This paper deals with the development of a numerical model for predicting the effect of purification countermeasures in polluted seas on the improvement of seawater quality and seabed sediment, and on the recovery of marine animals. The present model includes biological processes such as zooplankton, benthos and periphyton activities, as well as the processes of seawater circulation, dispersion, settling, the production of organic matter and its decomposition, release rate, etc.,
which have already been contained to the existing model. The present model can predict the effect of seabed sediment treatmnt on such biological aspects as the increase of biological mass and biological activities.
　The calibration test of this model is made for the case of the bay of Kure in Hiroshima Prefecture. The spatial treatment of the calibration test is a uni-segment and eleven layers. According to the calibration results, the seasonal variation of phosphate phosphorus (PO4-P) and dissolved oxygen (DO) agree well with the observed data, and the standing crop of phytoplankton and benthos is the agreeable value, but the abrupt increase of phytoplankton observed around June is not well
reproduced. The population of the calculated zooplankton exceeds the observed values during the term between December to February.