Modeling of point and non-point source pollution of nitrate with SWAT in the Jajrood river watershed, Iran

The Latian dam reservoir is one of the most important drinking water sources for Tehran, Iran. Nitrate is a major water quality problem in this reservoir. The Jajrood River, the most important water source for the reservoir, discharges large amounts of nutrients to it every year including high levels of nitrate, a pollutant of particular concern. This study presents the results obtained from simulating different point source and nonpoint source impacts on the fate and transport of nitrate in the 470 km2 Jajrood watershed using the Soil and Water Assessment Tool (SWAT) model version 2000 (SWAT2000). The SWAT model was calibrated and validated over an extended time period (1997-2005) for this watershed before evaluating the effect of various management practices on nitrate loadings into Jajrood River. The results of monthly calibration Nash-Sutcliffe coefficient of efficiency (E) and R 2 for runoff at the watershed outlet were 0.82 and 0.81 respectively, and for the validation, these statistics were 0.57 and 0.61 respectively. The values for calibration of daily nitrate load at the watershed outlet were 0.55 and 0.59 respectively, and for the validation these statistics were 0.36 and 0.56 respectively. The simulated results indicate that untreated wastewater and leaking or faulty septic systems are the main sources of nitrate loading in the Jajrood river system. Runoff from orchards is the other significant source of nitrate. Moreover, measurements indicate that the maximum flow rate and nitrate load in the Jajrood River occurs from February to June, which implies that at high flow rates the nitrate load increases in the river.