Saskatchewan researchers say the reason a local lake turned a bold shade of blue below the ice was due to a pigment that originated from decaying blue-green algae cells, their investigation found.
The particularly intense staining across Pasqua Lake lasted for all of March 2021, and had many citizens wondering and worrying about the water quality. So, the province’s Water Security Agency (WSA) teamed up with the University of Regina to get to the bottom of the mystery.
Initially, there was plenty of public speculation about the discoloration. Social media posts laid blame on everything from septic field releases, to toxic spills, urban pollution and even agricultural mismanagement.
Now, the results are in. The culprit — a harmless pigment called phycocyanin that had persisted from the autumn algae.
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“Algal colour depends on light conditions, which affects the species of algae that can grow, their abundance, and the degree of pigment or light adaptation used by the algae,” WSA announced in a statement about the blooms. “Common colours imparted by algae in lakes during the winter are golden or brownish in colour, the more common green to bluish-green colour, and pink to red and purplish,” the WSA continued.
For instance, researchers noted that the water beneath the ice covering another local water body, Perch Lake, had turned pinkish-red due to the species of Planktothrix, a type of algae that can produce toxins.
In particular, the deep blue colour of Pasqua Lake, as well as some of the ice, came from very high concentrations of the cyanobacterial pigment phycocyanin, used by cyanobacteria to regulate cellular nitrogen content.
It reached as much as ∼14 mg per litre, which is documented in the new study, “Marked blue discoloration of late winter ice and water due to autumn blooms of cyanobacteria”.
Researchers used analysis of in situ pigmentation from phytoplankton and remote sensors to document the discoloration.
Concerns over how much nutrient pollution continues to harm water quality in many Saskatchewan lakes continues to be a hot topic of discussion and the subject of intense research.
“Ecological surprises are likely to occur more frequently as the magnitude of lake fertilization and warming increases in uncharted waters,” notes the study published in Taylor & Francis Online.
According to the study, such a “blue-water event” was not something recalled “in the living memory of members of Pasqua First Nations,” whose reserve is located on the southern shore of Pasqua Lake.
The blue-water event did not coincide with greatly increased levels of common cyanobacterial toxins.