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Aquatic animals that feed on lake and stream bottom sediments burp out small amounts of nitrous oxide, a potent greenhouse gas, a new study finds.

While the biological emissions from these critters pales in comparison to the nitrous oxide emitted by fossil fuel burning, their contribution could increase as more and more nitrogen-rich fertilizer runs off into lakes, streams and seas, the authors of the study said.

Nitrous oxide (N2O) is more commonly known to anyone who has sat in the dentist's chair as laughing gas.

In the atmosphere it is a powerful greenhouse gas, packing about 310 times the punch as the same weight of carbon dioxide (though carbon dioxide is still the bigger driver because there is much more of it).

Studies of soil-dwelling earthworms had showed that the creepy crawlies emitted nitrous oxide because of the nitrogen-converting microbes they gobbled up into their guts with every mouthful of soil.

Peter Stief, of the Max Planck Institute for Marine Microbiology in Germany, and his colleagues noticed that no one had ever looked for similar nitrous oxide emission in aquatic animals, so that's where they turned their attention.

"We were looking for an analogy in the aquatic system," Stief said.