International Journal of Sediment Research, Vol. 29, No. 1, 2014, pp. 1–10 - 1 - International Journal of Sediment Research 29 (2014) 1-10 A long-term record of land use change impacts on sediments in Oualidia lagoon, Morocco Mehdi MAANAN 1,2 , Ana Carolina RUIZ-FERNÁNDEZ 3 , Mohamed MAANAN 1 , Paul FATTAL 1 , Bendahhou ZOURARAH 2 , and Mohamed SAHABI 2 Abstract An integrated approach, involving land use patterns and heavy metal contents of the surficial and cored sediment, was proposed to detect the characteristic spatial and temporal scale of point and non-point source human disturbances on the Oualidia lagoon in Morocco. Identification and description of the temporal and spatial distributions of the main contamination sources of heavy metals are analyzed using statistics and GIS methods. The results show that surficial sediments are highly enriched in heavy metals compared to their preindustrial background levels. Land-use types affected lagoon sediment pollution in different ways: 1) agricultural areas had the highest potential for sediment contamination by heavy metals, particularly Pb, Cu and Hg, 2) Ni and Cr are the main pollutants originating from urban sewage and 3) oyster farming and traditional land uses such as salt flats, pastures showed low levels of others metals. The enrichment factors (normalized by Al) obtained from the sediment cores indicated that the lagoon is (strongly/moderately) polluted by all metals which were attributed to agricultural activities and wastewater discharges from urbanized areas. Key Words: Land use change (LUC), Geographical information systems (GIS), Sediment pollution, Risk assessment 1 Introduction The deterioration of the coastal water quality that limits its use, is exacerbated by a continuous increase in population and socio-economic development, and will eventually result in water scarcity. Worldwide, contaminant loads delivered to surface water bodies are becoming so intense that coastal ecosystems are seriously degraded (Maanan, 2007; Yi et al., 2008; Affian et al., 2009; Sakan et al., 2009; Mhamdi Alaoui et al., 2010). Numerous studies on the impacts of land use change (LUC) and anthropogenic activities on coastal water quality have been carried out in the last three decades mainly focusing on urban expansion in coastal areas (Maanan et al., 2013; El Mrini et al., 2012a). The changes of coastal land use patterns certainly provide many social and economic benefits (e.g. tourism). However, they also come at a cost to the natural environment (El Mrini et al., 2012b). Expansion of land use in coastal areas results in natural resources being degraded, particularly by soil and water pollution. One of the major environmental problems of concern for marine pollution is the discharge of heavy metals to the natural environment derived from human activities (Maanan, 2008; Zhang et al., 2011). In the coastal system, these pollutants are rapidly removed from the water column and settle down with the particulate matters to form bottom sediments (Ruiz-Fernández et al., 2002; Maanan et al., 2004; Liao et al., 2008; Ruiz-Fernández et al., 2009). Although some of these contaminants can be mobilized via bio-activity from the sediment sink, undisturbed sediments can provide a valuable record to evaluate the pollution trends over a long period of time. Plotting the contaminant concentration against the depth of successive thin layers of sediment will provide time-based information useful for assessing the extent of contamination in different periods of urban development. Specific dating methods can be used to trace the time of deposit for each sediment layer and provide an accurate chronological study for the contamination history in past years (Flower et al., 2009; Romano et al., 2012). The objectives of this study were to assess land-use patterns and determine the influence of land-use types on sediment heavy-metal contamination in lagoon Oualidia, Morocco. 2 Study area Oualidia lagoon (34°47'N-6°13'W and 34°52'N-6°14'W) is one of the four Moroccan sites that were considered by the 1 Géolittomer, UMR 6554 LETG, Université de Nantes, BP 81227, 44312, Nantes, France. 2 Marine Geosciences Laboratory URAC 45, Earth Sciences department, Faculty of Sciences, 24000 El Jadida, Morocco. 3 Universidad Nacional Autónoma de México. Instituto de Ciencias del Mar y Limnología. Calz. J. Montes Camarena, Mexico Note: The original manuscript of this paper was received in Jan. 2013. The revised version was received in May 2013. Discussion open until Mar. 2015.