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This study conducts an in-depth analysis of 820 maps with a focus on the western coast of the Black Sea, from Bilhorod-Dnistrovskyi to Cape Kaliakra, and gives special attention to the Danube Delta. The research highlights Pietro Vesconte's critical role in the accurate depiction of the area and examines the stylistic developments over time and their effects on the mapping of the region. It also delves into the relationship between navigational practices and cartographic representation, noting the limited influence of Ottoman conquests on local mapping techniques. The study draws attention to a resurgence in the use of Ptolemaic principles, occurring simultaneously with the adoption of modern surveying techniques, such as triangulation. By concentrating on the Danube Delta and the adjacent coast of the Black Sea, the study provides a detailed understanding of the cartographic history of the area, highlighting the mix of precision and creative interpretation in maps. [ABSTRACT FROM AUTHOR]

The article demonstrates the importance of studying the assessment of economic potential for business entities in the Danube basin, considering the international community’s focus on issues affecting the delta region. It identifies the components essential for evaluating the economic potential for foreign economic activity of these entities: production, natural resources, labor, innovation, and investment. The natural resource potential for realizing the economic potential of foreign economic activities of entities located in Ukraine’s Danube basin is characterized. The indicators of the production component of economic potential for entities in the Odesa region are analyzed, covering the dynamics of the gross regional product, the number of economic entities, and the dynamics and structure of exports of goods and services, as well as the financial performance of leading enterprises. The analysis results of Odesa region indicators from 2017-2022 confirm strong economic potential for foreign economic activity in terms of the production component (including engineering, agriculture, transport, chemical, food, light industry, energy) and natural resource component (natural and climatic conditions, landscape diversity). The article highlights the predominance of agricultural products and transport services in exports. It is established that business entities remain dependent on imports of mineral products, machinery, and equipment for conducting foreign economic activity. Analyzing the results and reports allowed the identification of risks associated with foreign economic activity for business entities in the Odesa region. Recommendations for enhancing the foreign economic potential of business entities, considering influential factors and risks, can support the development of further strategies for Odesa region, Izmail district, and individual business entities. The scientific novelty of this research lies in expanding theoretical frameworks and improving the scientific and methodological foundations for assessing the economic potential of business entities engaging in foreign economic activity.

Rare plant species are particularly vulnerable to anthropogenic influences, which contribute to reducing their populations and restricting their distribution areas. The objective of this study was to reconfirm the information on the distribution of three rare plant species – Tripidium ravennae, Trachomitum venetum, and Stachys maritima, within the Danube Delta Biosphere Reserve, Romania. The research was carried out between 2019 and 2023. The results highlighted that the respective species are rare by showing limited distribution and small populations. Among the main threats to the survival of these species are tourism development, overgrazing, and soil compaction. Trachomitum venetum is a rare plant species in specific communities, showcasing its selective habitat preferences. Tripidium ravennae is a rare species in specific plant subassociations and plant associations, indicating its limited distribution. Stachys maritima is rare within different plant communities, reflecting its adaptability to varied environmental conditions within the Danube Delta Biosphere Reserve.

Within the framework of this paper, we proposed to analyze the evolution of demand for this destination during the restrictions generated by COVID 19, but also the interest of investors in this area. The Danube Delta represented the ideal destination of 2020, in a pandemic context, and continued to represent it in 2021. In this sense, the objectives of the research are represented by the analysis of the main indicators of sustainable tourism development, for which there are statistical data at the territorial level; they are recommended to be the most important for shaping the metamorphosed tourism paradigm. The purpose of the research carried out is to propose some measures/solutions to protect the ecosystem of the Danube Delta Biosphere, so that they can be implemented by the state institutions and even by the inhabitants of the local communities, in order to ensure the sustainability of the Danube Delta tourist destination in the future. The methodology for the analysis of the modeling the metamorphosed paradigm sustainable tourism post-COVID-19 in the Danube Delta was implemented through three successive stages: (1) the analysis of the main theoretical elements regarding sustainable tourism in the Danube Delta, (2) the evaluation of the main indicators proposed for shaping the metamorphosed paradigm of tourism and (3) calculating the average length of stay.

