The present environmental scenario of El Melah Lagoon (NE Tunisia) and its evolution to a future sabkha

Abstract

A multidisciplinary study of El Melah Lagoon (NE Tunisia) permits the analysis of the present scenario of this coastal environment. Salinity and pH values indicate a main marine origin for the permanent waters, which present locally high nutrient contents owing to the continuous flows coming from both the Slimene’s treatment station (STS) and the agricultural activities surrounding the southeastern margins of the lagoon. The heavy metal concentrations of the clayey-silty bottom sediments may be moderate to high near the STS’s effluent and close to a parapharmaceutical plant. Seven zones were distinguished in this limited area (200 ha), according to the physical–chemical parameters and nutrient contents of waters, the grain size and heavy metal contents of the bottom sediments and the distribution of ostracode assemblages (marine, high brackish and freshwater to low brackish). This analysis, together with the information provided by aerial photos (1948–1996), is the basis to hypothesize a future evolution of the system.