Spatial and seasonal variation of the physico-chemical parameters and the major ions of the groundwater in granitoids terranes of Tiébélé area (southern Burkina Faso)

Abstract

For the present study, 28 boreholes localized in granitoids terranes were sampled in Tiébélé area (southern Burkina Faso) in order to characterize the spatial and seasonal variation of their physico-chemical parameters. The laboratory analyzes were about HCO₃^-, SO₄^2-, NO₃^-, Cl^-, K⁺, Na⁺, Ca²⁺, Mg²⁺. The results show a high spatial distribution of the parameters. Most of the cations do not show an increase of theirs concentrations during the rainy season in comparison with dry season data. On the other hand, the anions show increase of their concentrations during the rainy season. Regarding the mean concentrations, the following order was found in the present study: HCO₃^->Ca²⁺>Na⁺>NO₃^-=Mg²⁺>Cl^->SO₄^2->K⁺ in the dry season and
HCO₃^->Ca²⁺>Na⁺>NO₃^->Mg²⁺>SO₄^2->Cl^->K⁺ in the rainy season. The dominant water facies is HCO₃-Ca-Mg. The main source of the major ions is due to natural conditions (alteration of the bedrock, leaching of soil and unsaturated zone). However, it is important to notice that some samples show anthropogenic contamination regarding the high concentrations of NO₃^-, Cl^-, and K⁺. Except three samples showing a concentration of NO₃^- above the limit of 50 mg/L recommended by WHO (World Health Organization), all the groundwater resources of the present study can be used as drinking water. In addition, only one is very hard and non-recommended.