Climate change is making lakes less blue

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The new study provides the most comprehensive map of lake color, revealing that most of the world’s lakes are indeed green-brown rather than blue. credit: AGU /Geophysical Research Letters

If global warming continues, blue lakes around the world are at risk of turning a brownish-green, according to a new study providing the first global inventory of lake color. Shifts in lake water color can indicate a loss of ecosystem health. The new research was published in Geophysical Research Letters.

While substances such as algae and sediment can affect the color of lakes, the new study finds that air temperature, precipitation, lake depth and elevation also play important roles in determining the most common water color of a lake.

Blue lakes, which account for less than a third of the world’s lakes, tend to be deeper and are found in cold high latitudes with heavy rainfall and winter ice cover. The study finds that brown and green lakes, which represent 69% of all lakes, are more prevalent and are found in drier regions, continental interiors, and along coasts.

The researchers used 5.14 million satellite images of 85,360 lakes and reservoirs around the world from 2013 to 2020 to determine their most common water colour.

“No one has studied the color of lakes on a global scale,” said Xiao Yang, a remote sensing hydrologist at Southern Methodist University and author of the study. “There have been previous studies of perhaps 200 lakes all over the world, but the volume we are trying here is much larger in terms of the number of lakes and also the coverage of small lakes. Although we do not study every single lake on Earth, we try to cover a large and representative sample of lakes that we’ve got “.

Lake color can change seasonally, in part, due to changes in algae growth, so the authors described lake color by evaluating the most common lake color over a seven-year period. The results can be explored with an interactive map developed by the authors.

Climate change is making lakes less blue

A new paper in Geophysical Research Letters reports that the world’s blue lakes, many of which are located in high northern latitudes, are at risk of losing blue hues as a result of climate change. Credit: Eric Stein Bildring/Unsplash

In addition, the new study explored how different degrees of warming could affect the color of the water if climate change continues. The study finds that climate change may reduce the proportion of blue lakes, many of which are found in the Rocky Mountains, northeastern Canada, northern Europe, and New Zealand.

“Warmer waters, which produce more algae, tend to turn lakes green,” said Catherine O’Reilly, an aquatic ecologist at Illinois State University and author of the new study. “There are a lot of examples of places where people have actually seen this happen when they studied one lake.”

For example, the Great Lakes of North America are experiencing an increase in algal blooms and are also among the fastest warming lakes, O’Reilly said. Previous research has also shown that remote Arctic regions have lakes that are “going greener,” Yang said.

While previous studies have used more complex and precise metrics to understand the overall health of a lake’s ecosystem, water color is a simple but applicable measure of water quality that can be seen from satellites globally, the authors said. This approach provides a way to study how remote lakes change with climate change.

“If you use lakes for fisheries or for sustenance or drinking water, changes in water quality that most likely occur as lakes become greener will likely mean that it will be more expensive to treat that water,” O’Reilly said. “There may be periods when the water is unusable, and fish species may not be around, so we’re not going to get essentially the same ecosystem services from those lakes when they turn from blue to green.”

Additionally, changes in water color may have recreational and cultural implications in locations such as Sweden and Finland where the lakes are culturally dispersed, O’Reilly said. As warming continues, lakes in northern Europe are likely to lose their winter ice cover, which could affect winter and cultural activities.

“Nobody wants to swim in a green lake,” O’Reilly said. “Aesthetically, some lakes that we may have always thought were sanctuaries or spiritual places, those places might disappear with a change of color.”

The world’s lakes are suffering from excessively high temperatures

more information:
Xiao Yang et al., The Color of Earth’s Lakes, Geophysical Research Letters (2022). doi: 10.1029/2022GL098925

Presented by the American Geophysical Union

the quote: Climate Change Making Lakes Less Blue (September 22, 2022) Retrieved September 22, 2022 from https://phys.org/news/2022-09-climate-lakes-blue.html

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