Evaluating cumulative impacts of nutrient enrichment, sedimentation, and neonicotinoid insecticide pollution on freshwater ecosystem functioning

CHARÁ-SERNA, ANA M.; EPELE LUIS BELTRAN; RICHARDSON, JOHN S.

Sacramento

Congreso; Society for Freswater Science, Annual Meeting; 2016

Even though agriculture is a primary agent of freshwater ecosystem degradation, information to disentangle the impacts of some of its most important ecological stressors is still lacking. For example, neonicotinoids rank among the most purchased insecticides in the world, but to date there are few studies documenting whether their combination with other agricultural stressors has synergistic or antagonistic impacts on freshwater biota. We conducted a 36-day experiment in 32 outdoor freshwater mesocosms, manipulating fine sediment, nutrients, and a neonicotinoid insecticide (imidacloprid) to evaluate individual and combined impacts of these three stressors on ecosystem processes (ecosystem metabolism, primary production, and leaf litter decomposition). Nutrient enrichment produced the quickest and strongest response on net ecosystem production, with significant positive effects evidenced from the first week after the treatment. Contrary to our expectations, there was no evidence for significant negative effects of imidacloprid or sedimentation, but these two stressors interacted additively with nutrient enrichment to affect net ecosystem production. Our results highlight the importance of experimental mesocosm manipulations to isolate stressor effects and disentangle stressor interactions, while offering relatively high levels of realism.