Section Of Danube Research Articles

Molecular identification and distribution of insect larvae in the Lower Danube River

As a major component of freshwater ecosystems, insect species play an important role in nutrient cycling and are often used as bioindicators of water pollution. Although extensive studies have characterized insects from freshwater habitats, little is known about the distribution of these species along the Lower Sector of the Danube River. Therefore, this survey conducted in the Danube section within the Romanian territory aimed to identify insect larvae belonging to seven different species of Odonata, Trichoptera, Ephemeroptera, Lepidoptera and Megaloptera by DNA barcoding and to investigate their distribution, density and frequency. A total of 41 quantitative macrozoobenthic samples were collected during two consecutive years (2019 and 2020). Species showed large differences in the distribution and density along different sections, and an overall tendency to populate downstream areas, except for Sialis morio. On the other hand, only Hydropsyche bulgaromanorum, Triaenodes bicolor and S. morio larvae were identified in the upstream section (Sulina branch). These data provide baseline information on the larger range of some of the most common aquatic insects in the Romanian Danube section in relation to several environmental parameters based on the first molecular identification of these species using COI gene sequencing.

Pratnja mađarskog kralja nakon bitke kod Nikopolja - dunavska sekcija puta

In the past decades, or even during the last hundred years, many books and articles were published on the Crusade in 1396 and the Battle of Nicopolis. It is no wonder that the Crusade of 1396 still intrigues many people, being one of the emblematic events of the Christian undertakings in the Middle Ages. The topic is huge, so the study presents a slice of the Crusade. The aim of the study is to provide new data and information about the Hungarian King's journey home after the Battle of Nicopolis, including the Danube section, which has not been included in the literature so far.

Mass appearance of the Ponto-Caspian invaderPontogammarus robustoidesin the River Tisza catchment: bypass in the southern invasion corridor?

The river Danube is the backbone of the ‘southern invasion corridor’, one of the most important passages for the spread of Ponto-Caspian invaders in Europe. However, not all of these species used the passive or active upstream movement in the main channel to reach the upper sections and tributaries, some found detours. Mass occurrences of the Ponto-Caspian peracarid,Pontogammarus robustoides(Sars, 1894) were recorded at 17 sites along the entire Hungarian section of the River Maros, for the first time in the River Tisza catchment and also in Hungary. Those populations are found ca. 707 km upstream from the closest known and confirmed locality in the lower Danube section. We confirmed their identity by DNA barcoding and showed that all individuals fit in with the lower Danube population, thus identifying the source of this introduction. The most likely vector allowing the jump dispersal of the species is fish stocking in the Romanian section of the River Maros, which − combined with downstream drift to the Serbian Danube section and the relatively busy ship traffic between Belgrade and Vienna − might provide the opportunity to bypass the dispersal barrier represented by the unregulated Middle Danube and open the way towards Western Europe.

Dynamic of Brassicogethes aeneus (F.) (Coleoptera, Nitidulidae) populations in Serbia’s downriver Danube section and their susceptibility to insecticides

This paper presents data on the dynamic of B. aeneus populations in winter oilseed rape in the downriver section of the Danube in Serbia, which were acquired by yellow water traps and a beating method. Their susceptibility to several insecticides of different classes (organophosphates, pyrethroids and neonicotinoids) (adult vial test and dipping test) was tested over two seasons (2009 and 2010). B. aeneus populations developing under the agroecological conditions that exist in Serbia were monitored to detect the moment of OSR infestation during its sensitive growth stages. Adults were counted, and the data revealed that they infest winter OSR crops during the stem elongation growth stage (BBCH 30-31), reaching a population peak at the green-yellow bud stage (BBCH 57-59), and exceeding the economic threshold, while the populations decreased substantially during the subsequent stage (BBCH 61-69). Laboratory test results did not confirm any changes in B. aeneus susceptibility/resistance to pyrethroid, organophosphate and neonicotinoid insecticides. Migration of B. aeneus populations was monitored as a way of developing predictive models for estimation of infestation severity and the timing of pest outbreaks under agroecological conditions existing in Serbia. As resistance to pyrethroids has been confirmed in B. aeneus populations in many European countries, their susceptibility will be further monitored.

