CONTRIBUTION TO THE ESTIMATION OF SOME MAJOR IONS AND MINERALS IN SURFACE SEDIMENTS OF THE LAKE LERE BASIN, MAYO-KEBBI WEST (REPUBLIC OF CHAD)

Subject to constraints linked to human activities and climate change, sediments in the Lake Lere basin have accumulated various inorganic materials. The objective of this study is to estimate the levels of several major ions and minerals, namely nitrate, sulphate, phosphate, carbonate,chloride,silica,calcium and magnesium,in the surface sediments of the Lake Lere basin. These ions were analysed in accordance with French standards after a series of physico-chemical treatments of the samples. The results showed that the concentrations of the different ions analysed varied from one ion to another and depended on the nature of the sites studied. The average concentrations (mg/kg) obtained are respectively: (17.75), (41.25), (61.05), (106.2), (2.81), (422.68), Ca2+ (849) and Mg2+ (636.11). According to these results, the levels of most minerals remain low compared to their concentrations in the geochemical reference background. However, phosphate levels are particularly high above the threshold. Consequently, the sediments of the Lake Lere basin are enriched in phosphate. Furthermore, principal component analysis made it possible to distinguish three groups of sites: G1 (S1, S4, S5 and S8), G2 (S2 and S3) and G3 (S6 and S7). Group G1 is enriched in nitrate, carbonate, sulphate and silica; group G2 is enriched in chloride and group G3 in phosphate, calcium and magnesium.