Search Results (52)

Freshwater ecosystems face escalating degradation, demanding real-time, scalable, and biodiversity-aware monitoring solutions. This review proposes an integrated framework combining artificial intelligence (AI), geographic information systems (GISs), and environmental DNA (eDNA) to overcome these limitations and support next-generation river health assessment. The AI-GIS-eDNA system was applied to four representative river basins—the Mississippi, Amazon, Yangtze, and Danube—demonstrating enhanced predictive accuracy (up to 94%), spatial pollution mapping precision (85–95%), and species detection sensitivity (+18–30%) compared to conventional methods. Furthermore, the framework reduces operational costs by up to 40%, highlighting its potential for cost-effective deployment in low-resource regions. Despite its strengths, challenges persist in the areas of regulatory acceptance, data standardization, and digital infrastructure. We recommend legal recognition of AI and eDNA indicators, investment in explainable AI (XAI), and global data harmonization initiatives. The integrated AI-GIS-eDNA framework offers a scalable and policy-relevant tool for adaptive freshwater governance in the Anthropocene. Full article

Since the introduction of the Sustainable Development Goals, and, in particular, with the goal of reducing marine pollution (SDG 14.1), riverine microplastics are attracting public and scientific attention. But standardized monitoring methods and comparable data are still missing. Therefore, the opportunity was taken to test three of the most common monitoring methods (multiple depths net-method, pressurized fractionated filtration and sedimentation-box) at seven sites in five countries along the Danube and the Tisza Rivers. Different boundary conditions (hydrological and morphological conditions, economic situation, equipment available, etc.) were considered for the evaluation, as well as different sampling methods and sample pre-treatments together with different methodologies for microplastic identification. The sampling methods were evaluated for their suitability to be used as a standard monitoring tool in the future. Only net sampling and pressurized fractionated filtration allow for the determination of microplastic concentration as well as load, and can therefore be recommended. The multi-depth net device, as a labor-intensive method, is recommended if the focus of the monitoring is on larger particles and it is important to calculate particle and mass concentrations. Pressurized fractionated filtration is a practical tool recommended for routine monitoring, having the advantage of less effort being required for sample preparation and simply considering small particle sizes below 500 µm. From a scientific perspective it is recommended to combine both the pump sampling and the net-based device. Full article

The assessment of surface water quality of the Danube River and Black Sea was performed taking into account the amounts determined for heavy metals (As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn), nutrients (compounds of N and P, chlorophyll a), emerging contaminants (CECs) (pharmaceutics and endocrine disruptors—19 quantified compounds, out of 30 targeted chemicals), heterotrophic bacteria and total coliforms, in thirty-two locations from the lower Danube sector (starting with km 375 up to the river mouths), the Danube Delta Biosphere Reserve (three Danube branches—Chilia, Sulina, and Sf. Gheorghe) and the Romanian coastal area of the Black Sea. The heavy metals levels were found in the following ranges: 3.0–6.5 μg/L As; 0.51–1.32 μg/L Cd; 21.6–61.2 μg/L Cr; 10.2–28.6 μg/L Cu; 196–351 μg/L Mn; 12.3–47.67 μg/L Ni; 5.2–15.5 μg/L Pb; 44–74 μg/L Zn; 0.01–0.08 μg/L Hg. The nutrient concentrations vary in the intervals: 0.04–0.45 mg/L N-NH₄; 0.01–0.06 mg/L N-NO₂; 0.07–1.9 mg/L N-NO₃; 1.0–3.2 mg/L N total; 0.01–0.05 mg/L P-PO₄; 0.02–0.27 mg/L P total, and 0.8–17.3 μg/L chlorophyll a. The concentrations of CECs from various classes (sulfamethoxazole, trimethoprim, ciprofloxacin, flumequine, amoxicillin, cefuroxime, dicloxacillin, carbamazepine, pravastatin, erythromycin, piroxicam, ketoprofen, diclofenac, naproxen, enilconazole (imazalil), clotrimazole, drospirenone, 17α-ethinylestradiol, and bisphenol A) were compared with values reported for European rivers and the Danube River water in various river sectors. The highest detection frequencies were registered for bisphenol A (100%), sulfamethoxazole (96%), carbamazepine and diclofenac (87%), trimethoprim (78%), pravastatin (46%), and imazalil (34%). Bisphenol A exhibited the largest concentrations (342 ng/L), followed by diclofenac (132 ng/L), carbamazepine (38 ng/L), and sulfamethoxazole (36 ng/L). For most of the contaminants, Black Sea coastal water showed lower concentrations than the Danube water and good ecological status for surface water. Correlations between CECs and total coliforms suggest insufficient treated wastewater effluents as a common contamination source and possible use of CECs as indirect fecal pollution indicator in aquatic systems. This is the first study carried out in the connected system Danube River–Danube Delta–Black Sea for a large palette of toxicants classes and microbial pollutants, which will serve as a baseline for future monitoring of water quality in the region. Full article

