Managing Global Resources for a Secure Future

2017 Annual Meeting | Oct. 22-25 | Tampa, FL

84-3 Direct and Indirect Nitrous Oxide Emissions from Saturated Riparian Buffers and Woodchip Bioreactors: Are We Trading a Water Quality Problem for and Air Quality Problem?.

See more from this Division: ASA Section: Environmental Quality
See more from this Session: Enhanced-Denitrification Technologies (includes student competition)

Monday, October 23, 2017: 2:05 PM
Tampa Convention Center, Room 4

Morgan P. Davis1, Thomas M. Isenhart1, Dan B. Jaynes2, Timothy Parkin2, Tyler A. Groh1, Michelle L Soupir3 and Kirsten Hofmockel4, (1)Natural Resources Ecology and Management, Iowa State University, Ames, IA
(2)1015 N. University Blvd., USDA-ARS National Laboratory for Agriculture and the Environment, Ames, IA
(3)Agricultural and Biological Engineering, Iowa State University, Ames, IA
(4)Environmental Molecular Sciences Laboratory, Department of Energy, Richland, WA
Abstract:
Edge-of-field conservation practices have the potential to remove large quantities of nitrate (NO3) from tile drained water. Practices including saturated riparian buffers (SRBs) and woodchip bioreactors utilize microbial denitrification to convert NO3 to nitrogen gas. Unfortunately, incomplete denitrification can result in nitrous oxide (N2O) production. The global warming potential of N2O is 298 times that of carbon dioxide and N2O is considered a major contributor to global climate change. The objective of this study was to quantify both direct and indirect N2O emissions from SRBs and woodchip bioreactors in Central Iowa. Direct emissions were measured from the soil surface of each conservation practice. Indirect emissions were measured as dissolved N2O concentrations from water flowing through SRBs and bioreactors. For comparison, N2O emissions were measured from conventional unsaturated riparian buffers and agricultural fields adjacent to the SRBs. Direct emissions from SRBs were only significantly greater than the unsaturated counterparts at one site, in one year. Direct emissions from both SRBs and bioreactors were significantly less than field emissions. Furthermore, N2O production was only a small fraction of the total NO3 removed, suggesting the majority of NO3 was taken up by plants or completely denitrified. Dissolved N2O concentrations in the SRBs were greatest closest to the distribution tile and negligible at the stream edge. Comparatively, dissolved N2O concentrations in the bioreactors increased from the inlet to the outlet. The increase of dissolved N2O from bioreactors increases the potential for indirect emissions after the treated water enters surface waters. Significantly reducing nitrate loss to surface waters is going to take a suite of conservation practices and it is important to evaluate potential pitfalls before mass implementation. The inclusion of both direct and indirect N2O emissions is essential for evaluating the global warming potential of edge-of field conservation practices.

See more from this Division: ASA Section: Environmental Quality
See more from this Session: Enhanced-Denitrification Technologies (includes student competition)