Dynamic evaluation of boreal aquatic ecosystems assessed by nitrogen isotope and food web structure

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To evaluate stability of aquatic ecosystems which are disturbed by interference such as by immigrant biota or by eutrophication, we studied and evaluated here stable nitrogen isotope proxies as a likely indicator assessing the state of nitrogen cycling and food chain structure of an ecosystem. Based on field works at Ishikari river water shed where it has been concerned about large discharge of anthropogenic nitrogenous compounds, and many dam ponds distributed in Toyama prefecture as being concerned about ecological disturbance by large-mouth bass recently. The nitrogen isotope analysis has been clarified as a useful and promising indicator to evaluate environmental problems occurring in ecology and/or nutrient cycling even though based on only snapshot observations.