基于改进型DNDC模型的小流域非点源氮迁移过程模拟与空间拓展应用

以长江上游紫色土区截流堰小流域（0.35 km2）和大兴小流域（4.65km2）为研究对象，应用基于水文过程的生物地球化学循环模型—改进型DNDC模型对紫色土区小流域径流、泥沙和氮流失过程进行研究。本文采用截流堰小流域2007～2009年和2010～2011年径流、泥沙和氮迁移监测数据分别对模型进行参数率定和验证，检验模型在紫色土区的适用性，然后利用大兴小流域2011年水文、水质监测数据对该模型进行拓展验证，探讨模型在具相似空间结构特征的小流域实现尺度拓展的可行性。结果显示：率定期和验证期月径流、土壤侵蚀、氮流失Nash-Sutcliffe效率系数Ens大多超过0.80，相对误差Re均在15%以内。拓展验证期间，月径流、土壤侵蚀、总氮（TN）和颗粒态氮（PN）的Nash-Sutcliffe效率系数Ens分别为0.70、0.55、0.76和0.71，相对误差Re分别为6.2%、31.2%、9.5%和30.4%，模型较好的反映了大兴小流域径流、泥沙和氮迁移过程。但是模型拓展验证期间，泥沙、颗粒态氮的模拟偏差有所增大。

Simulation of nonpoint source nitrogen transport in two separated catchments in the hilly area of purple soil

In this study, hydrology-biogeochemistry-based model was employed to simulate the water quantity and water quality of the Wanan watershed in the hilly area of purple soil. The enhanced DNDC model was calibrated with data of 36 months period (2007-2011) and validated with data of 24 months period (2011) in Jieliuyan watershed, and extended validated with data of 12 months period (2011) in Daxing watershed, both sub-watershed of Wanan watershed. The primary objective of this study was to compare hydrology, sediment and nitrogen simulation results in two separate, but similar, watersheds. The simulation results of monthly discharge, sediment and nitrogen showed that enhanced DNDC model performed satisfactorily in the study area (Ens=0.90, 0.92, 0.89, and 0.88 in calibration period and Ens=0.83, 0.87, 0.74, and 0.52 in validation period for discharge, sediment yield, total nitrogen and particulate nitrogen, respectively). The result indicated that the enhanced DNDC model is an appropriate model for the non-point source nitrogen pollution simulations in purple soil area. The possibility of extended validation was proved due to the encouraging results during the extended validation period. However, lower Ens and larger Re for sediment yield and particulate nitrogen were observed in the extended validation period in a larger watershed due to the model weakness of channel process.