Geochemical study of groundwater in the Oued El Hatiba Basin, pre-Saharan Atlas, eastern Algeria

The issue of water consumption and pollution presents a multifaceted challenge in Algeria. Rapid urbanization, industrial growth, and agricultural expansion have significantly increased the demand for water resources (Mekonnen et al. 2015; Karandish et al. 2020; Alam et al. 2024). However, inadequate infrastructure and inefficient water management exacerbate this problem. Furthermore, pollution from industrial discharge, agricultural runoff, and improper waste disposal further degrades water quality, posing serious health risks to both humans and ecosystems (Pericherla & Vara 2024). Addressing these issues requires comprehensive strategies that prioritize sustainable water use, improve infrastructure, enforce environmental regulations, and promote public awareness and participation in water conservation efforts (Hamiche et al. 2015).

In Algeria, the rising demand for drinking water persists in tandem with population growth. This demand, particularly for groundwater, faces significant challenges related to water quality. The region has experienced successive drought years, exacerbating the scarcity and irregularity of annual water inputs, both in surface water and groundwater sources. These conditions not only impede infrastructure development but also present substantial management hurdles, particularly in the agricultural sector, where water scarcity affects crop production and sustainability efforts (Masmoudi et al. 2016).

Recent research on groundwater quality in Algeria has provided valuable insights into the hydrogeochemical characteristics and potential contamination risks in various regions. Abdessamed et al. (2023) utilized GIS (Geographic Information System) and water quality indices to assess groundwater quality in the Ain Sefra watershed, highlighting its suitability for human consumption in arid areas. Similarly, Hennia et al. (2024) focused on the Middle Western Cheliff using hydrogeochemical methods to evaluate the quality of groundwater in the alluvial aquifer. Yahiaoui et al. (2023) employed hydrogeochemical and isotopic assessments to characterize groundwater in the Mitidja plain, revealing significant quality variations. The study by Kada et al. (2023) in Beida-Bordj identified nitrate pollution as a key concern, while Selmane et al. (2023) applied water quality indices and GIS to evaluate the Maadher plain's groundwater. Additionally, Maha et al. (2024) assessed health risks associated with non-carcinogenic elements in Ouargla's deep aquifer, and Benouara et al. (2024) examined groundwater quality for irrigation in the Seriana Plain using water quality indices and GIS techniques. These studies collectively enhance the understanding of groundwater quality across Algeria, emphasizing the need for sustainable management strategies.

The Aures region in Algeria grapples with substantial issues concerning water consumption. Rapid population growth, coupled with expanding agricultural and industrial activities, has intensified the demand for water resources in this area. However, inadequate infrastructure and inefficient water management exacerbate the situation, leading to chronic water shortages and escalating tensions over resource allocation. Furthermore, the region's vulnerability to climate change and recurring drought exacerbates the strain on water supplies. Urgent action is needed to address these challenges, including investments in water infrastructure, the adoption of sustainable water management practices, and the implementation of policies to ensure equitable access to clean water for all residents of the Aures region (Bendjerad et al. 2023).

This study undertakes a comprehensive geochemical analysis of groundwater in the Oued El Hatiba Basin, a crucial resource within the pre-Saharan Atlas of eastern Algeria. As the first of its kind in this region, the research aims to elucidate the hydrochemical characteristics of the basin's waters, offering essential insights for sustainable water management and informed decision-making to support the local community's needs.

In the studied area, the lower Cretaceous is represented by marly limestones, marls, sandy limestones, and compact limestones. The Aptian and Albian formations are exposed in the Aurès massif. The Albian is found within the anticlines of the Aurès, often exhibiting facies of sandstone, marl, and dolomite, becoming predominantly marly at its base (Villa, 1980). To the south of the basin, the Albian is represented on the edge of the Khenchela Anticline (Djebel Aidel) (Figure 1).

The Tertiary consists of gypsiferous red clays, resting directly, in discordance, on the Cretaceous. This formation comprises sandy marls and sandstone directly overlying the basal conglomerate. It should be noted that these Miocene marine formations, often classified under the term ‘sandstone’, actually contain only a few sandstone beds embedded within a significant thickness of sandy marls. Therefore, these sandy marls, appearing very friable at outcrop, actually constitute a rather hard rock and are likely to be impermeable (Villa 1980). (Figure 1).

The predominant formations are those of the Quaternary, with a relatively limited thickness, explaining the moderate permeability of the study area. However, erosion remains significant over most of the basin surface, particularly active on steep slopes devoid of vegetative cover. From a hydrogeological perspective, the region has two types of aquifers: the multilayered aquifers of the sedimentary basin, consisting of Plio-Quaternary aquifers, and the fractured carbonate aquifers of the Cretaceous formations.

