The world’s blue lakes, many of which are in high northern latitudes, are at risk of losing their blue hues as a result of climate change, according to a new paper published in Geophysical Research Letters.
Conducted by the American Geophysical Union, the study presents the first “global lake colour inventory” and takes into account changes in water colour to determine water quality.
Lakes less blue due to climate
While substances such as algae and sediment can affect the colour of lakes, the new study finds that air temperature, precipitation, depth and elevation of the lake also play a role in determining the colour of the water.
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 lakes, are more widespread and are found in drier regions, in the interior of continents and along coastlines, according to the study.
The researchers used 5.14 million satellite images of 85,360 lakes and reservoirs around the world between 2013 and 2020 to determine the most common colour of the water.
Lake’s colour change seasonally
“No one has ever studied the colour of lakes at a global scale,” said Xiao Yang, remote sensing hydrologist at Southern Methodist University and author of the study. “There were past studies of maybe 200 lakes across the globe, but the scale we’re attempting here is much, much larger in terms of the number of lakes and also the coverage of small lakes. Even though we’re not studying every single lake on Earth, we’re trying to cover a large and representative sample of the lakes we have.”
A lake’s colour can change seasonally, in part, due to changes in algal growth, so the authors characterized lake colour by evaluating the most frequent lake colour over seven years. The results can be explored through an interactive map developed by the authors.
Additionally, the new study explored how different degrees of warming might affect water colour if climate change persists. The study finds that climate change 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 colours of the lake toward green,” said Catherine O’Reilly, an aquatic ecologist at Illinois State University and an author of the new study. “There are many examples of people actually seeing this happen when they studied an individual lake.”
Changes in water quality
For example, the North American Great Lakes are experiencing increased algal blooms and are also among the fastest-warming lakes, O’Reilly said. Previous research has also shown that remote regions of the Arctic have lakes that are “increasingly green,” Yang said.
While previous studies have used more complex and finer-scale metrics to understand the overall health of the lake ecosystem, water color is a simple but viable metric for water quality that can be viewed from satellites on a global scale. they said. the authors. This approach provides a way to study how remote lakes are changing with climate.
“If you’re using lakes to fish, earn a living or drink water, the changes in water quality that are likely to 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 not usable and fish species are gone, so we’re not going to get essentially the same ecosystem services from those lakes when they go from blue to green.”
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