Tales of the tides: Pattern-based non-target analysis of the Elbe River.

Per- and polyfluoroalkyl substances (PFAS) are highly persistent contaminants. Current regulatory monitoring frameworks cover only a narrow set of regulated long- and short-chain PFAS, while ultrashort-chain compounds such as trifluoroacetic acid (TFA) remain largely unaddressed despite their widespread occurrence. Here, we present regional sources and tributary inputs of diverse PFAS (n = 83), including ultrashort-, short-, and long-chain PFAS as well as PFAS precursors along the 1,200 km Elbe River−North Sea continuum. Based on 129 samples from the Elbe, its tributaries, and wastewater treatment plants (WWTPs), we show that short- and long-chain PFAS concentrations in the Elbe were generally below 30 ng/L, but 1,653 ± 377 ng/L when including TFA. Major tributaries such as the Saale, Vltava, and Mulde delivered PFAS mass loads of several thousand g/day (2,340; 6,080; and 1,700 g/day, respectively, when including TFA) and together accounted for a total discharge of 160 m3 s−1, corresponding to approximately 67% of the Elbe’s water flux at Geesthacht (240 m3/s), which represents the downstream reference point for mass balance calculations prior to tidal influence. This suggests source-enriched inputs rather than simple dilution by tributary inflows, given the disproportionate increase in PFAS mass loads relative to discharge. WWTP effluents from Dresden and Pardubice added up to 185 g/day, mainly shaped by short-chain PFAS. The detection of Capstone B (CDPOS) and Bis(trifluoromethylsulfonyl)imide (NTf2), non-routinely monitored industrial PFAS, further highlights overlooked sources in the area of the Saale-Elbe confluence. Inclusion of TFA increased the median PFAS load in the Elbe River by nearly 50-fold (up to 39,958 g/day), demonstrating the dominant role of ultrashort-chain PFAS currently absent from regulatory monitoring. By linking source apportionment with river-to-sea transport, our study highlights critical gaps in existing monitoring frameworks and provides a transferable methodology for more comprehensive PFAS assessment and regulation in large river systems.

The explanatory content of measurements of suspended particulate matter (SPM) for legacy contaminants in the aqueous phase was evaluated at the Elbe River and its estuary, focusing on cadmium, zinc, cooper, mercury, hexachlorobenzene (HCB), dichlorodiphenyltrichloroethane (DDT) and its metabolites DDD and DDE and polychlorinated biphenyl congener PCB 180 at two locations: nontidal (station Cumlosen) and tidal conditions at the fluvial estuary (station Seemannshöft). Although the affinity of heavy metals and persistent organic pollutants for fine suspended solids and organic matter is well documented, transferring singular observational knowledge to longer timescales, considering SPM-cycles, remains underexplored. This understanding is crucial for identifying key processes affecting the distribution of contaminants that heavily depend on varying SPM composition along the river. We performed a statistical analysis of long-term time series, assessing the explanatory content of SPM-related and other environmental parameters for different contaminant species using the autoregressive-moving-average model with exogenous input (ARIMAX). We obtained the variance of contaminant species explained by cross-correlated parameters, prewhitened through ARIMA-modeling, in both freshwater and tidal conditions. The results suggest that, in the fluvial estuary, the seasonal distribution of pollutants in the aqueous phase is controlled by the presence of very fine particles including aged organic matter and resuspended matter, whereas in the nontidal Elbe, algae-related organic matter influences the advective and diffusive transport of metals. These insights are crucial for enhancing contaminant transport models, highlighting the necessity to consider fine (likely colloidal) particle transport when forecasting metal concentrations and their distribution in solid-water phase systems. In addition, the analysis revealed effects on the distribution of contaminants following the prolonged drought recorded in the Elbe River after 2013, which are expected to become more frequent as a result of climate change.

