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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>C. Zamora</dc:contributor>
  <dc:contributor>H. Essaid</dc:contributor>
  <dc:contributor>J.T. Wilson</dc:contributor>
  <dc:contributor>H.M. Johnson</dc:contributor>
  <dc:contributor>M.J. Brayton</dc:contributor>
  <dc:contributor>J. R. Vogel</dc:contributor>
  <dc:creator>L.J. Puckett</dc:creator>
  <dc:date>2008</dc:date>
  <dc:description>&lt;p&gt;Although numerous studies of hyporheic exchange and denitrification have been conducted in pristine, high-gradient streams, few studies of this type have been conducted in nutrient-rich, low-gradient streams. This is a particularly important subject given the interest in nitrogen (N) inputs to the Gulf of Mexico and other eutrophic aquatic systems. A combination of hydrologic, mineralogical, chemical, dissolved gas, and isotopic data were used to determine the processes controlling transport and fate of NO&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;in streambeds at five sites across the USA. Water samples were collected from streambeds at depths ranging from 0.3 to 3 m at three to five points across the stream and in two to five separate transects. Residence times of water ranging from 0.28 to 34.7 d m&lt;sup&gt;−1&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;in the streambeds of N-rich watersheds played an important role in allowing denitrification to decrease NO&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;concentrations. Where potential electron donors were limited and residence times were short, denitrification was limited. Consequently, in spite of reducing conditions at some sites, NO&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;was transported into the stream. At two of the five study sites, NO&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;in surface water infiltrated the streambeds and concentrations decreased, supporting current models that NO&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;would be retained in N-rich streams. At the other three study sites, hydrogeologic controls limited or prevented infiltration of surface water into the streambed, and ground-water discharge contributed to NO&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;loads. Our results also show that in these low hydrologic-gradient systems, storm and other high-flow events can be important factors for increasing surface-water movement into streambeds.&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.2134/jeq2006.0550</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>ACSESS</dc:publisher>
  <dc:title>Transport and fate of nitrate at the ground-water/surface-water interface</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>