Danube Research Articles

Habitat use of barbel (Barbus barbus) in a restored urban Danube tributary

Tributaries play a vital role in fish spawning and recruitment, significantly influencing mainstem river fish populations. However, in the Anthropocene era, tributaries within river networks suffered ecological degradation due to fragmentation and channelization. This has led to reduced distribution ranges and declining populations of various riverine species, underscoring the urgency of conservation and rehabilitation efforts. Our study explores the potential for reintroducing fish from the mainstem Danube River into the Wien River, an urban tributary that has undergone partial rehabilitation. We assessed habitat use and movement patterns of 20 adult barbel (Barbus barbus), a species classified as ‘near threatened’ in Austria, collected from the Danube River during the spawning season. These barbel were tagged with radio telemetry tags and relocated into the upper reaches of the Wien River, surmounting several artificial barriers in the lower sections. Although spawning activity was not observed among the barbel, possibly due to prevailing water temperatures, our data suggest that the Wien River could function as a viable temporary habitat. Barbel were notably inclined to inhabit deeper pool and run habitats. Their daily movements and home ranges were relatively limited, ranging from 0.0 to 1.1 km and 100 m to 2.9 km, respectively. One contributing factor to restricted movement was the presence of beaver and knotweed dams, which created temporary migration obstacles. On average, the barbel remained within the system for more than a month. Most of these fish migrated downstream at the onset of a significant high-flow event. Our assessment suggests that while the Wien River may not serve as a permanent habitat, it could function as a temporary habitat for migratory fish. However, to ensure accurate assessments of the restored Wien River as a spawning habitat, it is imperative to reevaluate the findings under stable spawning conditions and gather comprehensive data on relevant abiotic factors. This study advocates for the restoration of longitudinal connectivity between tributaries and mainstem rivers as a means to counteract biodiversity loss in Anthropocene river ecosystems.

Electrochemical Detection of Cd2+, Pb2+, Cu2+ and Hg2+ with Sensors Based on Carbonaceous Nanomaterials and Fe3O4 Nanoparticles.

Two electrochemical sensors were developed in this study, with their preparations using two nanomaterials with remarkable properties, namely, carbon nanofibers (CNF) modified with Fe3O4 nanoparticles and multilayer carbon nanotubes (MWCNT) modified with Fe3O4 nanoparticles. The modified screen-printed electrodes (SPE) were thus named SPE/Fe3O4-CNF and SPE/Fe3O4-MWCNT and were used for the simultaneous detection of heavy metals (Cd2+, Pb2+, Cu2+ and Hg2+). The sensors have been spectrometrically and electrochemically characterized. The limits of detection of the SPE/Fe3O4-CNF sensor were 0.0615 μM, 0.0154 μM, 0.0320 μM and 0.0148 μM for Cd2+, Pb2+, Cu2+ and Hg2+, respectively, and 0.2719 μM, 0.3187 μM, 1.0436 μM and 0.9076 μM in the case of the SPE/ Fe3O4-MWCNT sensor (following optimization of the working parameters). Due to the modifying material, the results showed superior performance for the SPE/Fe3O4-CNF sensor, with extended linearity ranges and detection limits in the nanomolar range, compared to those of the SPE/Fe3O4-MWCNT sensor. For the quantification of heavy metal ions Cd2+, Pb2+, Cu2+ and Hg2+ with the SPE/Fe3O4-CNF sensor from real samples, the standard addition method was used because the values obtained for the recovery tests were good. The analysis of surface water samples from the Danube River has shown that the obtained values are significantly lower than the maximum limits allowed according to the quality standards specified by the United States Environmental Protection Agency (USEPA) and those of the World Health Organization (WHO). This research provides a complementary method based on electrochemical sensors for in situ monitoring of surface water quality, representing a useful tool in environmental studies.

A data-driven global flood forecasting system for medium to large rivers.

