Seasonal Variations in the Hydrogeochemistry and the Domestic-Agro-Industrial Water Quality of the Granite-Gneiss Fractured Rock Aquiferous formations in Wum, North West Region, Cameroon

Variations in the and the Domes-tic-Agro-Industrial Water Quality of the Granite-Gneiss Fractured Rock Aquif- erous formations in Abstract Wum the capital of Men chum Division is an important agricultural area in the Northwest Region in Cameroon vital for the food security of the country. The study objective was to determine and evaluate the seasonal variations during four hydrogeological seasons; dry (March), drywet (June), wet (September) and wetdry (December) in the groundwater chemistry, groundwater rock interactions and do-mestic-agro-industrial groundwater quality using hydrogeochemical tools; physicochemical parameters, ionic ratios, gibbs diagrams, piper diagrams, durov diagrams, Total Hardness HT, Water Quality Index WQI, Sodium Adsorption Ratio SAR, Percent Sodium %Na, Kelly’s Ratio KR, Permeability Index PI, Magnesium Adsorption Ratio MAR, Residual Sodium Carbonate RSC and Wilcox index. From field physicochemical parameters; dry season, temperature, 21.5-25.3°C; EC0.01-0.51mS/cm; TDS, 0.01-0.34mg/L; drywet, pH, 2.6-6.9; Temperature, 21.7-23.1°C; EC, 0.01-6.30mS/cm, TDS, 0.01-4.22mg/L; wet pH, 3.3-7.1; Temperature, 20.8-26.6°C; EC, 0.17-3.90mS/cm, TDS, 0.11-2.61mg/L and wetdry, pH, 5.2-7.5; Tem- perature, 21.8-24.1°C; Kelley’s Ratio (KR), Sodium Adsorption Ratio (SAR), Electrical Conductivity (EC), Total Dissolved Solid (TDS), USSL and Wilcox index were determined, evaluated and found to be suitable for agro-industrial uses in all seasons. Permeability Index (PI) and Magnesium Adsorption Ratio (MAR) were not suitable in some areas and in some seasons. These hydrogeochemical facies, parameters and indices will serve as an important part of the toolkit for soil and water parameter eval- uation for future development of agro-industries in the area of Wum.


Introduction Geology and hydrogeology
Wum is located on the oku volcanic field on the Cameroon Volcanic Line CVL. The CVL is a N30E oriented tectonic structure made up of volcanic islands, continental volcanoes, plutonic and volcanic complexes ranging in age from 82 Ma to present. The CVL bears the active Mt Cameroon with latest eruptions in 1999 and 2000, with over 100 cinder cones and 40 maars presumed to be not older than 1 Ma Gaudru and Tchouankoue [3]. The Nyos maar is located in the southern continental part of the CVL and belongs to the monogenetic Oku volcanic field that culminates at Mt Oku (3011m). Volcanic activity in the Oku volcanic field ranges from effusive to explosive, and a wide range of compositions have been erupted including basanite, basalt, hawaiite, mugearite, trachyte, and rhyolite. Basement rocks are gneisses and granitoids, which formed during the Pan-African orogeny (~600 Ma) PinteÂ et al., [4]. The basement of Wum and its vicinity is mostly formed of granitic rocks of dominant micropegmatitic texture. Basaltic rocks appear as small flows directly overlapping the granitic basement. Pyroclastic surge deposits are found near the Lake Nyos crater and cap the basalt flows to the west of the volcano. The pyroclastic rocks contain broken pieces of basement granites and peridotite xenoliths Schmidt et al., 2017 [5]. The aquiferous formations of Wum are mainly the regolith and the fractured crystalline rocks; granites gneisses and basaltspresented in figure 2.
The suitability of water for irrigation depends on the effects of the mineral constituents of water on both the plant and the soil [6]. Excessive amounts of dissolved ions in irrigation water affect plants and agricultural soil physically and chemically, thus reducing the productivity, thus parameters such as Electrical Conductivity EC, sodium percentage (Na%), Sodium Adsorption Ratio (SAR), Magnesium Adsorption Ratio (MAR), Residual sodium carbonate and Permeability Index (PI) were used to assess the suitability of ground water for irrigation purposes [7].
Assessment of water for agro-industrial suitability is important inorder to determine whether the water will have an adverse effect on the soil properties if used as irrigation water [8].This is vital for the development of an agricultural zone like Wum where farming is the major occupation of the citizens and there are currently studies going on to create large scale cash crop plantations.   [5]. dustrial Water Quality of the Granite-Gneiss Fractured Rock Aquiferous formations in Wum, North West Region, Cameroon. J Environ Sci Curr Res: S1001.

