Sediments in the Mouths of Urban Rivers and its Influence on Hypoxia - Analysis by Field Surveys and Numerical Model -

Abstract

In some of urban tidal rivers on polluted riverbeds with high loads of nutrients water masses with the minimal concentration of DO near the bottom appear between the river mouths and the upper freshwater areas. Field surveys and numerical analysis are carried out to clarify the mechanism of the appearance in two rivers in Osaka. The 1D numerical benthic model of the type of Wijsman et al.(2002) are applied and represents the observed data well. The sediment is the most polluted in the area with the minimal concentration of DO. The cause of the above minimization is not the wastewater of sewage plants and would be relatively fast sedimentaion rate, the high concentration of sulfide in pore water because of the full supply of sulfate in saline water and the resuspension of the sediment with reducing substances such as sulfide.