The objective was to determine and monitor seasonal changes during four hydrological seasons: Wet season (September), Wetdry season (December), Dry season (March) and Drywet season (June) in the groundwater aqueous geochemistry and its domestic-agro-industrial quality using physicochemical parameters and hydrogeochemical tools: Temperature, Electrical Conductivity EC, pH, Total dissolved solids TDS, 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 diagram. Field physicochemical parameters ranged from: Wet season; pH 3.9 - 6.9; Temperature, 23.3°C - 29.1°C; EC, 10 - 1900 μS/cm; TDS, 6.7 - 1273 mg/L; Wetdry, pH, 5.7 - 11.7; Temperature, 23.6°C - 28.3°C; EC, 1 - 1099 μS/cm, TDS, 0.67 - 736.33 mg/L; Dry pH, 5.7 - 13.1; Temperature, 26.3°C - 30.2°C; EC, 12 - 770 μS/cm, TDS, 8.04 - 515.9 mg/L and Drywet, pH, 4 - 7.4; Temperature, 25.8°C - 30.7°C; EC, 10 - 1220 μS/cm, TDS, 6.7 - 817.4 mg/L. Seventy-two groundwater samples, 18 per season were analysed. All ionic concentrations fell below acceptable World Health Organization guidelines in all seasons. The sequence of abundance of major ions are; Wet, Ca + > Mg 2+ > Na + = K + > NH 4 +, HCO 3 ? > Cl ? > NO 3 ? > SO 4 2? > HPO 4 2?; Wetdry Ca + > K + > Mg 2+ > Na + > NH 4 +, HCO 3 ? > Cl ? > SO 4 2? > NO 3 ? > HPO 4 2?; Dry Ca + > K + > Mg 2+ > Na + > NH 4 +, HCO 3 ? > Cl ?> NO 3 ? > SO 4 2? > HPO 4 2?; Drywet NH 4 + > Ca + > K + > Mg 2+ > Na +; Cl ? > HCO 3 ? > NO 3 ? > SO 4 2? > HPO 4 2?. Groundwater ionic content was due to rock weathering and ion exchange reactions. CaSO 4 is the dominant water type in Wet and Wetdry seasons; followed by CaHCO 3, Na + K-Cl Wet, CaSO 4 and CaHCO 3 Wetdry; MgCl Dry and Drywet followed by CaCl, CaHCO 3 Dry and CaSO 4, CaHCO 3 Dry-Wet. The dominant hydrogeochemical facies are Ca-Mg-Cl-SO 4 followed by Na-K-SO 4 Wet and Ca-Mg-HCO 3 ? in all other seasons. Ion exchange, Simple dissolution and uncommon dissolution are the processes determining groundwater character. The water quality indices; WQI, HT, SAR, %Na, KR, PI, MAR,RSC and Wilcox diagrams, indicate that groundwater in Kumba is 80% - 100% excellent during the Drywet &Wet seasons, 5% - 10% unsuitable during the Wetdry & Dry seasons for domestic use while being excellent-good for Agro-Industrial uses in all other seasons. Physicochemical parameters in some areas exceeded permissible limits for drinking. All hydrogeochemical parameters vary with seasons and these variations show the impact of annual cycles of seasonal changes on the aqueous geochemistry of groundwater in Kumba.
Kumba is situated between longitudes 9.39 - 9.49E and latitudes 4.605 - 4.675N
The population of Kumba is about 144,268 mostly farmers and business people from almost every ethnic group in Cameroon including: the Hausas (at Hausa Quarters), the Bamilekes (at Bamileke Quarters), the Bakossis (around Krammar and Anglican), the Metasat Meta quarters) and foreign nationals (especially neighboring Nigerians, like the Igbos at Igbo Quarters). The indigenes are the Bafawsat Kumba Town and the Balondos at Kake. The indigenous tribes constitute only a small percentage of the entire population. The main languages spoken are English; French with pidgin and dialects amongst the various ethnic groups (Akoachere & Ngwese, 2016) .
Kumba generally has a hot and humid equatorial climate with two seasons: a short Dryseason of about 4 months (December to March) and a long rainy season
(April to November). Annual rainfall ranges from 2298 mm to 3400 mm. The average annual air temperature is 27˚C (Akoachere & Ngwese, 2016) .
Kumba is located in the tropical rainforest with vegetation that varies from savannah to forest (around Lake Barombi Mbo). The evergreen and semi-deciduous forests contain economically important tree species (iroko, mahogany, obeche, ebony, padouk, tiama, framire, sapelline, makore and bobinga, etc.). The herbaceous layer is dominated by Pennisetumpurpureum and Imperatacylindrica with a ligneous cover that is heavily affected by human activity. The river valleys are covered with Indian bamboo (Bambousa species) whose stems are used for handicraft activities (Akoachere & Ngwese, 2016) . Deforestation is the main cause of environmental degradation in Kumba. It arises from human activities, especially inappropriate farming practices (shifting cultivation), overgrazing, bush fires, poaching and illegal logging (Akoachere & Ngwese, 2016) .
A wide variety of soils exist in Kumba including: clayey soils (earthy) around Kake, Mbonge Road, Kumba Town, Krammer and Anglican; gravelly soils (brick red) around Buea Road; sandy soils (pale yellow to earthy) around Kossala; and laterites (brick red) in almost every part of the town. Soils’ grain-sizes range from coarsegrained to fine grained, poorly sorted to moderately well-sorted.
Kumba has numerous streams of small discharges (Kumba water, Kake water, Mbanga water), springs (including Cold spring and Mother Spring) and lake Barombi Mbo which constitutes a huge freshwater reserve.
Kumba is situate in the Kumba Plain, a grabben intercalated between the strato-volcanoes of Mt Cameroon and MtsRumpi (Sehar et al., 2011) , at the northwestern edge of the Douala Basin
The Douala basin probably formed from a Precambrian cratonisation, granitisation and sedimentation phase followed by the Pan-African orogenesis, the Afro-Brazilian depression (the site of the future Cameroon Atlantic basin) with epi-continental sedimentation which may have begun during the lower Cretaceous discordant Cretaceous to Pliocene sediments on the Precambrian Pan-African basement and covered in some areas by Miocene sedimentation and volcanism (Loko et al., 2013) . The geology of the Kumba Plain (Kumba Volcanic Field) is controlled by three main volcanic activities (which probably occurred between the Eocene and 1Ma ago). These include: old basaltic lavas covering the entire plain; cinder cones and phreatomagmatic units; and short vesicular basaltic lava flow (Prasad et al., 2014) . There are 4 maars in the Kumba Plain. These
include: the Barombi Mbo, Barombi Koto, Mbwadong and Dissoni Maars, with the first two occupied by Lakes Barombi Mbo and Lake Barombi Koto. Based on the composite fragments contained in the Barombi Mbo Maar (BMM) pyroclastic deposits, it is likely that the maar cuts through a geological succession composed by granite gneissic formations, sandstones, and basaltic lava flows; the same formations that make up the Kumba Volcanic Field (Al-Khatib & Arafat, 2009) (
Volcanic formations of the plain have been emplaced over Panafrican metamorphic formations intruded by granitoids and locally covered by Cretaceous continental sandstones. They commonly enclose mantle peridotite xenoliths (Nagarnaik & Patil, 2012) . Conglomerates outcrop at the Buea Road area. They are poorly sorted; containing grains ranging from clays to boulders, with intense weathering. Fine grained sandstones (pale yellow to earthy in color) outcrop around Kossala. Pyroclastic materials from ash to bombs (mostly ash) outcrop at the BMM. Lava flow structures outcrop at some parts of Kake water and Kumba Water (at Buea Road) river beds, and rounded basaltic boulders (both massive and phorphyritic) along the banks of Kumba Water (up to several meters away from the river in some places) at Up-station to Ntchako Street and around Kake Water at Ekoka Falls. Gneisses outcrop at Fomenky Street (Buea Road), Osheami quarter, three corners, Farm road and Solar quarters (Fiango).
