A System Dynamics Model to Analyze Nitrate and Ammonia in Reservoirs and Lakes

This paper developed a system dynamics model to stimulate nitrate and ammonia in reservoirs. Most algae and plants in surface water use ammonia and nitrate as nitrogen sources. The role of these nutrients is evident on algae and also cyanobacterial growth. Nowadays, computer tools, especially mathematical modeling, are often used to manage these chemicals in water bodies.
The current study aimed to introduce a suitable system dynamics model to analyze nitrate and ammonia in reservoirs.
The current paper developed a process model. First, a sketch of nitrate and ammonia storage, their specifications and parameters were set out and created on a page, and then, mathematical relations of each process were set up and entered into a VensimTM page. Finally, the model was calibrated and verified using data obtained from the Karkheh Reservoir.
After making a model and performing its initial test, it was calibrated according to 1991 data of Long Lake Reservoir in the United States and calibration coefficients were obtained. Finally the model was validated using a total of 2000 pieces of data from the reservoir. The results indicated that the output of the model for the layer beneath had better accordance with the measured values, in comparison with the outer layer, which could be due to higher modification in outer layer.
The results indicated that the model, compared with other models, was user-friendly and the desired results were obtained by a minimal data.