Abstract
A dynamic model, which predicts non-steady variations in sediment oxygen demand (SOD) and phosphate release rate, has been constructed. This theoretical model consists of four diffusion equations for dissolved oxygen (DO), phosphate, ferrous iron and sulfide. Mass fluxes are calculated from concentration gradients in the water where no biochemical reaction is assumed.According to this model, step changes in DO concentration and flow velocity make drastic changes in SOD and phosphate release rate within -30 minutes, but concentration profiles attain to the steady state in a half day. The difference of the response time is caused by difference in the time scale of diffusion in the water boundary layer and that of bio-chemical reactions in the sediment. Negative phosphate transfer from water to sediment can even occur under aerobic conditions. It was found that model predictions almost well reproduced experimental values of the SOD and phosphate release rate.
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