Sampling of 50 water points focused on groundwater from the Plio-Quaternary and Cretaceous formations; all groundwater samples were obtained at depths ranging from 100 to 150 m (Figure 1). Conducted in August 2016 for physicochemical analyses. Electrical conductivity, temperature, and pH were measured in situ using a multi-parameter brand YSI (Pro DSS).

Major element results were obtained at the chemistry laboratory of the Department of Earth Sciences at the University of Constantine and are presented in Table 1.

The ⁠, ⁠, ⁠, and Cl⁻ ions were measured by the titration method, while the other ions ⁠, ⁠, K⁺, and Na⁺ were measured using a UV (Ultra-Violet) spectrophotometer.

The realization of the maps was done with the ARC GIS 10.8 software (ESRI), the calculation of the saturationindices (SIs) was done with the software PHREEQC 3.7, and the descriptive statistics were done with XLSTAT 2015 software.

The groundwater temperatures in the Oued El Hatiba watershed basin range between 16 and 21 °C, with an average value of 18 °C. These temperatures indicate shallow groundwater, strongly influenced by the average air temperature of 16 °C. The pH of the waters in the study area varies between 6.8 and 8.7, with an average of 7.2, indicating neutral to alkaline conditions. Electrical conductivity ranges from 650 to 3,440 μS/cm, with an average of value 1,890 μS/cm.

The representation of major element concentrations from different sampled water points reveals that the waters predominantly exhibit chloride–calcium facies (48.88%), followed by sulfate–calcium (24.44%), bicarbonate–calcium (15.55%), magnesium–bicarbonate (08.88%), and magnesium chloride (02.22%).

These various facies underscore the aridity of the climate, leading to the dissolution of evaporitic formations and its hydrological consequences on the formation and control of water salinity in the endorheic basins of the Saharan Atlas (Houha 2007).

The relationship between Na⁺ and Cl⁻ (Figure 4) shows that all points lie below the mixing line. Since the Na content should balance the Cl⁻ content, the deficit in Na is explained by ion exchange phenomena between water and the aquifer, resulting in Na⁺ adsorption and Ca⁺ release (Belkoum et al. 2020). The Ca⁺ vs. Cl⁻ graph illustrates this, showing points lying above the freshwater–seawater mixing line (Belkoum & Houha 2017; Djoudi & Houha 2017).

The relationship between Mg⁺ and Cl⁻ indicates that the majority of points lie below the mixing line with a tendency toward Mg enrichment, likely associated with dolomite dissolution (Bouderbala 2015; Benmoussa et al. 2018).

The vs. Cl⁻ graph shows that all points lie above the freshwater–seawater mixing line. Sulfate enrichment is attributed to gypsum dissolution, leaching of evaporites, and the return of irrigation water laden with salts and fertilizers (Hamed et al. 2014), facilitated by the shallow depth of the aquifer and good permeability of aquifer formations (Belkoum & Houha 2017; Djoudi & Houha 2017; Benmoussa et al. 2018). The K⁺ vs. Cl⁻ relationship highlights that the majority of points lie below the freshwater–seawater mixing line.

A principal component analysis (PCA) was conducted on a data table consisting of eight variables and 50 individuals. The analysis was extended to two factors, explaining 75.38% of the variance. Table 2 shows that, except for bicarbonates, all elements are closely correlated with each other around electrical conductivity.

The hydrogeochemical study has revealed that the groundwater of the Oued El Hatiba watershed basin is characterized by the presence of four dominant facies: chloride–calcium, sulfate–calcium, bicarbonate–calcium, magnesium–bicarbonate, and magnesium chloride. These chemical facies are determined by water–rock interaction, dissolution, and mineral precipitation, mediated by cationic exchanges throughout the water flow toward its outlet. The infiltration of irrigation water laden with salts and fertilizers into irrigated areas is a secondary process of water mineralization in the Babar basin.

The significant results from all analyzed groundwater samples indicate that these waters are saturated with respect to calcite, aragonite, and dolomite, and undersaturated with respect to halite, anhydrite, and gypsum. The calculation of mineral saturation indices in the water indicates that only carbonate minerals tend to precipitate, particularly in the form of calcite and dolomite. Conversely, evaporitic minerals (gypsum and halite) tend toward dissolution.

The use of minor and major elements has allowed for the understanding of the water mineralization process. Thus, this mineralization would derive from dissolution–precipitation of the aquifer rock, evaporites, base exchange, and anthropogenic activity.

The PCA explaining 75.38% of the variance shows that, except for bicarbonates, all elements are responsible for the mineralization of groundwater in the Oued El Hatiba Basin.

Eventually, in order to preserve the water resources from degradation, we recommend to the farmers of this region to adopt best management practices: better control of irrigation through water-saving techniques, better reasoning of mineral fertilization, as well as the frequent addition of organic amendments to the soils.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.