Extreme hydrological events have become more frequent in the Danube River Basin in recent decades. In this research, we focus on the consequences of such events on the dynamic of invasive cyanobacteria Raphidiopsis raciborskii (Wołoszyńska) Aguilera et al. (formerly known as Cylindrospermopsis raciborskii (Wołoszyńska) Seenayya et Subba Raju). In the Danube floodplain lake used as a case study, the investigated period from 2003 to 2016 was characterized by the cyclical occurrence of extreme floods (2006 and 2013) and extreme droughts (2003 and 2015). As a result, the lake changed several times from a phytoplankton turbid state to a clear state characterized by a very low phytoplankton biomass. R. raciborskii was abundant in the phytoplankton and bloomed in summer 2003 (June–September) and then in summer 2007 (June–August) and in August 2013. Extreme summer drought triggered the bloom, and water temperature was the most significant environmental variable during the bloom. The observed declining trend in total cyanobacterial biomass, including the less frequent occurrence of the R. raciborskii bloom, can be linked to the ecological disturbances in the stable state of the lake caused by extreme hydrological events. This suggests that the effects of climate change may be less detrimental in preserved natural river–floodplain systems. Full article

Global warming and climate change cause large temperature oscillations and uneven annual rainfall patterns. The rainy cycles characterized by frequent high-intensity rainfall in the area of the Stubo–Rovni water reservoir, which in 2014 peaked at 129 mm of water in 24 h (the City of Valjevo, the Republic of Serbia), caused major floods in the wider area. Such extremes negatively affect erosion processes, sediment production, and the occurrence of flash floods. The erosion coefficient before the construction of the water reservoir was Z_m = 0.40, while the specific sediment production was about 916.49 m³∙km⁻²∙year⁻¹. A hydrological study at the profile near the confluence of the Jadar and Obnica rivers, i.e., the beginning of the Kolubara river, the right tributary of the Sava (in the Danube river basin), indicates that the natural riverbed can accommodate flows with a 20% to 50% probability of occurrence (about 94 m³/s), while centennial flows of about 218 m³/s exceed the capacities of the natural riverbed of the Jadar river, causing flooding of the terrain and increasing risks to the safety of the population and property. The paper presents the impacts of the man-made Stubo–Rovni water reservoir on the catchment area and land use as the primary condition for preventing erosion processes (specific sediment production has decreased by about 20%, the forest cover increased by about 25%, and barren land decreased by 90%). Moreover, planned and controlled management of the Stubo–Rovni reservoir has significantly influenced the downstream flow, reducing the risks of flash floods. Full article

