Isotopic signatures and hydrochemistry in assessing groundwater occurrence in the desert environs west Qena, Egypt

Background: Developing the desert zone outside the flood plain of the Nile River and targeting the reclamation of about 12,500 feddan in the desert environs of Qena governorate are considered one of the top priorities of both government and the private sectors. The present study is based on qualitative analyses of the groundwater of the Quaternary aquifer in the desert environs west Qena. Groundwater was chemically and isotopically analyzed to determine the origin of groundwater and assess its occurrence. Results: The obtained results indicate that the Quaternary aquifer represents the most important groundwater aquifer in the area. The water level ranges from + 40 to + 67 m above sea level. The groundwater movement direction in the study area is mainly from southeast to northwest direction, with some local flow groundwater directions from Nile River at the north to old alluvial plain and desert environs at the south. The hydraulic conductivity of the aquifer is determined from the pumping test range from 17.63 to 42.86 m/day, with an average value of 27.04 m/day, while the transmissivity ranges between 2142.8 and 1128.3 m/day, with an average value of 1456.74 m/day. The total dissolved solids range from 589 to 3832 mg/L. Isotopic analysis (oxygen eighteen and deuterium) of fifteen groundwater samples was carried out to define the recharge source of the Quaternary aquifer. The groundwater isotopic data reflect variability in recharge conditions during different ages and different climatic regimes. According to the minor and trace elements concentration and US Salinity Laboratory Staff nomogram, most water samples are suitable for drinking purposes, domestic use and irrigation. Conclusion: The current research concluded that from the foregoing hydrological study and the determined values of hydraulic conductivity and transmissivity, the Quaternary aquifer is classified as ranging between moderate and high potential aquifer. The high potentiality of the aquifer is detected close to the Nile River. In addition to the representative groundwater samples showing the isotope signature of the Nile River sample, this means that all these wells have the same source of recharge (meteoric water of the Nile River).


Background
In developing countries, increasing population constitutes a big problem because of its great effects on the national growth leading to the increase in poverty and social problems. The acquisition of new land for agriculture remains as one of the major solutions to minimize such harmful effects. In Egypt, there is a continuous Page 2 of 18 El Sabri et al. Bulletin of the National Research Centre (2022) 46:21 demand for more water necessary for reclamation of new land to be added to the existing cultivated land, so the development of groundwater resources in Egypt has received special attention a few years ago where the groundwater aquifers underlying the Nile Valley, the Delta, parts of the deserts and coastal area act as an auxiliary source of water in Egypt. Therefore, nowadays, the Egyptian Government and the private sector are interested in developing the desert zone outside the flood plain of the Nile River and targeting the reclamation of about 12,500 feddan in the west Qena area. The study area is located in the southern part of Upper Egypt, bounded by latitudes 25° 45′ 32.28″ and 26° 05′ 36.30″ N and longitudes 31° 57′ 12.30″ and 32° 45′ 6.84″ E and covers a surface area about 2000 km 2 (Fig. 1). Climatically, the study area is characterized by desert climatic conditions, dominated by long hot, rainless summer and arid warm winter. The annual mean Fig. 1 Location map of the study area Page 3 of 18 El Sabri et al. Bulletin of the National Research Centre (2022) 46:21 temperature is 31.5 °C, the annual rainfall is 3.83 mm, the annual mean of relative humidity is 30.68%, and the annual mean value of wind speed is 8.73 km/h (Tutiempo. net, 2018) and the intensity of evaporation is 11.28 mm/ day (Mahmoud 2005). The evaluation of groundwater resources for development requires an understanding of the hydrogeochemical properties of groundwater in the aquifer. The chemical characteristics of groundwater are mainly influenced by rock interaction, sources of recharge, direction and rate of groundwater movement in addition to other factors. Water chemistry plays an important role in hydrologic science, since it can be regarded as a tool revealing various hydrological processes in the past. Moreover, the occurrence of some ions and compounds in groundwater of a specific region may be used as indicators for the origin and formation of groundwater. This work aims to assess the chemical groundwater composition, isotopic signature and determine the origin of groundwater and the main recharge of the Quaternary aquifers in desert environs of the Qena area.
Geomorpholgically, the study area represents a portion along the western bank of the Nile River. The ground surface elevation decreases gradually from the southern limestone plateau to the Nile Valley plain. The giant deviation of the Nile River course, causing the Qena bend, was formed because of the intensive faulting (rift valley) and tectonic activities during different geologic ages. The area is subdivided into four geomorphic units (Said 1962). These are the young alluvial plains (the cultivated lands), the old alluvial plains (the Nile terraces which are a high level of the cultivated lands), the watershed area (the southern calcareous plateau) and water collectors' areas (alluvial fans and hydrographic basins) (Fig. 2).
Geologically, the sedimentary succession overlying the Precambrian basement rocks in west Qena area is belonging to the Paleozoic, the Upper Cretaceous, the Tertiary and Quaternary (CONOCO and EGPC 1987). A brief description of such succession is given in the following from older to younger (    Tectonically, the study area is slightly affected by tensional forces leading to several normal and wrench faults of NW-SE and NE-SW trends and mainly affecting the Eocene limestone. These faults are associated with some parallel folds ( Fig. 4) (Said 1962 andYoussef 1968).

