European Floodplains Research Articles

Flood insurance is a driver of population growth in European floodplains

Future flood risk assessments typically focus on changing hazard conditions as a result of climate change, where flood exposure is assumed to remain static or develop according to exogenous scenarios. However, this study presents a method to project future riverine flood risk in Europe by simulating population growth in floodplains, where households’ settlement location decisions endogenously depend on environmental and institutional factors, including amenities associated with river proximity, riverine flood risk, and insurance against this risk. Our results show that population growth in European floodplains and, consequently, rising riverine flood risk are considerably higher when the dis-amenity caused by flood risk is offset by insurance. This outcome is particularly evident in countries where flood risk is covered collectively and notably less where premiums reflect the risk of individual households.

Planning for sustainability: Historical data and remote sensing-based analyses aid landscape design in one of the largest remnant European floodplains

Large floodplain rivers are among the most threatened ecosystems on Earth and their utilization is expected to grow. Here, we integrated historical data and remote sensing-based landscape analyses and applied stakeholder evaluation of present-day utilization of different river–floodplain habitat types to understand the process of landscape development and provide a basis for sustainable landscape design in one of the largest remnant floodplains of the Danube River, Hungary. Temporal trajectories indicated drastic transformation of the landscape over almost four centuries as a result of river regulation works. Of these, the most substantial were the canalization of the main channel of the Danube into its largest side arm and cutting of large meandering segments, which resulted in the conversion of wetlands to other land uses, particularly agricultural land. The total area of aquatic habitats decreased by more than five-fold, and substantial changes occurred in the extent and composition of river–floodplain habitat types. Evaluation of present-day land use indicated that protected areas are under less human influence and have higher potential for the maintenance of aquatic biodiversity than unprotected ones. Although the protected area network still includes representatives of all floodplain habitat types, past changes and present-day utilization of the landscape limit conservation and restoration possibilities. We provide implications for management and conclude that the joint analyses of historical landscape conditions and present-day evaluation of human utilization can be fruitful to aid the sustainability design and management of river–floodplain ecosystems.

Hyd1d and hydflood - R packages to compute water levels and annual flood durations along the rivers Rhine and Elbe, Germany

Floodplains are environments characterized by fluctuating water levels. Spatial and temporal heterogeneity of habitat conditions driven by hydrology are the key factor for their high biodiversity because strong environmental filtering either creates favorable conditions for specialized organisms or eliminates competing generalists.hyd1d and hydflood are two R packages for simplified hydrological modelling in two large central European floodplains – along the rivers Rhine and Elbe in Germany – that enable users to simulate the dynamics of water level changes, flood extents and durations with high spatial and temporal resolution over long time periods and vast areas. They are simplified in the sense of not being based on physical equations, but they implement fast computing interpolation of 1d hydraulic data and GIS extrapolation algorithms. Annual and long-term products provide the possibility to predict the distribution of floodplain habitats.All input datasets are highly integrated into the packages and automatically updated. Computationally expensive products such as annual flood durations between 1960 and 2022 are provided as open data. The software itself is provided as open source software through CRAN and in public code repositories. With minimal efforts users can apply the software within the given conditions or integrate other river systems through data and source code contributions.

The changing face of floodplains in the Mississippi River Basin detected by a 60-year land use change dataset

Floodplains provide essential ecosystem functions, yet >80% of European and North American floodplains are substantially modified. Despite floodplain changes over the past century, comprehensive, long-term land use change data within large river basin floodplains are limited. Long-term land use data can be used to quantify floodplain functions and provide spatially explicit information for management, restoration, and flood-risk mitigation. We present a comprehensive dataset quantifying floodplain land use change along the 3.3 million km2 Mississippi River Basin (MRB) covering 60 years (1941–2000) at 250-m resolution. We developed four unique products as part of this work, a(n): (i) Google Earth Engine interactive map visualization interface, (ii) Python code that runs in any internet browser, (iii) online tutorial with visualizations facilitating classroom code application, and (iv) instructional video demonstrating code application and database reproduction. Our data show that MRB’s natural floodplain ecosystems have been substantially altered to agricultural and developed land uses. These products will support MRB resilience and sustainability goals by advancing data-driven decision making on floodplain restoration, buyout, and conservation scenarios.

