Organic contamination identification in sediments from a Mediterranean coastal ecosystem : The case of the Nador lagoon (Eastern Morocco)

The Nador lagoon ecosystem (North-East of Morocco) displays a major socioeconomic interest. In fact, it is essential to evaluate consequences of anthropogenic activities in the lagoon especially by organic matter studies (nature and distribution) in the sedimentary compartment. Surface sediments show variable rates in total organic carbon and in sulfur, high in some cases (7.5 and 1.8% respectively). These high contents are recorded in the center of the lagoon. Their distributions are controlled by the hydrodynamism and the anthropogenic degree. The molecular biomarkers analyses and especially n-alkanes distribution reveal: a zone of marine influence; and a zone of continental influence. The occurrence of pentacyclic triterpanes with a typical distribution of a thermally mature organic matter reveals a contamination due to petroleum products in the entire lagoon except for the center. Coprostanol occurrence near cities indicates wastewater effluents inputs and reducing conditions underlined by high values of stanols/sterol ratios. Thus, the organic contamination (petroleum by-products and wastewater effluents) occurs in the vicinity of the cities whereas the littoral edge and center remain weakly affected by these contaminations.Original Abstract: La lagune de Nador (Nord-Est du Maroc) est un ecosysteme presentant un interet socioeconomique local majeur. Il est donc important d'evaluer les consequences des activites anthropiques sur la lagune, notamment en etudiant la matiere organique (nature et repartition) du compartiment sedimentaire. Les sediments superficiels presentent des taux variables en carbone organique total (COT) et en soufre pouvant etre importants (7,5 et 1,8 % respectivement). Ces teneurs elevees sont enregistrees essentiellement dans le centre de la lagune. Leurs distributions sont controlees par l'hydrodynamisme et le degre d'anthropisation. L'analyse de marqueurs moleculaires et, en particulier, la distribution des n-alcanes revelent une zone a influence marine et une zone a influence continentale. De plus, la presence de triterpanes pentacycliques presentant des distributions typiques de matieres organiques thermiquement matures met en evidence une contamination par les produits petroliers dans toute la lagune, a l'exception du centre. La presence du coprostanol a proximite des villes souligne une contamination fecale (contributions d'eaux usees) et des conditions reductrices revelees par des rapports stanols/sterols eleves. Ainsi, les