Evaluation of the origin of nitrate influencing the Kljuc groundwater source, Serbia
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This paper describes the use of the dual isotope method involving delta N-15 and delta O-18 measurements of dissolved nitrates to assess the origin and fate of groundwater nitrate at the Kljuc groundwater source, Serbia. A sampling campaign was conducted in September 2007 during flow conditions obtaining groundwater from observation wells and river water fed by a shallow aquifer hosted in alluvial (sandy-gravel) sediments. Nitrate isotope ratios ranged from +5.3 to +16.9 parts per thousand and delta O-18(NO3) values varied from -2.3 to +5.0%. Two major contamination sources were identified with isotopic compositions characteristic for nitrate derived from nitrification of soil organic nitrogen (+5.3 to +7.8% for delta N-15) resulting in nitrate concentrations of 33.6 and 78.8 mg/L and nitrate derived from animal wastes or human sewage, e. g. via septic systems, yielding delta N-15 values of +9.9 to +11.9 parts per thousand and elevated nitrate concentrations of 31.2-245.8 mg/L. The occ...urrence of nitrification and denitrification was also revealed based on concentration and isotope data for dissolved nitrate.