1. INTRODUCTION

Groundwater plays a crucial role in sustaining populations, particularly in arid and semi-arid regions where surface water resources are scarce, unreliable, or highly seasonal (Ali Rahmani et al., 2017; Azlaoui et al., 2021; Ncibi et al., 2021; Mansouri et al., 2022; Chougar et al., 2024; El-Rawy et al., 2023). Due to its relative stability against climatic variability, groundwater is considered a strategic resource for drinking water supply and irrigation (Huan, 2018; Kalaivanan et al., 2018; Ben Moussa et al., 2021). Globally, it provides nearly half of the drinking water supply and 40 % of agricultural water needs (Lora-Ariza et al., 2024).

However, this vital resource is increasingly threatened by multiple pressures, both natural and anthropogenic. On the one hand, geochemical processes such as rock weathering and the dissolution of evaporitic and carbonate minerals contribute to groundwater mineralization (Muhammad & Ahmad, 2020; Downing et al., 2021; Rehman et al., 2024; Wei et al., 2024). On the other hand, human activities, including urbanization, intensive agriculture, industry, mining, and poor wastewater management represent major sources of pollution (Bawa & Dwivedi, 2019; Rezig et al., 2022; Ojo et al., 2024). This situation is particularly alarming in developing countries, where untreated or contaminated water is often used for domestic and agricultural purposes, exposing populations to serious health risks (Egbuikwem et al., 2021; Lamri et al., 2022).

In Algeria, the growing degradation of groundwater represents a major challenge for the sustainability of water resources (Negm et al., 2020; Allaoua et al., 2024). Studies conducted in semi-arid areas such as the Sidi Bel Abbès plain and the Béchar region have highlighted persistent trends of declining water tables and deteriorating quality due to sustained overexploitation of aquifers (Bellaredj & Hamidi, 2020; Kendouci et al., 2023). Moreover, in eastern Algeria (Oum El Bouaghi), several analyses have revealed increased contamination (nitrates, high electrical conductivity), threatening the sustainable use of groundwater (Allaoua et al., 2024). Recent artificial recharge initiatives (Cheria basin) further underscore the need for preventive measures to address a depletion process that has yet to be managed in an integrated manner (Djellali et al., 2023).

Between 2010 and 2019, the national water stress index increased from 104.92 to 137.2, while the annual renewable freshwater availability per capita dropped from 314 to 263 m³/year (Bakhtache & Hadjene, 2023). This quantitative stress is often compounded by deteriorating water quality, marked by increased salinity, elevated nitrate levels, and the presence of trace metals, often linked to anthropogenic activities (Bougherira et al., 2017).

Moreover, the use of contaminated water, particularly for domestic purposes or human consumption, can cause harmful health effects, both in the short and long term (Rezig et al., 2021; Peng et al., 2022).

The Bouira region, located in north-central Algeria, illustrates the growing challenges of sustainable groundwater management. Essential for irrigation and drinking water supply, this resource is increasingly under pressure due to the widespread use of chemical fertilizers, the expansion of industrial zones, and insufficient sanitation infrastructure (Lamri et al., 2022; Rezig et al., 2022).

Pollution observed in the Bouira dam (Rezki, 2024) may also impact local aquifers. Several recent studies have highlighted a correlation between declining water quality and health risks in areas irrigated by oueds (Rezig et al., 2021), underscoring the vulnerability of this strategic resource.

In this context, a rigorous and integrated assessment of groundwater quality is essential to preserve this strategic resource, ensure public health, and support sustainable water management policies. Although some studies have sporadically reported groundwater degradation in various regions of Algeria, comprehensive investigations combining physicochemical, microbiological, and multivariate statistical analyses remain limited, particularly in semi-arid areas such as the Bouira region. Yet such approaches are crucial for accurately characterizing pollution profiles, identifying potential contamination sources, and revealing spatial variability in water quality parameters (Xiao et al., 2023). 

Accordingly, this study aims to explore groundwater quality in the Bouira region by analyzing its physicochemical and bacteriological characteristics to evaluate its suitability for drinking water and to provide a scientific basis for sustainable management in a semi-arid environment.

