Danube Flows Research Articles

Wpływ działalności antropogenicznej w dorzeczu górnego Dunaju na reżim temperatury wody Dunaju w Bratysławie

The man activity in the basin affects the water temperature in the increasingly higher levels (construction of water reservoirs, construction of thermal and nuclear power plants or drainage of waste water to streams). In this paper, we focused our attention on the evaluation of the impact of anthropogenic activity to increase the thermal load of the Danube River for the period 1926–2020 at the Bratislava (Slovakia) station. In the first part, the long-term trends of a series of monthly and annual water temperatures in the Danube (period 1931–2020) are identified. In the second part, the dependence of the range of daily water temperature values is analysed at the temperature of the atmosphere in Vienna. The impact of an increase in the temperature of the Danube water due to human activity was tried to identify for lower, average, and higher flows (for Danube discharge at Bratislava water gauge 1500 m3s-1, 2000 m3s-1, and 3000 m3s-1) by comparing two periods: 1932–1961, and 1991–2020. As the effect of water heating in the river stream is most noticeable during low flow (dry) periods and high air temperatures, only daily water and air temperature data from the warm months between May and September were used in the calculations. At monthly flow rates of 1500 m3s-1, the water temperature was, on average, 0.5°C higher during the period of 1991–2020 than it was during the period of 1932–1960. This growth could be attributed to human activities in the Danube basin above Bratislava (warming of water in the built tanks, the wastewater flow to the Danube flow, etc.)

Implementation Instruments for Developing Sustainable Tourism on Recultivated Land in the Middle Danube Flow

Development of sustainable tourism is viewed through the scope of planning procedure, participation of all stakeholders, and resolving possible conflicts. The methodology is based on empirical exploration and compared two case studies of the Middle Danube Flow coast segment. The common denominator, apart from the location in the same region and on the bank of an international river, is the use of recycled land for the purpose of converting it into a tourist complex. This paper has a wider theoretical background, tailored and selected for this research purpose. Ambition was expressed to answer the questions of how to carry out the strategically set tasks at the level of detailed design and implementation, what kind of interactions to expect, and if it is possible to single out key approaches and steps and form recommendations for achieving satisfactory and non-conflicting results. The authors search and look for similarities among the chosen development directions and the decisions made which can point to a common methodological framework and options for creating an attractive, profitable, and sustainable tourist product. The conclusion is that desirable sustainable tourism can be reached through careful location and content selection, choice of adequate land use, and balanced alignment between protection and development. This paper indicates the possibility of an additional step towards a joint solution, which is not only a compromise, but is valued as being of high quality and desirable.

Genetic traces of dispersal and admixture in red deer (Cervus elaphus) populations from the Carpathian Basin

After the last glacial, the Carpathian Basin was repopulated from either eastward or northward colonisation routes for various species; one of these was the emblematic member of the European megafauna, the red deer, Cervus elaphus. We analysed 303 red deer individuals from the middle of the region, in seven Hungarian game reserves, at ten microsatellite loci (C01, C229, T26, T108, T123, T156, T172, T193, T501, T507), to investigate the genetic diversity of these subpopulations. We discovered high levels of genetic diversity of red deer subpopulations; allelic richness values ranging 4.99–7.01, observed heterozygosity 0.729–0.800, polymorphic information content 0.722–0.806, and Shannon’s information index 1.668–2.064. Multi-locus analyses indicated population admixtures of various degrees that corresponded to geographical location, and complex genetic structures were shown by clustering. Populations in the south-western and the north-eastern parts of the region formed two highly separated groups, and the red deer from populations in between them were highly admixed (in western Pannonia/Transdanubia, where the Danube flows into the Carpathian Basin). This pattern corresponds to the distribution of mitochondrial as well as Y-chromosome lineages. Assignment tests showed that a large fraction of individuals (29.4%) are found outside of their population of origin, indicating that the dispersal of red deer is rather common, which could be expected considering the life course of the species.

