Hellenic Centre for Marine Research, Institute of Marine Biological Resources and Inland Waters, 46.7 km Athens-Sounio Ave., 19013, Anavyssos, Greece; National Technical University of Athens, Department of Water Resources and Environmental Engineering, 5 Iroon Polytechniou Str., 15780, Athens, Greece.
National Technical University of Athens, Department of Water Resources and Environmental Engineering, 5 Iroon Polytechniou Str., 15780, Athens, Greece.
Water Res. 2020 Apr 15;173:115550. doi: 10.1016/j.watres.2020.115550. Epub 2020 Jan 30.
River restoration with the use of in-stream structures has been widely implemented to maintain/improve physical habitats. However, the response of aquatic biota has often been too weak to justify the high costs of restoration projects. The ecological effectiveness of river restoration has thus been much debated over claims that large-scale environmental drivers often overshadow the potential positive ecological effects of locally placed in-stream structures. In this study, we used a two-dimensional hydrodynamic-habitat model to evaluate the ecological effectiveness of habitat restoration with the use of in-stream structures in various water discharges, ranging from near-dry to environmental flows. The habitat suitability of benthic macroinvertebrates and of three cyprinid fish species was simulated for six restoration schemes and at four discharge scenarios, and was compared with a reference model, without in-stream structures. We found that the ecological response to habitat restoration varied by species and life stages, it strongly depended on the reach-scale flow conditions, it was often negative at near-environmental flows, and when positive, mostly at near-dry flows, it was too low to justify the high costs of river restoration. Flow variation was the major environmental driver that our local habitat restoration schemes attempted -but mostly failed-to fine-tune. We conclude that traditional river restoration, based on trial and error, will likely fail and should be ecologically pre-optimized before field implementation. Widespread use of in-stream structures for ecological restoration is not recommended. However, at near-dry flows, the response of all biotic elements except for macroinvertebrates, was positive. In combination with the small habitat-suitability differences observed among structure types and densities, we suggest that sparse/moderate in-stream structure placement can be used for cost-effective river restoration, but it will only be ecologically effective -thus justifying the high implementation costs-when linked to very specific purposes: (i) to conserve endangered species and (ii) to increase/improve habitat availability/suitability during dry periods, thus proactively preventing/reducing the current and future ecological impacts of climate change.
利用河流内结构进行河流修复已经被广泛应用于维持/改善物理生境。然而，水生生物群的反应往往过于微弱，无法证明修复项目的高成本是合理的。因此，关于大规模环境驱动因素经常掩盖当地放置的河流内结构可能产生的积极生态影响的说法，河流修复的生态效果一直存在争议。在本研究中，我们使用二维水动力-生境模型来评估在各种水流量（从接近干涸到环境流量）下使用河流内结构进行生境恢复的生态效果。模拟了六种恢复方案和四种排放情景下底栖大型无脊椎动物和三种鲤鱼科鱼类的生境适宜度，并与没有河流内结构的参考模型进行了比较。我们发现，对生境恢复的生态反应因物种和生活阶段而异，强烈依赖于河段尺度的水流条件，在接近环境流量时通常为负面，而在接近干涸流量时则为正面，但这种反应太低，无法证明河流修复的高成本是合理的。流量变化是我们当地生境恢复方案试图微调但大多未能成功的主要环境驱动因素。我们得出结论，基于试错法的传统河流修复可能会失败，并且应该在实地实施之前进行生态预优化。不建议广泛使用河流内结构进行生态恢复。然而，在接近干涸的水流条件下，除了大型无脊椎动物外，所有生物要素的反应都是积极的。结合我们观察到的结构类型和密度之间的小生境适宜度差异，我们建议稀疏/适度的河流内结构放置可以用于具有成本效益的河流修复，但只有当与非常具体的目的（i）保护濒危物种和（ii）在干旱期增加/改善生境可用性/适宜性相关联时，它才具有生态效果，从而证明高实施成本是合理的，主动预防/减少当前和未来气候变化对生态的影响。
