Small lakes keep popping up all over the world, and this is a big problem
A new study shows that small lakes on Earth have grown a lot in the last 40 years. This is a worrying trend because freshwater reservoirs release a lot of greenhouse gases.
Researchers say that the size of the world’s lakes grew by more than 46,000 square kilometers (17,761 square miles) between 1984 and 2019. That’s about the same amount of land as Denmark.
Carbon dioxide, methane, nitrous oxide, and other gases are always being made by lakes. This is because bacteria and fungi feed at the bottom of the water by eating dead plants and animals that have drifted to the bottom.
In total, this lake spread is equal to an annual increase in carbon emissions of around 4.8 teragrams (or trillion grams) of CO2. To continue the country comparisons, this is the same amount of CO2 that the UK added to the atmosphere in 2012.
Jing Tang, a terrestrial ecologist at the University of Copenhagen in Denmark, says that lakes have changed quickly and in big ways in the last few decades. These changes affect greenhouse gas accounts, ecosystems, and access to water resources.
“Now that we know more about the size and behavior of lakes, we can, among other things, figure out how much carbon they might release.”
The researchers looked at satellite images and deep learning algorithms to figure out how much water was in each lake. In total, about 3.4 million lakes were cut down.
The team says that smaller lakes (less than one square kilometer or 0.39 square miles) are important for figuring out greenhouse gases because they produce a lot of emissions for their size.
Only 15 percent of all lakes are made up of these smaller bodies of water, but they are responsible for 45 percent of the rise in carbon dioxide emissions and 59 percent of the rise in methane emissions from 1984 to 2019.
Tang says, “Small lakes give off a disproportionate amount of greenhouse gases because they tend to collect more organic matter, which breaks down into gases.” “And also because they are usually not very deep. This makes it easier for gases to rise to the surface and into the atmosphere.”
“At the same time, small lakes are much more affected by changes in the weather and climate, as well as by people. Because of this, their sizes and the chemicals in their water change a lot. So, it is important to find and map them, but it also takes more work. We’ve been able to do just that, which is good.”
The researchers say that more than half of the increase in lake area over the time period of the study is due to human actions, mostly the building of reservoirs. The rest is mostly caused by the warming of our planet, which is causing glaciers to melt and permafrost to thaw.
The researchers hope that their data will help them make better climate models in the future. As melting and warming continue, a large amount of greenhouse gases could come from the surface of lakes.
“Further, the dataset can be used to make better estimates of the amount of water in freshwater lakes and the risk of flooding. It can also be used to better manage lakes, since lake size affects biodiversity,” says Tang.
