Changes of dissolved silicate flux from the Changjiang River into sea and its influence since late 50 years

The materials recorded by Datong. Yushu and Shanghai hydrologic meteorological observatories since late 50 years, including rainfall, flow, concentrations of dissolved silicate (Dsi), DIN(NO₃^-), DIP(P₂O₅) and silt discharge were analyzed. The results show a sharp decrease trend of Dsi flux in the Changjiang River since late 50 years; and 53.33 μ mol/L of the dissolved silicate concentration decreased from 1959 to 1984, which came mainly from the dam constructions and the eutrophication formed by industry and agriculture of fertilizer, pesticide, etc. The relation of Dsi flux with silt discharge is positive, but negative with DIN and DIP; and complex with flow and rainfall: positive as flow < 27386 m³/s and rainfall < 1210 mm/a but negative as they are greater respectively. It will lead to the development of limiting factor of biologic nutrients in the Changjiang River estuary and East China Sea from N limiting and P limiting to Si limiting.