The Ponto-Caspian mysid Paramysis lacustris (Czerniavsky, 1882) has colonized the Middle Danube

In 2017, the mysid Paramysis lacustris (Czerniavsky, 1882) was found for the first time in the Hungarian Danube section, representing the first psammo-pelophilous Ponto-Caspian peracarid colonizing the Middle Danube. In 2018, a brief survey focusing on this species revealed its presence in a more than 500-km-long river section spanning from Austria (Vienna, river km 1926) to Croatia (Batina, river km 1425). The largest populations of P. lacustris might be formed in reservoirs and slow-flowing stretches, where the appearance of the species might imply a considerable impact in connection with its zooplanktivorous feeding and important role in the diet of fish. Similar to all the other Ponto-Caspian peracarids that have crossed the Middle Danube, P. lacustris can reasonably be expected to continue its spread toward Western Europe in the future.

Non-uniform grid based LBM for the Saint-Venant equations

A novel form of the lattice Boltzmann method for the Saint-Venant equations (LABSVE) is formulated and implemented. To eliminate equidistant property of the lattice structure being the major drawback of the LBM, and thus establish the LB model as tool for practical application (natural water bodies) fully competitive compared to the presently available computational models, new form of equilibrium distribution function (EDF) based on geometrically transformed Saint-Venant equations (SVE) is derived. Introducing the metric relation function between the physical and computational system, the non-uniform spatial discretization is managed by solving the transformed SVE rather than altering the symmetrical properties of lattice structure. Since the geometrical correlation between the two corresponding systems is introduced into the transformed SVE, the very basic structure of the LBM in terms of simplicity in implementing the boundary conditions and computational efficiency (owing to the parallel structure) is maintained and further improved by removing the limitations imposed by the equidistant lattice condition. Furthermore, the discharge-water level definition of the SVE as more applicable form when natural watercourses are considered, is applied. In this way the bed slope term is completely eliminated from the equations, establishing therefore a model more suitable for natural systems characterized by arbitrary cross sectional geometry. In order to test the proposed non-equidistant LABSVE model, steady flow in prismatic channel, unsteady flow in non-prismatic channel of simple cross section geometry, and unsteady flow along a Danube section is modelled. Additional simulations by using the HEC-RAS modelling tool are conducted in order to produce comparison basis for both unsteady simulations, while in case of the Danube River section actual water level and discharge measurements are additionally used for calibration and verification of the model. Very good agreement between compared results is obtained showing that the proposed non-equidistant form of the LABSVE is capable of solving complex environmental problems, maintaining the order of accuracy, simplicity and efficiency of the basic LBM.

The occurrence of selected xenobiotics in the Danube river via LC-MS/MS.

Having in mind that there is a general lack of monitoring plans and precaution measures in the developing countries and that the Danube is the second longest river in Europe, the estimation of the relevant concentration levels of unregulated xenobiotics is a topic of interest both on local and international level. The selected pharmaceuticals, caffeine, and benzotriazole presented in the collected water samples from seven representative locations around the territory of Novi Sad, Serbia, during 1-year period, were analyzed with the use of solid-phase extraction followed by the liquid chromatography coupled with triple quad tandem mass spectrometry. The most frequently detected compounds were caffeine and carbamazepine in the concentrations up to 621 and 22.2ng/L, respectively, while the maximum concentration of the analyzed pharmaceuticals was obtained for ibuprofen (60.1ng/L). The presence of benzotriazole along the analyzed section of the river was confirmed in the concentration levels up to 26.7ng/L. Although sulfamethoxazole and desmethyldiazepam were detected at trace levels (0.22 and 3.41ng/L, respectively); the presence of these pharmaceuticals in complex mixtures should not be neglected. Due to the frequent detection caffeine, carbamazepine, ibuprofen, and benzotriazole could be proper candidate for hydrophilic anthropogenic markers for quantification of wastewater contamination in surface water in the analyzed Danube section.

