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

Abstract

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.