西苕溪流域非点源氮污染特征

通过对西苕溪流域不同用地类型的子流域出口设置监测点并进行定期水质监测,探讨该流域非点源氮污染特征及其区域性差异。不同月份的监测结果表明,总氮（TN）、溶解性总氮（DTN）、硝态氮（NO3--N）浓度在12月最高,7月次之,4月最低;铵态氮（NH4＋-N）浓度在7月最高,12月次之,4月最低。典型子流域日监测数据表明：林地子流域水质监测点测得的氮明显低于耕地,降雨期林地子流域出口的氮浓度增加,耕地子流域降低,干旱期则相反。研究表明流域非点源氮污染主要受农业耕地用地类型的控制,降雨径流是西苕溪流域非点源氮输出的主要驱动因素,用地类型、不同形态氮的理化性质差异导致流域非点源氮呈现明显的季节、空间分布特征。

Characteristics of Non-point Source N Pollution in Xitiaoxi Catchment, China

With strictly controlling measures for point source pollution, non-point source pollution from the catchment is becoming an increasingly serious problem, which has caused deterioration of water quality of lake, reservoir and groundwater. Nitrogen pollution, mainly exported from forestland and arable land, for its high solubility, is playing an important role in non-point source pollution. Xitiaoxi catchment is located in the upstream of Taihu basin, where river water quality has become deteriorated heavily in recent years. To further analyze the spatiotemporal characteristics of non-point source N in Xitiaoxi catchment, water sampling points were set up at the outlet of sub-watersheds with different land use types, and monthly water samples were taken for December 2009, April 2010 and July 2010. The resuhs indicated that the peak concentrations of total nitrogen（TN ）, dissolved nitrogen（ DTN ）, nitrate nitrogen（ NO3^-N ） appeared in December, followed in July, and the lowest concentration in April, while the concentration of ammonia nitrogen （ NH4^-N ） was highest in July, followed in December, and lowest in April Furthermore, daily observations indicated that non-point source N from sub-watershed of forestland was far lower than that of arable land. During the wet seasons, nitrogen concentrations increased at the outlet of forestland sub-watershed while that of arable land decreased and the phenomena reversed during dry seasons. The main finding of this work was that non-point source N pollution in Xitiaoxi catchment was mainly caused by agricultural activities of arable land. Rainfall and runoff were the main driving factors to cause non- point source N exported from the catchment. Moreover, different land use types and physicochemical properties of nitrogenous substance might lead to the seasonal and spatial characteristics of non-point source N in Xitiaoxi catchment.