Microplastics legacy in the Grand River

KEY INSIGHTS

• Microplastics have been entering waterways for decades: Reservoir sediment cores show steady microplastics input since at least the 1950s, confirming that microplastics pollution is not new but has been accumulating over long time periods.
• Sediment delivery, not increased plastic use, controls microplastics loading: Although microplastic concentrations in sediments were similar between Belwood Lake and Conestogo Lake, microplastics flux was nearly twice as high in Conestogo Lake due to faster sediment delivery. This highlights erosion and land use as key drivers of microplastics pollution.
• Sediment cores are a powerful long-term monitoring tool: Dated sediment cores provide a validated way to reconstruct past microplastics pollution across river–reservoir systems and the Great Lakes basin, supporting future long-term monitoring frameworks (e.g., for the International Joint Commission).
• Land use and infrastructure leave clear fingerprints: Rubber-based microplastics increased after ~1990, consistent with the expansion of paved road networks and tire wear, helping identify transportation infrastructure as an important source of microplastics pollution.
• Reducing soil erosion can directly reduce microplastics pollution: This research shows that microplastics are delivered with sediment, therefore watershed management actions that reduce runoff and erosion, particularly in agricultural regions, can meaningfully lower microplastics loading to reservoirs and downstream waters.
• Remote sediment samples help define background conditions: Core samples from remote regions such as Wood Buffalo National Park help establish baseline and pre-plastic conditions, improving our ability to distinguish local human sources from long-range atmospheric transport.

WHY THIS MATTERS TO WATERSHED MANAGEMENT, MONITORING, AND POLICY

• Supports smarter monitoring design: Understanding where and how microplastics accumulate helps target monitoring efforts to key sediment sinks rather than relying on short-term water sampling alone.
• Connects land management to pollution reduction: The findings show that soil erosion control and runoff reduction can also reduce microplastics pollution, linking plastics management to existing watershed and agricultural programs.
• Provides evidence for long-term accountability: Records obtained from analysis of sediment cores allow agencies to track trends over decades, assess the effectiveness of interventions, and plan for future changes in land use and infrastructure.

RESEARCH PROCESS

Professor Roland Hall and MSc student Meredith Watson analyzed dated sediment cores from two headwater reservoirs in the Grand River Watershed, Belwood Lake and Conestogo Lake, to reconstruct past changes in microplastics abundance, flux, and composition. These reservoirs act as upstream sinks for sediment and contaminants, making them ideal locations to study how microplastics move through river–reservoir systems.

Their analyses show that while plastic production has increased dramatically since the 1950s, microplastics concentrations in sediments remained surprisingly stable. Instead, differences in microplastics loading were driven by sedimentation rates, with Conestogo Lake accumulating nearly twice the annual microplastics flux due to faster sediment delivery.

Additional analyses of sediment cores from remote regions, including Wood Buffalo National Park, were used to test methods and establish background levels of microplastics deposition before widespread plastic use.

This work provides one of the most detailed spatial and historical reconstructions of microplastics pollution in southern Ontario and contributes to basin-wide Great Lakes monitoring efforts.

RESEARCHERS & COLLABORATORS

Prof. Roland I. Hall
Professor of Biology, University of Waterloo: Expert in paleolimnology and long-term environmental change, with extensive experience using sediment records to reconstruct pollution histories.

Meredith Watson
MSc Researcher, University of Waterloo: Research focused on reconstructing historical trends in microplastics pollution using sediment cores and paleolimnological methods.

KEY PUBLICATIONS

Watson, M. (2024). Time trends in abundance and composition of microplastic particles deposited in profundal sediment of two headwater reservoirs within the Grand River Watershed (Ontario, Canada). MSc Thesis, University of Waterloo.

Watson, M. & Hall, R. I. (2025).Time trends of microplastics deposition and polymer composition at two headwater reservoirs within the Grand River watershed, Ontario, Canada. Manuscript in preparation.

Belontz et al. (2024). A temporal record of microplastic accumulation in sediment cores of the Great Lakes. FACETS, 9, 1–10.