(ORDO NEWS) — A new study has found that small lakes on Earth have expanded significantly over the past four decades, which is worrisome given the amount of greenhouse gases emitted by freshwater bodies of water.
Between 1984 and 2019, the area of global lakes increased by more than 46,000 square kilometers, experts say. This is slightly larger than Denmark area.
Carbon dioxide, methane, nitrous oxide, and other gases are constantly produced in lakes due to bacteria and fungi feeding on the bottom of the water, feeding on dead plants and animals that have sunk to the bottom of the lake.
Overall, this spread of lakes equates to an annual increase in carbon emissions of around 4.8 teragrams (or trillion grams), which is equal to the increase in CO2 emissions across the UK in 2012.
“In recent decades, lakes have experienced major and rapid changes that affect greenhouse gas emissions , as well as ecosystems and access to water resources,” says terrestrial ecologist Jing Tang from the University of Copenhagen in Denmark.
“Among other things, our new knowledge about the size and dynamics of lakes allows us to better calculate their potential carbon emissions.”
The researchers used a combination of satellite imagery and deep learning algorithms to estimate lake coverage. A total of 3.4 million lakes have been recorded.
According to the team of researchers, small lakes (less than one square kilometer) are very important for calculating greenhouse gases because they produce a large amount of emissions compared to their size.
These less extensive bodies of water account for only 15 percent of the total lake volume, but account for 45 percent of the increase in carbon dioxide emissions and 59 percent of the increase in methane emissions from 1984 to 2019.
“Small lakes emit a disproportionate amount of greenhouse gases because they tend to accumulate more organic matter that turns into gases,” Tan says.
“And also because they are often shallow. This makes it easier for gases to reach the surface and into the atmosphere.”
“At the same time, small lakes are much more sensitive to climate and weather changes, as well as to anthropogenic impacts.
As a result, their size and the chemical composition of water fluctuate greatly. So while identifying and mapping them is important, it also requires a lot of effort. Luckily, we were able to do just that.”
According to the researchers, more than half of the increase in the area of lakes during the study period is associated with human activities (we are talking about built reservoirs).
The rest is mainly due to the melting of glaciers and the melting of permafrost caused by the warming of our planet.
The researchers hope their data will prove useful for future climate models, as much of the greenhouse gases potentially come from the surface of lakes as the melting and warming continues.
“In addition, the dataset can be used to more accurately estimate water resources in freshwater lakes and to better assess flood risk, as well as better lake management, since lake area also affects biodiversity,” Tan says.
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