Gaussian simulation of nitrate concentration distribution in the Zagreb aquifer

Abstract

Nitrates present one of the most common groundwater contaminants in the world and one of the five major groups of contaminants in the study area. Gaussian simulation (GS) algorithm was used for determining the spatial distribution of average nitrate concentrations from 2010 to 2015 on 95 sampling points. Results indicate two main focus areas of nitrate contamination, located on the left and right bank of the Sava River. Those areas generally extend according to groundwater flow, while areas near Sava River have much smaller concentrations. GS showed that they can be useful for this kind of mapping because they favor abrupt changes in data values which are in this case a result of heterogeneous lithological composition of the aquifer. ARTICLE HISTORY

Estimation of Nitrate Trends in the Groundwater of the Zagreb Aquifer

“…The reason is seen in the appearance of statistically significant ascending trends in the area of well fields Petruševec, Sašnjak, and Žitnjak, all of which are located on the left bank of the Sava River. All results suggested that nitrate concentrations decrease over time in almost all areas, and this coincides with previous results [6,7]. In those areas where nitrate concentrations are increasing over time, concentrations are still much lower than 50 mg/L of NO 3 − , which is the maximum permissible concentration according to the Drinking Water Directive [41].…”

“…Nitrate concentrations are higher in the upper part of the unsaturated zone, while concentrations generally decrease with depth [33]. This is consistent with lower nitrate concentrations observed in the groundwater of Zagreb aquifer [6,7]. Shallower Holocene aquifer varies in thickness from five to 40 m, while deeper aquifer extends up to 60 m [34].…”

“…High nitrate concentrations have been observed in the groundwater of the Zagreb aquifer [5][6][7]. The Zagreb aquifer presents the only source of potable water for the citizens of the City of Zagreb and part of Zagreb County.…”

“…Previous research has shown that nitrates present one of the main groups of contaminants in the Zagreb aquifer [5]. Furthermore, two areas with elevated nitrate concentrations have been observed, while lower concentrations generally appear in the vicinity of the Sava River and in the eastern part of the aquifer [6,7].…”

“…With regard to natural conditions that prevail in the Zagreb aquifer, it can be assumed that nitrification presents a more important geochemical process than denitrification, especially in the alluvial part of the aquifer. Due to regional groundwater flow and major sources of nitrate contamination, it can be assumed that in the left bank of the Sava River, nitrate concentrations are generally associated with urban pollution sources (leaking from sewage system), while in the right bank, a combination of agricultural (application of fertilizer and manure) and urban inputs (leaking from the sewage system and septic tanks) is present [6,7]. right bank, a combination of agricultural (application of fertilizer and manure) and urban inputs (leaking from the sewage system and septic tanks) is present [6,7].…”