Tracking anthropogenic nitrogen-compound sources of surface and groundwater in southwestern Nile Delta: hydrochemical, environmental isotopes, and modeling approach

Abstract

This research aims to assign the specific and potential sources that control migration and transformation mechanisms of ammonium/nitrate contaminants of surface and groundwater systems in the southwestern Nile Delta, Egypt. To achieve that, an integration of hydrogeochemistry, multiple environmental stable isotopes (δ2H-H2O, δ18O-H2O, δ15N-NH4, and δ15N-NO3) coupled with three-dimensional nitrogen transport numerical model (MODFLOW-MT3D) was done. A set of representative water samples (20 canals and drainage water) and 14 groundwater samples were collected and analyzed for physical, chemical, and stable isotope analysis. NH4+ and NO3− concentrations in surface water samples varied from 0.29 to 124 mg/l and 0.52 to 39.67 mg/l, respectively. For groundwater samples, NH4+ and NO3− concentrations varied from 0.21 to 1.75 mg/l and 0.33 to 32.8 mg/l, respectively. Total risk quotient (THQ) level of nitrate (oral and dermal effects) from drinking water exceeds unity for all water samples indicating a potential noncancer risk for the southwestern Nile Delta residents. The potential sources of nitrogen compound pollution are water from sewage treatment plants used for irrigation, sludge and animal manure, septic tanks, soil nitrogen, and artificial fertilizers according to results of δ15N values. Results of ammonium/nitrate modeling in shallow groundwater aquifers are compared with observed concentrations and are found to be in good agreement. Some recommendations are given to decrease nitrogen loads in the study area through suggested a need for adoption of N-fertilizer management practices and treatment of sewage water before to application in agricultural activities.

Nitrate Source and Transformation in Groundwater under Urban and Agricultural Arid Environment in the Southeastern Nile Delta, Egypt

“…SH43, SH17, SH35, SH50, SH46, and SH38.2 being affected by mixing with the Tertiary aquifer. These findings are consistent with previous studies conducted by [51,66]. These results show that, although the NO3 − groundwater pollution in the west/east regions was low, it can result from irrigation water enriched with CF and SON.…”

“…High NO 3 − levels in the groundwaters have been reported (210 mg/L); however, the sources of pollution have not yet been identified, and the driving mechanisms still remain to be studied. There has been a lack of isotopic studies on NO 3 − pollution in the groundwaters in this region [50,51]. This seriously hinders the implementation of groundwater nitrate pollution prevention and control work in the region.…”

“…The groundwater flow direction exhibits a southwest-to-northeast pattern in the central, southern, and northern regions and a northwest-to-southeast direction in the southeastern part of the study area (Figure 1c). The groundwater recharge primarily occurs through two main sources: Nile River and irrigation canal seepage and infiltration of excess irrigation water, industrial usage, and surface water bodies (e.g., cesspools and drains) [51,56,57]. On the other hand, groundwater discharge is mainly attributed to pumping withdrawals for various purposes, such as agricultural irrigation, drinking water supply, and industrial usage.…”