A global study demonstrates the change in the color of these ecosystems and the loss of quality of their waters
If global warming persists, blue lakes around the world are at risk of turning a greenish-brown hue, according to a new study that also includes the first world inventory of the color of lakes. According to its authors, the changes in the tonality of the lakes can indicate a loss of ecosystem health.
While substances such as algae and sediment can affect the color of lakes, the new study concludes that air temperature, rainfall, depth and elevation of the lake are factors that also play a role in the color of lakes. these aquatic formations.
Accounting for less than a third of the world’s lakes, blue lakes tend to be deeper and are found in cold, high-latitude regions with high rainfall and winter ice cover. Greenish-brown lakes, which make up 69% of all existing lakes, are more widespread and are found in drier regions, inland interiors, and along coastlines.
The research was published in Geophysical Research Lettersthe magazine of the scientific entity AGU.
The researchers used 5.14 million satellite images of 85,360 lakes and reservoirs around the world, taken between 2013 and 2020, to determine the most common color of water in these ecosystems.
“No one has ever studied the color of lakes on a global scale”said Xiao Yang, a remote sensing hydrologist at Southern Methodist University and an author of the study. “There have been previous studies of perhaps 200 lakes around the world, but the scale we are looking at here is much larger in terms of quantity, including small lakes as well. Although we have not studied all the lakes on Earth, we have tried to analyze a large and representative sample of the planet & rdquor ;.
The color of a lake can change seasonally, in part, due to changes in algal growth, so the authors characterized the color by first evaluating the most frequent hue over seven years.
Global warming is changing the lakes
But climate change is causing a global change in this regard. Global warming of the planet may decrease the percentage of blue lakes, many of which are found in the Rocky Mountains, northeastern Canada, northern Europe, and New Zealand.
“Warmer water, which produces more algal blooms, will tend to change the colors of lakes towards green,” explained Catherine O’Reilly, aquatic ecologist at Illinois State University (USA) and author of the study. “There are many examples of people who have actually seen this happen by looking at an individual lake,” she says.
For example, the North American Great Lakes are experiencing increased algal blooms and are also among the fastest warming lakes on the planetO’Reilly said. Previous research has also shown that remote Arctic regions have lakes that are “increasingly green,” Yang said.
While previous studies have used more complex and detailed systems to understand the overall health of these ecosystems, water color is also a strong indicator of water quality, and can also be seen from satellites, the authors noted.
“If you’re using a lake to fish or to get water, the changes in the quality of that water when that lake turns green, that’s going to increase the difficulty of getting those resources,” O’Reilly said.There may be periods when the water is not usable and fish species are no longer presentso we won’t get the same ecosystem services from those lakes when they go from blue to green,” he added.
As warming continues, northern European lakes are likely to lose their winter ice cover, which could also affect social, economic and also cultural activities.
“No one wants to go swimming in a green lake & rdquor ;, O’Reilly said, “so aesthetically, some of the lakes that we always thought of as refuge or spiritual places might be disappearing as the color changes.”
Reference study: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL098925