Climate change is making lakes less blue

If global warming continues, blue lakes around the world are at risk of turning brownish green, according to a new study representing the first global lake color inventory.

According to a study published in Geophysical Research Letters, a change in the color of lake water could indicate a loss of ecosystem health.

While materials such as algae and sediment can influence the color of lakes, a new study has found that air temperature, precipitation, lake depth, and altitude also play an important role in determining the most common lake water color.

Blue lakes, which make up less than a third of the world’s lakes, tend to become deeper and are found in cold high latitudes where precipitation is plentiful and where there is an ice sheet in winter.

The study found that brown and green lakes, which make up 69% of all lakes, are more common and found in drier areas, inland areas and along coasts.

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 color.

“No one has studied lake color on a global scale,” said Xiao Yang, a remote sensing hydrologist at Southern Methodist University and author of the study. The number of lakes also includes the coverage of small lakes. While we don’t study every lake on Earth in isolation, we try to capture the largest and most representative sample of lakes that we have.”

Lake color can change seasonally, partly due to changing algae growth, so the authors described lake color by estimating its most common color over a seven-year period. The results can be studied using an interactive map drawn by the authors.

In addition, the new study looked at how varying degrees of warming could affect the color of water if the climate continues to change. The study found that climate change could reduce the proportion of blue lakes, many of which are in the Rocky Mountains, northeast Canada, northern Europe and New Zealand.

Katherine O’Reilly, an aquatic ecologist at the University of Illinois and author of the new study, explains: “Warm water, which produces more algae, tends to turn lakes green. There are many examples of places where people have actually seen it happen. .”.

For example, the Great Lakes of North America are seeing an increase in algal blooms and are also among the fastest warming lakes, O’Reilly says.

Yang said previous research has also shown that there are lakes in remote Arctic regions that are “getting greener.”

While previous studies have used more sophisticated and precise metrics to understand the overall health of a lake’s ecosystem, the scientists say water color is a simple yet useful indicator of water quality that can be observed from satellites around the world.

This approach provides an opportunity to study how remote lakes change with climate change.

“If you use lakes for fishing or for drinking, the changes in water quality that are likely to occur as the lakes become greener will likely mean that water treatment will be more expensive,” O’Reilly noted. .The fish may not be there, so we’re not going to get much of the same ecosystem services from these lakes when they go from blue to green.”