Methods
Fifty groundwater samples were collected from the Quaternary aquifer in addition to one surface water sample from Nile River for chemical analysis, also fifteen representative water samples were collected for isotopic analysis using plastic bottles, and each one was labeled with 6 number and highly sealed in December (2016). Direct measurements were made at each site in the field (in-situ measurements) giving readings for, total dissolved solids (TDS), electrical conductivity (EC), temperature and pH by using Combo pH and EC meter. The chemical analysis of these samples is carried out for major cations (Ca 2+ , Mg 2+ , Na + , K + ) and some major anions (Cl-, SO 4 2− ) by using ion chromatography (IC) in the water quality laboratory of the Desert Research Center (DRC), while carbonate (CO 3− ) and bicarbonate (HCO 3− ) were determined by titration. The analysis of some trace elements (Si 4+ , B 3+ , Al 3+ , Li + , Mo, Sr 2+ , Ba 2+ , Cr, Cu, Fe 2+ , Mn 2+ , Ni, Pb, V and Zn) for seventeen water sample was carried out by using inductively coupled plasma (ICP) in the Central Laboratory of the Desert Research Center (DRC). The isotopic analysis (measuring the isotopic ratios of O 18 and D) was carried out by (Hydrogeology Group of Freie Universitaet Berlin, Germany) using isotopes ratio mass spectrometer.

Results
The water-bearing sediments have a very wide geographical distribution in the Nile Valley and also in the adjacent desert Wadies. They are mainly composed of gravels, sands and clay, which relate to the Pliocene clay overlying the fissured carbonates form the base of the Quaternary aquifer in the area (Said 1981). The results are discussed under the following main topics; the hydrogeological aspect, the hydrogeochemical and isotopic characteristics.

Hydrogeological aspects
The characteristics of the study Quaternary aquifer in both the vertical and horizontal directions are studied through the hydrological cross section in NE-SW direction ( Fig. 5) (modified after El Sabri 2010). In this section, the author used new shallow and deep wells drilled in the investigated area and situated at different localities in the cultivated and the desert fringes, in addition to some subsurface geological and geophysical studies collected from (Abd El-Latif et al. 2012;El-Sheikh et al. 2015). The water in this aquifer is found under semi-confined conditions (under the old cultivated area) and unconfined conditions (under the reclaimed area) where the overlay Nile silts layer is absent. The thickness of the groundwater-bearing layer is different from one location to another within the aquifer and it is about 170 m recorded thickness.
The hydraulic conductivity of the aquifer which is determined from pumping test ranges from 17.63 to 42.86 m/day, with an average value of 27.04 m/day. While the transmissivity ranges between 2142.8 and 1128.3 m 2 / day, with an average value of 1456.74 m 2 /day. The total depth of the wells in the study area varies from 9 m in the cultivated land to 215 m in the newly reclaimed area and the depth to water ranges between 4 and 97 m. The constructed water level contour map during the year 2016 indicated that the water level decreases regionally from south to north direction and its direction is mainly from southeast to northwest direction, with some local flow groundwater directions from Nile River at the north to old alluvial plain and desert environs at south due to the presence of cone of depression near AL Marashdah and AL Waqf area ( Fig. 6 and Table 1). The Quaternary aquifer is mainly recharged by surface water systems (Nile River, main drainage and irrigation water) while the discharge is mainly represented by Nile River (in some localities), irrigation canals and groundwater wells.

