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Hydrogeochemical and Isotopic Investigations of Groundwater in the Reclaimed Desert Located between EL Nasr Canal and Mariut Tableland, NW Coast, Egypt

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11 September 2024

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14 September 2024

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15 October 2024

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Abstract
A complete understanding of groundwater dynamics and its interaction with surface water underthe impact of agricultural activities is vital for local agriculture, ecology, and residents of dry regions, which is not commonly recognized in arid areas. This research outlines the geochemical characteristics, recharge sources, and potential factors impacting groundwater quality in a new land reclamation located in the small basin of Abu Mina, which is part of the Western Nile Delta region.1 Thirty‑one groundwater samples and two surface water samples were collected in 2021 to represent the Pleistocene aquifer and were subjected to multivariate statistical, hydrochemical, and stable isotope analyses. Data analysis demonstrates that Na+ > Ca2+ > Mg2+ > K+ and SO4 2– > Cl– > HCO3 – > NO3 – are the predominant cations and anions, respectively. Groundwater salinity ranged from 465.60 to 6455.18 mg/l, with slightly alkaline. Most of the water samples fall into one of three types of facies: Ca–Cl, Na–Cl, and Mixed Ca–Mg–Cl, in decreasing order. The meteoric genesis index (r2) indicates that deep meteoric water percolation dominates the Pleistocene aquifer. The aquiline diagrams, correlation matrix, and different ionic ratios indicate that evaporation, reverse ion exchange reactions, and the dissolution of carbonate and silicate minerals are the main processes governing groundwater chemistry. Factor analysis (FA) indicated that three factors explain groundwater hydrochemistry, accounting for 71.98% of the total variance. According to the rotating components matrix (F1–F3), the chemistry of the Quaternary aquifer is principally affected by evaporation, ion exchange reactions, and anthropogenic influences. Additionally, salinity increases due to the return flow of irrigation activities and mixing between old and recent water. The stable isotopes (δ18O and δ2H) indicate that the Quaternary aquifer receives groundwater recharge through the return flow of excess irrigation and canal seepage. Under desert reclamation conditions, groundwater salinization processes should be given special consideration. All groundwater samples are appropriate for agricultural irrigation based on the Sodium Adsorption Ratio (SAR), Permeability Index (PI), Percent Sodium (%Na), and Residual Sodium Carbonate (RSC).
Keywords: 
Subject: Environmental and Earth Sciences  -   Water Science and Technology
Groundwater is an essential water resource in arid environments. It is crucial for providing drinking water and supporting irrigated agriculture. Population growth and economic development are major challenges for Egypt’s water resources sector. The Egyptian government has targeted the research region for reclamation initiatives, necessitating the assessment of water resources’ viability and their capacity to support future growth [1].
Egypt’s groundwater resources are influenced by a variety of factors, including climate change, altering rainfall amounts, patterns, and frequencies, associated drought events, changes in temperature cyclicalities, and changes in land cover and land use [2,3]. Numerous factors can cause groundwater salinity, including seawater intrusion, ion exchange reactions, the dissolution of secondary minerals, the flow of saline water from neighboring aquifers, the return flow contributions of surface water systems, evapotranspiration, anthropogenic input, climate change, and land use. Most of these sources are typically integrated [4,5,6,7,8].
The northwestern region of the Egyptian Delta has undergone significant changes in recent decades as a result of extensive agricultural projects and land reclamation. This has resulted in a range of ecological and environ- mental issues, including the fall of groundwater levels, waterlogging of the soil and the deterioration of its quality, as well as challenges to regional sustainable development [9]. Irrigation water quality is evaluated by looking at its chemistry and how it is used. Due to the presence of soluble salts in all bodies of water, whether on the surface or underground, the concentration of the soil solution increases when irrigation occurs [10]. Although prior studies conducted, there is still a significant lack of comprehensive evaluation of water quality in the reclaimed areas of the Abu Mina depression, which is located on the northwest coast of Egypt.
The research area is predominantly agricultural, industrial, and urban, which significantly impacts ground- water conditions. Groundwater levels and quality have changed greatly in the Western Nile Delta due to ancient agricultural practices [1,11]. Understanding the factors that lead to groundwater salinity and the impact of irrigation on salinity is crucial for the long-term sustainability of irrigation systems [12]. The effects of prolonged irrigation on groundwater systems depend on various factors, including drainage conditions, hydrogeochemical context, and irrigation water chemistry [13].
Numerous methodological studies have examined the main variables affecting groundwater chemistry in the Northern Nile Delta, Egypt. Multivariate statistical analysis is a proven method for grouping water samples and detecting significant factors controlling water quality. Factor analysis is a suitable technique for identifying correlations between data relevant to fundamental, indirectly visible characteristics [7,14]. Understanding the water cycle interaction is essential for creating and managing water resources in arid regions. The interactions between rainwater, surface water, and groundwater are crucial for this understanding [15].
Stable isotopes of hydrogen and oxygen (δ2H and δ18O) in groundwater are frequently used in hydrological and hydrogeological studies as natural tracers [16]. In general, the stable isotopic compositions of the groundwater body remain intact until it becomes mixed with other water that has altered stable isotopic signatures [17]. They are effective to figure out the primary flow processes and groundwater origin, analyzing the patterns of mix- ing between various groundwater bodies, and calculating the groundwater’s residence duration in aquifers [16]. The spatial variances between distinct groundwater end members for the Quaternary aquifer located in Abu Mina basin, which is a part of the Western Nile Delta region, have not been explained by any published studies, despite the significance of water’s isotopic compositions. Therefore, it is essential to comprehend how agricultural activities affect groundwater quality to manage groundwater in desert areas in the interests of sustainability [18]. Consequently, combining these approaches will help understand the geochemical processes affecting water chemistry in the investigated region. The overarching goal of this work is to integrate statistical analysis, hydro- geochemical, and stable isotope techniques with conventional tools to outline the geochemical characteristics impacting groundwater quality and to determine the effect of land reclamation on groundwater geochemistry. Irrigation water quality factors that promote sustainable irrigated cultivation in a recently developed land reclamation area were examined.

