Temporal evaluation of surface water quality in semiarid regions: a case study of the Ouled Mellouk dam in north-western Algeria Open Access

Nowadays, agricultural and industrial development, along with the heavily increased demographic growth, has raised the demand of water supplies from surface water and groundwater resources especially in semiarid and arid environments, such as the Mediterranean regions. Moreover, these regions start to face of a meaningful decrease in precipitation and an increase in pumped water rate to meet the requirement of drinking, agriculture, and industry water requirement (Busico et al. 2021). This situation has led to a significant decrease of the water volume (WV) in several dams, generating worrying issues related to the natural contamination and anthropogenic pollutions of these precious resources (Scott Winton et al. 2019).

In arid and semiarid regions, dam's waters are vulnerable to all kinds of pollution sources such as: (i) untreated solid and liquid wastes, (ii) overexploitation, (iii) intensive use of agricultural fertilizers, and (iv) strong evaporation processes (Kumari & Rai 2020).

In Algeria, a country with a semiarid/arid climate, the dam water is generally utilized for domestic and agricultural purposes. Additionally, in the Middle Eastern Cheliff basin, a region located in the north-western of Algeria, water demand is increasing due to the raising demand of water supply for irrigation, industrial, and municipal use. The region has experienced an important agricultural development in recent years especially after the implementation of two national programs for agricultural development: (1) the National Agriculture Development Program (PNDA) in 2000 and (2) the National Fund for the Regulation of Agricultural Development (FNRDA) in 2001. These two programs have generated an increase in the water demand for irrigation that, along with the higher frequency of severe drought periods, has led to a worrying decrease of dams’ water level in the region. Generally, surface water in the area is not only subject to overexploitation but also to an important quality degradation due to the wastewater discharges and geogenic salinization (leaching of geological formations of the Ouarsenis and Doui massifs). Moreover, in the Rouina-Zeddine sub-basin, a part of the Middle Eastern Cheliff watershed, the drinking water supply and irrigation is provided mainly by the surface water from the Ouled Mellouk dam.

For this reason, its quality must be evaluated to preserve the public health and ensure the high agricultural yields (Guenfoud et al. 2021). There are many parameters that can quantify physical or chemical status of water resources as well as its suitability for human consumption or other utilization (Rufino et al. 2019), such as temperature (T), electrical conductivity (EC), pH, cations and anions, dissolved oxygen, chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD₅), and nutrients. For a good management, the knowledge of these water resources and their quality is a mandatory condition (Busico et al. 2019).

In recent decades, many studies assessed all those processes responsible of water quality degradation in dams that are mainly related to the effect of human activities over the world both on spatial and temporal scales (Ouhmidou et al. 2015; Popovic et al. 2016; Etteieb et al. 2017; Vadde et al. 2018; Talhaoui et al. 2020) and in Algeria (Bouzid-Lagha & Djelita 2012; Mebarkia et al. 2017; Banerjee et al. 2019; Boulaksaa & Laifa 2020; Bouderbala 2021). In addition, several different investigation tools have been applied such as: (i) water quality indices (Sener et al. 2017), (ii) artificial intelligence (Bui et al. 2020), (iii) numerical modeling (Ntona et al. 2022), and (iv) remote sensing data (Elhag et al. 2019). Recently, several authors also evaluated surface water quality of dams located in Algeria using multivariate statistical technique to determine the temporal variation of surface water quality (Bouderbala et al. 2016; Guerraiche et al. 2016; Mebarkia & Boufekane 2020; Bouderbala 2021; Hallouz et al. 2022).

Water quality monitoring represents an effective tool to achieve a sustainable management of water resources (quantity and quality) and protection of aquatic life.

Accordingly, the aim of this study was to assess and quantify the degree of water quality degradation in the dam, particularly on spatial and temporal scales. Moreover, the work also aims to distinguish all those processes related to urban and industrial discharge, water surface evaporation, and siltation due to sediment deposits. For this reason, the monitoring of physicochemical parameters and water pollution of the Ouled Mellouk dam over a period of 7 years (2007–2013) was analyzed for better understanding of all those mechanisms governing the water chemistry and controlling the water mineralization. A multi-analysis approach combining multivariate statistical analysis and hydrogeochemical was applied to reach these aims.

