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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>Bryan D. Downing</dc:contributor>
  <dc:contributor>Carol Kendall</dc:contributor>
  <dc:contributor>Randy A. Dahlgren</dc:contributor>
  <dc:contributor>Tamara E.C. Kraus</dc:contributor>
  <dc:contributor>John Franco Saraceno</dc:contributor>
  <dc:contributor>Robert G. M. Spencer</dc:contributor>
  <dc:contributor>Brian A. Bergamaschi</dc:contributor>
  <dc:creator>Brian A. Pellerin</dc:creator>
  <dc:date>2009</dc:date>
  <dc:description>&lt;p&gt;1. We investigated diurnal nitrate (NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;) concentration variability in the San Joaquin River using an&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;in situ&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;optical NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;sensor and discrete sampling during a 5‐day summer period characterized by high algal productivity. Dual NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;isotopes (δ&lt;sup&gt;15&lt;/sup&gt;N&lt;sub&gt;NO3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and δ&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;NO3&lt;/sub&gt;) and dissolved oxygen isotopes (δ&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;DO&lt;/sub&gt;) were measured over 2 days to assess NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;sources and biogeochemical controls over diurnal time‐scales.&lt;/p&gt;&lt;p&gt;2. Concerted temporal patterns of dissolved oxygen (DO) concentrations and δ&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;DO&lt;/sub&gt;were consistent with photosynthesis, respiration and atmospheric O&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;exchange, providing evidence of diurnal biological processes independent of river discharge.&lt;/p&gt;&lt;p&gt;3. Surface water NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;concentrations varied by up to 22% over a single diurnal cycle and up to 31% over the 5‐day study, but did not reveal concerted diurnal patterns at a frequency comparable to DO concentrations. The decoupling of δ&lt;sup&gt;15&lt;/sup&gt;N&lt;sub&gt;NO3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and δ&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;NO3&lt;/sub&gt;isotopes suggests that algal assimilation and denitrification are not major processes controlling diurnal NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;variability in the San Joaquin River during the study. The lack of a clear explanation for NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;variability likely reflects a combination of riverine biological processes and time‐varying physical transport of NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;from upstream agricultural drains to the mainstem San Joaquin River.&lt;/p&gt;&lt;p&gt;4. The application of an&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;in situ&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;optical NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;sensor along with discrete samples provides a view into the fine temporal structure of hydrochemical data and may allow for greater accuracy in pollution assessment.&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1111/j.1365-2427.2008.02111.x</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Wiley</dc:publisher>
  <dc:title>Assessing the sources and magnitude of diurnal nitrate variability in the San Joaquin River (California) with an in situ optical nitrate sensor and dual nitrate isotopes</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>