Study Area Characteristics

Site Description

The study area is situated in the northwestern part of the Nile Delta, bordered by the Mariut Tableland to the north and El-Nasr Canal to the south, between longitudes 29° 28′ and 29° 54′ E and latitudes 30° 42′ and 30° 57′ N (Figure 1). The research covers 1023 km2 of the Western Nile Delta’s Abu Mina Basin, a prominent northwest Nile Delta reclamation project.
The geomorphology of the studied region is defined by successive ridges running parallel to the current coastline [19]. Four separate ridges have been identified: the coastal ridge (first), El-Max-Abu Sir ridge (second), Gebel Mariut ridge (third), and Khashm El-Ish ridge (fourth) (Figure 2a,b). These ridges consist of white oolitic and pseudo-oolitic calcareous sand grains and are separated by sabkha-lagoonal depressions [20]. The northern tableland and ridges, composed of Middle Miocene sandy limestone, act as water divides, while Abu Mina and El-Marbat depressions (morphotectonic depressions) serve as water collectors [21].

Geological and Hydrogeological Settings

Geologically, the research region is dominated by the Holocene, Pleistocene, and late Neogene sediments, while the depression areas are primarily composed of alluvial deposits. Tertiary rocks (Pliocene, Miocene, and Oligo- cene) crop out in the structural plain to the south (Figure 2c). Pleistocene sediments can be tentatively differentiated into two lateral units. The first unit consists of oolitic limestones, broadly exposed along the Mediterranean Sea coast, comprising detrital limestone associated with calcareous clayey soil [22]. The second unit (40–60 m thick) is mainly exposed in the Abu Mina Basin and consists of fluviomarine facies of sands, clays, and gypsiferous clays. The surface water system includes the El Nasr Canal, which receives Nile water from the El Nubariya Canal.
Over the past ten years, a network of artificially lined canals and open drains has been developed to circulate surface water. El Nasr Canal’s width ranges from 12 to 13 m, with a water depth of about 3.5 m and an estimated seepage rate to groundwater of approximately 0.08 m3/km/s [23].
The research area’s principal aquifers are Quaternary, Pliocene, Miocene, and Oligocene. The current surface water canals, mostly established through Quaternary strata, are hydraulically connected [24]. The predominant water source in the study area is the Pleistocene (Quaternary) aquifer. Water-bearing sediments in the area consist of alternating layers of sand clay and clay sand, determined by drilling (Figure 3). These layers are capped by a cal- careous loamy layer extending across the entire area [25]. Groundwater predominantly exists under semi-confined (Figure 4a). In the study area, the main sources of recharge are infiltration of occasional rainfall, lateral seepage from the El Nasr Canal and its branches, and return flow from excess irrigation. The transmissivity (T) of the Pleistocene aquifer varies from less than 500 m2/day to more than 5000 m2/day1.

Sampling and Analytical Techniques

In February 2021, thirty-four water samples were collected from the research area, including one sample from an agricultural drain, two from irrigation canals (El-Nasr canal), and thirty-one groundwater samples represent- ing the Pleistocene aquifer. Fresh aquifer samples were obtained by pumping the boreholes for around 10 min to remove stagnant water. Pre-washed plastic bottles, free of air bubbles, were used to store the collected water samples after filtration with 0.45-micron membrane filters. The physicochemical parameters, including electrical conductivity (EC), temperature (T), and pH, were measured on-site using portable devices.
Total carbonate and bicarbonate concentrations were determined by acid–base titration. The concentrations of Ca2⁺, Mg2⁺, Na⁺, K⁺, SO₄2⁻, and Cl⁻ were determined using an ion chromatography system (Dionex, ICS-1100).
Nitrate (NO₃⁻) concentrations were measured using colorimetry with a UV–visible spectrophotometer. Addi- tionally, ionic balance error (IBE) was calculated to check the accuracy of the analysis, with all water samples in the study area showing an IBE within the permissible limit of ± 5% [26]. These chemical analyses were performed in the laboratories of the Desert Research Center (DRC) in Cairo, Egypt. Isotopic analysis (oxygen (δ1⁸O) and deuterium (δD)) for eighteen groundwater samples and two surface water samples was conducted at the UC Davis Stable Isotope Facility using headspace equilibration with GasBench-IRMS. The precision of measurement was ± 0.1 ‰ for δ1⁸O and ± 1 ‰ for δD. Kyplot software (version 2) was employed to conduct factor analysis and correlation matrix analysis for 11 physiochemical parameters [27].