Weathered basement (regolith), fractured-gneiss, basalts, pyroclastics and recent alluvium are the aquiferous formations in the area. Saturated hydraulic conductivities of the aquiferous formations range from 2.88E-08 to 1.60E-06 m/d (Akoachere & Ngwese, 2016) , groundwater velocities from 1.96E+01 to 6.34E+02 m/d (Akoachere & Ngwese, 2017) , first estimates of well yields from 4.6E-01 to 2.28E+01 m/d (Akoachere & Ngwese, 2016) and the hydraulic conductivities of the vadose zone from 7.96E+02 to 3.27E+04 m/d. and stream discharges 1.79E+05 to 9.13E+05 m3/d (Ayuk & Mesode, 2017) .
A detailed field program of bore well data acquisition; field hydrogeological measurement/tests, sampling and laboratory analysis of collected groundwater samples was conducted in Kumba using appropriate equipment and softwares
Determination of indices for suitability of groundwater for Agro-Industrial uses was done using formulae in
1) Ionic ratio for indicative elements is a useful hydrogeochemical tool to identify source rock of ions and formation contribution to solute hydrogeochemistry (Hounslow, 1995) . These were useful in this study.
Equipment/Softwares | Specifications | Functions |
---|---|---|
Bike | Commercial bikes (Bensikin) | To transport fieldworkers to wells |
GPS | Garmin GPS map 60 CSx | To measure longitude, latitude and elevation |
EC Meter | Hanna HI 98,304/HI 98,303 | To measure Electrical Conductivity of water. |
pH Meter | Hanna HI 98,127/HI 98,107 | To measure pH of water. |
Water level indicator | Solinst Model 102M | To indicate static water levels of wells |
Measuring Tape | Weighted measuring tape | Measurement of well diameter and depth. |
Digital Thermometer | Extech 39,240 (−50˚C to 200˚C) | To measure temperature of water |
Water sampler | Gallenkampf 1000 ml | To collect well water sample from well |
Sample bottles | Polystyrene 500 ml | To hold sample for transmission to laboratory |
ArcGIS | Version 10.1 | GIS Drawing sampling/Tests location maps |
Global Mapper | Version 15 | GIS Geolocation of wells |
Surfer Golden Software | Version 12 | GIS plotting contours for spatial distribution |
AqQA/Aquachem | Version 15 | For the analysis/interpretation of chemistry |
Indices | Formula | Reference |
---|---|---|
Percentage Sodium | % Na = Na + + K + Na + + K + + Ca 2 + + Mg 2 + × 100 | (Wilcox, 1955) |
Kelly Ratio | KR = Na + Ca 2 + + Mg 2 + | (Kelley, 1940) |
Magnesium Absorption Ratio | MAR = ( Mg 2 + Mg 2 + + Ca 2 + ) × 100 | (Szaboles & Darab, 1964) |
Total Hardness | TH (CaCO3) mg/L = 2.5 Ca2+ + 4.1 Mg2+ | (Todd, 1980) |
Residual Sodium Carbonate | RSC = ( CO 3 + HCO 3 − ( Ca + Mg ) ) | (Eaton, 1950), (Raghunath, 1987) |
Sodium Absorption Ratio | SAR = Na Ca + Mg 2 | (Richard, 1954) |
Permeability Index | PI = ( ( Na + K ) + HCO 3 ) ∗ 100 Ca + Mg + Na + K | (Doneen, 1962) |
Water Quality Index | WQI = ∑ n i = 1 W i q i [ ∑ i = 1 n W i ] − 1 | (Sisodia & Moundiotiya, 2006) |
Gibbs Diagram is a plot of Na+/Na+ + HCO 3 − Ca2+) and Cl−/(Cl + HCO 3 − ) as a function of TDS are widely employed to determine the sources of dissolved geochemical constituents (Gibbs, 1970) . These plots revealed the relationships between water composition and the three main hydrogeochemical processes involved in ions acquisition; Atmospheric precipitation, rock weathering or evaporation crystallisation over the four seasons.
2) 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 HCO3, SO4 and Cl− apices. These two fields are projected onto a third diamond field (Piper, 1944) . The diamond field is a matrix transformation of the graph of the anions [sulphate + chloride]/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, 1966) . This has been used here for these purposes in the four seasons.
3) Durov diagram is a composite plot consisting of two ternary diagrams where the milliequivalent 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, 1948) . These are divided into nine classes which give the hydrogeochemical processes determining the character of the water types in the aquiferous formation (Lloyd & Heathcoat, 1985; Langguth, 1966) .
4) WQI was calculated by adopting Weighted Arithmetical Index method considering thirteen water quality parameters (pH, EC, TDS, total alkalinity, total hardness, Ca2+, Mg2+, Na+, K+, Cl−, SO 4 2 − , NO 3 − , NH4+) in order to assess the degree of groundwater contamination and suitability over the period of the four seasons (
For Agro-industrial suitability, the following parameters were used; sodium adsorption ratio SAR, permeability index PI, Magnesium adsorption ratio MAR, percent sodium %Na, Kelly’s ratio KR and Residual sodium carbonate RSC and Wilcox diagram.
The following Softwares; Surfer 12, Global mapper 11 and AqQA 1.5 AGIS 10.3 were used as platforms for data presentation, data interpretation and data analysis.
A field visit was done using hydrogeological traverse field mapping to determine appropriate hand-dug wells, boreholes, springs and streams. Kumba was divided into zones and work was carried out in four hydrogeological seasons; Wet season, September; Wetdry season, December; Dry season, March and DryWet season, June. GIS platforms were used to analyze field data for the creation of sample location, drainage and water level contour maps. All equipment used were calibrated according to manufacturer’s specifications.
Temperature, pH, Electrical conductivity Temperature, pH and electrical conductivity were measured onsite for 450 representative hand-dug wells during the four seasons: 1800 measurements for each of the four parameters. At each hand-dug well, a sample was collected and the Temperature, EC, pH and TDS meters were measured. 18 spatially representative groundwater samples were collected for four seasons: 72 water samples from; Kake 1, Mbongo Str., 3 Corners, New Layout, Maduku Str., Park, Krammar, Lawyer Enow, Kossala, Pulletin Str., Alaska Str., Anglican, New Quarter, GBHS, Cameroon Str., CCAS, Cow Fence and Paradise Str were analyzed.
