A global survey of 3.4 million lakes across the planet by researchers from the University of Copenhagen showed that the number of lakes has substantially increased in the last four decades. In particular, researchers noticed that there are more small lakes now than ever and they are contributing large amounts of greenhouse gases.
The discovery of increasing numbers of small bodies of water is of great importance for measuring the carbon account, global ecosystems, and human access to the water resources of Earth.
View to “Freibergsee” near Oberstdorf. Picture taken with DJI Mavic Pro on a hot summers day in June 2017.
Rapid Changes in Lakes Affecting Greenhouse Gases Emission
Researchers wrote in their study, titled "Mapping Global Lake Dynamics Reveals the Emerging Roles of Small Lakes" published in the journal Nature Communications, that global lake surfaces increased in size by over 17,761 square miles (46,000 square kilometers) between 1984 and 2019.
Greenhouse gases, such as carbon dioxide, methane, nitrous oxide, and others are constantly emitted from the lakes because of the bacteria and fungi feeding at the bottom of the water, Science Alert reported. They feed on dead plants and animals that have drifted down to the bottom of the lake.
Terrestrial ecologist Jing Tang from the University of Copenhagen in Denmark said that over the past decades, there have been major and rapid changes in lakes that contribute to greenhouse gas accounts, ecosystems, and access to water resources.
Lakes equate to an annual increase of 4.8 teragrams (or trillion grams) of carbon dioxide emissions in the country, which equates to the carbon emissions of the UK in 2012.
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Small Lakes Contribute Large Carbon Emissions
In the press release via EurekAlert! researchers noted that more and more small lakes, which measure less than 1-kilometer square have appeared since 1984. The findings are important because small lakes emit the most greenhouse gas in relation to their size. Small lakes account for 15% of all lakes, as well as accounting for 25% of carbon dioxide, and 37% of methane emissions.
Moreover, these lakes may be small but they contribute to the net increases of carbon dioxide and methane by about 45% and 59%, respectively, between 1984 and 2019.
Tang explained that small lakes typically accumulate more organic matter that is converted into gas, and also because they are often shallow. It is easier for gases to reach the surface and up into the atmosphere.
Furthermore, small lakes are more sensitive to changes in climate and weather, and human disturbances. That is why their size and water chemistry usually fluctuate.
Their map reveals that more than half of the increase in lake coverage during the study period could be attributed to human activity, such as constructing new reservoirs, but also could be linked to melting glaciers and thawing permafrost due to global warming.
The new dataset offers a range of regional and global applications. They have sent the estimates to the people behind the UN's IPCC climate reports in hopes of contributing to updated global emission numbers. The dataset can also be used to make better estimates of water resources in freshwater lakes and to better assess the risk of flooding, and for better lake management.
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