Danube River Catchment Research Articles

Distribution and diversity of fishes and lampreys in Transylvania (Romania): a complete survey and suggestions for new protected areas.

Freshwater fishes are in a serious state of decline across the world, making them one of the most threatened groups of vertebrates. The Danube River catchment area in Europe holds the richest freshwater fish community, but our knowledge of the current distribution of these species is limited. Transylvania, the largest region of Romania, is one of the important tributaries of the Danube, from where 77 fish and two lamprey species were recorded until now. Despite this large diversity of freshwater fishes, there is a lack of systematic survey of the fish fauna in this region for the past 50 years. In this study, we present data on the occurrence and distribution of fishes and lampreys collected in Transylvania from 2007 to 2022. This data covers 43% of Romania's surface and includes all major rivers from Transylvania. 65 species of fish and three species of lampreys are recorded, and an additional nine fish species are also reported based on information from competent people. Of the 77 fish and lamprey species recorded 19 (24.7%) are non-native, although their relative abundance was low (5.1%) compared to other similar regions in Europe. The first records of Eudontomyzonmariae, Neogobiusmelanostomus, Piaractusbrachypomus, Pygocentrusnattereri, and Salvelinusalpinus in Transylvanian rivers are presented, as well as the first record of Cobitiselongata outside the Nera River basin (from the Caraș River) and the detection of three new populations of the vulnerable Umbrakrameri. Data on changes in distribution that have occurred since the last comprehensive survey 50 years ago are also provided and the importance of our results in conservation planning are discussed, including the designation of new protected areas for freshwater bodies and the compilation of the Romanian Red List of fishes.

Endangered spined loach Cobitis species in Southwest Germany: A complex network of native, hybrid and newly emerged populations

AbstractSuccessful conservation of cryptic species such as representatives of the genus Cobitis presents a challenge for fishery managers. Only Cobitis taenia L. is currently assumed to occur in southwest Germany, where it is classified as critically endangered. Established genetic markers and eDNA analysis identified three Cobitis species in the study area. Cobitis taenia and Cobitis elongatoides were widely distributed in the Rhine River system, primarily forming hybrid species complexes in which polyploid individuals dominate but coexist with diploid parent species. A third non‐native species, Cobitis bilineata, has recently become established in the southern part of the Rhine to which it probably migrated naturally via the connected Aare River system. In the Danube River catchment, two populations, including one previously thought to be extinct, comprise both diploid and polyploid representatives of C. elongatoides. Our results provide an important basis for more targeted conservation strategies for Cobitis species currently found in the region.

Freshwater gobies (Gobiidae) of Bosnia and Herzegovina: a review of the current status and distribution

This review updates the information on the actual status and distribution of freshwater gobies in Bosnia and Herzegovina. The available literature has been critically reviewed to provide more complete and up-to-date information. Consequently four species are proposed for removal from the national checklist, given the lack of any data to support their presence: Knipowitschia panizzae, Pomatoschistus microps, Proterorhinus marmoratus and Zosterisessor ophiocephalus. Therefore, the freshwater gobiid fauna is confirmed to include seven species from six genera. The Adriatic Sea basin (Neretva River catchment) is inhabited by three endemic species: Knipowitschia radovici, Orsinigobius croaticus and Ninnigobius canestrinii, while the Black Sea basin (Danube River catchment) is inhabited by the invasive species: Babka gymnotrachelus, Neogobius fluviatilis, Neogobius melanostomus and Ponticola kessleri. However, due to the possibility of misidentify the finding of B. gymnotrachelus is questionable and needs confirmation. Distribution of both endemic Knipowitschia and Orsinogobius species is restricted to small areas in the lower Neretva River catchment on both sides of the Croatia-Bosnia and Herzegovina border. The vulnerability of these species is discussed, and the IUCN conservation and units meriting conservation attention were identified. The invasive character of other species is highlighted. This review indicates that the knowledge on the Bosnia-Herzegovinian freshwater gobiid fauna is still far from complete, hence this up-to-date checklist can serve as a basis for further ecological and zoogeographical studies. For better species inventory, finer scale distribution surveys are needed, followed by detailed morphological, molecular phylogenetic and ecological studies.

Relationships between macrophyte species, their life forms and environmental factors in floodplain water bodies from the Bulgarian Danube River Basin

The composition and structure of macrophyte assemblages in different water bodies from Bulgarian Danube River catchment area for a period of three years were studied. Main environmental variables: water depth and transparency, substrate type, nutrients (ammonium, nitrate, nitrite and total nitrogen, phosphate and total phosphorus) were simultaneously measured. Our aim was to investigate the spatial and temporal variability of macrophyte composition on the taxonomical (species) and functional (life forms) level in relation to environmental factors by means of multivariate analyses (PCA, CCA and RDA). The Bray-Curtis index was also used to investigate species similarities within and between different kinds of water bodies. Hydromorphology and connectivity were the main factors explaining the spatial variations of both species and life forms. The phosphate phosphorus, total nitrogen and temperature were the variables explaining temporal variation of species.

