Author(s): Izumi Katano; Hideyuki Doi; Naoko Hara; Junjiro N. Negishi; Tomoko Minagawa; Yuichi Kayaba

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Keywords: Dam; Collector-filterers; Chironomidae; Oligochaeta; Hydropsychidae

Abstract: Both dams and confluences of tributaries are common discontinuities in river ecosystems, and the tributary confluence could alleviate the impacts on the main stem reaches which are altered by dams. We conducted field investigations downstream of eight dams in Japan, and compared (1) the proportions of subject taxa in the downstream area of the dam (and upstream of the tributary confluence; UC) and tributary as a reference (TR), and (2) the proportions between upstream and downstream of the tributary confluence (DC). The subject taxa are collector-filterer (CF), Chironomidae, and Oligochaeta, which are reported to increase downstream of the dam. In the comparison of the Log Response Ratio (LRR) in TR and UC with high-level study taxa, the value and the 95% confidence of Chironomidae was significantly greater than zero, while that of CF tended to be greater than zero but not significantly, and that of Oligochaeta was almost zero. In the comparison of the proportion of occurrence of the taxa in DC and UC, the value and the 95% confidence interval of CF was significantly greater than zero, while that of Chironomidae tended to be greater than zero but not significantly, and that of Oligochaeta was almost zero. We also discussed more detailed taxa. As a result, we have made it clear that (1) only Chironomidae significantly increases in the downstream reaches, and (2) Collector-filterers, other than Hydropsychidae, are sensitive to the tributary inflow. Hydropsychidae would be a typical taxon that is strongly influenced by the characteristics of dam rivers.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1709-cd

Year: 2023