According to a unique global survey of 3.4 million lakes in which the University of Copenhagen took part, the number of lakes on our planet has significantly expanded in recent years.
There have been more tiny lakes than ever, which is terrible because they generate a lot of greenhouse gases.
The carbon cycle of the planet, the health of the world’s ecosystems, and human access to water supplies are all greatly impacted by the development.
Large amounts of CO2, methane, nitrous oxide and other gases are released by bacteria and fungi that feed on decaying plants and animals at the bottom of lakes.
These gases get into the atmosphere in some cases.
Lakes become greenhouse gas production facilities as a result of this mechanism.
In actuality, freshwater lake greenhouse gas emissions are probably equal to 20% of total worldwide CO2 emissions from fossil fuels into the Earth’s atmosphere.
According to projections, lakes will produce an increasing amount of greenhouse gases as a result of climate change.
This is only one of the reasons it’s crucial to understand how these lakes form, as well as how numerous and how big they are.
This information was unknown from before to now.
A more precise and comprehensive map of the world’s lakes has now been created by scientists from the University of Copenhagen and other universities.
3.4 million lakes were mapped together with their evolution over the last 40 years using high-resolution satellite photography and artificial intelligence.
The study reveals that between 1984 and 2019, the surface area of all lakes increased by almost 46,000 km2, which is slightly greater than Denmark’s surface area.
Greenhouse emissions from freshwater lakes are probably equivalent to 20% of all global CO2 fossil fuel emissions into Earth’s atmosphere
Lakes have seen significant and quick changes in recent decades that have had an impact on ecosystems, the availability of water resources, greenhouse gas emissions, and more.
We can now more accurately estimate lakes’ potential carbon emissions, among other things, thanks to our newfound understanding of their size and dynamics, says Jing Tang, an assistant professor in the biology department and a co-author of the study, which was just published in Nature Communications.
The study’s calculations show that annual CO2 emissions from lakes increased by 4.8 teragrams (1012 trillion) of carbon throughout the study period, which is similar to the United Kingdom’s increase in CO2 emissions in 2012.
Small lakes, large CO2 emissions
Since 1984, the number of little lakes (less than 1 km2) has increased.
Because they produce the greatest greenhouse gas relative to their size, the researchers believe that the quantity of these small lakes is particularly crucial.
Small lakes make up only 15% of all lakes’ surface area, yet they emit 37% methane and 25% CO2 emissions.
Additionally, they are responsible for 45% and 59%, respectively, of the net increases in lake CO2 and CH4 emissions between 1984 and 2019.
Small lakes emit a disproportionate amount of greenhouse gases because they typically accumulate more organic matter, which is converted into gases.
And also, because they are often shallow. This makes it easier for gases to reach the surface and up into the atmosphere,” explains Jing Tang, who continues: “At the same time, small lakes are much more sensitive to changes in climate and weather, as well as to human disturbances.
As a result, their sizes and water chemistry fluctuate greatly.
Thus, while it is important to identify and map them, it is also more demanding.
Fortunately, we’ve been able to justify that.”
The mapping also demonstrates that human activities and climate change are the primary causes of Earth’s numerous new lakes.
More than half of the additional lake areas, or manmade lakes, are reservoirs.
The thawing of permafrost and glaciers are the main cause of the other half.
New figures sent to the UN
According to the researchers, the new dataset offers a range of regional and global applications.
“I have sent our new greenhouse gas emission estimates to the people responsible for calculating the global carbon budget, behind the UN’s IPCC climate reports.
I hope they include them in updating the global emission numbers,” says Jing Tang.
She adds: “Furthermore, the dataset can be used to make better estimates of water resources in freshwater lakes and to better assess the risk of flooding, as well as for better lake management – because lake area impacts biodiversity too.
Source: University of Copenhagen
