Characterization of recent sediments and evaluation of environmental effects in the lagoon of Nador, Morocco.

The Nador lagoon is one of the most important ports on the coast of Morocco, and the second lagoon in North Africa by extension (115Km2). The lagoon is bordered to the north-west by the volcanic products of the Gourougou volcano complex (887 m asl) and south-east by the Jurassic carbonate succession of marine environment belonging to the Complex of Kebdana (932 m asl); the rest of the area around the lagoon is flat and is characterized by arenaceous-pelitic deposits linked to the Miocene and Quaternary magmatic activities. Along the banks of the Nador lagoon, are also located the towns of Beni Enzar and Kariet Arkmane, characterized by a dramatic increase in population over the past 30 years, for the opportunities offered by the business linked to the construction of summer houses, hotels, etc. as well as to the enlargement of the local port. The rapid increase in population was not accompanied by the realization of services and, most importantly, there are no appropriate treatment facilities for wastewater, with the associated environmental problems. The internal flows of the lagoon have low intensity; this fact and the shallow water depths determine an insufficient water supply and oxygenation. The lagoon in recent decades has been affected by eutrophication problems associated with environmental and hygienic discomforts: for this in 2012 a new channel between lagoon and Mediterranean Sea is opened with the aim of improving the water oxygenation. To fully describe the quality of Nador lagoon sediments, some samples along the banks and on the bottom of the lagoon were gathered and their distribution was analysed and compared with the patterns of water circulation in the lagoon. The samples were subjected to petrographic and geochemical characterization by x-ray Fluorescence (XRF) and mineralogical investigation by x-ray Diffraction (XRD). Furthermore, data distribution was obtained using GIS tools (ArcGis software, version 9.3) and thematic maps were created. The data demonstrate that the lagoon is characterized by an internal zoning and the area close to the Gourogou is more contaminated by heavy metals, with mean values of 79, 53, 27, 45, 156 and 124 ppm for Cr, Cu, Ni, Pb , V and Zn (compared to 44, 30, 21, 28, 94 and 68 ppm of the average value of the sediment of the entire lagoon). However, the data of the lagoon of Nador are in line with those of other lagoons linked to the same problems of anthropisation. The enrichment factor (EF) of the samples, compared to the values of the mother rock, highlights how the recent sediments are low enriched, with the exception of sediment near Gourogou This is due in part to the geology of the volcano (outcrops of basic rocks) and in part to the mobilization of the metals contained in the waste processing of the ancient iron mines exposed to the meteorological. Are also analyzed the shells of bivalves and gastropods which, despite the limitation of the study of specimens collected POST MORTEM, gave positive results: μ XRF analysis show no abnormalities for bioaccumulation of heavy metals, such as Fe, Cr or Pb, considered adverse to the health of the mollusk. In conclusion, the study outlines how the quality of bottom sediments of Nador lagoon is deeply affected by the increasing anthropogenic pressure and the geochemical intrinsic characteristics of local sediments rich of heavy metals. In general, the geochemical lagoon recent sediment data show similar values to those of other lagoons and the enrichment factor of heavy metals is due more to the geological and petrographic characteristics of the area than anthropogenic pollution.