All chemical and biological processes and living conditions for organisms in watercourses aresignificantly affected by oxygen conditions. The aim of this paper is to evaluate changes of theconcentrations of dissolved oxygen in water flow of Čaradice brook, which is located in the southwesternpart of the Slovak Republic, during the period 2005-2010. The watercourse springs in the mountains ofPohronský Inovec in the southern foot of Drienka hill and it is the right tributary of the Hron River.Samples of the water from watercourse were carried out on a regular basis, in the second decade of themonth. The places of taking samples were localized in a longitudinal profile of the watercourse to includeall sources causing the changes of dissolved oxygen concentration. Samples of water were collected fromsix sampling sites.Water samples were taken from the middle of the main stream. The results show thatthe average concentration of dissolved oxygen for the whole monitored period was 7.24mg.dm -3.Depending on the time of taking samples the highest average oxygen concentration was recorded inwinter and early spring time, with the highest values in the month of February. From March there was agradual decrease up to the minimum value in July. This decline was probably associated with anintensive degradation of organic substances by micro-organisms and also with higher water temperature.The sampling site had lower impact on the concentration of dissolved oxygen than the time of collectionof water. Its minimum average concentration was found in the south point of Kozárovce. This decrease isrelated to the oxygen consumption on biodegradation of organic pollutants which got to the water flowwith non-cleaned sewage effluent, as the village has not built a wastewater treatment plant. The highestconcentration was recorded under the eco-system of permanent grassland, in the north point of Čaradice.Calculated values of 10-th percentile of the dissolved oxygen in all sampling locations was lower, as isspecified in the requirements on the quality of the surface water in the Regulation of the Government ofthe Slovak Republic No. 269/2010 Coll. Based on the above mentioned it can be concluded that in thewater stream in terms of oxygen ratios are favorable conditions for the organisms that are lessdemanding on the dissolved oxygen.

watercourse, dissolved oxygen, Čaradice brook

Presentation: oral