Tech Talk 77
Blue-green algae, also known as cyanobacteria, can form unsightly and unhealthy algal blooms. Certain blue-green algae (Microcystis, Anabaena and/or Aphanizomenon) produce harmful toxins that damage nerves, cause muscle tremors, damage the liver and cause cancer. Recent evidence has shown that the probability that any blue-green algae bloom will be toxic is 45-75%. Since laboratory tests are needed to confirm toxicity, experts recommend that all blue-green algae blooms be treated as if they were toxic to humans and all animals.
Blue-green algae toxins, called cyanotoxins, have been linked to human and animal illness around the world. The World Health Organization has identified blue-green algae in drinking water as an "urgent concern" and established a 1 microgram per liter (1 part per billion, or ppb) standard for microcystin-LR, the most common cyanotoxin. Pet, farm and wild animal deaths occur when cyanotoxins are concentrated, which can happen when accumulated near the shore. People swimming in waters with concentrated cyanotoxins can experience skin irritations, gastrointestinal and respiratory problems and allergic reactions without actually ingesting any water.
Controlling Blue-Green Algae with Aeration
Artificial mixing of lakes using aeration has been shown to shift the dominant resident planktonic community towards more desirable green algae and diatoms. Aeration and destratification have been shown to dramatically reduce the abundance of Microcystis by circulating the water and reducing the amount of time the blue-green algae spend in water with enough light available for photosynthesis (photic zone). Mixing eliminates another condition for blue-green algae growth: the stable, warm layer of water that can form at the surface of lakes or ponds during warm months. In addition to removing blue-green algae from the photic zone and creating circulation, synergistic airlift destratification systems also dramatically increase lake bottom (hypolimnion) oxygen concentration, which reduces the level of phosphorus—a key nutrient for algal blooms—released from lake sediments.
Controlling Blue-Green Algae with Algaecides
In addition to controlling blue-green algal blooms with aeration, you can use algaecides. Algaecides with sodium carbonate peroxyhydrate are effective at rapidly eliminating blue-green algae. When added to water, these compounds break down into hydrogen peroxide and sodium carbonate and typically last for less than 48 hours. Hydrogen peroxide quickly destroys the thin–membraned cell wall of the blue-green algae at low concentrations of .3 to 1.7 ppm. These algaecides can also control both planktonic algae (green water) and filamentous algae (long, string-like algae) at higher concentrations. Algaecides that form hydrogen peroxide are 100% biodegradable. Unlike some copper-based ones, peroxyhydrate algaecides applied according to label directions will not harm fish and other freshwater animals.
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