Nutrient export coefficient modelling of the Melen watershed using estimated retention in the water body

The Melen Watershed provides fresh drinking water to most of Istanbul. According to The Ministry of Forest and Water Works of Turkey, regarding the pollution status, Melen River Basin should be primarily dealt with. Nutrient pollution such as nitrogen (N) and phosphorus (P) can cause water quality degradation in rivers, which are used as a source of drinking water. This situation raises the question of how the nutrients have moved depending on many factors such as land use and anthropogenic sources.Researchers developed several nutrient export coefficient models depending on aforementioned factors. For this purpose, statistical data includes a number of factors such as historical water quality data for the research field, land use, population and infrastructure were used. Nutrient export coefficients are estimates of the total load or mass of nitrogen (N) or phosphorus (P) exported from a watershed standardized to unit area and unit time (e.g., kg/km2/day). Almost no study has been conducted regarding this issue in Turkey.Within this study, nutrient export coefficients for the Melen Watershed were determined using the model that covers Frequentist and Bayesian approaches. River Retention Coefficient was determined and introduced into the model as an important variable. Frequently used hydrologic model, Soil & Water Assessment Tool (SWAT), was used as a tool for modeling of diffuse source pollution. As a brief recommendation, agricultural best management practices (BMP) were evaluated using SWAT model to determine the best management system to reduce nutrient loads in the Melen Watershed. This study is aimed to be an important precedent for other basins that are determined as in priority in terms of pollution by The Ministry of Forest and Water Works of Turkey.