川中丘陵区小尺度范围非点源氮素流失特征分析

为研究自然降雨条件下紫色土地块-小流域尺度农业非点源氮素随径流流失的特征,采用野外径流观测法,对2011年川中某紫色土丘陵区12次典型降雨产流事件进行了监测,测定径流量及径流中氮素浓度与负荷变化情况。结果表明:旱地流失负荷值远大于林地流失负荷值,且旱地氮素流失主要集中在施肥后的初期降水事件中,占流失总量的76.1%;壤中流氮素平均浓度为0.98~54.1mg/L;旱地氮素迁移有显著月变化特征,明显受到当地施肥习惯和汛期降雨量影响。陈家湾农林复合小流域氮素迁移特点分析表明,该小流域受到多种土地利用类型影响,径流氮素浓度波动范围不大;但在大雨降雨事件中,浓度在降雨后期有所升高,体现了"末期冲刷效应"。研究结果可为调控长江上游紫色土丘陵区氮素流失提供参考。

Characteristics of non-point nitrogen exported from small scale hilly area in middle Sichuan Province

In order to study the characteristics of agricultural non-point nitrogen loss in runoff from small purple plot-catchment of Sichuan, 12 rainfall events in the study area were selected to monitor the runoff yielding, nitrogen concentration and calculate the exported nitrogen load by runoff.The results showed that the exported nitrogen load from upland field was much greater than that from forest land and the amount of exported nitrogen from the upland field in the early rainfall accounted for 76.1% of the total loss after fertilization.The average concentration of nitrogen in subsurface flow was 0.98-54.1mg/L;the nitrogen exported from upland field varied monthly, which was apparently influenced by local fertilization and precipitation in rainy season.The nitrogen export characteristics in Chenjiawan agroforestry small catchment showed that the nitrogen concentration in runoff was stable because of the multiple land uses.However, the nitrogen concentration increased in the later stage of the heavy rainfall events, which exhibited a strong "end flush" effect of the total nitrogen(TN).The exported nitrogen load showed a significant monthly variation characteristics.This research can provide a reference for the regulation and control of non-point nitrogen loss in the hilly area of purple soil in upper Yangtze River.