Data from: Environmental context determines pollution impacts on ecosystem functioning

Global change assessments have typically ignored synthetic chemical
pollution, despite the rapid increase of pharmaceuticals, pesticides, and
industrial chemicals in the environment. Part of the problem reflects the
multifarious origins of these micropollutants, which can derive from urban
and agricultural sources. Understanding how micropollutants harm
ecosystems is a major scientific challenge due to asymmetries of stress
across trophic levels and ecological surprises generated by multiple
drivers interacting in human-impacted landscapes. We used field assays
above and below municipal wastewater treatment plants (WWTPs) in 60
sampling locations across 20 Swiss streams to test how micropollutants and
nutrients originating from WWTPs affect two trophic levels (microbes and
detritivores) and their role in leaf litter processing. Wastewater impacts
were asymmetric across trophic levels, with the detritivore contribution
declining relative to microbial-driven decomposition. The strength of
negative impacts was context-dependent, peaking at sites with the highest
upstream abundances of detritivorous invertebrates. Diffuse pollution from
intensive agriculture and wastewater-born micropollutants contributed to
reduced litter processing rates, including indirect effects apparently
mediated through negative influences of insecticides on detritivores.
Asymmetries in stress responses across trophic levels can introduce
quantitative changes in consumer-resource dynamics and leaf litter
processing. This means functional redundancies at different trophic levels
are insufficient to compensate for biodiversity losses, causing
environmental stressors such as chemical pollutants to have pervasive
ecosystem-level impacts.