DISTRIBUTION AND VARIATION OF SILICATE IN THE CHANGJIANG ESTUARY AND ITS ADJACENT WATERS

Based on the data obtained from quarterly investigations in the Changjiang estuary and its adjacent sea areas in 2004,the distributions and variations of SiO_3-Si are discussed.The results show that the concentrations of SiO_3-Si were higher near the Changjiang estuary and lower outside the sea.Generally,the concentrations of SiO_3-Si were higher in the surface than in the bottom in shore;the opposite distributions off shore.The SiO_3-Si concentrations both inside and outside the mouth in summer and autumn were higher than those in spring and winter. Distributions of SiO_3-Si varied with increase and decrease of runoff and with enlarge and reduce of the extent of Changjiang dilution water.The concentrations of SiO_3-Si in May were relatively less because of phytoplankton blooming.The seasonal variations of SiO_3-Si/ DIN and SiO_3-Si/PO_4-P ratios were mainly controlled by the variations of SiO_3-Si concentrations. Compared with the data of 1985-1986,the concentrations of SiO_3-Si have increased 2.3 times,both SiO_3-Si/DIN and SiO_3-Si/PO_4-P ratios have ascended 1.6 and 2.5 times respectively, which depended on the increasing of the SiO_3-Si concentrations.May is the fitting season of phytoplankton blooming compared with other seasons,in which it is the relatively least that SiO_3-Si/DIN and SiO_3-Si/PO_4-P ratios departure from Redfield ratios.The removals of SiO_3-Si in the estuary showed that aside from biological removal,there was a main effect coming from seawater dilution.