Use of mathematical models to estimate the effect of nutrient loadings on small streams

In this study mathematical modelling is used as a tool to estimate the water quality of a creek together with its nutrient loads transported to a lake. The study area was a coastal lagoon system located in the southwest of Turkey. Yuvarlakcay Creek is one of the important streams within the selected watershed joining to Koycegiz Lake, which, in turn, connects to the Mediterranean Sea through the lagoon channel. A computational framework was developed to estimate the stream's water quality. In the first step, data analysis was carried out with data available on the stream (such as flow rate and water quality) and its watershed (such as land use) and analyzed. In the second step, the nutrient loads from the diffuse sources to the stream were calculated. In the third step, the appropriate mathematical models for stream water quality simulations were selected after comprehensive surveys. QUAL2E and WASP/EUTRO models, developed by US Environmental Protection Agency (EPA) were found to be appropriate for steady-state and dynamic simulations, respectively. The fourth step was the model calibration and verification. The model can be used to estimate both the current water quality of the Yuvarlakcay Creek and its nutrient loads carried to Koycegiz Lake. These data calculated can be used for developing future scenarios. The methodology and computational framework referred in this study forms a guideline that may be utilized for small streams.