Water samples were collected from 17 sources using water sampling bottles. These sources include rivers, streams, and boreholes, with most being streams. Water sampling was conducted once during the coinciding harvest and rainy seasons (May). Multiple samples were collected from 17 irrigation sources which were rivers serving the district’s major farms to ensure broad representation. The locations of water samples were recorded with a handheld GPS. While sampling sites were distributed randomly across the district, selection was specifically guided by and focused on the dominant water sources utilised for agricultural irrigation in the region. The samples were sealed, stored in the ice chest at low temperatures, and transported to the Environmental and Safety Engineering laboratory at the University of Mines and Technology, Tarkwa, Ghana, for analysis. Figure 1 below shows the locations of the sampling points and their corresponding GPS locations.

Figure 1. Sample location.

Physicochemical parameters—including pH, electrical conductivity (EC), total dissolved solids (TDS), and salinity—were measured using a multi-parameter meter calibrated with standard buffer solutions (pH 4.01, 7.00, and 10.01), ensuring deionised water rinses between successive measurements. Total hardness (TH), total alkalinity (TA), and boron (B) concentrations were determined photometrically.

For major cation analysis (Na⁺, Mg²⁺, Ca²⁺ and K⁺), 100 mL sample aliquots were digested with 5 mL of concentrated nitric acid ( HCO 3 − ) and heated for 2.5 hours. Concentrations of Na⁺, K⁺, and Ca²⁺ were subsequently quantified using a flame photometer. Major anions (Cl⁻, SO 4 2 − , CO 3 2 − and HCO 3 − ) were systematically analysed using standard hydrochemical protocols.

Quality Assurance and Quality Control (QA/QC)

To ensure analytical precision and accuracy, rigorous QA/QC protocols were integrated into the laboratory workflow. Every analytical batch included procedural blanks to monitor for reagent-grade contamination, with all blank values falling below the method detection limits. Instrument precision was verified through replicate analyses of randomly selected samples, ensuring a relative percent difference (RPD) of <5%. Analytical accuracy was further validated using certified reference materials (CRMs) to determine the percentage recovery of each heavy metal, with acceptable recovery rates maintained within the 80% - 120% range. Additionally, mid-range calibration standards were re-analyzed every ten samples to check for instrumental baseline drift, ensuring that all reported concentrations met established threshold requirements for scientific reproducibility.

The Sodium Adsorption Ratio (SAR) assesses the potential for sodium to participate in soil cation-exchange reactions relative to calcium and magnesium. Expressed in milliequivalents per litre (meq/L) as defined in Equation (1), higher SAR values indicate elevated risk of soil sodication and reduced irrigation suitability. Waters with an SAR exceeding 13 are classified as sodic; however, an SAR between 1 and 3, paired with an EC < 700 μS/cm, indicates a negligible risk of impairment of soil infiltration rate ([8]).

SAR = Na⁺/√((Ca²⁺ + Mg²⁺)/2) (1)

where concentrations are in Meq/L.

The Magnesium Adsorption Ratio (MAR) evaluates the proportion of magnesium relative to total divalent cations, as high magnesium adsorption degrades soil structural properties. Soil physical degradation typically occurs when the MAR exceeds 50% (Equation (2)) ([9]).

MAR = (Mg²⁺ Ca²⁺) × 100/(Ca²⁺ + Mg²⁺) (2)

where concentrations are in Meq/L.

Assessing the sodium percentage (Na%) is critical because elevated sodium levels induce structural sodicity hazards and impair soil permeability, as calculated via Equation (3) ([9]).

Na% = (Na⁺¹ × 100)/(Ca²⁺ + Mg²⁺ + Na⁺¹ + K⁺¹) (3)

where concentrations are in Meq/L.

The Soluble Sodium Percentage (SSP), calculated via Equation (4), is a critical index for evaluating sodicity hazards, as highly elevated SSP values can impair seed germination and cause stunted vegetative growth.