2. MATERIALS AND METHODS

2.1. Study area

The Wilaya of Bouira is located in the northern part bordered to the north by the Wilayas of the country, southeast of Algiers (the capital), with a total area of 4,454 km². It has a population of 742,855 inhabitants, resulting in a population density of 167 inhabitants per km².

It is Boumerdes and Tizi-Ouzou, to the south by M’Sila and Medea, to the east by Bejaia and Bordj Bou Arreridj, and to the west by Blida and Medea (Figure 1).

The region's climate is a temperate Mediterranean type, characterized by hot and dry summers and cold, rainy, and humid winters. Annual precipitation reaches 665 mm, while average monthly temperatures range from 8.4 °C in January to 27.9 °C in July.

The proven water resource capacity across the Wilaya amounts to 235.4 hm³, with 35.5 hm³ coming from groundwater and 199.9 hm³ from surface water. Groundwater resources are mainly located in the northern region, particularly in the plateaus of El Asnam, Bled El Madjen, and the valleys of Oued Ed Dhous and Oued Sahel. These waters are extracted through wells, boreholes, and springs (Zerdane, 2013).

The region's drinking water supply is ensured through the transfer of surface water from the Tilesdit dam, with a regulated volume estimated at 672 m³/day, as well as groundwater sourced from boreholes, springs and wells.

2.2. Water Sampling and Analysis

The sampling covered two municipalities in the Bouira region: El Asnam and Oued El Berdi (Figure 1). Ten boreholes were carefully selected, considering their geographical location, geological characteristics, and the surrounding agricultural environment (Table 1). These boreholes are located near surface water flows, industrial and urban activity zones, as well as sources of liquid or solid waste discharges. They are primarily used for drinking water supply and irrigation.

Water samples were collected under strict aseptic conditions. Sterile 250 mL Pyrex glass bottles with wide necks and screw metal caps were used, previously sterilized at 180 °C for 20 minutes.

Samples were kept at 4 °C, protected from light, and transported to the laboratory within 6 hours after sampling. Negative controls were included to detect potential contamination during transport and handling. Each sample was analyzed in triplicate to ensure reproducibility and statistical robustness (Rodier et al., 2016).

2.2.1. Bacteriological Analysis

Bacteriological analyses were conducted in accordance with both the Algerian national standard for drinking water quality (NA 6360-1992) and international microbiological standards (ISO) (WHO, 2017). The aim was to assess the sanitary quality of groundwater intended for human consumption. The microbial indicators analyzed included total coliforms (TC), fecal coliforms (FC), intestinal enterococci (IE), sulfite-reducing clostridia (SRC), and total aerobic mesophilic bacteria (TAMB) incubated at 22 °C and 37 °C. 

TC and FC were quantified according to ISO 9308-2, using membrane filtration (0.45 µm) and incubation on Chromocult® Coliform Agar (Merck, Germany) at 37 °C for TC and at 44 °C for FC for 24 hours. Intestinal enterococci (IE) were enumerated following ISO 7899-2 by filtration and incubation at 36 °C for 48 hours on Slanetz and Bartley Agar (Biokar Diagnostics, France). Sulfite-reducing clostridia (SRC) were assessed using ISO 6461-2, by anaerobic incubation on Tryptose Sulfite Cycloserine (TSC) Agar at 44 °C for 24 hours. TAMB were determined by surface plating on Plate Count Agar (Biokar Diagnostics, France) incubated 
at 22 °C for 72 hours and at 37 °C for 48 hours, as recommended in ISO 6222.

2.2.2. Physicochemical Analysis

For these analyses, 1.5 L polyethylene bottles were used, rinsed three times with distilled water. These bottles were opened only at the time of sampling; once filled, they were sealed, labeled, and stored at 4 °C.

The analysis of the collected water samples was carried out according to the methods described by Rodier et al. (2016) and was conducted within a maximum timeframe of 24h.

The physico-chemical parameters (temperature, pH, conductivity, and turbidity) were measured in situ using a multiparameter device.

The total hardness (TH) was determined using the Mohr method, while ammonium, nitrates, sulfates, orthophosphate ions, chlorides, calcium, magnesium, sodium, potassium, and total iron (Fe2+, Fe3+) were analyzed using the spectrophotometry method.

