Phosphorus Budget For Lake Mogan Ankara Turkey

Lake Mogan Lake which is 20 km south of Ankara Metropolitan area was declared as a Specially Protected Area in 1990. Lake Mogan that is fed negligible amounts from groundwater receives most of its water from seasonal creeks which are dry most of the summer months. Mogan Watershed which has an area of 970 km2 is dominated by areas with dry agricultural practices (%65) and grazing lands (27%). As a result of surface runoff and irrigation return flows from agricultural lands, Lake Mogan has been severely affected by the diffuse pollution. Moreover, it has been negatively affected by the fast and poorly planned urbanization around the lakeshore. In addition, the water quality in Lake Mogan is susceptible to incremental changes in the inflows to the lake because of its hydrodynamic characteristics. Since it is a specially protected area, intense water quality, quantity and meteorological monitoring campaign has been conducted in the Mogan watershed by the central agencies. Because of its ecological importance, it is important to evaluate the different characteristics of the lake to develop efficient management alternatives to improve the water quality. In this study phosphorus budget model is used to estimate the particulate phosphorus settling velocity with the purpose of calculating the required reduction in the external phosphorus load to Lake Mogan to meet the water quality standards. Furthermore, the change in the total phosphorus concentration of Lake Mogan is examined and the possible factors that could cause these changes are discussed. The results show that the particulate phosphorus settling velocity is often at lower than the specified range (1-200 m/y) or even at negative values. Negative phosphorus settling velocities have been interpreted as an indication of the resuspension in the lake. Moreover, the fact that Mogan Lake is a shallow lake strengthens the possibility of resuspension. In May of 2008, because of the low water level in the lake due to drought, water from Kızılırmak is transported to Lake Mogan and it is thought that it leads to resuspension in the lake. From Lake Mogan TP graph it can be easily seen that in 2008 contrary to the general trend TP concentrations increase significantly and this supports the possibility of resuspension. By using calculated average phosphorus settling velocity, maximum phosphorus load to the lake was determined to ensure the eutrophication control limits. In the end, it was found that phosphorus load should be reduced by %86. In addition, a simple linear regression model was used to determine in-lake P concentrations for the future predictions since all the calculations are based on measurements conducted between 2007 and 2010. For regression analysis, easily measurable independent parameters pH, temperature, dissolved oxygen and electrical conductivity is used.
8th Shallow Lakes Conference, 2014


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Citation Formats
Z. Özcan and E. Alp, “Phosphorus Budget For Lake Mogan Ankara Turkey,” presented at the 8th Shallow Lakes Conference, 2014, 2014, Accessed: 00, 2021. [Online]. Available: