Experiment on nitrate-N pollutant generation process driven by nonlinear rainfall-runoff
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Abstract:
The special topography and soil characteristics of the hilly slopes in southern China make the hydrological process that drives the nitrateN 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 nitrateN 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 nitrateN 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 nitrateN 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.
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