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Abstract: In this paper, a novel self‐organizing network (SON) based similarity index and its application for the optimization of sampling locations in an existing river water quality monitoring network (WQMN) is presented. A rationalization of the River Danube WQMN on its stretch through Serbia was performed using the proposed SON2‐based similarity index. A high‐dimensional dataset was used, which is composed of 18 water quality parameters that were collected during the period 2002–2010 at 17 monitoring locations. The SON‐based seasonal classification that divides 12 months into the cold, moderate, and warm seasons was employed, whereas its second application on each seasonal class yielded subclasses that were used to compare the monitoring locations. The obtained SON2‐based similarity index can be utilized for analysing seasonal variations, as well as overall similarities among neighbouring sites. Based on the calculated similarities of locations and characteristics of the River Danube basin a rationalized WQMN, which uses 30% less monitoring sites, has been proposed. [ABSTRACT FROM AUTHOR]

Especially for extreme precipitation or floods, there is considerable spatial and temporal variability in long term trends or in the response of station time series to large-scale climate indices. Consequently, identifying trends or sensitivity of these extremes to climate parameters can be marked by high uncertainty. When one develops a nonstationary frequency analysis model, a key step is the identification of potential trends or effects of climate indices on the station series. An automatic clustering procedure that effectively pools stations where there are similar responses is desirable to reduce the estimation variance, thus improving the identification of trends or responses, and accounting for spatial dependence. This paper presents a new hierarchical Bayesian approach for exploring homogeneity of response in large area data sets, through a multicomponent mixture model. The approach allows the reduction of uncertainties through both full pooling and partial pooling of stations across automatically chosen subsets of the data. We apply the model to study the trends in annual maximum daily stream flow at 68 gauges over Germany. The effects of changing the number of clusters and the parameters used for clustering are demonstrated. The results show that there are large, mainly upward trends in the gauges of the River Rhine Basin in Western Germany and along the main stream of the Danube River in the south, while there are also some small upward trends at gauges in Central and Northern Germany. [ABSTRACT FROM AUTHOR]

This paper presents a methodological approach that can aid the assessment of variation in limnological variables in response to hydrological phases and seasonal temperature variation. The investigation was conducted in the Danube River floodplain, Kopački Rit, Croatia. The proposed approach facilitates a more accurate examination of the effects of first factor, while maintaining second factor less variable, and vice versa. Samples were collected in the floodplain channel and lake along a temporal connectivity gradient, and were grouped according to three hydrological phases (isolation, flow pulse and flood pulse) and according to three seasons (spring, summer and autumn). A permutational multivariate analysis of variance was used to analyse the hydrological effects within seasons, as well as seasonal effects within hydrological phases on selected limnological variables: pH, conductivity, dissolved oxygen, nitrites, nitrates, ammonium, total Kjeldahl nitrogen, total phosphorus, chlorophyll a concentrations and ratio of copiotrophic to oligotrophic bacteria. A multivariate data cloud was structured by hydrological phases during all investigated seasons, but not by all seasons during different hydrological phases. The strongest impact of hydrological phases on limnological variables occurred during summer. Seasonal effects were significant during the isolation and the flood pulse phases. The flow pulse phase somehow obscured the effects of seasonal change, resulting in temporal floodplain homogenization. One possible explanation is that water temperature determines potential limnological conditions, whereas hydrology determines actual conditions. Such results must be taken into account if the accurate effects of hydrology and seasonal change are to be assessed in temperate floodplain ecosystems. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract. This paper describes vegetation development after a severe drop in water level. Diversion of the Danube river in 1992 resulted in a substantial water level reduction and the appearance of new terrestrial habitats in the Szigetköz region, a unique part of the Danube Valley in Hungary. Plant colonization was very rapid in the recently exposed river bed, where the establishment of a new willow thicket zone took only 4 yr. Our results clearly indicate that the elevation/moisture gradient is primarily responsible for the small-scale vegetation heterogeneity that developed as succession proceeded. Further changes in vegetation patterns will be determined by the position of the water level as a result of water management. [ABSTRACT FROM AUTHOR]

