Intuitive and Non-Intuitive Implications of Gas Diffusion Theory on Chamber-Based Flux Measurements.

This presentation will focus on selection of a flux-calculation (FC) method to use with non-steady state chambers.  It will provide an overview of diffusion theory as it relatives to chamber measurements, and describe how some degree of simplification of diffusion theory is necessary in order to develop FC methods that are practical; however, with simplification comes more potential for error.  This trade-off will be illustrated using different available flux calculation methods. What is the best balance between theory and practicality? We will make the distinction between the accuracy and precision of a flux estimate, and discuss how methods that are more accurate also tend to be less precise.  What is the best balance between accuracy and precision? We will also discuss some common misconceptions including the ideas that (i) widely used non-linear calculation methods accurately account for the “chamber effect” in accordance with diffusion theory, (ii) a high r2 value indicates that the flux can be assumed to be linear and that linear regression yields an accurate flux estimate and (iii) errors in calculating fluxes are “systematic” and therefore do not affect relative flux estimates between treatments or sampling dates.