The present study aims to assess the ecosystem services of the Danube Delta through a complex multi-factor hierarchical regression analysis. Using three different regression models, the research addresses multiple dimensions of human-nature interaction in this area of major ecological and cultural importance. First, the attractiveness of ecosystem services (VF1) was investigated, identifying a positive impact of improved infrastructure and tourism service provision on the local economy and visitor experience. It was also found that this attractiveness needs to be weighed with specific demographic and social needs. Secondly, the current perception and potential for conservation and tourism (VF2) was examined, revealing the link between effective resource management and the region’s tourism value. Thus, positive perceptions of conservation practices were found to be determinant in establishing the value of the Delta as a tourist destination. Finally, the impact of obstacles to Delta development (VF3) was considered, highlighting the importance of an integrated approach to development planning in the region. The recognised obstacles involve environmental, economic and social factors, and indicate the need for balanced management of natural resources. The results of the study highlight the need for multidisciplinary collaboration for effective management of the Danube Delta, emphasising the need to protect this unique habitat while promoting sustainable and inclusive development for the benefit of current and future generations.

The palatability of a plant refers to the degree of attraction or preference that animals show toward that particular plant. Various factors can influence palatability, including the plant's chemical composition, texture, taste, aromas, and the circumstances under which herbivorous animals consume it. The study aims to assess the plant species composition in grasslands and pastures within the Danube Delta, Romania. Both old or new references on palatability were considered. The evaluation of plant composition and degree of plant palatability was carried out in 12 grazing areas in the Danube Delta and the surrounding region. The study revealed 121 plant species identified in some pastures. Of these, 31 were "Non-Palatable", 16 were "Highly Palatable", 32 were "Mostly Palatable", 16 were "Less Palatable", and 26 were "Rarely Palatable". Animals preferred 60 plant species in their fresh condition, with 29 preferred in fresh and dry. Most animals consumed whole plants (48 species), followed by leaves (43 species), fruits (three species), and inflorescences (two species). By analysing the feeding preferences of animals, it was found that cows exhibited a preference for the broadest range of plants (75 species), followed by sheep (67 species), goats (59 species), and horses (34 species). Domestic animals like goats, sheep, cows, and horses may prefer certain plants based on nutritional content or digestibility while avoiding toxic plants. The study showed that the investigated areas have a diverse flora with a varied supply of plants, including palatable species. The palatability index is essential in assessing the quality of pastures, especially in obtaining average daily gains based on the species of animals living on the pastures. Considering the dynamic climatic conditions and poor pasture quality in the Danube Delta, more detailed and interdisciplinary studies are needed to understand the deltaic biocenoses comprehensively. [ABSTRACT FROM AUTHOR]

Delta systems, as final receptors of the fluvial systems are under considerable and increasing influence of multiple anthropogenic stresses, such as hydropower plant developments in the basins, extraction of groundwater in delta plains, embankment of banks, dredging of the navigation channel, the land use change, channel engineering, that affect the sediment connectivity. Along the Sulina Canal, the cut-off program and construction of the groins and dikes had important responses in grain size distribution between the main channel, the rectified meanders, and the lakes of the Danube Delta. Two field campaigns (at high and low waters) were made in May and October 2023, focusing on the bed sediment composition and lithological constituents. Sediment samples were acquired throughout several cross-sections, to investigate the bed sediment characteristics. Grain size parameters (such as Median, Standard deviation, and Skewness) show the predominance of fine fraction (medium and fine sand, and silt), moderately and poorly sorted. The data were compared and larger modifications were found between the two analysed periods in the distribution of sediments. [ABSTRACT FROM AUTHOR]

This study delves into three distinct cartographic representations of the Danube River's course, stretching from Hârșova to the Black Sea, originating from the tumultuous era of the Russo-Ottoman conflict (1768–1774). The materials presently being examined are pivotal in redefining the cartographic perspective of the Danube region, a viewpoint that has largely relied on nautical charts or maps influenced by Ptolemy for more than four centuries. Although they were abundant in toponymic details and descriptions, they did not incorporate modern projection and coordinate systems. Published in Russian (1771), German (1778), and French (circa 1770s), these maps not only shed light on the geographical comprehension during the Cartographic Enlightenment but also underscore their primary military intent—to navigate a labyrinthine liquid territory. Through the synthesis of these materials, the research introduces consolidated figures and constructs a toponymic database reflective of late 18th century nomenclature. The article further delineates the wetland region's hydrographic structure, pinpointing the evolution and occasional misinterpretation of toponyms. These cartographical products provide insights into the local way of life and indirectly reference the Old Believers, thus serving as a prime example of cartography's capacity to illuminate human differences. [ABSTRACT FROM AUTHOR]

