2721	 The Digital Simulation of River Plankton Population Dynamics	 This paper deals with the development of a mathematical model for and the digital simulation in Fortran IV of phytoplankton and zooplankton population densities in a river using previously developed rate expressions. In order to study the relationships between the ecological mechanisms involved the simulation parameters were varied illustrating the response of the ecosystem to different conditions including those corresponding to certain types of chemical and thermal pollution. As an investigation of the accuracy of the simulation methods a simulation of the actual population dynamics of Asterionella in the Columbia River was made based on approximations of conditions in that river. Although not totally accurate the simulation was found to predict the general annual pattern of plankton growth fairly well and specifically revealed the importance of the annual velocity cycle in determining such patterns. In addition the study demonstrates the usefulness of digital simulations in the examinations of certain aquatic ecosystems as well as in environmental planning involving such examinations. digital simulation mathematical modeling plankton population dynamics phytoplankton zooplankton river ecosystems ecological mechanisms environmental simulation modeling ecosystems pollution environmental impact environmental planning
