Japanese Journal of Water Treatment Biology

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Necessity of introduction of ecosystem level environmental assessment method is pointed out by OECD and so on. The comparison of Microcosm–WET test and single species test was conducted under supplied condition of real drainage, and the efficiency of Microcosm–WET test by which ecosystem-level toxic assessment can be possible was investigated. Furthermore, a significance of the standardization of environmental impact risk assessment test method with high reproducibility, high stability, low cost and high versatility using microcosm system was stated. As experimental results, there was not recognized remarkable difference between Microcosm–WET test and single species test for the environmental influences, and Microcosm–WET test can be one of the effective test methods because of its superior characteristic as including basic ecosystem principles such as material circulation, energy flow and biological interaction and the same level susceptibility as single species test.

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There are many cases where eutrophication has become a common in irrigation pond, remarkable in ponds because the use of agricultural land irrigation has been abolished and it is operated as a park pond. Regular water drying is no longer carried out in these park ponds. Ecological disturbances such as water level fluctuation has disappeared in these ponds, and overgrowth of certain alien species is observed. Artificial water level disturbances were revived in these ponds, increasing predation pressure by birds on invasive crayfish Procambarus clarkii and bullfrog Rana catesbeiana. As a result, low density management of invasive crayfish and bullfrog was successful. The overgrown area of aquatic plants has expanded, and the population density of zooplankton such as Cladocera has increased. The effect spread widely to the biota through the food web, and the effect on water environment conservation was confirmed.

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