Avian diet composition studies are based on material collected from the Danube Delta (Romania) and adjacent areas, from the second half of the 20th century. In the socialist era, the ruling political regime regarded the avifauna as an exploitable natural resource, which either has to be converted into monetary income, or those species that were posing a threat to fish production in fisheries had to be ruthlessly decimated or even extirpated. Most culled birds were not subjected to scientific study. We succeeded to sample only a small fraction of the killed birds, and to publish the results of the studies. After the political changes in 1989, as nature conservation gained impetus in the Eastern Block, the publication of results based on invasive sampling generated unfavourable reactions in the society. Even so, we believe the publication of the findings based on the saved data is very useful. This study provides the results of the quantitative and qualitative examination of 247 individuals belonging to 9 bird species. We did not compare our findings to other data, but believe this work gives insight into an era long gone. [ABSTRACT FROM AUTHOR]

We present an analysis of the Danube Delta (Romania) that is focused on the evolution and use of roads, so as to highlight the primacy of movement in spatialisation and the fluidity of roads themselves. We demonstrate that local inhabitants of the Danube Delta have relied on a network of roads for survival and have in the process fitted themselves to a deltaic space full of affordances that foreign observers have missed. Our objectives are achieved by juxtaposing a cartographic archive spanning from the 19th century up to 2019 with the lived experience of the deltaic space. The maps we uncover and redraw show how the road infrastructure in the Danube Delta has evolved. We explain what has driven this evolution by interpreting the archive in light of long‐term field work (2015–2019). This allows us to re‐characterise the deltaic space as a hybrid of solidity and liquidity, and to show the evolution of the local perspective in relation to traversing this complicated land. This is a completely new historical and cartographic contribution to a severely understudied area, the Danube Delta. [ABSTRACT FROM AUTHOR]

In this article, we present the most important landmarks of the organization and functioning of the quarantines on the Danube in the period from 1812 to 1856. The analysis of published and unpublished sources allows us to conclude that the organization and operation of quarantines at the Danube border represented an important direction of the sanitary policy of the Russian Empire. The Danube quarantines, together with the cordon line and military guard vessels, represented the most requested links in the chain of the Russian border sanitary protection, from the Prut and Danube to the Caspian Sea, both from the point of view of the danger of the penetration of the oriental plague, as well as that of the difficult physical-geographical conditions in which they had to operate. An- other determining element was Russia's military and commercial interests at the mouths of the Danube, which in several cases were placed above the sanitary ones. This led to long discussions regarding the choice between Ismail and Reni for the location of the central quarantine. Our research shows that the combination of all these elements determined major design flaws, which had a substantial negative impact on the state of the Danube quarantines in the 1820s and 1830s. Major investments became urgent, and in the 1840s the Russian government had to allocate substantial sums to rehabilitate the Ismail, Reni and Sulina quarantines. [ABSTRACT FROM AUTHOR]

The objective of this study is to provide an updated account of the distribution history of two invasive molluscs, Corbicula fluminea and Dreissena polymorpha, both in Europe and worldwide. In addition to this, the study also intends to review their ecological requirements to gain a better understanding of their invasive potential and distribution dynamics. Specifically, the study focuses on updating the distribution and ecological characteristics of these freshwater bivalves in the lower sector of the Danube River and the lakes of the Danube Delta. The purpose is to better understand their invasive and distribution dynamics and to develop effective measures to limit their spread in the future. To achieve this, environmental proxies such as sediment particle size and Total Organic Carbon (TOC) concentrations were used to assess their tolerances. However, the results did not show a significant correlation between the densities of these bivalves and the analyzed environmental parameters. Despite this, the species were found in high densities and formed well-developed benthic communities in some stations. The study contributes to the understanding of the invasiveness of these bivalve species and their distribution range dynamics. Nonetheless, further investigation is required to fully comprehend the role of environmental parameters in their distribution. The study covers the period between 2010 and 2020 and focuses on the lower Danube River sector and Danube Delta. [ABSTRACT FROM AUTHOR]

The harbours are fascinating places. Their colourful world, their bustle, and their ethnic mixture create the image of one of a kind universe. They are the meeting place of cultures and values, as one can read in Radu Tudoran’s Un port la răsărit and Jean Bart’s Europolis. The former novel takes place on the shore of Limanu Lake in Basarabia, and the latter is placed in Sulina. They both share the multicultural and multi-ethnic approach as the young engineer telling the story faces the crossroad between the Western world that ends at the Limanu shore and the Eastern Slavic world that starts there. In Jean Bart’s novel, Sulina seems more cohesive, as the Greeks, who are in the centre of the story, master the town gathering together the other communities. Still, the feeling of a crossroad persists, as the harbour is the place where boats come and leave in a way that suggests that people come and leave. There are some characteristics that feature the harbours’ communities: a state of emptiness combined with bustle, the stereotypes that describe the minorities and the destinies that end tragically in these communities where they can’t find their space: Nadia dies tragically, leaving her lover in deep mourning, Evantia also ends her life, leaving an orphan daughter. The crossroad shapes their destinies, and stimulates chaos and confusion.

