Curbing phosphorous key to reducing algal blooms

A group of North American scientists is advising governments to control the amount of phosphorous in fresh water to decrease the intensity of algal blooms.

Blue-green algae presents an issue across the continent, contributing to oxygen-deprived areas where fish can’t survive. Large blooms can also affect plant life and the quality of drinking water. Lakes in central Alberta are particularly prone to algal blooms because they tend to be shallow and nutrientrich.

“Thirty-seven long-term wholelake studies conducted in nine countries in Europe and North America showed that controlling a single element — phosphorus — reduced algal blooms in lakes,” said University of Alberta professor David Schindler.

He added that controlling nitrogen, whether or not combined with the control of phosphorous, didn’t have an effect.

The scientists published their findings in the journal Environmental Science and Technology.

“Lakes where phosphorus reductions successfully reduced algal blooms ranged in size from small ponds to Lake Superior, in a wide range of climatic and geological settings,” Schindler added.

Phosphorous inputs into lakes have been regulated in Europe and North America since the 1970s. But some scientists don’t believe it’s enough to reduce algal blooms, and nitrogen needs to be controlled, as well. For example, certain agencies including the European Union require the removal of nitrogen from sewage outflow.

Schindler’s study suggests this wouldn’t help.

“The recommendations of some scientists for nitrogen control are based on correlations, or on the results of short-term assays where nutrients are added to small containers of algae,” he said. “These poorly represent the long-term responses of whole lakes, especially when nutrients are removed, rather than added.”

In one long-term study where nitrogen was reduced, the amount of blue-green algae, known as cyanobacteria, actually increased.

“In many ways, our conclusions are good news,” University of Ottawa professor Diane Orihel said, adding it’s cheaper to control phosphorous. “There are many reasons to control nitrogen pollution, but freshwater eutrophication is not one of them.”

Excess nitrogen can cause soil acidification and groundwater pollution, she added.