西藏高原灌区氮素迁移转化特性及模拟方法

Simulation of nitrogen transport and transformation processes in a Tibetan Plateau irrigation district

针对西藏高原灌区的水文和氮素迁移转化特性,于2014年和2015年青稞种植期在西藏林芝市丹娘灌区测定了土壤-松散岩体介质中径向渗流和地表排水过程中的流量、氨氮和硝态氮浓度变化过程。发展了分段连续演算方法描述径向通量过程,基于集总式一阶动力学方法计算径向渗流及排水过程中氮素的转化过程,构建了西藏高原灌区水文及氮素迁移转化模型。结果表明:灌区径向通量分别占降雨量和灌水量的26.2%和40.9%。进入排水沟的NH+4-N和NO-3-N通量分别占深层渗漏量的20.2%和25.1%。流量、NH+4-N和NO-3-N浓度模拟结果的系统偏差、Nash-Sutcliffe系数、相对均方根误差和累积偏差分别为0.043、0.694、0.081和0.242,表明所提出的方法有效地模拟了西藏高原灌区水文及氮素的迁移、转化和入河过程。

The objective of this study was to investigate the effects of hydrology processes on the nitrogen transport and transformation in a Tibetan Plateau irrigation district. Field experiments were conducted to measure the quality and quantity of leakage within the soil and loose rock medium and the surface drainage water in the Danniang irrigation district,Nyingchi,Tibet during the hulless barley growing periods in 2014 and 2015. The lateral seepage flux and the NH＋4-N and NO-3-N concentrations in the soil and loose rock medium and at the outlet of the drainage canal were monitored. A procedure using a stepwise method was proposed to describe the flow and transport processes in the loose rock,and a lump first-order kinetics method was used to describe the process of nitrogen transformation during the seepage and drainage processes. The deep seepage accounted for 26. 2% of the total rainfall and 40. 9% of the total irrigation. The total mass of NH＋4-N and NO-3-N discharged into the drainage canal accounted for 20. 2% and 25. 1% of the total mass of NH＋4-N and the total mass of NO-3-N leached from the soil into the loose rock,respectively. The mean values for system errors,Nash-Sutcliffe efficiency,the relative root mean square error,and the fractional gross error between the simulated and monitored flow rates and nitrogen concentrations at the outlet of the drainage canal were0. 043,0. 694,0. 081 and 0. 242,respectively,indicating that the developed method was applied successfully to simulate nitrogen transport and transformation in the seepage and surface drainage processes.