We performed a detrital zircon (DZ) U‐Pb geochronologic survey of the lower parts of the Danube River approaching its Danube delta, Black Sea sink, and a few large tributaries (Tisza, Jiu, Olt, and Siret) originating in the nearby Carpathian Mountains. Samples are modern sediments. DZ age spectra reflect the geology and specifically the crustal age formation of the source area, which in this case is primarily the Romanian Carpathians and their foreland with contributions from the Balkan Mountains to the south of Danube and the East European Craton. The zircon cargo of these rivers suggests a source area that formed during the latest Proterozoic and mostly into the Cambrian and Ordovician as island arcs and back‐arc basins in a Peri‐Gondwanan subduction setting (~600–440 Ma). The Inner Carpathian units are dominated by a U‐Pb DZ peak in the Ordovician (460–470 Ma) and little inheritance from the nearby continental masses, whereas the Outer Carpathian units and the foreland have two main peaks, one Ediacaran (570–610 Ma) and one in the earliest Permian (290–300 Ma), corresponding to granitic rocks known regionally. A prominent igneous Variscan peak (320–350 Ma) in the Danube's and tributaries DZ zircon record is difficult to explain and points out to either an extra Carpathian source or major unknown gaps in our understanding of Carpathian geology. Younger peaks corresponding to arc magmatism during the Alpine period make up as much as about 10% of the DZ archive, consistent with the magnitude and surface exposure of Mesozoic and Cenozoic arcs. Key Points: A detrital zircon U‐Pb study of modern sands from the lower Danube and its tributaries documents the main magmatic events that led to the continental crustal formation of the nearby CarpathiansThe great majority of basement was formed in latest Proterozoic‐Ordovician island arcs, a finding that is consistent with previous studiesAn unexpected and prominent Carboniferous magmatic peak in the detrital record has no known source in the nearby Carpathians [ABSTRACT FROM AUTHOR]

Abstract: Before reaching the Black Sea, the Danube River passes through a string of Para‐Tethyan (Vienna, Pannonian and western and eastern Dacian) basins. The key question is, when and how did the Danube River become a continental‐scale river with a drainage similar to present? New data presented here show that the Late Miocene deepwater strata in the Black Sea have a significant sediment source and depositional style change at about 4 Ma. However, the presence of active Miocene basins within the Danube catchment raises questions about the timing of Danube River inception and whether the upstream palaeogeography would have allowed or disallowed delivery of large sediment volumes to the deepwater Black Sea. Stratigraphic analyses in the Pannonian and Dacian basins reveal a phase of coeval sedimentary fill of the basins along the Danube at about 4 Ma. This multi‐basin observation points to a concurrent basin‐fill model rather than the basin fill‐and‐spill or Messinian‐type lowstand models previously proposed for Danube inception. [ABSTRACT FROM AUTHOR]

