Research on Eutrophication in the Backwater Reach of Tributaries of the Three Gorges Reservoir after Second Water Storage

Though the tributaries under 135 m lever maintained slim flow pattern after second storage in the Three Gorges Reservoir,the speed in the backwater reach reduced obviously,so it became the lake which was suitable for growth of algae.The total phosphorus(TP) and nitrate(TN) were high in general,which provided ample nutrition.The monitor data of April in 2005 indicated the concentration of TP and TN were 0.148 and 1.90 mg/L respectively,which were higher than critical concentrations of eutrophication(0.02 and 0.2 mg/L respectively).If the climate conditions were appropriate,the backwater reach of tributaries possessed the basic conditions of eutrophication that included flow,nutritional salt and temperature,and would occur water bloom.The monitor results suggested that among the 13 pieces of river in the Three Gorges Reservoir,there were 5 pieces of river whose backwater reach got to eutrophication,so they should arouse more recognitions.