Recent pollution records in Sidi Moussa coastal lagoon (western Morocco) inferred from sediment radiometric dating

The Sidi Moussa lagoon, located in western coastal Morocco and ranked as a wetland of biological and ecological importance (Ramsar site), is contaminated due to its proximity to the industrial phosphate plants and other anthropogenic activities around it. This study was carried out to assess the current environmental state of the lagoon as well as historical inputs of pollutants over several decades. Three sediment cores were collected and analyzed for the determination radionuclide activities (²¹⁰Pb, ²²⁶Ra, ²³⁸U and ¹³⁷Cs) by gamma spectrometry and element concentrations by Inductively Coupled Plasma - Mass Spectrometry. Age-depth relationships were established in two cores using ²¹⁰Pb and ¹³⁷Cs as chronometer and time-marker, respectively, and Constant Rate of Supply as radiometric dating model. ²¹⁰Pb and ²³⁸U were present in sediment in activities much higher than those reported for non-contaminated coastal systems. Sediment accumulation rates showed a slight increase over time with a depth-averaged value of 0.16 g cm^-2 y^-1. Enrichment Factors and practically derived sediment quality guidelines were used to assess sediment contamination/pollution and toxicological effects linked with the measured concentrations of sediment-bound elements. The profiles of Cr, Co, Cu, As and Ni displayed maximums at depths matching the start of the phosphate industrial plants, and decreasing concentrations in the sections above the maximums, revealing the positive effects of the environmental management system adopted by the phosphate company since early 2000s.