Source identification of nitrate in the upper aquifer system of the Wadi Shueib catchment area in Jordan based on stable isotope composition

摘要: Groundwater forms the main freshwater supply in arid and semi-arid areas, and contamination of this precious resource is complicated by the slow rate of recharge in these areas. Nitrate contamination of groundwater is a global water quality problem, as it entails threat to human health as well as aquatic ecosystems. Source identification of contamination is the cornerstone and a prerequisite for any effective management program of water quality. Stable isotope composition of the dissolved nitrate (δ15N-NO3– and δ18O-NO3–) has been applied to identify NO3– sources and the main transformation processes in the upper aquifer system (A1/2, A4, and B2/A7 aquifers) in the Wadi Shueib catchment area, Jordan. Moreover, the stable isotope compositions of the groundwater (δ2H-H2O and δ18O-H2O) in conjunction with the groundwater hydrochemistry were integrated to investigate the origin and evolution of the groundwater. Results revealed that groundwater in the study area is fresh and hard-very hard water, and mainly a Ca-Mg-Cl type. NO3– concentration was in the range of 7.0–74.0 mg/L with an average of 37.0 mg/L. Most of the samples showed concentration higher than the natural background concentration of NO3– (5.0–10.0 mg/L). The δ2H-H2O and δ18O-H2O values indicated that the groundwater is meteoric, and of Mediterranean origin, with a strong evaporation effect. The δ15N-NO3– values ranged between 6.0‰ and 11.3‰ with an average of 8.7‰, and the δ18O-NO3– values ranged between 1.6‰ and 5.9‰ with an average of 3.4‰. These values are in conformity with the stable isotope composition of nitrate derived the nitrification of wastewater/manure, and soil NH4. Nitrification and denitrification are the main transformation processes affecting nitrogen species. Statistical analysis revealed no significant differences in the δ2H-H2O and δ18O-H2O values, and δ15N-NO3– and δ18O-NO3– values for the three aquifers (A1/2, A4, and B2/A7), indicating that the groundwater of these aquifers has the same origin, and a common source of pollution.