Widespread agrochemicals differentially affect zooplankton biomass and community structure

Abstract

Anthropogenic environmental change is causing habitat deterioration at unprecedented rates in freshwater ecosystems. Despite increasing more rapidly than many other agents of global change, synthetic chemical pollution—including agrochemicals such as pesticides—has received relatively little attention in freshwater community and ecosystem ecology. Determining the combined effects of multiple agrochemicals on complex biological systems remains a major challenge, requiring a cross‐field integration of ecology and ecotoxicology. Using a large‐scale array of experimental ponds, we investigated the response of zooplankton community properties (biomass, composition, and diversity metrics) to the individual and joint presence of three globally widespread agrochemicals: the herbicide glyphosate, the neonicotinoid insecticide imidacloprid, and nutrient fertilizers. We tracked temporal variation in zooplankton biomass and community structure along single and combined pesticide gradients (each spanning eight levels), under low (mesotrophic) and high (eutrophic) nutrient‐enriched conditions, and quantified (1) response threshold concentrations, (2) agrochemical interactions, and (3) community resistance and recovery. We found that the biomass of major zooplankton groups differed in their sensitivity to pesticides: ≥0.3 mg/L glyphosate elicited long‐lasting declines in rotifer communities, both pesticides impaired copepods (≥3 µg/L imidacloprid and ≥5.5 mg/L glyphosate), whereas some cladocerans were highly tolerant to pesticide contamination. Strong interactive effects of pesticides were only recorded in ponds treated with the combination of the highest doses. Overall, glyphosate was the most influential driver of aggregate community properties of zooplankton, with biomass and community structure responding rapidly but recovering unequally over time. Total community biomass showed little resistance when first exposed to glyphosate, but rapidly recovered and even increased with glyphosate concentration over time; in contrast, taxon richness decreased in more contaminated ponds but failed to recover. Our results indicate that the biomass of tolerant taxa compensated for the loss of sensitive species after the first exposure, conferring greater community resistance upon a subsequent contamination event; a case of pollution‐induced community tolerance in freshwater animals. These findings suggest that zooplankton biomass may be more resilient to agrochemical pollution than community structure; yet all community properties measured in this study were affected at glyphosate concentrations below common water quality guidelines in North America.

Resistance, resilience, and functional redundancy of freshwater bacterioplankton communities facing a gradient of agricultural stressors in a mesocosm experiment

“…The absence of a bacterioplankton response is also consistent with the weak or undetectable response of zooplankton biomass to imidacloprid pulses in the same experiment (Hébert et al, 2021). The invertebrate community in the experimental ponds was mainly composed of the zooplanktonic groups Cladocera, Copepoda and Rotifera, and only copepods 3 declined over time after pulse 2, with no resulting effect in total zooplankton biomass (Hébert et al, 2021). Overall, these results indicate that the concentrations of imidacloprid applied in this experiment were not sufficient to strongly alter either zooplankton or bacterioplankton biomass or community structure.…”

“…Additional lake water was added on a biweekly basis (~10% of total volume) between May and August to ensure a continuous input of lake bacterioplankton, tracking seasonal changes in the source lake community, and to homogenize communities across ponds. The experiment reported here used 48 of these pond mesocosms from August 17 th (day 1) to September 1 th (day 43), and it is part of a collaborative experiment that also assessed responses of zooplankton in the same set of ponds (Hébert et al, 2021) and phytoplankton responses in a subset of these ponds for a longer period of time (Fugère et al, 2020).…”

A glyphosate-based herbicide cross-selects for antibiotic resistance genes in bacterioplankton communities

“…In a previous study, we used 16S ribosomal gene amplicon sequencing to assess how the composition of freshwater bacterioplankton communities respond to a GBH applied alone or in combination with a widely-used neonicotinoid insecticide [11]. As part of the same experiment, we also showed how phytoplankton undergo community rescue in response to lethal GBH doses [25], and how zooplankton community properties were differentially affected by pesticides, even at glyphosate concentrations below North American water quality guidelines [26].…”

“…An eight-week mesocosm experiment was conducted at the Large Experimental Array of Ponds (LEAP) facility (Fig. 1A) located at McGill University's Gault Nature Reserve (QC, Canada) from August 17 th (day 1) to October 12 th (day 57) 2016, as previously described [11,25,26]. Pond mesocosms were filled with 1,000 L of water and planktonic communities from Lake Hertel (45°32' N, 73°09' W).…”

“…Pond mesocosms were filled with 1,000 L of water and planktonic communities from Lake Hertel (45°32' N, 73°09' W). Lake water was passed through a coarse sieve to prevent fish introduction, while retaining lake bacterioplankton, zooplankton and phytoplankton, whose responses to experimental treatments have been described in previous studies [11,25,26]. Fig.…”