Danube Research Articles

Hunting during the Late Iron Age in the Region of the South Pannonian Danube Valley

During the human history, hunting has been an important economic and social activity, requiring various techniques and hunting equipment. In the literature discussing the Late Iron Age of the South Pannonian Danube valley, the hunting strategies and the importance and meaning of wild animals are rarely discussed. In order to better understand this aspect of life, this paper reconsiders the already existing archaeo-zoological data on wild animals from the settlements, as well as the objects usually interpreted as hunting equipment, as indicators of the hunting strategies, the mode of usage and the social role of wild animals, along with the potential status differences among the settlements of the Late La Tène period. On the grounds of the acquired data, it may be concluded that hunting was a regular activity in the majority of the Late La Tène settlements in the South Pannonian Danube valley. The differences in the frequency of wild animals in the settlements in Bačka and Banat, compared to the ones in Srem, may be interpreted as the consequence of differing economic/social strategies, and not as a sign of marked differences in the availability of resources. The results have shown that the high percentage of game animals is not restricted solely to the fortified settlements. However, the traces of aurochs and brown bear, registered only in the fortified settlements, as well as the preference towards hunting large wild boar males registered at Židovar, may be the indicators of the groups of inhabitants with higher social and economic capacities situated in the fortified sites. Although on the central European sites of the same period the high frequency of wild animals is not a common trait, on a number of spatially close sites in Romania a similar archaeo-zoological situation is registered and interpreted as the indicator of the presence of the elites. This interpretation is plausible, but it should also be taken into account that in the case of the settlements analyzed in this paper other potential causes may be cited, such as the times of crisis and the decrease in the number of the domesticated animals. This interpretation is plausible, but it should also be taken into account that in the case of the settlements analyzed in this paper other potential causes may be cited, such as the times of crisis and the decrease in the number of the domesticated animals visible in the archaeo-zoological assemblages. It is necessary, however, to bear in mind that the registered archaeo-zoological situation need not be explained by the same reasons on all the sites. Namely, although the period in question spans just over one century, the Late La Tène is the time of dynamic and perpetually changing internal and external relations, causing the changes in the subsistence strategies as well. The data on the hunting equipment is very scarce. Since very few finds are associated to these activities, it is necessary to conduct more detailed specialized studies, not only of the metal objects, but also of the ones made of other material, that may be associated to the hunting practices (e.g. net weights, bone and lithic projectiles).

Taxonomic composition of phytoplankton in various continental aquatic hydroecosystems of Ukraine

The paper deals with present-day taxonomic composition of phytoplankton in various continental aquatic ecosystems of Ukraine (Kaniv Reservoir, the Western Bug River (with tributaries), Prypiat River (with tributaries), Sula River (within Nyzhniosulskyi National Natural Park, ponds (Hostomel town), large lakes of the Danube River) according to the modern algological nomenclature AlgaeBase. Within 2000–2022 in the phytoplankton of aquatic ecosystems under study 455 species of algae were identified, represented by 467 infraspecies taxa from 206 genera, 102 families, 53 orders, 18 classes and 8 phyla. The most diverse were Bacillariophyta (25–50%), Chlorophyta (22–39%) and Cyanobacteria (7–16% of floristic spectrum). Phytoplankton responds to present climate change by increase in Cyanobacteria share. The taxonomic hierarchy of algae, identified in plankton, is characterized by the following regression: Bacillariophyta > Chlorophyta > Cyanobacteria > Ochrophyta > Euglenozoa. Analysis of the taxonomic composition of Bacillariophyta at different levels of their systematic hierarchy (families, genera — according to Kendall index; species (infraspecie taxa) — according to Sørensen index) has made it possible to reveal the following patterns. The Kendall index for leading families varied within 0.31–0.72. The highest level of similarity was observed for lotic ecosystems. The Kendall index for leading genera varied between 0.11 and 0.59. The highest similarity level was observed between ecosystems of one type, for example, lotic (the Prypiat River and the Western Bug River) or lentic (ponds of Hostomel town and large Danube lakes). Cluster analysis of species similarity according to Sørensen index shows that two clusters can be distinguished in the dendrogram: lotic ecosystems and lentic ecosystems. The long-term data on the taxonomic composition of phytoplankton (algae present in water column at the moment of sampling) give evidence of high diversity thereof in various aquatic ecosystems of Ukraine.