Materials
The field materials and equipment used in this study are listed in Table 1.

Methods
Prior to field tests, measurements and sampling, a reconnaissance field survey was carried out to identify and select representative wells and springs ISO 5667-1 [9].
Field measurements, tests and sampling were carried out in four hydrogeological seasons: dry (March), drywet (June), wet (September) and wetdry seasons (December). The study area was divided into 5 sections representing the main quarters. 31 representative wells and 7 springs were tested. 10 samples two samples per section were analyzed per season, except in the dry season where one sample was collected per section as many wells got dry. Seasonal measurements were carried out in situ for: coordinates of wells, Surface elevation, Well water level, dug wells depths well diameter, Electrical Conductivity (EC), pH, Total Dissolved Solids (TDS) and temperature. groundwater samples were collected in a High Density Polyethylene (HDPE) 500 ml bottles, sealed and sent to the laboratory using standardprotocols ISO 5667-3 [10], ISO 5667-11 [11] and methods APHA [12] to analyze for: Major cations in mg/L: Ca 2+ , Mg 2+ , Na + , K + and NH 4 + .
Major anions in mg/L: HCO 3 -, Cl -, SO 4 2-, HPO 4 2-and NO 3 -Ionic ratio for indicative elements is a useful hydrogeochemical tool to identify source rock of ions and formation contribution to solute hydrogeochemistry Hounslow [13]. These were used in this study.
Gibbs diagram is a plot of Na + / (Na + +HCO 3 -Ca 2+ ) and Cl -/ (Cl -+H-CO 3 -) as a function of TDS are widely employed to determine the sources of dissolved geochemical constituents Gibbs [14]. These plots reveal the relationships between water composition and the three main hydrogeochemical processes involved in ions acquisition; atmospheric precipitation, rock weathering or evaporation crystallisation. Pipers diagram is a graphical representation of the chemistry of water sample on three fields; the cation ternary field with Ca, Mg and Na+K apices, the anion ternary field with HCO 3 , SO 4 and Clapices. These two fields are projected onto a third diamond field Piper [15]. The diamond field is a matrix transformation of the graph of the anions [SO 4 2-+ Cl -]/Ʃ anions and cations [Na+K]/Ʃ cations. This plot is a useful hydrogeochemical tool to compare water samples, determine water type and hydrogeochemical facies Langguth [16].This has been used here for these purposes. Durov diagram is a composite plot consisting of two ternary diagrams where the mill equivalent percentages of cations are plotted perpendicularly against those of anions; the sides of the triangles form a central rectangular binary plot of total cation vs. total anion concentrations Durov [17]. The central rectangle is divided into nine classes which give the hydrogeochemical processes determining the character of the water types in the aquiferous formation Langguth [16], Lloyd and Heathcote [18].

Physicochemical parameters
The physicochemical parameters of groundwater in Wum: Temperature, pH, EC and TDS for 10 wells and springs were evaluated and presented in table 3. All physicochemical parameters vary with seasons indicating seasonal influence on the phreatic aquifer. The levels of groundwater in a basement environment like Wum is controlled by the presence and extent of the weathered overburden/ regolith as well as fissures, joints and fractures system in the underlying bedrock (Tijani et al.,2010) [28].

