Hydrogeochemical Fingerprints of Groundwater in Crystallizine Terrain of South-Western Nigeria

Abstract

A total of 63 representative water samples were collected from 50 hand-dug wells and 13 boreholes in the study area from December to January before the onset of rainy season. Two sets of samples were collected from every location; a set of the samples was acidified with two drops of nitric acid (10% by volume) for cations determination while the other was not acidified. Physico-chemical parameters (temperature, total dissolved solutes, electrical conductivity and pH) of the water samples were determined in-situ using a multimeter-probe. The water samples were analyzed for cations and anions using Atomic Absorption Spectrometry, Flame Photometry Emission and titrimetric methods. Results obtained were analysed using descriptive statistics, standard hydrochemical plots and irrigation indices. The results showed that physical stable parameters such as TDS ranged from 301.00-1753.00 mg/l, EC76.00-998.00µS/cm, Temperature 28.50–31.10°C and pH 5.60–10.00; The concentration of ions (mg/l) such as Na⁺ ranged from 2.60–22.50, K⁺, 2.50–16.30, Ca²⁺ 5.30–18.50, Mg²⁺, 1.28–34.70, SO₄²⁻, 7.10–25.70, HCO₃⁻, 15.30-192.50, Cl⁻, 18.20-102.80 and NO₃⁻, 0.00-5.60. The physico-chemical parameters revealed that the water samples are suitable for domestic usage with little exception of a few locations with high Mg. The dominant water types in the study area were calcium-chloride-type and mixed calcium-magnesium-chloride-type. The controlling mechanisms and processes of the groundwater were largely dominated by rock-water interactions (weathering) and reverse ion exchange. The geochemical signatures of the water showed that the water was under the influence of organic matter and CO₂, and that the water was rich in Mg²⁺ but depleted in Na⁺.