Hydrochemistry of shallow groundwater and surface water in the Ndop plain, North West Cameroon

Abstract

This study was conducted on the hydrochemistry of shallow groundwater and surface water in the Ndop plain, North West Cameroon. The objectives were to determine the physico-chemical characteristics of water, controls on water chemistry and suitability for drinking and irrigation. Forty-six shallow groundwater and 26 surface water samples were investigated. Field measurements of physical parameters were preceded by chemical analyses of the samples for major ions and F-. About 69% of the water sources had pH values below 6.5, classifying the water as barely acidic. Electrical conductivity (<282 μS/cm) and total dissolved solids (<183 mg/l) were low suggesting low-mineralised and freshwater. The relative abundance of major ions (meq/l) was Na²⁺>Ca²⁺>Mg²⁺>K⁺ for cations and HCO₃^->>NO₃ -≥ Cl^->SO₄^2- for anions. Major ion concentrations were low, and within the WHO guidelines for drinking water, but F- concentrations were much lower (<0.39 mg/l) and below guideline value. Main water types and proportions were Na-HCO₃ (53 %), Ca-HCO₃ (35 %) and a mixed Na-Ca-HCO₃ (11%). Predominant processes influencing water chemistry were incongruent dissolution of silicate minerals and cation-exchange of Na+ in rocks for Ca²⁺ in water. The low major ion concentrations indicated low water-rock interactions and short residence time. The analysed water was suitable for irrigation.

Key words: Water chemistry, hydrochemical controls, drinking-irrigation quality, Ndop plain, Cameroon.