Stable Isotopic Signatures (18O and 2H) and Hydrochemistry in Assessing Basement Aquifer Recharge and Driving Forces of Groundwater Quality in Parts of Ilorin, Northcentral Nigeria
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Date
2025-01-14
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Publisher
University of Technology Sarawak
Abstract
Groundwater resources in parts of Asa Local Government Area in
Kwara State, Nigeria are threatened by increasing pressure due to growing
population, and agricultural and industrial activities, which necessitates a
comprehensive assessment of the groundwater resources to ensure their
sustainability and safety for human consumption. Evaluation of groundwater
resources in parts of Asa Local Government Area in Kwara State, Nigeria was
undertaken using the integration of stable isotope of δ18O and δ2H and
hydrogeochemical tools including Water Quality Indexes, Gibbs diagrams, and
Chadha diagram towards deciphering the source of groundwater recharge as
well as factors controlling its chemistry in the study area. The collected
groundwater samples from shallow wells and deep boreholes were subjected to
major ions, trace elements, and isotope analyses. Hydrochemical models
revealed Ca-Mg-HCO3, mixed Ca-Na-HCO3, and Na-HCO3 water facies
suggesting the early transformation stage of the groundwater. The WQI indexes
ratings revealed essentially fair to good to excellent water quality for human
consumption. The isotope values in groundwater samples vary between -
4.12±0.1 ‰ and -2.60±0.1 ‰ and between -15.0±0.2 ‰ and -24.0±0.2 ‰ for
δ18O and δ2H, respectively, indicating isotopically relatively enriched
groundwater. The plot of δ18O and δ2H in groundwater samples along meteoric
lines indicate meteoric origin with little effect of evaporation. Residence time
evaluation using Ec and δ18O relationship identified recent recharge and recent
recharge but polluted groundwater. In addition, the relation between salinity
and δ18O revealed water-rock interaction as the main geochemical process
controlling groundwater chemistry.
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Keywords
Hydrogeochemical, residence time, meteoric water, stable isotopes, water-rock interaction.