Increase in the number of small lakes on Earth is bad news for the climate

Lakes, because of the bacteria and fungi at the bottom, emit a lot of greenhouse gases. And there is a worrying increase in their number on Earth.

5 ten
– 21:43

(updated 6/12/2022 at 3:08 pm)

Increase in the number of small lakes on Earth is bad news for the climate

Increase in the number of small lakes on Earth is bad news for the climate

Photo: Image: Christoph Hormann/Wikimedia Commons / Canaltech

Science has noticed an increase in the number of lakes on planet Earth over the past 40 years. And while it may not seem like it, this is worrying, as the development results in an increase in greenhouse gases emitted by the world’s water reservoirs.

Between 1984 and 2019, the land area covered by lakes grew by more than 46,000 km² worldwide, slightly larger than the area of ​​Denmark, for comparison purposes. These bodies of water constantly produce carbon dioxide, nitrous oxide, methane and many other gases, by-products of the feeding of fungi and bacteria from the bottom, which eat dead plants and animals from the place.

Consequences of rising lakes

In terms of carbon emissions, the annual increase proportional to the increase in lakes represents 4.8 teragrams (trillion grams), or almost 5 million tonnes of CO₂, equivalent to all emissions by the UK in 2012, for example. The changes, according to scientists, are bigger and faster than normal.

In addition to greenhouse gases, the ecosystem and access to water resources have also been suffering from these changes. New knowledge about the extent and dynamics of lakes in the world has allowed us to better calculate their potential to emit carbon dioxide.

For the research that collates this data, satellite imaging technologies and deep learning algorithms were used, covering 3.4 million lakes around the world. Small lakes (less than 1 km²), including, are especially important for the calculation of greenhouse gases, since they generate a high volume of emissions in relation to their size.

Influence of small lakes

The smaller lakes end up representing only 15% of the global coverage of these bodies of water, but they are responsible for about 45% of the increase in carbon dioxide emissions and 59% of the increase in methane gas emissions in the period studied by the scientists.

According to experts, the emission is disproportionate because, normally, small lakes end up accumulating more organic matter, which ends up being converted into gases. They are also usually shallower, which makes it easier for substances to rise to the surface and then into the atmosphere.

Furthermore, smaller bodies of water are more sensitive to changes in climate and weather, as well as human interventions. Their size and water chemistry, therefore, end up having large variations, which calls for more urgent identification and mapping, as they are also more costly.

More than half of the increase in lake coverage was due to human interference, mainly through reservoir construction; the remainder ends up falling to the account of melting glaciers and permafrost, resulting from global warming.

The data are expected to be useful for future climate models, as a considerable amount of potential greenhouse gases could come from lake surfaces as melting ice around the world continues to increase. With the data, it will also be possible to better estimate freshwater aquatic resources and assess the risk of flooding, as well as better management of sites, as this also impacts on biodiversity.

Source: Nature Communications, University of Copenhagen

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