Tracing the Sources of Groundwater Nitrate Contamination Using the Nitrogen and Oxygen Isotopes of Nitrate in Varamin Aquifer

Nitrate contamination of groundwater has been concerned as one of the major environmental problems during last few decades. Recent studies have established that the nitrogen (N) and oxygen (O) isotopes of nitrate (NO3) can be used to trace nitrogen dynamics including identifying nitrate sources and nitrogen transformation processes. Stable isotope ratios (δ15N–NO3, δ18O–NO3 and δD-H2O) of groundwater samples were determined used to identify contamination sources and transformation processes occurring in Varamin aquifer, Southeast Tehran, Iran with intense human activities. The approach is based on the realization that NO3 originating from different sources would be exhibit differing isotopic compositions. In addition, δ18O–NO3 is more useful to identify nitrate from atmospheric sources and nitrogen transformation processes. In case study, nitrate concentration of groundwater were in the range of 0.4 to 79.59 mg/l with mean value of 25.14 mg/l. The nitrogen and oxygen isotopic compositions of nitrate in pore water extracts from groundwater samples indicate at least two potential sources of nitrate in Varamin Aquifer. These sources include animal and human waste as well as soil N that most common sources of nitrate contamination in groundwater are wastewater. Denitrification process occurred in the West and South West of Varamin aquifer, specially.