Ecosystems lining rivers perform a number of functions making it reasonable to protect them from significant degradation. A natural characteristic of floodplains is their regular inundation, during which sediments, wood and nutrients are eroded, mobilized or deposited, thereby restoring these valuable ecosystems. However, the key attributes of floodplains, such as fertile soil, flat terrain, availability of water, sediments and wood, are also the subjects of human exploitation. The flood control embankments in urban and agricultural areas are justified and effective solutions to reduce flood risk. However, when combined with unnaturally incised and enlarged river channels, they are limiting natural flooding and connectivity of floodplains is fundamentally degraded. To analyze different approaches to floodplain protection, we conducted a review supported by the expertise of specialists in selected countries of Central and Southern Europe. We concluded that in most of these countries, there is no targeted protection of floodplains as an ecological phenomenon. Comprehensive protection is mostly only afforded to small-scale areas, valued due to the occurrence of Europe's most threatened species and habitats (Natura 2000 network). Except for segments of a few large rivers, these sites are not connected and therefore significant support for the longitudinal continuity of water-dependent ecosystems cannot be expected. This inevitably leads to the gradual degradation of floodplain ecosystem functions and services. The floodplain management in non-urban areas, wherever natural spillover of floods to the surroundings is possible and where floodplains have been inappropriately embanked, seems to be a suitable solution for supporting the ecological functionality of these ecosystems. This article is categorized under: Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness Water and Life > Nature of Freshwater Ecosystems

Floodplain habitat area and quality have decreased significantly over the last decades, mainly due to anthropogenic changes. Conservation efforts targeting floodplain species must consider changing climate when choosing suitable areas for restoration, especially for sessile organisms. Species distribution models, based on data from national and international databases on species’ occurrences and various environmental predictors, allow forecasting changes in species’ spatial distributions and facilitate planning at the catchment scale. Modelled predictions for floodplain organisms and communities suggest that current protected floodplains in Switzerland do not provide sufficient habitat and refugia for typical floodplain species and that climate-adapted conservation planning is needed which includes new areas. Similarly, visualisations of habitat which might potentially be occupied in the future can help to distinguish refugia from short-term sanctuaries. Temporal changes in water availability, for example, during periods of droughts, are likely to further lead to local habitat decrease of floodplain plant communities, as can be shown in hydrological models at reach scale for the Rhine in Germany. In fragmented landscapes along rivers, protected areas can provide refuge for specialised terrestrial species and promote species conservation, as we report for a floodplain which was protected for 30 years. Future restoration projects at the reach scale should, therefore, include planning at the catchment level, as well as consider hydrological regimes at the reach scale, especially for sessile floodplain species’ conservation under changing climate. Highlights Floodplain communities are threatened, especially sessile species; Climate-driven species distribution models distinguish refugia and sanctuaries; Hydrological predictions under changing climate show shifts of habitat for riverine plants at the local scale; A case study from a protected area shows that it promotes floodplain biodiversity; Prioritisation of local restoration projects should be based on planning at the catchment scale.

Water-mediated dispersal (hydrochory) connects spatially separated terrestrial and aquatic communities, facilitating the movement of reproductive materials and organisms through river networks. Anthropogenic pressures and climate change have altered these dynamics, potentially affecting biodiversity. Although dispersal distances and landing mechanisms are commonly attributed to interactions between channel flow, morphology, and particle properties, these relationships remain poorly investigated, especially in alpine rivers. We conducted field experiments in an 80-m-long channel of a braided river floodplain in Switzerland, releasing wooden cylinders as plant propagule mimics at three discharge rates. We used a 2D depth-averaged numerical model to quantify hydraulic variables and link them to measured particle travel distances and landing sites. We found that the number of floating particles decayed exponentially with distance, with decay rates primarily related to discharge. The deposition patterns were dictated by channel morphology rather than particle size, and the submergence of the river bed at low discharges strongly influenced the landing position. This study emphasizes the impact of small-scale channel heterogeneity on the dispersal of naturally buoyant materials. Our findings may help conservation and restoration measures, identify ecological flows and dispersal hotspots, especially in hydropower-impacted rivers.