The relationship between air (Ta) and water temperature (Tw) is very important because it shows how the temperature of a water body might respond to future changes in surface Ta. Mean monthly Tw records of three gauging stations (Bezdan, Bogojevo i Veliko Gradište) were analysed alongside mean monthly discharge (Q) for the same stations. Additionally, Ta series from two meteorological stations (Sombor and Veliko Gradište) were correlated with Tw variations over the period 1950-2012. Locally weighted scatter point smoothing (LOWESS) was used to investigate long-term trends in the raw data, alongside the Mann-Kendall (MK) trend test. Trend significance was established using Yue-Pilon's pre-whitening approaches to determine trends in climate data. Also, the rescaled adjusted partial sums (RAPS) method was used to detect dates of possible changes in the time series. Statistically significant warming trends were observed for annual and seasonal minimum and maximum Tw at all investigated sites. The strongest warming was observed at Bogojevo gauging station for seasonal maximum Tw, with +0.05 °C per year on average. RAPS established that the trend began in the 1980s. This behaviour is linked to climate patterns in the North and East Atlantic which determine the amount of heat advected onto mainland Europe. Statistically significant correlations were found for all Tw on an annual basis. Overall, the strongest correlations ( p < 0.01) between Tw residuals and the North Atlantic Oscillation (NAO) were recorded for the winter period. These findings suggest possible predictability of Tw over seasonal time-scales. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Fishery in the Danube River basin has been characterised over the past century by increasing fishing levels, illegal fishing practices and poor regulations. However, there is a remarkable lack of available information on the actual status of fish stocks, as well as on the trends and sustainability of fisheries, which poses a problem for the development of adequate policy and management measures. In this study, we assessed the trends in the commercial fishery in the Middle Danube in Serbia during 1969-1989 and 2006-2010 by evaluating the temporal changes in life history-related indicators that might point out unsustainable fishing pressures. Moreover, we present the approach of using the catch-weighted mean egg-per-recruit ( EPR) index as a proxy for the overall resilience of fish stocks to fishing. Results indicated a marked shift towards smaller fish that mature earlier and have a shorter lifespan. Landings also shifted towards species at lower trophic levels, with a mean trophic level decline at a rate of approximately 0.16 per decade. Results indicated likely presence of the 'fishing through the food web' phenomenon. At the same time, catch-weighted community mean of the 20% EPR threshold ratio (EPR20%) increased by 4.2%, indicating the increase of the overall resilience to fishing of the exploited species. Obtained results indicated the importance of using such metrics for the assessments of trends in fishery. The approach and results presented here could be of interest for the scientific community and stakeholders involved in fishery management. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

1. International river catchments pose challenges for effective water resource management. Catchment-wide strategies are often complicated by differences in national bioassessment and quality classification. Intercalibration efforts aim to harmonise these differences, but rely on the consistent delineation of near-natural reference sites that are almost unavailable in today's landscape, especially for large rivers. 2. We introduce the concept of alternative benchmarking that is based on the notion of aquatic communities at similar (low) levels of impairment associated with least-disturbed conditions (LDC) as defined by abiotic criteria. Using data acquired during the second Joint Danube Survey, we defined LDC sites based on a multivariate gradient of anthropogenic pressures, mostly related to morphological deterioration, that spans the entire navigable Danube. 3. The river was subdivided into four stretches, each featuring homogeneous biological assemblages. Indirect gradient analysis revealed relationships between the pressure gradient and selected features of the macroinvertebrate and macrophyte community but not for diatoms or phytoplankton. 4. We identified biological metrics suitable for the quality classification of individual stretches or the entire river. Impoundment is the major hydromorphological alteration on the Danube but various metrics still responded significantly to differences in the morphological condition of sites not affected by impoundment. 5. A comparison of macroinvertebrate sampling techniques (airlift versus kick-and-sweep) revealed differences in how the acquired data reflect the effects of anthropogenic pressure. Biological metrics based only on kick-and-sweep sample data were insensitive to habitat deterioration in the heavily modified Upper Danube. 6. This study exemplifies the empirical approach of alternative benchmarking in intercalibration and offers practical solutions to some of the challenges of large river bioassessment. [ABSTRACT FROM AUTHOR]

Effect-directed analysis (EDA) can be useful in identifying and evaluating potential toxic chemicals in matrixes. Previous investigations of extracts of sediments from the upper Danube River in Germany revealed acute nonspecific and mechanism-specific toxicity as determined by several bioassays. In the present study, EDA was used to further characterize these sediments and identify groups of potentially toxic chemicals. Four extracts of sediments were subjected to a novel fractionation scheme coupled with identification of chemicals to characterize their ability to disrupt steroidogenesis or cause mutagenic and/or teratogenic effects. All four whole extracts of sediment caused significant alteration of steroidogenesis and were mutagenic as well as teratogenic. The whole extracts of sediments were separated into 18 fractions and these fractions were then subjected to the same bioassays as the whole extracts. Fractions 7 to 15 of all four extracts were consistently more potent in both the Ames fluctuation and H295R assays. Much of this toxicity could be attributed to polycyclic aromatic hydrocarbons, sterols, and in fraction 7-naphthoic acids. Because the fraction containing polychlorinated biphenyls, polychlorodibenzodioxin/furan, dichlorodiphenyltrichloroethane, and several organophosphates did not cause any observable effects on hormone production or a mutagenic response, or were not detected in any of the samples, these compounds could be eliminated as causative agents for the observed effects. These results demonstrate the value of using EDA, which uses multiple bioassays and new fractionation techniques to assess toxicity. Furthermore, to our knowledge this is the first study using the recently developed H295R assay within EDA strategies. Environ. Toxicol. Chem. 2012; 31: 1053-1062. © 2012 SETAC [ABSTRACT FROM AUTHOR]

