The macroinvertebrate seedbank promotes community persistence in temporary rivers across climate zones

1. Aquatic macroinvertebrates inhabiting temporary rivers are typically described as having low resistance to riverbed drying. However, little research has examined the ‘seedbank’ within dry riverbed sediments, which comprises aquatic life stages that survive in dewatered sediments and from which active organisms may develop only after surface water returns. 2. We synthesised published and unpublished data from studies that had experimentally rehydrated sediments collected from dry riverbeds, to establish the importance of the seedbank in promoting macroinvertebrate community resistance. Studies from across climate zones were included, to examine seedbank importance in relation to environmental harshness and, in particular, sediment moisture. We also assessed the importance of the seedbank relative to alternative habitats promoting persistence of the flowing river (FR) assemblage. We predicted that the proportion of the FR assemblage present in rehydrated sediments (RS) would decrease with environmental harshness, due to conditions within the sediments becoming less conducive to the survival of biota. 3. A negative relationship between the proportion of FR taxa present in RS and harshness was observed, and this contributed to a reduction in the compositional similarity of FR and RS assemblages as harshness increased. Significant positive correlations were identified between sediment moisture content and macroinvertebrate community metrics (density and taxon richness) in some systems. 4. Habitats external to the dry reach, which contribute to community resilience, were invariably inhabited by a greater number of FR taxa than rehydrated sediments. However, rehydrated sediments included several FR taxa that were not found in any other habitats during the dry phase, including families of Coleoptera and Diptera. 5. Our results indicate the importance of the seedbank as a resistance mechanism for temporary river macroinvertebrates. With climate change scenarios predicting an increase in riverbed drying, maintaining habitats that facilitate the persistence of instream communities during dry phases is an increasing priority. We identified strong relationships between sediment moisture and taxon richness, and river management and rehabilitation activities should therefore aim to retain moisture in drying sediments, by manipulating parameters such as riparian shading

Benthic and hyporheic invertebrate community responses to seasonal flow recession in a groundwater-dominated stream

Natural hydrological variability in lotic ecosystems can include prolonged periods of flow recession. A reduction in discharge is accompanied by abiotic changes in benthic and hyporheic habitats, often including reductions in s habitat availability. Whilst the benthic invertebrate community response to low flows is well documented, little research has considered how the composition of the community within the hyporheic zone is affected. We examined benthic and hyporheic invertebrate community composition during flow recession in a temperate karst stream, at sites with contrasting historic flow permanence regimes. Changes in the benthic invertebrate community composition primarily reflected changes in habitat availability associated with discharge variability; in particular, the population density of the dominant amphipod, Gammarus pulex, increased as the area of submerged benthic sediments declined. Concurrent significant increase in the hyporheic abundance of G. pulex, and moderate increase in the proportion of the total G. pulex population inhabiting the hyporheic zone were recorded. It is postulated that G. pulex migrated into the hyporheic zone to reduce exposure to intensifying biological interactions in the benthic sediments. Increase in the hyporheic abundance of G. pulex was particularly pronounced at sites with historic intermittent flow, which could be attributed to downwelling stream water dominating vertical hydrologic exchange. The increase in G. pulex abundance reduced community diversity in the benthic sediments, but had no apparent detrimental effects on the hyporheic invertebrate assemblages

IRBAS: An online database to collate, analyze, and synthesize data on the biodiversity and ecology of intermittent rivers worldwide

International audienceKey questions dominating contemporary ecological research and management concern interactions between biodiversity, ecosystem processes, and ecosystem services provision in the face of global change. This is particularly salient for freshwater biodiversity and in the context of river drying and flow-regime change. Rivers that stop flowing and dry, herein intermittent rivers, are globally prevalent and dynamic ecosystems on which the body of research is expanding rapidly, consistent with the era of big data. However, the data encapsulated by this work remain largely fragmented, limiting our ability to answer the key questions beyond a case-by-case basis. To this end, the Intermittent River Biodiversity Analysis and Synthesis (IRBAS; http://irbas.cesab.org) project has collated, analyzed, and synthesized data from across the world on the biodiversity and environmental characteristics of intermittent rivers. The IRBAS database integrates and provides free access to these data, contributing to the growing, and global, knowledge base on these ubiquitous and important river systems, for both theoretical and applied advancement. The IRBAS database currently houses over 2000 data samples collected from six countries across three continents, primarily describing aquatic invertebrate taxa inhabiting intermittent rivers during flowing hydrological phases. As such, there is room to expand the biogeographic and taxonomic coverage, for example, through addition of data collected during nonflowing and dry hydrological phases. We encourage contributions and provide guidance on how to contribute and access data. Ultimately, the IRBAS database serves as a portal, storage, standardization, and discovery tool, enabling collation, synthesis, and analysis of data to elucidate patterns in river biodiversity and guide management. Contribution creates high visibility for datasets, facilitating collaboration.The IRBAS database will grow in content as the study of intermittent rivers continues and data retrieval will allow for networking, meta-analyses, and testing of generalizations across multiple systems, regions, and taxa