At each hand-dug well, a clean polyethylene bottle was rinsed thrice with well water and then filled to its brim.
The 73 (18 per season plus one rain) samples were collected in 500ml containers, sealed and sent to the Institute of Agricultural and one Research and Development-I.R.A. Dusing the standard methods (APHA, 1995) to analyze for:
1) Major cations in mg/L: Ca2+, Mg2+, Na+, K+ and NH4+.
2) Major anions in mg/L: HCO 3 − , Cl−, SO 4 2 − , HPO 4 2 − and NO 3 − .
To fully understand the relationship between the geology of the area and groundwater, hydrogeochemical tools were used such as ionic ratios, Gibbs Diagrams, Piper diagrams and Durov diagrams. For domestic agro-industrial water quality; Percent Sodium %Na, Kelly’s Ratio KR, permeability index PI, Magnesium adsorption ratio MAR, Residual sodium carbonate RSC and Wilcox diagram. These were done for four seasons to determine the seasonal variations in these aquiferous formations.
1) Physicochemical Parameters
The field measured physicochemical parameters of groundwater Kumba are, Temperature, pH, EC and TDS
The individual parameters are discussed below.
2) Depth to Water Level
Well diameters range from 0.6 - 1.5 m, well depths from 1 - 18 m. The wells have depth to water levels ranged from 0.02 m - 11 m in Wet season, 0.6 m - 11.66 m Wetdry season and 0.5 m - 11.48 m Drywet season
3) Groundwater Level Contours
From elevation and depth to water level, the groundwater contours were drawn with equipotential vectors simulating groundwater flow lines and flow direction
4) Temperature
The seasonal groundwater temperatures ˚C range from 23.3 - 29.1 in the Wet; 23.6 - 28.3 Wetdry; 26.3 - 30.2 Dry and 25.8 - 30.7 Drywet,
5) pH
pH ranges from 3.9 - 6.9 in the Wet season, 5.7 - 11.7 Wetdry season, 5.7 - 13.1 Dry season and 4 - 7.4 Drywet season. pH is strongly acidic to peralkaline in Wet and Drywet seasons and strongly acidic to strongly alkaline in Wetdry to Dry seasons
Wet | Wetdry | Dry | Drywet | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Min | Max | Mean | Std | Min | Max | Mean | Std | Min | Max | Mean | Std | Min | Max | Mean | Std | |
T (˚C) | 23.3 | 29.1 | 26.78 | 0.61 | 23.6 | 28.3 | 27.01 | 0.49 | 26.3 | 30.2 | 27.32 | 0.51 | 25.8 | 30.7 | 27.62 | 0.62 |
pH | 3.9 | 6.9 | 5.22 | 0.50 | 5.7 | 11.7 | 7.03 | 0.96 | 5.7 | 13.1 | 7.91 | 1.58 | 4 | 7.4 | 5.46 | 0.55 |
EC (mS/cm) | 0.01 | 1.27 | 0.16 | 0.15 | 0.01 | 0.74 | 0.15 | 0.13 | 0.01 | 0.52 | 0.12 | 0.11 | 0.01 | 0.82 | 0.15 | 0.15 |
TDS (mg/L) | 0.07 | 12.73 | 1.59 | 1.54 | 0.01 | 7.36 | 1.50 | 1.31 | 0.08 | 5.16 | 1.24 | 1.06 | 0.07 | 8.18 | 1.54 | 1.46 |
6) Electrical Conductivity (EC)
The EC mS/cm values ranged between 0.01 - 1.90 in the Wet season, 0.01 - 1.10 Wetdry season, 0.012 - 0.77 Dry season and 0.001 - 1.22 in the Drywet season
7) Total Dissolved Solids
TDS ranged from 0.007 - 1.27 in the Wet season, 0.007 - 0.74 Wetdry season, 0.02 - 0.52 Dry season and 0.006 - 0.82 in the Drywet season
The sequence of abundance of major ions for four seasons are; Wet season Ca2+ > Mg2+ > Na+ > K+ > NH 4 + ; HCO 3 − > Cl > NO 3 − > SO 4 2 − > HPO 4 2 − ; Wetdry season Ca+ > K+ > Mg2+ > Na+ > NH 4 + , HCO 3 − > Cl > SO 4 2 − > NO 3 − > HPO 4 2 − ; Dry season Ca+ > K+ > Mg2+ > Na+ > NH 4 + ; HCO 3 − > Cl > NO 3 − > SO 4 2 − > HPO 4 2 − and Drywet season NH 4 + > Ca+ > K+ > Mg2+ > Na+, Cl− > HCO 3 − > NO 3 − > SO 4 2 − > HPO 4 2 − . From Tables 4(a)-(d); Maduka Street, Cameroon Street and Mbongo Street have the highest cations/anions. Ca2+ and HCO 3 − are the most abundant in three seasons except for Drywetseason where
Wet Season mg/L | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
SN | Names | Na+ | K+ | Ca2+ | Mg2+ | NH 4 + | HCO 3 − | NO 3 − | SO 4 2 − | CL− | HOP 4 2 − |
1 | Kake 1 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 3.66 | 0.00 | 1.42 | 10.00 | 0.00 |
2 | Krammar | 0.48 | 0.48 | 22.80 | 4.11 | 0.39 | 1.00 | 0.00 | 0.00 | 23.00 | 0.00 |
3 | Lawyer Enow | 0.03 | 0.03 | 0.00 | 0.00 | 0.31 | 6.10 | 0.23 | 0.67 | 7.00 | 0.06 |
4 | Anglican | 0.09 | 0.09 | 15.20 | 3.88 | 0.58 | 3.66 | 0.00 | 0.00 | 10.00 | 0.01 |
5 | Mbongo Str. | 1.04 | 1.04 | 37.80 | 4.21 | 0.65 | 52.46 | 5.48 | 0.57 | 37.00 | 0.01 |
