Some freshwater algal blooms are becoming more toxic, and researchers blame climate change and increased nutrient levels in lakes and estuaries. In the most recent issue of the journal Science, researchers from Oregon State University and the University of North Carolina at Chapel Hill have focused their attention on a toxic species of Microcystis. Microcystis are cyanobacteria (also called blue-green algae) which flourish in warm, nutrient -rich water bodies. They are responsible for the green, paint-like scum often seen on the surfaces of lakes.
Microcystis species produce microcystin, a liver toxin and possible carcinogen, which may serve the species as an antioxidant. Increased water temperatures and carbon dioxide levels, as well as increased nutrient-rich runoff from urban and agricultural land are resulting in oxidizing conditions that favor these microcystin-producing cyanobacteria over their non-toxic counterparts.
Microcystin can be highly toxic to humans, and is usually most abundant at the surface where it can have harmful effects on swimmers, boaters and other recreational users. There is also some concern that increased bloom intensity and frequency associated with climatic changes may cause contamination of some drinking water supplies.
Cyanobacteria are some of the Earth’s oldest species, believed to be responsible for producing the oxygen which transformed the planet over 2 billion years ago. According to postdoctoral scholar Timothy Otten of the OSU Colleges of Science and Agricultural Services, it should be of no surprise that an organism that has outlived so many others on this planet would be extremely difficult to attack and remove once it has become entrenched in a lake. He says that the best option is most likely the suppression of conditions that foster growth.
With over 41,000 large US lakes already containing toxin-producing cyanobacteria, the need to curb this trend is growing. Impacts to freshwater systems are projected to intensify as the effects of climate change are fully realized. An important step, according to Otten is to increase public awareness, and to compel water quality managers to actively mitigate the problem.
by Kristen Daly