Not long ago, many of us believed that clean water was Canada’s natural heritage.
That was before summers were tainted by fear of blue-green algae and its toxic discharges in rivers and lakes threatening the health of wildlife, pets and people. Warming temperatures are aggravating the impact of excess nutrients, particularly phosphorus, in agricultural watersheds with high rates of surface and subsurface drainage—like those in southwestern Ontario.
Recent research by DUC quantifies the role of restored wetlands in capturing phosphorus in agricultural watersheds. Excess phosphorus plays a key role in the increase in algae outbreaks, an alarming trend that highlights the need to better understand the value and benefits of wetlands for capturing phosphorus from surface-water runoff before it moves downstream.
Results from two-year study of newly restored wetlands
As part of our large-scale conservation program in the Lake Erie watershed, researchers assessed eight recently restored wetlands for two separate years, regularly monitoring water inflows and outflows to measure their nutrient-capture (e.g., phosphorus, nitrogen) capacity and efficiency. Like most restored wetlands in the region, these can be described as “edge-of-field” sites, set in a low-lying area that receives runoff from the agricultural landscape.
Results show that the small wetlands were effective at settling and filtering water under a variety of conditions—protecting downstream rivers and lakes in all seasons.
- Results indicate the restored wetlands act as “phosphorus sinks,” with less phosphorus leaving the wetland basins than entering them.
- All eight wetlands efficiently captured the form of phosphorus that increasingly causes the most problems for Lake Erie (i.e., soluble reactive phosphorus or SRP).
- The mean SRP retention efficiency was 60 per cent over the two-year monitoring period.
- Restored wetlands were found to function in a nutrient retention role in all four seasons.
Phosphorus reduction in lakes is within our grasp
Canada and the United States have adopted phosphorus reduction targets (2012 Great Lakes Water Quality Agreement) for Lake Erie to minimize impacts from nuisance algae, which impacts millions of people’s drinking water source every year. Restored wetlands have been identified as natural infrastructure that can reduce phosphorus loads entering streams and rivers across the working landscape of southwestern Ontario. These results demonstrate that restored wetlands can effectively reduce nonpoint source nutrients from entering Lake Erie spanning a range of hydrological conditions.
Focus on phosphorus in Lake Erie
Natural infrastructure—wetlands, grasslands and forests that support productive landscapes—can play a key role in watershed resilience.
Canada and the United States adopted phosphorus reduction targets in 2016 to protect the western and central basins of Lake Erie and DUC has been hard at work since 2017, with our partners, carrying out 100s of conservation projects—which brings our historical total in the Lake Erie watershed to more than 500 wetland projects.
DUC and its many conservation partners have made strong progress in driving a systemic change in approach toward watershed-scale wetland conservation, a natural solution that will be increasingly needed in the Great Lakes region and beyond.
Determining the Nutrient Retention Capacity of Newly Restored Wetlands in Southwestern Ontario for a Second Water Year
Download the final report:
Research ReportSupport from participating landowners was integral to the research
Our thanks are due to the landowners who graciously allowed regular access to their wetland restoration projects over the course of two full water-years (September-October).
The Lake Erie wetland research is led by DUC’s Institute for Wetland and Waterfowl Research and received support from the North American Wetlands Conservation Act of the U.S. Fish and Wildlife Service for both years of the study. Year two of the study was funded in partnership with the Government of Canada via the Great Lakes Protection Initiative, and year one with the Ontario Ministry of Natural Resources and Forestry and the St. Clair Region Conservation Authority.
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