Phosphorous Nailed As Culprit

Phosphorous Nailed as Culprit
The Edmonton Journal (7/22/08)
Ed Struzik

EDMONTON - This is the time of year every cottage owner in Alberta both loves and loathes.

The love affair is with the lakeside cabin that offers refuge from the hustle and bustle and incessant noise of city life.

The loathing comes when the lake cottagers hope to swim in or sail on turns into a dead zone of blue-green algae that kills fish and other bottom-dwelling life forms.

After a remarkable 37-year experiment, University of Alberta scientist David Schindler and his colleagues have a definitive answer for this vexing problem that plagues not only western Canada's shallow lakes, but also thousands of freshwater and coastal ecosystems around the world.

By pumping various pollutants into Lake 227, a small pristine lake in the Experimental Lakes region of northern Ontario, they pinned down which of the chemical nutrients were key to triggering the blooms that can also make drinking water extremely toxic.

"Phosphorous really is the key to eutrophication," says Schindler, whose study is highlighted prominently in the U.S. based Proceedings of the National Academy of Sciences this week.

"Here in Alberta, it is especially important because the phosphorous content in the soil is naturally high, so you don't have to add a lot to create a serious problem."

Fifty years ago, no one knew what exactly caused algal blooms to appear on lakes and rivers.

There was some evidence that carbon, nitrogen and phosphorous associated with agricultural run-off and wastewater were responsible, but small experiments weren't able to show conclusively which was more important.

Schindler seemed to solve the problem when he and his colleagues conducted a number of groundbreaking experiments in northern Ontario in the 1960s and early 1970s. In a famous 1974 aerial photograph published by the journal Science, two portions of their experimental Lake 226 were highlighted. One side was treated with carbon, nitrogen and phosphorous; the other with just carbon and nitrogen.

The side that received phosphorous rapidly developed a huge bloom of blue-green algae; the other side remained in near-pristine condition.

The photo and the study that accompanied it were pivotal in convincing governments in North America and Europe to ban phosphates from detergents and to ramp up or build thousands of new treatment plants that removed phosphorous from wastewater.

That should have been the end of the debate. But over the years, the idea that nitrogen removal is needed to control eutrophication has persisted.

Schindler's latest series of long-term experiments shows that nitrogen removal is a terrible mistake. Not only does it not work, it actually makes the problem worse by favouring species that can float on the water and use nitrogen that occurs naturally in the atmosphere.

Schindler proved this by adding nitrogen and phosphorus to Experimental Lake 227 for five years. Then for the next 16 years, he reduced the amount of nitrogen. For the final 16 years, only phosphorous was added to the lake.

If nitrogen was the key, it should have controlled algal blooms in the lake. Not only did it fail to do so, the algal blooms that persisted were of the worst and most dangerous kind.

In a commentary published simultaneously in this week's issue of Proceedings of the National Academy of Sciences, American scientist Stephen Carpenter predicts that a single-minded focus on nitrogen control would have disastrous consequences for aquatic resources around the world.

Global expansion of dead zones caused by algal blooms is rising rapidly, Carpenter said. There are now 146 coastal regions in the world in which fish and bottom-feeding life forms have been entirely eliminated because of a lack of oxygen. One in the Gulf of Mexico is about the size of the state of New Jersey and growing.

Schindler warns that western Canada's struggle to control blue-green algae is only going to get worse because industrial, agricultural and municipal growth is pumping more nutrients into water supplies that are decreasing in size and volume.

Not only does the government have to pull out all stops to control phosphorous, it needs to protect wetlands that remove these nutrients from runoff before they reach lakes and streams, he said. It also needs to set up rules that create natural buffer zones that protect lakes and rivers from agricultural, municipal and cottage developments.