Some picturesque blue lakes may not be so blue in the future, thanks to climate change.
In the first global tally of lake color, researchers estimate that roughly one-third of Earth’s lakes are blue. But, should average summer air temperatures rise by a few degrees, some of those crystal waters could turn a murky green or brown, the team reports in the Sept. 28 Geophysical Research Letters.
The changing hues could alter how people use those waters and offer clues about the stability of lake ecosystems. Lake color depends in part on what’s in the water, but factors such as water depth and surrounding land use also matter. Compared with blue lakes, green or brown lakes have more algae, sediment and organic matter, says Xiao Yang, a hydrologist at Southern Methodist University in Dallas.
Sign Up For the Latest from Science News
Headlines and summaries of the latest Science News articles, delivered to your inbox
Thank you for signing up!
There was a problem signing you up.
Yang and colleagues used satellite photos from 2013 to 2020 to analyze the color of more than 85,000 lakes around the world. Because storms and seasons can temporarily affect a lake’s color, the researchers focused on the most frequent color observed for each lake over the seven-year period. The researchers also created an interactive online map that can be used to explore the colors of these lakes.
The approach is “super cool,” says Dina Leech, an aquatic ecologist at Longwood University in Farmville, Va., who was not involved with the study. These satellite data are “just so powerful.”
The scientists then looked at local climates during that time to see how they may be linked to lake color around the world. For many small or remote water bodies, records of temperature and precipitation don’t exist. Instead, the researchers also relied on climate “hindcasts” calculated for every spot on the globe, which are pieced together from relatively sparse records.
Lakes in places with average summer air temperatures that were below 19° Celsius were more likely to be blue than lakes with warmer summers, the researchers found. But up to 14 percent of the blue lakes they studied are near that threshold. If average summer temperatures increase another 3 degrees Celsius — an amount that scientists think is plausible by the end of the century — those 3,800 lakes could turn green or brown (SN: 8/9/21). That’s because warmer water helps algae bloom more, which changes the properties of the water, giving it a green-brown tint, Yang says.
Ext …