Article

Analysis of functional traits in reconfigured channels: Implications for the bioassessment and disturbance of river restoration

Journal of the North American Benthological Society (Impact Factor: 2.71). 03/2009; 28(1):80-92. DOI: 10.1899/07-122.1

ABSTRACT

Channel reconfiguration is a popular but controversial approach to river restoration, and ecological responses to channel reconfiguration have not been rigorously assessed. We compared physical-habitat variables, taxonomic and functional-trait diversities, taxonomic composition, and functional-trait abundances between 24 pairs of upstream (control) and downstream reconfigured (restored) reaches in 3 catchment land uses (urban, agricultural, rural) across the North Carolina Piedmont. We asked how environmental filters and functional species traits might provide insight to biological responses to restoration. Taxonomic and functional-trait differences between control and restored reaches suggest that restoration affected aquatic assemblages only in agricultural and rural catchments. Our results highlight 2 important aspects of channel reconfiguration as a restoration practice. First, responses to restoration differ between agricultural/rural and urban catchments, possibly because of modified hydrological regimes caused by urbanization. Second, we find evidence that channel reconfiguration disturbs food and habitat resources in stream ecosystems. Taxa sensitive to disturbance were characteristic of control reaches, whereas insensitive taxa were characteristic of restored reaches. Abundances of traits related to reproduction (voltinism, development, synchronization of emergence, adult life span), mobility (occurrence in drift, maximum crawling rate, swimming ability), and use of resources (trophic and habitat preferences) differed significantly between control and recently restored reaches. Our results suggest that taxa in restored habitats are environmentally selected for traits favored in disturbed environments. Our work suggests how functional-trait approaches could benefit the practice of river restoration when used to target restoration activities and to develop informed expectations regarding recovery following restoration activities.

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    • "In the last decade, however, trait-based rather than taxonomy-based approaches to biomonitoring have been increasingly advocated (Menezes, Baird & Soares, 2010; Statzner & Beche, 2010). Traits are defined as specific and measurable properties of an organism (McGill et al., 2006), related to, for example, mobility, reproduction, life history and use of resources (Tullos et al., 2008; Verberk, Siepel & Esselink, 2008b; Pollard & Yuan, 2010). The traits of an organism define its relationships to the biotic and abiotic environment. "
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    ABSTRACT: 1. Biological traits of organisms are expected to provide increased mechanistic understanding of species–environment relationships. Linking traits to environmental conditions is, however, not straightforward, as traits are interconnected within species and can affect the adaptive value of each other. The aim of our study was to evaluate the importance of these trait interrelationships for understanding environmental responses of freshwater macroinvertebrates. 2. To this end, we investigated whether environmental responses of macroinvertebrates sharing a given trait were consistent or differed according to their taxonomy or to their other traits. We divided the macroinvertebrates into groups based on single traits (49 single-trait modalities), on taxonomy (10 orders) and on their overall trait profile (10 trait profile groups [TPGs], defined using self-organising maps clustering). Abundances of each of these 69 groups were related to 24 environmental variables using boosted regression tree (BRT) modelling, to assess the environmental responses of single traits, orders and TPGs. 3. Cross-validated predictive power (R2) of the BRT models ranged from < 1% to 38%. Environmental responses of macroinvertebrates sharing a given trait were inconsistent and varied according to order and/or TPG. Single-trait responses often reflected the responses of the most abundant taxonomic group expressing the trait, suggesting that analysis of trait responses simply revealed patterns in habitat use by the most abundant species and not necessarily mechanistic relationships. 4. Further, taxa from the same TPG (hence showing large overlap in their traits) but belonging to different orders showed different environmental responses. This indicates that the order a taxon belongs to confers unique information related to its evolutionary history that was not captured by our 49 trait modalities. However, groupings by orders cannot replace trait-based approaches, since TPGs also revealed differences in trait profiles within some orders, which were associated with different environmental responses. 5. Our results highlight the importance of considering multiple rather than single traits when linking macroinvertebrates to environmental variables, including the potential information conveyed by evolutionary history.
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    • "The use of instream structures in warmwater streams (Thompson, 2005), particularly in an effort to stabilize channel reconfiguration projects (Miller and Kochel, 2013), has often been followed by structural failure or channel instability. Stream restoration outcomes for nonsalmonid fishes (Roni et al., 2008) and macroinvertebrates (Haase et al., 2012; Miller et al., 2010; Palmer et al., 2009; Sundermann et al., 2011; Tullos et al., 2006 Tullos et al., , 2009) are often weak or undetectable. Some of the key reasons for failure include @BULLET setting overambitious goals at the outset, @BULLET poor planning, @BULLET failing to establish an agreed 'vision' at the outset of a project to direct restoration of biophysical and ecological processes within the practical constraints of outline and detailed design, @BULLET too much focus on the reach rather than the watershed or catchment scale (Haase et al., 2012), @BULLET choosing the wrong technique or approach for a particular environment (or river type) under consideration (Simon et al., 2007), @BULLET neglecting to monitor and assess a project and to apply adaptive management where appropriate, @BULLET losing the faith or backing of stakeholders. "
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    ABSTRACT: Rivers and streams worldwide have degraded ecosystems due to a wide range of anthropomorphic drivers and pressures. Recent decades have seen the rise of an interdisciplinary science of stream restoration, which seeks to rehabilitate damaged systems to yield degraded or destroyed ecosystem services. About $1 billion is expended annually on such projects in the United States alone, exclusive of several extraordinary projects that target whole regions or long reaches of larger rivers. The best approaches for restoring rivers are far from settled, as few projects have been sufficiently monitored to positively document effects. Future efforts should feature monitoring and sharing of information, working at larger spatial scales, and restoration of key processes rather than forms.
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    • "The excessive use of pebble and gravel should be abandoned and replaced by generating a more natural substrate distribution, mimicking those of reference streams. More investigations should be carried out with focus on developing biological indicators of habitat improvements [62], [63]. Macroinvertebrates are an important organism/functional group in streams, but their mixed response to restoration and habitat improvement suggests than other organism groups should be included. "
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