Trend Analysis of Water Quality Parameters in the Middle Part of the Danube Flow in Serbia

Abstract The Danube River plays significant role not only for preserving natural ecosystems. The aim of this paper is to examine the Middle Danube water quality in the part flowing through Serbia in section Bezdan -Banatska Palanka. Water quality data were examined for seven control points for period 2004-2018, for seven parameters: suspended solids (SS), dissolved oxygen (DO), electrical conductivity (EC), nitrates (NO3 –-N), total phosphorus (Ptot), biochemical oxygen demand (BOD5) and chemical oxygen demand (COD). Data analyses included the application of ANOVA, linear regression analysis and Mann-Kendall trend test. The Mann-Kendall tests in most (32/49) cases, i.e. in 65 %, confirmed the non-existence of a significant trend. Significant downward trends were confirmed in 17 cases. Water quality improvement was confirmed at following control points: Bezdan for NO3 –-N, Ptot and BOD5; Bogojevo for NO3 –-N, Ptot, COD and BOD5; Novi Sad for Ptot, BOD5 and COD; Slankamen for BOD5 and COD; Smederevo for NO3 –-N and COD; Banatska Palanka for NO3 –-N. Slight deterioration of water quality was confirmed only in two cases, at the Zemun and Smederevo where DO was decreasing. Water quality for the examined period was stable and can be characterised as excellent and/or very good (class I or class II). Results emphasise fact that water quality trends monitoring reveals river sectors where the process of water quality degradation is ongoing. Timely detected critical river sectors can draw the attention of decision-makers, who can improve the existing legislation that would lead to water quality improvement.

Evaluation of Different Simulation Methods for Analyzing Flood Scenarios in the Danube Delta

The present work is focused on the analysis of flood scenarios for the settlements near the Danube discharge area into the Black Sea. From this perspective, the aim of the research is the development of flood extension maps for localities in the Danube Delta. The emphasis is on collecting the data and information needed for the entire analysis process, such as hydrological data on Danube flows and water levels (which were analyzed for 51 years), topo-bathymetric data (where 1685 cross sections were processed, measured on an 87-km section of the Danube), a digital terrain model (DTM), and others. Two methods of flood scenario analysis for the localities targeted were used in this paper. The first method was an analysis of the flood scenarios by modeling a real scenario, where it was supposed that a 20 m breach appeared in the dam which protects the localities and remained present for 24 h. The second method consisted of a Geographic Information System (GIS) analysis (static from a hydraulic point of view), where the maximum water level was superimposed over the DTM. This corresponded to a scenario in which the breach in the flood-control levee remains present for a longer period. The validated results show that the dynamic method is more efficient than the static method, both in terms of estimated flooded surfaces and in terms of simulation accuracy (taking into account more input parameters than the static method). Thus, from the obtained simulations it was observed that applying the dynamic method resulted in smaller flooded surfaces in the settlements analyzed than when considering the static method. In some cases, the differences between the flooded surfaces reached up to about 22%. This information is important and of general interest since it can be used in various fields of work, such as flood defense strategies, and investment promotion activities in the Danube discharge area or similar locations.

Preliminary investigation of lower Danube pollution caused by potentially toxic metals

