Nitrous oxide emission by aquatic macrofauna

doi:10.1073/pnas.0808228106

Nitrous oxide emission by aquatic macrofauna

Sections of ^aMicrobiology and
^bPlant Biology, Department of Biological Sciences, Aarhus University, DK-8000 Aarhus C, Denmark

Edited by Robert W. Howarth, Cornell University, Ithaca, NY, and accepted by the Editorial Board January 26, 2009 (received for review August 20, 2008)

Abstract

A large variety of aquatic animals was found to emit the potent greenhouse gas nitrous oxide when nitrate was present in the environment. The emission was ascribed to denitrification by ingested bacteria in the anoxic animal gut, and the exceptionally high N₂O-to-N₂ production ratio suggested delayed induction of the last step of denitrification. Filter- and deposit-feeding animal species showed the highest rates of nitrous oxide emission and predators the lowest, probably reflecting the different amounts of denitrifying bacteria in the diet. We estimate that nitrous oxide emission by aquatic animals is quantitatively important in nitrate-rich aquatic environments like freshwater, coastal marine, and deep-sea ecosystems. The contribution of this source to overall nitrous oxide emission from aquatic environments might further increase because of the projected increase of nitrate availability in tropical regions and the numeric dominance of filter- and deposit-feeders in eutrophic ecosystems.

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Footnotes

¹To whom correspondence should be sent at the present address:
Microsensor Group, Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany.
E-mail: pstief{at}mpi-bremen.de
Author contributions: P.S., L.P.N., and A.S. designed research; P.S. and M.P. performed research; H.B. contributed new reagents/analytic tools; P.S., M.P., L.P.N., H.B., and A.S. analyzed data; and P.S., M.P., L.P.N., H.B., and A.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. R.W.H. is a guest editor invited by the Editorial Board.
Data deposition: The partial narG and nosZ sequences described in this article have been deposited in GenBank under accession nos. EU052963–EU053020 and EU053069–EU053075, respectively.
This article contains supporting information online at www.pnas.org/cgi/content/full/0808228106/DCSupplemental.
Freely available online through the PNAS open access option.