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Application of geochemical and stable isotopic tracers to investigate groundwater salinity in the Ochi-Narkwa Basin, Ghana

Ganyaglo, Samuel Y., Osae, Shiloh, Akiti, Tetteh, Armah, Thomas, Gourcy, Laurence, Vitvar, Tomas, Ito, Mari, Otoo, Isaac A.
Hydrological sciences journal 2017 v.62 no.8 pp. 1301-1316
basins, chlorides, coasts, deuterium, geochemistry, groundwater, groundwater flow, ions, isotope labeling, mixing, models, oxygen, rain, saltwater intrusion, silicates, soil water, stable isotopes, water salinity, water salinization, weathering, Ghana
Rainwater, groundwater and soil-water samples were analysed to assess groundwater geochemistry and the origin of salinity in the Ochi-Narkwa basin of the Central Region of Ghana. The samples were measured for major ions and stable isotopes (δ ¹⁸O, δ ²H and δ ¹³C). The Cl ⁻ content in rainwater decreased with distance from the coast. The major hydrochemical facies were Na-Cl for the shallow groundwaters and Ca-Mg-HCO ₃, Na-Cl and Ca-Mg-Cl-SO ₄ for the deep groundwaters. Groundwater salinization is caused largely by halite dissolution and to a minor extent by silicate weathering and seawater intrusion. Stable isotope composition of the groundwaters followed a slope of 3.44, suggesting a mixing line. Chloride profiles in the soil zone revealed the existence of salt crusts, which support halite dissolution in the study area. A conceptual flow model developed to explain the mechanism of salinization showed principal groundwater flow in the NW–SE direction.