engleski

Impact of land use on groundwater quality in the Varaždin alluvial aquifer

The Varaždin aquifer is a vital source of water used by approximatelly 170, 000 inhabitants of the Varaždin County in NW Croatia for public supply, agriculture, and industrial purposes. Agriculture is dominant activity in this region, with 68% of total land use attributed to agricultural land. High nitrate concentrations in groundwater observed during the last decades raised public concern regarding groundwater quality. Within this work an interdisciplinary approach was used to investigate nitrate behavior in the critical zone, i.e. the upper layer of the Earth extending from vegetation to groundwater. Isotopic composition of groundwater (O-18 and H-2) revealed that the aquifer is recharged by surface waters and precipitation. A shift in the local meteoric water line indicates ongoing climate change during the last 10 years. A dual isotope approach in nitrate (O-18 and N-15) identified the main sources of nitrate in groundwater as: manure, wastewater, and soil organic nitrogen. The results of an isotope mixing model showed that manure is the dominant nitrate source in agricultural regions, wastewater in urban, and soil organic nitrogen in natural areas. Numerical groundwater flow and nitrate transport models confirmed that agriculture is the main controlling factor of nitrate contamination in the Varaždin aquifer. Our findings suggest that this region is particularly vulnerable to climate change. Longer droughts could further affect the groundwater quantity and reduce water reserves that are necessary for the local population. Conversly, intense precipitation events could facilitate nitrate leaching from the soil and unsaturated aquifer zone, further deteriorating groundwater quality regarding nitrate contamination.

land use ; water quality ; Varaždin alluvial aquifer

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