The use of ecological models to assess the effects of pesticides on the structure and function of aquatic ecosystems is of growing interest. Of utmost concern is assessment of pesticides that have the potential to biodegrade into metabolites that are as toxic as the parent pesticide. In this work, a mathematical model to predict and evaluate the effect of two pesticides on the population of aquatic biospecies where both pesticides are bio-available in water and sediments with one of the pesticides capable of biodegrading into the other but not vice versa is formulated and analyzed. Conditions for nonlinear stability, instability and Hopf-bifurcation are obtained. The model undergoes a Hopf-bifurcation when the rate of discharge of pesticides crosses a critical value, so that the population of the aquatic species follows an oscillatory pattern. Four hypotheses involving the concentration of the pesticides and the population of the aquatic species where qualitatively investigated: the aquatic species will completely die out with time, the population of the aquatic biospecies will remain under certain conditions, the pesticide will continually remain in water and there will be a periodic variation in the population of the aquatic species over time. Results also indicate that the biodegradation potential of one of the pesticides had significant effect on the population dynamics of the aquatic species.

使用生态模型评估农药对水生生态系统结构和功能的影响越来越引起人们的兴趣。最令人关注的是对可能生物降解成与母体农药一样有毒的代谢物的农药的评估。在这项工作中，建立了一个数学模型来预测和评估两种农药对水生生物物种的影响，其中两种农药都可以在水中和沉积物中被生物利用，其中一种农药能够生物降解为另一种，但反之则不然并进行分析。得到了非线性稳定性，不稳定性和Hopf分支的条件。当农药的排放速率超过临界值时，该模型将经历Hopf分支，因此水生生物种群遵循振荡模式。定性研究涉及农药浓度和水生物种的四个假说：水生物将随着时间的流逝而完全消亡，水生物种的种群将在一定条件下保留，农药将继续留在水中等。这将是水生生物种群随时间推移的周期性变化。结果还表明，其中一种农药的生物降解潜力对水生物种的种群动态具有显着影响。农药将继续留在水中，随着时间的流逝，水生物种的数量将有周期性变化。结果还表明，一种农药的生物降解潜力对水生物种的种群动态具有显着影响。农药将继续留在水中，随着时间的流逝，水生物种的数量将有周期性变化。结果还表明，其中一种农药的生物降解潜力对水生物种的种群动态具有显着影响。