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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. [ABSTRACT FROM AUTHOR]

The microbiological contamination of the water with faecal bacteria resulting from anthropogenic activity is an important issue for population health and the assessment of the presence of pathogenic bacteria in the water is a major concern for the protection of humans and animals. Coliform bacteria are indicators for the assessment of faecal pollution and a potential presence of pathogens, which is caused mainly by untreated wastewater. In this paper, a comparative study was carried out in 32 sampling sites of MONITOX network in two periods, June 2019 and June-July 2020, before and after COVID-19 pandemic lockdown, regarding the rate of the water microbiological contamination in Lower Danube (Calarasi/Silistra-Galati-Tulcea sectors, Danube Delta and the Black Sea coast, from the SE part of Romania, by counting of the bacteria indicators of the organic pollution (heterotrophic bacteria and total coliforms). The results demonstrate a decrease of microbiological contamination of surface water in 2020 during the COVID-19 lockdown in all the samples collected from the Black Sea coast, Danube branches, Danube-Black Sea confluence, and Danube river downwards the town of Galati. [ABSTRACT FROM AUTHOR]

The assessment of sediments quality from the Romanian part of MONITOX Network was performed using both single indices - Single Ecological Risk Index (ErMe), Contamination Factor (CF Me), Enrichment Factor (EF Me), Geoaccumulation Index (Igeo Me) - and integrated indices - Ecological Risk Index (RI), Global Pollution Index (PLI), Nemerow Pollution Index (PI N), Degree of Contamination (mCd), Probability of Toxicity (MERMQ), Contamination Security Index (CSI) - considering the heavy metals concentrations. The sediments were collected in 2019 and 2020 from 32 sampling points in the system of Danube river - Danube Delta - Black Sea, as follows: Lower Danube RO-BG (1), Lower Danube RO (10), Lower Prut RO-MD border (2), Danube Delta RO-UA border (7), Danube Delta -RO (2), Black-Sea area-RO (10). The selected heavy metals investigated in this work by the ICP-MS technique are: Cd, Cr, Cu, Pb, Zn, Mn. For the evaluation of defined indices, the standard quality levels and background concentrations corresponding to the selected heavy metals were used. At the individual and integrated levels, it was observed an annual decreasing trend. The sediments from the Black Sea area are much less contaminated with heavy metals than those from the Lower Danube (Romania), attributed to the historical pollution resulting from anthropogenic activities. CSI - an index that includes the biological effects - shows values indicating that in 2019 and 2020 the sediments were unpolluted with heavy metals; however, the CSI value for both years (0.402 for 2019 and 0.398 for 2020) is very close to 0.5, the limit which separates the two quality classes/risk levels for heavy metals in sediments - uncontaminated and very low contaminated. [ABSTRACT FROM AUTHOR]

The main propose of this study was to assess the levels of some toxic substances in expressing the pollution degree of the aquatic ecosystems. A ten-yearinvestigation of 4heavy metals(such as As, Pb, Ni, Cr) in surface water and sediments samples from a representative aquatic complex in the Danube Delta Biosphere Reserve (Matita-Merhei) was accomplished. The results (expressed in μg heavy metal/L for water samples and mg heavy metal/kg dry sediment samples) were annual mean concentrations (2006-2015) of heavy metals and were assessed according tothe European Water Framework Directive 2000/60/CE. The research conducted over the past decade has shown that the accumulation of the heavy metals in the Danube Delta Biosphere Reserve is, generally, determined by natural factors (natural frame, climate, drainage system), but also by the varied activities occurred in the border area. The analysis of the obtained results revealed that the quality standard was exceeded in the case of bottom sediment samples for Pb, Ni and Cr, with a general ascending trend as follows: As