Geodynamic hazard assessment for the archaeological park-museum by the town of Nikopol

This study was conducted to establish the engineering geological and hydrogeological conditions of the site and to assess the geodynamic hazard in relation to the design and construction of the archaeological park-museum and feeder road in the town of Nikopol (Bulgaria). The studied terrain occupies a river terrace and the foot of a delluvial slope with an elevation of 23-68 m. The tasks of the study are to identify: the geological structure of the slope, the area and depth range of the landslides, the location of the slip surface, the physical and mechanical properties of the engineering geological strata, the hydrogeological conditions, the current stability of landslides, the change of slope stability under the action of various factors. The ground investigation includes analysis of archival and published information on the area; geodetic survey of the landslide; engineering geological mapping; exploratory boreholes; geophysical surveys using the VES method; testing of soil and water samples; compilation of longitudinal engineering geological profiles and slope stability analysis using the computational models. To the south of the study site the slope is affected by an ancient landslide with a volume of about 30 million m3 developed on the right valley slope of the Danube River in the section between the plateau and the river terrace. Consistent landslides occur in its lower part. Slope stability calculations show that the landslides are triggered by a rise in the groundwater level, an earthquake and undermining of the slope base. Rock-falls has developed on the steep rock slopes, composed of moderately to highly weathered and fractured cherty and glauconitic limestones. The size of the rockfall blocks is in the range 0.3-0.8 m3 and their transport distance reaches from 10 m to 50 m from the base of the slope. Stabilization measures and facilities are proposed to strengthen the landslides and rockfalls in the considered section of the slope. For the landslides it is proposed to implement a counterfort embankment on which to build the feeder road, drainage ribs and drainage ditches. For protection of the buildings from collapsing rock debris, an anchored high-strength net is recommended. The design takes into account the trajectory of the falling blocks and their kinetic energy. For monitoring the condition of the landslides and rockfalls, as well as for evaluating the effectiveness of the implemented strengthening, drainage and coastal protection structures, a control and measurement system for regime observation was built.

Stable isotope and hydrogeological measurements: Implications for transit time and mixing ratio in a riparian system of the Danube River

Riverbank filtration has a very important role in the supply of drinking water globally. However, this water source is vulnerable, because rivers are easily contaminated. To assess its vulnerability, it is essential to understand the properties of the aquifer including the sources of the water and the transit time. Therefore, a comprehensive investigation of the Hungarian Danube River-riverbank system was conducted on two of its islands (Szentendre and Csepel). Water level, temperature and electrical conductivity were monitored in the wells located in the riverbank, and water samples were collected regularly from the wells and the river for stable hydrogen and oxygen isotope analyses over a year. It was found that the wells located at different distances from the Danube River have various responses to the hydrological changes occurring in the river. Transit time distributions (TTD) belonging to different production wells were determined by the lumped parameter method, based on the convolution integral. Differences in the TTDs of the wells are explained by their distance from the Danube River, spatial variations in the aquifer hydraulic properties and the varying pumping rates. Additionally, the estimated mixing ratio of different water sources (i.e., Danube River and background shallow groundwater infiltrated from precipitation) to the exploited water suggests that the contribution of precipitation is less than 20 %.Furthermore, the stable water isotope data of the Danube River in the Budapest area was measured from 1998 to 2021 was gathered and evaluated. It appears that the δ18O values of the Danube River at Budapest show systematically higher values than those from Vienna, indicating lowland water contribution and some evaporation effect.

First record of the freshwater sponges (Spongilla) in the inland waterways of Bulgaria

Abstract Records from freshwater sponges on Bulgarian territory are scarce. Only two exist in the scientific literature, one from the Zhrebchevo Dam and one from the Bulgarian part of the Danube River near the border with Serbia. Inland lotic ecosystems such as channels, streams, and rivers, as well as lentic ecosystems, were not studied for this potential biological indicator. Due to the existing knowledge gap, studies of entire rivers and other aquatic ecosystems focused on the monitoring of biological or physicochemical quality elements should be vigilant for Spongillidaе family representatives since even their random discovery and identification could be of great importance. Such records can be considered interesting for gaining knowledge of their distribution, species richness, habitat preference and particular environmental variables dependencies. We investigated macroinvertebrates and macrophytes from 16 sampling sites in a river with a length of about 200 km and a watershed of 1600 km2 to register two Spongilla lacustris individuals at two sites without any significant hydro-morphological pressure from big dams. Our results could serve for monitoring program optimization that aims to investigate rare protected species dependent on freshwater sponges and on seeking more localities with established Spongilla populations. This can be achieved by directing sampling efforts on sampling sites that have similar habitats and have a hydraulic connection with the found specimens.