Overbank silt-clay deposition and intensive Neolithic land use in a Central European catchment – Coupled or decoupled?

Hydro-sedimentary processes such as soil erosion, sediment transport, deposition, and re-deposition influence the environmental evolution of floodplains, especially in loess-covered catchments. Holocene floodplain deposits are thus a source of information on previous hydro-sedimentary dynamics and land use in the catchment. Resulting from forest clearings in the catchment, the onset of overbank silt-clay deposition is considered as an initial and significant human-induced process affecting Central European floodplain evolution and ecosystems. However, it is difficult to separate climate-related from anthropogenic forces on depositional environments, and the complexity of the hydro-sedimentary responses is part of an ongoing debate in geoscientific, ecological, and archaeological communities. This study focuses on the Central European Weiße Elster river system, where humans have been influencing hydro-sedimentary processes since the Early Neolithic due to land-use-induced soil erosion predominantly in the loess-covered sub-basin of the middle course. A catchment-scale XRF element record of fluvial sediment sources combined with the geochemical characterisation of Holocene floodplain deposits aim for a better understanding of the interplay between past soil erosion, overbank deposition in the floodplain, and potential changes in sediment provenances. The Weiße Elster floodplain chronosequences show a geochemical differentiation into a lower (Neolithic) and an upper (post-Neolithic) overbank silt-clay deposition. The construction of a sediment source fingerprinting mixing model yields the significant finding that the Neolithic overbank silt-clay deposition reveals a remote provenance signal from the upper catchment and less from the proximal loess-covered sub-catchment. According to a systematic archaeological data survey, the upper catchment was not permanently settled and used for agriculture in the Neolithic period. This contradicts the previous assumption that Neolithic overbank silt-clay deposition primarily originates from forest clearings and subsequent farming-induced soil erosion in the catchment. From a more general perspective, further examination of existing hypotheses concerning overbank silt-clay deposition in Central European floodplains is thus in order.

On the Way to the Fluvial Anthroposphere—Current Limitations and Perspectives of Multidisciplinary Research

Floodplains represent a global hotspot of sensitive socioenvironmental changes and early human forcing mechanisms. In this review, we focus on the environmental conditions of preindustrial floodplains in Central Europe and the fluvial societies that operated there. Due to their high land-use capacity and the simultaneous necessity of land reclamation and risk minimisation, societies have radically restructured the Central European floodplains. According to the current scientific consensus, up to 95% of Central European floodplains have been extensively restructured or destroyed. Therefore, question arises as to whether or when it is justified to understand Central European floodplains as a ‘Fluvial Anthroposphere’. The case studies available to date show that human-induced impacts on floodplain morphologies and environments and the formation of specific fluvial societies reveal fundamental changes in the medieval and preindustrial modern periods. We aim to contribute to disentangling the questions of when and why humans became a significant controlling factor in Central European floodplain formation, and how humans in interaction with natural processes and other chains of effects have modified floodplains. As a conclusion, we superimpose emerging fields of research concerning the onset of the Fluvial Anthroposphere and provide 10 specific thematic objectives for future multidisciplinary work.

Current and historical nephric and hepatic mercury concentrations in terrestrial mammals in Poland and other European countries

The long-term anthropogenic release of mercury (Hg) into the environment has led to contamination of the biosphere, with all forms of Hg showing toxic effects and the ability to accumulate in organisms. Since the 1970s, efforts have been made in Western Europe to reduce Hg emissions and for the economic use of Hg, leading to a reduction in Hg exposure to humans and entire ecosystems. The purpose of this research was to present the total mercury (THg) burden in three mustelids (the piscivorous Eurasian otter and American mink, and the invertebrativorous European badger) inhabiting north-western Poland (mostly floodplains) and other European countries (literature data). Moreover, we wanted to investigate whether reductions in the environmental Hg burden in Europe have resulted in reductions in liver and kidney levels in wild terrestrial mammals (Eurasian otter, wild boar, red deer, roe deer, cervids, leporids, rodents, and ecotrophic groups: piscivorous mustelids, non-mustelids whose diets include aquatic prey, canids and other carnivores, omnivores, herbivores), between samples collected before and after 2000. We revealed significantly higher nephric THg levels in roadkilled than in trapped American minks. As roadkilled piscivorous mustelids from the same floodplain had similar hepatic and nephric THg concentrations, we suggest that the European research on Hg ecotoxicology should more often use alien American mink instead of the protected Eurasian otter. Badgers inhabiting Polish and other European floodplains bioaccumulated higher amounts of THg than those from other areas, and as such, may be recommended as bioindicator of mercury soil contamination. Our analysis of abundant data on mammalian hepatic and nephric THg concentrations (excluding non-piscivores mustelids) showed that in 12 of 21 cases, Hg concentrations had dropped significantly since 2000. This data signals a reduction in Hg contamination in terrestrial mammals, such as the Eurasian otter, and may be reason for cautious optimism.

