Numerical evaluation of static-chamber measurements of soil-atmospheric gas exchange--Identification of physical processes

Soil Science Society of America Journal
By: , and 

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Abstract

The exchange of gases between soil and atmosphere is an important process that affects atmospheric chemistry and therefore climate. The static-chamber method is the most commonly used technique for estimating the rate of that exchange. We examined the method under hypothetical field conditions where diffusion was the only mechanism for gas transport and the atmosphere outside the chamber was maintained at a fixed concentration. Analytical and numerical solutions to the soil gas diffusion equation in one and three dimensions demonstrated that gas flux density to a static chamber deployed on the soil surface was less in magnitude than the ambient exchange rate in the absence of the chamber. This discrepancy, which increased with chamber deployment time and air-filled porosity of soil, is attributed to two physical factors: distortion of the soil gas concentration gradient (the magnitude was decreased in the vertical component and increased in the radial component) and the slow transport rate of diffusion relative to mixing within the chamber. Instantaneous flux density to a chamber decreased continuously with time; steepest decreases occurred so quickly following deployment and in response to such slight changes in mean chamber headspace concentration that they would likely go undetected by most field procedures. Adverse influences of these factors were reduced by mixing the chamber headspace, minimizing deployment time, maximizing the height and radius of the chamber, and pushing the rim of the chamber into the soil. Nonlinear models were superior to a linear regression model for estimating flux densities from mean headspace concentrations, suggesting that linearity of headspace concentration with time was not necessarily a good indicator of measurement accuracy.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Numerical evaluation of static-chamber measurements of soil-atmospheric gas exchange--Identification of physical processes
Series title Soil Science Society of America Journal
DOI 10.2136/sssaj1996.03615995006000030009x
Volume 60
Issue 3
Year Published 1996
Language English
Publisher Soil Science Society of America
Contributing office(s) Toxic Substances Hydrology Program
Description 8 p.
First page 740
Last page 747
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