Temperature:
The temperature of the groundwater in Wum is relatively low, ranged between 21.5-25.3 dry, 21.7-23.1 drywet, 20.8-26.6 wet and 21.8-24.1 wetdry seasons respectively figure 5. The temperature variation was similar in the different areas, suggesting a single aquifer since groundwater in the same aquifers have similar parameter values and temperature is one of them.

pH:
The pH of groundwater samples in the study area range from; 2.6-6.9 drywet, 3.3-7.1 wet and 5.2-7.5 wetdry season figure 6. This indicates that groundwater is acidic to per alkaline in all seasons.

Electrical conductivity:
The observed conductance in the study area was low in all seasons, ranging from 0.01-0.51mS/cm in the dry season, 0.01-6.30mS/cm in the drywet season, 0.17-3.90mS/ cm in the wet season and 0.01-3.29mS/cm wet-dry season as shown in figure 7. These low values of EC and TDS are a reflection of low salt content in groundwater. EC is highest in Magha and 3-corners for the dry season; Mile-50 in the drywet: Hausa quarter and naikom for wet and Courtyard for the wetdry season.     TDS is highest in drywet season due to the absence of rain in the formations, at this point the ionic concentration is higher but moving towards the heart of rainy season and groundwater becomes more dilute and keeps decreasing each season until the next drywet season.

Groundwater ionic content in Wum
The ionic content varied with seasons as presented in tables 4, 5, 6 and 7. During the dry season the ionic trend was Ca 2+ >Mg 2+ >N-H4+>K+>Na+, for cations and HCO 3 ->Cl ->SO 4 2->NO 3 ->HPO 4 2for anions. This same pattern was observed in most of the areas with exceptions in Hilltop, where K + was greater than NH 4 + . A different trend was observed in the anions where HPO 4 2was greater than NO 3 in Zongefu and Manyi. However, Clwas absent in most samples but whenever it was present, it usually had a higher value than SO 4 2giving it a higher total concentration.
In the drywet season the trend was Ca 2+ >Mg 2+

Ionic ratios of groundwater
Ionic ratios of groundwater in Wum have been determined as presented in table 8,9,10 and 11 and used to infer the sources and formation contribution to groundwater ionic contentin table 12.

Rock-groundwater interaction in wum
From Gibbs diagram, the sources of ionic content in groundwater are; 30% comes from evaporation and crystallization in the wet and wetdry seasons 50-70% comes from rock-weathering dominance for all seasons: 60% dry and drywet, 50% wet and 70% wetdry. 40% dry and drywet seasons together with 20% in wet season comes from atmospheric precipitation determined from figure 9 and presented in table 13. This indicates the weathering of the aquifer matrix is the primary dominant process in the acquisition of ions while atmospheric precipitation and evaporation-crystallization are the secondary contributing processes to the hydrogeochemistry in Wum.

Groundwater types
The diamond field of Piper's diagram has seven classes A-G classifying water types and designated with alphabets from A to G as in figure 10. Water from Wum falls into three; A, B, D categories as in table 14 and there are no category C, E, F and G in all seasons. Category A has 60-100% of samples for all four seasons. This indicates bicarbonate as prevailing ion of groundwater in Wum.   J Environ Sci Curr Res ISSN: 2643-5020, Open Access Journal DOI: 10.24966/ESCR-5020/S1001 Special Issue 1 • S1001 In the dry season there exist: Category A; 4 samples, 80% characterized by normal earth alkaline water with prevailing bicarbonate and Category B, 1 sample, 20% characterized by normal earth alkaline water with prevailing bicarbonate. In the drywet season: Category A 9 samples, 90% is characterized by normal earth alkaline water with prevailing bicarbonate and Category B; 1 sample, 10% are characterized by normal earth alkaline water with prevailing bicarbonate. In the wet season: Category A; 10 samples, 100%; characterized by normal earth alkaline water with prevailing bicarbonate. In the wetdry season: Category A is composed of 6 samples, 60% characterized by normal earth alkaline water with prevailing bicarbonate. Category B; 2 samples, 20% are characterized by normal earth alkaline water with prevailing bicarbonate or chloride and Category D; 2 samples, 20%; are characterized by earth alkaline water with prevailing HCO 3 -.
Groundwater in Wum is made up of 2 water types; CaHCO 3 is the dominant water type 80-100% in all seasons and CaSO 4 the minor water type 20% in the dry season presented in    J Environ Sci Curr Res ISSN: 2643-5020, Open Access Journal DOI: 10.24966/ESCR-5020/S1001 Special Issue 1 • S1001     Table 9: Ionic ratios of groundwater ions: Summary statistics for dry-wet season Wum.       The high contribution of alkaline earth elements in all seasons is due to direct ion-exchange processes which enrich groundwater with alkaline earth elements (Table 15).