Tourism is considered by the local inhabitants and businesses as an activity that could bring economic development to a very isolated and underdeveloped area such as the Danube Delta, UNESCO protected natural wetland. The aim of this study is to propose the Tourism Impact Model (TIM) as a tool that could be used by the local and regional authorities in managing tourism in such fragile ecosystems so that to maximise its positive effects while the honeypot sites of the delta to attract tourists without provoking irreparable damage to the environment. The results of the TIM analysis applied for Sfântu Gheorghe commune, Romania, evidence that the Danube Delta is under tourism pressure and at high risk of surpassing its human carrying capacity. The conclusions of the analysis show that TIM could be a very useful administrative and policy supporting tool in sustainable development governance if data collection improves in the future.

Many deltas around the world have recorded a decreasing sediment input, mostly due to retention in dams constructed on the river or in the river basin. The Danube River has recorded a significant decrease of its sediment supply to the Danube Delta and the NW Black Sea. This study uses 210Pb and 137Cs dating, to investigate the effects of the decreasing sediment flux in lakes, lagoons, delta front and prodelta area. Both the effects of the Iron Gate I and II dams and other local factors are discussed. These results define the period of 1960-1990 as the ‘major anthropic interventions period’ in the Danube Delta. Results show a decrease in siliciclastic flux, especially in lakes, the Sahalin lagoon and the prodelta area and a general increase in the Musura lagoon and the delta front area. Sand content is also shown to decrease in most areas and is replaced by silt. The changes in sediment accumulation rates depend mostly on the hydrological connectivity of the area and the local hydrotechnical works. Overall, the local anthropic interventions in the delta affect sediment flux in the subaerial delta and the delta front, while the prodelta is affected by the overall decrease caused by interventions in the river basin. This study can contribute to improving management strategies in the area and to a better understanding of future research needs in the Danube Delta-Black Sea system.

The pressure control of the anthropogenic factors has consequences on the fluvial systems, generating structural changes. The hydrology, hydraulics and sediment load of the rectified meandering systems depend on the hydrologic connectivity with the main stem of the river. The former meanders can be permanently, temporarily disconnected with the main channel producing interruptions in the transfer of fresh water and thus affecting the morpho-sedimentological processes and the biodiversity. This paper aims to investigate the distribution of the water and suspended sediment fluxes between the former meanders and the artificial man-made canals along the St. George distributary and thus, the hydrological connectivity. Understanding these complex human pressures are of high importance for reaching/maintaining the ecological status of the Danube. Herein, we made investigations along the St. George branch on many sub-systems river-channel-lake site type, formed by cutoff meanders, connective channels and lakes to observe how much the water and sediment inputs to the delta depressions is affected by the structural changes of the meander's physiography. [ABSTRACT FROM AUTHOR]

The Danube Delta, the second-largest wetland in Europe, provides people with multiple ecosystem services, consisting of drinking water, food, flood protection, nutrient recycling, and recreation, as it is a complex social–ecological system. Nowadays, the area faces heavy depopulation due to its failure in achieving an equilibrium between social, economic, and environmental issues. Therefore, its resurgence is the core element of its sustainable development strategy, and particular sectors such as fishing and aquaculture, agriculture, and tourism national strategies deal individually with essential issues without considering the potential conflicts that may arise from a particular sector's development. This study develops a complex method for decision making concerning the sustainable development of the Danube Delta Biosphere Reserve based on the consultation of both local and higher-level stakeholders in decision making, and the identification of social, economic, and environmental key problems. After their validation by experts, we developed a system dynamics model and ran the identified scenarios together with the stakeholders and recommended policies for the sustainable development of the area. The scenario that combines the transition towards the moderate Intensification of aquaculture with ecological agriculture and slow tourism brings a reduced impact on water quality, but measures to reduce nutrients are still recommended. [ABSTRACT FROM AUTHOR]

