Japanese Journal of Limnology (Rikusuigaku Zasshi)
Online ISSN : 1882-4897
Print ISSN : 0021-5104
ISSN-L : 0021-5104
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Volume 72, Issue 3
Displaying 1-3 of 3 articles from this issue
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Original articles
  • Fish assemblages in the riverside pools of a small stream
    Osamu KATANO, Maria KUROKAWA, Satoshi KITANO, Koji TOJO
    2011 Volume 72 Issue 3 Pages 181-192
    Published: 2011
    Released on J-STAGE: December 02, 2012
    DOIhttps://doi.org/10.3739/rikusui.72.181
    JOURNAL FREE ACCESS
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    Fish assemblages in the riverside pools of a small stream were investigated in Nagano Prefecture, Japan, and a total of 12 fish species were caught. There were greater numbers of Misgurnus anguillicaudatus and Cobitis biwae and fewer Tribolodon hakonensis and Zacco platypus in the riverside pools relative to the assemblage in the main stream. In the pools, fish species richness and total population density of fish were not correlated with the abundance of benthic invertebrates, but were strongly correlated with environmental factors. Fish species richness was highest when the degree of saturated dissolved oxygen was elevated in June and when the area and water depth were greatest in September. The total population density was positively correlated with the mean current velocity in June but was not correlated with any environmental factor in September. Fish fed primarily on chironomid larvae, ephemeropteran nymphs, benthic algae and detritus in the riverside pools. Detritus contributed to a greater proportion of the diet in the fish from the riverside pools compared with those in the main stream.
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  • Evaluation of groundwater discharge in Lake Ezu, Kumamoto, based on radon in water
    Masahiko ONO, Jun SHIMADA, Tsutomu ICHIKAWA, Takahiro TOKUNAGA
    2011 Volume 72 Issue 3 Pages 193-210
    Published: 2011
    Released on J-STAGE: December 02, 2012
    DOIhttps://doi.org/10.3739/rikusui.72.193
    JOURNAL FREE ACCESS
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    Approximately 400,000-500,000 m3 day-1 of groundwater are discharged at Lake Ezu from two aquifers with different depths. These two aquifers are separated by an aquitard composed of lacustrine deposits. Since this aquitard is partially absent, groundwater in both the deep and shallow aquifer can discharge into the lake. However, the amount of groundwater discharged from each aquifer into the lake is unclear. Our previous study showed that the radon concentration in groundwater could be used as an ideal tracer to separate shallow and deep groundwater components in the study area. In the present study, we collected water samples from around the study area once a month since June 2009 and then calculated the contribution ratio of groundwater discharge from both the shallow and deep aquifer into the lake using a radon mixing model. The results revealed that the groundwater discharge from the deep aquifer was estimated to be the dominant source of groundwater discharged into the lake (58% on average), with seasonal fluctuation. The results of this study could be used to more precisely estimate the mass balance in Lake Ezu.
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