Tintenstrich communities are specialized lithic biofilms dominated by free-living cyanobacteria, also occurring in lichen associations, forming a unique ecological interface between rock environments and aquatic habitats in mountainous areas. To better understand their composition and genetic and metabolic potential, we analyzed 207 samples from the Swiss Alps and Jura Mountains. We determined how key environmental factors shaped cyanobacterial abundance, assessed whether these communities harbor genes for toxin biosynthesis, characterized their taxonomic composition at the family and genus level, and evaluated the actual occurrence of cyanotoxins and other bioactive metabolites. Cyanobacterial abundance proved to be influenced by factors such as elevation, exposure, and their interaction with siliceous rock substrata. Targeted PCR and Sanger sequencing revealed the presence of toxin-encoding genes, particularly for ndaF/mcyE fragments, which may encode microcystin and/or nodularin biosynthesis, while specific genes for microcystins, anatoxins, and cylindrospermopsins were rather rare. Metabarcoding analysis identified 11 cyanobacterial families, with Chroococcaceae, Nostocaceae, and Leptolyngbyaceae being the most abundant. Complementary high-resolution mass spectrometry confirmed the occasional presence of nodularins and microcystins, alongside more frequent detection of other bioactive peptides such as anabaenopeptins and cyanopeptolins. Overall, these findings provide the most comprehensive insight to date into Tintenstrich-associated cyanobacteria, underscoring their environmental significance given their genetic and metabolic potential.

The transport and deposition of floating particles in flowing water is a key mechanism that drives the fate of contaminant, organic materials, and debris along river networks. The ability of human-made and naturally buyout particles to sit on the water surface makes them able to travel long distances. The mechanisms that allow these particles to deposit are closely linked to the hydraulics of the channel and the morphology of the river. Research has shown that particles such as plastics and debris tend to accumulate behind obstacles and recirculation areas, creating accumulation hotspots. The location of such hotspot also depends on the interplay between particle shape and size and flow conditions. Although the influence of river morphology and flow regime is well acknowledged, the precise interaction between these components remains unclear.To investigate this relationship, we used a new Eulerian-Lagrangian method based on a 2D depth-averaged flow solver simulating transport and dispersion of floating particles in a typical alpine river floodplain. This method offers a computationally efficient way to track the trajectory of single particles moving onto a flow field. Our approach integrates model simulations with data derived from outdoor and laboratory experiments, where we recorded deposition location of particles of different size, shape and material under different discharge conditions.The results show that the number of floating particles decreases exponentially with the distance from the release point, with decay rates primarily correlated with the water discharge. We find that the deposition of particles depends on the hydraulics of the channel and the roughness elements in the channel, with particle sizes playing a secondary role. Unsteady flow conditions, namely receding water levels, promote particle deposition on shallow areas and channel shorelines. The use of the particle tracking model allowed us to extend the parameter space investigated experimentally, allowing for an in-depth analysis of the spatial and temporal dynamics of particles transport and deposition during floods.These results deepen our understanding of transport processes of floating material at the reach scale, providing quantitative evidence on the central role played by channel hydromorphology. Although the effect of particle shape and size is not fully understood, the study can offer valuable insights into the dispersion mechanisms of different floating particles, from plastics to organic materials.

Many species of river riparia are threatened by habitat loss due to altered flood and sediment regime, and associated shifts in vegetation structure. However, their ecological niche is often obscure, especially in inconspicuous organisms such as lichens, hindering their conservation and use as indicator species in river restoration. We studied if variation in sediment size distribution, gravel bank elevation and vegetation structure drive presence-absence and fertility (fruit body production) in the endangered, soil-dwelling lichen Stereocaulon incrustatum along two Swiss braided rivers, using binomial generalized linear mixed effect models in a Bayesian framework. Data was sampled on 811 plots randomly placed along 41 transects perpendicular to the main channels. Presence probability was highest on the most elevated plots, at 30

