The results of long-term groundwater monitoring in the Bileća reservoir adjacent (eastern Herzegovina, Bosnia and Herzegovina) indicate that there is a good hydraulic connection between the reservoir and the karst aquifer located in the right bank of the reservoir. In remote parts of the right-bank karst aquifer, due to complex lithostratigraphic characteristics and a tectonic structure, the influence of the reservoir is very variable and has been insufficiently studied up until now. This paper presents the analysis and synthesis of new, relevant hydrogeological data, as a basis for the creation of a 3D spatial model, i.e., the analysis of the karst system’s behaviour, both under regular and artificial hydrological conditions of surface reservoir construction and its continuous use (filling and emptying). The interactive connection of the model and complex surface and groundwater time series monitoring data of this system is presented through the analysis of its hydrodynamic characteristics, which completes the spatial model of the karst regime caused by low and high groundwater levels and low and high reservoir water levels. The integration of all the data into one model and further multiparametric analyses revealed the different types of hydrodynamic conditions prevailing in the karst aquifer with regard to the influence of the high or low waters of the reservoir.

Hydrogeological survey of wider Majdanpek mining area in the Carpathian mountain arch of eastern Serbia, including open mine pits, tailings sites, and major karstic springs and caves has been undertaken in order to estimate environmental conditions in groundwater body (GWB) ?Krs?sever?, groundwater quality, and to investigate causes of their earlier indicated poor chemical status. Bearing in mind that Majdanpek copper mine field is directly bordering the karst aquifer and delineated GWB ?Krs?sever?, the two karst springs namely Valja Fundata and Kaludjerica were in situmeasured and sampled in high and low-water periods (spring 2019, late autumn 2019 and spring 2020). Sampling and analysis of groundwater were carried out under the frame of project ?Operational Monitoring of Groundwater of the Republic of Serbia?, established by the Ministry of Environmental Protection of Serbia. The field measurements of unstable chemical components and physical properties as well as laboratory analyses confirmed very poor and even hazardous water quality of both surveyed springs Valja Fundata and Kaludjerica. Registered concentrations of some ions, such as Fe2+, Mn2+, Ca2+, SO4 2?are high above maximal permitted level for potable water in Serbia. High turbidity rate also confirms impact of colloidal suspensions from the tailing which is located in karstic blind valley. Leakage of mine water passes through joints, open cavities and even large cave system Valja Fundata. Results of undertaken survey confirm that low-water period results with worse water quality and much higher concentration of hazardous substances than that characterized high-water season when infiltrated rainy water and/or melted snow dilute tailing?s wastewater. Strict application of environmental protection measures and de - sign/construction of the smaller water treatment facility at both surveyed springs should possibly mitigate the impacts of mining activities to karst groundwater and dependant ecosystem.

The monitoring of karst spring release regimes is becoming more and more relevant due to the fact that karst waters are of exceptional quality and most often it is only necessary to chlorinate these waters in order to use them for water supply. In addition to monitoring the discharge regime, it is certainly necessary to establish monitoring of quality parameters that are generally observed sporadically (seasonally or monthly). An example of a well-designed monitoring of quantitative and qualitative parameters is Banja spring (western Serbia). The paper presents the analysis of time series pH values, electrical conductivity, turbidity, suspended sediment, total number of bacteria (TNB), discharge (D) and precipitation (P) using autocorrelation and cross-correlation analyses.

The present research moves the focus from merely describing epikarst flow to quantifying its natural filtration performance and contaminant retention mechanisms through integrating in situ tracer experiments with controlled laboratory modelling—an approach seldom applied in previous studies. Two field experiments at Peč Cave demonstrated that the epikarst exhibits rapid hydraulic connectivity—evidenced by fast tracer breakthrough with virtual flow speeds between 0.0041 and 0.006 m/s—yet simultaneously provides strong attenuation, as shown by the low tracer recovery and near-complete removal of microbial contaminants as well as nitrogen compounds through retention, degradation, and dilution under natural infiltration conditions, including rainfall and snowmelt. Complementary laboratory simulations further confirmed this duality, with nitrate concentrations reduced by 30–50%. Field data and lab results consistently indicated that the epikarst does not merely transmit water but actively adsorbs and transforms pollutants. Overall, the epikarst on Suva Planina functions as an effective natural filtration layer that substantially improves groundwater quality before it reaches major karst springs, acting as a protective yet vulnerable “skin” of the aquifer. These findings highlight the epikarst’s critical role in Suva planina Mt. karst aquifer protection and results support consideration of epikarst in groundwater management strategies, particularly in regions where springs are used for public water supply.

?Valjevo karst? is an area of about 780 km2 in a broader sense, while the uncovered karstified limestone makes about 330 km2. It is a part of the Inner Dinarides (Western Serbia). In the litho-stratigraphic view, the karstified limestones of Middle?Upper Triassic dominate, in which karst aquifers are formed. Analysis and systematization of the available data of hydrogeological and other relevant research is carried out. A branched network of groundwater traces between swallow holes and discharge points is presented as well as main features of sixteen karst springs (or scattered discharge zones) and nine (group of) wells, divided into five sectors. Average karst aquifer discharge of the whole area is calculated on 5.18 m3/s. Total minimum flow rate of the analysed karst springs and discharge zones is estimated at 1.2 m3/s, while the total flow rate of the analysed wells is estimated at about 0.3 m3/s, which makes about 1.5 m3/s of total (minimum) discharge. All analysed waters are low-mineralized (<1 g/l), while temperatures range from 9?35 ??. Use of the waters is multipurpose: municipal and local water supply, commercial bottling, recreational pools etc.