Biomonitoring of intermittent rivers and ephemeral streams in Europe: current practice and priorities to enhance ecological status assessments

Intermittent rivers and ephemeral streams (IRES) are common across Europe and dominate some Mediterranean river networks. In all climate zones, IRES support high biodiversity and provide ecosystem services. As dynamic ecosystems that transition between flowing, pool, and dry states, IRES are typically poorly represented in biomonitoring programmes implemented to characterize EU Water Framework Directive ecological status. We report the results of a survey completed by representatives from 20 European countries to identify current challenges to IRES status assessment, examples of best practice, and priorities for future research. We identify five major barriers to effective ecological status classification in IRES: 1. the exclusion of IRES from Water Framework Directive biomonitoring based on their small catchment size; 2. the lack of river typologies that distinguish between contrasting IRES; 3. difficulties in defining the ‘reference conditions’ that represent unimpacted dynamic ecosystems; 4. classification of IRES ecological status based on lotic communities sampled using methods developed for perennial rivers; and 5. a reliance on taxonomic characterization of local communities. Despite these challenges, we recognize examples of innovative practice that can inform modification of current biomonitoring activity to promote effective IRES status classification. Priorities for future research include reconceptualization of the reference condition approach to accommodate spatiotemporal fluctuations in community composition, and modification of indices of ecosystem health to recognize both taxon-specific sensitivities to intermittence and dispersal abilities, within a landscape context

La zone hyporhéique, une composante à ne pas négliger dans l'état des lieux et la restauration des cours d'eau

Les projets de restauration des cours d'eau sont maintenant de plus en plus fréquents et ambitieux. Intégrant un grand nombre de composantes de l'hydrosystème, ils ne prennent néanmoins pas pleinement en compte sa dimension verticale et oublient souvent un compartiment fondamental, représenté par la zone hyporhéique. Cette zone constitue une seconde rivière dont l'écoulement souterrain est invisible, et dont l'existence et la fonction sont largement méconnues. Pourtant elle joue un rôle fondamental dans le maintien des processus écologiques et dans la préservation de la biodiversité du cours d'eau. Après avoir précisé les rôles du milieu hyporhéique et souligné l'effet des activités humaines qui altèrent souvent sa structure et ses fonctions, on montrera de quelle manière les projets actuels de réhabilitation pourraient être complétés grâce à l'intégration systématique de la zone hyporhéique dans leurs plans et leurs suivis de restauration. / Stream restoration projects are nowadays more and more numerous and ambitious. While they now integrate many components of hydrosystems, they are still ignoring a fundamental one, the hyporheic zone. This zone can be considered as a second river whose subsurface flow is invisible and whose functions are still poorly known. Nevertheless, the hyporheic zone plays a major role in sustaining stream ecological processes and preserving stream biodiversity. After pointing out how human activities can impair the hyporheic zone structure and function, we will show how restoration projects could be much improved by considering the hyporheic zone

An online database to collate, analyze, and synthesize data on the biodiversity and ecology of intermittent rivers worldwide

Key questions dominating contemporary ecological research and management concern interactions between biodiversity, ecosystem processes, and ecosystem services provision in the face of global change. This is particularly salient for freshwater biodiversity and in the context of river drying and flow-regime change. Rivers that stop flowing and dry, herein intermittent rivers, are globally prevalent and dynamic ecosystems on which the body of research is expanding rapidly, consistent with the era of big data. However, the data encapsulated by this work remain largely fragmented, limiting our ability to answer the key questions beyond a case-by-case basis. To this end, the Intermittent River Biodiversity Analysis and Synthesis (IRBAS; http://irbas.cesab.org) project has collated, analyzed, and synthesized data from across the world on the biodiversity and environmental characteristics of intermittent rivers. The IRBAS database integrates and provides free access to these data, contributing to the growing, and global, knowledge base on these ubiquitous and important river systems, for both theoretical and applied advancement. The IRBAS database currently houses over 2000 data samples collected from six countries across three continents, primarily describing aquatic invertebrate taxa inhabiting intermittent rivers during flowing hydrological phases. As such, there is room to expand the biogeographic and taxonomic coverage, for example, through addition of data collected during nonflowing and dry hydrological phases. We encourage contributions and provide guidance on how to contribute and access data. Ultimately, the IRBAS database serves as a portal, storage, standardization, and discovery tool, enabling collation, synthesis, and analysis of data to elucidate patterns in river biodiversity and guide management. Contribution creates high visibility for datasets, facilitating collaboration. The IRBAS database will grow in content as the study of intermittent rivers continues and data retrieval will allow for networking, meta-analyses, and testing of generalizations across multiple systems, regions, and taxa