2.3. Statistical analysis

A Principal Component Analysis was applied in order to highlight the possible relationships between the different physico-chemical tested parameters (pH, temperature, turbidity, electrical conductivity, calcium, magnesium, sodium, potassium, iron, nitrite, nitrate, ammonium, sulfate, bicarbonate and chloride). 

Although the dataset is relatively limited, several studies have demonstrated that multivariate statistical techniques such as PCA remain relevant and robust even with small sample sizes, as they help reduce dimensionality, reveal latent correlations among variables, and improve the interpretation of hydrochemical datasets (Shrestha & Kazama, 2007; Souley Moussa et al., 2018; Kouame et al., 2021; Rahmani et al. 2022; Guenouche et al. 2024).

An Ascending Hierarchical Classification (AHC) was applied as a complementary analysis with the aim of identifying the number and composition of each homogeneous subgroup of tested drilling water. This clustering method has been shown to be effective in hydrogeological studies, even with relatively small datasets, as it allows a clearer classification of sampling sites based on similarities in water quality (Gupta & Mehrotra, 2020; Kouame et al., 2021; Taşan et al., 2022; El Hammioui et al., 2023; Masmoudi et al., 2024).

All statistical analyzes and graphical representations were carried out by the statistical software SPSS version 26 (IBM SPSS 2019).

3. RESULTS AND DISCUSSION

The analysis of groundwater quality in the Bouira region reveals a complex interplay of natural and anthropogenic factors.

3.1. Bacteriological quality of borehole water

The bacteriological analyses of the studied boreholes revealed the absence of total coliforms (TC), fecal coliforms (FC), intestinal enterococci (IE), and sulfite-reducing clostridia (SRC) (0 CFU/100 mL) at all 10 sampling points (Table 2).

Regarding microbiological parameters, the guidelines of the World Health Organization (WHO/EU) stipulate the total absence of pathogenic microorganisms in drinking water.

The enumeration of total aerobic mesophilic bacteria (TAMB) is considered a broad indicator of microbiological pollution, as it determines the total bacterial load. The stability of bacterial counts is therefore a good indicator of water protection (Khaldi et al., 2018).

The results obtained for total aerobic mesophilic bacteria counts ranged from 16 to 25 CFU/100 mL at 22 °C in boreholes FOB2, FOB4, FOB5, and FAS7, and from 6 to 14 CFU/100 mL at 37 °C in boreholes FOB3, FOB4, FOB5, FOB6, and FAS8.

These values exceed the Algerian regulatory standards, which set the limits at ≤ 20 CFU/mL at 22 °C in 72 h and ≤ 5 CFU/mL at 37 °C in 24 h.

Microbiological results indicate the total absence of fecal coliforms, enterococci, and sulfite-reducing clostridia, confirming good sanitary quality in all sampled boreholes. These findings contrast with observations reported in other Algerian regions, such as El-Harrouch, where frequent fecal contamination has been documented (Ayad & Kahoul, 2016).

The absence of bacterial colonies at 22 °C in certain samples (F3, F6, F8), despite the detection of mesophilic bacteria at 37 °C, can be explained by the specificity of microbial groups targeted at each incubation temperature. Incubation at 37 °C promotes the growth of mesophilic bacteria, often environmental saprophytes such, which thrive at temperatures close to human body temperature, without necessarily indicating the presence of coliforms (Figrella et al., 2001).

The contrast observed between the two incubation temperatures highlights the ecological diversity of microbial niches. The absence of growth at 22 °C in boreholes F3, F6, and F8 may also be related to a viable but non-culturable (VBNC) state, in which certain bacteria remain metabolically active but undetectable using conventional culture-based methods (Health Canada, 2020).

3.2. Physicochemical characteristics of groundwater

The results of the physicochemical analyses of the water from the studied drillings are recorded in (Table 4). Table 3 presents the drinking water quality standards, the average and extreme values of the different measured physicochemical parameters of the drilling water.

