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This article in JEQ

  1. Vol. 28 No. 1, p. 263-269
     
    Received: Feb 13, 1998


    * Corresponding author(s): xue@unlinfo.unl.edu
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doi:10.2134/jeq1999.00472425002800010032x

In Situ Measurements of Denitrification in Constructed Wetlands

  1. Yuan Xue *,
  2. David A. Kovacic,
  3. Mark B. David,
  4. Lowell E. Gentry,
  5. Richard L. Mulvaney and
  6. Charles W. Lindau
  1. Dep. of Natural Resources & Environmental Sciences, Univ. of Illinois, W503 Turner Hall, 1102 S. Goodwin Av., Urbana, IL 61801;
    Dep. of Landscape Architecture, 101 Temple Buell Hall, 611 E. Lorado Taft Dr., Champaign, IL 61820;
    Nuclear Science Center, Louisiana State Univ., Baton Rouge, LA 70803.

Abstract

Abstract

Quantitative estimates of denitrification are needed in designing artificial wetlands to optimize nitrate (NO3) removal. Acetylene blockage and 15N-tracer methods were employed to quantify denitrification in constructed wetlands receiving agricultural tile drainage, using plastic tubes to enclose in situ mesocosms. Estimates were also made through NO3 disappearance from mesocosm water columns. The 15N and C2H2 methods yielded comparable rates. At 4 to 25°C, and with 9 to 20 mg NO3-N L−1 initially in the mesocosm water columns, denitrification rates by the C2H2 technique ranged from 2.0 to 11.8 mg N m−2 h−1. In the June–August 15N experiment, when wetland NO3 was below detection, a time series of denitrification rates followed a bell-shaped curve after a pulse input of NO3 (∼15 mg N L−1, 70 atom% 15N). The maximal denitrification rate (9.3 mg N m−1 h−1) was observed 5.4 d after the pulse. After 33 d, 58% of the 15NO3 had been evolved as N2, only ∼0.1% as N2O; 6 to 10% was recovered in plant shoots and as organic N in the upper 5 cm of sediment. From 32 to 36% of the 15NO3 spike was not recovered, and presumably seeped into the sediments. The NO3 disappearance rates in the water column ranged from 12 to 63 mg N m−2 h−1 at 11 to 27°C. Because water infiltration carries NO3 through the anaerobic sediment/water interface for denitrification, a subsurface-flow wetland may denitrify more NO3 than a surface-flow wetland.

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