This study aimed to assess the water quality of certain lakes (Bogdaproste, Trei Ozere and Radacinos) belonging to the Danube Delta, Romania. Deltaic ecosystems are subject to natural and man-made environmental stressors. If in the past these ecosystems were largely threatened by eutrophication and organic/inorganic pollution, nowadays, we must focus on hydro morphological impact. This refers to the physical character and water content of the aquatic environment, impoundment (dams and flood gate), channelization and embankments, as well as clog/siltation of lakes. Environmental parameters are those physical, chemical and biological indicators used to characterize a freshwater body, and, which vary in time and space. In this regard, 44 water samples were collected in the dry season from the three lakes, for analysis of physical-chemical quality indicators. A series of physical (T, EC, TDS, turbidity, TSS, transparency) and chemical parameters (pH, DO, nutrients, SiO2, TOC, SO42-, ORP, technophilic elements) were considered. The results obtained in the physical-chemical analyses revealed that the majority of parameters were found in line with enforcing environmental regulations. Despite that, P-PO43- and Cd concentration results of some samples were found above certain permissible limits set by the normative. Probably, these inadvertences can be associated with local conditions of the transitional deltaic environment. Further analysis is required conducting repeated measurements with the same question, meaning a routine monitoring, especially P-PO43- and Cd. Finally, it was concluded that the results of this study showed a good quality of water in investigated lakes that did not pose potential health and environmental problems related to the biota.

The Danube River has a large hydrographical basin, being the second largest river in Europe. The main channel flows through seven European countries with many species of fish inhabiting it. In this review we focused on the invasive species silver carp (Hypophthalmichthys molitrix), which plays an important ecological and economic role in its original habitat, but since introduced in Europe's rivers, the species has posed a serious ecological risk under global warming. In this review paper, we gathered data regarding silver carp, such as when and how it entered the Danube Delta and the water temperature suitable for its growth and reproduction, mainly in the context of global warming, as well as the nature of nutrition and the ecological risk the species poses. [ABSTRACT FROM AUTHOR]

The presence of Palingenia longicauda was considered to be restricted to the Tisza River basin (sub-basin of the Danube River Basin) and the Rába River (Austria and Hungary), but new reports indicate its presence in the Danube River (Hungary), the Danube Delta (Romania and Ukraine), and in the Prut River and the Dniester River (Republic of Moldova). We assessed the genetic diversity of the species by analysing the mitochondrial cytochrome c oxidase subunit 1 (mtCOI) and large ribosomal subunit 16S rRNA (mt16S LSU) sequences of individuals from Romanian, Ukrainian, and Hungarian populations. The identified high number of endemic haplotypes that are confined to the Danube Delta and the Prut River, and the statistically significant differentiation found between the populations, suggest that the populations of these two rivers had independent histories. These results confirm the survival and recovery of Palingenia longicauda in Southeastern Europe. The species is an indicator of good ecological conditions of large rivers, therefore, this recovery may be related to the hydro-morphological integrity of the studied river sections. Large colonies of larvae were found only on near-natural steep clay banks that were under the protection of local natural parks and biodiversity reserves, close to the state borders, where human activities are more restricted. Implications for insect conservation: The genetically differentiated populations from Romania can contribute to conservation and long-term survival of P. longicauda. As freshwater ecosystems are under constant anthropogenic pressure, our results lay the basis for a scientifically well-documented management of the conservation of the species in its whole range. [ABSTRACT FROM AUTHOR]

Floods have become more and more severe and frequent with global climate change. The present study focuses on the Black Sea's immediate riparian area over which the Danube Delta extends. Due to the accelerated increase in the severity of floods, the vulnerability of the deltaic areas is augmenting. Therefore, it is very important to adopt measures to mitigate the negative effects of these phenomena. The basis of the measures to limit the negative effects is the activity of identifying areas prone to flooding. Thus, this research paper presents a methodology for estimating flood susceptibility using the Analytical Hierarchy Process (AHP) and Fuzzy-Analytical Hierarchy Process (FAHP) models. To determine the susceptibility to these natural risk phenomena, the following eight flood predictors were taken into account: slope, elevation, altitude above channel, land use, hydrological soil group, lithology distance from the river, and distance from water bodies. Furthermore, the weights that each flood predictor has in terms of determining flood susceptibility were determined through the previously mentioned models. The results revealed that the slope is the most important predictor, followed by elevation, distance from the river, and land use. These weights were used in the GIS environment to evaluate the susceptibility to floods from a spatial point of view. The areas with a high/very high value for these phenomena occupy over 70% of the surface of the Danube Delta. [ABSTRACT FROM AUTHOR]

