Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2005
Publication Date: 9/1/2006
Citation: Livingston, G.P., Hutchinson, G.L., Spartalian, K. 2006. Trace gas emissions in chambers: a non-steady-state diffusion model. Soil Science Society of America Journal. 70:1459-1469. Interpretive Summary: Non-steady-state chambers are an important, and in many situations the only, approach for measuring trace gas exchange between soil and the atmosphere. It has long been recognized, however, that flux estimation models traditionally applied to NSS chamber observations, such as the linear, quadratic, and H-M-P (Hutchinson and Mosier (1981) and Peterson (2000)) models, do not accurately represent the diffusion process largely regulating emissions into the chamber headspace. The results summarized here suggest that NDFE provides the opportunity to clarify and extend soil emissions studies under the guidance of a physically meaningful model. Further evaluations of NDFE using empirical data re clearly now needed.
Technical Abstract: Non-steady-state (NSS) chambers are widely used to measure trace gas emissions from the Earth’s surface in the atmosphere. Unfortunately, traditional interpretations of time-dependent chamber concentrations often systematically underestimate predeployment exchange rates because they do not accurately represent the fundamental physics of diffusive soil gas transport that follows chamber deployment. To address this issue, we formally derived a time-dependent diffusion model applicable to NSS chamber observations and evaluated its performance using simulated chamber headspace CO2 concentration data generated by an independent, three-dimensional, numerical diffusion model. Using nonlinear regression to estimate the model parameters, we compared the performance of the non-steady-state diffusive flux estimator (NDFE) to that of the linear, quadratic, and steady-state diffusion models that are widely cited in the literature, determined its sensitivity to violation of the primary assumptions on which it is based, and addressed some of the practicalities of its application. In sharp contrast to the other models, NDFE proved an accurate and robust estimator of trace gas emissions across a wide range of soil, chamber design, and deploymnet scenarios.