Denitrification in sediment-water systems is a predominant process in the removal of nitrogen from wetlands and sediments receiving recycled water. In this study the impact of cadmium (Cd), copper (Cu) and zinc (Zn) on denitrification was examined for a wetland sediment receiving recycled water. Results from the study showed that application of 100 mg Cd kg−1 sediment had no effect (P<0.05) on denitrification (161±2.7 mg N kg−1 sediment) compared to the control (162±2.4 mg N kg−1 sediment) which did not receive Cd, Cu or Zn. Addition of 100 mg Cu or Zn kg−1 sediment significantly increased denitrification (170±1.8 and 168±2.7 mg N2O-N kg−1 sediment for Cu and Zn, respectively) compared to the control treatment. Addition of Cd, Cu or Zn at 500 or 1000 mg kg−1 sediment significantly decreased (P<0.05) total denitrification compared to the control and treatments, which received 100 mg Cd, Cu or Zn kg−1 sediment. For a given heavy metal concentration the largest denitrification inhibition occurred with Cd (30.9%) followed by Zn (24.9%) and Cu (18.9%) over a period of seven days. The amount of ammonium in the sediment water increased in all treatments receiving Cd, Cu or Zn and the concentration increased as the concentration of Cd, Cu or Zn increased in the sediment-water environment. For a given heavy metal concentration, the largest increase in ammonium occurred in treatments receiving Cd (31.1±0.9 mg N kg−1 sediment) followed by Zn (24.8±0.5 mg N kg−1 sediment) and Cu (17.0±0.3 mg N kg−1 sediment). Denitrification inhibition was linearly related to the concentration of ammonium in sediment water (r2=0.928). In general, the study showed that the addition of Cd, Cu or Zn inhibited denitrification and increased the concentration of ammonium in the sediment-water environment.

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