Alien aquatic macroinvertebrates along the lateral dimension of a large floodplain

Floodplains are simultaneously among the most species-rich and the most threatened ecosystems. Alien aquatic macroinvertebrates contribute to this threat but remain scarcely studied in the lateral dimension of floodplains. We modelled the realized ecological niches of the alien species occurring in 24 floodplain channels of the Rhône River. Environmental variables depicting the ecological niches were associated to the lateral hydrological connectivity and light availability, both being modified during floodplain restoration works. Eight alien species were observed and they demonstrated either ubiquity or a restricted niche, with no link to the date of introduction. For most of them, the main river channel appeared as an important dispersal route in the lateral dimension of the floodplain. An increase of both lateral connectivity and light availability favoured most of the modelled species. Consequently, we recommend that sector-scale restoration programmes preserve varying levels of lateral connectivity for floodplain channels to prevent the expansion of alien aquatic macroinvertebrate

DISPERSE, a trait database to assess the dispersal potential of European aquatic macroinvertebrates

Dispersal is an essential process in population and community dynamics, but is difficult to measure in the field. In freshwater ecosystems, information on biological traits related to organisms’ morphology, life history and behaviour provides useful dispersal proxies, but information remains scattered or unpublished for many taxa. We compiled information on multiple dispersal-related biological traits of European aquatic macroinvertebrates in a unique resource, the DISPERSE database. DISPERSE includes nine dispersal-related traits subdivided into 39 trait categories for 480 taxa, including Annelida, Mollusca, Platyhelminthes, and Arthropoda such as Crustacea and Insecta, generally at the genus level. Information within DISPERSE can be used to address fundamental research questions in metapopulation ecology, metacommunity ecology, macroecology and evolutionary ecology. Information on dispersal proxies can be applied to improve predictions of ecological responses to global change, and to inform improvements to biomonitoring, conservation and management strategies. The diverse sources used in DISPERSE complement existing trait databases by providing new information on dispersal traits, most of which would not otherwise be accessible to the scientific community. Measurement(s): dispersal • movement quality • morphological feature • behavioral quality Technology Type(s): digital curation Factor Type(s): taxon Sample Characteristic - Organism: Arthropoda • Mollusca • Annelida Sample Characteristic - Environment: aquatic biome • freshwater biome Sample Characteristic - Location: Europe Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.1314833

Aquatic macroinvertebrate diversity along the lateral dimension of a large river floodplain : application to the Rhône River restoration

Hydrological connectivity plays a major role in shaping both the habitat conditions and the biota in floodplain ecosystems. Current restoration strategies in large river floodplains often focus on the increase in lateral connectivity of secondary channels. However, the knowledge on the effect of restoration strategies on biodiversity remains limited. In this study, a framework was constructed to assess the level of lateral connectivity in thirteen cut-off channels of two braided sectors of the Rhône River (France). The effect of restoration measures on macroinvertebrate diversity was assessed. Changes were measured within (i.e. alpha diversity) and between channels (i.e. beta diversity). The coherence of the relationships established for some of the richness and trait-based metrics demonstrated their potential for the development of invertebrate-based tools to predict and monitor river-floodplain changes associated with restoration. At the channel scale, an increase in lateral connectivity induced a significant change in macroinvertebrate composition, a decrease of total richness and functional diversity. It is recommended that floodplain-scale restorations focus on diversification of the lateral hydrological connectivity of channels, thereby, conserving a maximum of biodiversity

Etat de référence hydrobiologique de huit annexes fluviales avant restauration (Haut-Rhône français)

