The Variations Of Nutrients In The Lower Main Channel Of The Yellow River From 2002 To 2004 And Water-sediment Regulation

In recent years, some great ecological changes have occurred in the ecosystem of Bohai Sea. Yellow River, as the largest river import into Bohai Sea, it brings a great deal of sand and nutrients that have the major impacts on Bohai's ecosystem. Therefore, the continuously monitoring and analysis of the nutrients in the lower main channel of Yellow River will redound to the study of the ecosystem and renovation of the environment of Bohai Sea.This paper focus on the variations and fluxes of dissolved nutrients with continuously monitored data in the lower main channel of Yellow River (Lijin) from 2002 to 2004 month by month and the period of water-sediment regulation in July 2002 and 2004.1. The study on the nutrients from 2002 to 2004.The concentration of nitrate and silicate have no significantly change , while the DIP,DTP level falls significantly from 2002 to 2004. Nitrate which is the main existing forms of the DTN accounts for 75.15%,81.69%,84.30% , DIP accounts for 59.06%,47.79%,49.28% of DTP in the lower main channel of Yellow River from 2002 to 2004 . Significantly relationship was found between SiO₃^2--Si and sediment discharge from 2002 to 2004.The concentration of DIN increased significantly in the last 20 years in the lower main channel of the Yellow River .The concentration of DIP is more than 1980', while decreased significantly in 2003 and 2004 . The concentration of SiO₃^2--Si is decreased significantly compared to 1985', and keep stable from 2002 to 2004 . The ratio of N/P is increased all along, while the ratio of Si/ N decreased, and keep stable from 2002 to 2004.Monthly fluxes of average variation of dissolved inorganic nutrients from 2002 to 2004 show a sensitive seasonally change of higher in flood season and lower in dry season. From 2002 to 2004 , the annual fluxes of DIN increased more than 4 times and the SiO₃^2--Si increased more than 3 times. The concentration of DIN and SiO₃^2--Si are stable, while the nutrients fluxes and water fluxes increase synchronously.2. The study on the nutrients during the period of Water-sediment regulationDuring the period of Water-sediment regulation in 2002 ,the concentration of nitrate due to the influence of erosion of farm land and dilution of river water . Negative correlation was found between nitrate and water discharge during the first period of Water-sediment regulation in 2004 .During the period of Water-sediment regulation in 2002 ,significantly negative relationship was found between NO₃^--N and DON. During the period of Water-sediment regulation in 2004 , significantly negative relationship was also found between DIP and DOP.In less than a month , the nutrients fluxes account for 50% and 25% of the whole year fluxes separately during water-sediment regulation in the lower main channel of the Yellow River in 2002 and 2004 . It caused the nutrients input to the sea concentrately, so the inter-annual nutrients fluxes into Bohai Sea is changed greatly.