Abstract
High concentrations of sodium, potassium, nitrates and sulphates inthe groundwater in the Mala Mlaka well field catchment area confirmthe impact of agricultural activities on water chemistry. Analysisof time trends has shown that a decrease in inorganic components(nitrates and sulphates), which are sensitive to changes in oxidation/reduction conditions in an aquifer, are caused by infiltration of oxygen-rich water rich in organic matter into the aquifers. Oxygen contentreduction due to oxidation of the organic matter causes oxygendeprivation in the groundwater and consequently a reduction in nitrateand sulphate levels. An increase in chloride levels in the groundwaterduring 1994–2000 is a consequence of human activities in the catchmentarea. Multivariate statistical analyses, i.e. factor analysis, clusteranalysis and multidimensional scaling (MDS) analysis have shownthat the registered pollution sources in the catchment area, particularlyillegal dump sites, cause degradation of the groundwater quality insome sites. This impact is detected over a distance of several hundredmetres downstream from the registered pollution sources.
Highlights
The Mala Mlaka well field is the largest near Zagreb and is very important for the city’s water supply
The hydrogeochemical facies analysis has shown that the groundwater in the Mala Mlaka well field catchment area mostly belongs to a Ca–Mg–HCO3 type of water (Fig. 4)
Inorganic quality indicators were used in analysis of the time series of the groundwater quality data for the Mala Mlaka well field catchment area
Summary
The Mala Mlaka well field is the largest near Zagreb and is very important for the city’s water supply. The article uses results of numerical simulation of the groundwater flow in the Zagreb aquifer system that were employed in determination of the Mala Mlaka well field catchment area under different hydrological conditions. – the observation well sites sampled for chemical and bacteriological analyses are mostly located within the borders of the Mala Mlaka well field protection zones;. This article reports on basic hydrogeochemical processes evolving in a shallow water-bearing layer in the Mala Mlaka well field catchment area. The groundwater quality time series were analysed to confirm significant hydrogeochemical processes in the catchment area. The analysis was used to determine the time series for significant chemical elements and compounds from the groundwater quality data for the period 1994–2000. Statistica for Windows 5.1 software package (STATSOFT, 1995) was used for statistical analyses
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