Long-term changes in copepods assemblages in the area of the Danube floodplain (Slovak–Hungarian stretch)

The present study investigates the relationship between hydrological connectivity and species diversity in a by-passed channel section, and in the adjacent water bodies of the Slovak–Hungarian Danube section (1,840.5–1,804.4 rkm). The study was designed to assess long-term temporal trends (from 1991 to 2013) in freshwater copepods assemblages and their ecological indices in different habitats of the Danube floodplain area. One of the purpose of this study was to monitor the species composition of copepods communities and ascertain their shift in various biotopes of the Danube floodplain system. Based on 23 years data, in the first step, the copepods habitat preferences using habitat values (HV) and indicator weights (IW), calculated from data collected over all the years of monitoring of planktonic communities of the Danube floodplain, were quantified. Subsequently, the floodplain index (FI) from a summary of the habitat values and indication weights of the current species was calculated, to evaluate changes in the connectivity of the anabranched section of the Slovak–Hungarian Danube. This confirmed the loss of active hydrological connectivity within the main river channel, ranging from the eupotamal to more or less isolated floodplain water bodies. Out of 50 recorded copepods species, 11 species manifest a preference for eupotamal habitats, 18 taxa preferred eupotamal B/parapotamal habitats and 21 species were found to prefer the plesiopotamal habitat type. The statistical analyses demonstrated that the structure of planktonic copepod communities in this area has changed since the Gabčíkovo hydropower plant was placed into operations. The NMDS analysis revealed shifts in the proportion of euplanktonic and tychoplanktonic species. Reversible community changes were found in the old river bed and in the eupotamal-B side arms.

The microbiological water quality of Vienna’s River Danube section and its associated water bodies

For the City of Vienna, the River Danube and its associated water bodies (Alte Donau, Neue Donau, Muhlwasser, Lobau backwater) play an important role for recreation and drinking water supply. Microbiological water quality is of highest relevance for all user-related aspects. Microbiological water quality monitoring for this area has been mainly based on the standard fecal indicator bacteria Escherichia coli and intestinal enterococci, but has also applied alternative fecal indicators Clostridium perfringens and somatic coliphages as well as selected pathogens, like Salmonella sp. and enteroviruses. This article presents and compares available monitoring results from the last decade – 2004 to 2014 – for Vienna’s River Danube section and its associated water bodies using a five-step classification scheme for fecal pollution. For one selected Danube site, a statistical long-term trend measurement and a correlation analysis with hydrological and seasonal patterns were performed as well. The challenge of this work was to combine, analyze and compare data from programs with different objectives, which used different parameters and methods. To our knowledge, this is the first comprehensive overview of microbiological water quality data of Vienna’s section of the Danube and its associated water bodies that is accessible to the public.

Sediment regime of the Danube River in Serbia

The total length of the Danube section in Serbia is 587.5 km, and it has three specific sections: (1) Pannonian Plain Danube (or the Middle Danube) has all characteristics of lowland rivers. The stretch downstream of Novi Sad is under the influence of the Iron Gate 1 backwater during low water flows; (2) Iron Gate Danube, where the river is confined in the gorge. Now it is a reservoir, with completely altered natural characteristics. (3) Western Pontic Danube (or the Lower Danube), downstream of the gorge. This paper presents the sediment regime in the Serbian sector of the Danube River, both upstream and within the Iron Gate Reservoir. Extensive field investigation data were used to describe the most important parameters of sediment transport and deposition processes, including riverbed composition and suspended sediment characteristics (grain size and concentration). The influence of large tributaries of the Danube (the Tisza, the Sava, and the Velika Morava) is also addressed. Activities conducted in the Iron Gate 1 reservoir under the Sediment Regime and Morphological Changes Monitoring Program is also described. Data obtained during implementation of the Program form the basis for the description of changes in the Danube sediment regime that occurred following erection of the Iron Gate Dam. It revealed that the most important consequence of the Iron Gate 1 HPNS Dam is permanent deposition of sediment in the Iron Gate Gorge portion of the reservoir, the water and environmental management implications of which are becoming increasingly important. However, upstream stretches of the reservoir are not subject to uniform sedimentation processes; instead, the sediment regime depends on current hydrologic and hydraulic conditions within the watercourse and/or the hydro-power plant operating mode.

