Statistical Indicators of Groundwater Geochemical Characteristics in a Quaternary Aquifer from the Mala Mlaka Well Field Catchment Area (Zagreb, Croatia)

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.