TOWARDS THE EDGE - EARLY DIAGENETIC GLOBAL EXPLANATION - A MODEL DEPICTING THE EARLY DIAGENESIS OF ORGANIC-MATTER, O2, NO3, MN, AND PO4

The ultimate fate of particles in aquatic environments is their burial and transformation in surficial sediments. There is an increasing need to relate quantitatively particle fluxes in the water column to the material recycled or preserved in the sediment. For this purpose, a transport-reaction model (EDGE) that represents the early diagenetic processes occurring in surficial sediments has been designed. This model uses the incoming flux of particulate matter and the overlying water composition in order to obtain simulated concentration profiles of chemical species in the bulk sediment and interstitial waters. It consists of a set of coupled nonlinear differential equations representing the oxidation of Particulate Organic Matter (POM) by a continuous sequence of electron acceptors (i.e., O2, NO3-, MnO2; in its present state). The distribution of the concentrations of six components: POM, O2, NO3-, MnO2, Mn2+, and SIGMA-PO4 are currently calculated. The Monod rate law has been used for representing the mineralization of POM coupled with the consumption of oxidants, and the sequence of oxidation of organic matter is represented using an inhibition function. The system of mathematical equations is solved using an appropriate numerical iterative method which assures convergence. For each calculation the quality of the approximated solutions is checked. The distributions with depth of the concentrations of the six chemical compounds are presented for different fluxes of POM at steady-state. These calculations show that the preservation of organic carbon and the extent of the mineralization processes are very sensitive to the organic carbon rain rate. For constant fluxes of POM and MnO2 arriving at the sediment water interface, the effect of an increasing sedimentation rate, as it might be produced by an augmentation of the detrital flux, is assessed on carbon preservation.