Monitoring of tritium, 60Co and 137Cs in the vicinity of the warm water outlet of The Paks Nuclear Power Plant, Hungary

Danube water, sediment and various aquatic organisms (snail, mussel, predatory and omnivorous fish) were collected upstream (at a background site) and downstream of the outlet of the warm water channel of Paks Nuclear Power Plant. Gamma emitters, tissue free-water tritium (TFWT) and total organically-bound tritium (T-OBT) measurements were performed. A slight contribution of the power plant to the natural tritium background concentration was measured in water samples from the Danube section downstream of the warm water channel. Sediment samples also contained elevated tritium concentrations, along with a detectable amount of 60Co. In the case of biota samples, TFWT exhibited only a very slight difference compared to the tritium concentration of the Danube water, however, the OBT was higher than the tritium concentration in the Danube, independent of the origin of the samples. The elevated OBT concentration in the mollusc samples downstream of the warm water channel may be attributed to the excess emission from the nuclear power plant. The whole data set obtained was used for dose rate calculations and will be contributed to the development of the ERICA database.

Changes of phytoplankton functional groups in a floodplain lake associated with hydrological perturbations

During the past decade, basic hydrological conditions of a floodplain lake in the middle Danube section have been altered with long-lasting extremely high flooding. The objective of the paper is to show the effectiveness of the functional approach to explain phytoplankton changes associated with hydrological events. Intensity and duration of flooding were qualified as the primary cause for the changes of functional groups. Flooding phase was characterised by diatoms (B, C, D, P, T B ) tolerant to water column mixing. Due to the dilution and washout effect their biomass was low during the long-lasting flooding despite their input from the river. Co-occurrence of coccoid green algae (X1, J, F) was associated with turbid and mixed waters. High-nutrient concentrations and water column stability during the long-term dry conditions led to the dominance and high biomass of cyanobacteria. Low-nitrogen H1 group was particularly sensitive to stress caused by flooding, while filamentous N2-fixing (S N ) and non N2-fixing species (S1) showed tolerance to short-term flooding. The development of euglenoids and dinoflagellates (W1, W2, L O ) was also associated with dry conditions and seasonal changes in autumn. The functional classification allows representing of the hydrological phases which characterise the phytoplankton succession in highly disturbed river-floodplain systems.

Type-specific reference conditions of fluvial landscapes: A search in the past by 3D-reconstruction

Abstract River/floodplain restoration programs are often based on type-specific reference conditions of the respective river section. Most large rivers in the industrialized world are heavily degraded and lack near-natural reference sites. For that reason, historical analyses of the pre-channelization state have been used to define adequate restoration targets at the Austrian Danube section in the Alluvial Zone National Park downstream from Vienna. This study compares new reference data derived from 3D-reconstructions in the form of digital terrain models from two historical Danube river landscapes: the Machland floodplain in 1812 and the former floodplain in Vienna in 1849. The focus is on the original hydrological surface and subsurface connectivity of the river-floodplain systems related to different flow situations. Here, we use water cover, shorelines, depth of the groundwater table and inundation depth as surrogates for measuring connectivity. The results show that the two study sites naturally constituted extreme formations of the Austrian anabranching Danube sections. The Machland section was one of the narrowest floodplains but highly dynamic, and the Vienna/Lobau section was one of the broadest, whereby only the central part close to the main channel originally showed high morphological turnover. The analyses of hydrological surface connectivity relative to total floodplain extension reveal significant differences due to their basic geological and geographical conditions. Despite these basic differences, both study sites – in absolute numbers – showed similar extensions of the water bodies at low and mean flow. The depths of the groundwater table related to mean flow were also comparable. Prior to channelization, the groundwater conditions in both floodplains favored the formation of wet to moist alluvial forest communities. Up until today, the two river landscapes continue to undergo different developments: both river sections are impounded, but the Machland floodplain still represents a rural site while the Vienna site has been utilized more intensively as building land and for urban infrastructure. As a consequence of the diverse human interventions in the 19th and 20th century, river bed degradation and aggradation of sediments in the floodplains have significantly truncated fluvial dynamics and hydrological connectivity. In addition, these phenomena have substantially deepened the groundwater table in both study sites. The results contribute to the identification of river/floodplain-type-specific reference conditions and provide an additional decision basis for discussing appropriate management strategies in the degraded riverine ecosystems.