Tourism is considered by the local inhabitants and businesses as an activity that could bring economic development to a very isolated and underdeveloped area such as the Danube Delta, UNESCO protected natural wetland. The aim of this study is to propose the Tourism Impact Model (TIM) as a tool that could be used by the local and regional authorities in managing tourism in such fragile ecosystems so that to maximise its positive effects while the honeypot sites of the delta to attract tourists without provoking irreparable damage to the environment. The results of the TIM analysis applied for Sfântu Gheorghe commune, Romania, evidence that the Danube Delta is under tourism pressure and at high risk of surpassing its human carrying capacity. The conclusions of the analysis show that TIM could be a very useful administrative and policy supporting tool in sustainable development governance if data collection improves in the future. [ABSTRACT FROM AUTHOR]

The small and medium-sized boats manufacturing industry is developing, being an area in which the finished product results after a lot of work and involvement. The production capacity varies depending on the type, destination and size of the ship and the number of units sold varies from one year to another, identifying an increase in demand in the last 2 years. From a geographical point of view, it can be said that the Danube Delta area is practically a concentrated node of development of this industry. The paper presents some aspects of developing a business in the field of production and services for small and medium-sized boats with ecological propulsion systems.

Taking into account the morphologic-hydrographic configuration of natural ecosystems or ecosystems partly modified by man the area, its flora and fauna communities and the long-term human impact, the two main categories of Danube Delta ecosystems associated with Razim-Sinoie lake complex, coastal marine waters and the Danube flood plain between Isaccea and Tulcea, as part of Danube Delta Biosphere Reserve, have been delimited: natural ecosystems or ecosystems partly modified by man; anthropic ecosystems. To identify and characterize ecosystems, there have been analysed the data on hydrography, morphology, biodiversity, human settlements, types of land use, spatial changes through the construction of agricultural, fisheries, forestry polders, modification of the network of channels and canals with consequences on the water circulation system inside the delta. The first category, of natural and partly modified by man ecosystems comprises 23 types (water bodies: running waters-Danube and its main branches, channels and canals; standing freshwater-lakes; standing brackish and salt waters-coastal lagoons, coastal, marine zones; wetlands: water fringe vegetation-flooded reed beds, floating reed beds , riparian willow formations, frequently flooded river levees; forests, shrubs and herbaceous vegetation: temperate riverine forests-mixed oak woods, shrubs and herbaceous vegetation, steppe meadows, meadows on low marine levees; dunes, beaches).The second category, of anthropic ecosystems includes 7 types (agricultural lands, forest areas-plantation on the river banks, fish farms, settlements-villages, towns). With the establishment of the Danube Delta Biosphere Reserve in 1990, with the statutory provisions on the protection and conservation of biodiversity, the deltaic landscape, some of the previous pressures were reduced, but the pollution of the Danube waters less consolidated beaches (Sulina, Sfântu Gheorghe, Chituc) and related with touristic activities, on ecosystems as a whole. The tourism activities also must represent not only a positive and dynamic development factor but also a practical solution to keeping the environment unaltered. These aspects were mentioned in the characterization of the ecosystems presented in this article.

The current paper estimated the physico-chemical properties of water in the Danube Delta (Romania), based on Sentinel 2 remote sensing data. Eleven sites from the Danube Delta were sampled in spring and autumn for three years (2018-2020) and 21 water physico-chemical parameters were measured in laboratory. Several families of machine learning algorithms, translated into hundreds of models with different parameterizations for each machine learning algorithm, based on remote sensing data input from Sentinel 2 spectral bands, were employed to find the best models that predicted the values measured in laboratory. This was a novel approach, reflected in the types of selected models that minimised the values of performance metrics for the tested parameters. For alkalinity, calcium, chloride, carbon dioxide, hardness, potassium, sodium, ammonium, dissolved oxygen, sulphates, and suspended matter the results were promising, with an overall percentage bias of the estimates of +/- 10% from the observed values. For copper, magnesium, nitrites, nitrates, turbidity and zinc the estimates were fairly accurate, with percentage biases in the interval +/- 10% - 20%, whereas for detergents, led, and phosphates the percentage bias was higher than 20%. Overall, the results of the current study showed fairly good estimates between remote sensing based estimates and laboratory measured values for most water physico-chemical parameters. [ABSTRACT FROM AUTHOR]