The article provides information on a study that evaluated the impact of climatic changes on water temperature in a two-step approach. It establishes whether long-term trends in water temperature do in fact exist. It determines the impact of air temperature and discharge rates on this trend. It cites the reasons for analyzing data from the Austrian section of the Danube River. It also investigates long-term trends and relationship of water temperature/air temperature/discharge. It examines scenarios for air and water temperature, discharge and nitrate load.

The article provides information on a study that analyzed records of water and air temperature and explained changes in water temperature records in some larger Croatian rivers that belong to the Danube River catchment. It discusses the annual minimum, maximum and average air and water temperatures in the study area. To study regional air temperature characteristics, data from meteorological stations in Zagreb and Osijek for the period 1900-2005 are used. The study found that the relationship between air and water temperatures in the study area is very strong.

Despite increasing information about postglacial recolonization of European freshwater systems, very little is known about pre-Pleistocene history. We used data on the recent distribution and phylogenetic relationships of stone loach mitochondrial lineages to reconstruct the initial colonization pattern of the Danube river system, one of the most important refuges for European freshwater ichthyofauna. Fine-scale phylogeography of the Danubian populations revealed five highly divergent lineages of pre-Pleistocene age and suggested the multiple origin of the Danubian stone loach. The mean sequence divergence among lineages extended from 7.0% to 13.4%, which is the highest intraspecific divergence observed so far within this river system. Based on the phylogeographical patterns, we propose the following hypothesis to relate the evolution and dispersal of the studied species with the evolution of the Danube river system and the Carpathian Mountains: (i) during the warmer period in the Miocene, the areas surrounding the uplifting Alps and Carpathians served as mountainous refuges for cold-water adapted fish and promoted the diversification of its populations, and (ii) from these refuges, colonization of the emerging Danube river system may have taken place following the retreat of the Central Paratethys. Co-existence of highly divergent mtDNA lineages in a single river system shows that range shifts in response to climatic changes during the Quaternary did not cause extensive genetic homogenization in the stone loach populations. However, the wide distribution of some mtDNA lineages indicates that the Pleistocene glaciations promoted the dispersal and mixing of populations through the lowlands. [ABSTRACT FROM AUTHOR]

Because of its efficiency as a sampling method, electrofishing of age-0 fish is often used to assess natural reproduction in rivers. However, little is known about the relative tradeoffs of accuracy and efficiency of different electrofishing methods. For monitoring purposes, it is important to find a method that accurately estimates age-0 fish assemblages and that is relatively quick and inexpensive. Though some studies have compared the suitability of different methods for addressing particular research or management questions, to our knowledge this is the first study comparing two different electrofishing sampling strategies: point abundance and continuous. We compared time effectiveness and accuracy of estimating age-O fish assemblages obtained by point abundance and continuous electrofish!ng on the lowland Morava River (Danube River basin, Czech Republic). Forty sites were surveyed by each strategy along two types of shoreline: submerged vegetation and boulder bank. Both strategies yielded similar qualitative data (species richness, relative proportion of species, and size structure) along each shoreline type. Point abundance sampling required a shorter amount of survey time than did continuous sampling. We conclude that point abundance sampling is the more suitable method for routine sampling of age-0 fish assemblages in lowland rivers. [ABSTRACT FROM AUTHOR]

Contends that the principle of equitable utilization must be applied in concert with sustainable water use as in the case of the Danube River. Conflict over the Gabcikovo Nagymaros Dam; Overview of the geographical features of the Danube River; Application of the international water law.