Water-quality indicators and trace elements were measured in the alluvial area of the Kostolac Basin, Serbia. The results revealed that the groundwater was naturally neutral, with a mean conductance of 920.10 μs/cm. The primary factors contributing to the decline in the groundwater quality in the researched area were electrical conductivity (EC), NO₃⁻, SO₄²⁻, Cd, and Pb; the water samples were deemed unfit for human consumption and the water was classified as having impaired quality. A Pearson correlation matrix, a principal component analysis (PCA), and a cluster analysis (CA) were applied to identify the pollution source and factors controlling the groundwater quality and the results indicated that both natural and anthropogenic factors influenced the groundwater of the studied area. The Nemerow pollution index indicated medium to high pollution levels along with the degree of contamination. A health risk evaluation was conducted to determine the non-carcinogenic risks posed by nitrates and heavy metals from oral consumption and skin contact in the researched area. Nearly all monitoring sites had hazard quotients (HQs) below 1, suggesting that potential concerns might be negligible. However, children showed the highest exposure levels, with HQs for nitrates at 2.26 and for lead (Pb) at 2.515. No carcinogenic risk from oral lead (Pb) exposure was found in any sample. Full article

The Tisza River is the longest tributary of the Danube, draining the eastern part of the Carpathian Basin (Central Europe). Five countries share its catchment with different waste production and management practices. Large amounts of waste, including macroplastics (MaPs), are washed into the river. Some of the litter is trapped by the riparian vegetation forming litter accumulations. The study aimed to map the amount of litter by a citizen science program and remote sensing data and to compare the MaP data to the amount of microplastic fragments in sediments. Volunteers reported 3216 riverine litter accumulations from five countries along the entire length of the Tisza (2016–2022). The results suggest that low flow conditions (e.g., impoundment by dams) support litter and MaP trapping. The volume of large accumulations registered by the citizens showed a good correlation with the area of drifting litter revealed on Sentinel-2 images (2016–2022) using machine learning algorithms. Though the MaPs probably fragmentate during their fluvial transport, no clear connection was found between the volume of litter accumulations and the mean microplastic fragment content of sediments (2019–2022). The “Clean Tisza Map“ reveals the high degree of stranded pollutants along rivers and supports public cleanup activities. Full article

The sterlet (Acipenser ruthenus) is the smallest-bodied endangered species among the six native sturgeon species of the Danube River, and self-sustaining populations still inhabit the Hungarian section of the Danube River and its largest tributary, the Tisza River. Their populations are drastically decreasing; however, they still have natural reproduction in these habitats. For the genetic conservation of the species, an ex situ gene bank is maintained in Hungary. The present study aimed to analyze the genetic resources of a gene bank with a near 40-year history and to compare it with natural populations and farmed stocks. Twelve microsatellites were used for population genetics analyses and individual genotyping of 268 specimens from two natural habitats (Danube and Tisza Rivers) and three captive stocks (a gene bank broodstock and two farms). Microsatellites revealed similar patterns among wild populations and gene bank stocks and did not show genetic differentiation (F_ST: 0.016–0.017) among them. These results confirmed that the gene bank broodstock properly represents the genetic background of the Danube and Tisza populations and is suitable as a source of breeding materials for the restocking programs. Negative trends were detected in the farmed stocks, reflected in reduced polymorphism at a few loci. The results of the principal component analyses indicate the farm stocks’ separation from the wild and gene bank stocks. The present genetic characterization study reveals a valuable captive stock of the endangered sterlet populations and provides unique information about the genetic similarities and differences among farms and wild stocks in Hungary. Our results provide information that contributes to preserving the genetic structure and variability in sterlet populations and supports the management of gene bank broodstock—avoiding inbreeding and preserving the unique genetic background of the Carpathian basin. Full article

The Sava River Basin (SRB) includes six countries (Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Albania, and Montenegro), with the Sava River (SR) being a major tributary of the Danube River. The SR originates in the mountains (European Alps) of Slovenia and, because of a recent Slovenian government initiative to increase clean, sustainable energy, multiple hydropower facilities have been constructed within the past ~20 years. Given the importance of this river system for varying demands, including hydropower (energy production), information about past (paleo) dry (drought) and wet (pluvial) periods would provide important information to water managers and planners. Recent research applying traditional regression techniques and methods developed skillful reconstructions of seasonal (April–May–June–July–August–September or AMJJAS) streamflow using tree-ring-based proxies. The current research intends to expand upon these recent research efforts and investigate developing reconstructions of seasonal (AMJJAS) precipitation applying novel Artificial Intelligence (AI), Machine Learning (ML), and Deep Learning (DL) techniques. When comparing the reconstructed AMJJAS precipitation datasets, the AI/ML/DL techniques statistically outperformed traditional regression techniques. When comparing the SRB AMJJAS precipitation reconstruction developed in this research to the SRB AMJJAS streamflow reconstruction developed in previous research, the temporal variability of the two reconstructions compared favorably. However, pluvial magnitudes of extreme periods differed, while drought magnitudes of extreme periods were similar, confirming drought is likely better captured in tree-ring-based proxy reconstructions of hydrologic variables. Full article

