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Phosphorus is the real enemy

Study suggests phosphorus, not nitrogen, is the real enemy when it comes to algae

March 11, 2013  by The Canadian Press

A University of Alberta ecologist says governments shouldn’t be wasting money on controlling nitrogen to stop algae blooms in lakes.

David Schindler says lawmakers should focus instead on controlling phosphorus – something that can be accomplished at only a fraction of the cost.

“There are very few good news stories in ecology these days but this is one,” Schindler says. “It saves us a lot of money that we can spend for other things.”

Numerous studies have linked summer algae blooms to both nitrogen and phosphorus getting into water through sewage, manure and fertilizer.


But in a peer-reviewed paper published recently in Proceedings of the Royal Society of London Series B, Schindler concludes that phosphorus is the real enemy.

Schindler says studies blaming nitrogen for blooms are short-term and do not take into account a lake’s entire ecosystem.

“Emperor Nitrogen has no clothes,” he writes. “The conclusion is we need to rely entirely on whole-lake data … for reliable environmental policy, not quick-and-dirty surveys with a few small bottles or little containers in lakes.”

Schindler reached his conclusions based on studies he did himself on nitrogen in the 1970s and 1980s, as well as a year-long review of about 500 other reports on the subject.

The phosphorus-nitrogen debate has been a huge issue in Manitoba, Canada, where the provincial government and the City of Winnipeg have been at odds over the health of Lake Winnipeg.

The province wanted the city to spend millions in upgrades to its sewage treatment plant to remove nitrogen, while the city insisted that phosphorus was the real battle to pick.

Last year, the province released a pollution reduction strategy that backed away from targeting nitrogen. Schindler says it was the right move.

He notes it’s much easier to control phosphorus than nitrogen.

Phosphorus is removed from water with iron or aluminum or sometimes calcium – a straightforward process. Getting rid of nitrogen is a two-step deal that relies on “finicky” biological processes.

It’s possible focusing on nitrogen may actually make water quality worse – at least when it comes to toxic blue-green algae.

Known scientifically as Cyanobacteria, blue-green algae needs both nitrogen and phosphorus to thrive. It can get the nitrogen it needs from the atmosphere, but the phosphorus has to come from the water.

“By adding phosphorus in a higher amount than nitrogen, you actually favor those species that you are trying to get rid of,” Schindler says. “Some of us worry that, if you were to tightly control both, we might get fewer algae but might get a higher proportion of blue-green algae.


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