2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 2:45 PM

Effects of Soil Physical Non-Uniformity on Chamber-Based Gas Flux Estimates

VENTEREA, Rodney T. and BAKER, John A., Soil and Water Mgmt Research Unit, USDA-ARS, 1991 Upper Buford Circle, 439 Borlaug Hall, St. Paul, MN 55108-6028, venterea@umn.edu

Chamber methods for measuring trace gases fluxes are prone to errors resulting in large part from alteration of near-surface concentration gradients. There is little information available for estimating the magnitude of such errors that simultaneously accounts for soil physical properties, chamber deployment methods, and flux-calculation options. The current study employed numerical modeling to examine how variations in these factors influence flux-estimate errors. Errors varied among profiles and flux-estimation techniques, resulting in potentially important biases. A theoretically-based flux model which assumes physical uniformity performed relatively well in non-uniform soils provided that precautions were taken. Errors using the theoretical model for non-uniform soils were minimized with larger effective chamber heights (h) and shorter deployment times (DT), as was the case for all flux-models. Recent studies that have recommended minimizing h and extending DT in order to enhance non-linearity of chamber data need to be reevaluated in light of these findings. Site-specific selection of chamber and flux-calculation methods should consider the physical characteristics of the soil profile as well as measurement error. It is also shown here that random measurement error can result in skewed flux-estimate errors. Techniques presented here can be used to develop soil- and method-specific error estimates, provided that errors from other sources are minimized.