Estimate Proportional Contributions of Multiple Nitrate Sources in Groundwater of Varamin Plain Using a Bayesian Isotope Mixing Model

Nitrate (NO3−) pollution of surface and ground water is a major problem in water quality on the planet. The scientific method of the relations between δ15N-NO3− and δ18O-NO3− to identified the dominant sources of nitrate in groundwater, despite the overlap of nitrate isotopic ranges and the occurrence of nitrate isotopic fractionation, have been used in numerous studies. NH4+ fertilizer, treated wastewater, sewage and manure, Shour River, NO3 in precipitation and soil organic N, are potential sources of nitrate pollution in the study area. To identify different nitrate sources and to estimate their proportional contribution in the groundwater of the Varamin aquifer, a dual isotope (δ15N-NO3− and δ18O-NO3−) method and a Bayesian isotope mixing model for 38 samples in November 2016 have been applied. Based on hierarchical cluster analysis, 38 groundwater samples are classified into three clusters (groups one to three) in terms of hydrochemical properties., the mean values of δ15N–NO3− in groups 1, 2 and 3 are +7.0± 2.1‰, +10.2 ±1.1‰ and +16.1±2.1‰, respectively. The mean of δ18O–NO3− values of the groundwater in groups 1, 2 and 3 are +2.3± 1.9‰, +0.6 ± 0.8‰ and +6.2 ± 1.4‰ , respectively. SIAR model results indicate that the highest contribution in the nitrate pollution of the Varamin aquifer are related to“NH4+ fertilizer” and “manure and sewage” while “soil N” and “NO3− in precipitation” have the lowest influence.