Composition and dynamics of benthic organic matter in the middle Danube section

The organic matter of the sediment is prerequisite for the detritivorous community in the river ecosystem. To quantify this organic matter content and its changes in time and space, investigations were performed at two typical sites of the Hungarian Danube, which differ in their local hydrological characteristics due to the deposition and erosion processes. The distribution of the benthic particulate matter and the organic matter content of that were analysed in the core samples of the river side and the near shore line in three layers (0-5, 5-10 and 10-15 cm) and in four fractions: C = coarse (2360-710 μm), F = fine (710-250 μm), V = very fine (250-63 μm), and U = ultra fine (<63 μm). The variability of the organic matter content was highest in the coarse fraction (CV: 86 %), while it was the lowest in the ultra fine fraction (CV: 20 %). Sites differed mainly in the organic matter content of the C and F fractions, and the vertical changes of the benthic organic matter. The first TBOM records from the studied section of the Danube show relatively high values in comparison with the literature. Results show that mainly the quantity of the fractions (i.e. hydrological characteristics) determined the BOM content of the bed sediments at the investigated sites.

Typology of Danube River sections based on environmental characteristics and benthic invertebrate assemblages

Based on a synopsis of environmental, mostly eco-geographical and hydraulic features and a multivariate ordination analysis of the benthic invertebrate assemblages, the Danube could be partitioned into ten Danube River sections: Upper Course of the Danube, Western Alpine Foothills Danube, Eastern Alpine Foothills Danube, Lower Alpine Foothills Danube, Hungarian Danube Bend, Pannonian Plain Danube, Iron Gate Danube, Western Pontic Danube, Eastern Wallachian Danube, and Danube Delta. The composition of the benthic invertebrate fauna within these sections is comparatively similar compared to the faunas of the other sections. This Danube Section Typology may serve as a foundation to conduct a reference-based quality assessment of the ecological river status.

Spatio-temporal pattern of mussels (Corbiculidae, Dreissenidae, Sphaeriidae) in the water-system of the Hungarian Danube

In 1998 and 2001 collections were carried out at 83 sampling sites in different water bodies of the Hungarian Danube section. In the period of 1996-2003 during the hydrobiological monitoring of the Szigetkoz area 15 sites, which are affected especially by the hydrological changes due to the diversion of the Danube, were studied. Regarding the sampling sites altogether, 16 small-sized mussel species of 3 families were found, which presents 73 % of the nation-wide fauna. Among them two species (Corhicula fluminea, Dreissena polymorpha polymorpha) are invasive mussels and four (Pisidium amnicum, Pisidium milium, Sphaerium rivicola, Sphaerium solidum) are rare species in Hungary. The radical alteration in the hydro-morphology of the Szigetkoz area caused by the diversion of the Danube to the operation channel of Bos/Gabcikovo hydroelectric power plant was followed by the impoverishment of the mussel fauna. The composition of mussel fauna had been considerably changed between 1996 and 2003. In the period before 2000 the small-sized mussel fauna contained 11 species, but in the period after 2000 the fauna increased with 2 fingernail clams (Sphaerium rivicola, Sphaerium solidum) and one pea clam (Pisidium casertanum var. ponderosum). Beside the increase in the number of species a process to uniformity could be detected, since the ratio of species occurring only in one water body gradually decreased. The number of species occurring in more than one water body increased until the beginning of 2000. The previous flood prevention classification of the Szigetkoz area could be found less and less typical in the spatial pattern of the mussel fauna. In the last years of the investigated period the water regime of the active alluvial floodplain followed the natural water fluctuation of the Danube. The water dynamics of the active alluvial floodplain differs both from the abandoned main channel and the protected area due to the changed mode of water supply. The decrease of similarity between the water bodies could represent a tendency towards the situation before altering the hydrological exchange conditions in the wetland.