Reintroduced Native Populus nigra in Restored Floodplain Reduces Spread of Exotic Poplar Species.

Exotic Populus taxa pose a threat to the success of riparian forest restoration in floodplain areas. We evaluated the impact of exotic Populus taxa on softwood riparian forest development along the river Common Meuse after introducing native Populus nigra and after the re-establishment of the natural river dynamics. We sampled 154 poplar seedlings that spontaneously colonized restored habitat and assessed their taxonomy based on diagnostic chloroplast and nuclear microsatellite markers. Furthermore, by using a paternity analysis on 72 seedlings resulting from six open pollinated P. nigra females, we investigated natural hybridization between frequently planted cultivated poplars and native P. nigra. The majority of the poplar seedlings from the gravel banks analyzed where identified as P. nigra; only 2% of the sampled seedlings exhibited genes of exotic poplar species. Similarly, the majority of the seedlings from the open pollinated progenies were identified as P. nigra. For three seedlings (4%), paternity was assigned to a cultivar of P. × canadensis. Almost two decades after reintroducing P. nigra, the constitution of the seed and pollen pools changed in the study area in favor of reproduction of the native species and at the expense of the exotic poplar species. This study indicates that, although significant gene flow form exotic poplars is observed in European floodplains, restoration programs of the native P. nigra can vigorously outcompete the exotic gene flows and strongly reduce the impact of exotic Populus taxa on the softwood riparian forest development.

Exploration of geochemical data with compositional canonical biplots

The study of the relationships between two compositions is of paramount importance in geochemical data analysis. This paper develops a compositional version of canonical correlation analysis, called CoDA-CCO, for this purpose. We consider two approaches, using the centred log-ratio transformation and the calculation of all possible pairwise log-ratios within sets. The relationships between both approaches are pointed out, and their merits are discussed. The related covariance matrices are structurally singular, and this is efficiently dealt with by using generalized inverses. We develop compositional canonical biplots and detail their properties. The canonical biplots are shown to be powerful tools for discovering the most salient relationships between two compositions. Some guidelines for compositional canonical biplot construction are discussed. A geochemical data set with X-ray fluorescence spectrometry measurements on major oxides and trace elements of European floodplains is used to illustrate the proposed method. The relationships between an analysis based on centred log-ratios and on isometric log-ratios are also shown.

The potential control of benthic biofilm growth by macrophytes—A mesocosm approach

Shallow lakes, ponds and wetlands are often colonized by high densities of photoautotrophic micro-organisms at their water–sediment interfaces. However, excessive growth of benthic biofilm may threaten ecosystem functioning. Under these conditions, ecological engineering solutions based on macrophyte introduction may be an efficient way to prevent biofilm development through biotic interactions (competition for light, nutrient and/or light, allelopathic effects). Therefore, the aim of this study was to evaluate the role of several macrophytes on biofilms developed at the water–sediment interface of sand filtration systems. Four species of allelopathic aquatic macrophytes common in European floodplains were selected: Vallisneria spiralis (L.), Berula erecta (Huds.) Coville, Ceratophyllum demersum (L.) and Chara globularis (L.). They were introduced in outdoor mesocosms filled with sandy sediments colonized by benthic biofilms. Monitoring was carried out for six weeks, with sampling of the 0–1cm layer in each mesocosm at the beginning and end of the experiment. Our results revealed a significant loss of biofilm algal biomass in treatments with V. spiralis and C. globularis. We also measured an inhibitory effect of C. globularis on the development of filamentous algae in the water column. These results demonstrate that the allelopathic activities of certain macrophytes could potentially prevent the excessive development of benthic biofilms in shallow lakes and wetlands.