Results and Discussion

Spatial Distribution and Hydrochemical Characteristics

The statistical analysis of the Quaternary aquifer’s results is presented in Table 1 and Figure 4b. Most parameters show wide ranges and high standard deviations, indicating that processes such as water–rock interaction and anthropogenic effects significantly influence the physicochemical characteristics of the groundwater. The analyzed samples exhibit pH values ranging from neutral to slightly alkaline (7.42–8.53) and EC values from low to high (820–9480 µS/cm). Groundwater salinity varies from fresh to brackish, with a median salinity of 32,988 mg/L.
The low salinities near wells 2 and 25 are attributed to natural sporadic replenishment from the El Nasr irriga- tion canal. The increasing groundwater salinity in the northeastern part of the study area is primarily due to geochemical processes within the aquifer.
In the study area, geographical distributions of land use/land cover (LULC) for 2022 were created. As depicted in Figure 1b, the region’s cultivated land was mostly located in the southwest and middle, while its bare land was primarily found in the north and south (the desert region). In the research region, the TDS value varies between 465.60 and 6455.17 mg/l. It is noticeable that all the selected LULC types influenced the spatial depletion in groundwater quality. Nonetheless, there is a correlation between the groundwater salinity distribution and the agricultural distributions in the area. The transition from barren land to development area had the strongest influence overall: it had a significant impact on the change in EC, TDS, and chloride.
Chemically, the major anions SO₄2⁻, Cl⁻, HCO₃⁻, and NO₃⁻ have median concentrations of 1456.90, 503.75, 153.70, and 14.56 mg/L, respectively. The major cations Na⁺, Ca2⁺, Mg2⁺, and K⁺ have median concentrations of 275, 200.17, 192.54, and 12.50 mg/L, respectively. Generally, the spatial distribution maps of major ions indicate that the concentrations of Na⁺, Ca2⁺, Mg2⁺, Cl⁻, and SO₄2⁻ increase towards the north and northeast of the study area in the direction of increasing total dissolved solids (TDS) and groundwater flow. Conversely, HCO₃⁻ con- centrations increase towards the southern part of the study area, indicating the influence of natural recharge from the El-Nasr canal (Figure 5a–h).

Constraints from Multivariate Statistical and Geochemical Approaches

To comprehend the relationships between the physicochemical components of the groundwater samples, factor analysis (FA) was performed. The analysis included 31 groundwater samples and the variables used were pH, EC, TDS, Ca2⁺, Mg2⁺, Na⁺, K⁺, HCO₃⁻, SO₄2⁻, NO₃⁻, and Cl⁻. The correlation matrix for these 11 variables is shown in Table 2. According to the factor analysis findings, the three most important components explain 71.98% of the total variance (Table 3).
Factor 1, revealed that EC, TDS, Na⁺, K⁺, and Cl⁻ accounted for 32.10% of the total variance. The sources of Na⁺ in groundwater in the research region are likely due to silicate weathering, evaporation, and ion exchange processes from the Pliocene clay. Na⁺ and Cl⁻ have strong positive associations (0.83), suggesting a common source. The high TDS content in the groundwater indicated salinity, commonly detected by a high Cl⁻ concentra- tion, which was proportionally associated with cations such as Na⁺. This suggests that Factor 1 depicts contami- nation by human or natural activity in the newly reclaimed areas of the research region [28,29]. Strong Cl⁻ loading (1.00) suggested the effects of saline water, industrial effluents, and extensive groundwater movement [30,31]. The Factor 1 score distribution pattern in the study area is precisely the same as the TDS distribution map (Figure 4c), providing additional evidence that the evaporation/rock-water interaction process, which is the prominent factor controlling the overall groundwater chemistry of the study area, has contributed to the high scores of factor 1. Factor 2, accounted for 20.45% of the total variance and was mainly associated with EC (0.53), TDS (0.63), Ca2⁺ (0.68), and SO₄2⁻ (0.78). High SO₄2⁻ loadings (0.78) were attributed to rock weathering, dissolution, and ion exchange processes affecting groundwater chemistry in the study area. The elevated SO₄2⁻ concentrations in groundwater at the newly reclaimed areas may be caused by the use of potassium sulfate fertilizers, the effect of rainfall, and the dissolution of gypsum-anhydrite filling fissures in Pliocene clay [32].
Factor 3, accounting for about 19.42% of the total variance, includes variables pH, Mg2⁺, and HCO₃⁻. The HCO₃⁻ ion is a product of calcite or dolomite dissolution; however, it is not a dominant process in the study area, as indicated by the lowest HCO₃⁻ concentration among the major ions. This suggests the dilution of groundwater and the impact of seepage and infiltration from irrigation water and canals due to new reclamation activities. The higher loading of Mg2⁺ and the moderately negative loading of pH suggest that these variables are also influenced by water–rock interactions and ion exchange between Na⁺ and Ca2⁺.

