University of Koblenz-Landau, Institute for Integrated Natural Sciences, Koblenz, Germany.
Bürogemeinschaft für fisch- und gewässerökologische Studien, Marburg, Germany.
Sci Total Environ. 2021 Feb 10;755(Pt 1):142547. doi: 10.1016/j.scitotenv.2020.142547. Epub 2020 Sep 28.
Eutrophication seriously threatens the ecological quality and biodiversity of running waters. In nutrient-enriched streams and shallow rivers, eutrophication leads to excessive periphyton growth and, in turn, biological clogging, oxygen depletion in the hyporheic zone and finally a reduction in the hyporheic habitat quality. Top-down control of the food-web by manipulating fish stocks, similar to the biomanipulation successfully applied in lakes, offers a promising approach to mitigating the effects of eutrophication in shallow rivers, especially those in which major reductions in nutrient input are not feasible. We conducted a reach-scale experiment over 4 years in a medium-sized eutrophic river to assess whether the top-down effects of two important large European cypriniform fish species, herbivorous common nase (Chondrostoma nasus) and omnivorous European chub (Squalius cephalus), would mitigate the effects of eutrophication. The enhancement of fish stocks was expected to reduce biological clogging, via the top-down control of periphyton by benthic grazing and enhanced bioturbation, thus increasing oxygen availability in the hyporheic zone as well as water exchange between the surface water and the hyporheic zone. As expected, enhancing the stocks of nase and chub increased both oxygen availability and vertical exchange flux of water in the upper layer of the hyporheic zone. However, periphyton biomass (chlorophyll a) was significantly reduced only in deeper pool habitat. Thus, while experimental biomanipulation in a shallow river significantly mitigated the effects of eutrophication in the hyporheic zone, top-down effects on periphyton biomass were rather small. Overall, to our knowledge, our results provide first evidence that the biomanipulation achieved by enhancing herbivorous and omnivorous fish stocks has the potential to mitigate the effects of eutrophication in medium-sized European rivers.
富营养化严重威胁着流水的生态质量和生物多样性。在富营养化的溪流和浅河中，富营养化导致过量的周丛生物生长，进而导致生物堵塞、底层区缺氧，最终降低底层生境质量。通过操纵鱼类种群对食物网进行自上而下的控制，类似于已成功应用于湖泊的生物操纵，为缓解浅水河流（特别是那些减少营养输入不可行的河流）的富营养化影响提供了一种很有前景的方法。我们在一条中型富营养化河流中进行了为期 4 年的河道尺度实验，以评估两种重要的大型欧洲鲤科鱼类（食草的圆吻鲴和杂食性的欧欧鳊）的自上而下的影响是否会减轻富营养化的影响。增加鱼类种群数量有望通过底栖摄食和增强生物搅动对周丛生物的自上而下的控制来减少生物堵塞，从而增加底层区的氧气供应以及地表水和底层区之间的水交换。正如预期的那样，增加圆吻鲴和欧欧鳊的种群数量增加了底层区上层的氧气供应和水的垂直交换通量。然而，只有在较深的池塘生境中，周丛生物量（叶绿素 a）才会显著减少。因此，虽然在浅水河流中的实验性生物操纵显著减轻了底层区富营养化的影响，但对周丛生物量的自上而下的影响相对较小。总的来说，据我们所知，我们的结果首次提供了证据，表明通过增加草食性和杂食性鱼类种群来实现的生物操纵有可能减轻欧洲中型河流的富营养化影响。
