312-13 Wood Chip Bioreactor Operation Over Nine Years: Denitrification, Nitrous Oxide Emissions, and Wood Loss.

Poster Number 969

See more from this Division: S03 Soil Biology & Biochemistry
See more from this Session: Soil Carbon, Nitrogen and GHG Fluxes: II
Wednesday, November 3, 2010
Long Beach Convention Center, Exhibit Hall BC, Lower Level
Share |

Thomas Moorman, Timothy Parkin, Dan Jaynes and Thomas Kaspar, USDA-ARS National Laboratory for Agriculture and the Environment, Ames, IA
Nitrate transport in subsurface drainage water from agricultural fields is an important problem in the Midwestern United States and elsewhere.  Denitrification bioreactors are one possible approach for reducing nitrate export, but the sustained operation of these reactors and their emissions of nitrous oxide (N2O) have received little attention. We report on the nitrate removal and denitrification activity of a wood chip-based bioreactor operating in the field for over nine years. Potential denitrification activity, measured using the acetylene block technique, was sustained over the nine year period, which was consistent with nitrate removal from drainage water in the field.  During the last 5 years of bioreactor operation denitrification potentials ranged from 8.2 to 34 mg N kg-1 wood.  Denitrifying bacterial populations were greater in the wood chips than in subsoil at similar depths.  Wood mass decreased through decomposition by 75% at the 90-100 cm depth with a wood half-life of 4.6 years. However, less than 20% of the wood was lost was at 155-170 cm depth and this corresponded to half-life of 36.6 years.  The differential wood loss at these two depths appears to result from sustained anaerobic conditions below the tile drainage line at 120 cm depth.  Pore space concentrations of oxygen and methane also increased at deeper depths within the wood chips.  Loss of N2O from tile water exiting the bioreactor accounted for 0.0062 kg N2O-N kg-1 NO3-N, but this was not significantly higher than N2O loss in tile water from the untreated control plots.
See more from this Division: S03 Soil Biology & Biochemistry
See more from this Session: Soil Carbon, Nitrogen and GHG Fluxes: II