Tintenstrich communities (TCs) mainly comprise Cyanobacteria developing on rock substrates and forming physical structures that are strictly connected to the rock itself. Endolithic and epilithic bacterial communities are important because they contribute to nutrient release within run-off waters flowing on the rock surface. Despite TCs being ubiquitous, little information about their ecology and main characteristics is available. In this study, we characterized the bacterial communities of rock surfaces of TCs in Switzerland through Illumina sequencing. We investigated their bacterial community composition on two substrate types (siliceous rocks [SRs] and carbonate rocks [CRs]) through multivariate models. Our results show that Cyanobacteria and Proteobacteria are the predominant phyla in this environment. Bacterial α-diversity was higher on CRs than on SRs, and the β-diversity of SRs varied with changes in rock surface structure. In this study, we provide novel insights into the bacterial community composition of TCs, their differences from other lithic communities, and the effects of the rock substrate and structure.

Flussauen sind Brennpunkte vieler Nutzungsinteressen wie Wasserkraft oder Naherholung. Sie bieten gleichzeitig Lebensraum für viele, auch spezialisierte und seltene Arten. Durch ein besseres Verständnis der Lebensraumansprüche solcher Organismen lassen sich Managementmassnahmen in Flussauen besser planen und umsetzen sowie die Kooperation zwischen Forschung, Naturschutz und weiteren Interessensgruppen verbessern: Das Beispiel der Verhüllenden Korallenflechte (Stereocaulon incrustatum) zeigt, wie der Schutz einer vom Aussterben bedrohten, geschützten Flechtenart und die Erhaltung der natürlichen Flussdynamik in Auenlandschaften Hand in Hand gehen können.

Le zone alluvionali fluviali sono utilizzate per vari scopi, come la produzione di energia idroelettrica o lo svago. Allo stesso tempo forniscono un habitat a molte specie, incluse quelle specializzate e rare. Una migliore comprensione delle esigenze ambientali di questi organismi può ottimizzare la pianificazione e l‘attuazione di misure di gestione e migliorare la cooperazione tra ricerca, conservazione della natura e altri gruppi di interesse. L‘esempio del lichene Stereocaulon incrustatum mostra come il mantenimento delle dinamiche fluviali naturali nei paesaggi golenali possa andare di pari passo con la conservazione di una specie protetta e minacciata di estinzione.

Les zones alluviales sont des points névralgiques à la croisée de nombreux intérêts comme l’énergie hydraulique ou les loisirs de proximité. Parallèlement, elles abritent de nombreuses espèces, dont certaines sont spécialisées et rares. Une meilleure compréhension des exigences en matière d’habitat de tels organismes permet de mieux planifier et mettre en oeuvre des mesures de gestion dans les zones alluviales et d’améliorer la coopération entre la recherche, la protection de la nature et d’autres groupes d’intérêt. L’exemple du lichen corail cendré des sables (Stereocaulon incrustatum) montre comment la protection d’une espèce de lichen menacée de disparition et la préservation de la dynamique fluviale naturelle dans les paysages alluviaux peuvent aller de pair.