6 | New Quarter | 0.00 | 0.00 | 11.40 | 4.00 | 0.65 | 3.66 | 0.00 | 0.21 | 2.00 | 0.01 |
7 | GBHS | 0.00 | 0.00 | 11.40 | 5.66 | 0.49 | 1.00 | 0.00 | 0.00 | 5.00 | 0.00 |
8 | Park | 0.00 | 0.00 | 0.00 | 0.00 | 0.48 | 1.22 | 0.00 | 0.00 | 7.00 | 0.00 |
9 | CCAS | 0.03 | 0.03 | 7.60 | 2.77 | 1.47 | 4.88 | 0.00 | 1.42 | 6.00 | 0.00 |
10 | Cow Fence | 0.00 | 0.00 | 7.60 | 4.31 | 1.25 | 0.00 | 0.00 | 0.00 | 7.00 | 0.00 |
11 | Alaska Str. | 0.03 | 0.03 | 19.00 | 5.51 | 0.41 | 1.22 | 0.00 | 0.00 | 9.00 | 0.00 |
12 | Cameroon Str. | 2.86 | 2.86 | 20.80 | 10.26 | 0.63 | 8.54 | 1.23 | 0.69 | 30.00 | 0.03 |
13 | Paradise Str. | 0.03 | 0.03 | 22.80 | 8.65 | 0.54 | 6.10 | 0.22 | 0.66 | 11.00 | 0.02 |
14 | Kossala | 0.17 | 0.17 | 3.80 | 2.71 | 0.45 | 3.66 | 0.00 | 1.08 | 10.00 | 0.00 |
15 | Pulletin Str. | 0.00 | 0.00 | 0.00 | 0.00 | 0.66 | 6.10 | 0.46 | 0.65 | 5.00 | 0.00 |
16 | New Layout | 0.39 | 0.39 | 11.40 | 2.06 | 0.61 | 6.10 | 0.00 | 0.64 | 28.00 | 0.06 |
17 | Maduku Str. | 1.63 | 1.63 | 60.60 | 20.51 | 0.20 | 31.72 | 4.45 | 5.23 | 47.00 | 0.00 |
18 | 3 Corners | 1.24 | 1.24 | 56.80 | 10.59 | 0.65 | 21.96 | 2.87 | 0.63 | 31.00 | 0.02 |
19 | Rain | 0.09 | 0.29 | 4.20 | 18.86 | 0.02 | 7.76 | 0.00 | 0.84 | 3.0 | 0.00 |
Min | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 2.00 | 0.00 | |
Max | 2.86 | 2.86 | 60.60 | 20.51 | 1.47 | 52.46 | 5.48 | 5.23 | 47.00 | 0.06 | |
Mean | 0.45 | 0.45 | 17.17 | 4.96 | 0.58 | 9.06 | 0.83 | 0.77 | 15.83 | 0.01 | |
Std. | 0.78 | 0.78 | 18.16 | 5.07 | 0.34 | 13.43 | 1.67 | 1.21 | 13.24 | 0.02 |
Wetdry Season mg/L | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
SN | Names | Na+ | K+ | Ca2+ | Mg2+ | NH 4 + | HCO 3 − | NO 3 − | SO 4 2 − | CL− | HOP 4 2 − |
1 | Kake 1 | 0.09 | 0.39 | 6.20 | 4.87 | 0.00 | 1.22 | 0.15 | 0.61 | 1.00 | 0.01 |
2 | Krammar | 0.81 | 8.97 | 30.80 | 0.59 | 0.10 | 2.44 | 0.17 | 0.00 | 21.00 | 0.04 |
3 | Lawyer EnowStr | 0.13 | 0.78 | 18.40 | 4.80 | 0.00 | 0.00 | 0.19 | 0.00 | 4.00 | 0.01 |
4 | Anglican | 0.35 | 1.95 | 18.40 | 4.38 | 4.32 | 2.44 | 0.11 | 0.00 | 10.00 | 0.04 |
5 | Mbongo Street | 0.85 | 12.09 | 30.80 | 0.59 | 0.30 | 23.18 | 0.38 | 0.00 | 25.00 | 0.05 |
---|---|---|---|---|---|---|---|---|---|---|---|
6 | New Quarter | 0.16 | 0.39 | 0.00 | 1.32 | 0.42 | 1.22 | 0.27 | 0.56 | 0.00 | 0.01 |
7 | GBHS | 0.04 | 0.00 | 0.00 | 2.90 | 0.38 | 3.66 | 1.25 | 1.02 | 0.00 | 0.01 |
8 | Park | 0.00 | 1.17 | 12.20 | 10.48 | 0.45 | 3.66 | 0.22 | 1.39 | 6.00 | 0.04 |
9 | CCAS | 0.00 | 0.39 | 12.20 | 7.43 | 0.21 | 1.22 | 0.22 | 0.69 | 2.00 | 0.03 |
10 | Cow Fence | 0.16 | 0.39 | 18.40 | 1.81 | 0.38 | 1.22 | 0.22 | 0.23 | 5.00 | 0.01 |
11 | Alaska Street | 0.25 | 2.34 | 18.40 | 11.38 | 4.33 | 2.44 | 1.48 | 0.00 | 12.00 | 0.04 |
12 | Cameroon Street | 0.39 | 2.73 | 18.40 | 1.84 | 0.44 | 3.66 | 0.23 | 6.88 | 30.00 | 0.02 |
13 | Paradise Street | 0.39 | 0.39 | 6.20 | 14.87 | 0.00 | 0.00 | 4.34 | 1.32 | 13.00 | 0.01 |
14 | Kossala | 0.48 | 5.85 | 12.20 | 1.32 | 0.53 | 6.10 | 0.25 | 1.34 | 9.00 | 0.06 |
15 | Pulletin Street | 0.30 | 0.39 | 18.40 | 4.32 | 0.45 | 3.66 | 0.37 | 0.00 | 3.00 | 0.03 |
16 | New Layout | 0.85 | 7.02 | 18.40 | 5.26 | 0.00 | 2.44 | 5.14 | 6.88 | 36.00 | 0.01 |
17 | Maduku Street | 1.70 | 26.52 | 73.80 | 20.90 | 0.49 | 61.00 | 4.21 | 10.21 | 44.00 | 0.02 |
18 | 3 Corners Fiango | 2.09 | 21.80 | 61.40 | 1.59 | 0.00 | 12.20 | 0.23 | 5.11 | 28.00 | 0.00 |
Min | 0 | 0 | 0 | 0.59 | 0 | 0 | 0.11 | 0 | 0 | 0 | |
Max | 2.09 | 26.52 | 73.8 | 20.9 | 4.33 | 61 | 5.14 | 10.21 | 44 | 0.06 | |
Mean | 0.50 | 5.20 | 20.81 | 5.59 | 0.71 | 7.32 | 1.08 | 2.01 | 13.83 | 0.02 | |
Std. | 0.58 | 7.75 | 19.11 | 5.55 | 1.33 | 14.48 | 1.65 | 3.07 | 13.55 | 0.02 |
Dry Seasonmg/L | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
SN | Names | Na+ | K+ | Ca2+ | Mg2+ | NH 4 + | HCO 3 − | NO 3 − | SO 4 2 − | CL− | HOP 4 2 − |
1 | Kake 1 | 0.08 | 0.35 | 2.91 | 2.71 | 0.28 | 0 | 0 | 0.11 | 3 | 0.03 |
2 | Krammar | 0.68 | 10.45 | 29.12 | 0.59 | 0.34 | 0 | 0 | 0.41 | 25 | 0.01 |
3 | Lawyer EnowStr | 0.08 | 0.7 | 5.82 | 4.88 | 0.21 | 0 | 0 | 0.42 | 5 | 0.01 |
4 | Anglican | 0.16 | 1.4 | 2.91 | 2.71 | 0.38 | 0 | 0 | 0.21 | 8 | 0.1 |
5 | Mbongo Str. | 1.16 | 17.39 | 46.59 | 5.04 | 0.66 | 28.06 | 0.63 | 0.11 | 4 | 0.04 |
