The Role of Iron in Suppressing Internal Phosphorus Loading and Toxic Cyanobacterial Blooms in Freshwater Lakes

• Author / Creator

  Orihel, Diane M.

• Harmful algal blooms occur in nutrient-rich lakes around the world, diminishing the value of these ecosystems for wildlife and humans. Management of algal blooms is an on-going challenge for lake managers and policy makers. The overarching goal of this research was to advance our understanding of the environmental factors leading to blooms of potentially toxic cyanobacteria in shallow eutrophic lakes, in order to guide effective management strategies to reduce their occurrence. First, I evaluated the nutrient conditions that lead to elevated levels of microcystins, a hepatotoxin produced by certain cyanobacteria, by consolidating a national database of nutrient and microcystin concentrations for Canadian lakes. Second, I tested whether nutrients released from sediments stimulate toxic cyanobacterial blooms by culturing the cyanobacterium Microcystis in overlying water harvested from incubated lake sediments. Third, I developed and evaluated a conceptual model to explain the biogeochemical pathways leading to toxic cyanobacterial blooms in shallow lakes, based on sediment and culture experiments and lake monitoring in a hypereutophic lake in Alberta, Canada. Fourth, I tested this conceptual model experimentally by manipulating iron loading to in-lake mesocosms and examining changes in sediment chemistry, nutrient cycling, algal biomass and community composition, and microcystin concentrations. The main conclusions of these studies are: (i) microcystins are prevalent in lakes across Canada, but only under high nutrient conditions and at low ratios of nitrogen-to-phosphorus; (ii) lake sediments release bioavailable nutrients that support the growth and toxin production of microcystin-producing cyanobacteria; (iii) toxic blooms of cyanobacteria in shallow lakes may result from the synergy between iron-deficient sediments and discontinuous polymixis; (iv) iron loading to lakes inhibits internal phosphorus loading, decreases algal biomass, discourages the dominance of cyanobacteria, and reduces microcystin concentrations. This research reaffirms the need for controlling internal phosphorus loading in shallow lakes of the Canadian Prairies, and suggests iron treatment may be an effective remediation strategy to complement external nutrient loading reductions. More broadly, this research emphasizes the important role of iron in influencing the trophic status of lakes, and raises concerns for how sulfur pollution and climate change may be exacerbating the problem of lake eutrophication. 

• Subjects / Keywords

  • Algae
  • Phosphorus
  • Lake sediments
  • Eutrophication
  • Iron
  • Microcystin
  • Cyanobacteria

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R32J68C9V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.