System Dynamics Modeling of Phytoplankton and Zooplankton in Reservoirs

The need for predictive water quality modeling has arisen largely as a result of increased eutrophication of lakes throughout the world. In 1919 Nauman introduced the concept of oligotrophy and eutrophy, distinguishing oligotorophic lakes with little panktonic algae and eutrophic lakes containing much phytoplankton. The phytoplankton consist of the assemblage of small plants having no or very limited powers of locomotion. A variety of formulations have been developed to represent the effect of temperature, light, and nutrient on phytoplankton growth. A number of processes contribute to the loss rate of phytoplankton. These processes are: respiration, excretion and predatory losses. The zooplankton include animals suspended in water with limited power of locomotion. Phytoplankton as well as zooplankton are usually denser than water, and constantly sink by gravity to lower depths. System dynamics is a method of solving problems by computer simulation. The typical purpose of a system dynamics study is to understand how and why the dynamics of concern are generated and to search for managerial policies to improve the situation. In this paper phytoplankton and zooplankton are simulated by system dynamics approach. Then we integrated a limiting nutrient into our phytoplankton-zooplankton scheme to complete our fundamental picture of how nutrient/food-chain interactions are modeled.