Plankton Response to a Mix of Environmental Stressors

Abstract

Water ecosystems face enormous, variable anthropogenic stressors that contribute to waterdegradation. This study explores the effects of three substances frequently found in high concentrations in natural environments linked to agricultural areas on plankton abundance, composition, and trophic interactions. We conducted a microcosm experiment where we exposed a natural plankton assemblage to excess copper (Cu), atrazine (At), and dissolved organic matter (OM), along with a control group encompassing all possible treatment combinations. Each treatment was replicated three times (n = 24), and the experiment lasted 96 h. At the beginning andend of the experiment, relevant limnological variables, including inorganic dissolved nutrients, weremeasured. We used one-way ANOVA analyses with total abundances and species richness as response variables for data analysis. Results showed that the response of each plankton group to these substances was unequal, with some benefiting at tested concentrations. For example, Cu was beneficial for Chlorophyceae and Euglenophyceae, while CuOM was beneficial for Cyanobacteria and Cryptophyceae. Regarding zooplankton, Copepoda density was depleted in all treatments where stressors were combined and when exposed to OM compared to the control. When richness was considered, phytoplankton showed depletion in CuOMAt compared to OM and AtCu. No treatments affected zooplankton richness. Zooplankton:phytoplankton ratios showed significanteffects for total zooplankton and Copepoda in all treatments compared to the control. These resultsindicate that the effects of contaminants on natural assemblages strongly depend on the plankton group and the combinations of contaminants, making predictions and extrapolations a challenging task that requires further study.