engleski

Determination of Groundwater Quality Status in the Drava Basin

The study area, the Drava basin, is situated in the southern edge of Pannonian basin. The characteristic of the Drava basin is great thickness of Quaternary sediments, within is accumulated substantial quantity of groundwater. The aquifer thickness increases towards the east. In the western parts, gravel with various shares of sand dominates in the lithological composition of the aquifer (BABIĆ et. al., 1978 ; URUMOVIĆ et. al., 1990 ; LARVA, 2008). In the central area, there is lateral and vertical alternation of gravel and sand, while in the eastern parts the aquifer is mostly composed of sand particles (MILETIĆ, 1969 ; MILETIĆ et. al. 1973). The covering aquitard is mostly composed of silt and clay. Its thickness is often less than 1 m in the western part and sporadically there is no covering aquitard at all (URUMOVIĆ et. al., 1990 ; MARKOVIĆ, 2007 ; LARVA, 2008). In the eastern direction, its thickness gradually increases attaining sporadically more than 30 m (MILETIĆ et. al., 1973). The chemical composition of groundwater is influenced by geological and hydrogeological conditions of aquifer. In the western and central parts of Drava basin groundwater belongs to Ca-HCO3 and CaMg-HCO3 hydrochemical facies as a consequence of dominant dissolving of carbonate minerals. On the other hand, in the eastern parts the groundwater belongs to CaMg-HCO3, MgCa-HCO3, CaMgNa-HCO3 and NaCa-HCO3 hydrochemical facies. In the western parts (surroundings of towns of Varaždin and Čakovec) the nitrate concentrations in the upper aquifer exceed MPC value of 50 mg/l, while the mean value is 75 mg/l. Moreover, the analysis of nitrate concentrations time series points to positive trend, i.e. to nitrate concentration increase. At the same time the nitrate concentrations in the lower aquifer are far below MPC value and the mean value amounts 19.8 mg/l. High nitrate concentrations in the upper aquifer are the consequence of the application of fertilizers and manure in agricultural production (MARKOVIĆ, 2007). Occasionally, high concentrations of ammonia, orthophosphates and nitrites have also been noticed in the upper aquifer. High concentrations of nitrates have also been noticed in the shallow aquifer of the central parts of the Drava basin, while, going further to the east, substantial decrease of nitrate concentrations is quite obvious. The decrease of nitrate concentrations in the eastern parts of study area is followed by high concentrations of Fe, Mn, As, Zn, Pb, NH4+ in particular aquifer horizons. Its origin is natural and is not induced by anthropogenic activity. The concentrations of sulphates and chlorides are below MPC values at the entire study area. Generally it can be stated that increased concentrations of Fe, Mn, As, Zn, Pb i NH4+ do not show any trend because their presence in groundwater reflects the natural condition of aquifers.

groundwater; quality; heavy metals; nitrates

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