Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science



Collaborative Specialization

Global Health Systems in Africa


Creed, Irena F.


University of Saskatchewan

2nd Supervisor

Trick, Charles G.



Browning of inland waters has been noted over large parts of the Northern hemisphere and is a phenomenon with both ecological and societal consequences. The increase in water color is generally ascribed to increasing concentrations of dissolved organic matter (cDOM) of terrestrial origin. Changes in water color will have profound effects on the phytoplankton composition in freshwater systems. Here, I examined the effect of changes in water color associated with coloured DOM (cDOM) on red and green phenotypes of the cyanobacterium, Pseudanabaena, which emerged to surface blooms in Dickson Lake (Algonquin Provincial Park, Ontario) in the summer of 2014. Results presented here indicated that: (A) the increased level of cDOM had little effect on the growth and photosynthetic activity of either phenotype when grown independently, suggesting that lake browning was a benign, rather than selective, ecological driver; and (B) neither phenotype achieved a competitive advantage when the two phenotypes were grown together under defined cDOM regimes suggesting coexistence of both phenotypes. These findings temper the ideas that, with climate change, only specific bloom forming cyanobacteria will prevail, as both phenotypes of Pseudanabaena were present and showed the ability to co-exist. Cyanobacteria of this genera are likely to thrive under warmer and browner conditions due to their photosynthetic pigment composition that allows them to capture light at a variety of wavelengths.

Summary for Lay Audience

Climate changes are having a profound impact on many of the Earth’s ecosystems. In northern lakes, these changes have led to the emergence of cyanobacteria blooms. For unknown reasons, red and green phenotypes of the cyanobacterium Pseudanabaena emerged in one northern lake, Dickson Lake in Algonquin Park, Ontario. Climate warming has enhanced the “browning” of lakes, reflecting an increase in the loading of terrestrial organic matter to lakes. Red phenotypes have photosynthetic pigments that absorb blue and violet colors of the visible spectrum, while green phenotypes contain photosynthetic pigments that absorb red and orange wavelengths. Browning decreases the amount of light and changes the availability of specific colors found in white light. My thesis aimed to understand the behavior of these cyanobacteria in response to browning; specifically, does browning favor one phenotype over the other, or do both coexist? My findings show that browning had little effect on the growth and photosynthetic activity of green and red phenotypes. Both cyanobacteria can coexist, indicating that cyanobacteria can thrive in warmer and browner waters associated with climate change.