The current study aims to assess the pollution status of the European river-sea system lower Danube River-Danube Delta-North West Black Sea, through an integrated analysis of metal concentrations in water, sediments and fish community. The Danube flows through numerous industrial cities and receives a significant amount of pollutants due to the reception of urban and industrial emissaries, as well as agricultural land runoff. Samples of water, sediments and fish (10 species) were collected from 7 representative sites along Danube River, Danube Delta and Black Sea shore. For the analysed fish species, potentially toxic and essential elements (Pb, Cd, As, Cu, Fe, Zn, Mg, Ca, Na, K) from muscle and liver samples were measured and discussed. Measurement of elements and other environmental quality parameters were determined for water and sediments. The Black Sea area, represented by S6 and S7, received sediments from Danube with the lowest concentrations of Cd (0.05 ± 0.01 μg g−1, respectively 0.01 ± 0.001 μg g−1), Pb (3 ± 0.03 μg g−1, respectively 2 ± 0.03 μg g−1), As (2 ± 0.02 μg g−1, respectively 1.4 ± 0.3 μg g−1), Ni (8.9 ± 0.1 μg g−1, respectively 5.2 ± 0.2 μg g−1), Cr (8 ± 0.7 μg g−1, respectively 5 ± 0.2 μg g−1), Cu (3 ± 0.1 μg g−1, respectively 2 ± 0.04 μg g−1), Fe(6 ± 0.3 μg g−1, respectively 3 ± 0.1 μg g−1) and Zn (0.03 ± 0.003 μg g−1, respectively 0.017 ± 0.001 μg g−1). These results suggest that the Danube Delta system plays an important role in filtering the pollutants. Based on the biota and water analysis, there was no correlation observed between Cd, respectively Pb concentration in the environment and fish body (Person Coef. = −0.02 in muscle tissue and −0.01 in liver tissue, respectively Pearson Coeff. = −0.06 in muscle tissue and 0.1 in liver tissue). Cadmium remained an active element in the pollution of the Danube area (S1 and S2), with high concentration in the water matrix (0.14 ± 0.02 μg L−1, respectively 0.05 ± 0.01 μg L−1) and fish muscle (0.15 ± 0.03 μg g−1f.w. in C. carpio – S2). This fact was confirmed by several other studies.

Preliminary results on species composition of the biting midges-fauna (Culicoides) in a wetland on Lower Danube Flow, Bulgaria

Biting midges of the genus Culicoides Latreille, 1809 (Diptera: Ceratopogonidae) are competent vectors of various pathogens in Europe with veterinary importance such as: Bluetongue virus, Schmallenberg virus, Epizootic hemorrhagic disease virus and avian haemosporidians. In order to reveal the potential role that they may play in spreading diseases in wildlife and thus the impact on ecosystems which they render, a reliable estimation of their faunistic diversity is required. Previous surveys conducted in the region of Kalimok Biological Station – a wetland on Lower Danube flow – were focused mainly on the ornithophilic species acting as vectors of avian haemosporidians, and thus leaving out the whole Culicoides diversity in the area underestimated (Bobeva et al. 2013, Bobeva et al. 2014, Bobeva et al. 2015). In the present study, we combined morphological and molecular approaches for species identification of the biting midges collected in the region of the field station in 2011, 2012, 2013 and 2018 years. Out of the 37 Culicoides species reported previously as national fauna (Nedelchev 2013, Pudar et al. 2018), we recorded 13 species in the studied area. In addition, three species namely, Culicoides duddingstoni, C. griseidorsum and C. кibunensis were newly recorded for the Bulgarian fauna, which raises the number of species of national fauna to 40. Interesting specimens affiliated to C. pseudopallidus have been collected in Kalimok. This latter species has not been reported in Central and Eastern Europe so far and therefore further attention is required prior being considered as a new record. Regarding the potential vectors of avian haemosporidians in the studied area, the present investigation raised the list of species suspected for spreading this disease in wildlife from three to six, namely: C. alazanicus, C. circumscriptus, C. duddingstoni, C. griseidorsum, C. kibunensis and C. pictipennis. The current study of the biting midges’ biodiversity improved the knowledge about the Bulgarian Culicoides fauna including the list of the potential vector species of avian malaria. However, faunistic studies on Culicoides in Europe remain sparse and such data serves as a basic knowledge for a better understanding of the Culicoides-borne diseases.

Assessment of Climate Driven Changes in Flow Series of Alpine Basin: A Case Study of Danube River Basin

This study was carried out in order to analyze the climate change driven influence on mean monthly flow series of Danube River and its tributaries during the last century. The study confirms some signs of climate driven alterations in monthly river flow series along with change in flow seasonality during the last century. In spite of this, man-made interference in the basin like i.e. groundwater extraction, irrigation, river regulation, land use alteration and urbanization, has significantly changed Danube flow regime in most areas of the catchment. The analysis of Achleiten station demonstrates that average annual flow regime is a little bit increased. Major increase is observed in winter and autumn months and decrease in summer months. These seasonal alterations clearly signal a future glimpse of reduced water availability in alpine basins. This will mainly occur due to the change in the form of precipitation in winter, from snow to rain and the consequent less snow accumulation, and the early melt of snow storage, less precipitation and high evaporation rate in summer.

