For managing the freshwater in the worldwide coastal aquifers, it is imperative to understand the hydrogeochemical processes and flow patterns in the mixing freshwater/saltwater zone. The Egyptian Nile Delta aquifer is a typical example. The management of seawater intrusion (SWI) requires detailed investigations of the intrusion wedge and the dynamic processes in the mixing zone. Thus, a multidisciplinary approach was applied based on holistic hydrogeochemical, statistical analysis, and DC resistivity measurements to investigate the lateral and vertical changes in groundwater characteristics undergoing salinization stressor. The results of cross plots and ionic deviations of major ions, hydrochemical facies evolution diagram (HFE-D), and seawater mixing index (SMI) were integrated with the resistivity results to show the status of the SWI where the intrusion phase predominates in ~2/3 of the study are (~70 km radius) and the compositional thresholds of Na, Mg, Cl, and SO₄ are 600, 145, 1200, and 600 mg/L, respectively, indicating that the wells with higher concentrations than these thresholds are affected by SWI. Moreover, the results demonstrate the efficiency of combining hydrogeochemical facies from heatmap and resistivity investigations to provide a large-scale characterization of natural and anthropogenic activities controlling aquifer salinization to support decision-makers for the long-term management of coastal groundwater.

With the intensification of human activities, nitrate pollutants in groundwater are receiving increasing attention worldwide. Especially in the arid Nile Delta of Egypt, groundwater is one of the most valuable water resources in the region. Identifying the source of nitrate in groundwater with strong human disturbances is important to effective water resource management. This paper examined the stable isotopes (δ¹⁵N/δ¹⁸O-NO₃ and δ²H/δ¹⁸O-H₂O) and the hydrogeochemical parameters of the shallow groundwaters in the arid southeast of the Nile Delta to assess the potential sources and transformation processes of nitrate under severe urban and agricultural activities. The results revealed that the groundwaters were recharged by the Nile River. Meanwhile, the infiltration of irrigation water occurred in the west, while the mixing with the deep groundwater occurred in the east regions of the study area. The TDS, SO₄²⁻, NO₃⁻, and Mn²⁺ concentrations of groundwaters (n = 55) exceeded the WHO permissible limit with 34.6%, 23.6%, 23.6%, and 65.5%, respectively. The NO₃⁻ concentrations in the shallow groundwaters ranged from 0.42 mg/L to 652 mg/L, and the higher levels were observed in the middle region of the study area where the unconfined condition prevailed. It extended to the deep groundwater and eastward of the study area in the groundwater flow direction. The δ¹⁵N-NO₃ and δ¹⁸O-NO₃ values suggested that the groundwater NO₃⁻ in the west and east regions of semi-confined condition were largely from the nitrification of soil organic nitrogen (SON) and chemical fertilizer (CF). In contrast, wastewater input (e.g., domestic sewage and unlined drains) and prevalent denitrification were identified in the middle region. The denitrification might be tightly coupled with the biogeochemical cycling of manganese. This study provides the first report on the groundwater NO₃⁻ dynamics in the Nile Delta, which generated valuable clues for effective water resource management in the arid region.

Water resources management is a vital need in arid and semi-arid regions such as Sinai Peninsula, Egypt. Accordingly, the sustainability of water resources in this arid environment should be examined in terms of the possibility of groundwater recharge, particularly through runoff water, while identifying the most appropriate potential sites for drilling new water wells to cover current and future needs. The aquifer system of El-Qaa Plain in South Sinai is considered one of the structural basins associated with the tectonic setting of the Gulf of Suez. It is the main source of high-quality water in South Sinai. The present work provided an integration of mathematical flow modeling, hydrochemical composition, environmental isotopic signature, watershed modeling system (WMS), and remote sensing (RS) tools to determine the aquifer sustainability and recharge mechanisms. The obtained results indicated the following: (a) the salinity of the water ranged between 326.4 and 2261 ppm, while the environmental isotope values ranged between −6.28 to −4.48‰ for δ¹⁸O and −29.87 to −21.7‰ for δ²H, which reveals the phase of recharge and mixing between ancient water and recent rainwater; (b) sites for three dams in three sub-watersheds were proposed to harvest approximately 790,000 m³/y of runoff water to enhance groundwater recharge of the aquifer system; (c) and five scenarios using MODFLOW indicated that water drawdown is acceptable by adding 10 new production wells (discharge rate increased by 3600 m³/day). Moreover, increasing the recharge rate by 2% from the base case, leads to an increase in the piezometric water level with an average value of 0.13 masl, which reflects the positive effects of the proposed runoff water harvesting facilities. The integration applied in this work represents an integrated management system for water resources (surface and groundwater) which is suitable for application in arid or semi-arid coastal and similar areas.

The need for freshwater supplies is increasingly rising according to the increase in the inhabitants’ expansion and economic growth. Available water resources are reduced by pollution and overpumping. This research’s prime objective is to study changes in the water quality of the Pleistocene aquifer in Minia Governorate. Historical hydro-chemical data of the groundwater in two years 2009 and 2019 were used to study the changes in the groundwater quality of the Pleistocene aquifer under the impact of the recharge and discharge processes. The Nile River, and the Al-Ibrahimia and Bahr Youssef Canals are considered the main sources of aquifer recharge. Collected data from 53 groundwater wells in the Pleistocene aquifer were used to calculate the sodium adsorption ratio (SAR), sodium percentage (Na%), Kelly index (KI), Soluble Sodium Percentage (SSP), magnesium ratio (MR%), permeability index (PI) and chloro-alkaline index (CAI). These data were used to evaluate and detect the quality and changes in groundwater through the years 2009 and 2019 using spatial mapping in the geographic information system (GIS). The values of SAR, KI and Na% varied between 0.06–1.22, 0.02–0.57 meq/L and 3.7–37.63%, respectively, in the year 2009, but these values changed to 0.4–0.75, 0.16–0.28 meq/L and 15.07–23.44% in the year 2019. The calculated MR and PI values indicate that 100% of the groundwater samples were in the “suitable” category. The calculated SSP reflects no changes in groundwater alkalinity between the years 2009 and 2019. The hydro-chemical analysis of the studied groundwater (G.W.) samples shows high pollution levels caused by Pb and Fe in some parts of the study area. Pb was found to be >40 µg/L in the middle parts, whereas Fe was found with high levels in 27% of the studied groundwater samples. The localities of these samples were affected by pollution from the industrial wastewater from the sugar factory of Abou-Qarqas city (e.g., El-Moheet drain), the fertilizer leaching process and pesticides seeping into groundwater from soils and agricultural wastewater.