Spatio-temporal evolution of the physico-chemical parameters of the Inaouen wadi and its tributaries

Abstract

In order to assess the water quality of the Inaouen Wadi and its main tributaries, a monitoring of the physico-chemical parameters of twelve stations has been carried out during an entire annual cycle (year 2019). We measured ten parameters (T°, pH, electrical conductivity, total hardness, sulphates, ortho-phosphates, dissolved oxygen and nitrogen compounds) and five heavy metals were determined (iron, zinc, copper, lead, silver). The upstream stations (S1, S3, S4, S5 and S6) are the most polluted. These stations have the highest sulphate, ortho-phosphate, biological oxygen demand and nitrogen compounds. This pollution is a consequence of the solid and liquid wild discharges brought by the S1 and S5 tributaries and the urban agglomerations installed on the Inaouen river banks, which have a direct and important impact on the quality of water in the whole wadi. In addition, heavy metals (Zn, Iron, Ag and Cu) present high levels upstream of the Inaouen while passing downstream. A statistical multi-variate study using PCA (Principal Component Analysis) revealed that the content of these parameters remains low downstream of this river (S11) and the tributaries S10, S9 and S7 compared to upstream (S5). This pollution generated upstream is mainly caused by human actions (wastewater discharges, agricultural and industrial activities) without prior treatment. The main factors that reduce the pollution load downstream of the Inaouen wadi are self-purification and the tributaries leaving the Middle Atlas characterized by good water quality.