On the total nitrogen balance and water quality controllable target in Taihu Lake
摘要
The analysis of total nitrogen balance in Taihu Lake is conducted using 2007-2010 patrol hydrometric and precipitation data.An investigation is carried out on the existing and planned engineering measures for controlling the total amount of pollutants entering Taihu Lake from multiple sources.Based on both analysis and investigation,a spatial and temporal reduction plan for total nitrogen loading from the Taihu Lake basin is proposed.A mathematical model for simulating lake water environmental problems is developed.The distribution of total nitrogen concentration in the lake is obtained using the model after the implementation of the engineering measures,and a controllable target is thus proposed.The result shows that the total volume of inflow and outflow in Taihu Lake reaches a value of 127.8×108 m3 including 24.9×108 m3 of precipitation that accounts for 19.5% of the total inflow.The annual exchange of total nitrogen loads is 4.47×104 t including 0.07×104 t of wet and dry deposition that can account for 15.5% of the total nitrogen loads.Thus,the nitrogen contribution from wet and dry deposition is significant and non-neglectable.The variation of wet and dry deposition is correlated well with precipitation.Using the simulation result of various water functional areas in the Taihu Lake basin,an average nitrogen value of 2.3 mg/L is proposed as the water quality controllable target for 2015 in the basin.The study provides the technical support and the scientific basis to water pollution control in Taihu Lake.