Nonpoint source pollution 2016-2021

Map the bodies of water present in Lake Saint-Pierre in support of water quality monitoring

Lake Saint-Pierre, a bulge in the river upstream from Trois-Rivières, is very rich in biodiversity. It is on the list of internationally significant wetlands (Ramsar site) and is part of UNESCO’s coastal biosphere reserves. However, it receives a large number of agricultural contaminants, including pesticides.

The researchers in this project will use hydrodynamic modelling to provide a daily mapping of the different bodies of water that form Lake Saint-Pierre according to average hydrological conditions of the 24 previous hours. The provided mapping will be representative of the contributions of each of Lake Saint-Pierre’s outlets in terms of flow and water quality. The maps provided will support water quality monitoring in three ways:

• By locating areas most susceptible to being affected by agricultural contaminants;
• By determining each outlet’s zone of influence; and
• By allowing the sampling plan to be adjusted by revising the locations of the data sampling sites.

Assess the effectiveness of wet-retention ponds to improve the water quality of agricultural watersheds

The waterways that empty into Lake Saint-Pierre often contain pesticides, nutrients (nitrogen and phosphorus) and suspended solids that can hinder aquatic life. A large proportion of these pollutants come from farming located within the lake’s watershed. We believe, however, that the use of the water retention ponds can attenuate the impacts of non-point source pollution in an agricultural environment. When the water slows while passing through the water retention pond, the pesticides and the nutrients are retained by the sedimentation and can degrade during contact with plants and organisms. As such, the water retention pond can reduce the contaminants present in surface water and in agricultural drainage.

The researchers in this new project will assess the effectiveness of such water retention ponds. If this approach is effective, it may become an economical and durable solution for the agricultural sector.

Improve knowledge about pathogenic organisms of the Lake Saint-Pierre watershed

Runoff brings organisms that are potentially dangerous for humans and wildlife into Lake Saint-Pierre. Indeed, in the first phase of the SLAP, our researchers observed a significant quantity of E. Coli in the tributaries of the lake, which indicates fecal contamination and the presence of potentially pathogenic organisms. They also discovered that these bacteria were resistant to several antibiotics. Furthermore, the Giardia and Cryptosporidium parasites were measured in raw water and four water intakes.

We do not as of yet know the actual risk of this type of pollution, or the source of the bacteriological contamination observed in the tributary waterways of Lake Saint-Pierre. Our researchers will therefore present the results of pathogenic organism measurements in these waterways at different locations. They will also identify the sources of the contaminants in order to help guide remediation actions.

Evolution of Lake Saint-Pierre’s aquatic-grass beds

Lake Saint-Pierre’s aquatic-grass beds provide an essential habitat for fish, amphibians and aquatic birds. Aquatic plants act as physical support for algae and crustaceans that feed vertebrates and provide them with shelter against predators. However, we do not clearly understand the plants that form these beds and the way in which the aquatic-grass beds evolve in time as a function of the quantity (depth and current) and the quality (transparency and nutrients) of the water.

Our researchers will produce a portrait of Lake Saint-Pierre’s aquatic-grass beds and the aquatic plant and algae biomass in order to characterize the available habitat for fish and invertebrates. By following the aquatic-grass beds over several years and working on the recent history of the abundance of plants, the researchers will assess the factors that influence the condition of the beds and determine their sensitivity to climate change. At the end of the project, our researchers will be able to determine the restoration measures that can be implemented in the next phases of the SLAP.

Prepare and hold an exchange workshop on Lake Saint-Pierre

Several factors contributed to the degradation of Lake Saint-Pierre’s coastal habitats and to major changes in the ecosystems that have been observed over the past years. Take, for example, the agricultural activities in flood-prone areas, the significant year-to-year variability in water levels related to climate change and the presence of several pesticides in the lake waters.

This project aims to bring together researchers from different disciplines in an exchange workshop in order to share the research results on Lake Saint-Pierre. These exchanges will provide an update on the evolution of susceptible stress factors that explain changes in this ecosystem’s support capacity.

Exchange workshop on Lake Saint-Pierre 2019 - Summary

Assess the effects of pesticides on aquatic organisms

Intensive agricultural activities in regions like Lake Saint-Pierre are a possible cause of the degradation of the aquatic environment. Presently, the effects of pesticides on Lake Saint-Pierre’s aquatic wildlife in sectors bordering the river or brought in by tributaries remains poorly understood. However, we know that these tributaries draining from agricultural lands dominated by corn and soybean cultivation and the herbicides most used for this type of cultivation, including atrazine, metolachlor and glyphosate, are detected in neighbouring rivers. More recently, the presence of neonicotinoid-type insecticides has also been reported. The combined presence of herbicides and insecticides can therefore affect the aquatic wildlife of this sector.

The researchers in this project will assess the effects of exposure of aquatic organisms to the pesticides used on agricultural lands of the St. Lawrence River watershed, particularly the aquatic organisms present in Lake Saint-Pierre. The study will determine the concentration of the various pesticides in the water, measure their effects on aquatic organisms, such as fish, frogs and invertebrates exposed in their natural environment or in a laboratory, and will monitor populations of fish and aquatic invertebrates.