Hydrochemical Facies

The results of the chemical analysis of the shallow Quaternary aquifer were plotted on a trilinear Piper diagram [33]. Three hydrochemical facies were identified: the Ca–Cl facies (comprising approximately 74% of the samples), the Na–Cl facies (approximately 19% of the samples), and the mixed Ca–Mg–Cl facies (samples 2, 26, and 34, representing approximately 7% of the samples) (Figure 6a).Based on the base exchange index (r₁) and the meteoric genesis index (r₂) proposed by [34] the water type was classified using Equations (1) and (2):
Base – exchange index (r1) = (Na+ − Cl−)/SO42−
Meteoric genesis index (r2) = (K+ + Na+)− Cl − /SO42−
The samples were classified as Na⁺–SO₄2⁻ water type (r₁ < 1). According to the meteoric genesis index (r₂), the majority of the samples are of deep meteoric water type (r₂ < 1), suggesting that they had longer residence times via deeper percolation (Figure 6b).

Hydrogeochemical Controls on Groundwater Chemistry

Evaporation Process

The Gibbs plot [35] (Figure 7a,b) shows that the evaporation process predominantly controls the major ion chemistry of groundwater [36], with rock-water interaction playing a partial role. The observed increase in total dissolved solids (TDS) against Cl/(Cl + HCO₃) (Figure 7b) suggests that ion exchange reactions also influence groundwater chemistry. Additionally, heavy fertilizer use, irrigation return flow, and anthropogenic activities contribute to increased salinity through elevated Cl⁻ and Na⁺ levels due to the evaporation process.
To confirm the significance of the evaporation process, a plot of Na/Cl versus electrical conductivity (EC) was prepared (Figure 7c). The plot reveals that the Na/Cl ratio (in nearly 68% of water samples) remains constant with increasing EC, indicating that evaporation is the dominant process. In contrast, in 32% of water samples, the Na/Cl ratio decreases with increasing EC up to 3000 µS/cm, likely due to Na⁺ depletion via ion exchange pro- cesses. In the scatter plot of Ca2⁺/Na⁺ versus HCO₃⁻/Na⁺ (Figure 7d), groundwater samples are primarily dispersed between evaporative dissolution and silicate weathering. This result aligns with the Gibbs plot, suggesting that evaporation is a more significant geochemical factor influencing groundwater chemistry than silicate weathering.

Ion Exchange Process

Enrichment or depletion of Na⁺ relative to Cl⁻ indicates ion-exchange processes where Ca2⁺ is held in the aquifer matrix, and Na⁺ is released into the groundwater [37]. Figure 8a shows a clear dominance of Cl⁻ over Na⁺ in 76% of samples, indicating Na⁺ depletion due to reverse ion exchange. In 24% of samples, the Na⁺/Cl⁻ ratio is greater than 1, revealing that ion exchange is the main process, replaced by silicate weathering [38]. Human activities and irrigation return flow may augment Cl⁻ in the groundwater, as halite is less prevalent in the investigated region [39].
A bivariate plot of (Na⁺–Cl⁻) against (Ca2⁺ + Mg2⁺–HCO₃⁻ + SO₄2⁻) (Figure 8b) shows that most groundwater samples fall on or close to a straight line with a negative slope of − 99.0 and a correlation coefficient of 0.98 (p < 0.01), indicating the reverse ion exchange process’s role in Na⁺ and Ca2⁺ variations in groundwater [40].
Chloro-alkaline index calculations (CAI-1 and CAI-2) further interpret the geochemical cation exchange process between groundwater and the aquifer matrix. The indices are computed as follows [41]:
CAI1 = C l−(Na+ + K+)/Cl−
CAI 2 = Cl−(Na+ + K+)/SO42− + HCO₃− + CO32− + NO3−
where the units of ions are in meq/L.
A negative CAI value implies that ion exchange is the dominant process, whereas a positive value indicates reverse ion exchange predominates. As shown in Figure 8c, 77% of samples have positive CAI values, suggesting a reverse ion exchange reaction where Ca2⁺ and Mg2⁺ in the aquifer matrix replace Na⁺ and K⁺ in groundwater. In contrast, 23% of samples have negative CAI values, indicating forward ion exchange where Na⁺ is emitted from the aquifer matrix, and Ca2⁺ is absorbed:
2NaX + Ca2+ → 2Na+ + CaX2 forward ion exchange
CaX2 + 2Na+ → Ca2+ + 2NaX reverse ion exchange
where X = aquifer solid, Ca2+, Na+, and Mg2+ are Calcium, sodium, and magnesium ions, respectively.
Moreover, a plot of total Ca2⁺ + Mg2⁺ ions versus HCO₃⁻ + SO₄2⁻ ions indicates that the reverse ion exchange process predominates in the aquifer, with 76% of samples showing a notable increase in Ca2⁺ + Mg2⁺ ions com- pared to HCO₃− + SO₄2⁻ ions [42] (Figure 8d). A bivariate plot of the (Ca2⁺ + Mg2⁺)/(Na⁺ + K⁺) ratio against total cations (Figure 8e) shows that 73% of samples fall within the reverse ion exchange region, although a few points (27% of samples) suggest direct ion exchange predominates [43,44]. Consequently, both forward and reverse ion exchange reactions govern the hydrochemistry of the aquifer in the studied region.

