A numerical model to estimate sediment oxygen levels and demand

Abstract

A numerical model that simulates sediment oxygen levels and demand (SOLD) was developed and tested against field data. The model accounts for changes in sediments due to advection, diffusion, chemically and biologically mediated redox reactions, and other chemical transformations. The microbial degradation of organic matter and the interactions of the subsequent chemical constituents are described using appropriate stoichiometric relationships. Sediment oxygen demand (SOD) is computed from fluxes of oxygen and reduced compounds across the sediment-water interface. To test the the model, simulations were compared against published data obtained from lake sediments. The model results displayed reasonable agreement with the measurements. The model was used to examine some of the major factors that affect the sediment oxygen demand. Results show that although fluxes of methane and ammonia increase with an increasing C rain rate, the oxygen nux remains almost constant for the simulations conducted. For an increase in bioturbation and/or temperature, however, all fluxes increase significantly. The oxygen concentration at the sediment/water interface also affects the SOD significantly, especially the fraction of the total SOD that is due to the nux of oxygen into the sediments. The fraction of the SOD that is due to the oxidation of ammonia increases with increasing oxygen concentration at the sediment/water interface, while the fraction associated to the methane release and its oxidation decreases slightly because more organic C is oxidized aerobically. The contribution of reduced manganese, iron, and sulfide to the SOD are relatively low, due to their precipitation with other chemical species.