Effects of combined nutrient and pesticide exposure on algal biomass and Daphnia magna abundance

Abstract Fertilisers and pesticides are increasingly used in agriculture to improve productivity and protect crops from fungi and insects. However, these farm inputs may lead to adverse effects on aquatic biodiversity through eutrophication and pesticide toxicity. This study aimed to establish the effects of nutrient-only, pesticide-only, combined nutrients and pesticides, and control on the abundance of Daphnia magna , and algal biomass. In each of the treatments, different concentrations of nutrients and pesticides residues were added separately or in combination. Responses were measured every 24 hrs, and the experiments ended after 168 hrs of exposure. The experiment was set in four concentration treatments comprising high, moderately high, moderately low, and low concentrations. Data analysis was done using Multiple Analysis of Variance (MANOVA)and ANOVA to determine the effect of time, concentrations and the interaction of time and concentrations for each of the treatments on D. magna abundance, and algal biomass. Higher concentrations of pesticide additives were associated with lower abundance of D. magna , and higher algal biomass over the exposure periods. There was a significant reduction in the abundance of D. magna in the combined treatment indicating the toxic effect of pesticide addition. Determination of effect concentrations based on combined nutrients-pesticides experiments becomes important in setting water quality standards, and monitoring the quality status, to avoid underestimating the ecological implications of combined contamination.