Abstract
The effect of the diffusive boundary layer on the sediment oxygen demand (SOD) is investigated theoretically. The oxygen consumption in the sediment is modeled to consist of the bacterial and the chemical consunmptions. Each reaction rate is formulated by the Michaelis-Menten and the first-order reaction kinetics of dissolved oxygen concentration, respectively. The effect of flow velocity is expressed in terms of a non-dimensional velocity, U*. This model suggests that, at very low flow velocity (U* < 1), the SOD is completely determined by the transport through the diffusive boundary layer and can simply be expressed as functions of the velocity, DO concentration in the bulk water and a friction coefficient. At higher velocity, the transport is so fast that the processes in the sediment become rate limiting. The velocity dependence of SOD through the boundary layer thickness agrees with observations by former researchers. Predicted profiles of DO concentration in the boundary layer and in the sediment reproduce the observed profiles using microelectrodes. The model also includes a dependence between the bulk DO concentration in the water and SOD. Effect of the vertical distribution of reactive organic carbon on the dependence is also discussed.