Losses from catastrophic floods are driving intense efforts to increase preparedness and improve response to disastrous flood events by providing early warnings. Yet accurate flood forecasting remains a challenge due to uncertainty in modeling, calibrating, and validating a useful early warning system. This paper presents the Requisitely Simple (ReqSim) flood forecasting system that includes key variables and processes of basin hydrology and atmospheric forcing in a data-driven modeling framework. The simplicity of the modeling structure and data requirements of the system allows for customization and implementation in any medium to large rain-fed river basin globally, provided there are water level or discharge measurements at the forecast locations. The proposed system's efficacy is demonstrated in this paper through providing useful forecasts for various river basins around the world. This include 3-10-day forecasts for the Ganges and Brahmaputra rivers in South Asia, 2-3-day forecast for the Amur and Yangtze rivers in East Asia, 5-10-day forecasts for the Niger, Congo and Zambezi rivers in West and Central Africa, 6-8-day forecasts for the Danube River in Europe, 2-5-day forecasts for the Parana River in South America, and 2-7-day forecasts for the Mississippi, Missouri, Ohio, and Arkansas rivers in the USA. The study also quantifies the effect of basin size, topography, hydrometeorology, and river flow controls on forecast accuracy and lead times. Results indicate that ReqSim's forecasts perform better in river systems with moderate slopes, high flow persistence, and less flow controls. The simple structure, minimal data requirements, ease of operation, and useful operational accuracy make ReqSim an attractive option for effective real-time flood forecasting in medium and large river basins worldwide.

The Expected Dynamics for the Extreme Wind and Wave Conditions at the Mouths of the Danube River in Connection with the Navigation Hazards

The entrance in the Sulina channel in the Black Sea is the target area of this study. This represents the southern gate of the seventh Pan-European transport corridor, and it is usually subjected to high navigation traffic. The main objective of the work is to provide a more comprehensive picture concerning the past and future expected dynamics of the environmental matrix in this coastal area, including especially the extreme wind and wave conditions in connection with the possible navigation risks. The methodology considered assumes analyses performed at three different levels. First, an analysis of some in situ measurements at the zero-kilometer point of the Danube is carried out for the 15-year period of 2009–2023. Together with the maximum wind speed and the maximum value of the wind gusts, the water level variation was analyzed at this point. As a second step, the analysis is based on wind speed data provided by regional climate models. Two periods, each spanning 30 years, are considered. These are the recent past (1976–2005), when comparisons with ERA5 reanalysis data were also performed, and the near future (2041–2070), when two different models and three climate scenarios were considered. The focus was on the extreme wind speed values, performing comparisons between the past and future expected extreme winds. Finally, the third analysis is related to the wave conditions. Thus, using as a forcing factor each of the wind fields that was previously analyzed, simulations employing a spectral wave model were carried out. The wave modeling system was focused using three different computational domains with increasing resolution towards the target area, and the nearshore wave conditions were evaluated. The results show that both the extreme wind and wave conditions are expected to slightly increase in the future. Especially in the wintertime, strong wind fields are often expected in this area, with wind gusts exceeding more than 70% of the hourly average wind velocity. With regard to the waves, due to the complex nearshore phenomena, considerable enhancements in terms of significant wave heights are induced, and there is also an elevated risk of the occurrence of rogue waves. This work is still ongoing, and taking into account the high navigation risks highlighted, the next step would be to elaborate the risk assessment of severe shipping conditions, particularly related to the likelihood or probability of adverse conditions with the potential of generating hazardous situations in this coastal environment.

Temporal and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in the Danube River in Hungary

The Danube is a significant transboundary river on a global scale, with several tributaries. The effluents from industrial operations and wastewater treatment plants have an impact on the river's aquatic ecosystem. These discharges provide a significant threat to aquatic life by deteriorating the quality of water and sediment. Hence, a total of 16 Polycyclic Aromatic Hydrocarbons (PAHs) compounds were analyzed at six locations along the river, covering a period of 12 months. The objective was to explore the temporal and spatial fluctuations of these chemicals in both water and sediment. The study revealed a significant fluctuation in the concentration of PAHs in water throughout the year, with levels ranging from 224.8 ng/L during the summer to 365.8 ng/L during the winter. Similarly, the concentration of PAHs in sediment samples varied from 316.7 ng/g in dry weight during the summer to 422.9 ng/g in dry weight during the winter. According to the Europe Drinking Water Directive, the levels of PAHs exceeded the permitted limit of 100 ng/L, resulting in a 124.8% rise in summer and a 265.8% increase in winter. The results suggest that the potential human-caused sources of PAHs were mostly derived from pyrolytic and pyrogenic processes, with pyrogenic sources being more dominant. Assessment of sediment quality standards (SQGs) showed that the levels of PAHs in sediments were below the Effect Range Low (ERL), except for acenaphthylene (Acy) and fluorene (Fl) concentrations. This suggests that there could be occasional biological consequences. The cumulative Individual Lifetime Cancer Risk (ILCR) exceeds 1/104 for both adults and children in all sites.

