Ecological study of Mediterranean wetland: Sediment dynamics and blue carbon storage
Aya Hammami1, Kerim Ben mustapha1, Oula Amrouni 1, Amjad Kallel2
1 University of Carthage, National Institute of Marine Sciences and Technologies, LR16INSTM04,2025, Tunis, Tunisia
2 University of Sfax, National School of Engineering, 3038 Sfax, Tunisia
The aim of this study is to monitor the sediment dynamic and to estimate the percentage of carbon sequestered by macrophytes in the coastal lagoon of Ghar El Melh, Gulf of Tunis Mediterranean. A total of 21 surface sediment samples were collected during the winter campaign, completed by a second floristic campaign in April 2021 for the identification of the spatial distribution of the phanerogam Posidonia oceanica. The results showed that the lagoon is characterized by two types of sedimentary facies: dominant silty facies (65%) with an average size D50 which varies from 4.3 µm to 8.7 µm and sandy facies (35%) with an Mz grain sized ranges from 2Φ to 3Φ. The mineralogical identification of the lagoon sediments shows the presence of a biogenic calcium carbonate (CaCO3) :4% to 100%. The rate of organic matter OM: 2% to 11%. Sedimentological and mineralogical analysis of the coastal lagoon shows the coupled origin of sediment supplies. At the level of the banks of the lagoon, the silty facies enriched in carbonated fraction are allochthonous via the fluvial yields of the lower valley of Medjerda. The muddy deposits in the center of the OM-enriched lagoon are formed by the phytoplanktonic primary production of zooplankton, indicative of bacterial activity in the water column. Floristic investigation of the coastal lagoon reveals the presence of the Posidonia oceanica species in sandy areas. The average carbon capture rate of Posidonia in the lagoon is estimated to be ~15.6 t/ha. Nevertheless, Posidonia meadows are absent in central areas and adjacent to urban areas, characterized by muddy facies with a relatively high level of organic matter.
Key words: Ghar El Melh lagoon, phanerogams, blue carbon, Mediterranean, Ecohydrology.