Pesticides alter ecosystem respiration via phytoplankton abundance and community structure: Effects on the carbon cycle?

Abstract

Freshwater systems are critical to life on earth, yet they are threatened by the increasing rate of synthetic chemical pollution. Current predictions of the effects of synthetic chemicals on freshwater ecosystems are hampered by the sheer number of chemical contaminants entering aquatic systems, the diversity of organisms inhabiting these systems, the myriad possible direct and indirect effects resulting from these combinations, and uncertainties concerning how contaminants might alter ecosystem metabolism via changes in biodiversity. To address these knowledge gaps, we conducted a mesocosm experiment that elucidated the responses of ponds composed of phytoplankton and zooplankton to standardized concentrations of 12 pesticides, nested within four pesticide classes, and two pesticide types. We show that the effects of the pesticides on algae were consistent within herbicides and insecticides and that responses of over 70 phytoplankton species and genera were consistent within broad taxonomic groups. Insecticides generated top-down effects on phytoplankton community composition and abundance, which were associated with persistent increases in ecosystem respiration. Insecticides had direct toxic effects on cladocerans, which led to competitive release of copepods. These changes in the zooplankton community led to a decrease in green algae and a modest increase in diatoms. Herbicides did not change phytoplankton composition but reduced total phytoplankton abundance. This reduction in phytoplankton led to short-term decreases in ecosystem respiration. Given that ponds release atmospheric carbon and that worldwide pesticide pollution continues to increase exponentially, scientists and policy makers should pay more attention to the ways pesticides alter the carbon cycle in ponds via changes in communities, as demonstrated by our results. Our results show that these predictions can be simplified by grouping pesticides into types and species into functional groups.Adopting this approach provides an opportunity to improve the efficiency of risk assessment and mitigation responses to global change.

Multiple stressor effects of a heatwave and a herbicide on zooplankton communities: Implications of global climate change

“…An increase in cyanobacteria may also have led to a spread of toxic bioactive compounds to prevent zooplankton grazing on them (Lyu et al, 2016), leading to lower reproduction rates (Zhou et al, 2020). We assume that the combined effect of HW and TER led to a reduction of primary productivity in green algae and to a lower relative abundance of palatable phytoplankton, as observed in comparable studies (Allen et al, 2021;Rumschlag et al, 2021), which may have caused food limitation for zooplankton, and, consequently, a decreased zooplankton abundance (Rumschlag et al, 2021).…”

“…Herbicides are known to pose direct toxicity to aquatic phytoplankton, which may lead to indirect effects on primary consumers such as zooplankton (Rumschlag et al, 2021). Such indirect effects include mortality (Ferrando and Andreu-Moliner, 1991), starvation, growth and reproduction inhibition (Navis et al, 2013;Oliveira dos Anjos et al, 2021), as well as the alteration of their swimming behaviour (Andrade et al, 2018), and predator scaping capacity (Hanazato, 2001).…”

Identifying low risk insecticides that can enhance food production without increasing mortality of biocontrol agents for human schistosomiasis

“…Thus, prawn survival was negatively associated with pyrethroid and not organophosphate use, despite our study sites actually averaging more total organophosphate than pyrethroid insecticide applications reported by households living nearby. Although the pyrethroid and organophosphates insecticides used in the field did not perfectly match those studied in the laboratory, in several studies, toxicity levels were more similar within than across pesticides classes (Rumschlag et al, 2022; Rumschlag et al, 2019b; Rumschlag et al, 2021). Consequently, our findings suggest that predicted rises in insecticide use associated with human population growth (Tilman et al, 2011) could be highly relevant to interventions employing Macrobrachium prawns.…”

Pesticides en viticulture

“…Cela met en danger la diversité et le fonctionnement des écosystèmes aquatiques, au même titre que la santé de l'homme via la consommation de produits de la mer (Walters et al, 2016). Ainsi, les polluants chimiques peuvent, de par leur impact sur le phytoplancton marin, avoir un effet indirect sur le cycle du carbone et la régulation du climat, comme suggéré récemment dans le cas des pesticides (Rumschlag et al, 2022).…”