Dams and canyons disrupt gene flow among populations of a threatened riparian plant

SummaryNatural and man‐made barriers have a significant impact on the population structure and genetic diversity of aquatic species. Little is known whether terrestrial, riparian species are affected in the same way by barriers.Here, we analysed the genetic structure of a threatened riparian shrub based on 20 microsatellite markers and 1176 individuals collected from 34 localities in four Alpine rivers in Europe (Isar, Lech, Rhine and Tagliamento). The catchments comprised a variety of potential barriers to gene flow for terrestrial riparian plants: dams, channelised stretches of river and canyons. We compared the average level of genetic differentiation (pairwiseFST) between connected localities and localities isolated by natural or man‐made barriers.Genetic differentiation was higher between localities isolated by a barrier than between connected localities, indicating genetic isolation caused by barriers. This increased degree of genetic differentiation across barriers was evident in geographic tree models.Our results demonstrate genetic isolation effects due to large dams in a characteristic plant of Central European floodplains, highlighting that these types of barriers may negatively impact riparian plant populations. We also found genetic isolation effects in populations separated by natural barriers (canyons). These results have important implications for understanding the dynamics of riparian plant populations and for designing suitable management strategies for an effective conservation of riparian plants.

Adaptations and Predispositions of Different Middle European Arthropod Taxa (Collembola, Araneae, Chilopoda, Diplopoda) to Flooding and Drought Conditions.

Simple SummaryThis review summarizes adaptations and predispositions of different arthropod taxa (springtails, web spiders, millipedes and centipedes) to flood and drought conditions. The main focus sis directed to arthropod species, which are living in Middle European floodplain forests and wetlands, because of the fast change of flood and drought conditions in these habitats. Furthermore the effects of the predicted regional climate change like increasing aperiodic summer flooding and decreasing winter and spring floods are also discussed. Floodplain forests and wetlands are amongst the most diverse and species rich habitats on earth. Arthropods are a key group for the high diversity pattern of these landscapes, due to the fact that the change between flooding and drought causes in different life cycles and in a variety of adaptations in the different taxa. The floodplain forests and wetlands of Central Amazonia are well investigated and over the last 50 years many adaptations of several hexapod, myriapod and arachnid orders were described. In contrast to Amazonia the Middle European floodplains were less investigated concerning the adaptations of arthropods to flood and drought conditions. This review summarizes the adaptations and predispositions of springtails, web spiders, millipedes and centipedes to the changeable flood and drought conditions of Middle European floodplain forests and wetlands. Furthermore the impact of regional climate change predictions like increasing aperiodic summer floods and the decrease of typical winter and spring floods are discussed in this article.

Knowledge-based classification of remote sensing data for the estimation of below- and above-ground organic carbon stocks in riparian forests

Floodplain forests play a crucial role in the storage of organic carbon (Corg). However, modeling of carbon stocks in these dynamic ecosystems remains inherently difficult. Here, we present the spatial estimation of Corg stocks in riparian woody vegetation and soils (to a depth of 1 m) in a Central European floodplain using very high spatial resolution remote sensing data and auxiliary geodata. The research area is the Danube Floodplain National Park in Austria, one of the last remaining wetlands with near-natural vegetation in Central Europe. Different vegetation types within the floodplain show distinct capacities to store Corg. We used remote sensing to distinguish the following vegetation types: meadow, reed bed and hardwood, softwood, and cottonwood forests. Spectral and knowledge-based classification was performed with object-based image analysis. Additional knowledge rules included distances to the river, object area, and slope information. Five different classification schemes based on spectral values and additional knowledge rules were compared and validated. Validation data for the classification accuracy were derived from forest inventories and topographical maps. Overall accuracy for vegetation types was higher for a combination of spectral- and knowledge-based classification than for spectral values alone. While water, reed beds and meadows were clearly detectable, it remained challenging to distinguish the different forest types. The total carbon storage of soils and vegetation was quantified using a Monte Carlo simulation for all classified vegetation types, and the spatial distribution was mapped. The average storage of the study site is 428.9 Mg C ha−1. Despite certain difficulties in vegetation classification this method allows an indirect estimation of Corg stocks in Central European floodplains.