6 | New Quarter | 0.12 | 0.52 | 2.91 | 4.06 | 0.84 | 7.32 | 0.92 | 0.24 | 3 | 0.03 |
7 | GBHS | 0.08 | 0.18 | 2.91 | 2.68 | 0.11 | 0 | 0 | 0.22 | 1 | 0.1 |
8 | Park | 0.12 | 0.69 | 5.82 | 4.51 | 0.11 | 0 | 0.02 | 0.21 | 7 | 0.01 |
9 | CCAS | 0.16 | 0.87 | 2.91 | 4.32 | 0 | 0 | 0.04 | 0.33 | 7 | 0.01 |
10 | Cow Fence | 0.16 | 0.52 | 5.82 | 4.87 | 0.43 | 0 | 0 | 0.23 | 8 | 0.01 |
11 | Alaska Str. | 0.02 | 2.42 | 8.74 | 0.65 | 0 | 0 | 0.03 | 0.33 | 7 | 0 |
12 | Cameroon Str. | 1.36 | 15.13 | 43.68 | 5.21 | 0 | 68.32 | 6.21 | 5.88 | 86 | 0.3 |
13 | Paradise Str. | 0.2 | 0.52 | 2.93 | 2.68 | 0.33 | 0 | 0 | 0.23 | 11 | 0.01 |
14 | Kossala | 0.36 | 3.12 | 11.65 | 1.33 | 0.31 | 0 | 0 | 0.11 | 12 | 0 |
15 | Pulletin Str. | 0.12 | 0.35 | 2.92 | 2.7 | 0.41 | 0 | 0 | 0.31 | 1 | 0.1 |
16 | New Layout | 0.68 | 7.64 | 20.38 | 4.3 | 0.45 | 0 | 0 | 0.23 | 31 | 0 |
---|---|---|---|---|---|---|---|---|---|---|---|
17 | Maduku Str. | 1.88 | 30.62 | 72.8 | 20.05 | 0 | 92.72 | 8.25 | 1.57 | 59 | 0.05 |
18 | 3 Corners | 0.2 | 1.74 | 5.82 | 4.87 | 0.21 | 0 | 0 | 0.21 | 7 | 0 |
Min | 0.02 | 0.18 | 2.91 | 0.59 | 0 | 0 | 0 | 0.11 | 1 | 0 | |
Max | 1.88 | 30.62 | 72.8 | 20.05 | 0.84 | 92.72 | 8.25 | 5.88 | 86 | 0.3 | |
Mean | 0.42 | 5.26 | 15.37 | 4.34 | 0.28 | 10.91 | 0.89 | 0.63 | 15.83 | 0.05 | |
Std. | 0.53 | 8.27 | 20 | 4.2 | 0.23 | 26.53 | 2.34 | 1.35 | 22.49 | 0.07 |
Drywet Season mg/L | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
SN | Names | Na+ | K+ | Ca2+ | Mg2+ | NH 4 + | HCO 3 − | NO 3 − | SO 4 2 − | CL− | HOP 4 2 − |
1 | Kake 1 | 0.13 | 0.37 | 3.6 | 2.98 | 0.28 | 0 | 0 | 0.15 | 5 | 0.01 |
2 | Krammar | 0.92 | 9.67 | 36.6 | 0.54 | 0.29 | 0 | 0.04 | 0.3 | 21 | 0 |
3 | Lawyer EnowStr | 0.3 | 1.29 | 3.6 | 6.03 | 0.33 | 0 | 0 | 0.38 | 6 | 0 |
4 | Anglican | 0.33 | 1.48 | 7.4 | 7.45 | 0.39 | 0 | 0.06 | 0.31 | 3 | 0.01 |
5 | Mbongo Str. | 0.46 | 7.29 | 40.2 | 32.94 | 3.53 | 0.51 | 0 | 0.12 | 8 | 0.01 |
6 | New Quarter | 0.21 | 0.9 | 0 | 6.11 | 0.81 | 9.45 | 0.32 | 0.12 | 6 | 0.02 |
7 | GBHS | 0.1 | 0 | 7.4 | 8.14 | 0.3 | 7.11 | 0.08 | 0.54 | 3 | 0.01 |
8 | Park | 0.23 | 0.55 | 3.6 | 0.45 | 3.84 | 0.41 | 0 | 0.19 | 9.3 | 0.02 |
9 | CCAS | 0.9 | 0.55 | 29.2 | 24 | 0 | 0 | 0.06 | 0.42 | 10 | 0.01 |
10 | Cow Fence | 0.23 | 0.37 | 7.4 | 5.43 | 0.46 | 0.17 | 0.04 | 0.34 | 10.1 | 0.03 |
11 | Alaska Str. | 0.26 | 2.57 | 3.6 | 0.62 | 0 | 0 | 0.04 | 0.33 | 8 | 0 |
12 | Cameroon Str. | 0.33 | 3.12 | 3.6 | 3.51 | 0 | 59.21 | 5.21 | 4.1 | 80 | 0.03 |
13 | Paradise Str. | 0.14 | 0.9 | 3.6 | 2.51 | 2.46 | 0.3 | 0 | 0.09 | 0 | 0.03 |
14 | Kossala | 0.25 | 2.93 | 7.4 | 0.42 | 0.4 | 0 | 0 | 0.11 | 11.94 | 0 |
15 | Pulletin Str. | 0.2 | 0 | 0 | 1.51 | 0.22 | 0 | 0 | 0.21 | 1.5 | 0.01 |
16 | New Layout | 0.13 | 7.87 | 11 | 0.03 | 0 | 0 | 0 | 0.12 | 24 | 0 |
17 | Maduku Str. | 2.44 | 33.42 | 61.4 | 0 | 80.2 | 7.14 | 0.56 | 1.44 | 51 | 0.03 |
18 | 3 Corners | 0.1 | 1.29 | 36.6 | 31.43 | 0.11 | 0 | 0 | 0.12 | 8 | 0.01 |
Min | 0.1 | 0 | 0 | 0 | 0 | 0 | 0 | 0.09 | 0 | 0 | |
Max | 2.44 | 33.42 | 61.4 | 32.94 | 80.2 | 59.21 | 5.21 | 4.1 | 80 | 0.03 | |
Mean | 0.43 | 4.14 | 14.79 | 7.45 | 5.2 | 4.68 | 0.36 | 0.52 | 14.77 | 0.01 | |
Std. | 0.56 | 7.86 | 17.82 | 10.59 | 18.76 | 13.94 | 1.22 | 0.95 | 20.05 | 0.01 |
NH 4 + and Cl− are most abundant. There is an increase of K+ and Mg2+ ions as seasons change from Wet to Drywet.
The ionic ratios of groundwater have been used to determine formation contribution to Kumba groundwater chemistry in
The ionic ratios indicate groundwater in Kumba is affected to a great extent by silicate weathering mostly Ca-silicates and Mg-silicates from the minerals found in basalts with little weathering of Na-feldspar and Na-silicates, no Na-absorption, some Sulphate from external sources, no oxidation of sulphides and no anthropogenic contribution. Rock weathering and rainwater; increase in Wet, deplete in Dry Wet season. Some plagioclase weathering occurs in all seasons except Wet season with sodium source other than halite-albite, ion exchange and rainwater; silicate weathering of ferromagnesian minerals from the basalts but without gneiss weathering, ion exchange/Calcium removal and Calcium source from weathering of the basalts.