SSP = (Na⁺ + K⁺) × 100/(Ca²⁺ + Mg²⁺ + Na⁺ + K⁺) (4)

where all concentrations are expressed in Meq/L.

The bicarbonate hazard is usually expressed as Residual Sodium Carbonate (RSC). RSC is always evaluated using Equation (5) below.

where all concentrations are expressed in Meq/L.

Elevated bicarbonate concentrations promote the precipitation of calcium and magnesium as carbonate minerals, raising the relative proportion of sodium and exacerbating sodicity hazards. This geochemical process is quantified via the Residual Sodium Carbonate (RSC) index; under the [7] classification framework, irrigation water is considered safe at an RSC < 1.25 meq/L, marginally suitable requiring targeted management between 1.25 and 2.5 meq/L, and entirely unsuitable at values exceeding 2.5 meq/L.

Irrigation water salinity originates from the geogenic weathering and dissolution of soil minerals such as calcite and gypsum ([13]). As irrigation water evaporates or is transpired, these dissolved salts accumulate in the root zone ([5]), elevating soil osmotic pressure and restricting plant water uptake to induce growth-stunting physiological moisture stress ([3]).

Under the [17] classification framework, irrigation suitability is categorized based on Total Dissolved Solids (TDS) concentrations: values below 450 mg/L are classified as “excellent”, 450 to 750 mg/L as “good”, 750 to 2000 mg/L as “permissible”, and concentrations exceeding 2000 mg/L as “unsuitable” for agricultural use. In this study, all monitored sampling locations fell within the highly safe, “excellent” range ([17]), confirming their suitability for sustainable agricultural irrigation based on TDS levels.

Total Hardness (TH) reflects the concentration of divalent metallic cations, primarily Ca²⁺ and Mg²⁺. While excessively high TH leads to mineral scale formation in irrigation piping and localised crop damage ([1]), extremely low hardness is also structurally problematic. In this study, all monitored samples fell within the “soft water” classification (Table 1).

Standard frameworks classify total hardness (as CaCO₃) into soft (0 - 60 mg/L), moderately hard (61 - 120 mg/L), hard (121 - 180 mg/L), and very hard (>180 mg/L) regimes ([17]; [16]; Table 1). Agronomically, continuous irrigation with soft water triggers clay dispersion, structural collapse, and impaired infiltration due to a deficiency of divalent Ca²⁺ and Mg²⁺.

Conversely, total alkalinity—the acid-neutralizing capacity driven by H₂CO₃, HCO 3 − , and CO 3 2 − —remained withinafe limits for most samples, except BH02, S02 and S03, which fell below recommended thresholds ([1]). Highly alkaline water exhibits strong buffering capacities that resist pH reduction ([13]), potentially locking soil pH in alkaline ranges and reducing the bioavailability of essential iron, manganese, and phosphorus.

Table 1. Hydrochemical characterisation and irrigation quality assessment indices.

Total Dissolved Salts

Total Dissolved Solids (TDS), originating from geogenic weathering and anthropogenic runoff, accumulate in the root zone during evapotranspiration. This raises soil osmotic potential and restricts moisture absorption, inducing “physiological drought”, stunted vegetative growth, and reduced crop yields ([1]). Within the study area, these geochemical pathways are heavily influenced by surrounding land-use activities, notably active quarry mining operations and the integration of livestock farming within the crop cultivation zones. Quarry mines accelerate geogenic weathering by mechanically fracturing bedrock and exposing fresh mineral surfaces to precipitation, thereby facilitating the dissolution and leaching of inorganic salts into nearby agricultural water and soil systems. Concurrently, the co-practised animal farming introduces a significant anthropogenic footprint; surface runoff and leaching from manure and livestock waste enrich the local hydrological system with highly soluble ions (such as nitrates, chlorides, sodium, and potassium), thereby compounding the regional TDS accumulation. Under the [17] classification framework, irrigation water is categorised as excellent (<450 mg/L), good (450 - 750 mg/L), permissible (750 - 2000 mg/L), and unsuitable (>2000 mg/L). In the present study, all analysed locations exhibited TDS concentrations well within the excellent threshold (<450 mg/L), representing negligible osmotic and salinity risks for local agricultural activities.