Diatom metabarcoding as a tool to assess the water quality of two large tributaries of the Danube River

This study examines the effectiveness of digital microscopic and molecular analysis (rbcL and 18S markers) in assessing diatom community composition and water quality in two international rivers (Sava and Tisa rivers). Also, two different approaches were applied for calculating diatom indices: based on the relative abundance of taxa and the presence/absence of taxa. The rbcL marker showed up as a more suitable choice for providing a comprehensive view of the diatom community compared to 18S, which can be partly attributed to variations in the coverage of reference databases. Furthermore, both morphological and molecular analysis pointed out statistically different ecological statuses of investigated rivers. Diatom indices derived from molecular data indicated one or two classes of lower ecological status than those based on morphological analysis. However, the average diatom indices derived from molecular presence/absence data were higher than those based on the relative abundance of taxa. After summarizing all the results, we can recommend using the rbcL marker with taxa presence/absence data for routine monitoring of large lowland rivers.

Current levels of inorganic and organic pollutants in Romanian marine waters: Implications for ecosystem health

Human activities continue to impact the Romanian Black Sea, with implications for the marine ecosystem. This study presents new data (2023) on the spatial distribution of heavy metals, persistent organic pollutants, and nutrients in Romanian Black Sea waters. Our findings reveal the influence of various pollution sources, including the Danube River, municipal and industrial discharges, and maritime activities. Nutrient loads, primarily from the Danube and diffuse sources, exert pressure on the pelagic habitat. While there has been some improvement in nutrient conditions, the potential for increased eutrophication due to climate change remains a concern. Understanding the spatial distribution of pollutants and identifying their sources is crucial for developing effective management strategies to protect the marine environment.

DAILY DANUBE RIVER WATER LEVEL PREDICTION USING EXTREME LEARNING MACHINE APPROACH

Anticipating water levels in vast riverbeds is crucial for preventing and mitigating floods or droughts, assessing power plant capacity, and facilitating navigation management. This study introduces an innovative water level prediction model utilizing an Extreme Learning Machine developed to solve the issues of low performance of existing forecasting methods. Development of such a system is of extreme importance when talking about the largest European river – the Danube River. Experimental findings reveal the model's satisfactory performance across various accuracy metrics, complexity considerations, and calculation speed. The prediction with the highest error rate based on MAPE criteria was for Prahovo water level prediction over a 365-day period at 2.02%, whilst the most accurate predictions were for Novi Sad and Banatska Palanka over 30 days and 180 days horizons, respectively, at 0.0550%. The highest coefficient of determination (R2) was achieved with the Novi Sad data at 0.9968, whilst the lowest was observed with the Prahovo data at 0.7353. The ELM model achieved high precision by adjusting the activation functions of the hidden layer neurons, which involved using different combinations of sigmoid and radial-basis activation functions.

The effect of urbanization on planktonic and biofilm bacterial communities in different water bodies of the Danube River in Hungary

Freshwaters play an essential role in providing ecosystem services worldwide, however, the water quality of different water bodies is strongly influenced by human activities such as urbanization, industry and agriculture. In this study, water and biofilm samples were collected from the main channel of the Danube River upstream and downstream of a metropolitan, from a regulated side arm within an urbanized area, and from two differently separated oxbow lakes located in nature conservation areas. The taxonomic diversity of bacterial communities was revealed by 16S rRNA gene-based amplicon sequencing using Illumina MiSeq platform. The results showed that all samples were dominated by phyla Pseudomonadota, Actinobacteriota and Bacteroidota. The bacterial community structures, however, clearly differentiated according to planktonic and epilithic or epiphytic habitats, as well as by riverine body types (main channel, side arm, oxbow lakes). The taxonomic diversity of biofilm communities was higher than that of planktonic ones in all studied habitats. Human impacts were mainly reflected in the slowly changing biofilm composition compared to the planktonic ones. Genera with pollution tolerance and/or degradation potential, such as Acinetobacter, Pseudomonas and Shewanella were mainly detected in biofilm communities of the highly urbanized section of the river side arm.

