Geochemical characteristics of water and sediment in summer period of the Loukkos and Sebou estuaries (NW Morocco): preliminary study

Abstract

The high touristic potential of the north-west region in Morocco plays an important socio-economical role, raising the question of the monitoring of its environmental quality. This study provides a preliminary dataset for dissolved heavy metal concentrations in water and grain-size, mineralogy, carbon (organic and inorganic) and heavy metal contents in surface sediments from the Loukkos and Sebou estuaries). The results refer to samples taken at six sites in June 2009. In this article, the concentrations of twelve heavy metals (Al, As, Cd, Cr, Cu, Fe, Hg, Li, Mn, Ni, Pb and Zn) in sediments with grain size and mineralogy, and concentration for 7 heavy metals (As, Cd, Cu, Fe, Ni, Pb and Zn) in water are reported. The results show, in general, a low concentration of almost all of the studied metals in water and sediments, but with random higher levels. In water, the highest levels were found for Cu, Ni and Zn denoting some toxicity for living organisms. For estuarine sediments, As and Cr show strong levels of contamination, ranging from 7.96 to 18.5 mg kg-1 for As and from 33 to 137 mg kg-1 for Cr in Loukkos and from 7.77 to 8.34 mg kg-1 for As and from 85 to 109 mg kg-1 for Cr in Sebou. Stations L1 and S1, with predominantly sandy sediments, present the lower metals concentrations (except L1 for As), which is in agreement with the knowledge that metal concentrations are generally higher in areas richer in clay sediments than in sandy sediments. The As and Cr values are above the upper-EAC (The Ecotoxicological Assessment Criteria) and can have long-term and acute biological effects. The strong Cr concentration can be explained by the presence of tanneries located along both rivers, upstream from collection sites, denoting a direct anthropogenic source. The As is linked to sand that has a beach and shelf sediments predominant source. The hypothesis that can be considered is these sediments richer in As are injected to the Loukkos lower estuary by the tidal influence