Development of diagnostic indicators for assessing effects of multiple stressors on stream ecosystem health.

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Each contaminant is considered separately in the development of water quality guidelines in Canada using data from single-species toxicity tests. However, neither contaminants nor species exist in isolation. For example, in agricultural systems, aquatic biota are impacted by mixtures of pesticides and nutrients due to spray drift, runoff and erosion. Unfortunately, nutrient enrichment, let alone community complexity, are but rarely considered in ecological risk assessment. Rather, lethal toxicity testing of single stressors in laboratory-reared species is the norm. A more holistic approach is needed. The proposed research will develop a combined approach using existing methods (e.g., lethality and structural indicators of community responses) while adding sublethal, diagnostic indicators (metabolomics, or the total metabolites within an organism) to provide the building blocks needed to diagnose the interactive effects that nutrients and pesticides have on food webs in rivers. This work will: (1) establish the effects of nutrient enrichment and pesticides on riverine insects, both alone and in combination by assessing additive, multiplicative and comparative effects model frameworks; (2) examine the role nutrients may have in masking the effects of pesticides through manipulative mesocosm experiments; and (3) assess the combined effects of nutrient subsidies across pesticide disturbance gradients. Key predictions are that: (1) river insects will respond to non-lethal stress through decreased body size and abundance; (2) negative effects of pesticides may be lessened by mild to moderate nutrient enrichment; and (3) increased nutrient enrichment will worsen the effects of pesticide exposure. The proposed research will train 2 PhD, 4 MSc, and 5 undergraduate students, and increase our knowledge of the interactive effects of nutrient and pesticide exposure in aquatic macroinvertebrate communities. This research will also help move regulatory water quality regimes from simple, single-stressor effects models to a more realistic evaluation of cumulative ecological effects resulting from multiple stressor exposure.