亚热带农业小流域暴雨过程硝态氮迁移特征及水文示踪研究

Characteristics of Nitrate-N losses through runoff and hydrological tracing in subtropical agricultural catchments

为揭示亚热带丘陵区农业小流域暴雨过程中硝态氮迁移规律及其主要水文输送途径,本研究通过对紫色土丘陵区典型农业小流域典型暴雨过程跨尺度（从3-1 236 hm^2）连续监测,分析径流硝态氮迁移动态特征及其尺度效应,并对比δ^18O和硝态氮作为示踪剂的端元混合分析（EMMA）解析结果,探讨硝态氮作为暴雨过程水文示踪剂的可行性。结果表明：（1）两场暴雨事件中源头小流域苏荣小流域（含集镇污水）径流中硝态氮浓度最高,而到达梯级小流域出口处（万安小流域）硝态氮浓度最低,林地来水的贡献是较大尺度小流域径流硝态氮浓度降低的主要原因,坡耕地壤中流补给可能是径流消退过程中硝态氮出现浓度峰值的主要原因。（2）EMMA模型解析结果显示：δ18O与硝态氮均能示踪农业小流域径流消退期间壤中流补给过程;但硝态氮在受人居活动强烈影响子流域的示踪应用需谨慎。以农业为主的亚热带丘陵区小流域中,硝态氮具有同时作为环境效应指示剂和水文示踪剂的潜力,但其应用效果仍有待于进一步验证。

In order to understand the hydrological pathways of nitrate-N in subtropical agricultural catch-ments,this study was carried out at a nested agricultural headwater catchment in Hilly area of purple soil.Rainfall,discharge,δ^18O,nitrate-N were monitored continuously in two storms. End member mixing analy-sis（EMMA） model was applied to quantify the contributions from different water sources. The results showthat：（1） Surong catchment has the highest nitrate-N concentrations,while Wanan has the lowest nitrate-N,indicating that nitrate-N decreased with lager catchment size attribute to water dilution effect from othersmall watersheds which are dominated by woodland;（2） Subsurface flow from sloped croplands contributesto peak nitrate-N concentrations increased during the recession period of storm flow. The results of EMMAshow that bothδ18O and nitrate-N successfully traced subsurface flow replenishment process during the flowrecession period. But intense human activity might lead a certain deviation. In sum,nitrate-N has the poten-tial to be environmental indicator and hydrologic tracer simultaneously during storm events for small agricul-tural catchments. But its application in more storm events at multiple sites remains to be further validated.