Long-term changes in cladoceran assemblages in the Danube floodplain area (Slovak–Hungarian stretch)

In this paper, the distribution of Cladocera species in the different sampling sites: the main channel/old river bed, parapotamal type side arms and plesiopotamal side arms, is described. The structure of cladoceran assemblages in the by-passed Danube section and in the adjacent floodplain water bodies has changed since the Gabčíkovo hydropower plant was put into operation. Great changes have been observed in the previous parapotamal side arm situated between river km 1840 and 1820, artificially fed with water from the head-race canal. The dominance of tychoplanktonic (benthic and phytophilous) species has increased, while the typical euplanktonic species have disappeared. Three characteristic groups of cladoceran assemblages were recorded when a different type of habitat was taken into consideration. Euplanktonic cladocerans prevailed on all sampling sites before damming. In periods after damming, littoral species, and later also a euplanktonic forms, dominated on the main channel sampling sites. In parapotamal and plesiopotamal side arms with rich littoral macrovegetation during periods after damming, phytophilous cladoceran species were the ones with the highest occurrence. The samplings from the first time period were rather homogenous. The samplings from the second and third period were more similar when considering the sample site than regarding the time period. In total, 64 cladoceran species were recorded in the course of 13 years (from 1991 to 2004). The increase in number of Cladocera species from 1991 to 2004 was significant. Chydorus sphaericus was found to be the most widely distributed species in the study area. The finding of Disparalona hamata is the first faunistic record from the central part of the Danubian watersheds.

Rehabitation of an impounded section of the Danube in Vienna (Austria) - evaluation of inshore structures and habitat diversity.

River regulation, urban development and the construction of a hydroelectric power plant have considerably changed the ecological condition of the Danube section in Vienna. In 1997, the previously straight shoreline of the Danube in this area was reconstructed by creating shallow water areas, coves, gravel banks and side channels. These inshore structures were created to increase habitat diversity in this area and to establish, together with existing ponds, a system of stepping stone biotopes, which serve as migration linkage through the municipal area of Vienna. A monitoring programme (1998-2001) was established to assess the functional integrity of these structures. A multi-species-approach using odonates, amphibians, and fish was developed to cover aquatic, amphibious and terrestrial habitat components. As demonstrated in this study, rehabilitation of heavily altered systems may play an important role in improving ecologically degraded areas and in reconnecting isolated landscape patches. A new metric (Floodplain Index) was applied for defining an ecological management objective, for characterizing the newly created structures and for assessing habitat heterogeneity.

Rehabilitation of a Heavily Modified River Section of the Danube in Vienna (Austria): Biological Assessment of Landscape Linkages on Different Scales

The ecological condition of the Danube section in Vienna (Austria) has been greatly impaired by urban development, regulation, channel straightening and the construction of a hydroelectric power plant. In 1997, the shoreline of the Danube in this area was restructured by artificial side channels, coves, gravel banks, pools and temporary waters. A monitoring programme has been established focusing on the investigation of the functional integrity of these inshore structures: first results show that the sites isolated from the Danube serve as stepping stone biotopes for dragonflies and amphibians. Particularly amphibians are suitable indicators of the ecological functioning of riparian migration linkages on a (macro-) habitat scale. Rheophilic fish species (e.g. Chondrostoma nasus) colonise side channels connected with the Danube and indicate a longitudinal connectivity on a landscape scale. The role of these structures within an urban greenway is discussed.

The relationship between habitat structure and biodiversity of the macrozoobenthos in the free-flowing section of the Danube in Austria — east of Vienna (preliminary results)

The habitat structure is described by the grain size distribution, whereas diversity indices were used to describe the biodiversity of the macrozoobenthos. At the sampling site, 112 species were identified, including 14 species of Mollusca, 32 of Clitellata, 5 of Crustacea and 49 of Insecta. Bootstrap and Jackknife techniques indicated that nearly all of the species which might occur in the sampling area were detected. Confidence intervals of the biodiversity of Mollusca and Oligochaeta were computed by Bootstrap procedure so that significant differences between sampling sites and dates could be obtained. For the analysis of further environmental variables, several water-flow variables were measured or calculated. The hiodiversity of the Mollusca was positively correlated with sediment heterogeneity and negatively correlated with hydrological conditions, whereas the biodiversity of the Oligochaeta was negatively correlated with sediment heterogeneity and stress. Canonical Correspondence Analysis showed similar results for the Mollusca and described the relation of the species and the biodiversity with environmental gradients of selected variables.