Die Donau als Lebensader in Harald Grills Reisebuch Hinter drei Sonnenaufgängen. Balkanstreifzüge durch Rumänien und Bulgarien bis Odessa (2018)

Abstract Harald Grill is a German author from Eastern Bavaria who predominantly writes poetry and travel books, as well as travel features for radio and television. He became known due to his project of a ‘returning home twice’, when he walked back on foot to his hometown of Regensburg, on the river Danube, two times, in 2000 starting from the North Cape, and in 2001 starting from Sicily. In 2015, he travelled to Southeastern Europe and wrote a book based upon the experiences and reflections during this voyage. In the following, it shall be demonstrated how the river Danube, to which Grill since his childhood has had close biographical ties, structures the text of this travel book and moreover serves as a medium of self-reflection and therapeutic remedy following the author’s loss of his mother.

Enhancing Compressive Strength of Cement by Indigenous Individual and Co-Culture Bacillus Bacteria

Using a Taguchi experimental design, this research focuses on utilizing indigenous bacteria from the Danube River to enhance the self-healing capabilities and structural integrity of cementitious materials. Bacillus licheniformis and Bacillus muralis were used as individual bacterium or in co-culture, with a concentration of 8 logs CFU, while the humidity variation involved testing wet and wet–dry conditions. Additionally, artificial neural network (ANN) modeling of the compressive strength of cement samples results in improvements in compressive strength, particularly under wet–dry conditions. By inducing targeted bacterial activity, the formation of calcium carbonate precipitates was initiated, which effectively sealed formed cracks, thus restoring and even enhancing the material’s strength. In addition to short-term improvements, this study also evaluates long-term improvements, with compressive strength measured over periods extending to 180 days. The results demonstrate sustained self-healing capabilities and strength improvements under varied environmental conditions, emphasizing the potential for long-term application in real-world infrastructure. This study also explores the role of environmental conditions, such as wet and wet–dry cycles, in optimizing the self-healing process, revealing that cyclic exposure conditions further improve the efficiency of strength recovery. The findings suggest that autochthonous bacterial co-cultures can be a viable solution for enhancing the durability and lifespan of concrete structures. This research provides a foundation for further exploration into bio-based self-healing mechanisms and their practical applications in the concrete industry.

Disentangling the Effects of Multiple Impacts of Natural Flooding on a Riverine Floodplain Lake by Applying the Phytoplankton Functional Approach

Riverine floodplains are ecologically remarkable systems that have historically faced strong anthropogenic pressures. The aim of this study was to examine whether the phytoplankton functional approach by Reynolds is a useful tool for disentangling anthropogenic pressure from the impact of natural flooding on a riverine floodplain lake. Lake Sakadaš, part of the large conserved river–floodplain system along the Danube River (Kopački Rit, Croatia), was used as a case study. Historical data on phytoplankton dynamics from the 1970s, when the lake was exposed to direct inflows of agricultural wastewater, were compared with current data from a time when the lake was a strongly protected area. Analysis of the phytoplankton community, based on functional groups and their beta diversities, revealed clear variation between the observed periods. The heavy bloom of species from only one functional group with extremely high biomass indicated a highly impacted environment in the past. Recent data suggest that, with the cessation of direct pollution, near-natural hydrological conditions with flooding as a fundamental environmental driving factor, support algal assemblages characteristic of a naturally eutrophic lake. Assessing multiple pressures on floodplain lakes and disentangling their specific impacts on ecological statuses are crucial for defining the protection and sustainable management of these particularly sensitive and endangered freshwater systems.

Characterization of the reproductive strategy of invasive Round Goby (Neogobius melanostomus) in the Upper DanubeRiver.

