, S. VAN DER GAAST3 and T. MORIKAWA4

1 Department of Earth Sciences, Faculty of Science, Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192 Japan, 2 1686 Yokoyama, Nyuzen, Shimoniikawa, Toyama, 939-0616 Japan, 3 Royal Netherlands Institute for Sea Research (NIOZ), P.O.Box 59, 1790AB, Den Burg, Texel, The Netherlands, and 4 Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192 Japan

* E-mail: kazuet{at}kenroku.kanazawa-u.ac.jp

(Received 8 October 2002; revised 15 December 2002)

In 1985, Dashidaira Dam, equipped with a flushing gate, was built on the Kurobe River in Toyama, Japan. Since the dam sediments were first flushed out in December 1991, benthic fish counts have decreased year by year due to repeated flushing of clay-rich dam sediments.

In June 2001, the flushed dam water contained a low oxygen concentration (1 to 2 mg/l) and high concentrations of smectite and vermiculite. To establish the cause of the death of the benthic fish, living flatfish were collected from Toyama Bay in order to examine their gills, which showed tissue damage and chemical changes caused by adherent expandable clays, derived from the flushed dam sediments. For comparison, exposure experiments on rainbow trout were carried out using smectite suspensions. Examination by optical microscopy revealed that the gills had shrunk because of the smectite concentrations. Low oxygen concentrations and large amounts of expanding clays have a significant effect on downstream benthic life.

KEYWORDS: flushing, dam sediments, expanding clays, smectite, vermiculite, flatfish, oxygen, trout






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