Blue carbon stock in Tunisian coastal sediments: First assessment and implications for ecosystem conservation and climate change mitigation

This work presents the first comprehensive study on carbon definitive sequestration in coastal marine sediments in Tunisia. It study aimed to provide insights into the potential role of coastal Tunisian sediments in mitigating carbon dioxide (CO₂) emissions and climate change. It compiles carbon data from 32 cores sampled in eight distinct ecosystems along the Tunisian coast, including lagoons (Ghar El Melh, Bizerte and Korba), Lake Ichkeul, seagrass meadows (Posidonia oceanica) in Sidi Rais and Monastir bays along with two gulfs (Tunis and Gabes). The study revealed carbon sequestration rates ranging from 2.1 to 177.6 gC m^-2 yr^-1, with the highest rates found in P. oceanica meadows while both lagoons seemed recalcitrant to sequestration due to enhanced organic matter degradation. Conversely, Lake Ichkeul, constitutes a good trap with carbon sequestration rate up to 49 gC m^-2 yr^-1 and remarkably Tunis and Gabes gulfs exhibit exceptionally high levels exceeding 40 %. Although P. oceanica meadows exhibited the highest sedimentation rates (414 and 115 gC m^-2 yr^-1, respectively), their carbon sequestration was low (40 %). The carbon permanently sequestered in the sediment of the studied environments was around 1243 KtCO₂ yr^-1, accounting for approximately 4 % of the total CO₂ emissions by Tunisia in 2021. However, considering the short and medium-term sequestration potentials of the 1,33,2815 ha of seagrass meadows in Tunisia, this percentage could attain >100 %.