The ecological restoration of large rivers needs science‐based, predictive tools meeting public expectations: an overview of the Rhône project

Abstract

Summary Effective environmental management needs models that reliably predict quantitative ecological changes as a function of restoration effort (e.g. cost) and meet expectations of stakeholders. Principal threats to large rivers are linked to human‐caused modifications of discharge and morphology of channels and floodplains. However, comprehensive large‐scale tests of the reliability of models predicting ecological consequences of restoring these elements are still lacking. Following a governmental decision, water managers, local authorities and the ‘Compagnie Nationale du Rhône’ financed a scientific programme to develop, test and subsequently use predictive models to assess the restoration (particularly minimum flow increases and reconnections of floodplain channels with the main channel) of eight regulated reaches of the French Rhône River. This approach was fostered by (i) the existence of local initiatives aimed at the ecological improvement of the Rhône; (ii) a history of interactions based on trust among stakeholders; and (iii) knowledge provided by a large interdisciplinary research group that studied the Rhône for two decades before the programme started in 1998. This Special Issue synthesises the insights gained over recent decades of research during which four river reaches (total length 47 km) were restored since 1999. It contains 11 articles including this overview. One article relates physical habitats in the floodplain to river hydrology and morphology; five articles test predictive models linking changes in habitat conditions to changes in taxa abundance, community metrics and biological traits of macroinvertebrates and fish; and four articles address the effects of restoration in larger contexts (long‐term community trends, optimisation of sampling strategies, social processes and bioindication). We describe the Rhône restoration project, explain the conceptual framework used to predict the effects of restoration on river biota and describe the contents of the Special Issue, the main results and their implications. The Rhône restoration led to more lotic and diverse aquatic communities and renewed social links with the river. When reliable pre‐restoration data are available, simple habitat models can be used to predict quantitative ecological changes as a function of restoration effort. The project illustrates the need to describe changes in hydraulic conditions in studies of physical river restoration and shows the effort required for a powerful assessment of restoration effects.

Introduction: The ecology of a river floodplain and the Emiquon preserve

“…Thus, large-scale projects are being undertaken in many parts of the world to recover natural services while also maintaining commercial uses such as navigation and water supply (Bernhardt et al, 2007;Lamouroux et al, 2015). Studies of the Emiquon Preserve as part of the Illinois River system make a significant contribution to understanding large river floodplain restoration in the central United States region, and have implications for restoration in critically threatened river ecosystems throughout the world.…”

Shifts in mollusc traits following floodplain reconnection: Testing the response of functional diversity components

“…flow restoration) or measures reconnecting aquatic floodplain habitats (like floodplain channels) are relatively well documented (e.g. Gallardo, Gasc on, Garc ıa, & Com ın, 2009; Lamouroux, Gore, Lepori, & Statzner, 2015; and studies therein; Reckendorfer, Baranyi, Funk, & Schiemer, 2006), knowledge about the actual success of semi-terrestrial floodplain restoration measures is scarce, especially in terms of the functional effects on the plant and animal communities in those intermittent habitats (Español et al, 2015). It remains to be tested whether floodplain reconnection sustainably recovers communities with trait compositions typical for floodplain ecosystems.…”

Application of key ecological attributes to assess early restoration of river floodplain habitats: a case study

“…Fragmentation of river channels by navigation dams and reduced hydrologic connectivity between floodplains and the main river channel due to levees are two primary impacts that threaten ecological integrity of these working rivers (e.g., Dynesius & Nilsson, 1994;Gore & Shields, 1995;Lamouroux et al, 2015). Hydrologic alteration and habitat degradation accompanying this infrastructure are two major drivers that have placed riverine floodplains among the most globally endangered ecosystems such that up to 90% of floodplains in Europe and North America have lost many of their natural ecological functions (Sparks, 1995;Tockner & Stanford, 2002).…”

“…As such, frameworks have been developed for large river restoration projects that link strategic management with monitoring and hypothesis testing (Koebel 1995;Rogers & Biggs, 1999;Davies et al, 2010;Lamouroux et al, 2015), and empirical research that measures effectiveness of restoration strategies continues to increase (Wortley et al, 2013;Palmer et al, 2014). Monitoring programs are integral to these frameworks by providing pivotal data that inform the restoration assessments that are subsequently integrated into management decisions.…”