Hydrogeochemical character of Wum groundwater
Based on Durov diagrams of groundwater in Wum shown in figure  11; Lloyd and Heathcoat classification seen in table 16, groundwater in Wum belongs to 3 classes: classes 3, 5 and 6. Two classes occur in dry season: Class 5 simple dissolution or mixing 1 sample (20%) and Class 6 probable mixing or uncommon dissolution influences: 4 samples (80%) respectively. Two classes occur during the drywet season; Class 3 ions exchange water 1 sample (10%) and Class 6 probable mixing or uncommon dissolution influences: 9 samples (90%) respectively. One class occurs in the wet season: Class 6 probable mixing or uncommon dissolution influences 10 samples (100%). Three classes of occur in the wetdry season: Class 3 ion exchange water: 2 samples (20%); Class 5 simple dissolution or mixing: 1 sample (10%) and Class 6 probable mixing or uncommon dissolution influences: 7 samples (70%) respectively. There are no Classes 1,2,4,7 and 9 in the wet season; 3,5,7,8 and 9 Wetdry; 6, 7, 8, and 9 dry seasons and no Classes 2,3,7,8 and 9 in the drywet season in Wum. In the wet season, fresh recently recharging water exchanges ions with the matrix of the formation, while simple dissolution or mixing also goes on between the recently recharging precipitation and the existing groundwater in the formation. In the dry season, recharging groundwater having spent more time in the formation continues to exchange ions to a lesser extent with the matrix of the formation while increasingly; simple dissolution or mixing also goes on between the recently recharging groundwater and the pre-existing groundwater in the formation, piston flow. The absence of samples in classes 1, 2, 4, 5, 7, 8, and 9 in all seasons indicates that the groundwater character in Wum is as a result of ion exchanges between the weathered formations, simple dissolution and mixing within the various groundwater types within the flow field.

Rock-groundwater interaction:
Based on the Durov diagrams of groundwater during various seasons in Wum shown in figure 11; Lloyd and Heathcoat classification seen in table 16, Wum groundwater samples plotted in:i) class 6; 80% Wet, 90% drywet, 100% wet and 70% wetdry seasons indicating water types resulting from mixing or uncommon dissolution influences. ii) class 5, 20% dry season and 10%, wetdry season indicating water exhibiting simple dissolution or mixing.iii) class 3, 10% drywet and 20% Wetdry indicating ion exchanged groundwater. The Durov diagram thus indicates that, simple dissolution, mixing and ion exchange are the dominant processes governing rock-groundwater interaction in Wum.

Water quality
Water Quality Index (WQI) for domestic use: Using the WHO guideline values of ions present in the groundwater WQI values were determined. Pradhan et al., [29]; Asadiet al., [30].WQI values ranged    [31] classification. All samples fell in the excellent to good category for dry and drywet seasons. In the wet and wetdry seasons, 6 samples fell in the excellent to good category while 2 and 1 fell in the good to permissible respectively. 2-3 samples fell in the doubtful to unsuitable category in Figure 14.

Fields
Hydrogeochemical facies       figure 17 indicating that the groundwater in Wum is not suitable for irrigation based on MAR. Some wells were dry in the dry season as such their samples could not be collected and analyzed.

