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This article in JEQ

  1. Vol. 31 No. 3, p. 1017-1024
     
    Received: Mar 27, 2001


    * Corresponding author(s): agold@uri.edu
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doi:10.2134/jeq2002.1017

In Situ Push–Pull Method to Determine Ground Water Denitrification in Riparian Zones

  1. Kelly Addya,
  2. D. Q. Kellogga,
  3. Arthur J. Gold *a,
  4. Peter M. Groffmanb,
  5. Gina Ferendoa and
  6. Carl Sawyerb
  1. a Dep. of Natural Resources Science, Coastal Institute in Kingston, Univ. of Rhode Island, Kingston, RI 02881
    b Dep. of Plant Sciences, Woodward Hall, Univ. of Rhode Island, Kingston, RI 02881

Abstract

To quantify ground water denitrification in discrete locations of riparian aquifers, we modified and evaluated an in situ method based on conservative tracers and 15N-enriched nitrate. Ground water was “pushed” (i.e., injected) into a mini-piezometer and then “pulled” (i.e., extracted) from the same mini-piezometer after an incubation period. This push–pull method was applied in replicate mini-piezometers at two Rhode Island riparian sites, one fresh water and one brackish water. Conservative tracer pretests were conducted to determine incubation periods, ranging from 5 to 120 h, to optimize recovery of introduced plumes. For nitrate push–pull tests, we used two conservative tracers, sulfur hexafluoride and bromide, to provide insight into plume recovery. The two conservative tracers behaved similarly. The dosing solutions were amended with 15N-enriched nitrate that enabled us to quantify the mass of denitrification gases generated during the incubation period. The in situ push–pull method detected substantial denitrification rates at a site where we had previously observed high denitrification rates. At our brackish site, we found high rates of ground water denitrification in marsh locations and minimal denitrification in soils fringing the marsh. The push–pull method can provide useful insights into spatial and temporal patterns of denitrification in riparian zones. The method is robust and results are not seriously affected by dilution or degassing from ground water to soil air. In conjunction with measurements of ground water flowpaths, this method holds promise for evaluating the influence of site and management factors on the ground water nitrate removal capacity of riparian zones.

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Copyright © 2002. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.31:1017–1024.