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Journal of Environmental Quality Abstract - Special Section: Moving Denitrifying Bioreactors Beyond Proof of Concept

Use of a Three-Dimensional Reactive Solute Transport Model for Evaluation of Bioreactor Placement in Stream Restoration

 

This article in JEQ

  1. Vol. 45 No. 3, p. 839-846
     
    Received: June 30, 2015
    Accepted: Jan 18, 2016
    Published: March 21, 2016


    * Corresponding author(s): cui1@umbc.edu
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doi:10.2134/jeq2015.06.0330
  1. Zhengtao Cui *a,
  2. Claire Weltya,
  3. Arthur J. Goldb,
  4. Peter M. Groffmanc,
  5. Sujay S. Kaushald and
  6. Andrew J. Millere
  1. a Dep. of Chemical, Biochemical and Environmental Engineering and Center for Urban Environmental Research and Education, Univ. of Maryland Baltimore County, Baltimore, MD 21250
    b Dep. of Natural Resources Science, Univ. of Rhode Island, Kingston, RI 02881
    c Cary Institute of Ecosystem Studies, Millbrook, NY 12545
    d Dep. of Geology and Earth System Science Interdisciplinary Center, Univ. of Maryland, College Park, MD 20742
    e Dep. of Geography and Environmental Systems and Center for Urban Environmental Research and Education, Univ. of Maryland Baltimore County, Baltimore, MD 21250
Core Ideas:
  • We used a 3D reactive transport model to design subsurface bioreactor placement.
  • Nitrate-N removal rates of strategically placed bioreactors more than doubled.
  • Bioreactor nitrate-N removal was nitrate limited.
  • Optimized bioreactors were 50% of the length of nonoptimized bioreactors.
  • Bioreactors achieved up to 85% denitrification of nonoptimized bioreactors.

Abstract

A three-dimensional groundwater flow and multispecies reactive transport model was used to strategically design placement of bioreactors in the subsurface to achieve maximum removal of nitrate along restored stream reaches. Two hypothetical stream restoration scenarios were evaluated over stream reaches of 40 and 94 m: a step-pool scenario and a channel re-meandering scenario. For the step-pool scenario, bioreactors were placed at locations where mass fluxes of groundwater and nitrate were highest. Bioreactors installed over 50% of the total channel length of a step-pool scenario (located to intercept maximum groundwater and nitrate mass flux) removed nitrate-N entering the channel at a rate of 36.5 kg N yr−1 (100 g N d−1), achieving about 65% of the removal of a whole-length bioreactor. Bioreactor placement for the re-meandering scenario was designed using a criterion of either highest nitrate mass flux or highest groundwater flux, but not both, because they did not occur together. Bioreactors installed at maximum nitrate flux locations (53% of the total channel length) on the western bank removed nitrate-N entering the channel at 62.0 kg N yr−1 (170 g N d−1), achieving 85% of nitrate-N removal of whole-length bioreactors for the re-meandering scenario. Bioreactors installed at maximum groundwater flux locations on the western bank along approximately 40% of the re-meandering channel achieved about 65% of nitrate removal of whole-length bioreactors. Placing bioreactors at maximum nitrate flux locations improved denitrification efficiency. Due to low groundwater velocities, bioreactor nitrate-N removal was found to be nitrate limited for all scenarios.

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