Numerical modelling of Phosphorus Advection and Diffusion in Water Bodies (Case study: Sefidrood River)

Phosphorus is one of the vital nutrients for plants and algae growth. Low solubility of phosphorus compared of other nutrients, has caused phosphorus plays key role in algae growth and its often limiting nutrient in most freshwater. So that excessive phosphorus level in water can produce more algae that cannot be cosumed by waterbody creatures and can cause eutrophication, water quality reduction and harmful condition for aquatic ecosystem. Therefore, it is important to identify the main sources of entering into rivers, recognizing the mechanism of transport and its distribution as well as the conditions created in rivers due to the advection and diffusion of phosphorus. For this purpose, in this research, after identifying the main sources of phosphorus entry into the river, it investigates and simulates the advection and dispersion of phosphorus in the Qezel-Ozan, Shahrood and Sefidrood Rivers based on field meusring data and using HEC-RAS software. Five scenarios were designed based on changes in environmental and anthropogenic factors and then by numerical simulating using HEC-RAS software, the impacts of phosphorus dispersion have been investigated in the region research area. The result presented that controlling human activities that entering phosphorus to Qezel-Ozan and Shahrood rivers can reduced total phosphorus concentration of Sefidrood river but mass of algae has been increased only by increasing air temperature and discharge of rivers and decreasing by decreased river discharge