次降雨过程中不同土地利用配置对径流中氮流失的影响

为了解天然次降雨过程中土地利用配置对径流氮流失的影响，本研究以重庆市忠县石盘丘小流域两个不同土地利用配置的A、B子集水区为研究对象，对集水区出口径流量和氮素进行监测.A集水区为农林水复合配置模式，B集水区为传统农业配置模式，利用EMC评估次降雨过程径流中氮的平均浓度，分析次降雨过程中不同土地利用配置对径流氮素的影响.结果表明，在次降雨径流氮流失过程中，B集水区的TN浓度（1.37~15.17 mg·L^-1）>A集水区（0.84~9.28 mg·L^-1）；A集水区第一次峰值占第二次峰值的比值62%远小于B集水区的97%；A集水区的平均可溶性总氮/总氮（DN/TN）为69%，B集水区的平均可溶性总氮/总氮（DN/TN）为75%，A集水区的平均硝态氮/可溶性总氮（NN/DN）为67%，B集水区的平均硝态氮/可溶性总氮（NN/DN）为80%.不同土地利用配置对氮流失的影响显著，与B集水区相比，A集水区能有效减少氮的流失，明显消减第一次TN峰值，减少DN和NN的养分占比.本研究为三峡库区小流域面源污染防控提供了科学依据.

Effects of Different Land Use Practices on Nitrogen Loss from Runoff During Rainfall Events

To understand the effect of nitrogen from runoff during rainfall events for different land uses, sub-catchments A and B in the small Shipanqiu watershed in Zhong County, Chongqing-which were managed using different land use practices-were taken as research objects. Runoff flow and nitrogen levels at the outlet of the catchment were monitored. Sub-catchment A is an agroforestry-water complex and sub-catchment B is the site of traditional agriculture. EMC was used to evaluate the average concentration of runoff nitrogen during rainfall events, and the effect of this runoff nitrogen on the small watershed with different land use systems was analyzed. The results showed that the TN concentration in catchment B (1.37-15.17 mg·L^-1) > catchment A (0.84-9.28 mg·L^-1); the ratio of the first peak to the second peak in catchment A was 62%, which was far less than the 97% in catchment B; the average DN/TN values were 69% and 75% in catchments A and B, respectively; and the average NN/DN values were 67% and 80% in catchments A and B, respectively. The different land use practices have significant impacts on nitrogen loss. Compared with the catchment where traditional agricultural practices were followed, the agroforestry-water complex catchment effectively reduced the loss of nitrogen and decreased the first TN peak value and DN/TN and NN/DN values. This study provides a scientific basis for the prevention and control of non-point source pollution in small watersheds in the area of the Three Gorges Reservoir.