From Gibbs diagram; 77.78% ionsin groundwater originate from rock-weathering dominance for Wet, Wetdry and Drywet seasons and 83.33% in Dry season originate from atmospheric precipitation dominance during the four seasons
Ionic Ratio | Wet | Wetdry | Dry | Drywet | Interpretation |
---|---|---|---|---|---|
SO/Cl | 0- 0.24 | 0 - 0.61 | 0.01 - 0.31 | 0 - 0.18 | Sulphate reduction and suggests additional sources of Sulphate |
Na/Cl | 0 - 0.10 | 0 - 0.10 | 0 - 0.29 | 0 - 0.13 | No Na-adsorption during freshening and absence of marine water. |
Mg/Cl | 0 - 2.0 | 0 - 4.87 | 0.02 - 2.70 | 0 - 4.12 | Depict a cation-exchange and silicate weathering environment |
Na/HCO | 0 - 0.48 | 0 - 0.35 | 0 - 0.04 | 0 - 0.90 | Low weathering of Na-feldspar or other Na-silicates. |
Ca/HCO | 0 - 22.80 | 0 - 12.62 | 0 - 1.66 | 0 - 78.82 | Ca-silicate weathering from country rocks |
Ca/SO | 0 - 90.16 | 0 - 17.68 | 0 - 423.55 | 0 - 335.00 | There is no gypsum dissolution in volcanic regions |
Ca/Mg | 0 - 8.98 | 0 - 52.20 | 0 - 49.36 | 0 - 366.67 | Typical of coastal regions due to cation-exchange |
Mg/Ca | 0 - 524.17 | 0 - 50.33 | 0 - 13.72 | 0 - 48.94 | Silicate weathering |
(Ca + Mg)/(Na + K) | 0 - 0.11 | 0 - 0.14 | 0 - 0.19 | 0 - 0.12 | Occurrence of silicate weathering over carbonate weathering. |
HCO 3 − /∑Anions | 0 - 0.01 | 0 - 0.01 | 0 - 0.02 | 0 - 0.01 | Rainwater |
NO3/∑Anions | 0 - 0.01 | 0 - 0.02 | 0 - 0.01 | 0 - −0.01 | No anthropogenicactivities. |
SO4/∑Anions | 0 - 1.0 | 0 - 0.95 | 0.12 - 0.99 | 0 - 0.99 | No oxidation of sulphides. |
Cl−/∑Anions | −10.26 - 31.53 | −4.51 - 2.02 | −21.11 - 11.76 | −11.12 - 1.88 | Rock weathering and rainwater; increase in Wet, deplete in DryWet season |
Na + + K + − Cl − Na + + K + − Cl − + Ca 2 + | 0 - 0.09 | 0 - 1.0 | 0 - 0.22 | 0 - 1.0 | Some plagioclase weathering in all seasons except Wet season |
Na + Na + + Cl − | 0 - 0.42 | 0.02 - 1.0 | 0.02 - 0.60 | 0 - 1.0 | Sodium source other than halite-albite, ion exchange and rainwater |
Mg 2 + Ca 2 + + Mg 2 + | 0 - 1.0 | 0 - 1.0 | 0.90 - 1.0 | 0 - 1.0 | Silicate weathering of ferromagnesian minerals but no evidence of granitic weathering |
Ca 2 + Ca 2 + + SO 4 2 − | 0 - 3316.02 | 0 - 439.35 | 18.13 - 3489.27 | 0 - 4876.00 | Ion exchange/Calcium removal and Calcium source from silicates |
Ca 2 + + Mg 2 + SO 4 2 − | 0 - 0.71 | 0 - 2.40 | 0.02 - 1.48 | 0 - 1.68 | No dolomite at all, Dedolomitization |
Rock-water Interaction | TDS mg/L | Wet | Wetdry | Dry | Drywet | ||||
---|---|---|---|---|---|---|---|---|---|
No | % | No | % | No | % | No | % | ||
Rock - Weathering Dominance | 50 - 1000 | 14 | 77.78 | 14 | 77.78 | 15 | 83.33 | 14 | 77.78 |
Atmospheric Precipitation dominance | 1 - 50 | 4 | 22.22 | 4 | 22.22 | 3 | 16.67 | 4 | 22.22 |
77.78% to 83.33% while atmospheric dominance reduces from 22.22% to 16.67% and vice versa. This causes a 5.55% increase in rock weathering dominance in the Dry season and a 5.55% increase in Atmospheric precipitation dominance in the rainy season. These variations in the aqueous geochemistry of the groundwater in Kumba are a direct consequence of hydrological changes.
The diamond field of Piper’s diagram was divided into seven classes A - G classifying water types and designated with alphabets from A to G
Piper-Langguth Classification Kumba | Wet | Wetdry | Dry | Drywet | |||||
---|---|---|---|---|---|---|---|---|---|
Class | Characteristic-Water type | No | % | No | % | No | % | No | % |
Diamond Field | |||||||||
A | Normal earth alkaline water; prevailing HCO 3 − | 0 | 0 | 2 | 11.11 | 1 | 5.56 | 1 | 5.56 |
B | Normal earth alkaline water; prevailing HCO 3 − or Cl− | 2 | 11.11 | 2 | 11.11 | 2 | 11.11 | 2 | 11.11 |
C | Normal earth alkaline water; prevailing Cl− | 15 | 83.33 | 14 | 77.78 | 15 | 83.33 | 12 | 66.67 |
E | Earth alkaline water with added portions of alkalis with prevailing chloride | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 16.67 |
G | Alkaline water with prevailing bicarbonate | 1 | 5.56 | 0 | 0 | 0 | 0 | 0 | 0 |
Cation Field | |||||||||
---|---|---|---|---|---|---|---|---|---|
1 | Ca-rich waters | 16 | 88.89 | 13 | 72.22 | 7 | 38.89 | 6 | 33.33 |
2 | Mg-rich waters | 1 | 5.56 | 5 | 27.78 | 11 | 61.11 | 12 | 66.67 |
3 | Na + K | 1 | 5.56 | 0 | 0 | 0 | 0 | 0 | 0 |
Anion Field | |||||||||
4 | HCO 3 − waters | 1 | 5.56 | 2 | 11.11 | 2 | 11.11 | 2 | 11.11 |
6 | Cl− waters | 17 | 94.44 | 16 | 88.89 | 16 | 88.89 | 16 | 88.89 |
Hydrogeochemical facies | |||||||||
Field I | Ca - Mg - Cl - SO4 | 17 | 94.44 | 16 | 88.89 | 16 | 88.89 | 16 | 88.89 |
Field II | Na - K - Cl - SO4 | 1 | 5.56 | 0 | 0 | 0 | 0 | 0 | 0 |
Field IV | Ca - Mg - HCO3 | 0 | 0 | 2 | 11.11 | 2 | 11.11 | 2 | 11.11 |
prevailing chloride and Class E; 3 sample 16.67%; characterized by earth alkaline water, with added portions of alkalis with prevailing chloride. The dominant water types are Class B: 11.11%, Class C: 83.33% and Class G: 5.56%; Wetdry Category A, B: 11.11% and Class C: 77.78%; Dry Class A: 5.56%, Class B: 11.11% and Class C: 83.33% while in the Drywet season Wetdry Class A: 5.56%, Class B: 11.11%, Class C: 66.67% and Class E: 16.67%. From
From the Piper’s diagram
Based on the Durov diagram
Class | Hydrogeochemical processes | Wet | Wetdry | Dry | Drywet | ||||
---|---|---|---|---|---|---|---|---|---|
No | % | No | % | No | % | No | % | ||
