Model study on Bohai ecosystem 2.Annual cycle of nutrient-phytoplankton dynamics

Using the coupled bio-physical model described in the first paper of this series of studies, the annual variations of algae biomass and nutrient concentration in the Bohai Sea are simulated.Modeled results show that the onset of spring bloom is induced by high nutrient stocks stored in winter, though the initial time is earlier in shallow waters than in deep waters, for which the evolution of the vertical stratification in deep waters plays an important role; on the other hand, newly added river-borne nutrients and resuspending sediment-borne nutrients are responsible for the outburst of autumn blooms.On the basis of modeled results, it is also found that the BS ecosystem, as a whole, is limited by nitrogen all the year round, though the phosphorus limitation is apparent in the Laizhou Bay where the ratio of nitrogen concentration to phosphorus concentration is higher than 16 due to the contribution of newly added nutrient species from Huanghe River discharges.