A model of sediment oxygen demand (SOD) is presented which
determines the SOD as a function of flow velocity over the sediment. A
quantitative relationship is established between SOD and the velocity and
dissolved oxygen concentration in the bulk water. Oxygen consumption in
the sediment is expressed as the sum of biological consumption with
Michaelis-Menten kinetics, and the chemical consumption assumed to be a
first order reaction of oxygen. At very low flow velocities, transport through
the diffusive boundary layer is the limiting factor of SOD, and SOD is
expressed as a linear increasing function of velocity. On the other hand,
when flow velocities are increased, SOD becomes independent of velocity,
since the reactions in the sediment are the rate limiting factor. The model
also suggests that SOD is an increasing function of dissolved oxygen
concentration in the water overlying the sediment and that SOD has no
upper limit when DO concentration is large. Combined with the linear
theory of internal seiche motion an average SOD in a rectangular,
two-layered lake is derived as functions of the wind velocity, aspect ratio of
the lake an the depth of the thermocline. The average SOD has a minimum
when the thermocline depth is 1/4 of the total depth.
Nakamura, Yoshiyuki; Stefan, Heinz G..
Sediment Oxygen Demand in Lakes: Dependence on Near-Bottom Flow Velocities.
St. Anthony Falls Hydraulic Laboratory.
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