Why are lakes becoming less blue? The science behind the phenomena

By Rhythm Sachdeva, CTVNews.ca writer

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Toronto, Ontario (CTV Network) — Climate change is leading to lakes becoming less blue, with many at risk of permanently turning green-brown, a new study has found.

Conducted by the American Geophysical Union, the study presents the first “global inventory of the lake color,” and takes into account changes in water color to determine water quality.

While a specific time frame wasn’t offered, researchers said that one in 10 lakes can expect to change color in “the future.”

Blue lakes are generally found in the Earth’s cooler regions and aren’t very common, representing just 31 per cent of the world’s lakes. Compared to lakes with greener or browner water, they’re typically deeper and more likely to be covered in ice during the winter.

The study, published Thursday in the journal Geophysical Research Letters, found that rising temperatures, leading to a decline in ice, are the main culprit for blue lakes’ color change.

“No one has ever studied the color of lakes at a global scale,” Xiao Yang, co-author of the study, said in a release.

“There were past studies of maybe 200 lakes across the globe, but the scale we’re attempting here is much, much larger in terms of the number of lakes and also the coverage of small lakes. Even though we’re not studying every single lake on Earth, we’re trying to cover a large and representative sample of the lakes we have.”

Covering the hues of 85,360 lakes and reservoirs worldwide from 2013 to 2020, the study’s researchers used 5.14 million satellite pictures.

Generally, a lake’s change in color is attributed to algae and other sediments, but the new research now suggests that various degrees of warming could also impact water’s color due to climate change.

The lakes that will likely be impacted are found in northeastern Canada, New Zealand, the Rocky Mountains and northern Europe, the study says.

The color change in lakes has already begun, according to Catherine O’Reilly, co-author of the study, who pointed to the North American Great Lakes that have “increased algal blooms” and are also “among the fastest warming lakes.”

Yang also said that a similar trend can be seen in the Arctic regions that are starting to have lakes with “intensifying greenness.”

The changes in lake colors could signify devastating impacts on those relying on lakes for drinking water, sustenance or fisheries.

“There might be periods where the water isn’t usable, and fish species might no longer be present, so we’re not going to get the same ecosystem services essentially from those lakes when they shift from being blue to being green,” said. O’Reilly.

It could also mean the lakes will no longer be used for recreational purposes.

“Nobody wants to go swim in a green lake,” said O’Reilly.

“So, aesthetically, some of the lakes that we might have always thought of as a refuge or spiritual places, those places might be disappearing.”

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