Silica Supply and Diatom Blooms in Jiaozhou Bay

The variations in nutrients (molar ratios) and chlorophyll-a in the Jiaozhou Bay were examined before and after a diatom bloom in a period that lasted from November 2003 to March 2004. Negative relationships between nutrient concentrations, Si/P, Si/N ratios, and chlorophyll-a content were found during the bloom, which reflected the relationship between nutrient concentrations, phytoplankton biomass, and growth. Large increase in nutrient concentrations, particularly SiO3–Si after the late autumn, is one of major reasons inducing the diatom bloom in winter, and the bloom was finally controlled due to SiO3–Si depletion by phytoplankton. The bloom was mainly controlled by SiO3–Si. Before 1998, relatively low level of SiO3–Si kept ecological balance of eutrophication waters in the Jiaozhou Bay. In recent years, however, human activities have increased SiO3–Si concentration, which is likely one of the primary causes for the increased diatom blooms in the Jiaozhou Bay. Therefore, it is necessary to control SiO3–Si concentration in the Jiaozhou Bay.