<p>Hydropower production has different recognized impacts on river ecosystems. In particular, it alters the natural hydrological regime with extended low-residual flow conditions interrupted by rapid daily and sub-daily flow fluctuations, i.e. hydropeaking. Hydropeaking impacts both biotic and abiotic compartments: an increasing body of literature suggests that it can influence the physiological activity of plants, seed germination, and seedling growth, altering the chance of survival of several plant species.</p><p>Riparian vegetation is a key indicator of the status of river hydro-morphological processes. Several riparian plant species are nowadays endangered because of the degradation of river ecosystems worldwide, as a result of the exploitation of river resources. River floodplains, by hosting large amounts of biodiversity and habitat types, are crucial objectives for river management and restoration.</p><p>Vegetation establishment in floodplains and in-channel morphologies is linked to river hydro-morphodynamic processes: seeds of many riparian species are transported along the river by water, deposited on shorelines as the water level recedes, and establish depending on different environmental factors. The hydrological regime at seasonal-yearly scale (for example flood-drought seasonality), has recognized effects on seed recruitment.</p><p>In this study, we applied a vegetation recruitment model based on the Windows of Opportunity concept to study the main hydro-morphological controls on seed recruitment in an Alpine river subjected to hydropeaking. The study site is a small gravel-dominated floodplain of Moesa River (Switzerland). The model predicts potential colonization sites for vegetation after seed dispersal events by comparing water stress caused by water level fluctuations and time-varying plant resistance to inundations. We test alternative hydrological scenarios, comparing business-as-usual and no-hydropeaking conditions, and also different morphological configurations, using river topographical scans from different epochs (pre- and post- natural floods). We use a two-dimensional depth-averaged hydrodynamic model to simulate water levels in every scenario. The different hydro-morphological configurations are then fed into the seed recruitment model, to finally evaluate spatially distributed maps of successful rate of seed recruitment. Each hydrological and morphological scenario is tested also against different vegetation resistance to water stress, hence comparing stress-intolerant and stress-tolerant plant species. In addition, we qualitatively compared our results with an existing dataset of German Tamarisk (<em>Myricaria germanica</em>) dynamics in the floodplain.</p><p>Our results show the influence of vegetation resistance on the successful recruitment rate in terms of spatial extension and distribution. The influence of hydropeaking seems to be increased/smoothed depending on the hydrological year. Morphological variations due to natural floods appear to have relevant impact on vegetation dislocation, but less on total amount. Developing quantitative tools to simulate eco-morphodynamic river processes is supportive for both river managers and scientists. Eventually the understanding of key physical drivers of riparian vegetation dynamics in hydropeaking rivers is crucial for the conservation and restoration of functional river ecosystems.</p>

River alterations for natural hazard mitigation and land reclamation result in habitat decline and fragmentation for riparian plant species. Extreme events such as floods are responsible for additional local species loss or population decline. Tributaries might provide refugia and subsequent source populations for the colonization of downstream sites in connected riverine networks with metapopulations of plant species. In this study, we analyzed the metapopulation structure of the endangered riparian shrub species Myricaria germanica along the river Isel, Austria, which is part of the Natura 2000 network, and its tributaries. The use of 22 microsatellite markers allowed us to assess the role of tributaries and single populations as well as gene flow up- and downstream. The analysis of 1307 individuals from 45 sites shows the influence of tributaries to the genetic diversity at Isel and no overall isolation by distance pattern. Ongoing bidirectional gene flow is revealed by the detection of first-generation migrants in populations of all tributaries as well as the river Isel, supporting upstream dispersal by wind (seeds) or animals (seeds and pollen). However, some populations display significant population declines and high inbreeding, and recent migration rates are non-significant or low. The genetic pattern at the mouth of river Schwarzach into Isel and shortly thereafter river Kalserbach supports the finding that geographically close populations remain connected and that tributaries can form important refugia for M. germanica in the dynamic riverine network. Conservation and mitigation measures should therefore focus on providing sufficient habitat along tributaries of various size allowing pioneer plants to cope with extreme events in the main channel, especially as they are expected to be more frequent under changing climate.

Cyanobacteria, also known as blue-green algae, are photosynthetic bacteria that can colonize different habitats, including extreme ones. They are of great interest to the scientific community, especially because of their ability to produce cyanotoxins: toxic secondary metabolites potentially harmful to organisms especially when released to surface waters.