Abrupt Drops in Water Table Level Influence the Development of Populus nigra and Salix alba Seedlings of Different Ages

Early seedling establishment is a demographic bottleneck for the sexual regeneration of many riparian tree species such as Populus nigra and Salix alba, two dominant species of European floodplains. Immediately after spring germination, seedling roots must track receding water tables to avoid desiccation. This may be especially difficult if the groundwater recession is too abrupt. In this study, seedling survival and growth under different abrupt drops in water table levels were examined using an experimental facility that allowed continuous and non-destructive measurements of above- and below-ground seedling development. A Cox proportional hazards regression model showed that the risk of mortality for a seedling was significantly lower in P. nigra than in S. alba, was lower for older than for younger seedlings, and increased with greater drops in water table level. In fact, almost no seedlings survived abrupt water level drops ≥40 cm. However, no substantial differences in any of the growth parameters were observed between species, age, and water table treatments, as shown by R-ANOVA and paired tests. This suggests that abrupt drops in water table level did not stimulate plant growth but only favoured the survival of the most resistant individuals. These findings should be considered when designing improved water flow prescriptions along managed river courses in Europe.

Challenging growth–survival trade-off: a key for Acer negundo invasion in European floodplains?

We compared the performances of juvenile Acer negundo with those of native species to assess how this species has invaded intermediate habitats along European riparian successional gradients. In the middle Rhône floodplain (France), we measured survival and growth of transplants of the invasive and of three native tree species from contrasted successional status within forests and in experimental gaps and at three positions along a riparian gradient: (i) a highly disturbed Salix – Populus stand, (ii) a moderately disturbed stand dominated by the invasive Acer , and (iii) a mature Fraxinus community. Acer’s growth in the gaps was as high as that of the two native early-successional species, Salix and Populus, and higher than that of the native late-successional Fraxinus. In contrast, Acer survived as well in the shadiest understory conditions of the Fraxinus community as did Fraxinus and better than the two early-successional species. Inconsistent with the resource trade-off of succession theory, Acer showed both a high survival in the shade and a high growth in full light. This particular suite of traits shared with other invasive and native Acer species could be an example of adaptive plasticity that certainly represents an advantage to give it a competitive advantage over native species.

Changes in Different Trophic Levels of Litter-dwelling Macrofauna Associated with Giant Knotweed Invasion

The highly invasive giant knotweed (Reynoutria spp.) often displaces nettle (Urtica dioica) dominated stands in European floodplains. Urtica-dominated stands differ from the monospecific Reynoutria stands in plant species richness and stand structure. We thus hypothesize that Reynoutria invasion profoundly alters ecosystem structure and function, with negative effects cascading up through the food chain. We performed a paired sampling design in six sites belonging to two different locations and studied effects on the soil and the litter-dwelling fauna. Reynoutria stands differed in habitat structure and were characterized by decreased soil pH and potassium depletion. The faunal analysis is based on model groups of herbivore generalists (Gastropoda), detritivores (Isopoda and Diplopoda), and predators (Opiliones). The gastropod assemblages from Reynoutria stands were severely impoverished subsets of those from Urtica stands with reduced densities, species richness and diversity. In general, snails were more sensitive to Reynoutria invasion than slugs such as the invasive Arion 'lusitanicus’. Among detritivores, the abundance of the Isopoda decreased, whereas Diplopoda were not affected by Reynoutria invasion. Yet, the relative abundance of detritivores was significantly higher within the Reynoutria stands. Abundance, species richness and diversity of the predatory Opiliones were higher in the relatively sparse Reynoutria stands. We conclude that ecosystem changes associated with Reynoutria invasion are characterized by shifts from a plant-based to a detritus-based food chain and that Reynoutria invasion primarily enhances predators that profit from the simplified vegetation structure.

