Requirements for Obtaining Accurate Chamber-Based Soil Gas Flux Measurements.

There are many physical and biological variables that have an impact on soil gas flux. While flux is mainly a diffusion based process, variables such as soil moisture, temperature, porosity, rainfall and organic matter content are just a few things that can have a large impact on the soil gas flux measurement. A chamber based measurement has to deal with proper mixing inside the chamber, pressure equilibrium between inside the chamber and outside ambient air, and maintaining minimal disturbance to the measurement area. A robust mathematical fit to the data is also needed to minimize the impact of changing diffusion gradient inside the chamber on the flux estimation and to ensure both a quality measurement and proper analysis. In this presentation fundamental requirements to obtain an accurate chamber-based soil gas flux measurement will be discussed. Examples that show the impact of soil moisture, temperature, porosity, organic matter and rainfall events will be presented. An example of an analysis software that provides the flexibility needed to accurately assess soil gas flux measurements and the final calculated flux data will also be shown. In this software we will emphasize the importance of a dead band, start and stop times, and various functions that allow proper analysis within the dataset.