Identification and apportionment of nitrate sources in the phreatic aquifers in Northern Jordan using a dual isotope method (δ15N and δ18O of NO3-)

Abstract

Contamination of groundwater resources from nitrates is a worldwide problem, and Jordan is not an exception. Source identification of contamination is a prerequisite for the protection of water resources and human health. Moreover, investigating the controlling processes of groundwater quality is essential for groundwater sustainability, especially in water-poor countries like Jordan. Environmental isotopes of nitrate (15N and 18O of NO3-) have been applied for the first time in Jordan to assess the origin and cycling of nitrogen pollution in two phreatic aquifer systems: Shallala aquifer (B5/B4) and Amman/Wadi Sir aquifer (B2/A7), hosted in multiple land use area in northern Jordan. The nitrate concentration exceeded the natural background (5–10 mg/L) in all samples, ranging from 14 to 251 mg/l as NO3- in both groundwater systems. About 46% of the samples showed NO3- concentration exceeding the WHO threshold of 50 mg/l in drinking water. Isotope values of nitrate (15N and 18O of NO3-) indicated that manure, urban wastewaters, and nitrified synthetic fertilizers were the main sources of nitrate in the groundwater resources in the study area. SIAR (Stable Isotope Analysis in R) model showed that synthetic fertilizers contributed least to nitrate in groundwater in the study area (average = 3.3%). Nitrified synthetic fertilizers contribution was higher in the B2/A7 aquifer (61%) than in B5/B4 aquifer (49%), whereas anthropogenic organic matter contribution in the B5/B4 (46%) is higher than in the B2/A7 aquifer (36%). Anthropogenic organic matter contribution in the B5/B4 aquifer varied from 20% in the west to 85% in east. Nitrified synthetic fertilizers contribution varied from 10% in the east to 74% in the west. Sustainable management of groundwater resources in the study area necessitates application of best management practices and proper land use planning.