Spatiotemporal study of zinc, copper and lead contamination of sediments in the Oued Moulouya (NE-Morocco)

Abstract

Sediment pollution by trace metals is a major environmental issue for aquatic ecosystems, particularly in regions impacted by historical mining activities. This spatiotemporal study conducted on the Oued Moulouya (northeast Morocco), one of the country’s largest river basins, aimed to assess the extent of copper (Cu), lead (Pb), and zinc (Zn) contamination in relation to abandoned mining sites at Zaida and Aouli. Eight sampling stations, distributed from upstream to downstream, were monitored during both dry and wet seasons. Results revealed maximum Zn concentrations at station S2 (96.51 mg/kg in the dry season, 84.21 mg/kg in the wet season) and Pb concentrations peaking at 182.14 mg/kg as a mean of the dry season, both far exceeding international guideline values and indicating persistent pollution. Cu concentrations showed a progressive decrease from upstream to downstream, with notable peaks at S1 nearest the Zaida mine site (35.04 mg/kg, wet season) and S7 on the Oued Za tributary, highlighting the role of tributaries in contaminant dispersion. Seasonal variations indicated slightly higher metal concentrations during the dry season, suggesting increased mobilisation and reduced dilution. These findings confirm the lasting impact of mining residues and underscore the urgent need for targeted management measures to protect the river and its ecological functions.