Silicate and Carbonate Weathering Implications

Table 4 demonstrates that the values of Cl/Σ anions, Na⁺/Cl⁻, Na⁺/(Na⁺ + Ca2⁺), and Mg2⁺/(Ca2⁺ + Mg2⁺) are less than 1, highlighting the impact of silicate weathering on groundwater chemistry in the area [45]. Silicate weathering significantly increases SO₄2⁻ and HCO₃⁻ ions (24% of samples) compared to Ca2⁺ and Mg2⁺ ions (Figure 8d). The Ca2⁺/Mg2⁺ ratio was less than 1 in most samples (52%), and between 1 and 2 in 33% of samples, indicating that dolomite and calcite dissolution contribute to high Ca2⁺ and Mg2⁺ levels, followed by silicate mineral dissolution [46] (Figure 9a). All water samples showed Ca2⁺ and Mg2⁺ concentrations above the 1:1 aquiline in the scatter plot of (Ca2⁺ + Mg2⁺) versus (HCO₃⁻), indicating that silicate weathering is more prevalent than carbonate weathering [47] (Figure 9b). The high concentrations of Ca2⁺ and Mg2⁺ in the groundwater are likely due to silicate mineral dissolu- tion, as 52% of samples have an Mg2⁺/(Mg2⁺ + Ca2⁺) ratio greater than 0.5 [48,49].
Scatter plots of Ca2⁺ + Mg2⁺ versus total cations and Na⁺ + K⁺ versus total cations show that all water samples are plotted below the 1:1 equiline (Figure 9c,d), indicating that silicate weathering mainly contributes Na⁺ and
K⁺ ions to the water system [50]. In bivariate plots (Figure 7c and Figure 9e), water samples predominantly scatter between the weathering of silicate and carbonate minerals’ dissolution, suggesting significant contributions from both processes to groundwater chemistry.
Approximately 10% of sampling points fall on the 1:1 line of Ca2⁺ + Mg2⁺ versus HCO₃⁻ + SO₄2⁻ scatter plot with HCO₃⁻ + SO₄2⁻ less than 10 meq/L, suggesting calcite dissolution (Figure 9f). Around 90% of samples with HCO₃⁻ + SO₄2⁻ greater than 10 meq/L in the scatter plot of Ca2⁺ + Mg2⁺ versus HCO₃⁻ + SO₄2⁻ are affected by gypsum dissolution. Samples falling above the unity line in the Ca2⁺/SO₄2⁻ molar ratio versus Cl⁻ (meq/L) plot had minimal influence from gypsum dissolution [5] (Figure 9g).

Indicators from Stable Isotopes for Recharge Sources and Salinization

The stable isotopic content of groundwater provides insights into recharge and mixing sources [51]. Isotopes (δ1⁸O, δ2H) are part of water molecules unaffected by water–rock interaction [52]. Isotopic signatures change due to evaporation, Rayleigh distillation, and mixing with water of different signatures [53]. The δ1⁸O concentrations in groundwater range from − 1.31‰ (well 15) to + 3.53‰ (well 8), while δ2H values range from − 8.38‰ (well 8) to 25.48‰ (well 13). In Figure 10a, δ1⁸O is plotted against δ2H, aligned with the Global Meteoric Water Line (GMWL, Craig 1961) and the Mediterranean Meteoric Water Line (MMWL), using rainwater, seawater, canal water, and paleowater samples as end members to evaluate the influence of various processes on groundwater quality. The rainwater samples are plotted close to the GMWL and MMWL [54], while groundwater samples (except well 15) collected in 2009 and 2020 are situated near the canal water on the evaporation trend line extending from rainwater. In Figure 10b, the groundwater samples have been plotted between three end members: the rainwater, the canal water, and the Quaternary groundwater, represented by sample No.1, indicating the prime source of recharge is return irrigations flux and seepage from the canals. Sample No. 15 is plotted close to the seawater indicating possible mixing with the seawater.

