Although such small ponds make up only 8.6 per cent of the surface area of the world's lakes and ponds, they account for 15.1 per cent of carbon dioxide (CO2) emissions and 40.6 per cent of diffusive methane (CH4) emissions.
"Our study is the first to include these small ponds in global estimates of CO2 and CH4 emissions, largely because they are difficult to map and were thought to play a small role in carbon cycling," said Meredith Holgerson from Yale University in US.
They found that concentrations were greatest in smaller ponds and decreased as the ponds and lakes grew larger.
The reason for this has to do with the physical makeup of very small ponds and the way they cycle carbon.
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Small ponds have a high perimetre-to-surface-area ratio, for example, and accumulate a higher load of terrestrial carbon - so-called 'leaf litter,' sediment particles and other material.
Small ponds also tend to be shallow, which means their terrestrial carbon loads are highly concentrated compared to larger lakes, researchers said.
"That makes small ponds an important player in the carbon cycle," said Holgerson.
The findings suggest that small ponds are likely breaking down terrestrial carbon that is not factored into assessments of the world's carbon stocks and fluxes.
"The carbon cycling that happens in freshwater systems needs to be accounted for in estimates of terrestrial production," said Holgerson.
The findings were published in the journal Nature Geoscience.