1. Dans le cadre du suivi scientifique du programme décennal de restauration écologique et hydraulique du Rhône français, huit annexes fluviales (appelées lônes) ont été étudiées dans les secteurs de Belley et de Brégnier-Cordon afin de fournir un état de référence des milieux avant restauration. 2. La description des milieux a tenu compte des caractéristiques physico-chimiques des eaux, de la teneur en matière organique des sédiments, des communautés de macroinvertébrés aquatiques et de leur habitat. Les macroinvertébrés fournissent une gamme de renseignements sur la qualité, le fonctionnement et les modifications anthropiques du milieu. Une exploration des relations entre la macrofaune et leur habitat a été entreprise afin de modéliser la réponse biologique des macroinvertébrés aux modifications de leur habitat potentiellement induites par la restauration. 3. La macrofaune des huit annexes fluviales a été échantillonnée à deux dates au printemps et en été (2003 ou 2004) à l’aide d’une épuisette au sein d’un quadrat de 50cm par 50cm et la structure de l’habitat a été décrite à l’intérieur de ce même quadrat. Cette opération a été répétée à chaque date en 4 points dans des sites à l’amont et à l’aval de chaque annexe. Les prélèvements d’eau et de sédiment ont été effectués dans les mêmes sites en période hivernale. 4. Après tri, détermination et dénombrement des macroinvertébrés, les données récoltées ont permis de calculer plusieurs métriques exprimant la diversité biologique du milieu (richesse taxonomique, composition faunistique, statut des espèces), ainsi que certains aspects du fonctionnement des milieux (métriques basées sur les traits biologiques et écologiques des taxons). 5. La chimie des eaux et les teneurs en matière organique des sédiments montrent que ces milieux sont très influencés par le cours actif du Rhône et par les terrains agricoles avoisinants, les milieux étudiés sont donc dirigés par des processus allogènes dominants. Ces milieux constituent un ensemble diversifié en terme de composition faunistique. Cette diversification est régie par leur degré de connexion avec le cours actif du Rhône. L’analyse des traits révèle un fonctionnement relativement homogène entre les différentes annexes et au cours des saisons. Des espèces exogènes au système rhodanien (principalement des mollusques) sont présentes dans toutes les annexes, à l’exception d’un seul site. Certaines annexes représentent des sites très diversifiés en Coléoptères ou en Trichoptères. La modélisation des richesses taxonomiques en fonction de la structure de l’habitat conduit à des premiers résultats satisfaisants et encourageants, mais nécessite encore des améliorations. 6. Ce travail offre une description instantanée des milieux et de leur originalité avant restauration. Le suivi après travaux permettra d’entreprendre une description de l’évolution de leurs composantes abiotiques et biotiques et d’évaluer les conséquences des opérations de restauration sur la biodiversité aquatique. Une attention particulière devra être apportée au suivi des espèces exogènes au système rhodanien

Aquatic macroinvertebrate response along a gradient of lateral connectivity in river floodplain channels

Large river floodplains potentially include the full range of freshwater ecosystems from permanently flowing channels to temporary pools and springs. Attempts to restore such complex systems require tools adapted to assess restoration success. In an analysis of invertebrate assemblages in the Rhoˆne River floodplain (France), taxonomic-based indices (rarefied richness and assemblage composition) were compared with functional metrics using trait-based ratios as surrogates of ecosystem processes. Their ability to respond to a gradient of hydrological connectivity was assessed in 7 cut-off channels. The sampling design included 2 sites/channel (upstream and downstream), 4 randomly chosen sampling points (0.530.5- m quadrats)/site, and 2 sampling seasons (spring and summer). Water physicochemical and habitat variables were recorded when invertebrates were sampled. Environmental variables, including water conductance, [NH3-N], submerged vegetation cover, diversity of sediment grain size, and organic matter content of the sediment, were used to construct a synthetic variable describing the hydrological connectivity of each site with the main river channel. A quadratic regression of rarefied taxonomic richness and the connectivity gradient was not quite significant, but assemblage composition was strongly related to the gradient. Four of 8 trait-based metrics were correlated with the connectivity gradient. Values of metrics that are surrogates for top-down control of assemblage structure and habitat stability (based on functional feeding groups) declined along the gradient from disconnected sites to more connected sites. Values of metrics that are surrogates for voltinism and food supply for water-column-feeding fish increased with connectivity. Top-down control and voltinism surrogates suggested a decline in predator–prey relationships and lower habitat stability, respectively, in the more connected sites. Assemblage composition and some of the trait-based metrics were sensitive to a flood that occurred before one of the sampling dates. Some of the trait-based metrics showed potential for explaining floodplain invertebrate assemblages and for monitoring postrestoration conditions in floodplain water bodies. However, the metrics were developed initially for studies of lotic systems and their use in heterogeneous floodplain water bodies will require further investigation, e.g., delineation of reference conditions for trait-based metrics

Short-term impacts of lateral hydrological connectivity restoration on aquatic macroinvertebrates

In floodplain ecosystems, the lateral hydrological connectivity between the main river channel and the secondary channels plays a major role in shaping both the habitat conditions and the macroinvertebrate diversity. Among other threats, human activities tend to reduce the lateral connectivity, which increases floodplain terrestrialization and induces a loss of aquatic biodiversity. Consequently, the restoration of lateral connectivity is of growing concern.We studied four secondary channels of the Rhône floodplain that were subjected either to no restoration or to three different restoration measures (river flow increase only, flow increase plus dredging and flow increase plus reconnection to the river). Macroinvertebrate and environmental data were analysed one year before and during a period of five years after restoration. We expected a progressive increase of lateral connectivity according to the type of restoration. Changes in macroinvertebrate assemblages were predicted to be towards more rheophilic communities and proportionally related to the changes in lateral connectivity. In the reconnected channel, lateral connectivity increased and remained high five years after restoration. In the dredged channel, the immediate increase of the lateral connectivity metric induced by sediment removal was followed by a rapid decrease. In the unrestored channel and the channel only influenced by flow increase, the metric remained constant in time. The macroinvertebrate composition and the rarefied EPT richness changes were proportionally related to the changes in lateral connectivity. Alien species richness and densities increased progressively in all channels after restoration. Our results showed that modifications of the lateral connectivity lead to predictable changes in macroinvertebrate diversity. Synergistic interactions between restoration and longer-term changes (e.g. climatic change, invasion of alien species) encourage long-term monitoring to assess the durability and trends of restoration measures