Irrigation Water Quality

The increased salinity of irrigation water has a negative effect on the soil and plants. The mineral salts that exist in the irrigation water can create changes in the structure of the soil, affecting its permeability and aeration, which leads to a disruption in the growth of plants [55]. The rise in the salinity of irrigation water has an adverse impact on the soil and plants. We assessed the proper suitability of groundwater for irrigation in the research region using qualitative indicators such as sodium adsorption ratio (SAR), electrical conductivity (EC), permeability index (PI), sodium percentage Na (%), residual sodium carbonate (RSC), and spatial representations. All the concentra- tions for these criteria are measured in meq/l (Table 5). In general, the spatial distribution map of groundwater acceptability for irrigation in the area under consideration shows that groundwater from the majority of wells is suitable for irrigation purposes (Table 5 & Figure 11a–d). Nevertheless, it is imperative to consider the salinization processes of groundwater. Suitable irrigation methods should be used in this area and similar areas with limited recharge to prevent the depletion of the aquifer, which results from over pumping.

Conclusion and Recommendations

Based on a comprehensive analysis of various water quality parameters and inorganic elements in the Abu mina basin, NW coast of Egypt, several key conclusions can be drawn, as follows:
The Pleistocene alluvium deposits host the main aquifer in the study area, namely the Quaternary aquifer. The results of a hydrogeochemical and isotopic investigation of Quaternary aquifer in the new land reclamation area of the northwestern Nile Delta, Egypt, are utilized to highlight the geochemical properties, recharge sources, and potential key processes controlling groundwater chemistry. The groundwater of the Quaternary aquifer is meteoric in origin. Groundwater salinity ranged from 465.60 to 6455.18 mg/l (fresh to brackish water), with slightly alkaline (7.42 < pH < 8.15). The greater range of total dissolved solids (TDS) in shallow groundwater suggests that the quality of shallow groundwater is affected by evaporation, infiltration of irrigated water, and convection of saline water from the deeper aquifer. The calculated meteoric genesis index (r2) indicates the dominance of deep meteoric water percolation effects on the groundwater chemistry of the Pleistocene aquifer. The concentration patterns of cations and anions demonstrate a consistent trend, with concentrations increasing towards the northeast.
In this research, the main anion sequence of groundwater is SO₄2⁻ > Cl⁻ > HCO₃⁻ > NO₃⁻, respectively. The main cation sequence is Na⁺ > Ca2⁺ > Mg2⁺ > K⁺, respectively. Most water samples belong to the Ca–Cl facies, Na-Cl facies, and mixed Ca–Mg–Cl facies, in decreasing order of abundance. Multivariate statistical analysis (FA) is a well-established methodology that was implemented for classifying waters and identifying critical com- ponents influencing water quality. The groundwater hydrochemistry can be explained by three factors, which together account for 71.98% of the total variance. According to the rotating components matrix (F1–F3), the chemistry of groundwater is principally affected by evaporation, ion exchange reactions, and human activities.
The Quaternary aquifer is salinized by natural and agricultural processes, including evaporation, ion exchange, and carbonate–silicate dissolution along groundwater flow and irrigation return flow. In general, surface water irrigation practices have affected the hydrogeochemical properties of groundwater. The study of environmental isotopes confirms this.
The isotopic data demonstrated that the surface water samples (δ 18O = 3.82‰ and δ 2 H = 27.65‰)) have significant isotopic content relative to the recent Nile River water (δ 18O = 3.03‰ and δ 2 H = 27‰). This indicates
that there is an evaporation process occurring in surface water bodies throughout its flow, resulting in an increase in isotopic content. The groundwater isotopic content generally increased to its maximum values in response to the recent Nile water, canals, and drain water, which reflects the mixed condition of groundwater that was recharged post the construction of the High Dam.
The depletion of δ1⁸O and δ2H values in groundwater samples indicates that the main sources of recharge are seepage from irrigation canals and possible mixing with seawater. Our research may prove helpful for the sustainable management of in desert reclamation projects in arid regions and its impact on groundwater quality. Understanding the most important hydrogeochemical processes is essential for future groundwater management and environmental protection.
All groundwater samples are appropriate for agricultural irrigation based on the Sodium Adsorption Ratio (SAR), Permeability Index (PI), Percent Sodium (%Na), and Residual Sodium Carbonate (RSC). While certain elements fall within safe limits for irrigation, others exceed permissible concentrations (as EC), posing risks to soil and plant health. This investigation will offer policymakers the necessary information to ensure the sustain- able administration of groundwater resources in the reclamation area.
The current work could be enhanced by.
  • Employing a groundwater flow model to provide a complete picture of water flow and groundwater quality via an aquifer.
  • More detailed land use maps are created by using high-definition satellite data.
  • Furthermore, the construction of an accurate water quality index based on numerous variables and water parameters could be important for improved understanding of water sources and their mixing patterns, particularly in shallow alluvial aquifers under arid conditions.
  • Sustaining groundwater quality management and protection requires ongoing monitoring of groundwater quality.