Assessment of water resources change of the Danube River in the XXI century under the scenario A1B using the model "climate-runoff"

The results of calculations of possible state of water resources within The Danube River basin in the XXI century were shown. This estimation was based on the model "climate-runoff", developed in Odessa State Environmental University. As the input to model data of climate scenario A1B (model REMO) were used. Average long-term annual flow values using meteorological data (air temperature and precipitation) from the scenario for different climatic periods of XXI century were calculated. 32 points (grid nodes) which were uniformly distributed over the catchment area of the Danube River were studied. Projection of changes in water resources was given by comparing the calculation results in the past (before 1989) and in the future (1990-2030, 2031-2070, 2071-2100). The major trends in climatic factors of the flow formation and water resources were established. It is shown that the climatic conditions in the XXI century on the Danube River catchment is unfavorable for the formation of runoff. The positive component of the water balance (precipitation) remains unchanged and the negative component (evaporation) increases. Isolines of norms of climatic annual flow within the whole basin were constructed. It is established that by 2030 a significant reduction of water resources will not occur; during the 2031-2070 diminution will be 17,9 %; during the 2071-2100 – 22,0 %.

Comparison of balance of tritium activity in waste water from nuclear power plants and at selected monitoring sites in the Vltava River, Elbe River and Jihlava (Dyje) River catchments in the Czech Republic

During the routine operation, nuclear power plants discharge waste water containing a certain amount of radioactivity, whose main component is the artificial radionuclide tritium. The amounts of tritium released into the environment are kept within the legal requirements, which minimize the noxious effects of radioactivity, but the activity concentration is well measurable in surface water of the recipient. This study compares amount of tritium activity in waste water from nuclear power plants and the tritium activity detected at selected relevant sites of surface water quality monitoring. The situation is assessed in the catchment of the Vltava and Elbe Rivers, affected by the Temelín Nuclear Power Plant as well as in the Jihlava River catchment (the Danube River catchment respectively), where the waste water of the Dukovany Nuclear Power Plant is discharged. The results show a good agreement of the amount of released tritium stated by the power plant operator and the tritium amount detected in the surface water and highlighted the importance of a robust independent monitoring of tritium discharged from a nuclear power plant which could be carried out by water management authorities. The outputs of independent monitoring allow validating the values reported by a polluter and expand opportunities of using tritium as e.g. tracer.

The Ponto-Caspian basin as a final trap for southeastern Scandinavian Ice-Sheet meltwater

This paper provides new data on the evolution of the Caspian Sea and Black Sea from the Last Glacial Maximum until ca. 12 cal kyr BP. We present new analyses (clay mineralogy, grain-size, Nd isotopes and pollen) applied to sediments from the river terraces in the lower Volga, from the middle Caspian Sea and from the western part of the Black Sea. The results show that during the last deglaciation, the Ponto-Caspian basin collected meltwater and fine-grained sediment from the southern margin of the Scandinavian Ice Sheet (SIS) via the Dniepr and Volga Rivers. It induced the deposition of characteristic red-brownish/chocolate-coloured illite-rich sediments (Red Layers in the Black Sea and Chocolate Clays in the Caspian Sea) that originated from the Baltic Shield area according to Nd data. This general evolution, common to both seas was nevertheless differentiated over time due to the specificities of their catchment areas and due to the movement of the southern margin of the SIS. Our results indicate that in the eastern part of the East European Plain, the meltwater from the SIS margin supplied the Caspian Sea during the deglaciation until ∼13.8 cal kyr BP, and possibly from the LGM. That led to the Early Khvalynian transgressive stage(s) and Chocolate Clays deposition in the now-emerged northern flat part of the Caspian Sea (river terraces in the modern lower Volga) and in its middle basin. In the western part of the East European Plain, our results confirm the release of meltwater from the SIS margin into the Black Sea that occurred between 17.2 and 15.7 cal kyr BP, as previously proposed. Indeed, recent findings concerning the evolution of the southern margin of the SIS and the Black Sea, show that during the last deglaciation, occurred a westward release of meltwater into the North Atlantic (between ca. 20 and 16.7 cal kyr BP), and a southward one into the Black Sea (between 17.2 and 15.7 cal kyr BP). After the Red Layers/Chocolate Clays deposition in both seas and until 12 cal kyr BP, smectite became the dominant clay mineral. The East European Plain is clearly identified as the source for smectite in the Caspian Sea sediments. In the Black Sea, smectite originated either from the East European Plain or from the Danube River catchment. Previous studies consider smectite as being only of Anatolian origin. However, our results highlight both, the European source for smectite and the impact of this source on the depositional environment of the Black Sea during considered period.