Abstract Understanding the contributions of diffuse and point sources to nitrate pollution is crucial for managing river water quality. We conducted a long-term modeling study for the Rhine and Elbe basins and their 146 subbasins from 1950 to 2021 to quantify the roles of diffuse and, in particular, point sources in driving stream NO ₃ –N concentrations. In both basins, simulated results show a decline in point source contributions from 1950 to 2000, followed by a relatively stable level at around 25% in the Rhine and fluctuations around 30% levels in the Elbe. The decline in the simulated stream NO ₃ –N concentrations in both basins after 1990 was largely driven by a decrease in point sources, and stream NO ₃ –N concentrations remained high (∼2 mg l −1 ) during 2010–2021, even when point sources were excluded. At the subbasin level, changes in point source contributions and stream NO ₃ –N concentrations reflected the overall trends of their respective basins, although individual subbasins exhibited diverse patterns. In subbasins with high stream NO ₃ –N concentrations during 2010–2021, point source contribution accounted for around 30% (median values across subbasins), and the fractions of agricultural, urban, and industrial land cover were relatively high. These results highlight that point source management alone is not sufficient to reduce stream nitrate to a good ecological status (< 2 mg l −1 ), and spatial targeted management is required to achieve good ecological status at both the regional and local levels.

Abstract. The current status of intertidal waters in the wake of global change was assessed in a baseline study with a 36 month time series of water level, temperature, and salinity measurements from Bottsand lagoon, Baltic Sea, and from the mudflats off Schobüll, North Sea coast of Schleswig-Holstein, Germany. At Bottsand lagoon, annual average water temperatures varied from 12.1 to 12.6 °C, the air temperatures varied from 11.1 to 11.2 °C. The water temperatures followed the air temperatures in winter, and were higher than the air temperatures in spring and summer. The annual average salinities ranged from 14.7 to 16.9 units. The lagoon showed a different variability than the open Baltic surface waters, where the temperatures and salinities were lower in summer and higher in winter. The seasonal salinity differences were less developed in the mid 1960s, when the connectivity of the lagoon with the Baltic Sea was less restricted. In Husum Bight off Schobüll, annual average water temperatures ranged from 10.8 to 11.4 °C, and the air temperatures ranged from 9.9 to 10.2 °C. The water temperatures were lower than air temperatures in winter and higher in spring and summer, when the high waters were warmer during the day than at night-time. The annual average salinities off Schobüll ranged from 24.0 to 27.2 units. They were higher in summer and lower in winter, when the Elbe river runoff was generally enhanced. The same seasonal cycle was recorded in the Sylt Roads time series. Cross-correlations revealed that it takes seven weeks for an Elbe river freshwater pulse to reach Schobüll, and three weeks more to proceed to Sylt. The average salinities were 2.7 units lower off Schobüll than off Sylt. This pervasive gradient of landward decreasing salinities was induced by a local, low-salinity lens on top of tidal waters, fed by groundwater seepage or by freshwater runoff. A cross correlation with the precipitation record revealed salinity decreases about one week after high precipitation. The cumulative salt marsh submergence times per period of observation, i.e. inundation frequencies, were consistently higher at Bottsand than at Schobüll, where the same halophyte assemblages prevailed. As the average salinity was 10 units higher at Schobüll, the differences of inundation frequencies suggested that a certain salinity has to be maintained in the soils to sustain specific halophyte assemblages. A mass occurrence of small Austrominius modestus plates was observed before the vegetation boundary off Schobüll in spring 2024. The data suggested a wipe-out of juvenile barnacles during a short period of strong frost in late November 2023, when daily mean temperatures of up to −10.2 °C were recorded. This biotic response to environmental extremes highlighted the vulnerability of Wadden Sea ecosystems at times of Global Change.

