Impact of Acid Mine Drainage from the Abandoned Kef Oum Teboul Mine on the Watershed of Lake Tonga (Algeria)

Acid Mine Drainage (AMD) from the abandoned Kef Oum Teboul mine in Northeastern Algeria poses a persistent environmental threat to the Lake Tonga watershed. This study aims to assess the spatial extent and geochemical dynamics of AMD contamination in water and soil along two main drainage routes leading from the mine’s Eastern and Western slopes. Through two sampling campaigns, key parameters such as pH, sulfate SO42-, and heavy metals (Pb, Zn, Fe) were analyzed to determine the mobility, attenuation, and retention mechanisms of contaminants. The results reveal strongly acidic water near the mine (pH as low as 3.2) with sulfate concentrations reaching up to 1200 mg/L, and high Pb levels exceeding 0.5 mg/L in some upstream locations. Downstream, water pH increases toward near-neutral values due to the buffering capacity of clay-rich soils, and heavy metal concentrations generally decline, with Pb and Zn reduced by over 70% in several stations. Fe shows complex behaviour, remaining elevated in oxidising zones and accumulating in sediments. Soils along the talwegs show elevated sulfate content and trace metal accumulation, particularly where water flow slows or evaporative conditions dominate. Geochemical variations between the two slopes reflect the influence of hydrodynamics and lithology on contaminant pathways, with higher mobility and dispersion observed on the eastern side. This integrated evaluation underscores the need for site-specific remediation approaches such as passive treatment systems and soil amendments and long-term monitoring to mitigate ecological degradation and protect vital ecosystem services in the region. Major Findings: Acid mine drainage from the abandoned mine causes strong local contamination with acidic pH, high sulfates, and elevated Pb, Zn, and Fe. Downstream attenuation occurs via dilution, clay adsorption, and secondary mineral formation, with hydrology and lithology controlling pollutant distribution.