Electrical conductivity (EC) is the primary indicator for assessing irrigation salinity hazards. Elevated EC increases soil osmotic pressure, inducing “physiological drought” that restricts moisture absorption and forces plants to expend metabolic energy to overcome osmotic barriers, leading to cellular dehydration and stunted development ([1]). According to the US Salinity Laboratory, EC values below 250 μS/cm represent low-salinity hazards, while values exceeding 750 μS/cm pose high-salinity hazards. In this study, all analysed water sources except sample BH02 exhibited low-to-medium salinity hazards, indicating high agricultural suitability with no immediate threat of root-zone salinisation.

Figure 2. Magnesium adsorption ratio.

The Magnesium Adsorption Ratio (MAR) assesses structural soil risks, as excess Mg²⁺ relative to Ca²⁺ induces sodium-like clay dispersion and deflocculation due to the larger hydrated ionic radius and weaker binding affinity of Mg²⁺ to clay complexes ([11]). Under the [11] framework, values exceeding 50% are categorized as unsuitable/hazardous, whereas those below 50% are considered suitable. In this study, the majority of analysed samples were unsafe (MAR > 50%), with sample BH02 recording a suitable peak of 46%, indicating no immediate magnesium hazard to regional soil structures (Figure 2).

The sodium percentage (Na%) assesses agricultural sodicity by calculating the ratio of monovalent Na⁺ and K⁺ to total cations ([13]; [6]; [14]). Excessive sodium displaces divalent Ca²⁺ and Mg²⁺ on clay complexes, triggering clay dispersion, colloid swelling, and macro-porosity collapse ([10]; [12]).

The [17] framework classifies irrigation suitability based on Na% limits: excellent (<20%), good (20% - 40%), permissible (40% - 60%), doubtful (60% - 80%), and unsuitable (>80%). Hydrochemical analysis showed that the majority of study samples were unsuitable (Na% > 80%), with only S01, S12, S14, and BH02 classified as doubtful ([13]) and S03 as permissible ([6]). This severe sodium footprint threatens long-term soil alkalization and compaction, necessitating calcium-rich soil amendments ([17]; Figure 3).

Figure 3. Sodium percentage distribution.

Compared to the sodium percentage, the Sodium Adsorption Ratio (SAR) is a more reliable predictor of soil permeability hazards because it accounts for the flocculating and mitigating effects of divalent Ca²⁺ and Mg²⁺ on clay dispersion ([13]). This mathematical relationship is defined in Equation (6), with all ionic concentrations expressed in milliequivalents per litre (meq/L).

SAR = [Na⁺]/√(0.5 × ([Ca²⁺] + [Mg²⁺])) (6)

Applying high-SAR water increases the soil’s exchangeable sodium percentage (ESP), causing clay lattice swelling, soil aggregate breakdown, and surface physical sealing, which severely restricts water infiltration and induces crop water stress and poor root aeration ([10]; [12]). Under standard classifications, water with an SAR < 10 is classified as “Excellent” (low hazard), while values exceeding 26 are unsuitable.

Under the [6] frameworks, irrigation water is classified by SAR into excellent (<10, low hazard), good (10 - 18, medium hazard), fair (19 - 26, high hazard), and poor/unsuitable (>26, very high hazard). Despite elevated sodium percentages (Na%) in this study, all calculated SAR values remained within the safe “Excellent” to “Good” ranges (SAR < 18), demonstrating that divalent cations successfully mitigate immediate soil sodicity risks (Figure 4).

Figure 4. Sodium adsorption ratio.

Distinct from SAR, the Soluble Sodium Percentage (SSP) evaluates irrigation sodicity hazards by calculating the ratio of soluble monovalent Na⁺ and K⁺ to total cations, expressed in meq/L in Equation (7).

