Impact of a lagoon with high anthropic activity on a World Heritage Site.

The Ichkeul-Bizerte Lagoon Complex (IBLC), a critical ecosystem for local biodiversity, faces a pressing threat due to climate change and severe pollution. Despite past conservation efforts, pollution persists, particularly in the Bizerte Lagoon. This study investigated the impact of water dynamics and climatic conditions on heavy metal contamination in the IBLC's sediments. During the dry hydrological year of 2019/2020, 80 surface sediment samples were collected and analyzed for heavy metal concentrations using inductively coupled plasma. Sediment quality was first evaluated by comparing heavy metal concentrations against sediment quality guidelines established by NOAA. Additionally, contamination indices, including the contamination factor (CF), pollution load index (PLI), and geo-accumulation index (I), were utilized to provide a more detailed assessment. Spatial and temporal variations in contamination were assessed, with seasonal variations mapped using the inverse distance weighting method. The findings revealed that El-Fouledh, the Menzel Jamil industrial area, and the Menzel Abderrahmane port are the primary pollution sources. The spatial distribution of pollution shows a decreasing gradient from the east (Bizerte Lagoon) to the west (Lake Ichkeul), with high levels of cadmium, lead, and zinc exceeding sediment quality guidelines and posing significant threats to this Ramsar-listed ecosystem. Spearman´s correlation coefficient highlighted the persistence of pollution across seasons, emphasizing the urgent need for comprehensive management strategies to mitigate pollution and preserve the IBLC's ecological integrity.