Author(s): Joseph H. W. Lee; F. Arega; C. P. Kuang
Linked Author(s): Joseph Hun-Wei Lee
Keywords: Sediment oxygen demand; Dissolved oxygen; Diffusion boundary layer; Mass transfer; SOD chamber flow; Computational fluid dynamics; Environmental hydraulics; Algal blooms; Water quality
Abstract: The sediment oxygen demand (SOD) is the rate of oxygen consumption exerted by the bottom sediment on the overlying water-due to both benthic respiration and the biochemical oxidation of reducing substances released from the sediment. The SOD is often a major component of the dissolved oxygen (DO) budget and hence a key parameter in water quality models, particularly in relatively shallow waters. In general, the benthic oxygen flux depends on the velocity and DO concentration of the overlying water, and the biochemical oxygen demand of the sediment. At present, there appears to be no universally accepted method of SOD measurement or prediction. The benthic oxygen flux is often measured in-situ by a sediment oxygen demand (SOD) chamber. In this paper, the key issues related to the measurement of SOD are summarized. The changes of SOD in response to environmental variables are illustrated by field observations during an algal bloom. The measurements are interpreted with the aid of a diffusional mass transfer theory and laboratory measurements of the DO micro-profile near the sediment-water interface. The importance of the fluid mechanics of SOD chambers is discussed in relation to the 3D flow field. Based on an understanding of the chamber hydraulics, the bulk SOD as measured by SOD chambers can be predicted in terms of the sediment type, DO concentration, and chamber flow rate; the predictions are compared with both laboratory and field data.