IJC Recommendations Spur Binational Effort to Tackle Phosphorus Pollution in Lake Champlain Basin

There’s an imbalance of phosphorus that fuels harmful algal blooms in Missisquoi Bay in the Lake Champlain basin. 

“Our watershed has more phosphorus going in than coming out,” explained Matthew Vaughan, Ph.D., chief scientist for the Lake Champlain Basin Program. “It’s been that way for a long time, over 100 years.”

But a binational project set to conclude this fall will bring tools meant to help stem the flow of excess nutrients like phosphorus that fuel these cyanobacterial blooms in the bay. 

Sources of phosphorus to the bay from upstream in the watershed include residential and agricultural inputs—from municipal wastewater discharges and failing septic systems to lake sediment and runoff from stormwater, fertilizers and livestock. 

Recommending Solutions

The project stems from a 2017 reference from the Canadian and United States governments to the International Joint Commission (IJC). 

The governments asked the IJC to collect and review information on reducing nutrient loads and harmful algal blooms in Missisquoi Bay, make recommendations to enhance efforts by Vermont and Québec, and accelerate progress toward reaching water quality goals for the bay. 

An IJC-led study developed a series of recommendations, including the need for a binational mass balance model demonstrating phosphorus inputs and exports in Missisquoi Bay. According to a 2024 “State of the Lake” report issued earlier this year by the Lake Champlain Basin Program, water quality goals for phosphorus concentration limits were set in 1991 for 13 segments of Lake Champlain, including the bay. But annual phosphorus levels there have consistently exceeded established limits since monitoring began.

The Lake Champlain Basin Program awarded funds to Stone Environmental Inc. in Vermont to conduct the project. The work began in 2022 with partners from the University of Vermont, and Quebec-based groups Research and Development Institute for the Agri-Environment (IRDA) and Organisme de Bassin Versant de la Baie Missisquoi (OBVBM). 

“This project is the first time there’s really been a common effort from both sides of the border, using coherent and similar protocols and approaches,” said Aubert Michaud, Ph.D., associate researcher at OBVBM. “Now you have a global picture of phosphorus inputs.”

Making a Mass Balance Model

Researchers set out to understand what strategies can be used to have lasting and beneficial impacts on reducing nutrients that enter the bay and cause water quality problems like harmful algal blooms. 

The study took a detailed look at all the phosphorous sources. 

“We call it mass balance because what we ultimately want is for phosphorus to be reduced in Lake Champlain,” Vaughan said. 

“Currently, we have a real good understanding of what’s moving into Missisquoi Bay because we monitor the Missisquoi River and Pike River and Rock River, the main tributaries.

“We think there are opportunities for where less phosphorus can be brought into the system to begin with.”

Edge-of-field monitoring stations like this one helped inform the development of a phosphorus mass balance model. Credit: Stone Environmental 

Michael Winchell is vice president of Stone Environmental.

“We’re tracing the phosphorus entering the bay, what happens to it once it enters the bay and how long does it take to make out of the bay,” Winchell said. 

The time it takes for phosphorus to leave the bay amounts to multiple years. Winchell says researchers are still evaluating how the bay responds to increases and decreases in phosphorus. 

Previous river measurements are being used to develop computer models to simulate what’s happening on the landscape and how changes to management practices, like manure applications on farm fields, could have an impact. 

That includes factoring in variables such as soils. Some soils are more vulnerable to runoff than others. Even the slope of an area can be important. So “critical source areas” can be targeted to create the greatest water quality benefit by curbing phosphorus runoff, Winchell said. 

Other types of nutrient management options include cover cropping, no tillage agriculture and vegetated buffers. 

“From a strategic aspect, you have to reduce those phosphorus inputs,” Michaud said. “From a tactical aspect, it’s also an interesting tool to work on the ground with farmers, with municipalities, with phosphorus emitters.”

Putting the Project to Work

The project results will be used by organizations like the Lake Champlain Basin Program, which funds research and awards grants to implement best management practices. 

“Let’s say there’s a region that would benefit from improved agricultural practices that we think will reduce phosphorus runoff from that type of farming. We can bring resources, expertise and incentives to the region,” Vaughan said. 

Winchell says the agricultural community has already been “very active” in looking at modifying practices to help reduce phosphorus losses from their land. 

“This analysis that we’re doing is going to let us look at what’s currently being adopted in terms of practices both in Vermont and Quebec and how that is projected to impact the lake and how widespread does the adoption need to be to see impacts in the lake,” he said. 

Michaud added: “It’s very inspiring to have that international cooperation on that common issue. And I think it’s helping because we’re asking farmers to do their share. Vermont is investing a lot of resources with the farmers who are doing their part and now we can say also, ‘We work together.’”

Besides the assessment, project partners are preparing a web-based tool to allow anyone to access a simplified version of the model and see how specific reductions to residential or agriculture sources of phosphorus would impact the lake over time.