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This article in JEQ

  1. Vol. 27 No. 2, p. 459-466
     
    Received: May 30, 1997


    * Corresponding author(s): m.gibbs@niwa.cri.nz
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doi:10.2134/jeq1998.00472425002700020029x

The Fate of Groundwater Ammonium in a Lake Edge Wetland

  1. Fleur E. Lusby,
  2. Max M. Gibbs *,
  3. A. Bryce Cooper and
  4. Keith Thompson
  1. Dep. of Biological Sciences, Univ. of Waikato, Private Bag 3105, Hamilton, NZ.

Abstract

Abstract

The removal of ammonium—nitrogen (NH4-N) from groundwater flowing through a grey willow (Salix cinerea) and native raupo (Typha orientalis) lake edge wetland was investigated over 10 mo. Monthly groundwater sampling showed that more than 95% of incoming NH2-N was removed by the wetland. Laboratory assays found that the potential for NH4-N removal by nitrification and subsequent denitrification was significantly higher in the organic surface sediments than in deeper, sandy, root zone sediments. In a laboratory 15N-tracer experiment, Salix cinerea and Typha orientalis readily assimilated NH2-N from the root zone and were found to enhance the natural diffusion of NH4-N up through the organic sediment layer and into the overlying water. Estimated rates of removal of NH2-N by coupled nitrification-denitrification and plant assimilation were 8 to 9 mg of N m−2 d−1 and 9 to 46 mg of N m−2 d−1, respectively. Assimilated N, returned to the overlying water-sediment surface via litter fall may be subject to sequential mineralization, nitrification, and denitrification, resulting in gaseous N loss. Sixty-five percent of the 15N in Salix leaf litter was transformed in such a way. The results of this study indicate that plants play a central role in the NH4-N processing capacity of wetlands. The relevance of our findings to constructed wetland design is discussed.

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