Cutting nutrient pollution may curb harmful algal blooms

Reducing nitrogen and phosphorus pollution may be an easier, more effective way to control harmful algal blooms in water than addressing warming temperatures, say researchers.

Cyanobacteria, also known as blue-green algae, can harm marine ecosystems and human health. They grow in fresh and marine waters, and are thought to be on the increase worldwide because of warming temperatures and changing land use.

But the key driver in their growth is the runoff of nitrogen and phosphorus into water supplies — for example from farms and cities — and controlling this could also mitigate the effects of warming on the blooms, conclude the authors of an article published in Science today (7 October) that looks at historical data analyses, and modelling and experimental studies.

"Lakes that received decreased nutrient loads generally exhibited fewer blooms over the following years, despite increasing water temperatures," Cayelan Carey, co-author of the article and a researcher at Cornell University, United States, told SciDev.Net.

"This is good news because we can control nutrient loading to water bodies at a regional [level] and short time-scale, whereas controlling global temperatures will require centuries and international cooperation," she added.

"The main challenge of reducing nitrogen and phosphorus [pollution] is getting communities on board with the treatment options," said Carey. These include wastewater treatment, implementing sewage diversion, and reducing agricultural and household fertiliser use.

While these methods require long-term investment, studies show that a significant decrease in the number of blooms occurs where they have been implemented, she said.

Hans Paerl, professor of marine and environmental sciences at the University of North Carolina, United States, told SciDev.Net: "Nitrogen and phosphorus reductions are the most direct and effective way to combat and control cyanobacterial blooms worldwide".

But he added that they need to be implemented in a more aggressive way to counter the effects of global warming.

David Adams, a researcher at the University of Leeds, United Kingdom, said that nutrient reduction would be difficult to implement in some areas where sources of these nutrients are abundant.

"Nutrient limitation will not always be adequate or even feasible in certain water bodies, so we should be looking at more than one method of control or a variety in combination," he said.

Other methods may include chemical control with algicides and biological control with viruses that target specifically algal cells.

Link to full article in Science