assessment of the methods. Biomanipulation, which has been brought to public attention, is one of the better examples of the remediation of water environment using the ecological technique. Biomanipulation aims to prevent the unusual growth of phytoplankton as a result of eutrophication in a lake. The basic concept of biomanipulation is that if the effective grazing of phytoplankton by zooplankton is achieved in a lake, the unusual phyto-plankton growth is suppressed at certain levels of nutrient loadings. To construct this adequate ecological structure, the biomass of planktivorous fish (which is a predator of zooplankton) should be suppressed and the biomass of piscivorous fish (which is a predator of the planktivorous fish) should be maintained. To do so, planktivorous fish is removed from a lake, and/or piscivorous fish is introduced into a lake in the implementation of biomanipulation. For more detailed information about the biomanipulation, the reader is referred to the literature. The success/failure of biomanipulation strongly depends on the structural change in lake ecosystem after the manipulations. Especially, the succession of zooplankton is thought to be the most important. In general, in cases where biomanipulation is a success, the large-size zooplankton such as Daphnia sp. dominates. It is clear that the large-size zooplankton can essentially graze phytoplankton of various sizes at a high rate and is effective in suppressing the unusual growth of phytoplankton. For successful biomanipulation, therefore, some kinds of zooplankton, which graze harmful phytoplankton such as Microcystis sp., should dominate. To do so, sufficient prediction of zooplankton succession should be required prior to the implementation of biomanipulation. That is why the analysis of structural dynamics in the lake is strongly required for the implementation ofbiomanipulation, and the structural dynamic models become a strong tool to deal with this subject.
One of the essential objectives of the structural dynamic models is to assess the dynamics of the irreplaceable ecosystems. Currently, one of the most important issues in global environment is the extinction of rare and endangered species. Accordingly, the concern for the importance of biodiversity has been growing today. These topics can be dealt with in the structural dynamic models. In this circumstance, the expectation from the structural dynamic models will increase more and more in the future.
On the other hand, some environmental purification and remediation methods using ecological techniques have been brought to public attention. These are especially, applied for water treatment, or remediation of water environments. Some of them require the ecological structural dynamic models as a tool for the
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