Title Podrijetlo nitrata u podzemnoj vodi zagrebačkoga aluvijalnoga vodonosnika : doktorski rad Title (english) Nitrate origin in groundwater of the Zagreb alluvial aquifer : doctoral thesis Author Zoran Kovač Mentor Zoran Nakić (mentor)Mentor Jadranka Barešić (mentor)Committee member Jelena Parlov (predsjednik povjerenstva)Committee member Zoran Nakić (član povjerenstva)Committee member Jadranka Barešić (član povjerenstva)Committee member Andrea Bačani (član povjerenstva)Committee member Drago Špoljarić (član povjerenstva)Granter University of Zagreb Defense date and country 2017-10-04, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 55 - Geology. Meteorology. Hydrology Abstract Nitrati predstavljaju jedno od glavnih onečišćivala podzemne vode u svijetu. U podzemnoj vodi zagrebačkoga vodonosnika okarakterizirani su kao jedna od pet glavnih grupa onečišćivala. Smanjenje koncentracije određenog onečišćivala najviše ovisi o definiranju njegovog podrijetla. Za potrebe određivanja podrijetla nitrata i povezanih geokemijskih procesa u podzemnoj vodi zagrebačkoga vodonosnika korištene su razne geokemijske i statističke metode. U okviru geokemijskih metoda određeni su stabilni izotopi kisika i vodika iz vode, te dušika i kisika iz nitrata. Također, napravljena je analiza molarnih omjera nitrata s kloridima, natrijem i kalijem. U okviru statističkih metoda korištene su korelacijske i multivarijatne statističke analize. Većina analiza napravljena je na dostupnim povijesnim kemijskim analizama podzemne vode, te na podacima izmjerenima u podzemnoj vodi i rijeci Savi uzorkovanoj za potrebe ovog rada. Stabilni izotopi vode pokazali su kako je podzemna voda izotopno najsličnija rijeci Savi i oborini iz Ljubljane. Interpretacijom rezultata stabilnih izotopa kisika i dušika iz nitrata utvrđeno je kako je podrijetlo nitrata za vrijeme uzorkovanja podzemne vode bilo organsko. Kao glavni izvori onečišćenja izdvojeni su otpadne vode i organsko gnojivo. Također, rezultati upućuju na to da denitrifikacija predstavlja zanemariv proces koji se odvijao u podzemnoj vodi zagrebačkoga aluvijalnog vodonosnika za vrijeme uzorkovanja. Korelacijske analize pokazale su kako kloridi i natrij predstavljaju vrlo bitne parametre u proučavanju podrijetla nitrata. Korištenje multivarijatnih statističkih analiza omogućilo je izdvajanje parametara koje su mogu koristiti kao pokazatelji antropogenog utjecaja. Također, korištenjem klaster analize određeni su piezometri na kojima glavni izvor onečišćenja predstavljaju otpadne vode, odnosno organsko gnojivo. Pritom se proučavanje molarnih omjera, prvenstveno nitrata i kalija, pokazalo kao ključno. Utvrđeno je kako se stabilni izotopi dušika i kisika iz nitrata, u kombinaciji s analizom molarnih omjera, mogu vrlo učinkovito koristiti u procjeni podrijetla nitrata na području zagrebačkoga vodonosnika. Osim toga, korelacijske i multivarijatne statističke analize pokazale su kako stabilnost i transformacija nitrata na promatranom području ovisi o koncentracijama otopljenoga kisika. Također, rezultati upućuju na to da se dušik u podzemnu vodu zagrebačkoga vodonosnika u velikim količinama unosi u obliku amonij iona nakon čega se nitrifikacijom pretvara u nitrate, što se slaže i sa izračunatim vrijednostima intervala karakterističnog za nitrifikaciju dušikovih spojeva. Trendovi su izračunati pomoću linearne regresije na četiri razine zajedno s njihovim intervalima pouzdanosti i predviđanja. Analiza
trendova nitrata utvrdila je postojanje statistički značajnih silaznih trendova koncentracija nitrata, osim u priljevnom području crpilišta Petruševec te Sašnjak i Žitnjak, na kojima su utvrđeni statistički značajni, uzlazni trendovi.