The dam under investigation has been used for the drinking water supply to some cities in the region (Rouina, Bourached, Zeddine, El Mayenne, Bathia, Belaas, El Hassania, and El-Attaf) and for the irrigation of cultivated land in this watershed. During the last years, the water's dam has been released to irrigate a part of the agricultural area in the Middle Eastern Cheliff plain, with an average volume of 20 Hm³, for a total irrigated area of 11,000 ha. Today, the land irrigated by this dam has been considerably reduced following a significant decrease in its water reserve over the last decade due to a decrease in rainfall and water quality degradation.

The Middle Eastern Cheliff watershed is characterized by a semiarid climate with Saharan influences in summer and Mediterranean influences in winter, with rainfall of about 600 mm on the southern slopes of the Dahra, Zaccar and Medjadja mountains and reduced in the valley of the upper and middle Cheliff where they vary between 300 and 400 mm (Madene et al. 2022). The average annual precipitation in the Rouina-Zeddine sub-basin, over a period of 40 years (1971–2012) is about 419 mm (Madene et al. 2020). The evapotranspiration is estimated at 379 mm, mobilizing 86% of the precipitation and the runoff represents 8% of the precipitation, which is 37.15 mm. The groundwater is fed by infiltration, which is estimated at 22.85 mm, or 5% of the precipitation, allowing the leaching of soluble chemical elements, particularly fertilizers and wastewater from urban areas. This region is characterized by an annual average temperature ranging from 13.7 to 18.3 °C with a monthly maximum of more than 31 °C, recorded in July. The dominant soil textures are clayey.

The water sampling was carried out monthly, at different depths during a period of 7 years (2007–2013) for a total of 84 samples, allowing the evaluation of the temporal variation of the surface water quality of this dam. The samples were collected according to standardized techniques, using polyethylene bottles with a capacity of 1 L. The samples were then transported in coolers at 4 °C and the analyses were performed according to the methods approved by Rodier et al. (2009). The temperature, pH, EC, and dissolved oxygen (O_2dis) were measured in situ using WTW ProfiLine 340i Universal Multi-parameter portable instrument (±0.1 °C, ± 0.01 pH, ± 1% CE, and ±1% O_2dis). The instrument was calibrated using appropriate standard solutions before being used. However, the water samples were analyzed for cation and anion concentrations using the standard analytical procedure described by APHA (2005) at the laboratory of the National Hydraulics Resource Agency. The calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), and potassium (K⁺) were acidified with 1% HNO₃⁻ and analyzed using a flame emission spectrometry (CORNING Model 410 Flame Photometer). The chloride (Cl⁻), sulfate (⁠⁠), bicarbonate (⁠⁠), nitrate (⁠⁠), nitrite (⁠⁠), ammonium (⁠⁠),and orthophosphate (⁠⁠) were determined by titration using 0.05 N HCl and calculated with pH 5.5 as end-point monitoring. The charge balance errors in the bulk chemical analysis were ≤ 5% for all water samples. The organic matter (OM), COD, BOD₅, total dissolved solids (TDS), and suspended matter (SM) were determined using atomic absorption spectrometry (HACH DR/2000 Visible Spectrophotometer). In addition, the ionic water chemistry and geochemical modeling (PHREEQC) were used to identify the ionic exchanges and to understand the mineral dissolution and mineral saturation in the surface water of this dam, while multivariate statistical techniques, such as principal component analysis (PCA), was applied to characterize water quality and determine its temporal variation. Statistical analysis was performed using SPSS 16.0 and XLstat 2015 software. The suitability of Ouled Mellouk water dam for drinking water supply and irrigation has been assessed compared to inorganic concentration with the WHO standards and applying the Richards method, respectively.

There is always a certain difference between the sum of cations and anions, but if the calculated error is less than ± 5%, the analysis can be considered acceptable. In this case, 99% of the samples present an ionic balance within this range.

