Diffusional Mass Transfer at Sediment-Water Interface of Cylindrical Sediment Oxygen Demand Chamber

Diffusional mass transfer of dissolved substances across the sediment-water interface in coastal waters is an important factor for realistic determination of sediment oxygen demand (SOD) and nutrient recycle. The benthic diffusive boundary layer inside a cylindrical chamber commonly deployed for in situ measurements of sediment oxygen demand is studied. In a series of laboratory experiments, the SOD is measured with the chamber operated in both continuous flow and batch modes, and a microelectrode is employed to measure the near bed dissolved oxygen (DO) profile for different chamber flows and sediment types. The dependence of the diffusive boundary layer thickness and the sediment-water mass transfer coefficient on the hydraulic parameters are quantified. Using the derived mass transfer coefficient, it is shown that for a given sediment type, the SOD is a function of the bulk DO concentration and chamber flowrate. The theoretical predictions are validated by both laboratory and field SOD data.