| dc.contributor.author | Punshon, Stephen. | en_US |
| dc.date.accessioned | 2014-10-21T12:37:18Z | |
| dc.date.available | 2004 | |
| dc.date.issued | 2004 | en_US |
| dc.identifier.other | AAINQ89813 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/54620 | |
| dc.description | Nitrous oxide (N2O) is a biogenic trace gas that contributes to climate warming and stratospheric ozone destruction. The coastal ocean is a globally important source of N2O, the magnitude of which could potentially be affected by human influence. Nitrification is known to yield N2O as a byproduct, and denitrification can act as both a source and sink for N2O, yet the relative importance of these microbial pathways remains poorly understood. This study seeks to resolve the role of these processes in coastal marine N2O production and consumption, particularly in response to changes in oxygen concentration. A stable isotope technique was developed for measuring N2O production and consumption rates in seawater. Samples were incubated with the appropriate 15N-labelled substrate (15NH4+, 15NO 3- and 15N2O), and the concentration of 15N2O was monitored by purge-and-trap gas-chromatography/mass-spectrometry. A novel internal standard (15 N218O) was employed to maintain a high level of analytical precision. Some trial measurements were made in the Labrador Sea during the spring bloom. This region was found to be slightly supersaturated in N2O at the time of the study (mean: 105%) with nitrification a contributing factor. | en_US |
| dc.description | An 18 month long study of the Bedford Basin, Halifax Harbour, showed that nitrification was the predominant N2O production mechanism, with rates ranging from undetectable up to 1.6 nmol N2O L -1 d-1 (about 8% d-1). The yield of N2O from ammonium oxidation (mol N2O:mol NH4+) displayed an inverse non-linear relationship with dissolved oxygen, varying from 0.01--0.11% over the range 27--290 mumol O2 L-1. N2O production from denitrification (range 20--40 pmols N2O L-1 d-1) was detectable on only two occasions coinciding with oxygen minima, and N2O loss was only observed at an oxygen level of 2.5 mumol O2 L-1. These measurements were supplemented by a series of laboratory experiments investigating denitrification processes. Net 15N2O production from nitrate reduction was restricted to ∼ 7--3 mumol O2 L-1. Consumption predominated at lower oxygen concentrations, resulting in net N2O loss rates of up to 10% d-1. These findings suggest that the increasing incidence of eutrophication, and oxygen depletion, in the coastal margin may have important implications for N2O cycling. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2004. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Biology, Oceanography. | en_US |
| dc.title | Nitrous oxide production and consumption in seawater. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