According to the general statistics (Supplementary material, Table S1), the standard deviation values for all elements are lower than the mean values indicating a hydrochemical homogeneity of the water sampled during the study period. Furthermore, the coefficients of variation are high for some variables such as NO₃ (CV = 73%), COD (CV = 83%), and BOD₅ (CV = 73%), and very high for the variables K (CV = 114%), SiO₂ (CV = 101%), NO₂ (CV = 140%), NH₄ (CV = 109%), PO₄ (CV = 230%), and TDS (CV = 106%), whereas this coefficient is lower for total hardness (TH) (CV = 5%). Generally, these high CV can indicate a significant variability, hence the necessity to evaluate the temporary chemical variation of the elements.

Several significant correlations exist between the different variables. For example, a high correlation (R > 0.7) was observed between the chemical parameters Ca²⁺, Mg²⁺, and the TH and between the chemical parameters Mg²⁺, ⁠, Cl⁻, and the total mineralization (TDS) indicating a mineralization of evaporitic origin which could suggest the dissolution of NaCl and MgSO₄ formations (gypsum and halite).

However, also high correlation between the WV and the Ca²⁺ is observable probably due to the leaching of clay and carbonate formations by the runoff. The TDS values were negatively or very weakly correlated with the WV of the dam.

The main purpose of PCA application was to characterize the water chemistry of the dam for the observation period (2007–2013) and to give a preliminary idea about the processes responsible of groundwater mineralization with a spotlight on pollution elements. Table 1 shows the correlation between the variables and the principal axes done to determine the possible factors contributing to the hydrochemistry of the water samples. Eleven parameters were involved, and three factors were identified (Supplementary material, Table S2). F1, F2, and F3 explaining the 81.30% of the total variance.

The first axis (F1) representing 49.92% of the total variance indicates a high positive correlation between Mg²⁺, ⁠, Cl⁻, O₂, EC, TH, and TDS indicate the concomitance of two different processes: (i) the influence of the anthropogenic pollution from the liquid and solid wastes and (ii) the dissolution of the evaporative and saliferous mineralization (halite). Also a very high correlation between the dry residue, EC, Cl⁻, Mg²⁺, ⁠, and TH was identified. However, the negative correlation between ⁠, Mg²⁺, and Cl− and the WV can be related to the decrease of the WV in the dam under the effect of several phenomena such as: (i) the interaction between the solid sludge and water, (ii) evaporation and precipitation of minerals. The second axis (F2) explains the 19.38% of the total variance and shows a high positive correlation between WV, Ca²⁺, Na⁺, K⁺, and TH. It is characterized by the water rich in Ca²⁺ and Na⁺. Calcium can be derived from the Jurassic limestone of the Doui mountain, while the Na⁺ can be derived from the dissolution of halite in Ouarsenis mountains (Amrouna mountain). The third axis (F3) explains the 12% of the total variance and shows a positive correlation between ⁠, ⁠, and SiO₂. It can be an indication of agricultural fertilizers, municipal solid and liquid wastes, and the weathering of silica-rich soils.

The pH values vary from 6.0 to 8.3 with an average of 7.8 during the study period (Figure 3(b)). This could be due to the presence of the limestone formation in the watershed rich in carbonates. Anyway, the pH values are classified within the WHO standards.

The EC values range from 800 to 1,800 μS/cm with an average of 1,340 μS/cm (Figure 3(c)). These values are between the threshold values of FAO standard (EC < 3,000 μS/cm at 25 °C for irrigation), otherwise the EC values higher than 666 μS/cm involve significant water mineralization of drinking water supply (Rodier 2009).

TDS values ranged from 92 to 382 mg/L with an average of 260 mg/L (Figure 3(c)), indicates a less-to-moderate water quality. The TDS limit value for irrigation water is 2,000 mg/L (Ayers & Westcot 1988).

