貯水ダムが底生動物に与える影響の支流流入による緩和
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概要
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We conducted a field survey in Hida River basin in Gifu prefecture on September, 2004, to reveal the impacts of storage dams on stream invertebrate assemblage and the mediation of the impacts by the confluence of tributaries. Study sites were established in upstream and downstream reaches of 4 storage dams, in 4 tributaries that confluent downstream of each dam, and in downstream of each confluence. The water depth and the value of the DCA axis 1, which indicates community structure of stream invertebrates, were lower, and the standing crop of particulate organic matter was higher in the downstream of the dams. However, these values in the downstream of confluence were similar to those in upstream of dams and in tributaries, implying that the impacts of storage dams were mitigated by the confluence of tributaries. We suggest that the confluence of tributary in downstream of dam mitigates the changes in the flow regime and the deposition of the organic matter caused by storage dams.