ダム構造物と魚類の生活 [in Japanese] Dam and fish life-history-ecological perspectives in the environmental conservation [in Japanese]
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Damming causes many changes to the river. A dam and the resultant man -made lake change the river environment through a complex web of biological and physical impacts. The change from the river ecosystem to the lake ecosystem at the dam site will inevitably result in alteration of species composition, food habits and population dynamics of fishes. River impoundment affects endemic fish fauna and their life-histories through the following mechanisms : i. e., transverse blocking of the river channel, alteration of flow regimes and thermal regimes, and hindering upstream and downstream migration. Changes in fish communities have been recorded within considerable distances both upstream and downstream of dams. Hydropower reservoirs suffer high mortality if fish pass through the turbines. Since reservoir becomes a sink for sediments, seston transport is dramatically affected. Turbidity will increase during the construction phase and often over long distances. These constraints may lead to catastrophic falls in the abundance or extinction of some fish populations. The extinction might be associated with the introduction of exotic species. Flow regulation by dam can prevent or delay the inundation of floodplains and riparian zones, reducing or eliminating areas for breeding and reprodution of fish. These rapid and often extensive changes in the discharge regime cause displacement of fish, particular-ly juveniles, and can lead to loss of the fisheries. The modification of seasonal and diurnal thermal regulation causing the alteration of fish assemblages, usually results in reduction of species diversity in the river, when the dam releases the hypolimnial and/or epilimnial waters. The numerous unfavorable effects of impoundments and other forms of river regulation must be well documented for the planning and execution of future projects for the rehabilitation of water courses. Ecological evaluation is essential part of the programme on the base of "long-term environmental sustainability". It is hoped that the principles and guidelines of habitat improvement including the idea of removing dams will be made based on long-term ecological assessment.
ECE 2(2), 165-177, 1999-11-19
Ecology and Civil Engineering Society