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Water 2019, 11(1), 132; https://doi.org/10.3390/w11010132

Simulation of Flow and Agricultural Non-Point Source Pollutant Transport in a Tibetan Plateau Irrigation District

1
Department of Water Resources and Civil Engineering, Tibet Agriculture and Animal Husbandry College, Nyingchi, Tibet 806000, China
2
State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China
3
State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China
4
Department of Geosciences Hydrology, University of Oslo, 0316 Oslo, Norway
*
Author to whom correspondence should be addressed.
Received: 30 November 2018 / Revised: 29 December 2018 / Accepted: 9 January 2019 / Published: 12 January 2019
(This article belongs to the Section Water Quality and Ecosystems)
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Abstract

Flow and transport processes in soil and rock play a critical role in agricultural non-point source pollution (ANPS) loads. In this study, we investigated the ANPS load discharged into rivers from an irrigation district in the Tibetan Plateau and simulated ANPS load using a distributed model. Experiments were conducted for two years to measure soil water content and nitrogen concentrations in soil and the quality and quantity of subsurface lateral flow in the rock and at the drainage canal outlet during the highland barley growing period. A distributed model, in which the subsurface lateral flow in the rock was described using a stepwise method, was developed to simulate flow and ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3-N) transport processes. Sobol’s method was used to evaluate the sensitivity of simulated flow and transport processes to the model inputs. The results showed that with a 21.2% increase of rainfall and irrigation in the highland barley growing period, the average NH4+-N and NO3-N concentrations in the soil layer decreased by 10.8% and 14.3%, respectively, due to increased deep seepage. Deep seepage of rainfall water accounted for 0–52.4% of total rainfall, whereas deep seepage of irrigation water accounted for 36.6–45.3% of total irrigation. NH4+-N and NO3-N discharged into the drainage canal represented 19.9–30.4% and 19.4–26.7% of the deep seepage, respectively. The mean Nash–Sutcliffe coefficient value, which was close to 0.8, and the lowest values of root mean square errors, the fraction bias, and the fractional gross error indicated that the simulated flow rates and nitrogen concentrations using the proposed method were very accurate. The Sobol’s sensitivity analysis results demonstrated that subsurface lateral flow had the most important first-order and total-order effect on the simulated flow and NH4+-N and NO3-N concentrations at the surface drainage outlet. View Full-Text
Keywords: irrigation district; Tibetan Plateau; agricultural non-point source pollution; Sobol’s sensitivity analysis; subsurface lateral flow irrigation district; Tibetan Plateau; agricultural non-point source pollution; Sobol’s sensitivity analysis; subsurface lateral flow
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Li, Y.; Zhou, Z.; Wang, K.; Xu, C. Simulation of Flow and Agricultural Non-Point Source Pollutant Transport in a Tibetan Plateau Irrigation District. Water 2019, 11, 132.

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