Age, Growth, and Mortality of Pontic Shad, Alosa immaculata Bennett, 1835, in the Danube River, Romania

This study aimed to evaluate the growth, mortality parameters, and exploitation rate of Pontic shad, Alosa immaculata Benett, 1835, in the Danube River, Romania (km 169–197). The sampling collection started with the first signs of Pontic shad migration, on 4 March 2023, and continued weekly until the beginning of June 2023, when the last specimens were caught in the nets. The estimation of the growth, mortality parameters, and exploitation rate was done in FiSAT (FAO-ICLARM Stock Assessment Tools). The von Bertalanffy growth equation was estimated at L∞ = 36.75 cm, the growth coefficient was k = 0.68 year−1, and the theoretical initial age was t0 = −0.67 year−1. The total mortality rate (Z) estimated was 2.76 year−1, with a natural mortality rate (M) and fishing mortality rate (F) of 0.89 year−1 and 1.87 year−1, respectively. The Z/k ratio was found to be 4.11 and the exploitation rate (E) was estimated at 0.68 year−1, indicating the overexploitation of Alosa immaculata stocks. In conclusion, this study provides valuable insights into the population dynamics of Pontic shad in the Danube River, Romania. The assessments of the growth parameters, mortality rates, and exploitation rates highlight a level of overexploitation of Alosa immaculata stocks. These findings underscore the importance of applying effective fishery management strategies to ensure the sustainability and conservation of this valuable fish species in the Danube River ecosystem.

Nutritional and Sensory Characterization of Some Fermented Food Products Made in the Carpathian-Danubian-Pontic Area

Abstract The territory of Romania has been known as the Carpathian-Danubian-Pontic space since ancient times, being traversed from one end to the other by the Carpathian Mountains and being bordered to the south by the Danube River (Danubius) which flows into the Black Sea (Pontic area). Fermented food products manufactured in Romania belong to the many categories, such as: lactic acid dairy products or fermented dairy products (yogurt, sana, buttermilk, kefir, fermented cream, fresh cheese), pickled vegetables (cabbage, cucumbers, red pepper), non-alcoholic fermented beverages (braga, borsch, vinegar, socata), traditional fermented bread, maturated cheeses, raw dried salami and alcoholic beverages (beer, wine). In the present article we will focus on a nutritional and sensory characterization of the most famous fermented products that are manufactured almost exclusively in the Carpathian-Danubian-Pontic area, of course also due to the influence of the neighbours, this being: fermented dairy products (yoghurt, sana and buttermilk), lactic fermented pickles (pickled cabbage) and non-alcoholic fermented drinks (braga, borsh and socata).

The Contribution of Naval Diplomacy to Regional Maritime Security

In the context of the military conflict in the Black Sea region, with implications for regional security, the approach proposes a solution to strengthen international relations by capitalising on the non-coercive potential of the naval presence on the maritime communication routes in the Black Sea, starting from the premise that the Romanian Navy is the military instrument of power through which the state projects its naval diplomacy, a mission manifested under the auspices of ways of asserting national maritime and fluvial interests. With a wide range of diplomatic instruments through which the Romanian state manifests and consolidates its geopolitical position and interests in the Black Sea and the Danube River, at the political-military level there is the possibility of using specific ways of contributing to the consolidation of regional maritime security. Practically, the proposal to carry out a regional cooperation initiative in the Black Sea, by establishing an air-land-naval battle group, under the auspices of the collaboration of allied partners, candidates, and the riverine countries of the Black Sea Extended Area. Punctually, through this approach, a solution is presented regarding the contribution of the Romanian Navy to the consolidation of regional, maritime, and fluvial security, through simple steps, resuming a previously applied model, and effectively using military instruments through regional cooperation.

