环太湖主要河流氮素组成特征及来源

以2012年太湖20条主要环湖河流中氮素的逐月调查数据为依据,探讨了河水中氮素的含量、形态组成和季节性分布规律,旨在为进一步实施入湖河流小流域的污染治理提供依据. 结果表明,太湖20条环湖河流的ρ(TN)平均值为2.53~6.31 mg/L,鉴于太湖水体中ρ(TN)多年来居高难下,水质类别主要由ρ(TN)决定,因此按ρ(TN)年均值,将环湖20条河流分为重度、中度和轻度污染3类. DIN(溶解态无机氮)是氮素的主要存在形式,ρ(DIN)平均占ρ(TN)的72%以上. 其中,重度和中度污染河流中ρ(NH₃-N)和ρ(NO₃--N)各占ρ(DIN)的约50%,轻度污染河流则以NO₃--N为主,ρ(NO₃--N)占ρ(DIN)的60%以上. 除个别河流外,重度和中度污染河流水体中非汛期(11月—翌年4月)ρ(TN)、ρ(NH₃-N)和ρ(NO₃--N)普遍高于汛期(5—10月),并且汛期和非汛期差异显著. 这可能与非汛期的水温较低并且污水处理厂及湿地等生态系统的氮素去除率低于汛期有关,此外,也说明点源污染占主要地位；轻度污染河流中ρ(NH₃-N)在汛期和非汛期差异不显著,说明点源和非点源负荷相当. 重度和中度污染河流应重点针对点源污染开展治理；轻度污染河流应将点源、面源污染协同治理,以利于进一步改善水质.

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 the water 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.