Study on the Sources and Characteristics of Nitrogen in the Major Rivers of Taihu Lake

Nitrogen level,species distribution and seasonal variation regularity of twenty major rivers around Taihu Lake in 2012 were analyzed,in order to provide relative data for the pollution control of the river regions of Taihu Lake. The results showed that the annual average TN( total nitrogen) concentrations of the rivers were between 2. 53-6. 31 mg/L. According to the average of TN concentration,the twenty rivers were divided into three types,i. e.,heavy,medium and light pollution. Inorganic nitrogen( DIN) was the major species of nitrogen,with its percentage exceeding 72% of TN. For the heavy and medium polluted rivers,the percentage of ammonia and nitrate nitrogen were about 50% of DIN,while for the light polluted rivers,the percentage of nitrate nitrogen was about 60% of DIN. The concentrations of TN,ammonia and nitrate in heavy and medium polluted rivers in the dry season were higher than those in the rainy season. Significant testing showed the significant variation,probably because the nitrogen removal efficiency of wastewater treatment plants and ecological systems,such as constructed wetlands in dry season,was less than those in rainy season,since the average temperature of air and water temperature in the rainy season( from May to October) is higher than that in the dry season( from November to the next April). Also,point source pollution is the dominant pollution source in heavy and medium polluted rivers. Differences of TN, ammonia and nitrate nitrogen concentrations in light polluted rivers between dry and rainy seasons were not significant,which indicated the different types of nitrogen have equivalent point source and non-point source loads. In order to improve thewater quality of the rivers,it is urgent to confirm and control the point source pollutions of heavy and medium polluted rivers,while for light polluted rivers,point source and non-point source pollution should be controlled together.