The combination of chemical, structural, and functional indicators to evaluate the anthropogenic impacts on...

Freshwater contamination by pesticides in agricultural landscapes is of increasing concern worldwide, with strong pesticide impacts on biodiversity, ecosystem functions, and ultimately human health (drinking water, fishing). In addition, the excessively large number of substances, as well as their low - and temporally variable - concentrations in water, make the chemical monitoring by grab sampling very demanding and not fully representative of the actual contamination. Tools that integrate temporal variations and that are ecologically relevant are clearly needed to improve the monitoring of freshwater contamination and assess its biological effects. Here, we studied pesticide contamination and its biological impacts in 10 stream sections (sites) belonging to 3 agricultural catchments in France. In each site, we deployed a combination of pesticide integrative samplers, biocenotic indicators based on benthic macroinvertebrates, and functional indicators based on leaf litter decomposition and associated fungal communities. The 3 approaches largely proved complementary: structural and functional indicators did not respond equally to different agricultural impacts such as pesticide contamination (as revealed by integrative samplers), nutrients, or oxygen depletion. Combining chemical, structural, and functional indicators thus seems an excellent strategy to provide a comprehensive picture of agricultural impacts on stream ecosystems.