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Figure 1. (a) A map depicting the location of the investigated region and water sampling locations (initiated using 59); (b). Land use and land cover map showing land use class incorporating Total Dissolved Solids (TDS) in the study area (conducted by 60). (Raster data are downloaded from https://earthexplorer.usgs.gov/).
Figure 1. (a) A map depicting the location of the investigated region and water sampling locations (initiated using 59); (b). Land use and land cover map showing land use class incorporating Total Dissolved Solids (TDS) in the study area (conducted by 60). (Raster data are downloaded from https://earthexplorer.usgs.gov/).
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Figure 2. (a) Geomorphologic map of the study area and its surroundings (modified after 21); (b) Cross-section along Burg El Arab area showing main geomorphic units (after 61); and (c) general geologic map of the study area (after 62).
Figure 2. (a) Geomorphologic map of the study area and its surroundings (modified after 21); (b) Cross-section along Burg El Arab area showing main geomorphic units (after 61); and (c) general geologic map of the study area (after 62).
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Figure 3. (a) Hydrogeologic cross section cuts the study area in a NE-SW direction (b) Hydrogeologic cross section cuts the study area in an E-W direction [modified after)25) using (59)].
Figure 3. (a) Hydrogeologic cross section cuts the study area in a NE-SW direction (b) Hydrogeologic cross section cuts the study area in an E-W direction [modified after)25) using (59)].
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Figure 4. (a) Groundwater level map overlayed by vector flow dirction and (b) Box and whisker plot of the major ion concentrations in groundwater of Quaternary aquifer (created using 63); (c) The first factor score (F1) distribution (a and c has created by (59).
Figure 4. (a) Groundwater level map overlayed by vector flow dirction and (b) Box and whisker plot of the major ion concentrations in groundwater of Quaternary aquifer (created using 63); (c) The first factor score (F1) distribution (a and c has created by (59).
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Figure 5. Spatial distribution maps of (a) TDS (b) Na+ (c) Ca2+ (d) Mg2+ (e) Cl− (f) SO 2− (g) HCO − and (h) NO − (data gridding and contouring using 59).
Figure 5. Spatial distribution maps of (a) TDS (b) Na+ (c) Ca2+ (d) Mg2+ (e) Cl− (f) SO 2− (g) HCO − and (h) NO − (data gridding and contouring using 59).
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Figure 6. (a) Piper diagram showing the various hydrochemical facies in the groundwater (created by 63); (b) Base-exchange and meteoric genesis indices (r1&r2) and) showing the various water types and percolation depth.
Figure 6. (a) Piper diagram showing the various hydrochemical facies in the groundwater (created by 63); (b) Base-exchange and meteoric genesis indices (r1&r2) and) showing the various water types and percolation depth.
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Figure 7. (a) and (b) Gibbs diagram representing controlling factors of groundwater quality (c) Relationship between EC and Na/Cl. (d) Na-normalized Ca versus HCO3 (carried out with 63).
Figure 7. (a) and (b) Gibbs diagram representing controlling factors of groundwater quality (c) Relationship between EC and Na/Cl. (d) Na-normalized Ca versus HCO3 (carried out with 63).
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Figure 8. Ions scatter diagram indicating various hydrogeochemical processes of groundwater in the study area (created by 63).
Figure 8. Ions scatter diagram indicating various hydrogeochemical processes of groundwater in the study area (created by 63).
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Figure 9. Equiline diagrams for groundwater showing the correlation of major ions to discriminate the entire processes act in the aquifer (created by 63).
Figure 9. Equiline diagrams for groundwater showing the correlation of major ions to discriminate the entire processes act in the aquifer (created by 63).