O_2dis values ranged from 4 to 10 mg/L (Figure 3(d)). These values show that the water of Ouled Mellouk dam is less oxygenated. The temporal evolution of O_2dis shows a decrease during the spring period than the summer period, probably due to the natural decrease of this element solubility when the temperature raises because the cold water contains a high amount of the O_2dis and the presence of the pollutants in the streams (Rodier et al. 2009). According to Gaujous (1995), the origin of oxygen in the natural environments is related to the photosynthetic activity of aquatic plants and its dissolution from the atmospheric oxygen.

The analysis of the mineralization parameters in the Ouled Mellouk dam for the period 2007–2013 (Figure 4) shows that:

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  The Ca²⁺ concentration varies between 29 and 170 mg/L. These values are acceptable according to the WHO standards (200 mg/L). The maximum value is observed in September 2012 due to the lithology of the land crossed (limestone formations) and gypsum formations (CaSO₄, 2H₂O).

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  The Mg²⁺ concentration ranges from 18 to 101 mg/L. The temporal evolution of the Mg²⁺ is almost stable. The presence of Mg is due to the dolomites dissolution of the Doui and Amrouna mountains.

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  The K⁺ variation observed is weak because of the dam water dilution.

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  The Na⁺ varies between 21 and 211 mg/L. The higher concentrations are recorded during the precipitation or flood periods due to the leaching of the evaporate deposits from the saline formations of the Ouarsenis mountains. In addition, the decrease in Na⁺ concentration is observed during the summer period due to the drought condition.

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  The TH is related to the leaching of the land crossed, it results from the contact of the groundwater and surface water with the rock formation (Belghiti et al. 2013). The value of the TH varies from 16 to 68 °F. This variation depends mainly on the geochemical nature of the rocks encountered in the Rouina-Zeddine basin, especially the dolomite–limestone rocks alteration of the Doui and Amrouna mountains.

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  The Cl⁻ can be of geological origin, mainly linked to the dissolution of saline formations, or anthropogenic in this region (Mastrocicco et al. 2021). Its concentration varies between 28 and 352 mg/L. The high values were recorded during the winter period, related to the nature of the land crossed during the runoff.

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  The concentration ranges from 92 to 382 mg/L. The high concentrations are recorded during the two rainy years (2012 and 2013) due to the evaporate deposits leaching from the gypsum formations of the Ouarsenis mountains and the oxidation of the sulfides found in the geological layers. The decrease in the sulfate concentrations is observed during the summer period. However, the concentrations are less compared to Cl− concentrations during the rainy periods (Melghit 2013).

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  concentration varied from 110 to 336 mg/L. The values recorded for during the observation period are important between January and February (wet period). This element has a geological origin, mainly linked to the limestone formations presented in the watershed.

The analysis of the nitrogen and phosphate parameters in the Ouled Mellouk dam for the period 2007–2013 (Figure 5) shows that:

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  Ammonium (⁠⁠) is largely derived from the domestic, agricultural, and industrial activities (wastewater, etc.) (Rodier et al. 2009). The concentration ranges from 0 to 0.276 mg/L (low concentration). It remains below 2 mg/L in the dam reflecting a good water quality according to the surface water suitability classes (Mebarkia & Boufekane 2020).

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  The presence of the nitrites (⁠⁠) in water is a sure sign of pollution phenomenon. The comes from an incomplete oxidation of the ammonium or from a reduction of the ⁠. The value of this parameter in the studied water is relatively low and varies between 0 and 0.46 mg/L.

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  Nitrate (⁠⁠) is the final stage of the organic nitrogen oxidation. In this study, concentration is low and ranges from 0 to 10.9 mg/L. Nitrate could be related to leaching from the agricultural soil in the watershed of the dam. The WHO regulations recommend a maximum limit value of 50 mg/L for the natural waters, while the content of this study remains within the norms.

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  In this study, the phosphate (⁠⁠) concentrations range from 0 to 1.652 mg/L. The high values are measured in years 2011, 2012, and 2013 where the peak is observed in February (1.652 mg/L). This increase of is connected to the rainy years which generates an increase of organic compounds in the water during flood, which favors a very high mineralization of OM. Phosphate is among the anion easily fixed by the soil and their natural presence in water is linked to the characteristics of the land crossed and the OM decomposition. Values higher than 0.5 mg/L must constitute an indication of pollution according to the WHO regulations. Phosphate plays a very important role in the development of algae. It is likely to promote their multiplication in lake waters where it contributes to eutrophication.

