River water quality is particularly of concern in semi-arid countries with limited water resources. Increasing anthropogenic activities can lead to the accumulation of trace metals (TM) in bottom sediments, which is a specific storage compartment. The present study aimed to investigate the geochemistry of trace metals (As, Cd, Co, Cr, Cu, Ni, Pb, Zn) and of some physico-chemical parameters in bottom sediments from the Sebou basin, which represents 1/3 of the surface water resources of Morocco. The order of abundance of the metals was Zn > Cr > Cu > Ni > Pb > Co > As > Cd. A major fingerprint of weathering on metal concentration, and point and non-point anthropogenic sources were highlighted. The origin and intensity of the contamination were determined using a combination of geochemical indicators. The contamination was on the whole moderate, with Cr, Zn, Cu, and Pb as the most enriched metals, especially at the A1, S3, and S4 stations located downstream of Fez city, well known for its intensive industrial and tannery activities. A multi-variate analysis evidenced the strong link between natural elements such as Co with clays and Fe oxides, and As with Ca, whereas Cd, Cu, Cr, Ni, Pb, Zn, partly originating from anthropogenic activities (industrial and domestic waste, agricultural inputs), were linked to phosphorus, oxides, carbonates, and/or POC, indicating their anthropic source and/or control by sediment compounds. Cadmium, Pb, and Cu were the most available metals. Finally, in addition to Cd, Pb and Zn were identified as hazardous metals in sediments as evidenced by the positive relationship between the proportion of the labile fraction and the enrichment factor revealing anthropogenic inputs.

Due to increasing anthropogenic activities, trace elements (TE) remain a major concern particularly in semi-arid countries of limited water resources. In this context, the present study aimed at understanding the geochemistry of trace elements in bottom sediments from the Sebou basin, representing 1/3 of the surface water resources of Morocco. Total concentrations of trace elements (As, Cd, Co, Cr, Cu, Ni, Pb, Zn) and some physico-chemical parameters were measured in the fraction <63µm. The order of abundance of the elements was Zn>Cr>Cu>Ni>Pb>Co>As>Cd. The enrichment factor calculation showed that 70% of the samples were naturally concentrated in trace elements, specially As and Ni, as well as Cd and Pb, except in some stations. On the opposite, the most enriched elements were Cr, Zn and Cu. Chromium presented an enrichment higher than 5 and toxicity risks at some stations, such as downstream the Fez city known for its important tanneries activities. A multi-variate analysis of the datas evidenced the strong link between the identified natural elements (As, Co, Ni) with clays, Fe, Al oxides, whereas elements (Cd, Cu, Cr, Pb, Zn) mainly originating anthropogenic activities (industrial and domestic wastes, agricultural inputs), were linked to phosphorus, to a lesser extent to particulate organic carbon.