Transformation and degradation of dissolved organic matter (DOM) are of considerable magnitude in large rivers but studies investigating a river system from source to sea are scarce. DOM composition changes from headwaters to tide-impacted river stretches due to natural processes, but is also influenced by anthropogenic impacts on river morphology and water quality. We tested the hypotheses that (1) aromatic, oxygen-rich, and large molecules of terrestrial DOM in upstream regions are transformed to more saturated, nitrogen-rich, and smaller molecules towards the tidal and coastal parts, and (2) chlorophyll a concentration and salinity are important explanatory variables of DOM transformation. We tracked the longitudinal dynamics of DOM composition and relevant drivers along the Elbe River in Central Europe from the Czech headwater region via the lowland freshwater section and the tidal region to the coastal waters of the North Sea applying a Lagrangian sampling approach. Chlorophyll a concentration and oxygen saturation increased longitudinally in the river but showed a distinct minimum in the estuary upstream of the salinity gradient whereas dissolved nutrients were depleted by algae in the freshwater part and were released at algal die-off in the estuary. DOM was dominated by aromatic, oxygen-rich components of terrestrial origin in the upstream region. However, the imprint of this terrestrial signal constantly decreased with increasing river stretch while the proportion of organic nitrogen increased towards the estuary and coastal regions. Analyses of DOM transformations along the river-estuary-ocean gradient revealed that decarboxylation was the most frequent transformation and that phytoplankton and salinity were major explanatory variables of DOM quality. Overall, our unique data set demonstrated a distinct sequence of DOM transformation along the land-ocean gradient highlighting the large activity of riverine and estuarine systems in terms of organic carbon dynamics.

The crucian carp ( Carassius carassius ) is a native freshwater fish and an important indicator of wetland ecosystem health across Central Europe. However, its populations are increasingly threatened by habitat degradation and hybridization with non-native congeners. In this study, we present a mitochondrial cytochrome b (cytb) dataset from C. carassius populations sampled across various tributaries of the Danube and Elbe River basins in Czechia to evaluate genetic diversity and taxonomic clarity within the Carassius genus complex. Our preliminary results reveal multiple distinct mitochondrial haplotypes within nominal C. carassius , highlighting the presence of cryptic genetic diversity. These findings underscore the urgent need for integrative taxonomic approaches to support accurate species identification and conservation management. We advocate for the use of molecular tools in conservation monitoring programs to safeguard the genetic integrity of native C. carassius populations in vulnerable wetland habitats.

River systems often retain the imprint of historical mercury (Hg) contamination over long time scales since decreasing trends after reduced Hg inputs are impeded by legacy storage in sediments. Here, we report temporal and spatial variations of total mercury (THg) concentrations in sediments of the Elbe River, Germany. Temporal THg trends (1996–2019) were investigated at five long-term monitoring sites in harbors and groyne fields. In contrast to well-documented declines of THg in suspended particulate matter (SPM) in recent decades, significant trends of decreasing THg in sediments were only found for two harbors, while the other sites exhibited no decreasing trends. Spatial distribution patterns of THg in sediments (0.11–10.6 mg kg−1) showed increases in areas of the Middle Elbe downstream of the confluences of the tributary rivers Mulde and Saale. Similar spatial patterns of increasing concentrations were observed in floodplain soils (0.04–4.20 mg kg−1) and SPM (0.37–1.84 mg kg−1). Regardless of the spatial origin or sample type (sediments, floodplain soils, SPM), the binding forms of Hg studied by sequential extraction showed a clear dominance of strongly bound Hg extractable with 12 M HNO3. While this seems to indicate a low mobility of Hg, uptake into aquatic food webs may occur following methylation. Our results demonstrate that the reduction of Hg releases into the Elbe River basin has so far only been able to improve sediment quality in some parts. Deposits of Hg-containing sediments will therefore remain a future problem with implications for the continued exceedance of environmental quality standards and the management of waterways.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10661-025-14881-y.

Abstract. The Elbe River drains an intensely used agricultural area and cuts through a series of consolidated and unconsolidated aquifers with heterogeneous hydraulic properties and dimensions. For decades and as a result of overfertilization, particularly in the former GDR, the hosted groundwater transport nutrients into the river with serious implications for water quality and ecosystem health. As fertilization practices changed over time, nutrient loads in the groundwater recharge declined since the 1990s. This study investigates the residence time scales of groundwater along the river, as a measure to estimate the input periods of the associated nutrients entering the river using multi-environmental tracers (3H/3He, SF6, CFCs, 14C). By applying lumped parameter models, we conclude that the average ages of groundwater range from a few up to 41 years, with infiltration occurring predominantly after 1985. Our results identify a young groundwater system with measurable denitrification and minimal to moderate admixtures of older water fractions clearly discernible with 4He. That indicates, the groundwater that was recharged during the GDR period (1945–1989) at maximum fertilizer application has already run off, the nutrient concentrations in the groundwater have peaked and may continue to decline in the coming decades. These results are crucial for informing river basin management strategies aimed at mitigating eutrophication and protecting aquatic ecosystems. It provides valuable insights into the temporal dynamics of groundwater contributions to surface waters and their regional implications for sustainable resource management.