Contribuția diplomației navale la securitatea maritimă regională

In the context of the military conflict in the Black Sea region, with implications for regional security, the approach proposes a solution to strengthen international relations by capitalising on the non-coercive potential of the naval presence on the maritime communication routes in the Black Sea, starting from the premise that the Romanian Navy is the military instrument of power through which the state projects its naval diplomacy, a mission manifested under the auspices of ways of asserting national maritime and fluvial interests. With a wide range of diplomatic instruments through which the Romanian state manifests and consolidates its geopolitical position and interests in the Black Sea and the Danube River, at the political-military level there is the possibility of using specific ways of contributing to the consolidation of regional maritime security. Practically, the proposal to carry out a regional cooperation initiative in the Black Sea, by establishing an air-land-naval battle group, under the auspices of the collaboration of allied partners, candidates, and the riverine countries of the Black Sea Extended Area. Punctually, through this approach, a solution is presented regarding the contribution of the Romanian Navy to the consolidation of regional, maritime, and fluvial security, through simple steps, resuming a previously applied model, and effectively using military instruments through regional cooperation.

Romanians and Bulgarians – Incidents at the Danube River Border (1890-1901)

On 2/14 September 1829, the Peace Treaty of Adrianople between the Tsarist Empire and the Ottoman Empire was concluded with important effects for the two Romanian countries, Moldavia and Wallachia. Their political development was regulated by a separate document, an integral part of the text of the Treaty. The separate Act confirmed the agreements made by the Tsarist Empire and the Ottoman Empire in the text of the Akkerman (White Citadel) Convention on 25 September/7 October 1826, on the election of the Romanian ruler, following the wish and consent expressed by the Sublime Porte. In addition to these political issues, important for the topic covered in this article were the provisions related to the protection of the borders, especially the right bank of the Danube and the islands close to the left bank of the great river that were in proximity to the Ottoman Empire. According to the Adrianople Treaty of 1829, the thalweg along the Danube was considered the border between Moldova and Wallachia on the entire common sector up to the confluence with the Prut River, agreement protected by the Sublime Porte. In 1830, after the Treaty of Adrianople, a commission composed of the delegates of Wallachia, Moldavia, the Tsarist Empire and the Ottoman Empire proceeded to delimiting the river border between the Ottoman Empire and the Romanian Countries by fixing the existing thalweg at that time. Obviously, natural phenomena contributed over time to its modification, so that, after the Congress of Berlin in 1878, when it was decided to trace the land border between the countries bordering the Danube, a series of incidents at the Romanian-Bulgarian river border occurred. In this context, it is highlighted the strategic and economic importance of the Danube.

Romanians and Bulgarians – Incidents at the Danube River Border (1890-1901)

On 2/14 September 1829, the Peace Treaty of Adrianople between the Tsarist Empire and the Ottoman Empire was concluded with important effects for the two Romanian countries, Moldavia and Wallachia. Their political development was regulated by a separate document, an integral part of the text of the Treaty. The separate Act confirmed the agreements made by the Tsarist Empire and the Ottoman Empire in the text of the Akkerman (White Citadel) Convention on 25 September/7 October 1826, on the election of the Romanian ruler, following the wish and consent expressed by the Sublime Porte. In addition to these political issues, important for the topic covered in this article were the provisions related to the protection of the borders, especially the right bank of the Danube and the islands close to the left bank of the great river that were in proximity to the Ottoman Empire. According to the Adrianople Treaty of 1829, the thalweg along the Danube was considered the border between Moldova and Wallachia on the entire common sector up to the confluence with the Prut River, agreement protected by the Sublime Porte. In 1830, after the Treaty of Adrianople, a commission composed of the delegates of Wallachia, Moldavia, the Tsarist Empire and the Ottoman Empire proceeded to delimiting the river border between the Ottoman Empire and the Romanian Countries by fixing the existing thalweg at that time. Obviously, natural phenomena contributed over time to its modification, so that, after the Congress of Berlin in 1878, when it was decided to trace the land border between the countries bordering the Danube, a series of incidents at the Romanian-Bulgarian river border occurred. In this context, it is highlighted the strategic and economic importance of the Danube.

