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<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Julie Granger</dc:contributor>
  <dc:contributor>Craig R. Tobias</dc:contributor>
  <dc:contributor>J.K. Bohlke</dc:contributor>
  <dc:contributor>Richard L. Smith</dc:contributor>
  <dc:creator>Danielle S. Boshers</dc:creator>
  <dc:date>2019</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;Measurements of the stable isotope ratios of nitrogen (&lt;/span&gt;&lt;sup&gt;15&lt;/sup&gt;&lt;span&gt;N/&lt;/span&gt;&lt;sup&gt;14&lt;/sup&gt;&lt;span&gt;N) and oxygen (&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O/&lt;/span&gt;&lt;sup&gt;16&lt;/sup&gt;&lt;span&gt;O) in nitrate (NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;) enable identification of sources, dispersal, and fate of natural and contaminant NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;&amp;nbsp;in aquatic environments. The&amp;nbsp;&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O/&lt;/span&gt;&lt;sup&gt;16&lt;/sup&gt;&lt;span&gt;O of NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;&amp;nbsp;produced by nitrification is often assumed to reflect the proportional contribution of oxygen atom sources, water, and molecular oxygen, in a 2:1 ratio. Culture and seawater incubations, however, indicate oxygen isotopic equilibration between nitrite (NO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;) and water, and kinetic isotope effects for oxygen atom incorporation, which modulate the NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O/&lt;/span&gt;&lt;sup&gt;16&lt;/sup&gt;&lt;span&gt;O produced during nitrification. To investigate the influence of kinetic and equilibrium effects on the isotopic composition of NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;&amp;nbsp;produced from the nitrification of ammonia (NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;), we incubated streamwater supplemented with ammonium (NH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;) and increments of&amp;nbsp;&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O-enriched water. Resulting NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O/&lt;/span&gt;&lt;sup&gt;16&lt;/sup&gt;&lt;span&gt;O ratios showed (1) a disproportionate sensitivity to the&amp;nbsp;&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O/&lt;/span&gt;&lt;sup&gt;16&lt;/sup&gt;&lt;span&gt;O ratio of water, mediated by isotopic equilibration between water and NO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;, as well as (2) kinetic isotope discrimination during O atom incorporation from molecular oxygen and water. Empirically, the NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O/&lt;/span&gt;&lt;sup&gt;16&lt;/sup&gt;&lt;span&gt;O ratios thus produced fortuitously converge near the&amp;nbsp;&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O/&lt;/span&gt;&lt;sup&gt;16&lt;/sup&gt;&lt;span&gt;O ratio of water. More elevated NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;18&lt;/sup&gt;&lt;span&gt;O/&lt;/span&gt;&lt;sup&gt;16&lt;/sup&gt;&lt;span&gt;O values commonly reported in soils and oxic groundwater may thus derive from processes additional to nitrification, including NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;&lt;span&gt;&amp;nbsp;reduction.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1021/acs.est.8b03386</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>ACS</dc:publisher>
  <dc:title>Constraining the oxygen isotopic composition of nitrate produced by nitrification</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>