Simulation of nitrate input from agricultural land to the river using the SWAT model (Case Study: Zanjanrood)

In this study, the amount of nitrate input from agricultural land to Zanjanrood River has been simulated using the SWAT model. In order to calibrate and validate the results, SWAT-CUP software and measured mean monthly average flow rate at Sarcham hydrometeric station (1996-2013) were used, and 26 sensitive parameters were selected for sensitivity analysis. Three scenarios for irrigation practices, three scenarios for fertilizer rates and two integrated scenarios were defined. The p-factor and r-factor indices were used for uncertainty analysis and two statistical indices of determination coefficient (R2) and Nash-Sutcliff (NS) coefficient were used for quality analysis of the results,. In the monthly runoff calibration, at the basin outlet, the coefficients r-factor, p-factor, R2, NS were 0.27, 0.11, 0.83, and 0.53 respectively, and at the validation stage, they were 0.6, 0.18, 0.73 and 0.53. The results showed that with increasing pressurized irrigation areas, nitrate pollution in the basin was not significantly affected. With regard to fertilizer levels, by reducing consumption of urea fertilizers up to 50%, the amount of nitrate input into the Zanjanrood River reduced up to about 16.7%. On the other hand, an increase of 50% in fertilizer use has increased nitrate input into the river by 17.2%. Therefore, changing the surface irrigation method does not lead to a significant change in the average nitrate output from the basin. Also, reducing the amount of fertilization and preventing unnecessary fertilization by farmers, pollution of water resources can be greatly prevented.