The rice cultivation area of Maga is located in the Far North Region of Cameroon, in the Mayo-Danay department. This area covers an area of 2000 km² and is situated between 10˚32'57'' and 11˚58'00'' latitude North, and between 14˚34' and 15˚10'13'' longitude East. The climate here is Sahelian-Sudanese, with a long dry season starting in early October and ending in early May, and a short rainy season from June to September characterized by heavy rainfall episodes. The rainfall varies between 530 and 630 mm/year, with peaks in August and September. The average temperature is 28˚C, and the annual evapotranspiration is 1800 mm ( Ngatcha et al., 2007 ). The morphological aspect is dominated by a floodplain that is part of an extensive geomorphological unit that extends to Nigeria, Niger, and Chad ( Sighomnou, 2003 ).

The study area (Maga) is located in the Logone-Chari floodplain, which consists of recent and old Quaternary formations from the Lake Chad Basin. The thickness of these formations generally varies between 50 and 70 m ( Schneider & Wolff, 1992 ; Biscaldi, 1970 ). These sedimentary formations have a large extension and cover the central plain up to Lake Chad ( Figure 1 ).

The Logone-Chari floodplain is composed of yayrés, which are territories prone to flooding by the Logone River and where water stagnated for five to seven months before the construction of the artificial lake and the SEMRY rice fields in Maga in 1979 ( Ngatcha et al., 2007 ). In this area, the dominant soils are vertisols and hydromorphic black clays ( Brabant & Gavaud, 1985 ). During the dry season, hydromorphic soils exhibit desiccation cracks that become waterlogged at the beginning of the rainy season. This waterlogging causes the soil to swell, the closure of these cracks, and a decrease in surface permeability. Previous studies on the analysis of the sources of water mineralization in the area by studying resistivity have shown a decrease in resistivity when moving from Logone to the west.

These studies have also highlighted some irregularities, such as the values of 2000 Ω∙cm⁻¹ to 3000 Ω∙cm⁻¹ in the southwest of Guirvidig, indicating a supply from surface waters. However, the low resistivities obtained between Pouss and Mazera indicate low infiltration of surface waters due to impermeable clayey soils ( Seignobos & Moukouri, 2000 ). The majority of the waters belong to a calcareous carbonate facies, with a possible enrichment in sodium.

In order to study the mineralization of groundwater, sampling was carried out during 06 campaigns from October 2017 to June 2019, resulting in a total of 90 samples. A network of 15 points was established to ensure good coverage of the variability of groundwater quality in the area. The selection of sampling points took into account parameters such as the depth of the groundwater level and the location of the point relative to the lithology. For all water samples, pH, temperature, TDS, and EC were measured in situ using a multiparameter probe (Hanna HI 98130). For chemical analysis, the samples were transported and stored in the laboratory according to standard methods of the WHO (2011) . The main ions were analysed using the following methods: volumetry for calcium (Ca²⁺), magnesium (Mg²⁺), bicarbonates ( $HC{O}_3^{-}$) and chlorides (Cl⁻); spectrophotometry for sulfates ( $S{O}_4^{2-}$) and nitrates ( $N{O}_3^{-}$); flame photometry for sodium (Na⁺) and potassium (K⁺) ions. These analyses followed the recommended methods by Rodier (2009) and WHO (2011) .

The obtained results of physicochemical analysis were processed using hydrochemical data interpretation methods. The Piper diagram ( Piper, 1953 ) was used to determine the water typology, binary diagrams were used to understand the origin and processes of groundwater mineralization, and the Chadha diagram ( Chadha, 1999 ) was used to identify various processes involved in groundwater mineralization.

The results of physicochemical analysis of groundwater during the observation period are recorded in Table 1 .

The average (Aver) temperature of groundwater ranges between 29˚C and 30˚C. The lowest temperature recorded was 27˚C in February 2019, while the highest was 34.1˚C in February 2018. The pH values throughout the campaigns varied from 6.44 in October 2017 to 8.33 in October 2018. Generally, pH values near 8 were obtained in the Pouss area, while values closer to 6 were observed in the Guirvidig area. The spatial distribution of electrical conductivities varied on average between 110 µS/cm and 1260 µS/cm. The highest EC values were observed in October, which corresponds to the period of high-water levels in the study area.

The concentrations of Ca²⁺ ranged from 0 to 61 mg/L. These extreme values were obtained during the same campaign in October 2017, which also had the highest average concentration (12 mg/L) and the highest standard deviation (19.63 mg/L) among all the campaigns. However, the concentration of Mg²⁺ in the area varied from 3 to 28 mg/L over the six campaigns. The highest average concentration was observed in June 2019 with a value of 15.27 mg/L. The variation in concentrations during this campaign was remarkable, with the highest standard deviation (7.11) and a coefficient of variation of 0.47. Higher values were found in the Guirvidig area. Additionally, the concentrations of Na⁺ throughout the campaigns ranged from 8 mg/L to 285 mg/L, with average concentrations ranging from 72.59 to 94.88 mg/L. The standard deviation and coefficient of variation were high, at 70.01 mg/L and 0.89, respectively. The lowest concentrations were observed during the dry season campaigns (February). The concentrations of K⁺ were relatively low, with an average value ranging from 0.41 to 2.93 mg/L, a moderate standard deviation of 0.25, and a high coefficient of variation of approximately 1.54. The minimum and maximum values were 0.1 and 12.2 mg/L, respectively.

