Climate change could mean that many picturesque blue lakes are not as blue in the future.
Researchers estimate that this is the first global count of lake color. roughly one-third of Earth’s lakes are blue. The team reports that crystal waters could become murky green or brown if the average summer temperatures rise by a few degree. Geophysical Research Letters.
The changing hues may alter the way that people use the water and provide clues to how stable lake ecosystems are. Lake color depends in part on what’s in the water, but factors such as water depth and surrounding land use also matter. According to Xiao Yang (a hydrologist at Southern Methodist University, Dallas), green and brown lakes contain more algae, sediment, and organic matter than blue lakes.
Yang and coworkers used satellite photos between 2013 and 2020 to examine the color of 85,000 lakes all over the globe. 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. Researchers also created An interactive online mapThese can be used to discover the colors of these lake’s 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.”
To determine if local climates were affected by lake color, the scientists looked at data from that period. 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. The researchers found that up to 14 per cent of blue lakes are within this range. If average summer temperatures increase another 3 degrees Celsius — an amount that scientists think Is possible by the end of this 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.
It is difficult to extrapolate beyond this small sample of lakes. “We don’t even know how many lakes there are in the world,” says study coauthor Catherine O’Reilly, an aquatic ecologist at Illinois State University in Normal. Although many lakes are too small for satellite detection, some estimates suggest that there could be tens to thousands of larger lakes with a blue color change.
If some lakes do become less blue, people will probably lose some of the resources they have come to value, O’Reilly says. Lakes are used often for water, food and recreation. It could make the water unattractive for recreation or be more expensive to clean.
But the color changes wouldn’t necessarily mean that the lakes are any less healthy. “[Humans] don’t value lots of algae in a lake, but if you’re a certain type of fish species, you might be like ‘this is great,’” O’Reilly says.
Lake color can hint at the stability of a lake’s ecosystem, with shifting shades indicating changing conditions for the critters living in the water. One benefit of the new study is that it gives scientists a baseline for assessing how climate change is affecting Earth’s freshwater resources. Scientists could detect future changes by continuing to monitor lakes.
“[The study] sets a marker that we can compare future results to,” says Mike Pace, an aquatic ecologist at the University of Virginia in Charlottesville, who was not involved with the study. “That’s, to me, the great power of this study.”
