Assessment of the water quality of the Niger River in Bamako, Mali, based on the Water Quality Index

The Niger River, threatened by human activities, is the main drinking water source for the population of Bamako city. This study assesses the trend of Niger River pollution in Bamako using the Water Quality Index (WQI). Fourteen parameters, namely Turbidity, Potential of Hydrogen (pH), Electrical Conductivity, Dissolved Oxygen, Total Dissolved Solids, Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), Nitrate, Nitrite, Ammonium, Phosphate, Sulphate, Chloride and Copper, were employed to characterise the Niger River water quality during the period from 2016 to 2020. Parameters were measured at 15 sampling locations. High values of Turbidity, pH and high concentrations of BOD5, COD, Nitrite, Ammonium and Phosphates were recorded. The results showed that the Niger River water quality was good for 4 months and poor for 5 months during the dry season in a low flow period. Moreover, the water quality was poor during the 3 months of the wet season in the high flow period. The calculated WQI average values ranged from 75 to 100, indicating very poor water quality from upstream to downstream of Bamako city. Therefore, the Niger River water is polluted and cannot be used for drinking or industrial uses without any treatment. HIGHLIGHTS Human activities affected the Niger River in Bamako.; Quantitative and qualitative assessments reveal the river pollution status.; The water quality trend deteriorated further upstream to downstream of Bamako.; WQI indicated that the Niger River water is poor and needs appropriate treatment before any use.; Principal component analysis (PCA) showed ion distribution, indicating water mineralisation and the weak capacity of the Niger River for self-purification.;