The average temperature of the water from the selected drillings is 18.7 ± 1.8 °C, ranging between 15.9 °C and 21.2 °C, which is consistent with the trends generally observed in groundwater, as it is 
less subject to thermal variations compared to surface water (Rodier, 2016). The temperatures reported in this study are similar to those obtained by Rahmani et al. (2022) in the Djelfa syncline, where groundwater temperatures range from 16 °C to 22.5 °C. This variation in groundwater temperature may be related to the depth of the aquifer.

Electrical conductivity values range between 1014 µS/cm and 1998 µS/cm, with an average of 1271.8 ± 293.76 µS/cm for all the studied drillings. Electrical conductivity is one of the key parameters used to assess the degree of mineralization in water (El Haissoufi et al., 2011).

These values sometimes exceed the WHO limit for drinking water (Table 3), suggesting potentially high salinity due to the dissolution of mineral salts from the geological substrate. Additionally, high conductivity may result from a slow recharge of aquifers or anthropogenic contamination, such as agricultural activities or industrial discharges (Bougherira et al., 2017).

The pH values vary between 6.71 and 7.53, with an average of 7.05 ± 0.22, indicating neutral to slightly basic water. which are typical of carbonate aquifers. These results are consistent with those reported in the Hodna Basin and the Merdja aquifer (Belhadj et al., 2017; Gouaidia et al., 2017). 

The variation in pH among samples could be explained by the geological nature of the terrain. The geological origin of aquifers significantly influences pH, as water circulating in limestone-rich formations often exhibits a more alkaline pH.

Nitrites (NO₂⁻) and ammonium (NH₄⁺) were detected in very low quantities, with average concentrations of (0.0007 ± 0.001) and (0.01 ± 0.02), respectively, suggesting good oxidation of organic matter and the absence of recent pollution.

The analysis of water from the studied boreholes revealed elevated chloride concentrations, ranging from 129.22 mg/L to 350 mg/L, with an average of 230.30 ± 70.96 mg/L. Given that chlorides are present in nearly all water sources at highly variable concentrations (Ould Cheikh et al., 2011), the high levels observed in these samples likely indicate the dissolution of evaporitic minerals (Bencer et al., 2016). 

All compounds have values below the maximum allowable limit according to Algerian drinking water standards (JORA, 2014), except for nitrates, which exceed the standards, ranging from 50 mg/L to 103.66 mg/L with an average of 79.9 ± 17.81 mg/L, and bicarbonates, which range between 352.85 mg/L and 425.25 mg/L, with an average of 395.1 ± 24.9 mg/L, exceeding the 120 mg/L limit set by the WHO.

High nitrate concentrations can result from the use of fertilizers in agricultural activities. Both synthetic and organic fertilizers are widely used, leading to excessive fertilization. However, poor agricultural practices, such as leaving manure on the surface, facilitate the transfer of nitrogen-based fertilizers through runoff. Additionally, nitrogen enrichment can also originate from wastewater discharges.

This effect is explained by diffuse sources, mainly originating from agricultural and residential areas. These sources include sewage discharges, septic tank leaks, as well as the use of natural and synthetic fertilizers in agricultural practices (Ustaoğlu et al., 2020; Masmoudi et al., 2024).

The high bicarbonates (HCO₃⁻) concentrations in groundwater can be attributed to various processes, including the dissolution of atmospheric CO₂, silicate weathering, and the dissolution of carbonate minerals such as limestone and dolomite, which contribute to increased HCO₃⁻ levels in groundwater (Roy et al., 2020).

3.3. Correlations Between the Different Physico-Chemical Parameters of the Studied Borehole Waters

The correlation matrix (Table 5) was used to identify statistically significant relationships between the physico-chemical parameters of groundwater. This tool helps detect interdependencies that may reveal common sources of contamination or similar geochemical behavior. It is also a prerequisite step for further multivariate analyses such as Principal Component Analysis (PCA) or Hierarchical Cluster Analysis (HCA), which require prior exploration of variable interactions. Similar approaches have been successfully applied in groundwater quality studies in Algeria and other arid regions (Souley Moussa et al., 2018; Kouame et al., 2021; Sakaa et al., 2022; Allaoua et al., 2024).

The Principal Component Analysis (PCA) performed on the 15 physico-chemical parameters shows that the two axes account for 57.06 % of the total variance (the first axis explains 32.29 %, and the second axis 24.77 % of this variance).

