Models predict planned phosphorus load reduction will make Lake Erie more toxic

• Published in: Science (American Association for the Advancement of Science) Vol. 376; no. 6596; pp. 1001 - 1005
• Main Authors: Hellweger, Ferdi L., Martin, Robbie M., Eigemann, Falk, Smith, Derek J., Dick, Gregory J., Wilhelm, Steven W.
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 27.05.2022
• Subjects: Aquatic animals; Cyanobacteria; Drinking water; Environmental conditions; Hydrogen peroxide; Lakes; Light transmission; Meta Analysis; Microcystins - analysis; Microcystis; Molecular modelling; Nitrogen; Nutrients; Phosphorus; Photosynthesis; Reduction; Toxins; Lake Erie
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.abm6791

Harmful cyanobacteria are a global environmental problem, yet we lack actionable understanding of toxigenic versus nontoxigenic strain ecology and toxin production. We performed a large-scale meta-analysis including 103 papers and used it to develop a mechanistic, agent-based model of Microcystis growth and microcystin production. Simulations for Lake Erie suggest that the observed toxigenic-to-nontoxigenic strain succession during the 2014 Toledo drinking water crisis was controlled by different cellular oxidative stress mitigation strategies (protection by microcystin versus degradation by enzymes) and the different susceptibility of those mechanisms to nitrogen limitation. This model, as well as a simpler empirical one, predicts that the planned phosphorus load reduction will lower biomass but make nitrogen and light more available, which will increase toxin production, favor toxigenic cells, and increase toxin concentrations. Lake Erie receives water from important agricultural areas of Canada and the United States and is subject to high levels of nitrogen and phosphorus in runoff. These nutrients can lead to rapid growth of photosynthetic organisms, some of which produce toxins that harm aquatic animals and compromise drinking water. Recent efforts have focused on reducing phosphorus loading. With support from a large literature meta-analysis, Hellweger et al . developed an agent-based model of cyanobacterial metabolism to determine how toxin production changed under a range of nutrient and environmental conditions and defined the associated molecular mechanisms (see the Perspective by Ofiţeru and Picioreanu). They found that phosphorus reduction alone was potentially harmful, lowering total biomass but increasing toxin production. The proposed mechanism involves response to hydrogen peroxide stress and increased light transmission. —MAF A mechanistic, molecular-level model of a toxin-producing cyanobacterium explains ecology and informs management.