Diagenetic processes and nutrients diffusive fluxes at the sediment-water interface in the Bizerte Lagoon (North Tunisia)

Diagenetic reactions occurring in the sediments of Bizerte Lagoon along with their seasonal variation were assessed through examining the concentration profiles of nutrients and dissolved Fe and Mn in the supernatant water and pore waters, as well as the profiles of total organic carbon, carbonates, Fe and Mn contents in the particulate phase. The results indicate that these diagenetic reactions followed the classical sequence of oxidant reduction following the degradation of organic matter with a successive reduction of NO3-, MnO2, Fe (OH)3 and SO42-. In particular, a delay was observed in the winter sequence which occurred at greater depth due to higher Eh in surface layer. Generally, NO3-, NH4+ and PO43-seem to originate from sediments as reflected by their measured flux from sediments to the water column while the reverse was quoted for SO42-as reported from other Mediterranean environments. In addition, oxygenation of the water column reduces the diffusive fluxes of (NO3-, NH4+, PO43-) released into the pore water during mineralization of organic matter.