Originating from the Black and Caspian seas, the Round Goby (Neogobius melanostomus) has become one of the most successful invaders of freshwater ecosystems. In this study, we provide a characterization of the reproductive strategy of an established population of Round Gobies in the Upper Danube river including sex ratio, fluctuations of gonadosomatic index (GSI), analysis of timing of spawning as well as of clutch and egg size. We compare these results to other studies from the native and invaded range. In the Danube, the Round Goby population was found to be female dominated, however fluctuations in magnitude of female bias were observed between months. Monitoring of the population across 1.5 years revealed that GSI was highest from April to June, while lowest values were observed in August and September. Using time-series analysis, a delayed effect of temperature on GSI was found for females and males, while a quicker response of GSI levels to photoperiod and discharge was observed for females. GSI increased with body size for females and eggs were found to be significantly larger in May, however clutch sizes did not differ between months. Results of a literature review revealed great differences in timing and length of spawning season as well as sex ratio between populations throughout the distribution range, which can probably be explained by climatic and photoperiodic conditions together with the time since invasion and the high plasticity of Round Gobies.

Composition, divergence and variability: A comprehensive analysis of fish trait responses to connectivity

Connectivity, a fundamental concept in ecology, refers to the extent to which different habitats or ecosystems are interconnected through the movement of organisms, nutrients, and energy. Lateral hydrological connectivity (LHC) plays an especially critical role in shaping aquatic community organization in river-floodplain systems. However, a comprehensive understanding of various trait responses to LHC remains elusive. We characterized how attributes of fish community traits, specifically composition, divergence, and temporal variability respond to LHC in the Austrian-Hungarian floodplains of the Danube River using environmental DNA (eDNA) metabarcoding. Trait composition was quantified by community-level weighted means (CWM) as the degree of changes in trait responses along the LHC gradient from isolated oxbows to the main river. Divergence was measured using Rao’s quadratic functional diversity index and a null model approach to calculate standardized effect sizes (SES), with larger SES values indicating greater divergence and smaller values indicating convergence. Temporal variability, representing the degree of instability in community traits over time, was calculated using a functional beta diversity measure for multiple communities. Our findings revealed apparent compositional changes for many trait variables, highlighting the significance of LHC in shaping community functional diversity. Divergence patterns indicated that isolated habitats foster trait convergence presumably due to habitat filtering, whereas more connected areas promote trait divergence due to higher species richness and habitat availability. Temporal variability of traits associated with flow preference exhibited a hump-shaped relationship with LHC, suggesting intermediate connectivity zones are hotspots of ecological dynamism. The study suggests that examining composition, divergence, and temporal variability together provides a more complete understanding of trait responses to connectivity, stressing the importance of maintaining diverse connectivity levels in river-floodplain systems for effective conservation and ecosystem management.

Round gobies (Neogobius melanostomus) in the River Rhine: Population genetic support for invasion via two different routes

The round goby, Neogobius melanostomus, is a successful invasive fish species. Originating from the Caspian and Black Sea, it is now distributed widely within European fresh- and brackish waters. The River Rhine was colonized in 2008 only a few years after the opening of the Rhine-Main-Danube canal and only four years after N. melanostomus was first reported in the upper Danube River. Its invasion history of the River Rhine was unclear because the species was first detected close to the Rhine river delta which would suggest a route of invasion other than via the Rhine-Main-Danube canal. To investigate the colonization history of N. melanostomus in the Rhine, we combined abundance estimates with molecular analysis. Abundance estimates found N. melanostomus to be dominant in the Lower Rhine (> 90% of all catches). Molecular analysis was done on 286 individuals from four different sites. Using the mitochondrial control region (d-loop), we found three different haplotypes in both Rhine sites. None of the potential invasive source populations in the rivers Danube and Trave exhibited all three haplotypes. The molecular data therefore supported a scenario of two different colonization directions. Our results show that the invasion history of the River Rhine is complex and warrants further investigation.

