Abstract Dam sedimentation is a crucial issue that interferes with flood control and electric power generation. To address this, sediment dredging, bypass tunnel, flushing, and sluicing have been applied. Despite the potential impacts of these operations on stream environments, few studies have explored the environmental/ecological consequences of such regime shifts in sediment dynamics. Specifically, impacts of sediment sluicing on stream fauna have never been reported. This study assessed primary impacts of sediment sluicing events operated with the two cascade dams (the Saigo and Ouchibaru Dams) on stream insects in the lower Mimi River, Japan. The sediment sluicing, accompanied by a major flooding event in the river, was first operated in September 2017. Stream insect data downstream of the four cascade dams, including the two sluicing dams and a reference river, were collected yearly or biyearly in winter and summer from 2010 to 2018. Following the initiation of retrofitting the Saigo Dam for optimizing sediment sluicing, a downstream reach of the dam experienced marked perturbations in terms of both individual density and species richness. The density and richness dramatically decreased and the community significantly differed in winter 2017 from pre-impact conditions. The density, richness, and community composition subsequently recovered in winter 2018, even after the sediment sluicing impact, suggesting that the anticipated negative ecological impacts of the sluicing are limited. Non-metric multidimensional scaling and permutational multivariate analysis of variance revealed distinct differences in communities between summer and winter samples at non-regulated sites or sites farther downstream of the dam that are characterized by fewer Simuliidae in summer and relatively abundant Heptageniidae. This could serve as a reference for assessments of ecological consequences of sediment sluicing in the region.

中文翻译：

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日本咪咪河泥沙泄洪事件对溪流昆虫影响的初步评价

摘要 大坝淤积是影响防洪和发电的重要问题。为了解决这个问题，已经应用了沉积物疏浚、旁路隧道、冲洗和冲洗。尽管这些操作对河流环境有潜在影响，但很少有研究探讨沉积物动力学中这种制度转变的环境/生态后果。具体而言，从未报道过沉积物对河流动物群的影响。本研究评估了使用两个梯级大坝（西乡和大内原大坝）运行的沉积物泄流事件对日本咪咪河下游河流昆虫的主要影响。2017 年 9 月，随着河流发生重大洪水事件，泥沙泄洪事件首次运行。 四个梯级大坝下游的溪流昆虫数据，从 2010 年到 2018 年，在冬季和夏季每年或每两年收集两座泄洪坝和一条参考河流。随着西乡大坝开始改造以优化排沙，大坝下游河段在这两个方面都经历了明显的扰动。个体密度和物种丰富度。2017 年冬季，密度和丰富度急剧下降，群落与撞击前的条件有显着差异。密度、丰富度和群落组成随后在 2018 年冬季恢复，即使在沉积物泄流影响之后，表明泄流的预期负面生态影响是有限的。非度量多维标度和方差的置换多变量分析揭示了在非管制地点或大坝下游更远地点的夏季和冬季样本之间的群落存在明显差异，其特征是夏季 Simuliidae 较少，而 Heptageniidae 相对丰富。这可以作为评估该地区沉积物泄洪生态后果的参考。