Estimation of contribution of nitrate pollution sources on the spatial distribution of the pollutant in the Caspian Sea

Seas are one of the most important sources of protein in the world. For a long time, it was thought that the oceans are so vast that the amount of their pollutants could be ignored. Nowadays, seawater pollution is a very important issue due to its direct and indirect effects on human life.    Assuming the relatively similar behavior of important pollutants and their different levels of importance, nitrate pollution is considered as a pollutant indicator in the Caspian Sea and is modeled as a conservative parameter in this study. Although these initial assumptions may cause some errors in results, owing to the main purpose of the study which is to determine the amounts of the contribution of main sources of pollution (and not their absolute amounts), the assumptions are largely acceptable.By modeling different sources of pollutant, the contribution of these sources on spatial distribution of the pollutant in the Caspian Sea has been estimated. The main source of pollution in the Caspian Sea is the Volga River with the Kura River in the second place.    In order to estimate the contribution of different pollutants in the concentration of the pollution in the Caspian Sea, the main sources of pollution are separated and introduced to the model as individual contaminants. However, in conventional methods for simulating a type of contaminant from different sources that enters an aquatic environment, all sources of pollutants are treated in the same way. The modeling of different sources of pollution as different contaminants leads to the fact that superimposing the effects of contaminants emitted from different sources, estimates total concentration of the pollutant indicator in each region, and also, the contribution of each source in different regions can be easily identified. For this purpose, 10 points of pollution sources were considered. Each source has a contaminant with a different name and amount, but with the same characteristics. The result obtained from the advection and dispersion of these sources of pollution is analyzed later to estimate the total concentration of nitrate in the Caspian Sea, and also, to calculate the contribution of each source.Comparing the concentration of total nitrate of the observed data with the results of numerical model, it is shown that the model has a good accuracy in the Southern Caspian Sea. It seems that it is the first research that considers the contribution of each polluting source in the pollution of different regions of the Caspian Sea. So, the results can be used in other studies about pollution in the Caspian Sea.