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  For the silica element, high values are measured in periods of flooding and rain. The silica concentrations vary between 0 and 10.27 mg/L. The increase in SiO₂ content can be due to the presence of the colloidal matter silica grains for the organic or mineral origin.

The projection of Ca²⁺ vs. shows that the water points are all located above the line indicating an excess of Ca²⁺ over ⁠. This excess in Ca²⁺ is due to the dissolution phenomenon of carbonates and gypsum. The high correlation between calcium–sulfate–bicarbonate confirms the evaporitic origin of the calcium by dissolution of anhydrite and gypsum.

In natural water, the presence of the Na⁺ and Cl⁻ is attributed to the halite dissolution found in Triassic formations or even another origin (natural or anthropogenic). The water points present a stoichiometric distribution of Cl⁻ and Na⁺ ions indicating the dominance of the dissolution phenomenon of saliferous formations (Triassic formation) of the Ouarsnis mountain which increases the concentration of Na⁺ and Cl⁻ after infiltration of water toward the aquifer. The evolution diagram of (Ca²⁺/(⁠ + ⁠) vs. Na⁺/Cl⁻ confirmed an excess of Na⁺ compared to Ca²⁺. This excess in Na⁺ is due to the phenomenon of base exchanges where the bedrock clays can release Na⁺ ions after fixing Ca⁺.

Several authors have used others diagrams and relations to determine the dominant geochemical processes in the dam water. However, the study of the relationship between (Ca²⁺ + Mg²⁺) vs. (⁠ + ⁠) gives a clearer relation on the exchange processes of cations (Figure 6) (Farid et al. 2013, 2015).

Figure 6(e) shows that the points around the equilibrium line (Ca²⁺ + Mg²⁺ = + ⁠) are clearly due to the dissolutions of calcite, dolomite, and gypsum(Rajmohan & Elango 2004).

The relationship between and Na⁺ (Figure 6(f)) shows that several points are below the equilibrium line, suggesting the silicate weathering. The graph (⁠/Na⁺ vs. Ca²⁺/Na⁺) related to the evaporative dissolution and silicate weathering processes highlights the silicate mineral phases in the hydrochemistry of the water dam for the study period (2007–2013). The graph (⁠/Cl⁻ and ⁠) – EC – shows the presence of two poles: the first is gypsiferous with many water samples where the ions Cl⁻ and are dominant. This pole is accompanied by the high conductivity value, reaches 1,800 μS/cm. The second pole is carbonated; it is characterized by a dominance of ions for the conductivity values less than 1,000 μS/cm which are linked to the carbonate formations.

The and Cl⁻ ions are derived from two different formations, from gypsum and Cl⁻ from halite dissolution and probably from the anthropogenic pollution. Figure 6(i) shows that most of the water points present a ratio (Cl⁻/⁠) lower than 1, indicates the dominance of ions over Cl⁻, which explains an evaporitic origin.

To summarize, the water quality deterioration of Ouled Mellouk dam is the consequence of several factors, such as the following: (1) climate variation (low precipitation and high temperature), (2) anthropogenic impact (wastewater, urban and industrial waste, the use of fertilizers, etc.), (3) the influence of geological formations in the basin (in association with the climatic parameters of the region: high temperature, high evaporation, and low precipitation), and (4) increase of the erosion phenomena in the basin. This has led to a very high concentration of the chemical elements of the dam water through time, causing in some cases water quality deterioration.

Finally, the Mellouk dam. The undersaturation in gypsum, anhydrite and halite causes a continuity in the dissolution and an enrichment of the runoff; and water infiltration by these elements. In addition, the carbonate minerals are sometimes close to the equilibrium, often, in oversaturation and tend to precipitate in the form of calcite and dolomite.

