Cyanobacteria – known as the “cockroaches” of aquatic environments – have been around for more than 2 billion years. Over their long evolutionary history, they have learned to tolerate many extreme conditions and are one of the toughest microorganisms on Earth. Cyanobacteria are also largely responsible for creating the oxygen-rich conditions that stimulated modern life.
But the bacteria, known for their blooms, have become quite a problem in the 21st century.
In a research brief letter published in the October edition of Science, researchers from UNC Chapel Hill and Oregon State University describe how outbreaks of these bacteria are choking lakes and rivers across the globe – and how such outbreaks may worsen with climate change and human development.
“My interest in harmful cyanobacterial blooms first developed when I was an undergraduate student at the University of California at Davis, back in the late 1960s,” said Hans Paerl, professor of engineering and environmental sciences at UNC’s Institute of Marine Sciences.
“I was fascinated by how these blooms could become so dense in the water that it seemed you could walk on them.”
Cyanbacterial blooms can occur in many aquatic ecosystems – from lakes to rivers, ponds, reservoirs and estuaries. The outbreaks are “explosive” and widespread, and theycolor// the surface of large areas of water a bright yellowish-green. They usually occur in response to excessive runoff of nutrients, such as phosphorous and nitrogen.
Once the bacteria have taken hold, numerous evolutionary advantages allow them to thrive. Cyanobacteria need only a small amount of nutrients, and they can tolerate excessive heat, cold, UV radiation and other conditions that would kill other species of bacteria. They are also difficult to remove from aquatic systems, because of their microscopic size. Additionally, the bacteria grow optimally at high temperatures, which means outbreaks may worsen if climate change continues.
“They like it hot,” Paerl said. “No one continent (maybe excepting Antarctica) is free of this problem. Developing regions such as Asia, Africa, and South America are especially prone to outbreaks.”
In order to combat the bacteria, Paerl and others have developed nutrient-reduction strategies to minimize agricultural and industrial runoff, in North Carolina and in developing countries.
Paerl says these nutrient-reduction strategies represent the only “knob that can be tweaked,” in dealing with outbreaks, since global temperatures can’t be controlled in the short term.
“With other researchers from UNC Chapel Hill and NCSU as well as researchers at North Carolina’s Division of Water Quality, we have developed a series of nutrient-reduction recommendations that ultimately led to the arrest and control of blooms in the Neuse and Chowan rivers,” Paerl said.
“Currently, we are helping the Chinese government develop nutrient-input reduction strategies to counter the explosion of toxic blooms that is negatively impacting lakes and reservoirs.
“These blooms are highly undesirable from an ecosystem ‘health’ and human use (like drinking water) perspective,” Paerl said.