Dynamics of the nitrogen cycle in a lake and its stability

Recent eutrophication of lakes or sea water has caused serious damage to the ecological balance in aquatic systems and to the quality of water for human use. The purpose of this study is to construct a dynamic model of the nitrogen cycle in a lake and to study the dynamic behavior of the various nitrogen forms such as organic, inorganic and plankton in connection with the mechanism of algal blooms in lakes. The dynamics of the system are represented by a system of non-linear differential equations which include the predator-prey relation between plankton types, and are discussed with the stability analysis of the critical points of differential equations. The effects of seasonal changes of environmental parameters are studied with computer simulations.