Abstract River floodplain systems are challenged by drought, which may trigger excess nutrient concentrations and greenhouse gas emissions. Increasingly frequent short-term droughts may exacerbate both problems by altering hydrological connectivity and thereby restructuring microbial communities and dissolved organic matter (DOM), which, in combination, may regulate sediment phosphorus and methane release. However, the combined effects of drought and connectivity on phosphorus and methane release via changes in DOM composition and microbial activity remain poorly understood. We incubated sediments from three floodplain sites along a hydrological connectivity gradient to the River Elbe and subjected them to two short-term drought intensities, corresponding to sediment moisture losses of 0.5–2.5% (moderate drought) and 19–21% (intense drought), followed by rewetting. Drought had surprisingly limited effects on phosphorus and methane release, while the site had a consistently higher impact and shaped the direction and magnitude of drought effects. Moreover, our results suggest that fluxes may be more pronounced at sites that were formerly well-connected to the river. Phosphorus was released under oxic conditions and was linked to heterotrophic microbial carbon use and humic-like DOM, implying that the effects of DOM-mediated microbial activity on phosphorus release need to be considered in future research efforts. Our findings suggest that long-term changes in hydrological connectivity, like lower discharge and changed DOM delivery, could have stronger effects on nutrient dynamics and microbial processes than short-term drought. Preserving floodplain connectivity is therefore critical to limiting nutrient and greenhouse gas release under climate change.

Abstract The safety and service life of cable-stayed bridges directly depend on the structural condition of individual stay cable. The diagnostics of the cables and their anchorage systems is an integral part of the complete bridge assessment. The paper summarizes the results of an extensive diagnostic survey carried out on three major bridge structures in the Czech Republic: the single-span bridge in Hrachovec, the single-span bridge in Židlochovice, and the three-span highway bridge over the Elbe River near Poděbrady. The basic diagnostic phase included visual inspection of the outer sheath, acoustic tracing, and moisture measurement of the prestressed reinforcement. The advanced phase employed dynamic testing of natural frequencies and strain gauge monitoring to verify tensile forces and prepare data for force rectification. Calibration of the dynamic methods using hydraulic post-tensioning confirmed the high accuracy of these non-invasive techniques. The results demonstrate that the combination of standard and advanced diagnostic methods provides an effective tool for predictive maintenance and enhanced reliability of cable-stayed bridge structures. Moreover, dynamic analysis offers new possibilities for long-term monitoring and targeted extension of the structural service life.

The port of Hamburg represents a transition zone between upstream, shallow regions of high net primary production and downstream deep and more turbulent waters in the tidal Elbe River in northwestern Germany. Correspondingly, strong gradients of degradable organic matter (OM) on a distance of a few river kilometers had been identified. This study links microbial community composition using 16S metagenomic amplicons and extracellular polymeric substances (EPS) composition to the observed gradients of sediment OM lability. It was hypothesized that lability gradients caused by higher concentrations of biogenic, autochthonous OM upstream and greater share of already stabilized OM downstream reflect in gradients of microbial community composition, diversity and EPS characteristics. Indeed, available OM was found to act as key driver regulating syntrophic microbial community composition and associated metabolic features, with location-specific overriding the effect of seasonal variations. Upstream sites with high available OM featuring lower bacterial but increased archaeal diversity and elevated methane and carbon dioxide fluxes, whereas lower OM lability downstream fostered a more diverse bacterial but decreased archaeal diversity. The ratio between microbial taxon richness and biomass correlated inversely with OM transformation rates. These patterns also reflected in increased EPS concentration produced in response to metabolic needs (i.e. polysaccharides and proteins), whereas structural components such as lipids, which can be more resistant under the prevailing anoxic conditions, remained more evenly distributed along the transect. Although bacterial relative abundances exceeded archaeal abundances (<1%) by far, archaeal functional significance remained pivotal for the final release of carbon as methane and carbon dioxide under the mostly reducing conditions in the deposited sediment.

