In situ measurements of denitrification in constructed wetlands

Yuan Xue, David A. Kovacic, Mark B. David, Lowell E. Gentry, Richard L. Mulvaney, Charles W. Lindau

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Quantitative estimates or 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- (approximately 15 mg N L-1, 70 atom% 15N). The maximal denitrification rate (9.3 mg N m-2 h-1) was observed 5.4 d after the pulse. After 33 d, 58% of the 15NO3- had been evolved as N2, only approximately 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.

Original languageEnglish (US)
Pages (from-to)263-269
Number of pages7
JournalJournal of Environmental Quality
Issue number1
StatePublished - 1999

ASJC Scopus subject areas

  • Environmental Engineering
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution
  • Management, Monitoring, Policy and Law


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