降水产流非线性驱动下坡地硝态氮产污过程试验

Experiment on nitrate-N pollutant generation process driven by nonlinear rainfall-runoff

为正确认识坡地氮素流失过程,同时为降水产流非线性驱动下流域污染负荷模型的构建提供理论依据,研发自动化程度高、接近天然降雨的人工模拟降雨产流产污试验装置,试验研究不同降雨强度和前期土壤含水率条件对产流及近地表土壤中硝态氮溶出过程的影响,利用演绎推理法探讨近地表土壤中硝态氮溶出系数与降雨产流及土壤含水率的关系。结果表明:降雨强度越大,前期土壤含水率越高,产流量、累积产流量越大;产流量以幂函数形式随时间不断增加趋于稳定,同时,降雨初期地表产流中硝态氮负荷及累计负荷量也越大;后期随着产流量的增加而呈幂函数形式衰减,最终又随着产流量的稳定而趋于稳定;近地表土壤中硝态氮的溶出系数受控于降雨产流,同时与土壤湿度存在指数函数关系。探讨的降雨产流-溶出系数-土壤含水率的数值关系对模拟高时间分辨率降雨产流非线性驱动下坡地硝态氮产污过程具有一定的参考价值。

The special topography and soil characteristics of the hilly slopes in southern China make the hydrological process that drives the nitrate-N transport showing highly non-linear.Thus,the study of slope nitrate-N loss process varying with time associated with nonlinear rainfall-runoff is very important.The rainfall and antecedent soil moisture are the significant factors influencing the natural runoff process and non-point source pollution loss.Most scholars consider the pollutant generation coefficient as a constant for the sake of simplicity,and it lacks the detailed quantitative description and mechanism study.An artificial simulation rainfall-runoff-pollutant generation experiment equipment close to natural rainfall with a high degree of automation observation was developed.The designed contrast control experimental method was employed to study the runoff generation and nitrate-N generation process near the surface soil under different rainfall intensity and antecedent soil moisture.The mathematical derivation method was used to discuss the relationship between the nitrate-N generation coefficient,runoff,and soil moisture near the surface soil.The runoff generation escalated with time in a power function form initially and then keeps stability later.The larger the rainfall intensity and the higher the antecedent soil moisture,the runoff-yielding time was faster,the runoff generation and the cumulative runoff generation were larger,the time for the runoff stabilization was shorter,and the runoff stabilization value was higher.The nitrate-N load and cumulative nitrate-N load were higher at the beginning of the rainfall.It showed decreasing trend in a power function form,and finally became stable along with the runoff.With the increase of the rainfall intensity and antecedent soil moisture content,the nitrate-N load and cumulative nitrate-N load increased,and the time for the nitrate-N load stabilization was shorter.The two parameters relationship formula between the nitrate-N generation coefficient and the soil moisture driven by the nonlinear rainfall-runoff could better describe the nitrate-N generation process near the surface soil.The rainfall-runoff plays a decisive role for the nitrate-N generation coefficient,and it has an exponential function relationship with the soil moisture under the nonlinear rainfall-runoff condition.The discussed relationship between the rainfall-runoff,the nitrate-N generation coefficient,and the soil moisture could provide a certain reference value for simulating the nitrate-N generation coefficient process near the surface soil driven by the nonlinear rainfall-runoff with high time resolution.