The Sava River Basin (SRB) extends across six countries (Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Albania, and Montenegro) and is a major tributary of the Danube River (DR). The Sava River (SR) originates in the alpine region of Slovenia, and, in support of a Slovenian government initiative to increase clean, sustainable energy, multiple hydropower facilities have been constructed within the past ~20 years. Given the importance of this river system for varying demands, including energy production, information about past (paleo) drought and pluvial periods would provide important information to water managers and planners. Seasonal (April–May–June–July–August–September—AMJJAS) streamflow data were obtained for two SRB gauges (Jesenice and Catez) in Slovenia. The Jesenice gauge is in the extreme headwaters of the SR, upstream of any major water control structures, and is considered an unimpaired (minimal anthropogenic influence) gauge. The Catez gauge is located on the SR near the Slovenia–Croatia border, thus providing an estimate of streamflow leaving Slovenia (entering Croatia). The Old World Drought Atlas (OWDA) provides an annual June–July–August (JJA) self-calibrating Palmer Drought Severity Index (scPDSI) derived from 106 tree-ring chronologies for 5414 grid points across Europe from 0 to 2012 AD. In lieu of tree-ring chronologies, this dataset was used as a proxy to reconstruct (for ~2000 years) seasonal streamflow. Prescreening methods included the correlation and temporal stability of seasonal streamflow and scPDSI cells. The retained scPDSI cells were then used as predictors (independent variables) to reconstruct streamflow (predictive and/or dependent variables) in regression-based models. This resulted in highly skillful reconstructions of SRB seasonal streamflow from 0 to 2012 AD. The reconstructions were evaluated, and both low flow (i.e., drought) and high flow (i.e., pluvial) periods were identified for various filters (5-year to 30-year). When evaluating the most recent ~20 years (2000 to present), multiple low-flow (drought) periods were identified. For various filters (5-year to 15-year), the 2003 end-year consistently ranked as one of the lowest periods, while the 21-year period ending in 2012 was the lowest flow period in the ~2000-year reconstructed-observed-historic period of record. The ~30-year period ending in 2020 was the lowest flow period since the early 6th century. A decrease in pluvial (wet) periods was identified in the observed-historic record when compared to the paleo record, again confirming an apparent decline in streamflow. Given the increased activities (construction of water control structures) impacting the Sava River, the results provide important information to water managers and planners. Full article

In this mini-review, we present evidence from the vast literature that one essential part of the coupled atmosphere–ocean system that makes life on Earth possible, the water cycle, is exhibiting changes along with many attributes of the global climate. Our starting point is the 6th Assessment Report of the IPCC, which appeared in 2021, where the almost monograph-size Chapter 8, with over 1800 references, is devoted entirely to the water cycle. In addition to listing the main observations on the Earth globally, we focus on Europe, particularly on the Carpathian (Pannonian) Basin. We collect plausible explanations of the possible causes behind an observably accelerating and intensifying water cycle. Some authors still suggest that changes in the natural boundary conditions, such as solar irradiance or Earth’s orbital parameters, explain the observations. In contrast, most authors attribute such changes to the increasing greenhouse gas concentrations since the industrial revolution. The hypothesis being tested, and which has already yielded convincing affirmative answers, is that the hydrological cycle intensifies due to anthropogenic impacts. The Carpathian Basin, a part of the Danube watershed, including the sub-basin of the Tisza River, is no exception to these changes. The region is experiencing multiple drivers contributing to alterations in the water cycle, including increasing temperatures, shifting precipitation regimes, and various human impacts. Full article