The concentrations of Cl⁻ varied between 0 and 43 mg/L, with average concentrations ranging from 1.73 to 4.68 mg/L. The distribution of chloride concentrations was highly variable, as indicated by the standard deviation (ranging from 3.95 to 10.93) and coefficient of variation (ranging from 2.06 to 3.24). On the other hand, $N{O}_3^{-}$ concentrations ranged from 1 mg/L to 93.7 mg/L, with average concentrations ranging from 9.01 to 20.31 mg/L. The contribution of each sampling point to mineralization varied, as evidenced by standard deviations ranging from 7.0 to 21.35 and coefficients of variation ranging from 0.50 to 1.66 over the six campaigns. The values of $S{O}_4^{2-}$ ranged from 0 to 57 mg/L, with average concentrations ranging from 1.13 to 6.67 mg/L. The highest values were recorded during the October campaigns, which correspond to the high-water period, while the lowest concentrations were observed during the February campaigns, which represent the low-water period. Finally, the $HC{O}_3^{-}$ concentrations in groundwater ranged from 53 mg/L to 702.32 mg/L, with averages ranging from 233.30 to 355.90 mg/L. The concentrations varied considerably, with high standard deviations ranging from 120.72 to 171.33 and coefficients of variation ranging from 0.46 to 0.68.

The data on major ions plotted on the Piper diagram ( Piper, 1953 ) generally show that the groundwater in the Maga irrigated rice perimeter is mainly of the bicarbonate-sodium and potassium, and bicarbonate-calcium and magnesium types ( Figure 2 ). The first facies are characteristic of the waters of the cultivated areas of the irrigated perimeter of Maga East and West, and the second facies are dominant in the Pouss areas. The diagram indicates a dominance of weak acids for both water facies, with a dominance of alkaline earth metals in the bicarbonate-calcium and magnesium facies ( Figure 2(a) , Figure 2(c) , Figure 2(e) , Figure 2(f) ), and a dominance of alkalis over alkaline earth metals in the bicarbonate-sodium and potassium facies ( Figures 2(a)-(f) ). Consequently, the waters in the cultivated area of the irrigated perimeter are enriched in sodium and potassium concerning cations, while bicarbonates remain the dominant anion.

The creation of a graphical representation of facies based on the quantities of reacting ions is important for confirming the presence of different facies characterizing groundwater. Given the dominance of bicarbonate, sodium, and magnesium ions, two diagrams ( Figure 3 ) using the ratios Na⁺/Mg²⁺ - Cl⁻/ $HC{O}_3^{-}$ and Na⁺/Ca²⁺ - Cl⁻/ $HC{O}_3^{-}$ have been constructed. Both diagrams show the concentration of ion ratios in three poles with a predominance of the Bicarbonate Sodium facies, indicating the previously determined facies that characterize the aquifer. This result will lead to studying the source of mineralization by considering the overall average of all analyses.

The dissolved chemical species in water and their relationships with each other can reveal the origin of mineralization and the processes that have contributed to the mineral composition of the analyzed water ( Aboubaker et al., 2013 ; Diaw et al., 2012 ; Kuldip-Singh et al., 2011 ; Jalali, 2009 ; Gupta et al., 2008 ).

Saturation indices (SI) of minerals are used to evaluate mineralization because the water chemistry is controlled by the equilibrium of solid phases ( Appelo & Postma, 1993 ). SI was calculated using PHREEQC V.2 ( Parkhurst & Appelo, 1999 ), which can be accessed through the free version of the software Diagrammes ( Simler, 2007 ). The software was utilized to calculate the SI of the following water minerals: calcite (CaCO₃), dolomite CaMg (CO₃)₂, aragonite (CaCO₃), anhydrite (CaSO₄), gypsum (CaSO₄, 2H₂O), and halite (NaCl).

The calculations showed that carbonate minerals have different degrees of saturation. The saturation index of dolomite ranges from −3.31 to −0.34, while the intervals for calcite vary from −2.19 to −0.27, and aragonite SI ranges from −2.34 to −0.41 ( Figure 4 ). Assuming equilibrium occurs within the range of −0.5 to +0.5, the results indicate that dolomite, calcite, and aragonite are in an undersaturated state. Evaporite minerals exhibit lower degrees of saturation than carbonate minerals ( Figure 4 ). Gypsum records indices ranging from −5.17 to −3.11, followed by anhydrite with an index ranging from −5.39 to −3.33, and finally halite with indices ranging from −9.64 to −6.85. All these minerals are in a highly undersaturated state ( Dindane et al., 2003 ).

