Bottom-up control of phytoplankton growth in spring blooms in Central Yellow Sea, China

The source and significance of three nutrients - nitrogen, phosphorous and silicon - were investigated by a modified dilution method performed on seawater samples from the Central Yellow Sea (CYS), in spring blooming period of 2007. This modified dilution method accounted for the phytoplankton growth rate, microzooplankton grazing mortality rate, the internal and external nutrient pools, as well as nutrients supplied through remineralization by microzooplankton grazing. The results indicate that phytoplankton growth during the bloom is mostly contributed by internal nutrient pools (K_I=0.062-1.730). The external nutrient pools (K_E=<0-0.362) are also of importance for phytoplankton growth during the bloom at some sampling sites. Furthermore, the contribution of the recycled-nutrient pool by remineralization (K_R=<0-0.751) is significant when microzooplankton grazing rate was higher than 0.5d^-1 during the spring phytoplankton blooms in the Central Yellow Sea. Compared with internal phosphorus, internal nitrogen and silicon contribute more to the phytoplankton production at most sampling stations.