Biological invasions can have major impacts on freshwater and marine ecosystems. Therefore, it is vital that non-indigenous species are accurately identified and reported when potential or confirmed invasions occur. The present study reports the first occurrence of Marenzelleria neglecta (Annelida, Spionidae) and the spread of Laonome xeprovala (Annelida, Sabellidae) in the Danube Delta–Black Sea ecosystem. Spionidae is one of the most diverse families of annelid worms and is a dominant group in terms of the number of species that have been introduced to non-native areas, while the members of Sabellidae are among the most visible polychaetes commonly found in fouling communities and are colonizing new geographic areas. Based on 20 samples collected in 2021, we provide an overview of the distribution of the investigated species and possible arrival pathways for Marenzelleria neglecta. Specimens were identified based on morphological descriptions. Both species have invasive behaviour, colonizing large areas in relatively short time periods and reaching relatively high densities (M. neglecta—1400 ind.m−2; L. xeprovala—40 ind.m−2). Due to their distribution and high abundances, the biology and ecology of these species in the Danube River–Danube Delta–Black Sea system need to be investigated further in order to assess their impact on ecosystem structure and functioning. [ABSTRACT FROM AUTHOR]

Hydrological and sedimentological data were collected on several cross-sections of both natural and artificial canals of three cutoff meanders (Mahmudia, Dunavăţul de Sus, and Dunavăţul de Jos meanders) of the Sfântu Gheorghe branch at the beginning of June 2017. The hydrological data shows a heterogeneous distribution of water discharges: on the meanders of Mahmudia and Dunavăţul de Jos, most of the liquid flow passes through artificial channels. In the case of the Dunavăţul de Sus meander, the cut meander is the main transport channel for the liquid flow. The statistical analysis of chemical data evidenced an excellent quality of the bottom sediments, with few parameters exceeding the limits (for Ni, Cu, and Cr). These results correlated with the hydrological measurements made on each investigated cross-section. [ABSTRACT FROM AUTHOR]

Plastics are widely used due to the variety of their structure and their chemical and physical properties. At the beginning of the twenty-first century, new environmental problems were discovered related to the accumulation of plastics in the environment. During long-term storage, plastics, which are resistant to aggressive environments, undergo degradation and turn into microparticles. These microplastics are found in the air, soil and sediments, fresh water, seas, oceans, plants, animals and even in the human body. The main problem is solid domestic waste disposal in cities and villages of the Ukrainian part of the Danube Delta since the waste is not either sorted or processed. It is simply buried at a certain depth instead. This method of disposal of municipal solid waste poses a significant threat to the groundwater since microplastic particles can accumulate in the ground composition. We have studied drinking water that was taken at a depth of 40 m from the surface of the earth. Water samples were taken at the enterprise with coconut and coal filters for additional purification of drinking water on an industrial scale. This water is purified in order to be sold to the population. We have examined the obtained samples under an optical microscope MICRO med XS-XXXX. The samples were examined under the magnifications of 400x and 900x. However, particles smaller than 100 μm were not detected. It can be assumed that there are no particles smaller than 100 μm either. However, this assumption has not been experimentally proven. It is necessary to study the distribution of plastic microparticles in the Ukrainian Danube Delta, including the groundwater of the region. The researchers should use the developed methods for the detection of microparticles and nanoparticles of plastic.

The present study aims to collect and analyse the data related to the water circulation system and the hydrological risk, for the channels in the Danube Delta, near the Letea and Caraorman units. The data collected supports the researches to understand the water circulation system in the context of an accelerated dynamics of the hydro-morphology of the Danube Delta complexes. Also, the context of climate change by modifying the rhythm of high water – low water cycle as well as by intensifying the extreme hydrological phenomena, imposes the population of the databases and the updating of the hydrological model to know and understand the current state of the deltaic ecosystem. For the data acquisition, there were 3 expeditions of field measurements to allow quantification of changes during a period (respectively low water period), to set up a data series. The channels where the hydrological data were collected during the three expeditions are Crișan - Caraorman, Eracle, Căzănele, Bogdaproste, Dovnica, Busurca, Cordon Litoral, Tataru, Cernovca, Sulimanca, Ceatal Izmail. Updating this information in the hydraulic modeling process is mandatory. The use of new techniques for collecting data on the water circulation system (discharge and water level) adds to the accuracy of the hydraulic model. If now the discharge calculation is done with the help of the rating curve, updating these data series in real-time at low, medium and high water, increases the accuracy of the results after running the model. Considering the high sedimentation rate, as well as the increase of investments for the unclogging works, in the context of the dynamics of the deltaic system, the updated hydraulic model of the Danube Delta is one of the key tools.

This paper aims to assess the level of perceptions of stakeholders on algal blooms in aquatic systems of Danube Delta in order to apprehend potential adaptation and mitigation strategies for the future, and to analyze for political targets and deficits. Hence, by means of questionnaires were engaged 24 stakeholders representing natural resource managers, local authorities, scientists, NGO’s. Even though the results indicated that not all stakeholders are aware with algal bloom terminology, stating a lack of institutional communication and availability of information to the public in the area, it was an overall consensus that the phenomenon represents more than a serious issue for deltaic aquatic ecosystems. The level to which national, regional and local resources can be focused on treating algal blooms issues depends in part of the strengths and interests in the area.

