Pollution magnitude before and after restoration activities on Mediterranean lagoon sediments

Nador Lagoon, located in northeastern Morocco, is a site of biological, ecological and economic interest. It receives pollutant inputs from various anthropogenic sources. To limit the impact of these contaminants, a depollution project has been undertaken around this lagoon in 2008-2011. This study evaluates the impact of depollution on the quality of the surface sediment of Nador Lagoon. Different environmental indices were used to assess sediment pollution from 2005 to 2018. The results show that the content of heavy metals in the sediments was increased for Zn, Cu, Cr, and Pb from 2005 to 2013 and then decreased from 2013 to 2018, except for Pb. From 2005 to 2013, it was noted that the percentage of samples with concentrations exceeding the effect range low (ERL) and probable effect level (PEL) increased for Cr, Cu, and Zn, in addition to Pb for PEL, then decreased from 2013 to 2018. For Pb, all sediment samples exceeded ERL in 2018. In addition, the mean contamination factor decreased for Cr, Cu, and Zn, but for Pb, the contamination factor increased from 2013 to 2018 and remained greater than 3. Moreover, the mean pollution load index value decreased in 2018 in contrast with the modified degree of contamination value, which increased. From this study, we can conclude that, by 2018, depollution actions for Nador Lagoon had a positive impact on the quality of the surface sediments, particularly on Zn, Cu, and Cr. For Pb, special efforts must be made to control its sources and limit its accumulation in sediments.