1. The hyporheic zone is an important habitat for benthic invertebrates and early‐developmental stages of gravel spawning fish. However, the eutrophication of running waters and, in turn, the excessive periphyton biomass leads to its biological clogging. The result of these processes is oxygen depletion and a reduction in the habitat quality of the hyporheic zone.
2. This study assessed whether top‐down effects of two important European river fish species, the large herbivorous cypriniform common nase (Chondrostoma nasus, L.) and the large omnivorous cypriniform European chub (Squalius cephalus, L.), can reduce eutrophication effects in the hyporheic zone. A 4‐week mesocosm‐based field experiment in a eutrophic river was conducted using cage enclosures stocked or not with either nase or chub.
3. The top‐down control of periphyton was expected to reduce biological clogging and thereby increase oxygen availability in the hyporheic zone. Accordingly, we hypothesised that in enclosures stocked with either fish the concentrations of dissolved oxygen in the hyporheic zone would be higher and the periphyton biomass would be lower than in enclosures without fish stocking.
4. Hyporheic oxygen concentrations were significantly higher in enclosures stocked with either nase or chub than in enclosures without fish stocking. However, periphyton ash‐free dry mass was significantly reduced only in enclosures stocked with nase, not in those stocked with chub. Thus, the positive effects of nase and chub on hyporheic oxygen availability were caused by different mechanisms.
5. Our results demonstrate that nase and chub can reduce eutrophication effects in the hyporheic zone of running waters. Hence, protecting and enhancing stocks of herbivorous and omnivorous fish will contribute to restoring the hyporheic zone in efforts to preserve biodiversity in eutrophic rivers.

中文翻译：

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流水中的楔形鱼类减少了富营养化河流中的低氧耗氧

1. 泄水带是底栖无脊椎动物和卵石产卵早期阶段的重要栖息地。然而，自来水的富营养化以及反过来的过度浮游生物量导致其生物堵塞。这些过程的结果是耗氧，并降低了流变带的栖息地质量。
2. 本研究评估的两个重要的欧洲河流鱼类，大型食草cypriniform共同ASE（λ自上而下的作用是否Chondrostoma鲚，L）和大杂食性cypriniform欧鲢（Squalius法罗斯， L.） ，可以减少水体富营养化的影响排液区。在富营养化河流中进行了为期4周的中观基于田间试验，使用了装有或不装有nase或chub的网箱围栏。
3. 自上而下控制周生植物有望减少生物阻塞，从而增加流变区的氧气供应。因此，我们假设与没有鱼类种群的圈养相比，在放养两种鱼类的圈养圈中，在流变带中溶解氧的浓度会更高，而浮游生物的生物量会更低。
4. 装有nase或chub的圈养箱中的低氧浓度明显高于没有鱼类放养的圈养箱。但是，仅在装有nase的围栏中，而非附有的围栏中，无浮游生物的无灰干重才显着减少。因此，nase和chub对流血性氧气供应的积极影响是由不同的机制引起的。
5. 我们的结果表明，nase和chub可以减少自来水流域的富营养化作用。因此，保护​​和增加草食性和杂食性鱼类的种群将有助于恢复水生流失带，以保护富营养化河流中的生物多样性。