Nitratenitrogen and Oxygen Isotope Characterization of the Shiraz Aquifer (Iran)

The Shiraz aquifer undergoes anthropogenic pressure from local urban, agricultural and industrial activities that result in dissolved nitrate (NO3−)reaching concentrations as high as 149 mg/L, well above the 50 mg/L guideline defined by the World Health Organisation. We coupled classical chemical and dual isotope (δ15N and δ18O of NO3−) approaches to characterize sources and processes controlling itsbudget. Our data indicate that NO3− in this aquifer is explained by distinct end-members: while mineral fertilizers isotopically show to have no impact, our isotope approach identifies natural soil nitrification and organic NO3− (manure and/or septic waste) as the two main contributors. Isotope data suggest that natural denitrification may occur within the aquifer, but this conclusion is not supported by the study of other chemical parameters.