Ecological effects of nutrient-contaminant-sediment interacations on riverine food webs

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Diagnosing the cause of degraded river ecosystem condition is difficult because river organisms are simultaneously exposed to multiple environmental stressors (e.g., toxic chemicals, nutrients, suspended sediments) that can adversely affect them. Although environmental stressors can have complex, interactive effects on biological communities, these cumulative consequences are rarely considered in regulatory guidelines. Organisms living in rivers draining agricultural landscapes are at particular risk because they are exposed to sediments, nutrients and pesticides. The proposed research will provide the building blocks needed to improve knowledge of the interactive effects that pesticides, excess nutrients and sediments have on food webs in agricultural rivers. The research will: (1) establish the effects on river insects of commonly used pesticides, both alone and in combination, and evaluate competing predictive models; (2) examine the role nutrients may have in masking the effects of pesticides through experiments conducted in artificial streams; and (3) test the combined effects on river invertebrates of pesticides, nutrients and excess sediments across a simulated agricultural gradient. Key predictions are that: (1) river insects will respond to non-lethal pesticide exposure through decreased abundance and body size; (2) these negative effects will be moderated by mild nutrient pollution; and (3) sedimentation will worsen the negative effects of pesticides. The research will train 2 MSc, 2 PhD and 5 undergraduate students, and increase our knowledge of nutrient-contaminant-sediment effects on river communities. The work will have important implications for managing agricultural aquatic ecosystems, which are some of the most threatened in Canada and worldwide.