Application of experimental design for the optimization of artificial neural network-based water quality model: a case study of dissolved oxygen prediction.

This paper presents an application of experimental design for the optimization of artificial neural network (ANN) for the prediction of dissolved oxygen (DO) content in the Danube River. The aim of this research was to obtain a more reliable ANN model that uses fewer monitoring records, by simultaneous optimization of the following model parameters: number of monitoring sites, number of historical monitoring data (expressed in years), and number of input water quality parameters used. Box-Behnken three-factor at three levels experimental design was applied for simultaneous spatial, temporal, and input variables optimization of the ANN model. The prediction of DO was performed using a feed-forward back-propagation neural network (BPNN), while the selection of most important inputs was done off-model using multi-filter approach that combines a chi-square ranking in the first step with a correlation-based elimination in the second step. The contour plots of absolute and relative error response surfaces were utilized to determine the optimal values of design factors. From the contour plots, two BPNN models that cover entire Danube flow through Serbia are proposed: an upstream model (BPNN-UP) that covers 8 monitoring sites prior to Belgrade and uses 12 inputs measured in the 7-year period and a downstream model (BPNN-DOWN) which covers 9 monitoring sites and uses 11 input parameters measured in the 6-year period. The main difference between the two models is that BPNN-UP utilizes inputs such as BOD, P, and PO43-, which is in accordance with the fact that this model covers northern part of Serbia (Vojvodina Autonomous Province) which is well-known for agricultural production and extensive use of fertilizers. Both models have shown very good agreement between measured and predicted DO (with R2 ≥ 0.86) and demonstrated that they can effectively forecast DO content in the Danube River.

The evolution of an asymmetric deltaic lobe (Sf. Gheorghe, Danube) in association with cyclic development of the river-mouth bar: Long-term pattern and present adaptations to human-induced sediment depletion

The asymmetric Sf. Gheorghe lobe is the only active lobe in the Danube delta associated with a river-mouth bar (and related barrier islands and spits) that has continuously displayed cyclic development during the last 1500years. During the early cycles, the Sf. Gheorghe distributary experienced a significant increase in sediment load (by an order of magnitude) as a result of the successive avulsions occurred 1.5–1.2ka, which redistributed more water and sediment captured from the neighboring branches of Împuţita (southern distributary of the Sulina arm) and Dunavăţ. Morphological and sedimentological analyses together with a newly obtained chronology throw light on the multiple ridgeset (10) structure of Sf. Gheorghe lobe, each of them (excepting the first one) following a common evolutionary pattern reflected by the cyclic succession of the recurring stages: i) subaqueous mouth bar building, ii) barrier island emergence, and iii) transformation into a barrier spit with several secondary spits. The spits become encased into the muddy deltaic plain as narrow sandy ridges building out on the downdrift side of the lobe as a barrier-marsh plain, whereas the updrift side constantly accreted fed by longshore currents, forming a classic beach ridge plain. The size of each ridgeset increased exponentially with every new cycle due to the constant lengthening of the coastline as the downdrift side of the lobe advanced seaward through a series of progressively larger similar quadrilaterals, yielding a corresponding geometric progression of the delta front size. Even though each newly formed ridgeset (cycle) had a longer lifespan (the latest cycles lasting 4–5 times longer than the first ones: 200–440years versus 50–80years), the evolutionary model remained unchanged as long as the balance between wave- and river-borne sediments, defined by the sedimentary index (Si), remained constantly low (Si≤0.1), whereas the mean advance rates of the river mouth remained constant at c.10m/year. Abrupt changes occurred within the last cycle (since the beginning of the 20th century) as a consequence of human-induced depletion of sediment supplied by the Danube flow, and is mainly expressed by the complete cessation of the updrift coastal progradation and the prevalence of erosion in front of the river mouth. These changes, which engendered a threefold increase of the Si (0.37 at present), are reflected by the recent (1930s–present) river mouth dynamics, characterized by cessation of its long-term seaward expansion in favor of downdrift migration. This is indicative of the transition of the Sf. Gheorghe mouth from an asymmetric to a deflected wave-influenced delta morphology whose current developments mark a significant change in the multicentennial cyclic evolutionary pattern. The asymmetric to deflected transition reflects the net increase in the influence of wave-driven sediment circulation on river mouth morphology, corresponding to a critical Si threshold of ca. 0.2 (≤0.2: asymmetric; >0.2: deflected).

