Study of oxygen uptake by tidal river sediment

Abstract

This paper presents a study on the kinetics of chemical and biological oxygen uptakes within tidal river sediment and thereby modelled the oxygen uptake by the sediment. Sediment cores were taken from a major tidal river, the Shing-Mun River in Hong Kong. Characterization of the core found that the sediment contained high concentrations of iron and organic matter. The kinetics within the sediment were investigated with a set of batch tests using dispersed subsamples taken from different depths of the core. The results showed that the chemical oxygen uptake followed zero-order kinetics with respect to sediment quantity, and its uptake rate coefficient varied less with the depth. The mean value of the coefficient was found to be 8.25×10 −4 day −1. The batch tests also confirmed that the biological oxygen uptake rate in the sediment can be described by a Monod function of dissolved oxygen (DO). It was also found that potential bioactivity of the sediment was kept constant in its 10-cm thick upper layer. Based upon these results, the concept of a hybrid benthic biofilm was introduced to develop a model of the sediment oxygen uptake (SOU). To verify the proposed SOU model, comparisons of experimental data with model predictions were conducted, which showed that the proposed SOU model perfectly fitted the experimental results at different water temperatures ranging from 11 to 27°C.