Phytoplankton and zooplankton concentrations in Pishin reservoir are predicted employing a
three-dimensional numerical model in this paper. Modeling is performed using a numerical model based on mass transport equation. Advection, diffusion and source/sink processes are considered as separate subroutines for predicting the concentrations of phytoplankton and zooplankton in the reservoir. Finite volume method is used for solving the governing equations of water quality and water flow. The model is adopted for drought periods and dry climates. Water flow in the reservoir is simulated by Fluent software that is a finite volume numerical model. The model also uses a sub-model for compatibility providing of geometry between software and water quality model. A one-year period of experimental works and sampling is done in the study area.
Phytoplankton and zooplankton cycles are used to determine the sources and sinks. Standard methods are chosen for experimentation. The concentrations of phytoplankton and zooplankton are calculated and measured in a one-year period. The concentrations of phytoplankton and zooplankton decrease in the depth of water and the decease rate is not linear. Also the concentrations are increase in the times after the maximum floods because of the inflows contain high amounts of nutrients. The calculated values by the model are in good agreement with measured values of laboratory works. It was concluded that the model can be used for water
quality prediction in such aquatic environments.