Do the societal benefits of river restoration outweigh their costs? A cost-benefit analysis

Switzerland plans to restore 4000 km of rivers by 2090. Despite the immense investment costs, river restoration benefits have not been valued in monetary terms, and a cost-benefit analysis (CBA) does not exist for any river restoration project in Switzerland. We apply stated preference methods to elicit public preferences and willingness to pay for restoring two specific but representative river sites. The benefits of restoration are compared with its costs. Upscaling the results to the national level shows that the government budget allocated for river restoration (CHF 1200/m) is insufficient to cover the costs of local restoration projects. However, the surveyed local populations are willing to pay substantially more for restoring rivers in their area of residence than they are legally obliged to do. The CBA results demonstrate that the benefits outweigh the costs in the two case studies, and hence that restoration efforts are justified from an economic point of view. A sensitivity analysis shows that the main results and conclusions do not change when we change some of the key assumptions underlying the CBA

Les coléoptères aquatiques de la zone alluviale du Rhône à Belley (France: Ain, Savoie): inventaire et observations préliminaires sur les effets des mesures de restauration

An inventory was established for adult water beetles on 7 sites of 4 cut-off lateral channels in the upper Rhône floodplain near Belley (Ain, Savoie), in 2004 and 2005. Overall, 89 species were collected, accounting for up to 75 % of the species known to that region. Laccobius albipes, Haliplus mucronatus, H. fulvus, Bidessus delicatulus, Laccobius sinuatus, Ochthebius crenulatus and Agabus brunneus were among the rarest species on a regional scale. Sampling sites contained between 12 and 63 species. The pond-like (disconnected) appearance, the good quality of the ground water, the surrounding rather natural landscape, the presence of well vegetated gently-sloping margins and the very low densities of fishes were positive factors. The effect of the restoration measures was evaluated on one site which was completely refreshed during the winter of 2004–2005. The following spring, the community was found to be severely reduced but then recovered very quickly. This could be explained by the high mobility of these insects and the presence of reservoir-populations nearby. Sites along the channels with steep margins contained few species. Restoration measures should include, besides the re-digging of continuous, flowing lateral channels, the digging of series of isolated, permanent or temporary ponds

Large river floodplain restoration: predicting species richness and trait responses to the restoration of hydrological connectivity

1. Floodplains are species-rich environments often strongly impacted by human activities. In particular, the negative effects of progressive and rapid disconnection of secondary channels have led to restoration programmes and a growing interest in restoration ecology. 2. Current restoration strategies in large river floodplains focus on the macroinvertebrate response related to the increases in lateral connectivity of the secondary channels. We constructed a framework to assess a gradient of hydrological connectivity among 13 secondary channels and the main channel of a large river, and we modelled the response of a set of macroinvertebrate metrics to this gradient. Comparisons between predicted and observed metrics in restored channels allowed us to measure the effect of an increase in the hydrological connectivity on the biological characteristics of macroinvertebrate assemblages. 3. The pre-restoration framework enabled a clear ordering of channels into three types according to levels of hydrological connectivity. Rarefied richness and species traits, responding to the connectivity gradient, showed a net difference between disconnected channels and the main river channel. We were able to highlight a predation–colonization trade-off along the gradient of hydrological connectivity with a maximum colonization potential in the most connected channels. 4. Post-restoration sampling showed deviations of the restored channels from their expected ecological state. A large proportion of colonizers were favoured by the restoration operations and non-native species occurred in the restored channels. 5. Synthesis and applications. Macroinvertebrate biodiversity in large river floodplains is shaped by lateral hydrological connectivity. Increasing hydrological connectivity led to an increase in colonization rate. One year after restoration, the increase in lateral connectivity had shifted the restored sites away from the predicted state. This unpredictability is, in part, a consequence of the rapid colonization by non-native species of new habitats created by the restoration measures. We recommend that floodplain-scale restoration should focus on diversification of the hydrological connectivity of channels, thereby conserving a maximum of functional characteristics in macroinvertebrate communities