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


By Rhythm Sachdeva, author of CTVNews.ca

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TORONTO, Ontario (CTV Network) – Climate change is causing lakes to turn less blue, with many at risk of turning permanently green-brown, a new study has found.

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

Although no specific time frame was offered, the researchers said that one in 10 lakes can expect to change color in “the future.”

Blue lakes are generally found in the cooler regions of the world and are not very common, accounting for only 31 percent of the world’s lakes. Compared to lakes with greener or browner water, they are usually deeper and tend to be ice-covered in winter.

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The study, published Thursday in the journal Geophysical Research Letters, found that rising temperatures, leading to ice retreat, are the main cause of the blue lakes’ color change.

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

“There have been previous studies of maybe 200 lakes around the world, but the scale we’re trying to try here is much, much larger in terms of the number of lakes and also the coverage of small lakes. While we don’t study every single lake on Earth, we try to cover a large and representative sample of the lakes we have.”

The study’s researchers covered the tones of 85,360 lakes and reservoirs worldwide from 2013 to 2020, using 5.14 million satellite images.

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

The lakes likely to be affected are in northeastern Canada, New Zealand, the Rocky Mountains and northern Europe, the study said.

The color change in lakes has already begun, according to study co-author Catherine O’Reilly, who pointed to North America’s Great Lakes having “more algal blooms” and also being “among the fastest warming lakes.”

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

The changes in lake colors could mean devastating effects on those who depend on lakes for drinking water, food or fisheries.

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“There may be times when the water is unusable and fish species may be gone, so we’re not getting essentially the same ecosystem services from these lakes as they go from blue to green,” he told O’Reilly.

It could also mean that the lakes are no longer used for recreational purposes.

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

“From an aesthetic point of view, some of the lakes that we may have always considered as sanctuaries or spiritual places could disappear.”

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