Linking Multiple Stressors To Adverse Ecological Responses Across Watersheds

Multiple stressors, such as urbanization, habitat destruction, and pollution negatively impact the aquatic environment. Their combined effects can significantly alter the services they provide to society, including clean water and habitat for wildlife. Understanding and predicting how numerous stressors interact to impact ecosystem function is a major challenge. 

In the Linking Multiple Stressors to Adverse Ecological Responses Across Watersheds project, researchers aimed to improve the ability to predict environmental risk associated with cumulative effects of multiple stressors. The team developed contaminant fate models to predict exposure to contaminants associated with municipal wastewater outfalls in the Grand River, Ontario. By integrating contaminant fate modeling with observed biological effects in the river, the team gained new insights into the impact of various stressors and natural variability on aquatic ecosystems. 

The Region of Waterloo is the largest urban area within the Grand River watershed and is home to 13 municipal wastewater treatment plants (WWTPs). Studies focused on the two largest plants located in Kitchener and Waterloo as these discharges were known to contain a complex mixture of contaminants that were impairing the health of fish the Grand River. Significant investments were made to upgrade the WWTPs over the last 15 years, aimed at improving water quality. This offered us an opportunity to document and model the ecosystem response to these major remedial measures. 

Link exposure to effects in aquatic ecosystems

The ecology of rivers can change rapidly in response to natural and anthropogenic stressors (including wastewater treatment plant effluents), making it difficult to isolate and assess the harm of specific contaminants or stressors. 

We combined the opportunity associated with the infrastructure upgrades with detailed historical data on aquatic ecosystem responses in the Grand River watershed to model how contaminant exposure changed, and ecosystems recovered. This was assessed over time before and after the upgrades. We established relationships between specific contaminants such as estrogens and their impact on a sentinel fish species like the rainbow darter under controlled lab conditions as well as in the river. We also explored how key responses to contaminants are altered in the presence of additional stressors to better understand and predict potential cumulative effects across watersheds. 

The WWTP upgrades immediately benefitted the environment. They reduced contaminant exposure including to estrogens, resulting in the rapid recovery of fish health, such as their reproductive performance. This data was then used in an integrated fate and exposure model to reliably predict the responses in fish downstream of the wastewater outfalls, such whether there was the presence of eggs in male testes. The validated models allowed researchers to simulate how environmental change and management actions influence ecosystems in the future. More specifically, the models were applied to: