小流域氮流失特征及其影响因素

由非点源流失的氮是造成水体污染的主要因子之一，而土地利用方式往往对氮的流失产生重要影响。本课题在福建省九龙江流域遴选了4个不同土地利用方式的小流域，通过在自然降雨条件下现场采样与室内分析相结合，研究不同土地利用结构的小流域氮的流失特征和影响因素。研究结果表明：总氮、可溶态氮和泥沙结合态氮的浓度通常比径流先达到峰值，然后开始降低；氮的流失以可溶态氮为主(占73%～98.3％)，因此其流失量主要受径流量的影响与雨强关系不大；土地利用方式对氮的流失有明显影响，一般植被覆盖度提高可以降低流失，而农业活动会加剧流失；此外，在高植被覆盖度的天然林地，氮的流失呈现出以泥沙结合态为主。通过本研究可以看出土地利用结构的调整和合理布置是九龙江流域非点源污染控制的重点。

Characteristics and influencing factors of nitrogen loss of subwatershed

Nitrogen loss from non-point sources is the important pollution source of water and remarkably affected by the pattern of land use.Four small watersheds with various land use patterns,located at Jiulong River,Fujian Province,are selected as the typical watersheds to investigate the characteristics of nitrogen loss and the influencing factors in different land use patterns.In-situ water samples monitoring are carried out.The result demonstrates that nitrogen loss reaches the peak value earlier than the runoff and then decreases gradually.The major part of loss is in the form of dissolved nitrogen and affected by the runoff rather than the rainfall intensity.The land use pattern has significant impact on nitrogen loss and vegetation can reduce the loss.Whereas,the agricultural activities will intensify the loss.Besides,the nitrogen loss will change into a form of combining with sediment if the land use is dominated by forest.It is concluded that the optimization of land use structure and spatial pattern as well as the control of fertilizer use are key measures for controlling the nitrogen loss of non-point pollution sources.