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Figure 10. (a) δ2H‰ vs δ18O‰ values for water resources; (b) Change of δ18O‰ vs Cl (mg/l) values for water resources associated with different salinization processes (created by 63).
Figure 10. (a) δ2H‰ vs δ18O‰ values for water resources; (b) Change of δ18O‰ vs Cl (mg/l) values for water resources associated with different salinization processes (created by 63).
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Figure 11. Spatial distribution maps of irrigation water quality in the study area. (a) EC (b) SAR (c) Na% and (d) PI (created by 59).
Figure 11. Spatial distribution maps of irrigation water quality in the study area. (a) EC (b) SAR (c) Na% and (d) PI (created by 59).
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Table 1. The statistical characteristics of groundwater hydrochemical parameters.
Table 1. The statistical characteristics of groundwater hydrochemical parameters.
Chemical Parameter Minimum Maximum Median Standard Deviation
pH 7.42 8.53 7.88 0.28
EC (µS/cm) 820.00 41,000.00 4850.00 6549.46
TDS (mg/l) 466 44,774 2988 7295.74
Na+ (mg/l 50 13,400.00 275.00 2253.04
Ca2+ (mg/l) 33.36 889.65 200.17 282.38
Mg2+ (mg/l) 30.40 1168.74 192.54 194.39
K+ (mg/l) 4.00 200.00 12.50 33.46
Cl− (mg/l) 130.00 21,125.00 503.75 3532.20
SO₄2− (mg/l) 52.00 7850.00 1456.90 1340.27
HCO₃⁻(mg/l) 93.90 298.90 153.70 53.16
NO32− (mg/l) 1.82 36.40 14.56 9.95
IBE error (%) − 2.43 1.79 − 1.30 1.52
δ2H (‰) − 8.39 27.66 22.02 7.44
δ18O (‰) − 1.32 3.52 2.90 1.07
Table 2. Pearson correlation matrix of hydrogeochemical parameters determined on groundwater in the study area. Bold text Indicate the correlation coefficients is statistically significant at < 0.05 level.
Table 2. Pearson correlation matrix of hydrogeochemical parameters determined on groundwater in the study area. Bold text Indicate the correlation coefficients is statistically significant at < 0.05 level.
pH EC TDS Na+ Ca2+ Mg2+ K+ Cl− SO42− HCO3− NO3−
pH 1.00
EC − 0.03 1.00
TDS − 0.15 0.96 1.00
Na+ 0.35 0.78 0.65 1.00
Ca2+ − 0.42 0.38 0.54 − 0.18 1.00
Mg2+ − 0.23 0.61 0.64 0.41 0.00 1.00
K+ 0.16 0.62 0.55 0.52 0.31 0.11 1.00
Cl− 0.14 0.80 0.70 0.83 0.09 0.40 0.61 1.00
SO42− − 0.34 0.73 0.86 0.28 0.65 0.63 0.28 0.25 1.00
HCO3− 0.68 − 0.07 − 0.22 0.29 − 0.37 − 0.37 0.32 0.22 − 0.50 1.00
NO3− 0.11 0.55 0.50 0.46 0.23 0.19 0.60 0.36 0.40 0.06 1.00
Table 3. Factor loadings of Factor 1, Factor 2 and factor 3. Bold text represents significant factor.
Table 3. Factor loadings of Factor 1, Factor 2 and factor 3. Bold text represents significant factor.
Factor1 Factor 2 Factor 3
pH 0.12 − 0.05 − 0.57
EC 0.79 0.54 0.20
TDS 0.69 0.63 0.35
Na+ 0.82 0.20 − 0.12
Ca2+ 0.07 0.69 0.16
Mg2+ 0.43 0.12 0.77
K + 0.59 0.39 − 0.30
Cl− 1.00 0.04 − 0.04
2−SO4 0.24 0.79 0.57
−HCO3 0.20 − 0.14 − 0.77
−NO3 0.34 0.49 − 0.11
Proportion 0.32 0.20 0.19
Cumulative Proportion 0.32 0.53 0.72
Table 4. Ratio of ion exchange reaction and silicate weathering in Quaternary aquifer.
Table 4. Ratio of ion exchange reaction and silicate weathering in Quaternary aquifer.
Parameter Minimum Maximum Average
Na+/(Na+ + Ca2+) 0.10 0.93 0.54
CAI1 − 1.82 0.82 0.16
CAI2 − 0.48 0.57 0.13
Cl−/∑Anions 0.19 0.72 0.39
Mg2+/(Ca2+ + Mg2+) 0.19 0.93 0.59
r1 − 1.82 0.50 − 0.24
r2 − 1.66 0.51 − 0.21
Na+/Cl− 0.16 2.80 0.82
Table 5. Irrigation water quality parameters from Quaternary aquifer based on EC, SAR, Na%, RSC, and PI.
Table 5. Irrigation water quality parameters from Quaternary aquifer based on EC, SAR, Na%, RSC, and PI.
Parameter References Formula Adopted Categories Ranges % Samples
EC [56] Excellent < 250 –
Good 250–750 –
Permissible 750–2250 16.7
Doubtful 2250–5000 13.3
Unsuitable > 5000 50.0
SAR [57] √ N a + C a 2 + + M g 2 + 2 Excellent 0–10 90
Good 10–18 10
Doubtful 18–26 –
Unsuitable > 26 –
Na % [56] N a + + K + C a 2 + + M g 2 + + N a + + K + × 100 Excellent 0–20 36.6
Good 20–40 26.7
Permissible 40–60 26.7
Doubtful 60–80 10.0
Unsuitable 80–100 –
RSC [57] C O 3 2 − + H C O 3 − − C a 2 + + M g 2 + Good < 1.25 100
Medium 1.25–2.5 –
bad > 2.5 –
PI [58] N a + + H C O 3 − ( N a + + C a 2 + + M g 2 + ) × 100 Preprints 117974 i001Unsuitable 0–25 46.7
Good 25–75 53.3
Excellent ≥ 75 –
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