Romanians and Bulgarians – Incidents at the Danube River Border (1890-1901)

On 2/14 September 1829, the Peace Treaty of Adrianople between the Tsarist Empire and the Ottoman Empire was concluded with important effects for the two Romanian countries, Moldavia and Wallachia. Their political development was regulated by a separate document, an integral part of the text of the Treaty. The separate Act confirmed the agreements made by the Tsarist Empire and the Ottoman Empire in the text of the Akkerman (White Citadel) Convention on 25 September/7 October 1826, on the election of the Romanian ruler, following the wish and consent expressed by the Sublime Porte. In addition to these political issues, important for the topic covered in this article were the provisions related to the protection of the borders, especially the right bank of the Danube and the islands close to the left bank of the great river that were in proximity to the Ottoman Empire. According to the Adrianople Treaty of 1829, the thalweg along the Danube was considered the border between Moldova and Wallachia on the entire common sector up to the confluence with the Prut River, agreement protected by the Sublime Porte. In 1830, after the Treaty of Adrianople, a commission composed of the delegates of Wallachia, Moldavia, the Tsarist Empire and the Ottoman Empire proceeded to delimiting the river border between the Ottoman Empire and the Romanian Countries by fixing the existing thalweg at that time. Obviously, natural phenomena contributed over time to its modification, so that, after the Congress of Berlin in 1878, when it was decided to trace the land border between the countries bordering the Danube, a series of incidents at the Romanian-Bulgarian river border occurred. In this context, it is highlighted the strategic and economic importance of the Danube.

Microplastics in the Danube River and Its Main Tributaries—Ingestion by Freshwater Macroinvertebrates

This study was carried out at the Danube River and its tributaries during the Joint Danube Survey 4 (JDS4) expedition. Three freshwater benthic species were used to estimate the quantity of microplastics (MPs): Corbicula spp., Limnodrilus hoffmeisteri (Claparede, 1862), and Polypedilum nubeculosum (Meigen, 1804). Following the kick and sweep technique, individuals were sampled using a hand net or dredge. In order to estimate the number of MP particles/individual particles/g wet body mass, the body mass and total length of all specimens were measured. Alkaline (Corbicula spp. and L. hoffmaisteri) and enzymatic (P. nubeculosum) protocols were performed for tissue degradation. All samples were filtered through glass microfiber filters (mesh size 0.5 µm). The particles were photographed, measured, and counted. A total of 1904, 169, and 204 MPs were isolated from Corbicula spp., L. hoffmaisteri, and P. nubeculosum, respectively. To confirm the chemical composition of isolated MPs, a subsample of 46 particles of the fragmented particles from 14 sampling sites was analysed via µ-ATR-FTIR spectroscopy analysis. The particles were characterised as polycarbonate (PC), polyethylene terephthalate (PET), polypropylene–polyethylene copolymer (PP-PE), nylon (polyamide-PA) and cellophane, with the domination of PET.

Northwest Transdanubia from the end of the Early Bronze Age until the Koszider Period

Review article of the PhD dissertation submitted in 2023 to the Archaeology Doctoral Programme, Doctoral School of History, Eötvös Loránd University, Budapest, and written under the supervision of Gábor V. Szabó. The dissertation investigated the processes taking place at the end of the Early and in the Middle Bronze Age in northwest Hungary, predominantly in Győr-Moson-Sopron County, based on sites at Nagycenk, Hegyeshalom, Enese, Győr-Ménfőcsanak, and Mosonszentmiklós. This region between the Devín Gate and the confluence of the Rába and Danube rivers is important for European research on prehistory, as it could have been a gateway between the Carpathian Basin and the western parts of Central Europe. The complex statistical evaluation of the collected archaeological finds and their contexts has revealed the diversity of the material culture (Gáta–Wieselburg, Kisapostag, Transdanubian Encrusted Pottery Culture) and mortuary practices (inhumation and cremation burial rites, diverse patterns of grave furnishing) in the study area and period. In addition, a spatial analysis of the sites indicated a change in the settlement pattern between 2200 and 1500 BC. The typochronological analysis and the radiocarbon data helped specify the chronology and refine the connections maintained with Central European territories.