Sodium adsorption ratio:
The sodium adsorption ratio reflects sodium concentration in water which accumulates during irrigation in soils presents a hazard. The sodium adsorption ratio is presented in figure 18 and table 21. All samples fall in the excellent class for all seasons.
Based on SAR, all samples are good for irrigation. When the SAR values and specific conductance of water are known, combining them strongly explains the effect of alkali hazard and salinity hazard as in table 16. Most of the groundwater samples in Wum fell in C0-S0 type, C1-S1 types and are characterized by medium salinity-low alkali hazard and low salinity-low alkali hazard respectively and hence are suitable for irrigation.      figure  19. Therefore groundwater increases in salinity hazard in the wet and wetdry seasons. None fell in Classes C2, C3 and C4, in dry and drywet seasons.

Permeability index:
The groundwater samples of the study area fell in class-I and II as presented in figure 20 and table 23: Class II, 100% in the dry season, 50% in the drywet season, 60% in the wet season and 40% in the wetdry season that indicated water is good for irrigation. Class III, 50% in the drywet season, 40% in the wet season and 60% in the wetdry season which indicates the water is unsuitable for irrigation.
Groundwater indices of: Sodium percent, residual sodium carbonate, Kelley's ratio, sodium adsorption ratio, electrical conductivity, total dissolved solid, USSL and Wilcox index were determined, evaluated and found to be suitable for agro-industrial uses in all seasons but for Permeability index and Magnesium adsorption ratio that were not suitable in some areas and in some seasons. The significance of low values of these indices is that the groundwater in the study area will have no adverse effect on the soil properties and is thus suitable for irrigational purposes whereas high magnesium adsorption ratio may be due to the passage of surface water and subsurface water through formation in the study area [33].
High permeability indices could be due to high concentration of sodium, calcium, magnesium and bicarbonate in the groundwater which could affect the soil structure and other soil properties.

Conclusion
Groundwater levels vary in rhythm with changes in precipitations in all four seasons, water level contours are similar to surface elevation contours and groundwater table mimics topography typical of phreatic aquifers with all physicochemical parameters varying with seasons indicating seasonal influence on the phreatic aquifer. An evaluation of the ionic ratios indicates ions in the groundwater in Wum are from rock weathering and rainwater; portrays a cation-exchange and silicate weathering environment.   Rock-Groundwater Interaction in Wum has the weathering of the aquifer matrix as the primary dominant process in the acquisition of ions while atmospheric precipitation and Evaporation-Crystallization are the secondary contributing processes to the hydrogeochemistry in Wum.
Groundwater in Wum is made up of two water types; CaHCO 3 is the dominant water type in all seasons and CaSO 4 the minor water type occurs in the dry, drywet and wetdry seasons.
There are two hydrochemical facies: Ca-Mg-Cl-SO 4 hydrogeochemical facies characteristic of groundwater some distance along its flow path and Ca-Mg-HCO 3 hydrogeochemical facies characteristic of freshly recharged groundwater that has equilibrated with CO 2 and soluble carbonate minerals under open system conditions in the vadose zone typical of shallow groundwater flow systems in crystalline phreatic fractured rock aquifers.
Hydrogeochemical character of Wum groundwater varies with season: In the wet season, fresh recently recharging water exchanges ions with the matrix of the formation, while simple dissolution or mixing also goes on between the recently recharging precipitation and the existing groundwater in the formation. In the dry season, recharging groundwater having spent more time in the formation continues to exchange ions to a lesser extent with the matrix of the formation while increasingly; simple dissolution or mixing also goes on between the recently recharging groundwater and the pre-existing groundwater in the formation, piston flow.
The groundwater in Wum is hard in wetdry season and soft to moderately hard in all seasons. The Water Quality Index for groundwater in Wum is excellent-good for domestic use. The groundwater indices of; Sodium Percent, Residual Sodium Carbonate, Kelley's ratio, Sodium Adsorption Ratio, Electrical Conductivity, Total Dissolved Solid, USSL and Wilcox index were determined, evaluated and found to be suitable for agro-industrial uses in all seasons.
Permeability Index and Magnesium Adsorption Ratio are not suitable in some areas and in some seasons, Therefore, more attention should be paid on groundwater quality monitoring (PI and MAR) in Wum, for ensuring dependable, affordable groundwater and protecting the quantity available for future use during the planning stage of large scale farming in Wum.