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Mathematical Model of Ammonium Nitrogen Transport to Runoff with Different Slope Gradients under Simulated Rainfall

1
College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China
2
State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China
*
Author to whom correspondence should be addressed.
Water 2019, 11(4), 675; https://doi.org/10.3390/w11040675
Received: 4 March 2019 / Revised: 26 March 2019 / Accepted: 29 March 2019 / Published: 1 April 2019
(This article belongs to the Section Water Quality and Ecosystems)
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Abstract

The removal of nutrients by overland flow remains a major source of non-point pollution in agricultural land. In this study, a mathematical model of ammonium nitrogen transport from soil solution to overland flow was established. The model treated the mass transfer coefficient (km) as a time-dependent parameter, which was not a constant value as in previous studies, and it was evaluated with a four-slope gradient and three rainfall intensities. The kinematic-wave equation for overland flow was solved by an approximately semi-analytical solution based on Philip’s infiltration model, while the diffusion-based mass conversation equation for overland nutrient transport was solved numerically. The results showed that the simulated runoff processes and ammonium nitrogen concentration transport to the overland flow agreed well with the experimental data. Further correlation analyses were made to determine the relationships between the slope gradient, rainfall intensity and the hydraulic and nutrient transport parameters. It turned out that these parameters could be described as a product of exponential functions of slope gradient and rainfall intensity. Finally, a diffusion-based model with a time-dependent mass transfer coefficient was established to predict the ammonium nitrogen transport processes at the experimental site under different slope gradients and rainfall intensities. View Full-Text
Keywords: mass transfer coefficient; ammonium nitrogen transport; slope gradient; rainfall intensity mass transfer coefficient; ammonium nitrogen transport; slope gradient; rainfall intensity
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Xing, W.; Yang, P.; Ao, C.; Ren, S.; Xu, Y. Mathematical Model of Ammonium Nitrogen Transport to Runoff with Different Slope Gradients under Simulated Rainfall. Water 2019, 11, 675.

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