Rivers and their watersheds have been subject to various changes, including biodiversity, caused by anthropogenic activities. The Danube River and Black Sea basin overlap the geographic range of six species of anadromous fish belonging to the family Acipenseridae. Nowadays, they are endangered or at risk of extinction in the wild due to fragmentation and destruction of natural habitats, blocking their migration to spawning grounds, water pollution, and poaching. This paper presents a review of the historical and current distribution and evolution of the sturgeon populations of sturgeon species in the Danube River basin. Conservation status and measures for species protection, conservation, and restoration at the national, regional, and global levels are presented. Full article

In hydrological practice, individual elements of the hydrological cycle are most often estimated and evaluated separately. Uncertainty in the size estimation of extrema discharges and their return period can affect the statistical assessment of the significance of floods. One example is the simultaneous occurrence and joining of extremes at the confluence of rivers. The paper dealt with the statistical evaluation of the occurrence of two independent variables and their joint probabilities of occurrence. Bivariate joint analysis is a statistical approach for the assessment of flood threats at the confluence of rivers. In our study, the annual maximum discharges monitored on four selected Slovak rivers and their tributaries represent the analyzed variables. The Archimedean class of copula functions was used as a set of mathematical tools for the determination and evaluation of the joint probability of annual maximal discharges at river confluences. The results of such analysis can contribute to a more reliable assessment of flood threats, especially in cases where extreme discharges occur simultaneously, increasing the risk of devastating effects. Finally, the designed discharges of the different return periods calculated by using the univariate approach and the bivariate approach for the gauging station below the confluence of the rivers was evaluated and compared. Full article

Studying the historical and future trends of water resources in a basin and explaining the causes of water resource changes is very important, which is key to the management of water resources in a basin. The Hanjiang River Basin is an important water supply source for southwestern Fujian and eastern Guangdong, but it has an uneven spatial and temporal distribution of water resources and an outstanding conflict between supply and demand. In this study, the SWAT model was used to simulate the conditions of the Hanjiang River Basin in the last 50 years, using long time series climate data to study the characteristics and driving mechanism of water resources trend change. The results show that the water resources in the basin have not increased significantly in the last 50 years, but evapotranspiration has increased significantly. The forecast results for water resources in the future are reduced. The water resource changes in the basin have been unevenly distributed in the last 50 years. Climate change has been the main factor in total water resource change in the basin, while the difference in water resource change trends within the basin is caused by land use. The key reason for the decrease in water resources in the Hanjiang River Basin is the significant increase in evapotranspiration due to the significant increase in temperature. If this situation continues, the available water resources in the basin will continue to decline. In fact, many basins around the world are currently likely to have such problems, such as the 2022 summer drought in the Danube River Basin in Europe and the Yangtze River Basin in China, so this article is informative and representative of future water resources management in the basin. Full article

Wastewater treatment plants (WWTPs) represent an important input of contaminants in the environment. Therefore, it is critical to continuously monitor the performance of WWTPs to take appropriate action and avoid an influx of contaminants in the environment. In this study, a battery of seven in vitro bioassays covering a selected spectrum of toxicity effects is proposed for quality control of wastewater effluents. The bioassays address mixture toxicity, which is the combined adverse effect of multiple contaminants and can act as an early warning system. The proposed battery was applied to samples from 11 WWTPs of representative technology from the Danube River Basin (DRB). The order of toxic effects in terms of extent of exceedance of effect-based trigger values (EBTs) was PAH (PAH activity) > PXR (xenobiotic metabolism) > ER_α (estrogenic activity) > PPAR_γ > Nrf₂ (oxidative stress) > anti-AR > GR. A mitigation plan for WWTP operators based on EBT exceedance is proposed. This study demonstrates that the proposed effect-based monitoring battery is a complementary tool to the chemical analysis approach. A regular application of such time- and cost-effective bioanalytical tools in the WWTPs of the DRB is proposed to provide a ‘safety net’ for aquatic ecosystems. Full article