Presence and Distribution of Sun-Blocking Agents in the Danube River: Implications for Aquatic Ecosystem Health

Organic sun-blocking agents are recognized as emerging pollutants of the aquatic environment. The consequences and effects of these harmful substances on aquatic organisms are not fully understood, particularly in the context of Romania. This study examines the presence and environmental hazards posed by ten UV filters found in the Danube River. Six of the ten targeted contaminants were detected in surface water samples: 2-hydroxy-4-methoxy-benzophenone (BP-3), 2,4-dihydroxy benzophenone (BP-1), 2,3,4-trihydroxy benzophenone (234HBP), 2,2′-dihydroxy-4-methoxy-benzophenone (BP-8), 2-hydroxy-4-methoxy-4′-methyl-benzophenone (BP-10), and benzyl salicylate (BS). In sediment samples, seven of the ten compounds were identified: BS, BP-3, 4-hydroxybenzophenone (4HBP), BP-1, 234HBP, 2,2′,4,4′-tetrahydroxybenzophenone (BP-2), and BP-10, with different frequencies. The correlation coefficients showed strong relationships between benzophenone derivatives in surface water samples and a common contamination source for BP-3 and BS in sediment samples. In the assessment, the risk quotient (RQ) for BP-1 in fish was determined to be 1.81. Similarly, RQ values for BP-3 were calculated as 1.24 for Daphnia magna and 57 for fish, suggesting that these UV filters could potentially present substantial hazards to the aquatic ecosystem. The study findings indicate that additional research is needed to investigate the presence and potential risks of organic sun-blocking agents in surface waters, with a particular emphasis on densely populated areas in Romania.

Distribution of selenium: A case study of the Drava, Danube and associated aquatic biotopes

This paper presents the results of the research on the overall distribution of selenium (Se) in various aquatic compartments (water, sediment, plankton and macrophytes) at six selected sites of the Croatian part of the Drava and Danube rivers, the connected floodplain lake and the melioration channel system carried out in two sampling periods (flooding in June and the drought period in September). In addition, the physicochemical water properties, plankton composition and biomass were analysed. Our study revealed low mean Se contents in sediments and water, indicating Se deficiency in the studied freshwater systems. The physicochemical environment, including Se distribution, was primarily influenced by hydrology rather than site-specific biogeochemical and morphological characteristics. The flooding period was characterised by higher Se content in water and higher transparency, nitrate and total nitrogen concentrations than drought conditions. At the river sites, sediment Se content was the highest during the flood period, while at all other sites, higher concentrations were found during the drought, reaching the maximum in the lake. Although Se concentrations were below the threshold for aquatic ecotoxicity, they increased in the following order: water (0.021–0.187 μg Se L−1) < sediments (0.005–0.352 mg Se kg−1) < macrophytes (0.010–0.413 mg Se kg−1) < plankton (0.044–0.518 mg Se kg−1) indicating its possible biomagnification at the bottom of the food chain. Species known for high Se accumulation potential dominated the biomass of the main plankton groups and the composition of the macrophyte community, which may provide a more sensitive and accurate steady-state compartment monitor for Se assessment in freshwater biotopes.

A harmonized Danube basin-wide multi-compartment concentration database to support inventories of micropollutant emissions to surface waters

BackgroundThe European Water Framework Directive foresees the establishment of emission inventories for micropollutants (MP) to facilitate an evidence-based development of mitigation measures. Regionalized pathway analysis constitutes a moderately data-intensive approach to quantify the contribution of different pathways to the total pollution of surface waters. So far, only few European member states have created an inventory that includes diffuse pathways. The fundamental basis to enable it is an accessible, well-structured and harmonized database with data on the concentration of MPs in multiple compartments, such as soils, groundwater, atmospheric deposition and urban systems. Combined with the water and suspended substance balance in river basins, such data enables the estimation of emission loads via specific pathways. In the Danube River Basin, but in general in Europe, a public data management platform with such scope and criteria is still lacking.ResultsWe collected and harmonized MP measurements across multiple compartments and countries together with key metadata, harmonized and combined them into a new database. The resulting tool, available for download, facilitates the assessment of current data availability, in terms of quantity and quality. For example, while the majority of available data stems from groundwater and surface water, other highly relevant compartments are scarcely represented. By examining differences in MP concentration level across compartments, the database can lead to understand the relevance of specific emission pathways and thus to prioritize data-retrieval and calculation efforts in modelling applications. Selected examples show how to exploit the metadata associated to the measurements to extrapolate the results to regions not covered by specific monitoring programmes. For example, PFAS concentrations in treated wastewater show significant dependence on the design capacity of the treatment plant.ConclusionsThis study showcases how such database can support the setup of emission inventories, guide data providers and national authorities in prioritizing the allocation of resources for new surveys and in optimizing their national data collection and management systems. The process tested showed a great need for enhanced data literacy across countries and institutions to increase data availability and quality to secure the exploitation of the full information potential generated via monitoring programmes.

