Contrasting the roles of section length and instream habitat enhancement for river restoration success: a field study of 20 European restoration projects

Abstract

1. Restoration of river hydromorphology often has limited detected effects on river biota. One frequently discussed reason is that the restored river length is insufficient to allow populations to develop and give the room for geomorphological processes to occur. 2. We investigated ten pairs of restored river sections of which one was a large project involving a long, intensively restored river section and one represented a smaller restoration effort. The restoration effect was quantified by comparing each restored river section to an upstream nonrestored section. We sampled the following response variables: habitat composition in the river and its floodplain, three aquatic organism groups (aquatic macrophytes, benthic invertebrates and fish), two floodplain-inhabiting organism groups (floodplain vegetation, ground beetles), as well as food web composition and land-water interactions reflected by stable isotopes. 3. For each response variable, we compared the difference in dissimilarity of the restored and nearby non-restored section between the larger and the smaller restoration projects. In a second step, we regrouped the pairs and compared restored sections with large changes in substrate composition to those with small changes. 4. When comparing all restored to all non-restored sections, ground beetles were most strongly responding to restoration, followed by fish, floodplain vegetation, benthic invertebrates and aquatic macrophytes. Aquatic habitats and stable isotope signatures responded less strongly. 5.When grouping the restored sections by project size, there was no difference in the response to restoration between the projects targeting long and short river sections with regard to any of the measured response variables except nitrogen isotopic composition. In contrast, when grouping the restored sections by substrate composition, the responses of fish, benthic invertebrates, aquatic macrophytes, floodplain vegetation and nitrogen isotopic composition were greater in sections with larger changes in substrate composition as compared to those with smaller changes. 6. Synthesis and applications. The effects of hydromorphological restoration measures on aquatic and floodplain biota strongly depend on the creation of habitat for aquatic organisms, which were limited or not present prior to restoration. These positive effects on habitats are not necessarily related to the restored river length. Therefore, we recommend a focus on habitat enhancement in river restoration projects.

Evaluating good-practice cases for river restoration across Europe: context, methodological framework, selected results and recommendations

“…In the 20 restoration projects investigated in REFORM, the effect of restoration on richness and diversity was higher for terrestrial and semi-aquatic compared to aquatic organism groups. Restoration had no or only little effect on species richness or diversity of macroinvertebrates and fish (see Verdonschot et al and Schmutz et al, 2015), while restoration had a clear positive effect on richness or diversity of organism groups inhabiting river banks or adjacent shallow shoreline habitats like ground beetles and macrophytes (see Januschke & Verdonschot as well as Ecke et al, 2015). However, the most floodplain-related organism group (floodplain vegetation) showed no increase in total richness or diversity (see Göthe et al, 2015), in contrast to other studies reporting a significantly higher richness in restored compared to degraded sections (Jähnig et al, 2009;Januschke et al, 2011).…”

A Long-Term Study of Ecological Impacts of River Channelization on the Population of an Endangered Fish: Lessons Learned for Assessment and Restoration

“…These efforts inform project-specific management questions but can also, if properly designed and analyzed, provide valuable insights to enhance the efficacy of future assessment and management actions. In this paper, we draw from previous syntheses of river restoration [5][6][7][8][9][10][11][12][13][14] to show how the proper application of scientific approaches can lead to more effective and informative assessment and restoration efforts.…”

Hydromorphological restoration stimulates river ecosystem metabolism

“…Based on legislative frameworks such as the EU Water Framework Directive (WFD) and the Clean Water Act in the United States, large investments have been made to restore rivers. In Europe, degraded river hydromorphology is considered one of the central impacts to the ecological status of rivers (EEA, 2012;Hering et al, 2015). For example, the German national river habitat survey, which evaluates 31 hydromorphological parameters for 100 m river sections, concluded that the majority of German rivers are severely degraded (Gellert et al, 2014;UBA, 2013).…”

“…Recently, increasing attention has also been given to the response of floodplain organisms (e.g., Hering et al, 2015;Göthe et al, 2016;Januschke and Verdonschot, 2016), while functional characteristics, i.e., the rates and patterns of ecosystem processes, have rarely been addressed. Ecosystem functions are life-supporting processes that are directly linked to ecosystem services, i.e., the benefits people obtain from the environment (Palmer and Filoso, 2009).…”