The Danube as a development resource: Perception and activities of local administration

The paper presents the results of multidisciplinary studies that were reached during the interviews in the local administrations in 24 cities and municipalities through which the river Danube flows on the territory of the Republic of Serbia. The Danube is an extraordinary resource that links the North and the Black Sea through the Rhine-Main-Danube Canal, and flows through 13 European countries. There are almost 3 million inhabitants on its banks in Serbia, and it is also the region with the largest economic activity in the territory of the Republic of Serbia. Local administrations took responsibility for their own development by making a series of strategic documents related to local economic development in which they analyzed the current situation and predicted development measures and incentives to improve the investment environment. In this paper we analyze the eco-chemical characteristics of water, arrangements of banks and riverbed, supporting infrastructure, business infrastructure, development measures and incentives, as well as cooperation with other local communities in the Danube region. The aim of this study was to determine awareness, knowledge and commitment of decision-making capabilities of local communities on the Danube as a development resource, especially in the context of the modern concept of sustainable development.

Long-term seasonal changes of the Danube River eco-chemical status in the region of Serbia

Seasonal spatial and temporal changes of selected eco-chemical parameters in section of the Danube River flowing through Serbia were analyzed. Data for electrical conductivity (EC), dry and suspended matter, residue on ignition, chemical oxygen demand (COD), biochemical oxygen demand (BOD-5), ultraviolet extinction, dissolved oxygen (DO), oxygen saturation, pH, nitrates, total phosphorus, and nitrogen were collected between 1992 and 2006. The use of monthly medians combined with linear regression and two-sided t test has been proven to be the best approach for resolving trends from natural variability of investigated parameters and for determining trend significance. Patterns of temporal changes between different months were examined. It was also determined that spatial trends of some parameters oscillate in predictable manner, increasing in one part of the year and declining in the other. Regression slope coefficients, an excellent indicator for determining when the water quality is changing the most along the course of the Danube, reach their maximum during summer for temperature (t), electric conductivity, nitrates, and total N, while in the same season suspended matter, COD, BOD-5, DO, and oxygen saturation coefficients reach their minimum. Correlations for used data sets of selected parameters were analyzed for better understanding of their behavior and mutual relations. It was observed that as Danube flows through Serbia, its general eco-chemical status either stagnates or improves, but the rate of river self-purification often depends on the season of the year.

Long-term changes in the eco-chemical status of the Danube River in the region of Serbia

The Danube River is an international river, one part of which flows through Serbia. The eco-chemical status of the Danube River is a constant topic of interest both at the local level, in each country through which the Danube flows, and at the international level. General interest to ensure the sustainable and equitable use of waters and freshwater resources in the Danube River Basin led to the development of a system for monitoring the river, which has produced data sets of its eco-chemical status. These have been collected over many years in Serbia; however, the present interest was focused only on the period from 1992 until 2006, i.e., a 15-year period. The process of defining trends of selected eco-chemical parameters, using linear regression analysis with a defined level of significance, and their separation from natural variability is of the highest importance for defining the changes in the water parameters. Through them, the fate and behavior of the eco-chemical parameters of the Danube in Serbia can be recognized and the prediction of their trends in the near future can be attempted. The obtained results revealed a constant improvement and acceptable trends of the eco-chemical status of the Danube River, as well as, substantial differences in the quality of the inflowing and out flowing water.

Seasonal prediction of Danube flow variability based on stable teleconnection with sea surface temperature

It is shown that spring Danube flow anomalies are significantly related to winter SST anomalies from several key regions. These areas are identified through stable teleconnections between flow and SST. A forecast scheme is developed and applied to predict flow anomalies using SST anomalies from these key regions. Small potential predictability of winter flow anomalies from autumn sea surface temperature anomalies was also detected. The predictability of the flow anomalies from summer and autumn using SST from the previous seasons is limited by the instability of teleconnections.

