Reservoir Metalimnion Oxygen Demands

Field data show that oxygen demanding substances, both biotic and abiotic, are concentrated in the metalimnions of stratified lakes and reservoirs. The result of this is that high rates of oxygen depletion occur in the depth zone and the dissolved oxygen is often depleted. Consideration of the settling dynamics of organic particles according to Stoke's Law shows that the changes in water density and viscosity with temperature result in reduced terminal settling velocities through the metalimnion. Thus, these particles are settling into the metalimnion faster than they are settling out and higher concentrations are effected. The calculated changes in settling velocities are compared to changes in dissolved oxygen, chlorophyll a, phytoplankton, zooplankton, and BOD. These materials are concentrated in the metalimnions of lakes and reservoirs and the end result is loss of dissolved oxygen in this critical depth zone.