Abstract: A coupled bio-physical model is used to simulate the seasonal variation of primary production,chlorophyll a,nitrogen and phosphorus in the Bohai sea,and the modeled results agree with the observations reasonably. Based on the validated simulations,the impact of two external nutrient sources on the Bohai ecosystem is further examined. It is found that the influence of river-borne nutrients mainly concentrate on estuaries,whereas the reduction of sediment-borne nutrients may seriously inhibit the onset of algaelbloom in the whole Bohai sea.