1 | HCO3 and Ca dominant; indicates recharging waters groundwater | 14 | 66.67 | 10 | 55.56 | 4 | 22.22 | 9 | 50 |
2 | This water type is dominated by Ca and HCO3 ions. Na is significant, ion exchange is presumed | 3 | 16.67 | 4 | 22.22 | 2 | 11.11 | 0 | 0 |
3 | HCO3 and Na are dominant, normally indicates ion exchanged water, although the generation of CO2 at depth can produce HCO3 where Na is dominant under certain circumstances | 0 | 0 | 0 | 0 | 1 | 5.56 | 0 | 0 |
4 | SO4 dominates, or anion discriminate and Ca dominant; mixed water or water exhibiting simple dissolution may be indicated. | 0 | 0 | 2 | 11.11 | 10 | 55.56 | 5 | 27.78 |
5 | No dominant anion or cation, indicates water exhibiting simple dissolution or mixing | 0 | 0 | 0 | 0 | 1 | 5.56 | 3 | 16.67 |
6 | SO4 dominant or anion discriminate and Na dominant; is water type that is not frequently encountered and indicates probable mixing or uncommon dissolution influences. | 0 | 0 | 2 | 11.11 | 0 | 0 | 1 | 5.56 |
---|---|---|---|---|---|---|---|---|---|
8 | Cl dominant anion and Na dominant cation, related to reverse ion exchange of Na-Cl waters | 1 | 5.56 | 0 | 0 | 0 | 0 | 0 | 0 |
22.22%; Class-4: Mixed water or water exhibiting simple dissolution, 2 samples 11.11% and Class-6 Mixing and uncommon dissolution influences, 2 samples 11.11%. Five classes occur in Dry season; Class-1: Recharging groundwater; 4 samples, 22.22%; Class-2; Ion exchange; 2 samples, 11.11%; Class-3 ion exchanged water, 1 samples, 5.56%, Class-4: Mixed water or water exhibiting simple dissolution; 10 samples 55.56% and Class-5 Simple dissolution or mixing, 1 samples 5.56%. Four classes occur in Drywet season; Class-1: Recharging groundwater; 9 samples, 50%; Class-4: Recharge, 5 samples 27.78% and Class-5 Simple dissolution or mixing, 3 samples 16.67% and Class-6 Mixing and uncommon dissolution influences, 1 samples 5.56%. There are no Classes; 3, 4, 5, 6, 7 and 9 in the Wet season; 3, 5, 7, 8 and 9 Wetdry; 6, 7, 8, and 9 Dry and no Classes; 2,3,7,8 and 9 in the Drywet season in Kumba.
In the Wet season, fresh recently recharging water from precipitation, exchanges ions with the weathered matrix of the aquiferous formations, while simple dissolution or mixing also goes on between the recently recharging groundwater and the existing groundwater in the aquiferous formations. In the Wetdry season, recharging groundwater having spent more time in the aquifer continues to exchange ions to a lesser extent with the matrix of the formation. While in the Dry season precipitation is absent, increasingly simple dissolution and mixing goes on between the remnants of the recently recharging groundwater and the pre-existing groundwater in the formation. In the Drywet season, new recharging water from precipitation emerges, exchanges ions with the weathered matrix of the aquiferous formations, while increasingly, simple dissolution or mixing also goes on between the recently recharging groundwater and the existing groundwater in the aquiferous formations.
The presence of Class-8 samples showing Na+/Cl− as dominant cation/anion, absence of Classes; 3, 4, 5, 6, 7 and 9 in the Wet season; Classes; 6, 7, 8, 9 in the Dry season indicates that, the groundwater in Kumba has an input related to reverse or inverse ion exchange of Na-Cl in the Wet seasonprobably of precipitation from the Atlantic Ocean nearby.
From WHO guideline values (WHO, 2017) of ions present in the groundwater have been used to calculate Water Quality IndexWQI for domestic use for four seasons in Kumba (Pradhan et al., 1998; Asadi et al., 2007) . The weighted arithmetic water quality index was calculated and recorded on
Classifications of the groundwater hardness in the study Kumba in Kumba (Sawyer & McCarthy, 1967) ; HT values were recorded as 0 - 235.59 mg/L in the Wet season, Wetdry 5.41 - 270.19 mg/L, Dry 18.26 - 264.21 mg/L and Drywet 6.19 - 235.55 mg/L. Groundwater in Kumba is soft in most areas in all the seasons 66.67% - 77.77%
Remarks | Wet | Wetdry | Dry | Drywet | |||||
---|---|---|---|---|---|---|---|---|---|
Index | Quality | No | % | No | % | No | % | No | % |
0 - 25 | Excellent | 18 | 100 | 11 | 61.11 | 12 | 66.67 | 18 | 100 |
26 - 50 | Good | 0 | 0 | 6 | 33.33 | 3 | 16.67 | 0 | 0 |
51 - 75 | Poor | 0 | 0 | 0 | 0 | 1 | 5.56 | 0 | 0 |
76 - 100 | Very poor | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
>100 | Unsuitable | 0 | 0 | 1 | 5.56 | 2 | 11.11 | 0 | 0 |
In the Dry season 5.56% is hard around Maduku Str.; Moderately hard 16.67% around Mbongo Str., Cameroon Str., Paradise, Alaska. Dry-Wet 11.11% is hard around Maduku Str. and 3 Corners; Moderately hard 16.67% around Mbongo Str., Cameroon Str.
Remarks | Wet | Wetdry | Dry | Dry-Wet | |||||
---|---|---|---|---|---|---|---|---|---|
Hardness HT | Classification | No | % | No | % | No | % | No | % |
0 - 75 | Soft | 13 | 72.22 | 12 | 66.67 | 14 | 77.77 | 13 | 72.22 |
76 - 150 | Moderately Hard | 3 | 16.67 | 4 | 22.22 | 3 | 16.67 | 1 | 5.56 |
151 - 300 | Hard | 2 | 11.11 | 2 | 11.11 | 1 | 5.56 | 4 | 22.22 |
The variations of hardness has Agro-industrial implications since in Kumba there are presently food processing plants and related business being built that might develop scaling problems if the hardness variations of 18% - 28% with seasons are not taken into consideration at the planning stage.
