Nitrogen debate wastes time, money


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The Manitoba government is to be congratulated for its announcement this week that its policy for Lake Winnipeg will focus on aggressively reducing phosphorus inputs to the lake.

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Hey there, time traveller!
This article was published 02/06/2011 (4138 days ago), so information in it may no longer be current.

The Manitoba government is to be congratulated for its announcement this week that its policy for Lake Winnipeg will focus on aggressively reducing phosphorus inputs to the lake.

For several years, there has been debate about how to control the rapid increases in algal blooms on Lake Winnipeg. Some have recommended that major reductions to inputs of phosphorus are key, based on evidence from long-term, whole-lake experiments and many successful lake recoveries following phosphorus control.

Others have argued that nitrogen must be controlled as well, because, in short-term experiments, lasting hours to a few weeks, nitrogen is often found to affect algal growth in summer. They have also argued that the nitrogen would cause eutrophication in far-off Hudson’s Bay.

JOE.BRYKSA@FREEPRESS.MB.CA Farm fields lie flooded along the Red River north of St. Jean Baptiste last April.

These spurious claims have unnecessarily delayed policies to protect and restore the lake. No whole-lake study has ever shown that cutting nitrogen has reduced algal blooms. In contrast, studies at the Experimental Lakes Area show clearly that decreasing nitrogen inputs rather than phosphorus favours the very nuisance species that need to be controlled.

The study by Peter Leavitt and his colleagues at the University of Regina seems to have finally persuaded provincial policy makers to control phosphorus. Curiously, the report also recommends that nitrogen should be controlled, based on studies elsewhere.

I hope the government ignores this advice.

There is no evidence from Lake Winnipeg that nitrogen removal is necessary. The evidence suggests the opposite: that phosphorus control is key to solving the problem.

Hedy Kling’s studies of Lake Winnipeg algae since 1969 show one group of algae, the so-called bluegreens (Cyanobacteria), has been responsible for more than 90 per cent of the increases in algae in the lake. These are the algae that form smelly, unsightly windrows along lakeshores in late summer, and produce toxins that can cause illnesses or even death. Many species in this group can take nitrogen from the atmosphere, giving them an advantage over species that can’t use atmospheric nitrogen when a lake is enriched disproportionately with phosphorus. Long-term trends show that phosphorus has increased much more rapidly than nitrogen, favouring nitrogen-fixing species. Reducing nitrogen would favour these nuisance species even more.

It is a waste of money.

The Lake Winnipeg Consortium has documented changes to nutrient concentrations, stratification patterns, and the food web of the lake. These studies reveal that since the mid-1990s, phosphorus concentrations have increased by more than 50 per cent. Environment Canada’s scientists have shown that most of the increases come from the Red River watershed. Both synthetic fertilizer applications to soils and manure from cattle and hogs are major contributors. The city of Winnipeg contributes 10 per cent of the phosphorus load to the lake, a significant part of the total. All of these sources must do their share to reduce phosphorus if Lake Winnipeg is to be saved.

Environment Canada’s monitoring of the river is essential to determine the effectiveness of the recovery plan. Unfortunately, their staff in Manitoba has just been cut significantly by the federal government.

Manitobans should protest.

Scientists from the Freshwater Institute and the University of Manitoba led by Greg McCullough have put the pieces of the Lake Winnipeg puzzle together in a convincing model. It shows clearly that the increased frequency of spring floods in the Red River in recent years has greatly amplified the transfer of phosphorus to the lake.

During floods, water stands for weeks on phosphorus-saturated land, then runs off to the lake, carrying its nutrient load with it. The amount of phosphorus being spread on the land will have to be cut, and measures to reduce flooding need to be taken.

Much of this fine science will appear later this year in a special issue of the Journal of Great Lakes Research. Meanwhile, Manitobans should brace themselves for another wave of algal blooms, the result of this year’s flood.

Reducing nitrogen in sewage is much more costly than controlling phosphorus. A recent study of the nutrient inputs to the Baltic Sea shows that cutting phosphorus alone would cost only about 12 per cent of the cost of controlling both nutrients. Focusing on phosphorus alone allows much more aggressive reductions for the same costs. Increasing global evidence shows we should be conserving phosphorus to use as fertilizer, as global sources are quickly being exhausted.

Phosphorus control has reduced algal blooms in hundreds of lakes in the U.S., Europe and Canada, and there is no evidence that it will not solve Lake Winnipeg’s problems.

The pivotal work done by Winnipeg scientists should be trusted. Attempting to divert the focus from phosphorus to nitrogen serves no real purpose. It has already significantly delayed action to clean up the lake.

David Schindler was a scientist at the Freshwater Institute from 1968 to 1989. He was part of a team studying Lake Winnipeg in 1969, and is the founding director of the Experimental Lakes Project. His work on eutrophication has been the basis for nutrient management policies in many countries.

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