For the first time, the researchers used agent-based simulation in Lake Erie to depict the behaviour of blue-green algae in their new modelling study. On the computer, each blue-green alga is represented as an individual, behaving slightly differently depending on its assumed life history.
“The big advance here was to integrate our understanding of the microbiology of the blooms into predictive models,” says Gregory Dick, an environmental microbiologist at the University of Michigan and study co-author. He added that the findings suggest that biologically informed models can reproduce emergent properties of blooms that traditional models cannot predict.
The simulation shows that lowering phosphorus levels to control harmful algal blooms in places like Lake Erie is beneficial to toxic cyanobacteria strains, which can lead to an increase in toxins in the water. Lake Erie is the fourth largest of North America’s five Great Lakes and the eleventh largest lake in the world.
When cyanobacteria, also known as blue-green algae, die, they can produce toxins and deplete lakes of oxygen. Phosphorus is an important nutrient for these algae, and efforts are being made around the world to reduce phosphorus levels and inhibit cyanobacterial growth.
However, as the total number of cyanobacteria decreases, the remaining cyanobacteria have a greater supply of another important nutrient which is nitrogen. Furthermore, higher nitrogen concentrations promote the production of a toxin that protects cyanobacteria from oxidative damage.
The researchers used an agent-based model to simulate how cyanobacteria behave in Lake Erie. They advocate for a paradigm shift in water management, as well as the adoption of a strategy that reduces not only phosphorus but also nitrogen loading in bodies of water.
Cyanobacteria can be harmful to both pets and humans. Due to contaminated drinking water, nearly 500,000 people in the Toledo area were without tap water for nearly three days in August 2014. This is because microcystis, a type of blue-green algae, had produced particularly high levels of the liver toxin microcystin (MC) in Lake Erie.
According to Ferdi Hellweger, chair of Water Quality Engineering at TU Berlin’s Institute of Environmental Technology and lead author, while microcystin is a strong toxin for humans and animals, it is extremely beneficial to cyanobacteria.
Microcystin can occupy specific sites on enzymes that are essential for bacterial life processes. It protects the bacteria from aggressive hydrogen peroxide, which would otherwise attack these binding sites, oxidise the enzymes, and render them ineffective.
Because phosphorus is a nutrient that is only available to a limited extent in nature for bacteria, previous efforts have focused on reducing the use of phosphates as fertilisers in agriculture and reducing the phosphorus content of wastewater through tertiary treatment of wastewater to slow the growth of blue-green algae, even in larger bodies of water like Lake Erie.
Furthermore, a blue-green alga, for example, that was frequently at the water’s surface would have been particularly exposed to sunlight and thus hydrogen peroxide. This increases the chances that it will fully utilise its microcystin production capabilities.
Sunlight can also activate the gene responsible to produce microcystin. Because more light can penetrate to greater depths and stimulate production, this mechanism contributes to the fact that less biomass leads to more toxins.
For their simulation, the researchers used the blue-green alga Microcystis and Lake Erie as the model organism and environment, respectively. The National Oceanic and Atmospheric Administration, the National Institute of Environmental Health Sciences, and the National Science Foundation all contributed to the research.