African Swine Fever is an infectious, viral, highly contagious disease that affected the population of Wild Boars in Danube Delta in 2018. Prior to this zoonotic outbreak, the population of Wild Boar in Danube Delta Biosphere Reserve was estimated to over 1,000 individuals. After the outbreak, in January and February 2019 we estimated a population of 60 - 300 individuals. The Wild Boar population in DDBR decreased by 75 – 95 %. In some areas the entire populations were depleted. Most affected areas were large stretches of reed bed and the coastal areas.

Abstract Background Culicoides biting midges are potential vectors of different pathogens. However, especially for eastern Europe, there is a lack of knowledge on the host-feeding patterns of this vector group. Therefore, this study aimed to identify Culicoides spp. and their vertebrate hosts collected in a wetland ecosystem. Methods Culicoides spp. were collected weekly from May to August 2017, using Biogents traps with UV light at four sites in the Danube Delta Biosphere Reserve, Romania. Vectors and hosts were identified with a DNA barcoding approach. The mitochondrial cytochrome c oxidase subunit 1 was used to identify Culicoides spp., while vertebrate hosts were determined targeting cytochrome b or 16S rRNA gene fragments. A maximum likelihood phylogenetic tree was constructed to verify the biting midge identity against other conspecific Palaearctic Culicoides species. A set of unfed midges was used for morphological confirmation of species identification using slide-mounted wings. Results Barcoding allowed the species identification and detection of corresponding hosts for 1040 (82.3%) of the 1264 analysed specimens. Eight Culicoides spp. were identified with Culicoides griseidorsum, Culicoides puncticollis and Culicoides submaritimus as new species records for Romania. For 39 specimens no similar sequences were found in GenBank. This group of unknown Culicoides showed a divergence of 15.6–16.3% from the closest identified species and clustered in a monophyletic clade, i.e. a novel species or a species without reference sequences in molecular libraries. For all Culicoides spp., nine mammalian and 24 avian species were detected as hosts. With the exception of C. riethi (n = 12), at least one avian host was detected for all Culicoides spp., but this host group only dominated for Culicoides kibunensis and the unknown Culicoides sp.. The most common host group were mammals (n = 993, 87.6% of all identified blood sources) dominated by cattle (n = 817, 70.6%). Conclusions Most Culicoides spp. showed a broad host-feeding pattern making them potential bridge vectors. At the same time, new records of biting midge species for Romania, as well as a potentially unknown Culicoides species, highlight the lack of knowledge regarding the biting midge species and their genetic diversity in eastern Europe.

The results of investigations on contents of several heavy metals in aquatic environments within the Danube Delta, Romania, are presented. The distribution of these heavy metals in the delta lakes was studied taking into consideration hydrochemical characteristics of the water catchment areas and the potential sources of contamination. The water sampling was done during several field campaigns in 2019, 2020 and 2021. A total of 143 water samples from 25 lakes, were collected for quantification of heavy metals content in water of studied lakes. The total concentration of technophile elements was determined using the ICP-EOS method. The results of analyses showed that the content of Cd, Co, Cr, Cu, Ni, Pb and Zn (μg/L) in the water samples were mainly within the acceptable limits set for Quality Class I (Very Good) and II (Good). Incidentally, the content of Cd (μg/L) reaches or exceeds the limit set for Quality Class III (moderate). In conclusion, the degree of heavy metal contamination in the investigated waters of the Danube Delta lakes is acceptably low and consequently presents a low environmental risk to aquatic life. In addition, the results obtained in three consecutive years showed that the environmental state of lakes is relatively stable. The results obtained concerning the heavy metals content in the water of Danube Delta inter-distributary depressions lakes represent a baseline data set that will be used for planning future delta water quality monitoring. [ABSTRACT FROM AUTHOR]

The topic was chosen out of a desire to explore the impressive biodiversity of the Danube Delta Biosphere Reserve. A considerable amount of time was allocated for the preparation of the paper, in order to try to produce a study that would contain as concrete and complex information as possible. To this end, three trips to the Danube Delta were made in previous years, and the research area was located in the south-east of the Danube Delta (Sfântu Gheorghe arm). The paper describes the physical-geographical framework of the area, presents informations on the history of research in the field of biodiversity of species and ecosystems in the research area, details the material and the working method, the results, the discussions and the conclusions of the study. [ABSTRACT FROM AUTHOR]