Geochemical fractions of copper in soil chronosequences of selected European floodplains

The influence of soil formation on copper sorption is documented based on chronosequences of soils from three river floodplains in Europe (Danube, Ebro and Elbe). Sequential extraction was used to fractionate copper in original and spiked soils in order to study the long-term and short-term behaviour of copper retention. Copper partitioning among defined geochemical fractions was mainly determined by soil pH and the contents of carbonates, organic matter and Fe-/Mn-oxides and hydroxides. Copper extracted with NH 2OH·HCl correlated well with the contents of crystalline Fe-oxides and hydroxides, demonstrating increasing retention capacity with progressing soil development. Copper retained in original soils was found in more strongly bound fractions, whereas sorption of freshly added copper was primarily influenced by the presence of carbonates. Beyond the effect of progressing soil formation, variations in organic carbon contents due to different land use history affected the copper retention capacity of the investigated soils.

Comparison of nitrogen and phosphorus fluxes in some European fens and floodplains

AbstractQuestion: How do nitrogen and phosphorus budgets and balances differ between eutrophic fens and floodplains in western Europe and fens and floodplains in Poland, where we expect less eutrophication to occur?Location: Wetlands along the rivers Dommel (The Netherlands), Zwarte Beek (Belgium) and Biebrza (NE Poland).Methods: Assessment of external input and output fluxes as well as net N‐mineralization rates. Annual N‐ and P‐balances were estimated by the sum of all external input and output fluxes: atmospheric deposition, input of dissolved matter by flooding, input of sediment by flooding, input by groundwater, output by leaching, output by hay‐making and for N also input by N2‐fixation. For N we also estimated net annual N‐availability for plant growth, i.e. the N‐budget, which includes net mineralization in soil.Results: The studied wetland sites had a negative balance, which means that nutrients are depleted but only if mown annually, except for the Dutch/Belgian fens which had an equilibrium N‐balance and the Polish fen which had an equilibrium P‐balance. For the N‐budget it appeared that atmospheric deposition added significantly to the budget of Dutch/Belgian fens and N‐mineralization added significantly to fen and floodplain budgets, except for the Polish fens. Mineralization dominates the N‐budget of the western European floodplains. Hay‐making is the most important output pathway, particularly if practised annually. It seems to diminish N‐enrichment in the Dutch fens and floodplains.Conclusions: We conclude that western European fens and floodplains as well as Polish floodplains have a significant positive N‐budget indicating that there is a surplus of N for plant growth. In the Polish fens this is less due to low atmospheric deposition and lower N‐mineralization rates. The latter is associated with less drying out of the studied Polish ecosystems in summer. Our approach, although an approximate quantification, is helpful for assessing priorities focused on nutrient management.

Application of genetic markers to the discrimination of European Black Poplar (Populus nigra) from American Black Poplar (P. deltoides) and Hybrid Poplars (P. x canadensis) in Switzerland

European Black Poplar (Populus nigra) is considered a rare and endangered tree species because of severe reduction of its natural riverine habitat and potential hybridisation with the related non-indigenous taxa P. deltoides and P. x canadensis. As it is difficult to distinguish these taxa solely based on their morphology, we applied a PCR-based assay with an easy-to-use and robust molecular marker set (cpDNA trnL-trnF/RsaI RFLP, nDNA win3 and nDNA POPX/MspI RFLP) in order to identify pure P. nigra. Different plant tissues could be used for fast and standardised DNA extraction. The application of the three marker types was tested on a number of different Populus taxa, and they were also used for the verification of pure P. nigra in a sample of 304 putative P. nigra individuals from Switzerland. Cross-checking of the DNA data with those using a traditional allozyme approach resulted in complete agreement. The availability of molecular identification methods is an important prerequisite for the conservation of European Black Poplar, because pure, non-introgressed plant material can then be used in restoration projects of European floodplains.

Holocene floodplains and their distribution in urban areas—functionality indicators for their retention potentials

Floodplains are among the natural areas in central Europe which—depending on the formative power of flowing water—possess a high natural potential for the regulation of water and matter flows. Many floodplains and urban development share a long common history in central Europe. Numerous, sharply varying historical views exist on how to distinguish European floodplains. Therefore, the aim of this paper is to examine relevant indicators such as floodloam expansion, groundwater table, relief and land use to see how useful they are for characterising current floodplain functionality in urban areas and to ‘flesh them out’ for a case study.