Abstract
The purpose of this study was to estimate influences of temporal changes on the ecosystems of stream basin environments and material cycle during the past two to three decades by using an alternative research method. We compared stable isotope signatures of formalin-fixed fish specimens of the 1980s and the 2000s for 17 plots of small streams in Aomori, Japan. In addition, we investigated changes of the land use such as farmlands and urban areas and impacts of river improvement. Subsequently, we considered these investigation data and stable isotope signatures. As a result, we confirmed that changes of land use and promotion of the sewer improvement caused the change of the δ15N value, and furthermore, river improvement works made aquatic food chains simple as shown in the fact of the convergence of stable isotope signatures.
