Changes in the sediment trace metal contamination after the commissioning of a municipal wastewater treatment plant in the Souss estuary (South Morocco).

Monthly samples of sediment were collected from the Souss estuary, to determine the changes which have occurred in the concentrations of ten metals between 2001 when the low estuary was receiving the wastewaters from Agadir city and 2003 after stopping the sewage dumping. The annual contents of Cu, Fe, Zn (in 2001) and those of Cr, Cu, Fe, Mn, Ni, Pb, and Zn (in 2003) showed significant correlations with those of Al, indicating that fluctuations of their concentrations were only due to those of the aluminosilicate fraction of the clayey sediment. After normalization of these metallic concentrations in relation to those of Al, the contents of the different metals showed insignificant correlations between both years, except for Zn which significantly dropped in 2003 and Cu which increased in 2003. The observed metallic fluctuations are more influenced by the natural conditions of the estuary than the anthropogenic ones.