Hydrogeochemical and isotopic characteristics
The water samples analyses are discussed and interpreted referring to the following items: salinity, water type, hypothetical salt combinations and Piper diagram. This discussion has led to the following results: 1. According to the groundwater salinity distribution map ( Fig. 7 and Table 2), the lower values were observed for water samples of the western, central and northeastern parts of the study area (near the desert fringes), while the higher values were observed for water samples of northern and northwestern parts (near Al Marashdah, Al Waqf area and Abu Tisht) and southeastern part (Naqadah area) along the young alluvial valley of the Nile River. The total dissolved solids (TDS) ranged from 589 to 3832 mg/L. 2. According to the concentrations of cations and anions (epm) in the groundwater samples of the Quaternary aquifer, two water chemical types are prevailing in the study area for the Quaternary groundwater samples, indicating the effect of dissolution and ion exchange processes for sediments rich in clay or shale interbeds during the slow movement of groundwater and one water chemical type for Nile River as follows: i. Chloride-Sodium This is the dominant water type (86%) and characterizes the high salinity groundwater in the study area.  This is considered as a good indication for both surface water contamination and possible changeable environment of deposition and also reflects the meteoric fresh water origin most probably from the Nile River.
4. The plotting of water samples in Piper diagram (1944) (Fig. 8) indicates that most of water compositions (92%) are plotted in subarea 7, reflecting primary salinity properties (sodium chloride type), while three groundwater samples are plotted in subarea 9 (fresh water-mixed type) and one sample located in sub-area 6 (calcium chloride type). The major water type in the area is alkaline water with prevailing sulfate and chloride.     Table 4, has led to the following results:  i. The content of oxygen eighteen and deuterium in water samples ranges from − 5.73 to 4.46‰ and from − 66.48 to 32.67‰, respectively. ii. The representative groundwater samples show the isotope signature of the Nile River sample; this means that all these wells have the same source of recharge (meteoric water of Nile River). iii. According to the relationship between 18 O and D (Table 4 and Fig. 9), almost all groundwater samples belong to the global precipitation with a slight influence of evaporation. iv. The saline water samples show a high δ 18 O values (more positive δ 18 O) according to the relationship between TDS and 18 O (Fig. 10). v. All analyzed samples show the isotopic signature of Nile River sample (Sample No zero), which is extremely heavy, due to the intensive evaporation of Nile River which tends to enrich the heavy isotopes in the water, and also found that at samples (No. 39 and 40), which were collected from hand dug wells with low depth to water and exposed to evaporation. vi. The groundwater isotopic data reflect variability in recharge conditions during different ages and different climatic regimes (secondary fractionation has occurred). Depending on the groundwater local meteoric line, 3 groups can be defined as shown in Fig. 9. Group A characterizes samples that exhibit enrich-   Sabri et al. Bulletin of the National Research Centre (2022) 46:21 ment in heavier isotopic composition (positive δ18O and δ D), due to the intensive evaporation exposed to it, and it includes samples No. (zero, 40 and 39). Group B characterizes samples that display the same recharge conditions (closed basin) affected by local recent recharge events from the surface water bodies ex. canals, drains, Nile River and rain precipitation and includes samples (No 1,3,7,8,11,15,18,19,42 and 48). Group C characterizes samples that show light isotopic composition (more negative δ D and δ18O values) and gives an indication that these samples were ancient (paleowater) and originated from rains of a different climatic regime and/or may be recharged from deep aquifers. It includes samples (No. 24 and 37). vii. The relationship between TDS and 18 O (Fig. 10) shows the effect of evaporation as the cause of the rise in salinity with R = 0.0187. The saline water samples show high δ 18 O values (more positive δ 18 O). With increasing salinity of ground water samples, it results in the isotopically enriched groundwater.

