Assessment of the Accuracy of Salinity Simulation Using Heavy Metal and Nitrogen Cycle in SWAT Model in an Area Exposed to Intensive Agriculture, Navrood Basin, Iran

The quality of water resources has been considerably changed by human activity in recent decades, resulting in current contamination or posing a risk for the future. Compared to other activities, agriculture contributes more to the depletion of surface water and the degradation of water quality. One of the primary strategies to improve the quality of water resources is agricultural management on watershed-level and water quality simulation models are useful tools for simulating the effects of different activities The catchment basin was Navrood (West Guilan, Iran), and the SWAT model was applied. The salinity load was simulated under two cycles: heavy metals and nitrogen, and the two models were compared. Data series of salinity and discharge from 2006 to 2013 were used to calibrate and validate SWAT. R2 and Nash-Sutcliffe coefficients (NS) were computed to evaluate the model's efficacy. The R2 and NS values were obtained in the river discharge simulation at 0.81 and 0.52, respectively indicating a good model fit. The model makes an acceptable performance of modeling the salinity load in the nitrogen cycle, according to the statistical index that was computed during calibration. Based on the results, the SWAT model can be used to analyze the salinity-induced transfer phenomena in the Navrood basin, considering the values of NS obtained for two stations during the calibration stage, which were equivalent to 0.43 and 0.51. The second method, which simulated the salinity load under the cycle of heavy metals in the basin, did not demonstrate a proper correspondence between the simulated and measured data of the salinity load. The R2 and NS under the cycle of heavy metals were 0.30, -0.71. Therefore, based on the results, simulating the Navrood basin's salinity load using the nitrogen cycle is recommended. Zeynab Kougir Chegini is funded by the Stipendium Hungarian scholarship under the joint executive program between Hungary and Iran. The study was elaborated under the research project NKFI K138079. Keywords: paddy fields, surface water, solute transport