Determination of nutrient loads in Mogan watershed through modelling approach

Lake Mogan which is located in Gölbaşı County, 20 km south of Ankara, Turkey is one of the most important wetlands of Turkey and it was declared as a Special Environmental Protection Region in 1990 because of its ecological value. Mogan Watershed which has an area of 970 km2 is dominated by agricultural land use. The ecological integrity in Lake Mogan is under threat due to high level of urbanization, industrial and agricultural activities. In this study, unit diffuse pollution loads resulting from different land use classes in the basin were estimated with Soil and Water Assessment Tool (SWAT) model. The pollution loads estimated by SWAT at the outlets of Yavrucak Creek were used to calculate simulated pollution loads per unit watershed area. In addition, the unit pollution loads for different land use classes were estimated by nonlinear programming. SWAT model outcomes showed that the unit total nitrogen (TN) and total phosphorus (TP) loads (0.46 kg TN/ha/yr and 0.07 kg TP/ha/yr) generated from Mogan watershed are very close to the minimum values of the loads specified in the literature. In addition, the calculated values for agricultural land use (0.59 kg TN/ha/yr and 0.09 kg TP/ha/yr) are consistent with the literature values