Burping fish are destroying the environment

Now it looks like we can blame burps, not just from cattle but from aquatic animals too, for the greenhouse effect.

Helen Scales: Animals that live in rivers, lakes and in the seas emit burps or farts, if you like, of nitrous oxide which is a potent greenhouse gas, and a new study has shown for the first time this is what’s going on.

Chris Smith: It’s a laughing gas, nitrous oxide, isn’t it?

Helen: It is, absolutely.

Chris: So tell us about these animals. Why are they producing it?

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Goldfish and bubbles

Helen: Well, it’s coming from their guts of these various creatures, and it’s actually the bacteria inside their guts that are beginning to break down nitrates which are taken in from the environment. This was a study in the journal, PNAS, led by Peter Steef and colleagues from Aarhus University in Denmark, and they went out and collected 21 different types of animals from lakes and rivers and from coastal areas in Denmark and in Germany, and that included various invertebrates like various molluscs and insect larvae, including something called Chironomus plumosus, which is a midge.

What Steef and his team did, they brought these animals into the lab, and they measured the gas that was coming out of them, and that's both from intact animals, still alive, and from their dissected guts, and they discovered that nitrous oxide is indeed produced by a variety of species, in particular ones that filter their food from the water, or scoop and scrape it up from muddy sediments, and they’re called deposit feeders.

Chris: Now you mentioned earlier that what they’re doing is metabolising nitrates that are in the water. So does that mean there’s a strong association between putting fertiliser on fields and then these animals putting this out as nitrous oxide in the air?

Helen: Yes, this is what’s particularly worrying about this is we know that the amount of nitrate in rivers and seas is going up, and that’s mostly, like you say, due to fertiliser. We put nitrates on the land, so we can grow bigger crops faster, but they do wash out in rainwater into these water systems. And in this particular case, having more nitrate could end up leading to more nitrous oxide being emitted by these creatures.

Chris: And the bottom line is less fertiliser on fields means less nitrous oxide coming out of these bacteria, is it?

Helen: That should be the case, and it’s certainly points the way towards another reason why we really have to look at what we’re putting on the land and how that’s affecting our ecosystems and eventually maybe the global climate.

Listen to the whole edition of Breaking Science, originally broadcast on BBC Radio Five Live, March 2009

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