o:4690 The comprehensive evaluation of nitrate origin and transformation pathways in the oxic alluvial aquifer in Serbia en Abstract: Accurate pollution source identification is essential for establishing adequate water management strategies, particularly in groundwater with slow flow and prolonged recharge process allowing long-term pollution retention. An integrated study based on hydrogeochemical, dual isotopic (δ15NNO3 and δ18ONO3), and microbiological approaches (DN, IRB, and SRB BART tests) along with the statistical data processing was conducted to determine nitrate origin and fate in oxic alluvial groundwater source Ključ in Serbia. The findings from a comprehensive investigation, encompassing 20 groundwater sampling locations during the period 2010–2019, delineated three distinct zones — the hinterland (anthropogenic impact area-untreated sewage inflow), the middle zone (area of mixed influence from fertilizer application, accompanied by a mitigated anthropogenic impact), and the zone of riparian denitrification. Significant linear relationship between anthropogenic impact parameters (Na, Cl, B, NO3−, NH4+, and electrical conductivity) along with the isotopic signatures (δ15N-NO3− ranking from + 10.01 to + 11.18‰ and δ18O-NO3− ranking from + 1.15 to + 6.24‰) and grouped sampling objects by cluster analysis indicated that hinterland is burdened by the nitrates originating from anthropogenic impact. The cross-section of groundwater flow data, concurrent increase of NH4+, and pH levels, along with the highest values of δ15N-NO3− (+ 12.90‰) and δ18O-NO3− (+ 9.70‰), indicated area of fertilizers (urea) impact. BART test results, pH increase, and low oxygen concentration, along with the groundwater flow data in riparian zone, indicated the unfolding of denitrification process. Presented research emphasizes the importance, necessities, and advantages of simultaneous and complementary use of hydrogeochemical, microbiological, and isotopic data. Keywords: BART tests, Groundwater, Isotopes, Nitrate, PCA 1552101 0944-1344 1552099 https://doi.org/10.1007/s11356-024-33403-w 2024-06-05T07:33:58.055Z 44 no 46 Marija Perović Institut za vodoprivredu "Jaroslav Černi"; Jaroslav Černi Water Institute 0000-0003-2045-001X Kay Knoeller Department Catchment Hydrology, Helmholtz Centre for Environmental Research – UFZ, Germany, Institute for Applied Geosciences, Technical University of Darmstadt person David Mitrinović Institut za vodoprivredu "Jaroslav Černi"; Jaroslav Černi Water Institute person 0000-0002-8097-2998 Zoran Čepić University of Novi Sad, Faculty of Technical Sciences person Vesna Zuber-Radenković Institut za vodoprivredu "Jaroslav Černi"; Jaroslav Černi Water Institute person Vesna Obradović Institut za vodoprivredu "Jaroslav Černi"; Jaroslav Černi Water Institute person 0009-0008-2157-0615 application/pdf 2584645 https://unilib.phaidrabg.rs/o:4690 no yes 1 1556225 2025-05-01 70 92000001 2024-04-16 71A04 Environmental Science and Pollution Research 31 33030 33046 Ecomed Verlagsgesellschaft AG & Co. KG 2024 Received: 6 December 2023 Accepted: 16 April 2024 Published 26 April 2024