Impacts of Climate Change on the Hydrological Regime of the Danube River and Its Tributaries Using an Ensemble of Climate Scenarios

Information about the potential impacts of climate change on river runoff is needed to prepare efficient adaptation strategies. This study presents scenario projections for the future hydrological runoff regime in the Danube River Basin. The eco-hydrological watershed model Soil and Water Integrated Model (SWIM) was applied for the entire Danube River catchment, considering 1224 subbasins. After calibration and validation of the model, a set of high-resolution climate projections (bias-corrected and non-bias-corrected) served as meteorological drivers with which future daily river discharge under different climate warming scenario conditions was simulated. Despite existing uncertainties, robust trends could be identified. In the next 30 years, the seasonal stream-flow regime of the Danube and its tributaries is projected to change considerably. Our results show a general trend towards a decrease in summer runoff for the whole Danube basin and, additionally, in autumn runoff for the Middle and Lower Danube basin, aggravating the existing low flow periods. For the winter and early spring seasons, mainly January–March, an increase in river runoff is projected. Greater uncertainties show up in particular for winter runoff in the Dinaric Alps and the Lower Danube basin. The existing trends become very distinct until the end of the 21st century, especially for snow-influenced river regimes.

Estimating emissions of PFOS and PFOA to the Danube River catchment and evaluating them using a catchment-scale chemical transport and fate model

Novel approaches for estimating the emissions of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) to surface waters are explored. The Danube River catchment is used to investigate emissions contributing to riverine loads of PFOS and PFOA and to verify the accuracy of estimates using a catchment-scale dynamic fugacity-based chemical transport and fate model (STREAM-EU; Spatially and Temporally Resolved Exposure Assessment Model for European basins). Model accuracy evaluation performed by comparing STREAM-EU predicted concentrations and monitoring data for the Danube and its tributaries shows that the best estimates for PFOS and PFOA emissions in the Danube region are obtained by considering the combined contributions of human population, wealth (based on local gross domestic product (GDP)) and wastewater treatment. Human population alone cannot explain the levels of PFOS and PFOA found in the Danube catchment waters. Introducing wealth distribution information in the form of local GDPs improves emission estimates markedly, likely by better representing emissions resulting from consumer trends, industrial and commercial sources. For compounds such as PFOS and PFOA, whose main sink and transport media is the aquatic compartment, a major source to freshwater are wastewater treatment plants. Introducing wastewater treatment information in the emission estimations also further improves emission estimates.

Spatio‐temporal variability of dryness/wetness in the Danube River Basin

AbstractThe present study focuses on the analysis of dryness/wetness conditions in the Danube River catchment area from 1901 to 2013 based on reanalysis data. The spatio‐temporal variability of dryness/wetness conditions is analyzed by means of the Standardized Precipitation Index (SPI) for an accumulation periods of 6 months. To characterize the spatial variability of SPI6 at monthly time scales, an empirical orthogonal function (EOF) analysis was applied. The leading mode of SPI variability captures in‐phase variability of SPI over the entire catchment area of Danube River. The leading mode of dryness/wetness variability was found to be strongly related to the different phases of the Arctic Oscillation. The second and third modes of variability show a more regional character of the dryness/wetness variability over the Danube River catchment area. Based on a composite map analysis, between the time series corresponding to the first three leading modes of dryness/wetness variability and the geopotential height at 850 mb and precipitation totals, it is shown that dryness (wetness) conditions over the Danube catchment area are associated with an anticyclonic (cyclonic) circulation, transport of dry (humid) air towards the Danube catchment area and reduced (enhanced) number of rain days. Copyright © 2015 John Wiley & Sons, Ltd.

Anomalies of temperature and annual runoff of the Danube River in the wide range of solar variability scales

Analyzed is the variability of precipitation in the area of the southern coast of the Crimea and the Danube River catchment as well as of the Danube River runoff. It is demonstrated that minimum precipitation and minimum runoff of the Danube River were observed in the years with the minimum of the quasicentennial cycle of solar activity (1879–1933), when the index of North Atlantic Oscillation (NAO) was maximum. The precipitation and the Danube River runoff were maximum in the years with the quasicentennial maximum of solar activity (1934–1996), when the NAO index was minimun. It is obtained that in the regions under consideration precipitation and the Danube River runoff are minimum in the years of the even cycle of solar activity and maximum in the years of the odd cycle. Discussed is the considerable difference in the interannual distribution of total precipitation in the catchment of the Danube River and its runoff in the years of even and odd cycles of solar activity.