According to the hydrochemical analysis results for this study, the major ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, ⁠, ⁠, and Cl⁻) in the dam water originate, mainly, from the dissolution of the saline and calcareous geological formations during runoff (wet periods) which is related to the water–rock interaction process. The suspended solid values indicate that more than 16% of the samples exceed 35 mg/L, due to the leaching of solids and OM which can be attributed to the influence of heavy rainfall during the flood periods. Also, an increase in the nitrogen and phosphate elements (⁠⁠, ⁠, ⁠, and ⁠) has been observed during the wet periods (heavy rainfall) than the dry periods due to the leaching of fertilizers used in agriculture .

In the semiarid regions, the dam water provides a portion of the crops' irrigation since the surface water of the Ouled Mellouk dam is used for the irrigation of the Kherba-Abbadia agricultural perimeter on a surface of 8,533 ha.

The Richards’ diagram (Figure 8(b)) classify the water sample mainly as C3S1, indicating water that can be used without particular control. The classes C3S1 and C3S2 can be used for the irrigation, although the salinity must be controlled. Finally, and according to the Wilcox classification (Figure 8(c) and 8(d)), the water of the Ouled Mellouk dam is classified to be good.

This study focuses on the monitoring and evaluation of the water quality in Ouled Mellouk dam which represents a large hydraulic complex in the Rouina-Zeddine basin, located in north-western Algeria. It is intended for drinking water supply and irrigation. It covers the water needs of the neighboring cities (Rouina, Bourached, Zeddine, El Mayenne, Bathia, Belaas, El Hassania, and El-Attaf) and the irrigation of El Amra and Abadia.

The results of the physicochemical and nutrient analysis of water samples from this dam obtained during the study period (2007–2013) show that:

• The water is classified as a chloride–calcium water with an alkaline water quality; the pH values generally exceed 7.5; an average conductivity of 1,340 μS/cm reflecting an excessive mineralization for domestic uses. However, important rates of dry residue, OM, and TSS revealing an organic pollution marked by strong organic and mineral loads during the spring period than in summer period accompanied by a slight decrease of dissolved oxygen.

• 42% of the samples from the study period indicate O_2dis values higher than 8 mg/L, which favors the development of algae in this dam.

• Suspended solid values indicate that more than 16% of samples exceed the standard value (SM = 35 mg/L), which is due to leaching of particulate solid and OM upstream of this dam. On the other hand, the COD expresses the amount of oxygen needed to oxidize the OM in the water with an oxidizer represents only a rate of 5% of the samples that exceed the WHO standards.

• The major ions in the dam water may originate from the dissolution of the saline and carbonate geological formations traversed during river runoff and related to the water–rock interaction process and anthropogenic activities. The contents of nitrogenous and phosphate materials (⁠⁠, ⁠, and ⁠) indicate the surface water of poor quality to excessively polluted. It is due to the oxidation of nitrogenous OM.

• The PCA identified three major components representing 81.3% of the total variance of the water quality variables for this period, which can be related to the influence of anthropogenic pollution from the solid and liquid waste discharge, intensive use of agricultural fertilizers and due to the probable dissolution of some minerals, water–solid interaction and weathering processes of carbonates and silicates.

• The pollution index mainly shows that the water quality of this dam can be either moderately polluted or more polluted for most of the samples.

• The Richards and Wilcox classifications show the eligibility of the water quality for irrigation.

For a deeper understanding of the hydrochemical behavior of surface water in the middle Cheliff, the following recommendations aim to clarify some of the problems observed:

• Monitoring and reducing the use of fertilizers and pesticides to minimize or avoid migration of excesses to the dam.

• Regular monitoring of all sediment physicochemical parameters aimed at building a database to assess water quality trends.

• The extension of investigations to other organic pollutants, such as hydrocarbons and pharmaceuticals.

• The assessment of biological water quality of the dam through the presence or absence of benthic macroinvertebrates and microscopic algae.

• Providing additional treatment facilities for other tributaries of the Cheliff wadi and avoiding the infiltration of domestic and industrial effluents into surface water and the use of pipeline transfers to existing treatment plants.

The study is carried out within the framework of the SWATCH project (Prima project) funded by the DGRSDT, Algeria.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.