Discussion
The evaluation of water samples for irrigation according to the plotting of groundwater samples within the US Salinity Lab. Staff nomogram (1954) revealed the following characters as shown in Fig. 11 and Table 5: 1. Eight percent of the groundwater samples (No. 1, 6, 15 and 33) are located in class C 3 -S 1 (high salinity and low sodium). The waters of such class can be used for all soils particularly those with moderate to good permeability and leaching while it cannot be used in soil with restricted drainage. Even with adequate drainage, special management for salinity control may be required, and plants with good salt tolerance should be selected. 2. Twenty eight percent of the groundwater samples No. (4,5,9,11,12,14,17,18,28,30,31,32' ,38 and 44) are located in class C 3 -S 2 (high salinity and medium sodium). The water of such class is preferably used in coarse textured or organic soils with good permeability while it is unsatisfactory for highly clayey soils with low leaching. The waters of this class can be improved by adding gypsum to the soil periodically. 3. Sixteen percent% of the groundwater samples No. (3, 16, 21, 23, 26, 32, 34 and 37) are located in class C 4 -S 2 (very high salinity and medium sodium). Due to high salinity, this water is not suitable for irrigation under ordinary conditions but may be used occasionally under very special circumstances. The soils must be permeable, drainage must be adequate, irrigation water must be applied in excess to provide considerable leaching, and very salt-tolerant crops should be selected. 4. Twelve percent of the groundwater samples No. (8,10,13,29,35 and 36) are located in class C 3 -S 3 (high salinity and high sodium), may produce harmful levels of exchangeable sodium in most soils and will require special soil management good drainage, high leaching, and additions of organic matter, not used in soil with restricted drainage, require chemical amendments. While 20% of the groundwater samples No. (2, 7, 12' , 19, 20, 22, 25, 27, 45 and 46) are located in class C 4 -S 3 (very high salinity and high sodium), these types cause harmful sodium accumulation in most soils; needs good drainage, high leaching and organic matter addition. Chemical amendments may be required for the replacement of exchangeable sodium, except those amendments may not be feasible with waters of very high salinity. 5. Six percent of the groundwater samples No. (24,43 and 48) are located in class C 3 -S 4 (high salinity and very high sodium). It is generally unsatisfactory for irrigation purposes except at low and perhaps medium salinity where the solution of calcium from the soil or use of gypsum or other amendments may make the use of these waters feasible, while 10% of the groundwater samples No. (39, 40, 41, 42 and 47) are located in class C 4 -S 4 (very high salinity and very high sodium). This water is generally unsuitable for irrigation except for high permeable soils with frequent leaching and high tolerant plants. Chemical amendments must be used for exchanging sodium ions from these light sodium-affected soils.
The evaluation of the groundwater for drinking uses in the present work is determined on basis of salinity and minor and trace elements as follow:

Conclusions
The desert environs west Qena area consists of three types of water-bearing formations, Nubain sandstone, Eocene and the Quaternary aquifer. The Quaternary aquifer represents the most important groundwater aquifer in the area. It is mainly composed of graded sands and gravels. The water in this aquifer is found under semi-confined conditions (under the old cultivated area) and unconfined conditions (under the reclaimed area). It ranges from + 40 to + 67 m above sea level. The groundwater movement direction is mainly from southeast to northwest direction, with some local groundwater flow directions. The lower values of salinity are observed near desert fringes while the higher values are observed along with the young cultivated plain. Sodium and chloride are the main ions constituents of examined wells. The groundwater belongs to one genetic water type, alkaline water with prevailing sulfate and chloride. According to the isotopic analysis result (δ 18 O and δ 2 H), the representative groundwater samples show the isotope signature of the Nile River sample; this means that all these wells have the same source of recharge (meteoric water of Nile River) with various recharge conditions during different ages and different climatic regimes. Almost all groundwater samples belong to the global precipitation with slightly influence of evaporation. According to the minor and trace elements concentration and US Salinity Lab. Staff nomogram; most of the water samples are suitable for drinking purposes, domestic use and irrigation.