Abstract This contribution highlights the measures taken by the Franks in the eighth and ninth centuries to control the movement of goods and people on the peripheries of the empire. It focuses on the northeastern frontier zone of the Carolingian empire, where Charlemagne adopted a series of restrictive policies aimed at channelling trade into centres, often fortified, administered by royal envoys. In the context of studies of the mobility of goods and people in the Early Middle Ages, restrictions of this kind were nothing new: in the first half of the eighth century, the Lombard kings Ratchis and Aistulf had already created trade posts at the chokepoints of the Alpine passes to control the passage of travellers and merchants into and out of Italy. Charlemagne himself had similar laws in place for the trade of certain types of goods, such as weapons, armour and grain. However, they were only possible if they were adequately accompanied by logistical and military infrastructure. This contribution argues that the Capitulary of Diedenhofen, listing trade centres located along the Elbe and Saale rivers that were fortified from 806 and onwards, offers the opportunity to study such intertwined efforts. It shows that for the Carolingian kings, and for the central authorities of the Early Middle Ages, the management and control of the mobility of people and goods was a fundamental tool through which they could impose their authority. Part of this article was written during my stay at the Center for Advanced Research ‘Migration und Mobilität in Spätantike und Frühmittelalter’ at the University of Tübingen. I would therefore like to thank Steffen Patzold, Mischa Meier and Sebastian Schmidt-Hofner for the opportunity to work in Tübingen. I would also like to thank Francesco Veronese for his suggestions and help during the first draft of this article. I also received many suggestions from Becca Grose, Sonsoles Costero-Quiroga, Marco Stoffella, Francesco Borri and Courtney Luckhardt, whom I would like to thank for their help and support. The corrections and suggestions of the two reviewers have also been fundamental in improving this article, and I am therefore grateful to them for their work. Any other errors of language, grammar or content are my own.

ABSTRACT Preservation of urban aquatic ecosystems is of primary importance for human well‐being, biodiversity protection and the future of society. Lake–groundwater–river interactions within urban floodplains harbour intrinsic fragility, yet remain largely understudied. Appropriate environmental management can help assure the conservation of these sites through strategies that are based on physical, chemical and isotope constraints. Here we present the example of the Groundwater and Lakes Urban Observatory (GLUO) in Magdeburg, Germany, where monitoring has been carried out since 2022. Our database for the year 2023 includes data from the Elbe River, two lakes named Lake Salbker South and Lake Salbker North, and two groundwater wells. Major ion patterns point to the Elbe River and Lake Salbker South as the end‐members for water compositions within the system, although contributions from the former appear less significant. Stiff plots suggest the existence of a more saline end‐member that may receive inputs from the Zechstein Formation and drives the geochemistry of Lake Salbker South. Dissolved oxygen (DO) concentrations in Lake Salbker South during stratification show a marked depletion in the hypolimnion with values down to 1.8 mg L −1 that we attribute to mineralization of organic matter as well as oxidation of sulphur compounds. This feature acknowledges Lake Salbker South as a natural hydrogen sulphide (H 2 S) reactor. Water stable isotope compositions (δ 2 H H2O and δ 18 O H2O ) of the water bodies within the GLUO outline a trend that is compatible with moderate evaporation. We discuss that dissolution of saline deposits may also play a role. These findings emphasize the need to implement the study of lake–groundwater–river interactions within floodplains, especially when hypertrophic or sulphur‐rich water bodies are involved. Due to the inherent vulnerability and potential hazards associated to these environments, we stress the importance of establishing a multidisciplinary monitoring framework to evaluate their geochemical fluxes and ecological integrity.

