Effect of Flow Velocity on Sediment Oxygen Demand: Experimental Results

Sedimentary oxygen demand, SOD, frequently the major oxygen consumer in lakes, is the uptake of dissolved oxygen, DO, by sediments. The oxygen is removed from the water column by chemical oxidation processes and by the respiration of microbes in the sediments. To effectively counteract oxygen dep1etion especially in lakes, an improved understanding of SOD is required. In 1994 Nakamura and Stefan published a theory relating SOD to flow velocity using boundary layer concepts. This paper is an experimental validation and extension of those results. In this study SOD is investigated in laboratory experiments in which sediments are exposed to water flowing at different velocities. The experiments were performed in a recirculating channel with well defined flow characteristics. The results verify that SOD increases with the velocity of the water above the sediments. However, this velocity effect is found to have an upper bound. The rate of increase with velocity as well as the upper bound of SOD are shown to depend on the sediment material, the benthic biology, and the temperature. SOD is approximated by linear and Michaelis-Menten type equations with velocity being the independent variable.