Effects of re‐braiding measures on hydromorphology, floodplain vegetation, ground beetles and benthic invertebrates in mountain rivers

Abstract

Summary 1.Medium-sized and large mountain rivers are among the most degraded river types in Europe and numerous river restoration projects are currently carried out to achieve 'good ecological status'. Surprisingly little is known about the effects of river restoration measures on aquatic and terrestrial organisms. We investigated the effects of restoration on hydromorphology, floodplain vegetation, ground beetles and benthic invertebrates of Central European mountain rivers by comparing seven restored, multiple-channel sections with seven nearby non-restored, straight sections. (134) were taken per habitat type and section. Two hydromorphological metrics and 13 biotic metrics were calculated. 3. The number of floodplain mesohabitats was significantly higher in restored sections, but there was no significant effect on the number of aquatic microhabitats. Floodplain vegetation reacted most strongly to restoration, with more vegetation assemblages and higher number of species in restored sections. The number of ground beetle species also increased, but there was no effect on number of species or diversity of benthic invertebrates. 4. Habitat composition and assemblages were compared by cluster analysis. When using mesohabitat data, restored vs. non-restored sections clustered to separate groups, while the use of aquatic microhabitat data produced mixed groups. Floodplain vegetation data clustered in restored and non-restored sections. For benthic invertebrates, the restored and non-restored sections of each individual river were always clustered together. Ground beetle assemblages responded more strongly to restoration than benthic invertebrates but less than floodplain vegetation. 5. Synthesis and applications. River restoration measures which re-created multiple-channel patterns differ in their effect on floodplain vegetation, ground beetles and benthic invertebrates. The strong increase in the number of floodplain vegetation species is due to the creation of additional habitats, while riparian ground beetles react mainly to the increased availability of gravel bars. The lack of response of benthic invertebrates to restoration measures is due to the comparatively small changes in aquatic microhabitat composition. Our results indicate that floodplain habitats react more strongly to re-braiding as a restoration measure compared to in-stream habitats and that floodplain communities might be best suited to judge the immediate effects of restoration.

Hydromorphological restoration stimulates river ecosystem metabolism

“…Recent monitoring and evaluation of restoration projects report positive effects on hydromorphology and habitat composition (Jähnig et al, 2009(Jähnig et al, , 2010Poppe et al, 2016). Similarly, we found greater habitat complexity of restored reaches, as indicated by wider and more diverse river channels.…”

“…The majority of restoration measures is implemented at the reach scale, covering short river stretches typically of 1 km or less (Bernhardt et al, 2005;Palmer et al, 2014). A variety of reach-scale measures have been implemented (Lorenz et al, 2012): for instance, restoration activities along mountainous rivers in central Europe mainly targeted re-braiding and widening of streams, leading to greater habitat and hydrodynamic heterogeneity (Jähnig et al, 2009;Poppe et al, 2016). In combination with other characteristics of the river ecosystem -e.g., light, organic matter, nutrient availability, temperature, hydrologic and disturbance regimes -such hydromorphological changes likely affect biological community composition and ecosystem functioning, including ecosystem metabolism (Bernot et al, 2010;.…”

Lessons from practice: assessing early progress and success in river rehabilitation

“…The variable response of different ecosystem elements also poses challenges for rehabilitation monitoring. River restoration effects reveal spatial and temporal differences in the response of organism groups (Jahnig et al, 2009). In the Kissimmee River project in Florida, it was projected that aquatic plants would recover in 3-8 years, invertebrates in 10-12 years and fish in 12-20 years (Trexler, 1995).…”

The Importance of Providing Multiple-Channel Sections in Dredging Activities to Improve Fish Habitat Environments

“…Multiple-channel rivers are complex systems resulting from the interaction of various discharge regimes and sediment loads, so they can produce complex hydromorphological conditions [18]. Therefore, multiple-channel rivers have higher diversity as compared to single-channel rivers [2,29,32].…”

“…The caught fish were identified and standard The aims of this study are (1) to compare the differences in habitat between multiple-and single-channel sections; (2) to compare the differences in fish assemblages between multiple-and single-channel sections; (3) to compare the differences in the habitat environments inhabited by fish in both multiple-and single-channel sections; (4) to compare the differences in habitat use by fish species in both multiple-and single-channel sections; (5) to explore which environmental factors have the most influence on fish species. As described above, researchers in the past have studied the differences between multiple-and single-channel sections based on restoration [2,32]. Second, only a few studies have explored the relationship between environmental factors and fish assemblages in multiple-channel sections.…”