Quality Status of Surface Sediments of Lake Ichkeul (NE Tunisia): an Environmental Protected Area and World Heritage Site

Coastal regions are in general subject to a high environmental impact, even in areas under environmental protection, such as the Lake Ichkeul located in northeastern Tunisia (N Africa) and the southern Mediterranean Sea. It is a Ramsar site, Biosphere Reserve, and World Heritage Site, but since the 1980s, this area has been threatened by the construction of dams on the main rivers which has been causing a negative impact on this ecosystem. Therefore, this study aims to contribute to the assessment of the sediment quality of Lake Ichkeul and the surrounding catchment areas. The work is based on the analysis of granulometric, mineralogical, and geochemical data (total organic carbon and elemental concentrations of Cd, Cu, Pb, Mn, Zn, and Fe) in 19 surface sediment samples. The results allowed observing that the bottom of Lake Ichkeul consists of muddy sediments with high contents of phyllosilicates, quartz, and calcite and moderate organic matter contents. The high contents of fine sediments and phyllosilicates are mainly related to the weak currents in the lake, the characteristics of the watershed (natural influence), and the presence of dams (anthropogenic influence). Sandy sediments and high organic matter content were found at the mouth of most of the surrounding streams, suggesting that fine particles are transported in suspension and introduced into the lake as well as organic materials from the watershed that surround it. The spatial distribution and toxicity assessment based on the SQGs for the analyzed elements indicate the presence of high levels of metals in several sectors of the study area. In addition, it suggests that the trace elements might originate from different sources, namely municipal wastewater discharges close to the southeast sector and from agricultural fields in front Doumiss stream and Melah stream, which also load organic matter. The results suggest that the metal pollution of the lake was a result of runoff from the streams and dams, which allows us to deduce that it may develop into an increasing environmental degeneration due to its natural function and the different contributions of the watersheds that flow to it.