Vertical movements through subsurface stream sediments by benthic macroinvertebrates during experimental drying are influenced by sediment characteristics and species traits

1. Streambed drying is becoming more common due to climate change and increasing anthropogenic water resource pressures. Subsurface sediments are a potential refuge for benthic macroinvertebrates during drying events in temporary streams. 2. Sediment characteristics are important controls on the distribution of macroinvertebrates in subsurface habitats, but difficulties making observations impedes quantification of vertical movements. Species traits (e.g. subsurface habitat affinity) also influence vertical movements of macroinvertebrates into the subsurface sediments, but most species-specific responses remain uncharacterised. 3. Transparent artificial mesocosms were used to directly observe the vertical movements of individuals of three aquatic insect nymphs and two crustaceans. Mixtures of three types of transparent sediment of varying particle size were combined to produce six treatments with differing interstitial pore volumes and, hence, differing subsurface porosity. Macroinvertebrate vertical movements were measured during incremental reductions in water level from 5 cm above to 20 cm below the sediment surface. These species comprised a variety of trait categories including feeding group, species affinity to temporary streams and subsurface habitats. Active and passive vertical movements were determined by conducting experiments with both live individuals and their cadavers. 4. Sediment treatment influenced the vertical movements of individuals as reducing subsurface porosity decreased vertical movements for most species. Vertical movement into subsurface sediments in response to water level reduction was the result of active, not passive, movements for all species. 5. Species identity influenced the vertical movements made by individuals. Nemoura cambrica had the highest affinity for temporary streams and subsurface habitats and its vertical movements were unaffected by sediment treatment, generally reaching depths between 20 and 25 cm. Most individuals of species with a weaker subsurface affinity (i.e. the benthic grazer Heptagenia sulphurea and the filter-feeder Hydropsyche siltalai) became stranded as water levels were reduced in all sediment treatments. Vertical movements of Gammarus pulex and Asellus aquaticus were restricted primarily by pore volume, these taxa becoming stranded most commonly in sediments with smaller interstitial volumes. 6. Our results highlight the need for the development and implementation of river management strategies that increase streambed porosity, allowing macroinvertebrates to access to the saturated subsurface habitat during stream drying

Low flow controls on benthic and hyporheic macroinvertebrate assemblages during supra-seasonal drought

Despite the widely accepted importance of the hyporheic zone as a habitat for stream macroinvertebrates during floods, few data exist regarding community composition and distribution during periods of low flow or drought in perennial streamsi Integrating research on hyporheic invertebrates with results from a long-term study of a U K river provided the opportunity to examine how surface and hyporheic macroinvertebrate communities respond to inter-annual variability in river flow and periods of groundwater drought. Changes in the riverine macroinvertebrate community associated with low flow included a reduction in species richness and the number of individuals per sample, particularly aquatic insects. The hyporheic community was characterized by a relatively homogeneous composition during a period of severe low flow, punctuated by short-term changes associated with variation in water temperature rather than changes in discharge. We present a conceptual model of the processes influencing benthic and hyporheic invertebrates under low-flow conditions. Previous studies have seldom integrated these two assemblages and their interactions. The model presented highlights the potential importance of surface water and hyporheic zone linkages for riverine invertebrate communities under a range of flow conditions

Protecting U.S. temporary waterways

International audienc

MASS DISPERSAL OF TERRESTRIAL ORGANISMS DURING FIRST FLUSH EVENTS IN A TEMPORARY STREAM

Temporary streams expand and contract seasonally, forming a complex mosaic of aquatic, amphibic and terrestrial habitats. We studied the terrestrial arthropod fauna at the surface of the dry river bed as well as the fauna of Coarse Particulate Organic Matter (CPOM) deposits 0, 5 and 10 days after first flush events (years 2004–2006) along the Pardiela stream (SE Portugal). During the dry period, large amounts of organic material accumulated at the surface of the dry bed, colonized by abundant terrestrial arthropods (mean density: 13.3 ± 15.29 Ind gDM (Dry Mass of CPOM)). Arthropod density peaked in fresh flood deposits (mean density: 35.8 ± 33.4 Ind g DM), and subsequently decreased within time. Concurrently, the relative composition of the arthropod community changed from Day 0 to Day 10. The present results demonstrated that the dry bed of temporary streams served as a major habitat for terrestrial arthropods. During the first flush events, a mass dispersal of terrestrial arthropods, rafting on floating CPOM, occurred, subsequently forming distinct deposits along the channel margin. These deposits may constitute critical habitats, refugia and food resources for local and regional terrestrial arthropod assemblage