River restoration success depends on the species pool of the immediate surroundings

Abstract

Previous studies evaluating the success of river restorations have rarely found any consistent effects on benthic invertebrate assemblages. In this study, we analyzed data from 24 river restoration projects in Germany dating back 1 to 12 years and 1231 data sets from adjacent river reaches that lie within 0-5, 5-10, and 10-15 km rings centered on the restored sites. We calculated restoration success and recolonization potential of adjacent river reaches based on stream-type-specific subsets of taxa indicative for good or bad habitat quality. On average, the restorations did not improve the benthic invertebrate community quality. However, we show that restoration success depends on the presence of source populations of desired taxa in the surrounding of restored sites. Only where source populations of additional desired taxa existed within a 0-5 km ring around the restored sites were benthic invertebrate assemblages improved by the restoration. Beyond the 5-km rings, this recolonization effect was no longer detected. We present here the first field results to support the debated argument that a lack of source populations in the areas surrounding restored sites may play an important role in the failure to establish desired invertebrate communities by the means of river restorations. In contrast, long-range dispersal of invertebrates seems to play a subordinate role in the recolonization of restored sites. However, because the surroundings of the restored sites were far from good ecological quality, the potential for improvement of restored sites was limited.

Acid mine drainage and stream recovery: Effects of restoration on water quality, macroinvertebrates, and fish

“…Biological recovery can be highly variable and contingent on factors other than water chemistry (e.g. Louhi et al, 2011;Sundermann et al, 2011, Johnson et al, 2014, but the results of our study also show large improvements in most aspects of the biological community of our study system. Local macroinvertebrate taxonomic richness, mean macroinvertebrate density, mean live biomass, and Shannon Wiener diversity index were all significantly higher in 2011 (post-restoration) than in 1967 (pre-restoration), and regional taxonomic richness throughout the watershed more than doubled after remediation efforts were implemented.…”

Trophic organization and fish assemblage structure as disturbance indicators in headwater streams of lower Sorocaba River basin, Sao Paulo, Brazil

“…In addition, it can provide allochthonous organic matter inputs (e.g., large woody debris, leaf litter, terrestrial insects) that serve as food and habitat for stream organisms, as fish communities (Pusey & Arthington, 2003;Casatti et al, 2009). At last, it is essential to ensure that these streams are connected with preserved or less disturbed ones that might act as native species sources, favoring species dispersion and the establishment of long term populations (Sundermann et al, 2011). In synthesis, our results indicate changes in fish assemblages with stream environmental homogenization pointed out by differences in species diversity, richness and trophic groups composition.…”

Severity Multipliers as a Methodology to Explore Potential Effects of Climate Change on Stream Bioassessment Programs

“…In addition, we did not consider adaptive potential of species or species gains. For the latter, we had no information on surrounding species pools for each site, which are a source of primary colonizers in restoration projects [42,43]. Arguably, generalist taxa and/or invasive species would be most likely to immigrate [44,45], in turn reducing ecological quality.…”