DENITRIFICATION POTENTIAL OF SOILS FROM CONSTRUCTED AND NATURAL WETLANDS

Laboratory experiments were conducted to determine the NO3- removal (reduction) potential of wetland soils currently used for the disposal of reclaimed wastewater. Surface soil samples were collected, incubated under anoxic conditions with two levels of NO3-, and the evolution of N2O was measured with time. Denitrification rates ranged from 0.06 to 0.92 g N m-2 day-1, when 10 mg NO3-N per kg soil was added. Complete reduction of NO3- to N2 occurred in the soils collected from two constructed wetlands (mineral soils) and one natural wetland (organic soil). However, the final reduction step was inhibited in the soils collected from two wetlands with organic soils. The inhibition was most likely the result of the lower pH of these soils. The results suggest that the addition of wastewater enhances the potential for denitrification in these soils.