Abstract The Elbe River basin, located in Germany and the Czech Republic, is vulnerable to changing climate extremes and has experienced multiple natural hazards over the years. Therefore, assessing the impacts of climate change on extreme events across the basin is vital to adapt and improve resiliency. Unfortunately, data on variations of climate extremes usually have a very coarse spatial resolution, which limits any regional application. Thus, to improve the quality and availability of climate extreme data, we estimated climate indices mostly from the Expert Team on Climate Change Detection Monitoring and Indices (ETCCDI). The indices were based on temperature, precipitation, and agrometeorology. They were estimated on a regional scale using an ensemble of high-resolution (12.5 km) climate model data. Two different climate scenarios, rcp26 and rcp85, were considered. The eight climate indices estimated in this study (1) help better understand the variation in climate extreme events, (2) identify vulnerable areas, and (3) analyse their impact on natural resources (e.g., agriculture). The results showed that by the end of this century, temperature-based extremes will increase with minimal spatial variation for summer months, while precipitation-based extremes show that conditions which promote flood events will increase in the headwater regions located in the South of the basin. Additionally, agrometeorological indicators imply that factors favourable for agricultural processes will become more common, but their trend and seasonal analysis show extreme events will hinder the application of best farming practices. Lastly, policy recommendations for adaptation measures (e.g., green infrastructure) have been highlighted in this study to address different climate risks, enabling resilient resource management across the basin. Graphical Abstract In this study, we prepared and analysed eight climate indices datasets using projected climate model data from the European Coordinated Regional Downscaling Experiment (EURO-CORDEX) on a subbasin scale. The indices were based on temperature, precipitation, and agrometeorology and were estimated for two different climate scenarios rcp26 and rcp85. The results from our study further highlight (1) the complex impacts a warming climate will have on the intensity of extreme events, (2) the effect of changing extremes on regional natural resources, and (3) help identify vulnerable regions. The results showed that by the end of this century, temperature-based extremes will increase with minimal spatial variation for summer months, while precipitation-based extremes show that conditions which promote flood events will increase in the headwater regions located in the South of the basin. Additionally, agrometeorological indicators suggest that factors favourable for agricultural processes will become more common; however, their trend and seasonal analysis indicate that extreme events will hinder the application of best farming practices.

Abstract Carbon dioxide removal (CDR) strategies like enhanced weathering and river/ocean alkalinity enhancement have been suggested to increase alkalinity in rivers, coastal areas, and eventually oceans. The effectiveness and sustainability of these CDR approaches depend on the persistence of added alkalinity, since exceeding certain Ω-thresholds for a given water composition may lead to carbonates formation, causing the loss of previously added alkalinity. In this research, stability of alkalinity was tested using incubation experiments with Elbe estuary freshwater from two seasons (March and August). Alkalinity was increased up to 4000 μmol kgw−1, with varying salinity from 0 to 16. This study shows that the stability of alkalinity depends on the presence and quantity of suspended particles, seasonality of water chemistry, and salinity. Based on the experimental data, the Elbe estuary may take up additional alkalinity in the freshwater part, corresponding to ∼3.0 MtCO2 yr−1 being transported towards the North Sea. Estimates of alkalinity additions from the 1970s to 2010s show a decreasing potential due to changes in pCO2 and pH. The upper geochemical limit for transporting additional alkalinity through estuarine systems serves as a critical boundary. Environmentally feasible levels may be lower than identified here and depend on environmental regulations.

We report a quantification approach for directly determining total tin and tin-based pollutants/species in sediments via electrothermal vaporization/inductively coupled plasma-mass spectrometry (ETV/ICP-MS) utilizing an on-line isotope dilution mass spectrometry (IDMS) approach. The method was developed and validated using an estuarine sediment reference material (BCR-277R), yielding a recovery of 106%. A relative standard deviation (RSD) of 14%, comparable to published data using a similar method, was obtained. A limit of quantification (LOQ) was estimated at 0.008mg Sn kg-1 and sufficient for quantifying the total tin mass fraction of surface sediments along the tidal River Elbe course. Hereby, a decrease towards the river mouth, presumably due to dilution effects by less polluted marine sediment, was observed. Besides total tin, monitoring of organotin compounds (OTCs)/species is of interest in sediments due to their toxic effects on aquatic life. The method's capability was extended by separating an OTC fraction in a sediment certified reference material (CRM) through the ETV temperature program. While spiking experiments with OTC standards confirmed the assignment, only a small fraction of the total certified OTC amount (3%), likely due to matrix effects, was recovered. However, applying the method to real-world samples, OTCs were detectable along the River Elbe course. By this, we demonstrated the potential of our method as a complementary fast-screening approach to species-specific analysis procedures.

