See more from this Session: General Soil Biology & Biochemistry: II
Wednesday, October 19, 2011
Henry Gonzalez Convention Center, Hall C, Street Level
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 NO3− input. 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.