Numerical Study Of The Principle Of Transformation Of Nitrogen And Phosphorus In Shallow Lake

Lake Taihu, which is the third largest lake in China , belonging to shallow lake, confront a serious problem of eutrophication. The worldwide reasearch and control practice of eutrophication showed that the sediments in the lake are an important source of nutrients. According to the monitoring data of hydrology and water quality in 2000 and the nitrogen circle and phosphorus circle theory in WASP5 model, a two-dimensional flow-pollutants coupled model was developed on the basis of RBFVM-2D model in this paper, simulating the current field, relationship between concentration field and sediments and the relationship between blue algae bloom and current field & concentration field under the influence of wind field from May to August in 2000.According to the simulation, results showed that the current field, concentration field of TN and TP calculated by the two-dimensional flow-pollutants coupled model fitted well with the measured values;the pollution loads of TN and TP discharged by the river around Lake Taihu were the main source of outer-source pollution load and the fundamentally cause of the concentration field of TN and TP, TP became the limited nutrient in most area in Lake Taihu;the net flux of TN and TP released by the sediments in Lake Taihu was the main source of the inner-source pollution and an important cause of the concentration field of TN and TP, the net flux of TN and TP had a direct relationship with the thickness and the distribution of the sediments, and was influenced by the wind field and the concentration of TN and TP in the water;blue algae bloom had a close relationship with wind field and the concentration of TN and TP, when the concentration of TN and TP was high(TN>2 mg/L ,TP>0.2 mg/L), the value of TN/TP was between 10~20 and the velocity of the water was slow, the blue algae bloom was likely to break out.