SSP = ([Na⁺] + [K⁺]/[Ca²⁺] + [Mg²⁺] + [Na⁺] + [K⁺]) × 100 (7)

An SSP > 50% promotes exchangeable sodium accumulation, clay dispersion, and pore blockage, severely degrading soil permeability and inducing root-zone waterlogging and stunted crop growth ([5]). All analyzed samples exceeded this critical threshold, making them unsuitable for continuous irrigation without amendments. This elevated sodium footprint stems from both geogenic silicate weathering and anthropogenic contributions (e.g., fertilizer leaching, greywater runoff). Standard agricultural classifications ([17]) define suitability based on SSP: excellent (<20%), good (20% - 40%), permissible (41% - 60%), doubtful (61% - 80%), and unsuitable (>80%).

3.7.1. Potential Hydrogen (pH) and Overall Salinity HazardSource Apportionment

Irrigation water pH controls soil chemical equilibrium and nutrient bioavailability. While alkaline water (pH > 8.5) promotes calcium carbonate (CaCO₃) precipitation and physical blockages in micro-irrigation systems ([5]), sub-optimal acidic water (pH < 6.5) was observed in samples BH03, S01, S03, S05, S06 and S12. Continuous acidic irrigation enhances the solubility of toxic trivalent aluminum (Al³⁺) and divalent manganese (Mn²⁺), causing phytotoxicity and stunted root elongation, while accelerating basic cation leaching (Ca²⁺, Mg²⁺, K⁺) and fixing orthophosphates into insoluble complexes.

Conversely, overall salinity poses no immediate osmotic hazards. Elevated salinity disrupts root moisture uptake by lowering soil osmotic potential, inducing physiological drought, leaf necrosis, and yield loss ([5]). All analyzed water samples remained safely below the FAO “No Restriction” threshold (EC < 0.7 dS/m; TDS < 450 mg/L), indicating negligible osmotic risks.

3.7.2. Specific Ion Hazards: Boron (B) and Chloride (Cl⁻)

Boron (B) possesses an exceptionally narrow safety margin; deficiency halts meristematic growth, while excess accumulates in leaf margins, causing chlorosis, photosynthesis disruption, and necrosis ([5]). In this study, 100% of the samples exceeded the FAO safety threshold of 0.7 mg/L (ranging from 0.80 to 1.70 mg/L), indicating a widespread boron toxicity risk. This elevated footprint is attribute to geogenic weathering of borosilicates, exacerbated by anthropogenic fertilizers and detergent-laden greywater.

Table 2. Hydrochemical analytical results of monitored water samples.

Conversely, chloride (Cl⁻) poses no agricultural threat. Although excess chloride can accumulate in foliar tissues via transpiration to cause leaf necrosis ([5]), concentrations across all monitored sites were exceptionally low (<0.50 to 6.30 mg/L), remaining orders of magnitude below conservative FAO thresholds of 142 mg/L (surface) and 106 mg/L (sprinkler). The comprehensive hydrochemical concentrations of these major anions and cations across the monitored locations are compiled in Table 2.

3.7.3. Operational and Agronomic Hazards: Iron (Fe) and Residual Sodium Carbonate (RSC) Source Apportionment

Dissolved iron (Fe) concentrations exceeded the FAO safety threshold of 1.0 mg/L in the majority of samples ([5]), with severe elevations in S11 (9.75 mg/L), S12 (9.27 mg/L), R01 (8.33 mg/L), and S09 (7.62 mg/L); only BH01, BH02, BH03, S02, and S14 were safe. Operationally, dissolved Fe²⁺ undergoes aeration-induced oxidation to precipitate as insoluble ferric hydroxide (Fe(OH)₃) slime, which promotes bacterially mediated emitter clogging. Agronomically, excess soluble iron under acidic conditions binds with phosphate anions to form insoluble complexes, locking out essential phosphorus and molybdenum.

Lastly, bicarbonate-induced hazards, assessed via the Residual Sodium Carbonate (RSC) index, were negligible. All samples fell safely within the acceptable limit of <1.5 meq/L, indicating zero risk of bicarbonate-induced soil or crop degradation.