River ecosystems host a continuum of various discontinuities, such as dams and tributary inflows, which shape the habitats of aquatic organisms; this makes it important to evaluate the interactions among discontinuities and effects of a single discontinuity point. Herein, we focused on tributaries in dammed rivers to elucidate a manner to mediate discontinuities and hypothesized that the effects of the tributary inflow on the downstream river were mediated by the (1) distance between the dam and tributary inflow, (2) size ratio between the dam and tributary, and (3) ability of the tributary to transport fine sediments, such as sand and gravel. We conducted field investigations to measure 24 environmental factors, including the water column, riverbed, and river topography, along eight dammed rivers to test the three hypotheses. Only five factors differed significantly between the upstream and downstream sites of the tributary confluence, whereas 12 factors differed significantly between the tributary and mainstem. We also classified the variation pattern using principal component analysis (PCA). The correlation between each PCA axis and environmental factors suggests that the modifications of the water quality factors by tributary inflow were significantly correlated with the distance between the dam and the tributary inflow, and that the flux of various riverbed factors, that is, was significantly correlated with the ability to resupply of fine riverbed sediments by the tributary. Overall, tributary-inflow downstream of a dam has the potential to be applicable in environmental restoration, especially in terms of resupplying fine sediment.

中文翻译：

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支流通过水坝减轻河流的不连续性，具体取决于水坝到支流汇合处的距离

河流生态系统具有各种不连续性的连续体，例如水坝和支流流入，它们塑造了水生生物的栖息地；这使得评估不连续性之间的相互作用以及单个不连续点的影响变得非常重要。在此，我们重点关注筑坝河流中的支流，以阐明调节不连续性的方式，并假设支流流入对下游河流的影响是由（1）大坝与支流流入之间的距离，（2）水坝与支流流入之间的尺寸比来调节的。大坝和支流；(3) 支流输送沙子和砾石等细沉积物的能力。我们对8条筑坝河流进行了实地调查，测量了24个环境因素，包括水柱、河床和河流地形，以检验这三个假设。支流汇合处上下游仅有5个因素存在显着差异，而支流与干流之间存在显着差异的因素有12个。我们还使用主成分分析 (PCA) 对变异模式进行分类。各PCA轴与环境因子的相关性表明，支流入流对水质因子的修改与大坝与支流入流的距离显着相关，即各河床因子的通量显着相关。具有通过支流补给细小河床沉积物的能力。总体而言，大坝下游的支流流入有可能适用于环境恢复，特别是在补给细泥沙方面。