356-6 Long-Term Nitrate Removal In a Denitrification Wall.



Wednesday, October 19, 2011
Henry Gonzalez Convention Center, Hall C, Street Level

Lauren M. Long, Earth and Ocean Sciences, University of Waikato, Hamilton, New Zealand, Louis A. Schipper, University of Waikato, Hamilton, New Zealand and Denise A. Bruesewitz, Biological Sciences, University of Waikato, Hamilton, New Zealand
Denitrification walls are a low-cost approach for removing excess nitrate (NO3) from shallow groundwater.  Denitrification walls need to be maintenance-free for a number of years to remain cost effective, but little is known about the longevity of these walls.  In this study, a denitrification wall constructed on a New Zealand dairy farm in 1996 was monitored to determine NO3 removal by the wall 14 years after installation.  The farm has been spray-irrigated with effluent from the nearby dairy factory for over 30 years.  The NO3 input to the wall had decreased since first constructed from an average of 9 mg N L-1 to 2.6 mg N L-1 in year 14, which was attributed to a change in upslope irrigation practices on the farm. After 14 years, the denitrification wall removed 92% of NO3input.   Denitrifying enzyme activity (DEA) remained high after 14 years at 695 ng N g-1 hr-1 (compared to 740 ng N g-1 hr-1 in year 1) and the wall remained NO3 limited.  However, total C in the wall has decreased by half, from an average of 4.7 g C kg-1 soil in year 1 to 2.2 g C kg-1 soil in year 14.  By applying a first order decay curve to the total C data, it was determined that total C in the denitrification wall would not be depleted for 66 years, but it is unclear at what amount of total C that denitrification would become limited.  This long-term study suggested that denitrification walls are cost effective solutions for remediating groundwater NO3 pollution, as they can be effective for a number of years without any maintenance.
See more from this Division: S03 Soil Biology & Biochemistry
See more from this Session: General Soil Biology & Biochemistry: II