Parameters that are generally considered for evaluation of the suitability of groundwater for irrigation were the percent sodium (% Na), magnesium hazard (MH), residual sodium carbonate (RSC), Kelley’s ratio (KR), sodium adsorption ratio (SAR), electrical conductivity (EC), total dissolved solid (TDS) and USSL and Wilcox diagram.
a) Sodium Percentage% Na
Percentage of sodium values ranged from 0 - 100 Wet season; Wetdry, 0.71 - 19.18; Dry, 2.15 - 16.50 and Drywet, 0.41 - 27.30. Based on Wilcox classification (Wilcox, 1955) ; all 18 samples fall in the excellent to good category for all seasons
b) Kelly’s Ratio KR
Kelley’s ratio was used as one of the basis of rating groundwater for irrigation purposes (Kelley, 1953) . Values ranged from 0 to 0.07 in Wet season, 0.01 - 0.07 Wetdry season 0 - 0.026 Dry season and 0.0 - 0.07 Drywet season. All samples had KR value less than 1.00 in all four seasons thus fell under Class suitable; which is acceptable range for irrigation purposes all four seasons,
c) Residual Sodium Carbonate RSC
RSC values of groundwater samples in Kumba
d) Magnesium Adsorption Ratio MAR
MAR values of all the samples varied from −2 - 54.31 Wet season, Wetdry 0.005 - 100, Dry 1.02 - 75.22 and Drywet 1% - 100. 94.44% in the Wetdry and 61.11% Wet seasons of groundwater was suitable for irrigation while 61.11% in the Dry and 66.67% in the Drywet seasons respectively were unsuitable
e) Sodium Adsorption Ratio SAR
The sodium adsorption ratio (SAR) indicates the sodium concentration in groundwater as USSL classification of the salinity hazard (USSL, 1954) . Salinity
MAR | Class | Wet | Wet-Dry | Dry | Dry-Wet | ||||
---|---|---|---|---|---|---|---|---|---|
No | % | No | % | No | % | No | % | ||
<50 | Suitable | 17 | 94.44 | 11 | 61.11 | 7 | 38.89 | 6 | 33.33 |
>50 | Unsuitable | 1 | 5.56 | 7 | 38.89 | 11 | 61.11 | 12 | 66.67 |
hazard to crop irrigation is measured on the basis of specific conductance.
The EC values indicate majority of the samples are in the Excellent class S1C0; 50% in Wet, 38.89% in Wetdry, 38.89% in Dry, and 44.44% in Drywet. Very good S1C1 class had 33.33% in Wet, 38.89% Wetdry, 33.33% Dry and 22.22% inDrywet seasons. The Good class S1C2 had 16.67% in the Wet, 22.22% Wetdry, 27.78% Dry and 33.33% Drywet. All in the groundwater fell in the S1 salinity hazard class Excellent which is suitable for irrigation in all seasons in
From the USSL classification most of the ground water samples fell in S1-C0; S1-C1; S1-C2 classes characterized by low alkalinity-very low salinity hazard, low alkalinity-low salinity hazard and low alkalinity-medium salinity hazard respectively and hence all groundwater are suitable for irrigation during all four seasons
f) Permeability Index PI
The PI of groundwater samples in the study Kumba in m.eq/L
Depth to water varies with the seasons and the water table is the lowest during the Dry season. Most wells with depths less than eight meters dry up with just a few centimeters of water at during this period. During the Wet season, the water table is at the surface in the lowest lying areas with an exceedingly high pollution potential as run off fills the wells with all kinds of runoff loads since many wells are poorly constructed.
Ionic ratios indicate groundwater in Kumba is affected to a great extent by silicate weathering mostly Ca-silicates and Mg-silicates from the minerals found in basalts with little weathering of Na-feldspar and Na-silicates, no Na-absorption, some Sulphate from external sources, no oxidation of sulphides and no anthropogenic contribution.
Four groundwater types occur varying with seasons; CaSO4 is the dominant water type in the Wet and Wetdry seasons; MgHCO3 and Na + K-Cl Wet season; MgCl and MgHCO3 in the Wetdry; CaSO4 and CaHCO3 in the Dry and Drywet
Alkalinity Hazard | EC Class | EC (µS/cm) | Quality Remark | Wet | Wetdry | Dry | Dry-Wet | ||||
---|---|---|---|---|---|---|---|---|---|---|---|
No | % | No | % | No | % | No | % | ||||
S1 Low | C0 Very low | 0 - 100 | Excellent | 9 | 50 | 7 | 38.89 | 7 | 38.89 | 8 | 44.44 |
S1 Low | C1 Low | 101 - 250 | Very Good | 6 | 33.33 | 7 | 38.89 | 6 | 33.33 | 4 | 22.22 |
S1 Low | C2 Medium | 251 - 750 | Good | 3 | 16.67 | 4 | 22.22 | 5 | 27.78 | 6 | 33.33 |
Salinity Hazard Class | SAR meq/mole | Remarks | Wet | Wetdry | Dry | Drywet | ||||
---|---|---|---|---|---|---|---|---|---|---|
No | % | No | % | No | % | No | % | |||
S1 | <10 | Excellent | 18 | 100 | 18 | 100 | 18 | 100 | 18 | 100 |
Table14. Permeability Index classification of groundwater four Seasons (Doneen, 1962) .
seasons. Three hydrogeochemical facies occur and vary with the seasons: Ca-Mg-Cl-SO4 the most dominant occurs in the Wetdry, Dry and Drywet seasons; Ca-Mg-HCO3 hydrogeochemical facies occurring in the Wetdry, Dry and Drywet season and Na-K-SO4 occurring only in the wet season. The presence of Na + K-Cl groundwater type in Kumba has an input related to reverse or inverse ion exchange of Na-Cl in the Wet season probably of precipitation from the Atlantic Ocean nearby.
The Hydrogeochemical character of groundwater in Kumba indicates that weathering of the aquifer matrix is the primary process in the acquisition of ions while atmospheric precipitation is the secondary process controlling the groundwater aqueous geochemistry in Kumba for all seasons.
In the Wet, Wetdry, Dry and Drywet seasons; fresh recently recharging water from precipitation, exchanges ions with the weathered matrix of the aquiferous formations, while simple dissolution or mixing also goes on between the recently recharging groundwater and the existing groundwater in the aquiferous formations.
WQI Water of groundwater for domestic use is mostly excellent in all seasons.
Agro-industrial water quality evaluation of the suitability of groundwater for irrigation found indices for; % Na, RSC, KR, SAR, EC, PI, TD, USSL classification and Wilcox diagrams are within the suitable range for irrigation purposes during all four seasons. However, while Magnesium Absorption Ratio MAR for more than half of the samples were suitable during the Wet and Wetdry seasons, more than half were unsuitable in the, Dry and Drywet season. This is significant since it is during the drier seasons that irrigation water is needed.
Groundwater in Kumba is mostly soft with few moderately hard and lesser hard groundwaters in few areas in all the four seasons. These variations of hardness with seasons has Agro-industrial implications since in Kumba there are presently food processing plants and related business being built that might develop scaling problems if the hardness variations with seasons are not taken into consideration at the planning stage.
All hydrogeochemical parameters vary with seasons and these variations show the impact of annual seasonal changes on the aqueous geochemistry of groundwater in Kumba.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
We sincerely thank all the field workers and the private well owners for access and well data.
The authors declare no conflicts of interest regarding the publication of this paper.
Akoachere, R. A., Ngwese, Y. M., Egbe, S. E., Eyong, T. A., Edimo, S. N., & Tambe, D. B. (2018). Groundwater Monitoring in the Gneisso-Basaltic Fractured Rock Aquiferous Formations of Kumba, Southwest Region Cameroon: Seasonal Variations in the Aqueous Geochemistry and Water Quality. Journal of Geoscience and Environment Protection, 6, 18-50. https://doi.org/10.4236/gep.2018.611003