Consistent Effects of Pesticides on Community Structure and Ecosystem Function in Freshwater Systems

Abstract

20Predicting ecological effects of contaminants remains challenging because of the sheer number 21 of chemicals and their ambiguous role in biodiversity-ecosystem function relationships. We 22 evaluated responses of pond ecosystems to standardized concentrations of 12 pesticides, nested 23 in four pesticide classes and two pesticide types. We show consistent effects of herbicides and 24 insecticides on ecosystem function, but slightly less consistent effects on community 25 composition. Effects of pesticides on ecosystem functions were often mediated by changes to 26 biodiversity, and our analyses show that consistency in effects of pesticide types on functions 27 was driven by functional redundancy among species. These results suggest that risk assessment 28 of the thousands of registered chemicals on ecosystem responses could be simplified to a smaller 29 number of chemical groups and to groups of functionally redundant taxa. 30 Freshwater systems are the most biodiverse in the world and provide important 31 ecosystem services (1), yet they are imperiled by pesticide contamination (2). Two major 32 challenges, among many, impede prediction of responses of freshwater ecosystems to pesticides. 33First, the extent to which individual pesticides have consistent effects on ecosystem functions 34 and biodiversity is unknown. In the U.S. and Europe, tens of thousands of synthetic chemicals 35 are registered, and in the U.S. >350 pesticides are applied annually (3). If the effects of pesticides 36 are consistent within 'pesticide classes' (those with similar chemical structures) or 'pesticide 37 types' (those targeting similar pests), then the complexity in predicting impacts of pesticides 38 could be markedly reduced (4). Such consistency would improve efficiency of risk assessment 39 and allow a greater focus on exceptions to general patterns. Second, the role of pesticides in 40 biodiversity-ecosystem function relationships has not been elucidated (5). Historically, random 41 and direct manipulations of single-trophic level communities and measurement of associated 42 ecosystem processes (6) have established causality between biodiversity and ecosystem function 43 (7). However, this approach overlooks the importance of anthropogenic factors, whose 44 influences on communities are far from random (8), alter multiple trophic levels (9), and occur 45 via direct and indirect pathways (5). 46In an effort to suggest improvements to risk assessment, the objectives of the current 47 study were to: 1) evaluate the consistency of effects across pesticide types, classes, and 48 individual pesticides on ecosystem processes and communities, 2) assess whether the effects of 49 pesticides on ecosystem processes and communities were the result of sublethal, non-target 50 effects or changes in abundance of 'targeted taxa', and 3) determine if disruptions in ecosystem 51 processes from pesticides were mediated by changes in biodiversity. We propose three 52 hypotheses. First, ecosystem processes respond consistently to different...

Pesticide-induced Alterations to Phytoplankton Abundance and Community Structure Alter Ecosystem Respiration: Implications for the Carbon Cycle?

“…Few studies have attempted to evaluate how synthetic chemical disturbances in communities are associated with changes in ecosystem functions (Bernhardt et al 2010;Rosi-2014;Rumschlag et al 2020). Our study found that insecticides led to persistent, and non-trivial, increases in ecosystem respiration, while herbicides lead to short-term decreases in ecosystem respiration that varied with pesticide classes.…”

“…Further, predicting the effects of pesticides could be simplified if organisms that are taxonomically related or share similar functional roles within an ecosystem have similarities in their responses to pesticides, a trend that has been shown in previous toxicological research (Ippolito et al 2012;Hua & Relyea 2014). For example, our previous research has shown consistency in the effects of pesticides by class and type on parasite transmission, ecosystem functions, and macroinvertebrate and amphibian communities (Rumschlag et al 2019(Rumschlag et al , 2020. In addition, organisms that share functional roles in a community have been shown to respond similarly to types and classes of pesticides (Rumschlag et al 2020).…”

“…Respiration was calculated as DO at dusk minus DO at dawn from the following day. Three previous manuscripts, which use the same design as the current manuscript, also describe this experimental design and methods in detail (Rohr et al 2008;Rumschlag et al 2019Rumschlag et al , 2020.…”

“…Despite the magnitude of the threat that pesticide pollution imposes on freshwater systems, it is somewhat surprising that ecologists and their funding agencies have largely ignored the intricacies that these disturbances can yield on communities and ecosystems (Bernhardt et al 2017;Burton et al 2017). For instance, while pesticides have the potential to alter carbon cycling in freshwater systems via changes in the abundance or composition of community members, few studies have evaluated this possibility (but see McMahon et al 2012;Halstead et al 2014;Rumschlag et al 2020). Classic toxicological research has employed lab-based exposure experiments, documenting that scores of pesticides harm model organisms.…”

“…For example, our previous research has shown consistency in the effects of pesticides by class and type on parasite transmission, ecosystem functions, and macroinvertebrate and amphibian communities (Rumschlag et al 2019(Rumschlag et al , 2020. In addition, organisms that share functional roles in a community have been shown to respond similarly to types and classes of pesticides (Rumschlag et al 2020). But to date, no study has attempted of evaluate the consistency of responses of phytoplankton community members to pesticide classes and types.…”