Technical Note: Simultaneous measurement of sedimentary N<sub>2</sub> and N<sub>2</sub>O production and a modified <sup>15</sup>N isotope pairing technique
Dinitrogen (N<sub>2</sub>) and/or nitrous oxide (N<sub>2</sub>O) are produced through denitrification, anaerobic ammonium oxidation (anammox) or nitrification in sediments, of which entangled processes complicate the absolute rate estimations of gaseous nitrogen production fr...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-12-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/10/7847/2013/bg-10-7847-2013.pdf |
| Summary: | Dinitrogen (N<sub>2</sub>) and/or nitrous oxide (N<sub>2</sub>O) are produced through
denitrification, anaerobic ammonium oxidation (anammox) or nitrification in
sediments, of which entangled processes complicate the absolute rate
estimations of gaseous nitrogen production from individual pathways. The
classical isotope pairing technique (IPT), the most common <sup>15</sup>N nitrate
enrichment method to quantify denitrification, has recently been modified by
different researchers to (1) discriminate between the N<sub>2</sub> produced by
denitrification and anammox or to (2) provide a more accurate denitrification
rate under considering production of both N<sub>2</sub>O and N<sub>2</sub>. In case 1,
the revised IPT focused on N<sub>2</sub> production being suitable for the
environments of a low N<sub>2</sub>O-to-N<sub>2</sub> production ratio, while in case 2,
anammox was neglected. This paper develops a modified method to refine
previous versions of IPT. Cryogenic traps were installed to separately
preconcentrate N<sub>2</sub> and N<sub>2</sub>O, thus allowing for subsequent measurement
of the two gases generated in one sample vial. The precision is better than
2% for N<sub>2</sub> (<i>m/z</i> 28, <i>m/z</i> 29 and <i>m/z</i> 30), and 1.5% for
N<sub>2</sub>O (<i>m/z</i> 44, <i>m/z</i> 45 and <i>m/z</i> 46). Based on the six <i>m/z</i> peaks of
the two gases, the <sup>15</sup>N nitrate traceable processes including N<sub>2</sub> and
N<sub>2</sub>O from denitrification and N<sub>2</sub> from anammox were estimated.
Meanwhile, N<sub>2</sub>O produced by nitrification was estimated via the
production rate of unlabeled <sup>44</sup>N<sub>2</sub>O. To validate the applicability
of our modified method, incubation experiments were conducted using sediment
cores taken from the Danshuei Estuary in Taiwan. Rates of the aforementioned
nitrogen removal processes were successfully determined. Moreover, N<sub>2</sub>O
yield was as high as 66%, which would significantly bias previous IPT
approaches if N<sub>2</sub>O was not considered. Our modified method not only
complements previous versions of IPT but also provides more comprehensive
information to advance our understanding of nitrogen dynamics of the
water–sediment interface. |
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| ISSN: | 1726-4170 1726-4189 |