According to the correlation matrix (Table 5) and the circle of correlations established by the 
PCA (Figure 2), electrical conductivity was positively correlated with potassium and nitrite (r ranging from 0.51 to 0.66) and negatively correlated with temperature, magnesium, and pH (r ranging from -0.56 to -0.58) (Table 5). The turbidity of the drillings was positively correlated with nitrate and calcium (r ranging from 0.50 to 0.78) and negatively correlated with potassium, sulfate, and magnesium (r ranging from -0.50 to -0.65) (Table 5).

According to the results of Ascending Hierarchical Classification (AHC) (Figures 3 and 4), the ten groundwater samples were grouped into four distinct and relatively homogeneous subgroups, each characterized by specific hydrochemical profiles:

- The 1st subgroup, composed only of drilling FOB2, which exhibits the highest concentrations of electrical conductivity, potassium, nitrite, and chloride, combined with low levels of temperature, magnesium, and a slightly acidic pH (6.71). These features may indicate local contamination sources, likely of anthropogenic origin, such as agricultural runoff or proximity to urban wastewater discharges. 

- The 2nd subgroup, consisting only of FOB3, is distinguished by elevated levels of temperature, magnesium, sodium, iron, ammonium, and chloride, with a moderately neutral pH (7.11). It also shows the lowest levels of potassium and bicarbonate, and no detectable nitrite. The singularity of this profile suggests a site-specific hydrogeological or contamination context.

- The 3rd subgroup, represented by of drillings FAS8 and FAS10, is characterized by high concentrations of calcium, sodium, and bicarbonate, intermediate levels of temperature and conductivity, and absence of nitrite and ammonium. This may reflect moderate mineralization possibly linked to geogenic processes, with limited anthropogenic influence.

- The last subgroup consisting of the remaining boreholes (FOB1, FOB4, FOB5, FOB6, FAS7 and FAS9) presents a heterogeneous profile in terms of the physicochemical parameters analyzed. The diversity within this cluster may be attributed to variable land use patterns and degrees of exposure to human activities.

From a practical standpoint, these groupings reveal spatial heterogeneity in groundwater quality and provide useful insight for targeted monitoring and management. Although some sites belong to different municipalities (Oued El Berdi and El Asnam), their hydrochemical similarities suggest that contamination pathways may be influenced more by land use and pollution sources than by administrative boundaries. This emphasizes the need for integrated, cross-regional groundwater management strategies in semi-arid contexts such as Bouira.

To enhance the understanding of groundwater vulnerability and pollution pathways, future investigations should adopt a multidisciplinary framework combining temporal sampling, hydrogeological modelling, and advanced microbial detection methods. Seasonal monitoring would help capture dynamic changes in water quality, particularly in response to agricultural runoff and climatic variability (Zhang et al., 2023; Zehra et al., 2024). 

The integration of molecular tools, such as quantitative PCR, could improve the detection of pathogenic or VBNC bacteria, thus strengthening health risk assessments (Guo et al., 2021; Fan et al., 2024). An integrated assessment combining microbiological, geospatial and chemical data can deliver a more complete understanding of contamination sources and support evidence-based groundwater management strategies in semi-arid regions (Shehata et al., 2024).

4. CONCLUSIONS

This study explored the physicochemical and microbiological quality of groundwater in the Bouira region to evaluate its suitability for human consumption and provide a scientific basis for sustainable management in semi-arid environments. 

The results highlighted that, although most parameters were within national and WHO standards, elevated nitrate, bicarbonate, and chloride concentrations in several boreholes reflected both geogenic contributions and anthropogenic pressures, particularly from agriculture and domestic wastewater. Multivariate analyses (PCA and AHC) proved effective in identifying contamination patterns and grouping boreholes with similar hydrochemical characteristics, thus supporting a more integrated interpretation of water quality variability.

Microbiological results confirmed the absence of fecal contamination but revealed low levels of mesophilic flora, suggesting minor environmental inputs.

Overall, these findings underline the importance of continuous monitoring, stricter land-use regulation, and preventive management strategies to ensure groundwater safety for drinking purposes and long-term resource sustainability in semi-arid regions such as Bouira.

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