Costly efforts to reduce toxic algae blooms on Lake Winnipeg by controlling the amount of nitrogen flowing into the water could have little to no impact, according to the results of a decades-long study.

Scientists working in the Experimental Lakes Area in northwestern Ontario conducted a whole-ecosystem experiment on one lake, beginning in 1969. They examined the roles of the nutrients carbon, phosphorus and nitrogen in controlling algae blooms that suck the life out of lakes and create messes that harm local economies.

"It's a very big issue because the costs associated with managing these nutrients are very high. They're measured in the billions, if not trillions of dollars when you're talking about North America," said Scott Higgins, lead author of the study, which was published in the December edition of the journal Ecosystems.

In 1990, the researchers completely cut off the flow of nitrogen while maintaining the artificial flow of phosphorus into the lake. They found that nearly 25 years after they cut off the flow of nitrogen, the size and duration of the blooms on the lake remained largely unchanged.

Efforts to reduce nutrients flowing into Lake Winnipeg have focused on removing both phosphorus and nitrogen. In 2003, the Manitoba government ordered the City of Winnipeg to upgrade sewage treatment facilities to cut outflows of both nutrients.

The cost for upgrades to the North End sewage treatment plant is now estimated at $1.4 billion.

Focus on phosphorus

Higgins says the study results indicate focusing on just reducing phosphorus would be a better approach.

Nitrogen can exist in the water and in the air — Earth's atmosphere is mostly nitrogen — and nitrogen in the air can dissolve into the water of the lake. Some species of algae are able to take this form of nitrogen out of the water.

When the scientists cut off the flow of nitrogen into the lake, they found that the community of species that make up algae blooms — consisting of hundreds of species — shifted toward those species that could use the form of nitrogen from the air.

The total amount of algae on the lake didn't change, Higgins said.

Algae is seen on Hillside Beach in August 2015, which was transformed into a green mess with thick, sludgy waves washing up on the eastern shore of Lake Winnipeg. (Bert Savard/CBC)

Phosphorus, on the other hand, only comes from the water.

"And so if you can reduce the amount of phosphorous that comes in through rivers and overland … then they can't get it from anywhere else."

Other efforts to reduce phosphorus, such as eliminating it from laundry detergent, were costly but supported by research that showed it was a successful approach to reducing algae blooms, Higgins said.

"I think what it means is keep your eyes on the prize," he said. "It's easy to become overwhelmed.… I think what this research says is the policy should remain focused on reducing phosphorus, and if you're successful at doing that, then the lakes will respond."

Algae blooms are the primary water quality issue facing countries around the world, and there have been heated debates over whether efforts should focus on controlling phosphorus by itself or controlling it along with nitrogen, Higgins said.

The study provides further evidence in support of the former approach, he said.

"This research really points to the fact that removing nitrogen is controversial and its success is uncertain, whereas managing phosphorus and reducing phosphorus loads to the lake is successful and has a certain outcome."

'It's a question of political will'

Lake Winnipeg Foundation executive director Alexis Kanu says this latest study emphasizes the value of the research done at the Experimental Lakes Area.

"This is really the culmination of decades of research that have pointed to phosphorus as the driver of eutrophication, the driver of the algae blooms that we see on our lakes in the summer," she said. "And I think it really emphasizes how much we need to focus on reducing phosphorus to address this issue."

Kanu says last summer was a bad season for algae blooms, with LWF members submitting photos and emails describing beaches clogged with thick, blue-green muck during their holidays.

Current knowledge on the overall health of the lake is out of date, because the most recent scientific data available is from 2007, Kanu says, "so we've got about a decade gap there in terms of our understanding of how the lake has changed."

Although there is no single solution to nutrient overload in Manitoba's lakes — the mineral comes from point sources such as wastewater treatment plants and non-point sources such as agricultural fertilizer runoff — Kanu hopes the latest study will serve as a wake-up call on the need to aggressively target phosphorus.

"I think it's a question of political will in a lot of cases. We have the science that we need, and now we need citizens who care about these lakes to speak up," she said.

The Experimental Lakes Area in Ontario is run by the Winnipeg-based International Institute for Sustainable Development.