Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: December 15, 2010
Publication Date: December 15, 2010
Citation: Parkin, T.B., Venterea, R.T. 2010. USDA-ARS GRACEnet Project Protocols, Chapter 3. Chamber-based trace gas flux measurements4. In: Follett, R.F., editor. Sampling Protocols. Beltsville, MD. Available at: http://www.ars.usda.gov/SP2UserFiles/Program/212/Chapter%203.%20GRACEnet%20Trace%20Gas%20Sampling%20Protocols.pdf. p. 1-39.
This protocol addresses N2O, CO2 and CH4 flux measurement by soil chamber methodology. The reactivities of other gasses of interest such as NOx O3, CO, and NH3 will require different chambers and associated instrumentation. Carbon dioxide is included as an analyte with this protocol; however, when plants are present, interpretation of soil CO2 flux data in the context of net GHG flux is not straightforward because soil CO2 emissions do not represent net ecosystem CO2-C exchange. This protocol adopts chamber-based flux methodology (the least expensive option available) in order to allow inclusion of as many sites as possible. Since micrometeorological techniques require expensive instrumentation, they will be used only at locations with current micrometeorological capability. In deciding on a chamber design, our goal was to adopt methodology which is sensitive, unbiased, has low associated variance, and allows accurate interpolation/extrapolation over time and space. Because of our inability, at this time, to precisely assess the extent of bias associated with a given chamber design and sampling protocol under the range of conditions which might exist, we have adopted our 'best guess' protocol. Assessment, refinement and/or modifications of this protocol may continue in the future. At some sites this may include evaluation of chambers against fluxes determined by micrometeorology or performing comparisons of alternate chamber designs. Recognizing that any measurement technique will have disadvantages, the best we can do at this time is to select a
technique which minimizes potential problems. In addition, adoption of common methodology will aid in site inter-comparisons. To facilitate the adoption of a common technique, it is important to attain a common understanding of the potential shortcomings associated with chamber-based flux measurement techniques (Rochette and Eriksen-Haamel, 2008). The following section summarizes some of these issues.