Methods for measuring denitrification: diverse approaches to a difficult problem.
Denitrification, the reduction of the nitrogen (N) oxides, nitrate (NO3-) and nitrite (NO2-), to the gases nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2), is important to primary production, water quality, and the chemistry and physics of the atmosphere at ecosystem, landscape, regional, and global scales. Unfortunately, this process is very difficult to measure, and existing methods are problematic for different reasons in different places at different times. In this paper, we review the major approaches that have been taken to measure denitrification in terrestrial and aquatic environments and discuss the strengths, weaknesses, and future prospects for the different methods. Methodological approaches covered include (1) acetylene-based methods, (2) 15N tracers, (3) direct N2 quantification, (4) N2:Ar ratio quantification, (5) mass balance approaches, (6) stoichiometric approaches, (7) methods based on stable isotopes, (8) in situ gradients with atmospheric environmental tracers, and (9) molecular approaches. Our review makes it clear that the prospects for improved quantification of denitrification vary greatly in different environments and at different scales. While current methodology allows for the production of accurate estimates of denitrification at scales relevant to water and air quality and ecosystem fertility questions in some systems (e.g., aquatic sediments, well-defined aquifers), methodology for other systems, especially upland terrestrial areas, still needs development. Comparison of mass balance and stoichiometric approaches that constrain estimates of denitrification at large scales with point measurements (made using multiple methods), in multiple systems, is likely to propel more improvement in denitrification methods over the next few years.
Groffman
Peter M
PM
Institute of Ecosystem Studies, Box AB, Millbrook, New York 12545, USA. GroffmanP@ecostudies.org
Altabet
Mark A
MA
Böhlke
J K
JK
Butterbach-Bahl
Klaus
K
David
Mark B
MB
Firestone
Mary K
MK
Giblin
Anne E
AE
Kana
Todd M
TM
Nielsen
Lars Peter
LP
Voytek
Mary A
MA
D000114:Acetylene; D001128:Argon; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D009587:Nitrogen Isotopes; D009589:Nitrogen Oxides / Q000378:metabolism; D012987:Soil / Q000032:analysis; D014867:Water / Q000032:analysis
D009566:Nitrates; D009573:Nitrites; D009587:Nitrogen Isotopes; D009589:Nitrogen Oxides; D012987:Soil; D014867:Water; D001128:Argon; D009584:Nitrogen; D000114:Acetylene