<?xml version='1.0' encoding='utf-8'?>
<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>Teresa J. Naimo</dc:contributor>
  <dc:contributor>Mark B. Sandheinrich</dc:contributor>
  <dc:creator>Bradley E. Frazier</dc:creator>
  <dc:date>1996</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;We examined the temporal and vertical distribution of total ammonia nitrogen (TAN) and un-ionized ammonia nitrogen (NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N) in sediment pore water and compared the temporal patterns of TAN and NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N concentrations in overlying surface water with those in pore water. Pore water was obtained by core extraction and subsequent centrifugation. We measured TAN concentrations and calculated NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N concentrations from February through October 1993 at four sites in Pool 8, upper Mississippi River, at depths of 0 to 4, 4 to 8, and 8 to 12 cm below the sediment-water interface. Total ammonia nitrogen and NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N concentrations were significantly different among sampling dates (&lt;/span&gt;&lt;i&gt;p&lt;/i&gt;&lt;span&gt;&amp;nbsp;= 0.0001) and sediment depths (&lt;/span&gt;&lt;i&gt;p&lt;/i&gt;&lt;span&gt;&amp;nbsp;= 0.0001). Concentrations of TAN and NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N in surface water were significantly less than those in pore water from all sediment depths (&lt;/span&gt;&lt;i&gt;p&lt;/i&gt;&lt;span&gt;&amp;nbsp;&amp;lt; 0.05). Concentrations in pore water ranged from 0.07 to 4.0 mg TAN/L and less than 1 to 20 μg NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N/L in winter, and from 0.07 to 10.0 mg TAN/L and 1 to 175 μg NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N/L in summer; greatest concentrations were usually found in sediments 8 to 12 cm deep. Annual mean TAN concentrations were positively correlated with silt and volatile solids content and were negatively correlated with sand content. Because of the high variability of TAN and NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N concentrations in pore water, sediment toxicity studies should take into account the season and the depth at which sediments are obtained. The annual mean NH&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;-N concentration in pore water at one site (55 μg/L) exceeded the concentration (30 μg/L) demonstrated to inhibit growth of fingernail clams in laboratory studies. However, these concentrations apparently were not lethal, as evidenced by the presence of fingernail clams at this site.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1002/etc.5620150204</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Society of Environmental Toxicology and Chemistry</dc:publisher>
  <dc:title>Temporal and vertical distribution of total ammonia nitrogen and un-ionized ammonia nitrogen in sediment pore water from the upper Mississippi River</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>