A new study has revealed that small lakes on Earth have expanded considerably over the last four decades – a worrying development, considering the amount of greenhouse gases freshwater reservoirs emit.
Between 1984 and 2019, the global lake surface extents Researchers claim that it has grown in size by more 46,000 kilometers (17,761 miles). This is slightly less than the Danish area.
The bacteria and fungi living in the bottom of lakes produce carbon dioxide, methane, and other gases. They eat dead plants and animals which have drifted to the lake’s floor.
This lake’s spread results in an annual increase in carbon emissions of around 4.8 Teragrams (or trillion) of CO.2 – which to continue the country comparisons equals the increase in CO2The entire UK emitted in 2012.
“Lakes have seen rapid and significant changes in the last decade that have had an impact on greenhouse gas accounts as well as ecosystems, and access to water resources.” Jing Tang, a terrestrial ecoologist, says soThe University of Copenhagen in Denmark.
“Our new knowledge of the lake’s dynamics and extent allows us to calculate their potential carbon emission.”
For their assessment of lake coverage, the researchers combined satellite imagery with deep learning algorithms. The total number of lakes logged was 3.4 million.
Because they emit high volumes of greenhouse gases relative their size, smaller lakes (less that one square kilometer, or 0.39 sq miles) are important for the calculation of greenhouse gas emissions.
These smaller bodies of water make up just 15% of total lake coverage. However, they are responsible for 45 percent of the rise in carbon dioxide output and 59% of the increase methane emissions over the period 1984-1919.
“Small lakes emit more greenhouse gasses than large ones because they have higher organic matter. This organic matter is then converted to gasses.” Tang. “And, they are often shallow. This allows gasses to easily reach the surface and into the atmosphere.
“Little lakes are also more vulnerable to changes in weather and climate, as well human disturbances. Their water chemistry and size fluctuate greatly as a result. It is therefore more difficult to map and identify them. We have been able accomplish this, thanks to our team.
More than half of the increase in lake coverage over the study period is due to human activity, the researchers say – essentially, newly constructed reservoirs. The melting glaciers and the thawing of permafrost due to global warming are responsible for most of the rest.
Researchers hope that their data will be useful in future climate models. A significant portion of greenhouse gases could come from lake surface melting as more warming and melting continues.
“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,” Tang.
The research was published in Nature Communications.
