Learning from the past: Microplastics in the Grand River watershed
By Meredith Watson
Microplastics have been found in freshwater ecosystems around the world. Yet, because they are still an emerging contaminant, we lack long-term data about their abundance and sources. One way to fill this gap is by analyzing radiometrically dated lake sediment cores to generate a historical record of microplastic pollution in freshwater environments. These cores act like time capsules, preserving microplastics that have settled over the years.
In the Grand River Watershed (GRW), where the University of Waterloo campus is located, we don’t yet have a detailed history of microplastic pollution. This watershed includes both agricultural lands and some of Ontario’s fastest-growing urban areas, making it likely that a substantial amount of microplastics are present. My master’s research focused on uncovering the history of microplastics in two reservoirs in this watershed: Belwood Lake and Conestogo Lake.
What we found
By analyzing the microplastic in sediment cores from the reservoirs, we were able to track how the amount and type of microplastics have changed over time. Surprisingly, the overall amount of microplastics has not increased dramatically since records began (1957 for Belwood and 1985 for Conestogo). This was unexpected, given the exponential increase in plastic production since the 1950s.
One possible reason could be improved plastic waste management and environmental conservation efforts in the region over the decades. Additionally, the rural nature of this part of the watershed means there has been minimal land use change to contribute to more plastic pollution.
Still, microplastics have been accumulating in these reservoirs for decades. Since 1985, an estimated 55.9 tonnes of microplastics have settled in Belwood Lake, while Conestogo Lake has accumulated about 105.7 tonnes. The difference is likely due to Conestogo Lake’s higher sedimentation rate, which traps more material, including microplastics.
The Role of Rubber
Another interesting finding was that rubber particles made up about 30 per cent of the microplastics in both lakes. The rubber particles have increased in abundance and mass since the 1990s. Research shows that most rubber mostly comes from tire wear on paved roads. This rise coincides with the expansion of road networks in southern Ontario during the 1970s–1990s, which likely contributed to more tire particles being washed into the water bodies through road runoff.
Management Implications
Understanding how microplastics have entered these reservoirs gives us valuable insight into how to prevent further pollution, especially in rural areas of southern Ontario. For example, we now understand that common pathways for microplastics entering lakes include runoff from roads and agricultural areas, as well as soil erosion. As such, strategies such as runoff management and erosion control techniques could be used to prevent and mitigate future microplastic accumulation in these reservoirs and other similar rural catchments.
By learning from the past, we can take steps to protect our freshwater systems for the future. These findings provide a foundation for developing practical solutions to tackle microplastic pollution in southern Ontario and beyond.