Assessment of Surface Water Quality Using the Water Quality Index (WQI) and Multivariate Statistical Analysis (MSA) in Nyanga River, Republic of the Congo
The aim of this study was to assess the physico-chemical and mineralogical quality of surface waters used by populations for their domestic and agro-pastoral activities in the Nyanga district in the south-west of the Republic of the Congo. Descriptive statistics, hydrochemistry (Piper diagram), Principal Component Analysis (PCA) and hierarchical ascending classification (HAC) were used to determine the quality, chemical facies and mineralization phenomena of surface waters. Physico-chemical analyses were carried out on 6 samples taken in May 2023. The results showed that the waters studied are acidic, with a pH between 4.99 and 5.76. They are poorly mineralized, with an average electrical conductivity of 12.37 μS/cm. In the study area, the water is chloride-calcium-magnesium and bicarbonate-calcium-magnesium. Analysis of heavy metals shows that all values, with the exception of iron and nitrate, comply with WHO guidelines on water potability, with the exception of the point sampled at the confluence of the Nyanga, where values were slightly higher than normal, i.e. 0.06 μg/L for manganese and 0.03 μg/L for nitrate. Other heavy metals such as Lead (Pb) and Copper (Cu) were analyzed and confirmed that their concentration was within the authorized detection limits. Water mineralization is controlled by phenomena such as soil rainwashing, acid hydrolysis of rocks and input from high rainfall. This study shows that water resources in the Nyanga watershed are not subject to anthropogenic pressure, but to a totally natural phenomenon. Given its acidity, untreated consumption of this water could present health risks for the population.
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