Nutrient-phytoplankton-zooplankton models with a toxin

Models of nutrient-plankton interaction with a toxic substance that inhibits either the growth rate of phytoplankton, zooplankton or both populations are proposed and studied. For simplicity, it is assumed that both nutrient and the toxin have the same constant input and washout rate. The effects of toxin upon the existence, magnitude, and stability of the steady states are examined. Numerical simulations demonstrate that the system can have multiple attractors when phytoplankton’s nutrient uptake rate is inhibited by the toxin.