Nagayama, Shigeya Hokkaido University|Gifu University
Ishiyama, Nobuo Hokkaido University|Hokkaido Research Organization
Seno, Taro Hokkaido University|Green Power Investment Corporation
Kawai, Hideyuki Hokkaido University|Mitsubishi Materials Corporation
Kawaguchi, Yoichi Hokkaido University|Tokushima University Tokushima University Educator and Researcher Directory KAKEN Search Researchers
Nakano, Daisuke Hokkaido University|Central Research Institute of Electric Power Industry
Nakamura, Futoshi Hokkaido University
Despite a steep increase in dam removal projects, there are few studies on the biophysical responses to dam removal. In this study, we evaluated the short-term (1.5 years) and long-term (5.5 years) effects of partial check dam removal on fish assemblages and their habitats. First, the habitat preferences of fish were examined at a channel unit scale: pools, rapids, and side channels satisfied the seasonal habitat requirements of the fish assemblages. Partial check dam removal increased the abundance of these habitats and diversified the habitat structures owing to the sediment release from the dam; in contrast, the bedrock distinctly decreased 1.5 years after dam removal. However, 5.5 years after dam removal, the bedrock proportion increased, and the habitat structures were simplified again owing to the re-transportation of sediments. Similar temporal changes were also determined through a reach-scale analysis with a change in the bed materials. Anadromous Oncorhynchus masou began to spawn and recolonize in the upstream section of the dam after the dam removal, causing similar assemblage compositions between the downstream and upstream sections. The abundance of Salvelinus malma and Noemacheilus barbatulus toni in the upstream reaches decreased over time after the dam removal. The temporal changes in the biophysical responses suggest that long-term monitoring is indispensable for the reliable evaluation of dam removal effects.
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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Science and Technology