The Chilia branch is the north branch of the Danube River at the Romania-Ukraine border in the Danube Delta; it is a complex system with economic and ecological values. The surface water quality is a major concern and monitoring programs have been developed at the national and international level. The objective of this study was to evaluate the water quality of the Chilia branch in different sampling points from the mouth to the discharge in the Black Sea. The assessment of water quality was done at the individual level taking into account the nutrient concentrations and the standard limits for good ecological status and at integrative levels, using CCME WQI. The longitudinal distribution of Chilia branch water quality was done using GIS method. A total of 106 water samples were collected between 2013 and 2019 from five sampling points. At the individual level, the Chilia branch has a good ecological status except for its levels of total nitrogen, due to the organic nitrogen contribution in 2015. In 90% of nutrient concentrations, low values predominate and high values are considered extreme; only in 10% do high values predominate and low values are considered extreme concentrations. In equal percentages, 50% of the nutrient concentrations have a high degree of heterogeneity and the other 50% of concentration values are very close to the average values, with a high degree of homogeneity. CCME WQI method indicated that 39.93% of surface waters from the Chilia branch had an excellent quality, 45.45% a good quality, and only 14.62% a fair quality.

Addressing complex interactions within water, energy, and food (WEF) resources, innovative tools for in-depth analysis and decision-making are imperative. This study introduces chorematic focus maps (CFMs) as a groundbreaking method to visualize and tackle the WEF nexus’s complexities, focusing specifically on the Danube Delta Biosphere Reserve (DDBR). By merging geospatial analysis with on-site validation, this research reveals intricate interdependencies within the nexus and positions CFMs as an effective tool for stakeholders. This study adopts a methodological approach that focuses on identifying human activities and evaluating their impacts on the WEF nexus, with the goal of developing practical and grounded strategies for managing these essential resources. By testing this approach within the DDBR, the potential for wider application is demonstrated, offering a promising framework for addressing similar socio-environmental challenges across various regions. Future research directions include refining CFMs’ precision and practicality through extended fieldwork and stakeholder engagement, testing the framework’s adaptability across various locations and nexus dynamics. Additionally, incorporating cutting-edge technologies such as machine learning could provide deeper insights and reinforce CFMs’ role in decision support for the WEF nexus. Conclusively, this investigation into the WEF nexus through CFMs emphasizes the critical need for strategies that navigate the complexities of environmental management and resource optimization, marking CFMs as a significant tool for both decision-makers and researchers.

In this study, we report the findings regarding the toxicity of surface waters collected in March 2023 from five sampling stations in the Zaghen restoration area, located within the Danube Delta Biosphere Reserve, Romania. The assessment of acute toxicity was conducted using two microbiotests: the Thamnotoxkit F and the Daphtoxkit F^TM magna. Even if the acute toxicity effects are less than 50% and do not allow the calculation of a toxicity score for the water samples, the experiments show a different vulnerability of the two zooplanktonic species to the presence of heavy metals in the water with mortality being higher in Thamnocephalus platyurus (20%) than in Daphnia magna (15%).

Managing Water, Energy, and Food (WEF) resources within socio-environmental systems demands innovative strategies that provide decision-makers with actionable insights. This article explores the challenges and potential solutions of employing Focus Maps and choremes as a novel approach for assessing anthropogenic impacts and enhancing the visualization of the WEF Nexus in specific geographic areas. By integrating geospatial data, multi-criteria analysis, and involving stakeholders, our research aims to develop Choreomatic Focus Maps (CFMs) that offer a comprehensive spatial representation of the WEF Nexus, facilitating better-informed decision-making at the community level. Our current work outlines visualization of WEF Nexus, as an initial stages of creating CFMs through a detailed step-by-step process. This includes identifying the main drivers for WEF nexus, such as anthropogenic activities and their distribution, evaluating environmental factors, linking anthropogenic impact with environmental indicators over time, and conducting on-site validation. Our focus is on advancing through these crucial steps, particularly emphasizing field validation within the Local Decision-Makers Tools, visualized here by using Focus Maps. This phase is vital for ensuring our approach is grounded in reality and meets the needs of the communities within the Danube Delta region. By doing so, we aim to provide a visual summary of the WEF Nexus that not only captures the complexity of this fragile ecosystem but also incorporates local insights and priorities, identifying key areas where human activities have significant impacts.

Wetland vegetation dynamics, at reedbed margins, provide sensitive indicators of hydrological alteration, salinisation, nutrient loading and land-use change. Reedbeds also provide important ecosystem services, including habitat provision, shoreline stabilisation, nutrient retention and biomass resources. We resurveyed 33 permanent sampling points in reedbed-margin habitats of the Danube Delta, originally sampled in 2002 and revisited in 2024, to assess vegetation change over 22 years in communities dominated by common reed (Phragmites australis) and narrowleaf cattail (Typha angustifolia). Due to some points containing more than one plant community, the original 43 relevés (2002) and 44 relevés (2024) were aggregated into a single paired community vector per point-year for analyses, while individual relevés were syntaxonomically analysed. Relevés were recorded using the Braun–Blanquet approach and classified into syntaxa of Phragmito-Magnocaricetea, Salicetea purpureae, Franguletea and Thero-Salicornietea. Community composition changed significantly between years; the 2024 vegetation differed significantly among the five transition pathways since 2002. Temporal change was driven mainly by species replacement rather than nestedness. Of the 33 sampling points, 7 (21.2%) retained reed-dominated structure, 14 (42.4%) shifted toward reed– Salix sp. mosaics, 9 (27.3%) toward shrub-dominated communities, and 3 (9.1%) toward sedge or halophytic communities. Species richness increased overall from 24.9 ± 7.5 species in 2002 to 32.3 ± 6.9 in 2024, but richness peaked in transitional reed– Salix sp. mosaics rather than increasing monotonically through shrub establishment. More permanently flooded reedbeds remained comparatively stable, whereas marginal stands showed divergent transitions toward Calamagrostio-Salicetum cinereae, Salicetum triandrae subass. amorphosum fruticosae, Salicetum albae, Caricetum ripariae, and locally Salicornietum prostratae. Invasion by Amorpha fruticosa, Acer negundo and Morus alba further altered the typical species composition. The results indicate that Danube Delta reedbed margins function as long-term ecotonal transition zones, where shifts in community composition are expressed as changes in syntaxonomic affiliation and structural complexity.

The Danube Delta, a dynamic alluvial plain, serves as a substantial carbon sink due to its extensive stands of reeds, specifically Phragmites australis. This study quantifies carbon storage across five distinct reedbed types based on substrate characteristics, using biomass assessment, soil carbon analysis, and GIS-based spatial mapping. Results show that reeds on salinized organic soils (S-Pa) have the highest carbon storage capacity (8.595 t/ha C), while those on gleyic soils (S-F) have the lowest storage levels (0.463 t/ha C). Furthermore, an analysis of heavy metal contamination (Cr, Ni, Pb, Zn) over 5 years revealed concentrations below regulatory thresholds, with a declining trend. The analysis indicates that reeds have notable potential for pollutant sequestration, particularly in aquatic vegetation and soil. These findings highlight the crucial role of deltaic wetland ecosystems in carbon sequestration and contaminant retention, underscoring the need for sustainable management strategies.