The effect of ship-induced wave trains on periphytic algal communities in the littoral zone of a large regulated river (River Danube, Austria)

Riverine ecosystems are profoundly influenced by hydrological dynamics and natural flow regimes, which dictate the temporal variability of water levels and the amplitude of fluctuations. Human activities, particularly navigation and hydropower generation, have significantly altered these natural patterns, leading to detrimental impacts on the physical, chemical, and biological integrity of river ecosystems. The littoral zone, in particular, is highly susceptible to anthropogenic disturbances, experiencing disruptions in biological activity and biogeochemical processes. This study evaluates the effects of ship-induced wave trains on the structural and functional properties of periphytic algal communities in a regulated river environment. Using data from the Austrian Danube River, periphytic algae's immediate and long-term responses to wave events generated by different types of ships were investigated. Immediate reactions of periphytic algae to wave trains were characterized by reductions in the effective quantum yield of PS II, indicating stress-induced down-regulation of photosystem II photochemistry. Abrasion and remobilization of periphytic algae due to wave action led to increased resuspension of chlorophyll-a into the water column. Furthermore, ship-induced wave trains influenced the pigment composition of periphyton, with photoprotective mechanisms being activated in response to fluctuating light conditions. Long-term effects of wave impact on periphytic algae biomass varied depending on water depth and exposure to aerial stress. While wave action mitigated desiccation stress in shallow areas, it resulted in biomass reduction and alterations in community composition in deeper zones. Notably, the occurrence of diatoms decreased in wave-impacted areas, potentially shifting the community towards Chlorophyceae dominance. Overall, this study underscores the complexity of ship-induced wave impacts on riverine ecosystems and highlights the importance of considering both immediate and long-term responses of periphytic algal communities. Understanding these dynamics is crucial for informing sustainable management strategies aimed at mitigating the adverse effects of navigation activities on riverine biodiversity and ecosystem functioning.

Simulation‐Based Assessment of Fine Sediment Transport to Support River Restoration Measures

ABSTRACTA three‐dimensional coupled hydrodynamic and sediment transport model was employed to simulate the suspended sediment transport at a section of the Danube River, in Hungary. The case study is characterised by a highly complex hydromorphological system due to the nearby tributary inflow, the high number of river regulation structures as well as the several side‐arms connected to the Danube mainstem. The numerical model is set up, parameterised and validated against thorough field data of flow velocities and sediment concentrations measured at different hydrological regimes. Through the selected case study, the paper introduces (i) why 3D description is necessary at a reach‐scale analysis of complex hydromorphological systems; (ii) what sort of field data is needed to parameterise and validate a hydrodynamic and sediment transport model considering the spatial inhomogeneity of the flow and sediment features and (iii) an example for a quantitative impact assessment of side‐arm revitalisation measures on the sedimentation processes, playing a crucial role in the quality of riverine habitats.

GIS-based spatial modeling of landslide susceptibility using BWM-LSI: A case study – city of Smederevo (Serbia)

Abstract Landslides and slope processes constitute one of the most frequent natural hazards in valleys near major rivers and mountainous regions. The surface layer, characterized by its relatively loose composition, is prone to sliding due to a combination of distinct natural and human-related factors. Specific sections along the right bank of the Danube River in Smederevo city exhibit significant susceptibility to landslide activation, often leading to substantial material losses and posing a risk to the local population. The initial step in the provided research involves analyzing existing literature and mapping landslides within the study area. The initial analysis covers both natural conditions and anthropogenic activities. The second step includes establishing a geospatial database in the Geographic Information System and generating eight thematic maps. In the third step, different weight coefficients were assigned to the criteria, which facilitated the creation of the Landslide Susceptibility Index using the Best–Worst Method. Subsequently, in the fourth step, a composite map illustrating landslide susceptibility was produced. According to this research, about 4% of the territory of Smederevo, or 19.3 km2, is highly or very highly susceptible to landslides. These localities are located on the right bank of the Danube River and around the Ralja River. Receiver operating characteristic-area under the curve value indicates very high predictive power (approximately 1), thus suggesting the reliability of the used methodology. This visualization of areas highly prone to such occurrences empowers policymakers to implement more effective environmental protection measures and institute sustainable management practices for agricultural parcels in this region. Also, the provided research represents the inaugural integration of advanced remote sensing techniques and interdisciplinary investigations, offering deeper insights into landslide activity in the study area and yielding more comprehensive results.

