PHYSICO-CHEMICAL CHARACTERIZATION OF THE SURFACE WATER IN THE LOWER VALLEY OF THE OUEME IN SOUTH BENIN

Surface water in the lower Oueme valley is prone to various pressures from anthropogenic activities as well as poor hygiene practices that favour its pollution. The present research aims to study the physicochemical quality of surface waters. Thus, seven (07) sampling sites have been selected with eighteen (18) parameters analysed. These are variables such as: hydrogen potential, temperature, electrical conductivity, dissolved oxygen, turbidity, suspended matter, calcium, magnesium, potassium, ammonium, nitrates, ortho-phosphates, chloride, sulphates, sodium, COD and BOD5 during high and low waters. The data were then processed through the Water Quality Assessment System (SEQ-Water) to determine the overall water quality. Similarly, Principal Component Analysis (PCA) is used to assess the relationships between the variables studied and their spatial distribution. The results show that during the two periods, surface waters are of very good quality 47.06% and 52.94%, of good quality 41.18% and 11.76%, of fair quality 17.65% observed only in low waters, of poor quality 5.88% and 11.76% and finally of very poor quality with 5.88%. As for the multivariate statistical study carried out through the PCA, it indicates the strong positive correlation of the variables NH4+, Na+, Cl-, CE and SO42- in periods of low water as well as the variables Mg2+ and T° strongly correlated in high water. Wastewater discharges, agricultural activities and poor hygiene practices are the main cause of water pollution.