Fate of dissolved oxygen and survival of fish population in aquatic ecosystem with nutrient loading: a model

In this paper, a nonlinear mathematical model is proposed and analyzed to study the depletion of dissolved oxygen and survival or extinction of fish population in a nutrient enriched aquatic ecosystem. It is assumed in the model that there is an external constant input of nutrients (phosphorus and nitrogen) in the water body on account of anthropogenic activities. Stability analysis of the equilibria of the model is carried out and from the analysis it is shown that the fish population will survive at very low equilibrium level due to reduced concentration of dissolved oxygen and excessive presence of algal biomass on account of nutrient loading. Further, it is shown in this paper that the fish population tend to extinction due to decrease in the concentration of dissolved oxygen from its threshold level. Numerical simulations are also carried out in this paper to support the analytical results.