Data underlying the publication: Freshwater fish biodiversity restoration in floodplain rivers requires connectivity and habitat heterogeneity at multiple spatial scales

With a sixth mass extinction looming and freshwater biodiversity declining at unprecedented rates, evaluating ecological efficacy of river restoration efforts is critical in combatting global biodiversity loss. Here, we present a comprehensive study of the functioning for fishes of 46 river restoration projects in the river Rhine, one of the world's most heavily engineered lowland rivers. Floodplains with permanent, either one- or two-sided lateral connectivity to the main channel, favour total fish abundance, and are essential as nursery areas for riverine fishes. Habitat heterogeneity had a strong positive effect on species richness but was negatively related with fish abundances. However, the effects of environmental variables varied between ecological groups and spatial scales. Surprisingly, richness of critical rheophilic fishes declined with large-scale habitat heterogeneity (~1000 m), while it increased at small scales (~100 m), possibly because of the presence of unfavourable habitats for this ecological group at larger scales. Clearly, there is no one-size-fits-all design for river restoration projects. Whether a river section is free-flowing or impounded dictates the scope and efficacy of restoration projects and, within a river section, multiple complementary restoration projects might be key to mitigate freshwater fish biodiversity loss. An essential element for success is that these projects should retain permanent lateral connection to the main channel.

第六次生物大灭绝（Sixth Mass Extinction）已然迫近，淡水生物多样性正以前所未有的速度衰退，因此评估河流修复工程的生态效益，对于遏制全球生物多样性丧失至关重要。本研究以全球受人工改造程度最高的低地河流之一的莱茵河（Rhine）为研究对象，对其46个河流修复项目的鱼类群落功能表现展开综合分析。与主河道具备单侧或双侧永久性侧向连通性的洪泛平原，可显著提升鱼类总丰度，同时是河栖鱼类不可或缺的育幼栖息地。生境异质性对物种丰富度具有显著正向影响，但与鱼类丰度呈负相关关系。然而，环境变量的影响效应因生态类群与空间尺度的不同而存在显著差异。令人意外的是，关键的喜急流鱼类（rheophilic fishes）的物种丰富度随大尺度（约1000米）生境异质性的提升而下降，但在小尺度（约100米）下则呈上升趋势，这可能是因为大尺度生境中存在不利于该类群鱼类的栖息环境。显而易见，河流修复工程并无通用的统一设计方案。河流断面是否为天然畅流或筑坝拦蓄，决定了修复工程的实施范围与效益；而在同一河流断面内，多个互补型修复项目或许是缓解淡水鱼类生物多样性丧失的关键。修复工程取得成功的核心要素之一，是需保留其与主河道的永久性侧向连通性。