A number of water-dwelling species emit the greenhouse gas nitrous oxide, researchers announced today in the journal Proceedings of the National Academy of Sciences . Although nitrous oxide is low in concentration globally, it is considered the fourth largest contributor to climate change. This is due to its potency: in a hundred year period nitrous oxide by weight packs 310 times more punch as a greenhouse gas than carbon dioxide.
The researchers found that while numerous aquatic species emit nitrous oxide, the largest emitters are bottom and deposit feeders like snails, mussels, mayflies, midges, and clams. The cause of the greenhouse gas emission was found to be bacteria in the animal’s stomach that went through a process known as denitrification, in which nitrate becomes nitrous oxide,.
The emissions are most present in aquatic environments with high levels of nitrate pollution from agriculture, such as lakes, streams, and marine coasts. Nitrate-heavy ecosystems are also dominated by bottom and deposit feeders.
The continuing spread of agriculture in the tropics led the researchers to warn that they expect nitrous oxide emissions to become a larger issue in the tropics. Due to this they encouraged studies of the nitrous oxide emissions of aquatic species in the region. Certain ecosystems in the tropics, such as mangroves, already have a high output of nitrous oxide.
The researchers believe their findings should “prove valuable for predicting the effect of local management of nitrate pollution”. They suggest two methods to curb these emissions of nitrous oxide: reducing nitrate pollution in aquatic ecosystems and removing excess bottom and deposit feeders so that the ecosystem is more balanced.
The study looked at 21 species in seven different sites, including rivers, creeks, lakes and the seashore.
CITATION: Peter Stief, Morten Poulsen, Lars Peter Nielsen, Hans Brix, and Andreas Schramm (2009). ” Nitrous oxide emission by aquatic macrofauna ” PNAS March 2, 2009 www.pnas.org_cgi_doi_10.1073_pnas.0808228106
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