The study of correlations through binary graphs between the concentrations of major elements (Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, $S{O}_4^{2-}$, $HC{O}_3^{-}$, and $N{O}_3^{-}$) and the total dissolved solids (TDS) ( Figure 5 ) helps identify the origin of mineralization in the sampled water.

Observing Figure 5 highlights the contribution of each major element to the total mineralization of water. The results of chemical analysis of groundwater projected onto the binary diagrams have revealed a significant relationship between sodium and bicarbonates in water mineralization, with respective correlation coefficients of r = 0.73 and r = 0.88. It also appears that magnesium ions (r = 0.61) have a moderate influence on the mineral content of these groundwater samples. Calcium, potassium, chlorides, nitrates, and sulfates show only a weak relationship with mineralization (r = 0.40, r = 0.47, r = 0.35, r = 0.33, and r = 0.23).

Dissolved chemical species and their relationships with each other can reveal the origin of solutes and the processes that have generated the chemical composition of water ( Touhari, 2015 ). The interrelation is studied through the analysis of binary diagrams, which allow the identification of the source of dissolved salts in water. Considering that the studied water facies are bicarbonate sodium to potassium, bicarbonate magnesium, and then calcic, diagrams Na⁺ + K⁺ and Ca²⁺ + Mg²⁺ based on $HC{O}_3^{-}$ appear most relevant.

1) Na⁺/Cl⁻ ratio

The Cl⁻ and Na⁺ ions present in groundwater can have various origins. Their presence can be natural, either linked to the dissolution of halite present in the surrounding geological formations, or due to inputs from meteoric precipitation, particularly enriched in Cl⁻ and Na⁺ from seawater. However, these ions can also have anthropogenic origins. The binary diagram ( Figure 6(a) ) representing the evolution of Na⁺ as a function of Cl⁻ shows an excess of Na⁺ content for almost all samples, indicating the existence of another source for sodium ions other than the dissolution of halite. The analytical data in Figure 6(a) deviating from the slope of 1 indicate that a significant fraction of sodium is associated with an anion other than chloride.

2) Ca²⁺/ $HC{O}_3^{-}$ and Mg²⁺/ $HC{O}_3^{-}$ Ratio

The study of the relationship between the dissolved concentrations of Ca²⁺, Mg²⁺, and $HC{O}_3^{-}$ ( Figure 7 ) in water allows for the identification of the main reactions involved in the dissolution of these ions, as described by the following equations [40]:

$CaC{O}_3+H_{2}C{O}_3\to C{a}^{2+}+2HC{O}_3^{-}$ (1)

$CaMg{\left(C{O}_3\right)}_2+2H_{2}C{O}_3\to C{a}^{2+}+M{g}^{2+}+4HC{O}_3^{-}$ (2)

$CaMg{\left(C{O}_3\right)}_2+2H_{2}C{O}_3\to CaC{O}_3+M{g}^{2+}+2HC{O}_3^{-}$ (3)

The linear correlation between Ca²⁺ and $HC{O}_3^{-}$ allows for the classification of water points into two distinct groups. The first group, characterized by points located above the slope of 1, indicates an excess of Ca²⁺ compared to $HC{O}_3^{-}$, suggesting the dissolution of gypsum with an ion exchange effect. The second group consists of points below the slope of 1, indicating a deficit of Ca²⁺ compared to $HC{O}_3^{-}$. This could be explained by the secondary precipitation of calcite and dolomite and/or base exchange (Na⁺ for Ca²⁺ and Mg²⁺ for Na⁺) on the clay minerals of the aquifer, followed by carbonate dissolution.

3) $\left[\left(N{a}^{+}+K^{+}\right)-C{l}^{-}\right]$ vs $\left[\left(C{a}^{2+}+M{g}^{2+}\right)-\left(S{O}_4^{2-}+HC{O}_3^{-}\right)\right]$ ratio

To determine the dominant geochemical processes in groundwater, researchers have used various diagrams. One of these diagrams is the study of the relationship between $\left[\left(N{a}^{+}+K^{+}\right)-C{l}^{-}\right]$ and $\left[\left(C{a}^{2+}+M{g}^{2+}\right)-\left(S{O}_4^{2-}+HC{O}_3^{-}\right)\right]$, which provides a clearer understanding of cation exchange processes by focusing solely on the reactions that may occur between clay minerals and the solution, while excluding ions potentially derived from other dissolution reactions of carbonate and evaporitic minerals ( Farid et al., 2015 ; Kraiem et al., 2015 ; Garcia et al., 2001 ). Plotting the data obtained from water analyses on this diagram ( Figure 8 ) shows that the samples are located in zones 3 and 4, where the difference between cations (Ca²⁺ and Mg²⁺) and anions ( $HC{O}_3^{-}$ and $S{O}_4^{2-}$) is negative.