River relocations due to realization of infrastructure projects or flood protection provide a high potential for ecological restorations and the creation of near-natural habitats. Colonization success of new riparian habitats in the dynamic riverine zone is rarely predictable, as the survival of sessile plants is highly dependent on flood events. Relocated rivers offer a unique opportunity to study restoration success, and using genetic information allows tracing to source populations and assessing connectivity. This study focuses on the colonization of a new, 3.4 km long river stretch in the Inn catchment (Switzerland), with an artificial, stable shoreline and a dynamic riverine zone with gravel bars. We assess the colonization success of Myricaria germanica, a flagship species for floodplain pioneer vegetation, 14 years after river relocation. The population with over 600 individuals of which 147 were used for genetic analysis based on 22 microsatellite markers in comparison to 11 potential source populations up- and downstream of the new site. Our results on demography and genetic composition together with information on flood events allow tracing the origin of the subpopulation along the stable shoreline to a single founder event but several founder individuals further upstream. The subpopulation in the dynamic zone is younger and more likely strongly dependent on gene flow from the stable shoreline subpopulation, but allows for rejuvenation at the site. Genetic patterns along the catchment indicate ongoing gene flow, suggesting potential for colonization success for further restorations in the catchment. Our data reveals that near-natural flood dynamics with repeated larger flood events is a key factor for successful colonization of dynamic riparian habitats.

The distribution of sessile riparian plant species and their habitats along riverways are highly dependent on river dynamics and connectivity. River restoration and conservation of riparian plant species rely on expert knowledge and more recently also on modelling approaches to predict species’ occurrence. Ecological modelling on habitat suitability for terrestrial species is usually based on climatic and topographic features, whilst river hydrodynamics is rarely considered. Our study aims at predicting suitable habitat for a characteristic pioneer species for dynamic riverine habitats, the German Tamarisk (Myricaria germanica). Habitat predictions are tested in a case study on a floodplain along Moesa river in canton Grisons in South-East Switzerland. We link two modeling approaches having two different spatial scales using a hierarchical process. First, we define a large-scale habitat suitability matrix based on climatic, geological and topographic predictors. Using a two-dimensional hydrodynamic model, inundation frequency maps and flood level maps for several significant months for German Tamarisk establishment are constructed, to further refine the niche for the riparian plant. The predicted habitat suitability is evaluated with species presence data for both adult and offspring plants. Our results allow gaining insights into the importance of linking ecological and hydraulic models having different spatial and temporal scales, for more refined predictions of riparian species distribution.

Protected areas with restricted management can provide refugia for fungi, but are usually selected based on conservation strategies for flora and fauna. Despite the important role of fungi in floodplains, they are rarely considered in conservation projects. The SwissFungi database covering all biogeographic regions in Switzerland, and consisting of 84% citizen science data, provided a valuable basis to define fungal riparian species: 99.29% of 990 species were reported at least once from the riparian zone, while 15% of species showed a measurable riparian affinity. Species distribution modelling for 129 riparian macrofungi revealed that the predicted distribution is driven by temperature for most species. There were significantly more records per species inside compared to outside protected areas, when correcting for size differences (21% of the area in Switzerland is protected). In contrast, the model predicted significantly more suitable habitat outside currently protected areas. Unprotected areas harbor a high potential for the creation of newly protected areas for the conservation of riparian fungi. The database information and the modelling approach provided crucial information for future monitoring and conservation projects along rivers.

Context Riparian areas are considered to undergo major alterations under changing climate, making floodplain habitats targets for conservation and landscape planning. Protected areas might provide sanctuaries especially for sessile riparian plant species, but these niches are not always persistent over time. Objectives We investigate if plant species of floodplain forests are provided with suitable habitat within currently protected areas and if these refugia persist. A coupled-modelling approach is used to gain spatially explicit information on new areas for sanctuaries. Methods We use species distribution models to predict the niche of 12 Salicion albae and 7 Fraxinion floodplain forest species along rivers in Switzerland, under current, moderate and extreme climate change scenarios up to 80 years to the future (2100). The spread of plant species from current habitat to suitable future habitat is simulated using dispersal vectors and life history traits. Results Salicion albae species are more flexible under both climate change scenarios than Fraxinion species. The main limitation for the spread of species is their dispersal ability, as only a minority of the suitable cells is colonized during the simulation process. The predicted future presence within currently protected areas decreases under both climate change scenarios in the model. Conclusions Current protected floodplains do not provide persistent refugia for the plants studied, but might still be of importance to other organisms. Planning of sanctuaries for riparian plant species and communities need to focus on connectivity along rivers to maintain viable source populations in dynamic riverine landscapes under changing climate.