Assessment of groundwater recharge in Egbako aquifer, Northern Bida Basin using geochemical and stable isotope data

Abstract

Most Sub-Saharan Africa countries including Nigeria rely heavily on groundwater resource for their domestic, agricultural and industrial uses because of its ease of development, naturally great quality and growing demand arising from rapid population growth. Understanding the evolution and recharge of groundwater is mandatory for preserving and effective use of water resources. This study employed hydrochemical and stable isotope analyses to assess groundwater recharge and evolution of the Egbako aquifer in the Northern Bida Basin, Central Nigeria. Thirty-five (35) water samples from boreholes, hand-dug wells and springs were collected in the study area for this purpose. Results revealed that about 50% of the water are mixed Ca – Na – HCO₃ and mixed Ca – Na – HCO₃ and mixed Ca – Mg – Cl; while Ca – HCO₃ type accounts for 36%. Ionic loading is in the order Ca²⁺ > K⁺ > Na⁺> Mg²⁺ for the cations while it is HCO_3ˉ> Cl-> SO₄^2-> NO₃^-> NO₂^- for the anions, with Ca, Mg, K, SO₄, Cl playing leading roles in the groundwater mineralization. Groundwater quality is generally within the WHO drinking water guideline, with elevated nitrate (> 50 mg/L) in 11% of the samples pointing to some anthropogenic influence. Bivariate plots showed that silicate weathering, cation exchange and evaporite dissolution are the major hydrochemical processes controlling groundwater chemistry. Results of stable Isotope shows a depletion of δ¹⁸O (-2.87 to -4.81‰ VSMOW) signifying that the Egbako aquifer is recharged largely from meteoric sources through rapid infiltration of rainwater with low imprint of kinetic evaporation.