Uticaj cirkulacije podzemnih voda u karstu na pojavu bakteriološkog zagađenja / Microbiological pollution as the function of karst groundwater circulation

Karstic groundwater, because of its unique hydrological characteristics, is extremely sensitive to contamination with pathogens. In this paper results of contamination of karst aquifers are presented, especially from bacteria of faecal origin that usually cause of failure of non-tapped and tapped karst groundwater before any water treatment. The question and explanation is in which level the occurrence of bacterium in karst water can affect water supply and water abstraction, predominantly in the water intake object, and later, along the water distribution system. Continuous monitoring of faecal bacteria and other bacterial "contamination", as well as physical and chemical parameters, allowed a better understanding of the processes governing the transport of pathogens in karst groundwater and possible microbial contamination of drinking water from karst springs. On the other hand, it is also important how the type of underground karst water circulation can affect the transport of microbial contamination. Bacterial contamination changes are shown through the analysing of Kavak and Krupac springs case study (tapped for water supply of Pirot) the karst spring system with two types of discharge, deep siphonal and gravity, or sub-gravity type of circulation. The proper monitoring of these karst springs is shown through the analysis of a sufficient number of bacteriological analysis and its correlation to physical and chemical characteristics in seasonal intervals, gives us an insight into the functioning of karst aquifer and a level of autopurification properties. The Kavak spring is deep siphonal circulation spring and the presence of coliform bacteria of faecal origin was not observed in it, which justifies the fact that ground water circulation through the long system of cracks and channels, in anaerobic conditions, do not present environment suitable for reproduction of microorganisms. Unlike the Kavak spring, the Krupac spring is typical gravitational spring, with clear seasonal changes of bacterial pollution, observed in the form of total coliform bacteria and coliform bacteria of faecal origin, that usually occurs in period of low water discharge (summer and winter), which is associated to intensive land use during previous seasons in terms of agriculture and grazing. Key