Analyzing surface water quality and assessing environmental impacts downstream of the Tafna river (northwest Algeria)

The Tafna river serves as a model for assessing surface water and environmental quality by combining water quality and pollution indices using multivariate statistical methods. Thirty-six surface water samples were analyzed to assess 13 indicators. The results indicate contamination of the surface waters of the Tafna river by organic matter and the influence of lithology (presence of calcite), leading to an enrichment in Cl⁻, SO₄²⁻, and Ca²⁺ by dissolution (9.6–4.8 and 4.06 mg.l⁻¹, respectively). During the summer and autumn, pH, electrical conductivity (EC), biochemical oxygen demand (BOD) reaching 57 mg.l⁻¹, chemical oxygen demand (COD) at 90.9 mg.l⁻¹, N-NH₄⁺, and N-NO₃⁻ showed significant increases. In addition, the pollution index revealed the absence of pollution during winter and early summer but moderate levels of pollution in autumn. In addition, the spatial distribution of the water quality index (WQI) indicates good water quality in the estuary upstream to 54.94, but progressive deterioration upstream. However, analysis of the correlation matrix highlighted the influence of various sources, both natural and human, on surface water quality. In particular, a significant correlation (R² = 0.9) was observed between Ca²⁺ and HCO₃⁻ concentrations, indicating a close relationship between these two elements. Organic pollution of the waters of the Tafna river has been strongly influenced by wastewater discharge and agricultural activities, which could lead to potential health risks if consumed. The results of this study provide a sound scientific basis to support decision-making and the implementation of measures to preserve and sustainably manage the Tafna river.