Nitrate Origin in the Zagreb Aquifer System

Abstract

Nitrates are among the most common groundwater contaminants worldwide, and the same situation is present within the Zagreb aquifer. The Zagreb aquifer presents the only source of potable water for inhabitants of the City of Zagreb and part of Zagreb County. Isotopic composition of water (δ2H and δ18O) and nitrates (δ15N and δ18O), groundwater chemistry, and molar ratios, in combination with correlation and multivariate statistical methods, have been used for the estimation of nitrate origin. Nitrate stable isotopes excluded synthetic fertilizer as the main source of nitrate contamination. They showed insignificant influence of denitrification on nitrate concentrations but could not define the main source of nitrate contamination. The usage of molar ratios, especially NO3−/K+, helped to clarify this issue. Waste water has been defined as the main source of nitrate contamination. All results indicate that nitrogen in a large extent enters the aquifer in the form of ammonium ion, which is transformed to nitrates by the process of nitrification.

Tracing the Origin of Groundwater Nitrate in an Area Affected by Acid Rain Using Dual Isotopic Composition of Nitrate

“…For example, the ranges of isotopic compositions of nitrate suggested that the major sources of nitrate in the large Changjiang (Yangtze) River come from modified fertilizer and urban sewage effluent [21]. Wastewater was found to be the main source of nitrate contamination in urban areas [22]. The nitrate input from rainfall to groundwater is often neglected, but nitrification is generally regarded as a prerequisite for nitrate leaching [23].…”

Nitrate contamination risk of the Zagreb aquifer

“…The existence of elevated nitrate concentrations in the Zagreb aquifer have been confirmed through recent research (Kovač, Cvetković, & Parlov, 2017;Kovač, Nakić, & Pavlić, 2017). It has been shown that nitrate trends are declining in most parts of the Zagreb aquifer (Kovač, Nakić, Špoljarić, Stanek, & Bačani, 2018), and that nitrate origin is mostly organic, generally associated with wastewater leaching from permeable sewage and septic tanks (Kovač, Nakić, Barešić, & Parlov, 2018). Furthermore, nitrate stable isotopes composition has shown that the denitrification process is negligible in most parts of the Zagreb aquifer.…”

“…Data used to create the risk of nitrate contamination map in the area of the Zagreb aquifer were adjusted to the area of approximately 300 km 2 . Data were collected from previous research (Kovač, 2017;Kovač, Nakić, Barešić, et al, 2018;Ružičić, 2013), official documents of the Republic of Croatia and various registers of the Republic of Croatia: Hydrogeological map of the Republic of Croatia M 1:300,000 (Biondić, Brkić, Biondić, & Singer, 1996), Outlines of Water Management of the Republic of Croatiasection Groundwater (Biondić & Brkić, 2001), CORINE Land Cover 2012 (Croatian Environmental and Nature Agency, 2018a), WFS layer of The Register of industrial plants in which the presence of dangerous substances was established (Croatian Environmental and Nature Agency, 2018b) and Farm register used in Kovač (2017). Higher concentrations of nitrates in groundwater are thought to be a consequence of multiple different sources, as well as the aquifer properties.…”

“…The agricultural activity follows sewage systems and septic tanks with the amount of nitrogen compounds produced (Balderacchi et al, 2012). Some authors consider septic tanks to be the main source of nitrates and nitrates contamination, others find problems in both sewage systems and septic tanks of the big cities, which is also the case with the Zagreb aquifer (Kovač, Nakić, Barešić, et al, 2018). Sewage systems and septic tanks tend to be overloaded with high amounts of wastewater, which leads to leaking through the systems and infiltration in groundwater systems (Almasri, 2007;Delleur, 2007).…”

“…Sewage systems and septic tanks tend to be overloaded with high amounts of wastewater, which leads to leaking through the systems and infiltration in groundwater systems (Almasri, 2007;Delleur, 2007). Many research has shown that sewage systems and septic tanks are the main sources of nitrogen compounds in groundwater systems (Gutiérrez, Biagioni, Alarcón-Herrera, & Rivas-Lucero, 2018;Kovač, Nakić, Barešić, et al, 2018;Lee et al, 2006). The polygon that shows the area at the Zagreb aquifer system where the sewage system was built, was used in previous research (Kovač, 2017;Kovač, Nakić, Barešić, et al, 2018).…”