Assessing natural and disturbed population structure in European grayling Thymallus thymallus: melding phylogeographic, population genetic and jurisdictional perspectives for conservation planning

Natural and human-mediated population structure of European grayling Thymallus thymallus was assessed in primarily Austrian reaches of the Danube River catchment. Data on phylogeographic structure based on mitochondrial DNA (mtDNA) were combined with variation found across 13 microsatellite loci to assess introgression stemming from stocking activities. Populations north of the Alps generally showed no signs of long-term introgression from allochthonous stocks, although one population comprised two distinct genotypic groups, one of which may stem from recently stocked material. South of the Alps, levels of introgression with stocks from the north were extensive and only one of six populations is believed to represent a reference state. Allelic diversity and expected heterozygosity were positively correlated with mtDNA admixture supporting more recent introgression and that there is little or no reproductive barrier between these two major lineages north and south of the Alps. A third unrelated mtDNA lineage is described from the Lafnitz, a tributary of the Raab drainage. The high lineage diversity in the upper Austrian Danube is not concordant with an existing model of T. thymallus evolutionarily significant units in Europe. Caveats in naming such units or following a strict hierarchical conservation unit structure for broadly distributed species with complex phylogeographic distributions stretching over various jurisdictions are discussed. The necessity of using both phylogeographic and population genetic approaches in evaluating the history and conservation value of populations in a conservation context is additionally highlighted.

Spatial and temporal variation in biomass and size structure of Corbicula fluminea in Danube River catchment, Hungary

AbstractThe aim of this study was to reveal the spatial and temporal variation in biomass, density, and size structure of the invasive clam, Corbicula fluminea in the Danube River catchment and to explore the environmental factors determining these patterns. Samples were taken seasonally during the years 2007 and 2008 at 15 sites located along a river continuum from a second order stream to the Danube River. C. fluminea was the most abundant species in the main arm of the Danube; however, it was found in great density in the side arms, too. In the Ipoly River it only occured close to the conjuction, and it was not present at all in the second and third order streams. Regression models were developed to predict dry mass (DW, g) from linear body dimension [shell length (L), mm]. For the description of length-dry mass relationship, the power function (DW = a * Lb) was applied. The highest density, biomass, and mean shell length were 178 ind. m−2, 24.9697 g DW m−2, and 21.99 mm, respectively. ANOVA detected significant spatial variation in biomass; however, significant temporal variation was not recorded between the years, only among the seasons. Multiple linear regressions were used to find the relationship between the biomass and the environmental parameters. The coarse and very fine sediment fractions and the high water temperature provided suitable habitat for C. fluminea. Although statistically significant correlation was not detected between the chlorophyll-a content of water and the biomass, the highest biomass values were recorded at sites with high chlorophyll-a value.

Pb isotope evidence for contaminant-metal dispersal in an international river system: The lower Danube catchment, Eastern Europe

Lead isotope signatures (207Pb/206Pb, 208Pb/206Pb, 208Pb/204Pb, 206Pb/204Pb), determined by magnetic sector ICP-MS in river channel sediment, metal ores and mine waste, have been used as geochemical tracers to quantify the delivery and dispersal of sediment-associated metals in the lower Danube River catchment. Due to a diverse geology and range of ore-body ages, Pb isotope signatures in ore-bodies within the lower Danube River catchment show considerable variation, even within individual metallogenic zones. It is also possible to discriminate between the Pb isotopic signatures in mine waste and river sediment within river systems draining individual ore bodies. Lead isotopic data, along with multi-element data; were used to establish the provenance of river sediments and quantify sedimentary contributions to mining-affected tributaries and to the Danube River. Data indicate that mining-affected tributaries in Serbia and Bulgaria contribute up to 30 of the river channel sediment load of the lower Danube River. Quantifying relative sediment contributions from mining-affected tributaries enables spatial patterns in sediment-associated metal and As concentrations to be interpreted in terms of key contaminant sources. Combining geochemical survey data with that regarding the provenance of contaminated sediments can therefore be used to identify foci for remediation and environmental management strategies. © 2010 Elsevier Ltd.

Project tocoen ‐ the fate of selected organic pollutants in the environment part XXI. ‐ The contents of PAHs, PCBs, PCDDs/Fs in sediments from Danube river catchment area

As a part of cooperation between Chemical Time Bombs Program and Project TOCOEN, the contamination of sediments in Moravian and Slovakian part of Danube river catchment area by PAHs, PCBs, PCDDs/Fs was determined. The total contents of PAHs ranged between 25.5 and 4,690.3 ng•g‐1, PCBs between 4.9 and 232 ng•g‐1 and PCDDs/Fs were detected at one site in concentration 0.0005 pg•g‐1 TEQ.