EXAMINING THE ROLE OF IRON IN PROMOTING CYANOBACTERIA DOMINANCE

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Cyanobacteria blooms in nutrient-rich (eutrophic) lakes remain a significant global problem including Canada, in spite of decades of scientific research and billions of dollars spent on nutrient removal to reduce the risk of bloom formation. Blooms pose a threat to environmental health because many strains produce liver and nerve toxins and they can impair the taste and odour of drinking waters. It is clear that excessive input of the nutrient, phosphorus (P) to lakes and rivers is responsible for increased aquatic primary productivity and that P is a very strong risk factor for bloom formation and displacement of benign algal species. However, the reason why P leads to blooms of cyanobacteria in eutrophic waters has not been clearly established. In addition, P alone does not explain increasing incidence of blooms in recent years in lakes with low P levels that were considered to be at low risk. Recent evidence from my lab shows that increased availability of a particular form of iron, ferrous iron, promotes dominance of phytoplankton (algal) communities by cyanobacteria and that the timing of blooms is influenced by physical and chemical factors that control release of ferrous iron from oxygen-depleted sediments. This proposal addresses several knowledge gaps in the emerging model about how P and iron work together to increase the risk of bloom formation. It also examines whether increasing incidence of bloom formation may be a climate change signal.