Bacterioplankton dynamics in the well system of water supply Vinogradi near the city of Osijek

Mikroorganizmi su dobri bioindikatori, s obzirom da su vrlo osjetljivi na promjene nastale u njihovoj životnoj sredini. Promjene u omjeru broja oligotrofnih (rastu u okolišu niske koncentracije organskih tvari) i eutrofnih bakterija (rastu u okolišu visoke koncentracije organskih tvari) ukazuju na stanje nekog vodenog ekosustava. Na osnovi bakterioloških analiza sanitarne kvalitete vode može se ocijeniti prikladnost vode za piće. Crpilište Vinogradi nalazi se zapadno od grada Osijeka i obuhvaća 18 bunara gdje se analiza kvalitete i zdravstvene ispravnosti vode kontinuirano provodi. Uzorkovanje je provedeno u proljeće 2013. i 2015. godine, te su rezultati uspoređeni s analizama uzetima u proljetnom razdoblju 1995. do 2010. godine, u petogodišnjim intervalima. Unutar bunarske vode ispitivanog vodocrpilišta, zabilježena je prisutnost većeg broja kolonija oligotrofnih bakterija (BKB-O), u odnosu na broj kolonija eutrofnih bakterija (BKB-E), što ukazuje na nisku koncentraciju organskih tvari u vodi. Tijekom godina se mijenjala dinamika razvoja kolonija oligotrofa i eutrofa, a 2000. godine u bunaru B-6 omjer BKB-O / BKB-E iznosio je samo 0,51. Nijednom nije utvrđeno da su CFU vrijednosti oligotrofa i eutrofa prelazile 100 CFU / ml, što ukazuje na zdravstvenu ispravnost vode. Zabilježene niske koncentracije kisika - ispod 1,5 mg/l su bile očekivane, s obzirom da se radi o podzemnim vodama. Nažalost, utvrđene su koncentracije željeza, mangana i amonijeva iona iznad maksimalno dopuštenih koncentracija (MKD) propisanih Pravilnikom o zdravstvenoj ispravnosti vode za piće, no to je najvjerojatnije posljedica podloge s koje se crpi voda. Voda koja se nalazi u vodoopskrbnoj mreži grada Osijeka je zdravstveno ispravna voda.Microorganisms are very sensitive to the changes in their environment, what makes them good bioindicators. Changes in the ratio of the number of oligotrophic (bacteria that grow in an environment with low concentration of organic matter) and eutrophic bacteria (found in water rich in organic matter) can indicate the status of an aquatic ecosystem. Based on the bacteriological analysis of sanitary water quality we can now evaluate hygienic suitability of drinking water. The pumping station Vinogradi is located west of the city of Osijek, it includes 18 wells and there is a continuous monitoring of the water quality and health safety. Samplings were conducted in the spring of 2013 and 2015 and the results were compared to the results of previous samplings, in five-year intervals, from the period 1995 to 2010. The higher number of colonies of oligotrophic bacteria than eutrophic bacteria indicates a low concentration of organic matter in the water. Differences of the colony development dynamics between research years were established, and during the year 2000, in the B-6 well, the oligotrophs/eutrophs ratio was only 0,51. Recorded CFU values were never higher than 100 CFU per 1 ml, what indicates good quality of the water. Low oxygen concentrations, below 1,5 mg/l, were expected since water sources are below ground. Unfortunately, recorded concentrations of iron, manganese and ammonium ion were higher than the maximum concentration allowed by the Ordinance on sanitary quality of drinking water, what could be a consequence of the soil type. The water in the water supply of the city of Osijek is sanitary correct and suitable for human consumption