Abstract (english) Nitrates present one of the major groundwater contaminants in the world. In the groundwater of Zagreb aquifer they are characterized as one of the five main groups of contaminants. The most important thing associated with decrease of contaminant concentration is the definition of its origin. Various geochemical and statistical methods have been used for the determination of nitrates origin and related geochemical processes in the Zagreb aquifer. Within geochemical methods, water stable isotopes and nitrate stable isotopes were calculated on sampled river and groundwater. Sava River and groundwater was sampled in the period from November 2015 to October 2016. Sampling was preliminarily performed on 56 observation wells, after which 30 observation wells were selected for monitoring of nitrate stable isotopes in time. Molar ratios of nitrate and chlorides, nitrate and sodium, and nitrate and potassium were calculated for both historical groundwater chemical analysis and for chemical analysis conducted on sampled river and groundwater. Correlation and multivariate statistical analysis have been used within statistical methods. All of the statistical analysis were done on historical groundwater quality data as well as on data measured on sampled river and groundwater. Historical data analysis of nitrate concentrations showed that there are two main areas of Zagreb aquifer where elevated nitrate concentrations have been identified. One area is located on the left bank of the Sava River, in the dominantly urban area, while other is located on the right bank, in the dominantly rural area, where agricultural activity is also present. Water stable isotopes showed that groundwater is isotopically most similar to Sava River and precipitation from Ljubljana, and least to the precipitation that falls in the area of Zagreb aquifer. Interpretation of nitrates stable isotopes showed that nitrate origin within the sampling period was organic. Wastewater and manure have been recognized as main sources of nitrate contamination. Comparison of δ15N-NO3- with nitrate concentrations, as well the values of calculated enrichment factors, suggest that denitrification is a negligible process that takes place in alluvial part of Zagreb aquifer. Results also suggest that nitrogen in Zagreb aquifer is in large extent introduced in the form of ammonium ions, after which is transformed to nitrates by nitrification. This assumption is supported by the calculated interval of δ18O-NO3- characteristic for nitrification of organic nitrogen compounds. Correlation analysis showed that chloride and sodium concentrations present very important parameters in study of nitrate origin. Factor and cluster analysis conducted on chemical analysis data showed that chlorides, sulphates, sodium and potassium present variables that can be used as main indicators of anthropogenic influence on groundwater
quality in the Zagreb aquifer. The use of cluster analysis allowed the definition of observation wells where nitrates concentrations were mostly related to wastewater or manure. Four clusters of observation wells were defined based on nitrate, chlorides, sulphates, sodium and potassium concentrations, values of stable nitrate isotopes and molar ratios of nitrates to all other used ions. For observation wells in three clusters wastewater was defined as main source of contamination. In that sense the study of the molar ratios, especially nitrate and potassium, was found to be crucial. Groundwater from observation wells were manure was identified as main source of contamination had the highest molar ratios and lowest δ15N-NO3- values. It has been concluded that investigation of molar ratios, in combination with nitrate stable isotopes, can be very effectively used in estimation of nitrate origin in groundwater of Zagreb aquifer. In addition, correlation and multivariate statistical analysis have shown that nitrates present parameter whose stability and transformation in the groundwater of Zagreb aquifer is basically dependent on the dissolved oxygen concentrations. The nitrate trend analysis established the existence of statistically significant decreasing trends of nitrate concentrations, except in Petruševec and Sašnjak and Žitnjak well field influence area. It has been shown that evaluation of nitrate trends in different levels, in combination with confidence and prediction intervals, can provide more realistic insight in areas where nitrates contamination occurs. Also, it has been concluded that linear regression presents appropriate method for estimation of nitrate trends.
Keywords
podrijetlo nitrata
zagrebački vodonosnik
stabilni izotopi vode i nitrata
molarni omjeri
korelacijska analiza
multivarijatne statističke analize
linearna regresija
trendovi nitrata
Keywords (english)
nitrate origin
Zagreb aquifer
water and nitrate stable isotopes
molar ratios
correlation analysis
multivariate statistical analysis
linear regression
nitrate trends
Language croatian URN:NBN urn:nbn:hr:169:453378 Study programme Title: Applied Geosciences, Mining and Petroleum Engineering Catalog URL http://katalog.nsk.hr/F/?func=direct&CON_LNG=ZAG&local_base=ZAG01_WEB&doc_number=000636091 Type of resource Text Extent 255 str. ; 30 cm File origin Born digital Access conditions Open access Terms of use Created on 2017-11-07 09:58:03
