Impacts lithologiques et anthropiques sur la qualité des eaux du petit bassin versant de chiémbûh dans le plateau bamoun (Ouest- Cameroun)

Abstract

Climate variability and/or change associated with anthropogenic activities are at the root of water degradation and quantitative and qualitative availability on a global scale in general, and in sub-Saharan Africa in particular. It is in this context that the present study aims to assess the lithological and anthropogenic impacts on water quality in the upstream Chiémbùh watershed (BVAC) at Foumban (West Cameroon). To achieve this, in addition bibliographical research, field and laboratory work has been carried out, including: in-situ measurement of physico-chemical parameters, water sampling during the dry (February) and rainy (August) seasons hydrology, physiographic characterization and analysis of physico-chemical and bacteriological parameters of BVAC waters. In physiographic terms, the BVAC has a surface area of 28.55 km, a perimeter of 24.75 km and a compactness index of 1.30, giving it an elongated shape similar to an equivalent rectangle, 9.35 km long and 3 km wide. The Chiémbùh stream, which drains this basin, flows from northwest to southeast, emptying into the Mfû river after a journey of around 18 km. Physico-chemically, the waters of the BVAC are acidic (4.38 ≤ pH ≤ 6.35), weakly to very weakly mineralized (7.6 ≤ CE ≤ 180.2 μS/cm, 124.60 ≤ TZ ≤ 1346.65 μeq/l) with a hydrochemicalfacies : bicarbonate calci-magnesian. This is explained by its plutono-metamorphic lithological substratum and thick ferralitic soil cover. Statistical analyses (correlation matrix and PCA) highlight two hydrochemical processes responsible for water mineralization: (i) water-rock interaction and (ii) anthropogenic activities. The presence of fecal coliforms and streptococci indicates fecal pollution of animal origin. These bacterial colonies are elevated in the dry season in wells and in the rainy season in springs. On the whole, this water complies with WHO and ANOR standards, except for certain parameters (pH, NO, CF and, SF) and can be used for other purposes (agricultural, livestock, domestic). But a preliminary treatment is necessary before any human consumption.