Abstract Herein we describe the first record of the Pannonian endemic Anostracan species Chirocephalus carnuntanus (Brauer, 1877) from northern Central Europe. The presence of the species was recorded approximately 25 km north of the city of Magdeburg (Germany) in a relatively high abundance in a temporarily flooded agricultural area in 6.4 km distance to the mouth of the river Ohre into the river Elbe. The first observation was on 15 March 2024. Subsequent surveys and collections of specimens were made until 22 April 2024. Near surface natural salt banks seem to have contributed to the relatively high salinity and conductivity of the ephemerally water filled habitat. We suggest that the new population of C. carnuntanus in Germany was founded via zoochory by migrating birds.

Flood events caused by high rainfall can have profound biogeochemical impacts on riverine systems but also on the receiving coastal waters. The winter flood in Germany in December 2023/January 2024 affected the Elbe and Weser River systems. We obtained unique data during the peak of the flood and compared these with the monthly means from previous years (2018-2023). Hydrographic parameters and nutrients were determined by standard methods. Low salinity values were observed in the Elbe estuary and the adjacent German Bight (part of North Sea). At Helgoland the lowest average salinity was observed in January 2024 with 31.3 ± 0.5 compared to an average salinity of 32.7 ± 0.7 for the years 2016 to 2023. Nutrient loads (nitrate, phosphate) in the rivers showed a six- to 11-fold increase in the Elbe and Weser rivers compared to years without flood events. Enhanced concentrations of nitrate and silicate were found in the German Bight in January. Nutrients were diluted with North Sea waters, indicating a conservative behavior of nutrients in winter. Atypical prevailing meteorological conditions in January 2024, with predominantly easterly winds, potentially affect the dispersal of the river plume and the nutrients in the North Sea. In March 2024 the chlorophyll-a concentration strongly increased to 2.9 ± 1.8 µmol/L and was twice as high compared to only 1.5 ± 0.7 µmol/L observed in previous years. The observed intensified spring bloom in March in the German Bight near the island of Helgoland indicates the impacts of the flood-derived nutrient inputs three months after the flood event, as the timing of light and nutrient availability was optimal. It is assumed that seasonality and magnitude of flooding in the Elbe estuary and adjacent coastal region will change in future due to climate warming. Thus, the timing of light and nutrient availability will also change, with unconstrained impacts on primary producers and higher trophic levels.

Hybridization can create novel chemical traits and enhance plant adaptability to diverse environments. This study examined the effects of hybridization on chemical diversity and ecological interactions in Salix alba×fragilis hybrids from the Elbe River basin (Czechia). We analysed leaf metabolites of hybrids and their parental species for concentration, richness, and structural α- and β-diversity, linking them to herbivorous insect assemblages and soil conditions. Hybrids exhibited intermediate metabolite concentration and richness but showed higher structural α-diversity and distinct structural β-diversity compared with their parents. Hybrid-specific metabolites were structurally related to parental metabolites, indicating minor structural modifications rather than major changes to metabolic pathways following hybridization. Herbivore assemblages were influenced by metabolite richness or structural α-diversity. However, insect group responses varied, and herbivory damage did not correlate with leaf chemistry or differ between hybrids and parents. Soil nitrogen correlated with metabolite structural β-diversity, with hybrids displaying greater chemical variation along nitrogen gradients. These results highlight that hybridization significantly altered structural metabolite diversity. Yet, the structural changes were relatively minor which, together with group-specific responses of herbivores, could explain their modest effect on herbivory. Instead, they may enable these hybrids to flexibly respond to soil conditions, possibly contributing to their widespread occurrence.