Dredging on the Lower Danube in Romania

The river Danube is the second longest river in Europe, with a total length of some 2680 km and a catchment area of 817 000 km2. The source of the river lies in the Black Forest in Germany, at the confluence of two smaller streams, the Brigach and the Breg, in Donaueschingen. Navigation is possible between Kelheim in Germany and Sulina in Romania, where the Danube flows into the Black Sea. In Romania, the Danube is 1075 km long, the last 175 km of which (as far as the city of Braila) is navigable for seagoing vessels. This stretch is called the Maritime or Lower Danube (in Romanian: Dunarea de Jos). The seaports of the Lower Danube lying within Romanian territory are Braila, Galati, Tulcea and Sulina. The ports of Reni, Izmail and Kilija are in the Ukraine. Near the city of Tulcea the Danube splits into three branches, known as Kilia, Sulina and Saint Georges. For navigation purposes the Sulina branch or, as it is called today, the Sulina Canal, forms the vital link between the Danube seaports and the Black Sea. The permissible draught of vessels on the Lower Danube is 24 ft (7·32 m). Vessels with a length of 225 m and a breadth of 36 m have found their way to sea after construction at shipyards on the Lower Danube.

Dredging on the Lower Danube in Romania

The river Danube is the second longest river in Europe, with a total length of some 2680 km and a catchment area of 817 000 km2. The source of the river lies in the Black Forest in Germany, at the confluence of two smaller streams, the Brigach and the Breg, in Donaueschingen. Navigation is possible between Kelheim in Germany and Sulina in Romania, where the Danube flows into the Black Sea. In Romania, the Danube is 1075 km long, the last 175 km of which (as far as the city of Braila) is navigable for seagoing vessels. This stretch is called the Maritime or Lower Danube (in Romanian: Dunarea de Jos). The seaports of the Lower Danube lying within Romanian territory are Braila, Galati, Tulcea and Sulina. The ports of Reni, Izmail and Kilija are in the Ukraine. Near the city of Tulcea the Danube splits into three branches, known as Kilia, Sulina and Saint Georges. For navigation purposes the Sulina branch or, as it is called today, the Sulina Canal, forms the vital link between the Danube seaports and the Black Sea. The permissible draught of vessels on the Lower Danube is 24 ft (7·32 m). Vessels with a length of 225 m and a breadth of 36 m have found their way to sea after construction at shipyards on the Lower Danube.

Dredging on the Lower Danube in Romania

The river Danube is the second longest river in Europe, with a total length of some 2680 km and a catchment area of 817 000 km2. The source of the river lies in the Black Forest in Germany, at the confluence of two smaller streams, the Brigach and the Breg, in Donaueschingen. Navigation is possible between Kelheim in Germany and Sulina in Romania, where the Danube flows into the Black Sea. In Romania, the Danube is 1075 km long, the last 175 km of which (as far as the city of Braila) is navigable for seagoing vessels. This stretch is called the Maritime or Lower Danube (in Romanian: Dunarea de Jos). The seaports of the Lower Danube lying within Romanian territory are Braila, Galati, Tulcea and Sulina. The ports of Reni, Izmail and Kilija are in the Ukraine. Near the city of Tulcea the Danube splits into three branches, known as Kilia, Sulina and Saint Georges. For navigation purposes the Sulina branch or, as it is called today, the Sulina Canal, forms the vital link between the Danube seaports and the Black Sea. The permissible draught of vessels on the Lower Danube is 24 ft (7·32 m). Vessels with a length of 225 m and a breadth of 36 m have found their way to sea after construction at shipyards on the Lower Danube.

Long-Term Water Level Variations in the Kiliya Branch of the Danube Delta

Water level variations in the Kiliya Branch of the Danube Delta over the period of 40 years (1958–1997) were analyzed. These level variations were subdivided into three components related to long-term variations of the share of the branch runoff and its redistribution within a year resulting from the Danube flow regulation; subsidence of deltaic deposits; and backup caused by the rising Black Sea level. It was revealed that, during the low-flow period, this backup had propagated to the river mouth at a distance of 160 km.