<?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>J.K. Bohlke</dc:contributor>
  <dc:creator>Richard L. Smith</dc:creator>
  <dc:date>2019</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;Concentrations and emissions of greenhouse gases CO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;, CH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;, and N&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O commonly are examined individually in aquatic environments in which each is expected to be relatively important; however, their co-occurrence and dynamic interactions in fluvial settings could provide important information about their controlling biogeochemical processes and potential contributions to global climate change. Spatial and temporal variability of CH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;, N&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O, and CO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;concentrations were measured from June 1999 to September 2003 in two nitrate-rich (40–1200 μM) streams draining agricultural land in the midwestern USA that differed ~13-fold in flow. Seasonal (biweekly), diel (hourly), and transport-oriented (reach-scale) sampling approaches were compared. Dissolved gas concentrations exceeded atmospheric equilibrium values up to 700- and 16-fold, for CH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;&amp;nbsp;and N&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O, respectively. Mean concentrations were higher in the larger stream than in the smaller stream. In both streams, CH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;&amp;nbsp;emissions were generally higher in summer-fall and negatively correlated with flow and NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;concentration while N&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O emissions were generally higher in winter/spring and positively correlated with flow and NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;. In the small stream, diel variations in the concentrations, emissions, and isotopic compositions of CH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;, N&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O, and NO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;resulted from diel variations in sources, sinks, and air-water gas exchange velocities. Seasonal mean total (CH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt; + N&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O) area-normalized emission rates, expressed as CO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;warming potential equivalents, were similar for the two streams, but the total reach-scale emission rate for the larger stream, including CO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;, was about 2.9 times that of the smaller stream (131.6 vs 46.0 kg CO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;equivalents km&lt;/span&gt;&lt;sup&gt;−1&lt;/sup&gt;&lt;span&gt; day&lt;/span&gt;&lt;sup&gt;−1&lt;/sup&gt;&lt;span&gt;, respectively). The CH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;contribution to this flux was 9–28%, despite the relatively high NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;and O&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;concentrations in the streams, indicating contributions from upwelling groundwater or reactions in streambed sediment.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1016/j.scitotenv.2019.05.374</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Elsevier</dc:publisher>
  <dc:title>Methane and nitrous oxide temporal and spatial variability in two midwestern USA streams containing high nitrate concentrations</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>