A Spatial–Seasonal Study on the Danube River in the Adjacent Danube Delta Area: Case Study—Monitored Heavy Metals

Monitoring and protecting flowing watercourses is a complex and challenging task that requires the collaboration and coordination of various stakeholders such as governments, industries, farmers, consumers and environmental groups. The study of the dynamics of the concentration of polluting factors and especially the concentrations of heavy metals and highlighting a seasonal variation is a necessary element from this point of view. In this article, we present the results of our analyses carried out in two measurement campaigns executed in 10 monitoring points along the Danube River, between Braila city and Isaccea city in the pre-deltaic area, during the summer season and autumn season 2022. The importance of this area is given by the fact that the Danube Delta is part of the UNESCO heritage, and the monitoring of polluting factors is a necessity in the desire to protect this area. The data measured during the July and August 2022 campaign cover a wide range of chemical species: Phosphate, CCO, CBO5, NH4+, N-NO2, N-NO3−, N-Total, P-PO4 3−, SO42−, Cl−, phenols, as well as metals with a harmful effect: Al, As, Cd, Cr, Fe. The study includes an evaluation based on the statistical approach of the results to highlight the significant correlations and differences identified between the two data sets. Next, to highlight the obtained results, a numerical model was considered using HEC-RAS and ESRI ArcGIS applications in a two-dimensional unsteady flow model in order to obtain the non-homogenous concentrations’ distributions in the studied area. These two-dimensional models have been less studied in the specialized literature. In this way, interesting results could be obtained, and prediction methods regarding the dynamics of metal concentrations could be structured. The data obtained were used for the terrain model from the USGS service, and the flows of the Danube and its two tributaries were simulated using the data provided by the national services. In this work, we present the results obtained for the dynamics of the concentrations of the metals Al, As, Cd, Cr and Fe and the evaluation of the specific absorption coefficients for the explanation and correlation with the results of the measurements. Except for the numerical model presented, we would like to highlight the existence of some contributions of the main tributaries of the Danube in the study area. Such a systematic study has not been carried out due to conditions imposed by the border authorities. From this point of view, this study has an element of originality. The study is part of a more complex project in which the spatio-temporal distribution of the polluting factors in the water was evaluated, and the habitats in the study area were inventoried—especially those of community interest. In this way, we were able to expose the self-purification capacity of the Danube and highlight the existence of a concentration reduction gradient along the course of the river. The aspects related to the influence of the distribution of polluting factors on the state of health will be the subject of another article.

Downstream change of luminescence sensitivity in sedimentary quartz and the rearrangement of optically stimulated luminescence (OSL) components along two large rivers

Recently, it has been proposed that the luminescence sensitivity of quartz grains, i.e. their luminescence response to unit dose, might be used for sediment fingerprinting. Sensitivity is determined both by the origin of quartz grains and the sedimentary processes they underwent. However, a more detailed understanding of the factors influencing sensitivity is essential in order to expand and specify the applicability of the parameter in sediment sourcing and geomorphological studies alike. In the present research, we examined the spatial changes of sensitivity parameters of coarse grain quartz in modern sediments of the largest rivers of the Carpathian Basin, Central Europe, to determine the role of source areas and transportation distance.Based on the luminescence analysis of 39 samples, quartz extracts with a Carpathian origin (catchment of the Tisza River have a significantly higher sensitivity, except the LM-OSL medium component, than those originating from the Alpine domain (catchment of the Danube River). No clear relationship could be identified between natural sensitisation and transportation distance. In terms of the Tisza the observed downstream increase of quartz sensitivity is due to high sensitivity quartz grains supplied by its tributaries. In the meantime, a recurring change was observed along the Danube, which can be attributed mostly to local erosional processes. Consequently, tributaries and erosion can overprint the potential downstream sensitisation of quartz grains in large rivers.Meanwhile, in terms of the Danube on sections where a significant downstream increase was detected in LM-OSL fast component sensitivity, LM-OSL medium component sensitivity systematically decreased. Additionally, during laboratory sensitization, the CW-OSL sensitivity of Danube samples increased considerably, whereas changes were more moderate in the case of Tisza samples. Moreover, in the case of Tisza-related quartz extracts, the 110°C TL sensitivity and the LM-OSL fast and medium components showed a strong correlation, indicating the stability of luminescence processes (trapping and recombination). Whereas, in the case of the Danube both LM-OSL components show a weak correlation with the 110°C TL intensity. All these indicate that Alpine-origin quartz grains are more susceptible to the rearrangement of electron traps and/or recombination centres, which can also be an indicator of sediment sources in Quaternary studies in the region.