Natural stable isotopes of iron: a new tool to trace Fe cycling for management of risk from harmful cyanobacterial blooms in lakes and reservoirs

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Harmful algal blooms in lakes and reservoirs constitute a major threat to human health and, by extension, to all aspects of the Canadian economy. Harmful algal blooms (HABs), especially those associated with cyanobacteria (cyano-HABs) have direct impacts on the safety of drinking water supplies by producing a variety of liver and nerve toxins in addition to causing taste and odour problems. Cyano-HABs have been increasing in recent years across Canada from Newfoundland to British Columbia. Causes of this increase are unknown but various exacerbating effects have been suggested, among these are changes in nutrients, a decrease in acid precipitation and climate change. There is an urgent need to evaluate the science and to manage risk with regard to cyano-HABs. Inputs of the main nutrients, phosphorus (P) and nitrogen (N), have been the focus of much research and management effort. Recently a new theory centres on the importance of the availability of iron (Fe) in the form of Fe(II) as the key to cyanobacterial blooms. Determining the source of Fe(II) available to cyanobacteria is, however, problematic. Fe is low in surface waters because Fe(III) is very insoluble and oxygen quickly changes Fe(II) to Fe(III). We have discovered that the natural stable isotopes of Fe hold great promise to decipher the source of Fe used by cyanobacteria. Our project will evaluate this novel isotopic tool for understanding Fe cycling in lakes and reservoirs at risk from cyano-HABs. The work will be focussed at the Experimental Lakes Area (ELA) where background information on chemistry, biology and physics of lakes has been collected over the past 47 years. One of the key components is the intensive research ongoing at a globally unique whole lake experiment where one lake has received nutrient additions for 47 years and has recurring cyanobacterial blooms. A series of field campaigns at ELA and laboratory experiments will evaluate the use of natural stable Fe isotopes. In addition, carefully selected samples from other lakes and reservoirs across Canada, collected by collaborating scientists, will be analyzed to evaluate the potential for widespread application of this promising novel technique.