This work analyses changes in the content of nutrient components and trace metals and metalloids at three tributaries of the Maritsa River flowing in Southern Bulgaria with catchments affected by mining and agricultural activities. Input data includes information about 14 chemical water quality parameters (N-NH 4 , N-NO 3 , N-NO 2 , N-tot, P-tot, P-PO 4 , Al, As, Fe, Cu, Mn, Ni, Pb, and Zn) obtained from the Executive Environment Agency for the period 2015-2018. Two documented methods were used in this work to determine the pollution status of river waters-Heavy metal pollution index (HPI) and CCME Water Quality Index. The results based on the CCME WQI ranked water quality as "Poor" (WQI values range from 31.2 to 39.9). The HPI ratings achieve scores exceeding the critical pollution value of 100 for some of the metals (Al, Cu, Mn, and Zn), which indicates that water is seriously polluted concerning those variables. Therefore, it can be summarized that the river waters are not appropriate for safe drinking , agriculture, and household use because of significant nutrient and metalloids and trace metalscon-tamination.

Anthropogenic activities deteriorate the quality of water resources, which reduces their socio-economic suitability, endangers public health, and affects aquatic life. This work presents the results of physicochemical monitoring of the Provadiyska River (Northeastern Bulgaria) and aims to assess water quality status according to the guidelines pointed out in the National regulatory standard - Regulation H-4/2012 for characterization of the surface waters. The selected river has become one of the most seriously polluted streams in the territory of the country due to the effect of various human practices occurring in the drainage basin, such as agriculture, industry, and urban development. Data about the values of ten physicochemical variables (pH, EC, DO2, N-NH4, N-NO3, N-NO2, N-tot, P-PO4, P-tot, and BOD5), recorded at four measuring points during the period 2015-2020 have been used. Results obtained indicate that almost all of the parameters considered do not meet the reference norm for "Good status", thus water quality could be assessed as "Moderate". Failed variables appear to be EC, N-NH4, N-NO3, N-NO2, N-tot, P-PO4, P-tot, and BOD5 whose highest observed content remains from two up to nine times above the maximum permissible limits of Regulation H-4/2012. Water contamination arises from different sources and activities, including the excessive fertilization of croplands, the unregulated release of animal manure from livestock farms, the uncontrolled discharge of municipal and industrial effluents into the river, etc. The expansion of sewerage systems in the settlements, the construction of wastewater treatment facilities, as well as the adoption of codes for best farming practices are among the most important actions that should be taken to reduce the deleterious effects of various anthropogenic activities on water quality.

The present article seeks to estimate water pollution with nitrogen and phosphorus and to analyse the territorial specifics in the content of those physicochemical variables along the length of a river. As a case area, the watercourse of the Osam River (Northern Bulgaria) is selected. Data concern the values of the following parameters: ammonium nitrogen (N-NH₄), nitrate nitrogen (N-NO₃), nitrite nitrogen (N-NO₂), total nitrogen (N-tot), orthophosphates (P-PO₄), and total phosphorus (P-tot), collected at four sampling points during the period 2015–2020. The assessment is based on the guidelines of Regulation 4/2012 for characterization of the surface waters. The spatial changes in the content of the examined variables are related to land use and for this purpose a map of CORINE Land Cover (2018) is prepared. The resulting information reveals that parameters with the most frequent excesses over the reference norm include N-NO₃, N-tot, P-PO₄, and P-tot, whose highest observed concentrations remain up to four times above the permissible limits for ”Good status” recommended in Regulation 4/2012. However, the reported values appear to be lower than those established for previous periods, which shows a positive tendency in water quality. There are also spatial features as moving from upstream to downstream – the upper part is contaminated with P-PO₄ and P-tot due to the release of raw municipal and industrial effluents, while the lower section is loaded with N-NO₃ and N-tot as a result of the excessive fertilization of arable lands. This work enriches past studies with new data for a recent period.

High flow events are the main prerequisites for floods with negative social and environmental consequences. Their study under uncertain and changing climate gives informative knowledge for further management decisions. This paper seeks to analyze the spatio-temporal parameters of high flow periods within the Danube drainage basin in Bulgaria. Three characteristics of the hazard phenomena: time of occurring, frequency and duration are investigated. The analysis is based on daily discharge data collected from 20 gauging stations for the period 2000–2005. The surplus water quantities are identified by the Threshold level method using fixed values – Q25 and Q5, derived from the flow duration curve. Results show a concentration of the high flow periods during the spring hydrological season, with an average duration up to six weeks. The calculations establish positive correlations between the duration of high flow, the altitude of catchments, and the density of drainage network. The resulting information can serve as a support for the development of preliminary flood risk assessments in the Danube River Basin.

The study of high flow characteristics within the Alpine catchments represents one of the most challenging tasks for the modern hydrological science, because of high vulnerability response of these areas to the global and regional climate changes, including to the proven positive air temperature trends. The current picture of the hydro-climatic processes in the Rila Mountain – the highest mount within the Balkan Peninsula, is not exception. Study area covers eight Alpine catchment areas, located above 1600 m sea level in the Rila Mountain. The aim of this research is to perform a spatio-temporal analysis of the extremely high streamflow characteristics within the researched drainage basins. Study period includes six years in the beginning of the XXІ century: there are very dry (2001), very wet (2005) and four normal water years. The analysis is based of Threshold level method (TLM) with fixed constant threshold value: 5th percentile of all discharge daily data for the given term. Results obtained show the number of extremely high streamflow events ranges from 6 to 26 – for the catchments of the Stara River at Kostenets and the Blagoevgradska Bistritsa River at Bistritsa, respectively. The maximal duration of these events varies from 15 (for the Mesta River at Yakoruda) do 39 days (the Stara River at Kostenets), but the oneweek extremely high flow periods are most typical here (a frecquency to 88% of all cases). The temporal analysis shows a concentration of studied hydrological events during the spring season (in the months of April, May and June), when occurs also a high streamflow phase, due to the snow melting and rainfalls. An exception of this statement is the wettest year in Bulgaria from the beginning of this century – 2005. Then because of heavy prolonged rainfalls during the months of July, August and September, were detected sharp peaks of the hydrographs. Present work establishes some spatial differences of extremely high flow characteristics (time of occurring, duration, frequency) in study area due to the slopes exposition peculiarities. Results obtained supplement previous scientific works and give new information about the risk hydrological processes within the mountainous catchment areas in Bulgaria.