History, Life History, and Fate of a Salmonid Flagship Species: The Danube Salmon

The Danube Salmon Hucho hucho, endemic to the Danube River basin, is one of the largest members of the salmonid family. Here, we describe the distribution, ecology, and status of this flagship species in the upper Danube River basin. We model the historical distribution of Danube Salmon in the Austrian Danube River basin based on a review of the literature and species records. Fish sampling data over the past few decades illustrate the dramatic decline of the species and the population characteristics within the ecological niche that the species occupies. In conclusion, measures for the long‐term conservation of Danube Salmon in the upper Danube River, as well as possibilities for sustainable management, are addressed and discussed.

Morphologic Adjustment of a River Reach with Groynes to Channel Bypassing

AbstractThis article is focused on the investigation of the spatio-temporal variability of the Danube River reach’s vertical accretion thickness due to the response of the Danube River reach to bypassing. Five groyne-induced benches (GIBs) of the bypassed channel developed after water diversion in 1992 was studied by changes in topography for three-time spans (for the original gravel surface, for the surface before the 2013 flood and for the surface after the 2013 flood). The allostratigraphic approach was applied to 548 drilling probes at all GIBs and toptop, supra-platform, tail and backchannel geomorphic units have been identified at each GIB. The main to side-channel system connectivity increase sedimentation rates and the accretion was controlled by large flood events. The 100-year flood in 2013 contributed to the total volume by almost 26%. During study period 1992–2017, totally 1,146,589 m3 was accreted on five GIBs, of this 209,752 m3 during flood event in 2013 and 267,700 m3 in post flood period 2014–2017. The top geomorphic unit exhibits the highest median values of vertical accretion and for all GIBs accretion thickness are not related to the height above the mean channel water level. The thickness of accretion varied, likely because the variability of the vegetation cover caused variable hydraulic conditions and accretion rate span from 3.8 cm.year−1 to 5.3 cm.year−1. The investigation of the sediment thickness over long time spans 24 years and a large flood event) allowed us to conclude that the thickness is spatially variable for individual GIBs; however, its trend over time remains constants depending on the intake of sediments during large floodsd events. This article also provides a methodological template for the detailed investigation of river channel adjustment due to bypassing.

Electrochemical Sensing of Cadmium and Lead Ions in Water by MOF-5/PANI Composites.

For the first time, composites of metal-organic framework MOF-5 and conjugated polymer polyaniline (PANI), (MOF-5/PANI), prepared using PANI in its conducting (emeraldine salt, ES) or nonconducting form (emeraldine base, EB) at various MOF-5 and PANI mass ratios, were evaluated as electrode materials for the electrochemical detection of cadmium (Cd2+) and lead (Pb2+) ions in aqueous solutions. Testing of individual components of composites, PANI-ES, PANI-EB, and MOF-5, was also performed for comparison. Materials are characterized by Raman spectroscopy, scanning electron microscopy (SEM) and dynamic light scattering (DLS), and their electrochemical behavior was discussed in terms of their zeta potential, structural, morphology, and textural properties. All examined composites showed high electrocatalytic activity for the oxidation of Cd and Pb to Cd2+ and Pb2+, respectively. The MOF/EB-1 composite (71.0 wt.% MOF-5) gave the highest oxidation currents during both individual and simultaneous detection of two heavy metal ions. Current densities recorded with MOF/EB-1 were also higher than those of its individual components, reflecting the synergistic effect where MOF-5 offers high surface area for two heavy metals adsorption and PANI offers a network for electron transfer during metals' subsequent oxidation. Limits of detection using MOF/EB-1 electrode for Cd2+ and Pb2+ sensing were found to be as low as 0.077 ppm and 0.033 ppm, respectively. Moreover, the well-defined and intense peaks of Cd oxidation to Cd2+ and somewhat lower peaks of Pb oxidation to Pb2+ were observed at voltammograms obtained for the Danube River as a real sample with no pretreatment, which implies that herein tested MOF-5/PANI electrodes could be used as electrochemical sensors for the detection of heavy metal ions in the real water samples.