Qualitative Simulation of Nitrate and Phosphate along the Dez River using QUAL2KW Model

Various wastewaters such as household, industrial and agricultural wastes are entered along the Dez River from different locations. Regarding the water scarcity crisis, a comprehensive study on quantitative and qualitative pollution and using management tools such as mathematical and computer models is needed to predict water quality of this river and to prevent its further pollution. In this research, the qualitative QUAL2K model was used for simulation of NO3-, PO4-3 parameters at seven stations; Chamgolak, Dolat park, third bridge, new bridge, floating bridge, fifth bridge and Gavmishabad. The calibration and prediction of the model was done using quality parameters of the river and other information obtained from the field studies. Also, root mean absolute error (MAE) and coefficient variation (CV) were used to validate the model by comparing the observation and prediction data. The results of the model represent the real conditions of the river to an acceptable level, which indicates the ability of the Qual2kw model for simulation of the quality parameters. Most of the river pollution is caused by urban sewage. According to the results, PO4-3 parameter during the studied period is considered to be threaten to aquatic life. But, according to water quality standard for agricultural use, there is no limitation for Dez River. The low discharge at the river downstream and the high loading of pollutants have increased the concentration of water quality parameters. According to the results of the EF, MAE and CV parameters, the model had the best fit for water nitrate.