Abstract
The widespread degradation of lotic ecosystems has prompted extensive river restoration efforts globally, but many studies have reported modest ecological responses to rehabilitation practices. The functional properties of biotic communities are rarely examined within post-project appraisals, which would provide more ecological information underpinning ecosystem responses to restoration practices and potentially pinpoint project limitations. This study examines macroinvertebrate community responses to three projects which aimed to physically restore channel morphologies. Taxonomic and functional trait compositions supported by widely occurring lotic habitats (biotopes) were examined across paired restored and non-restored (control) reaches. The multivariate location (average community composition) of taxonomic and functional trait compositions differed marginally between control and restored reaches. However, changes in the amount of multivariate dispersion were more robust and indicated greater ecological heterogeneity within restored reaches, particularly when considering functional trait compositions. Organic biotopes (macrophyte stands and macroalgae) occurred widely across all study sites and supported a high alpha (within-habitat) taxonomic diversity compared to mineralogical biotopes (sand and gravel patches), which were characteristic of restored reaches. However, mineralogical biotopes possessed a higher beta (between-habitat) functional diversity, although this was less pronounced for taxonomic compositions. This study demonstrates that examining the functional and structural properties of taxa across distinct biotopes can provide a greater understanding of biotic responses to river restoration works. Such information could be used to better understand the ecological implications of rehabilitation practices and guide more effective management strategies.
Highlights
A significant number of river restoration projects aiming to rehabilitate degraded lotic ecosystems have been carried out globally (Ormerod 2004; Bernhardt et al 2007; Miller et al 2010; Kail et al 2015)
This study examines macroinvertebrate taxonomic and functional trait responses to three river restoration projects conducted within the River Tame (East and West Midlands, UK), a historically polluted and physically modified catchment
PERMANOVA highlighted that control and restored reaches possessed significantly different multivariate locations for both taxonomic (F = 4.05, p = ≤0.001) and functional trait compositions (F = 5.17, p ≤ 0.001), but this only accounted for 6% (r2 = 0.06) and 7% (r2 = 0.07) of the statistical variance, respectively
Summary
A significant number of river restoration projects aiming to rehabilitate degraded lotic ecosystems have been carried out globally (Ormerod 2004; Bernhardt et al 2007; Miller et al 2010; Kail et al 2015). Limited ecological responses to river restoration works have been attributed to a multitude of reasons, including socio-economic constraints (Langford and Shaw 2014) and inappropriate spatial scaling of projects (Miller et al 2010). Palmer et al (2010) reviewed 78 river restoration projects globally and found no association between habitat heterogeneity and the richness of macroinvertebrate taxa, suggesting that existing restoration techniques have been inappropriate in facilitating ecological recovery. Quantifying changes in taxonomic richness after restoration works may not necessarily be a suitable biological end point (besides being consistently reported within post-project appraisals) and the need to report functional responses to river restoration efforts is being increasingly advocated (e.g., Dolédec et al 2015; Kail et al 2015)
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