October 25, 2013
Rise In Toxic Algal Blooms Due To Climate And Nutrient Enrichment
Brett Smith for redOrbit.com - Your Universe Online
Algae is probably best known for the green scum it forms on top of stagnant water, and in addition to looking unpleasant, some algal blooms host strains of cyanobacteria that are highly toxic.
According to a new study in the journal Science, nutrient enrichment and rising global temperatures are increasing the toxicity of some algal blooms in freshwater lakes, ponds and estuaries around the world. As these 'eutrophic' processes increase, so will the ratio of toxin-producing strains of cyanobacteria in harmful algal blooms.
The two study authors, from Oregon State University (OSU) and the University of North Carolina, emphasized the near-ubiquitous species Microcystis sp. cyanobacterium is of particular concern. The bacterium can regulate its position in the water column and produces microcystin, a toxin that causes liver damage.
In many environments, microcystin-producing cyanobacteria have a distinct advantage over non-toxic cyanobacteria. The poisonous strains can eventually out-compete the nontoxic strains, resulting in blooms that are increasingly toxic.
"Cyanobacteria are basically the cockroaches of the aquatic world, they're the uninvited guest that just won't leave," said study author Timothy Otten, a postdoctoral scholar in the OSU College of Science and College of Agricultural Sciences.
"When one considers their evolutionary history and the fact that they've persisted even through ice ages and asteroid strikes, it's not surprising they're extremely difficult to remove once they've taken hold in a lake," he added. "For the most part, the best we can do is to try to minimize the conditions that favor their proliferation."
While the lack of an extensive historical record of algal toxicity prevents scientists from putting current observations into long-term context, Otten said, "If you go looking for toxin-producing cyanobacteria, chances are you won't have to look very long until you find some."
With hundreds of thousands of lakes spread out across the United States, according to the most recent EPA National Lakes Assessment, at least one-third may contain toxic cyanobacteria. Dams, rising temperatures, carbon emissions, droughts and increased runoff of nutrients from urban and agricultural lands are all feeding the proliferation of these organisms, the researchers said.
Scientists have speculated that the toxic nature of some cyanobacteria probably did not evolve as a way to ward off predators since their arrival on the scene 3.5 billion years ago predates any known predators. New research indicates that microcystin actually helps cyanobacteria respond to oxidative stress, which explains why the genes involved in its biosynthesis are so widespread across cyanobacteria and have been been maintained for millions of years.
Whatever its origin, the presence of microcystin raises concerns for swimming, boating and other recreational water activities. Otten said chronic exposure to contaminated drinking water is another important concern that needs more attention.
"Water quality managers have a toolbox of options to mitigate cyanobacteria toxicity issues, assuming they are aware of the problem and compelled to act," Otten said. "But there are no formal regulations in place on how to respond to bloom events.
"We need to increase public awareness of these issues," he added. "With a warming climate, rising carbon dioxide levels, dams on more rivers than not, and overloading of nutrients into our waterways, the magnitude and duration of toxic cyanobacterial blooms is only going to get worse."