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Vents and seals in non‐steady‐state chambers used for measuring gas exchange between soil and the atmosphere
Author(s) -
Hutchinson G. L.,
Livingston G. P.
Publication year - 2001
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1046/j.1365-2389.2001.00415.x
Subject(s) - atmosphere (unit) , diffusion , seal (emblem) , mechanics , steady state (chemistry) , outgassing , flux (metallurgy) , porosity , environmental science , tube (container) , flow (mathematics) , soil water , volume (thermodynamics) , stack (abstract data type) , gaseous diffusion , materials science , chemistry , soil science , physics , thermodynamics , composite material , computer science , art , organic chemistry , electrode , metallurgy , visual arts , programming language
Summary Despite decades of research to define optimal chamber design and deployment protocol for measuring gas exchange between the Earth's surface and the atmosphere, controversy still surrounds the procedures for applying this method. Using a numerical simulation model we demonstrated that (i) all non‐steady‐state chambers should include a properly sized and properly located vent tube; (ii) even seemingly trivial leakiness of the seals between elements of a multiple‐component chamber results in significant risk of measurement error; (iii) a leaking seal is a poor substitute for a properly designed vent tube, because the shorter path length through the seal supports much greater diffusive gas loss per unit of conductance to mass flow; (iv) the depth to which chamber walls must be inserted to minimize gas loss by lateral diffusion is smaller than is customary in fine‐textured, wet or compact soil, but much larger than is customary in highly porous soils, and (v) repetitive sampling at the same location is not a major source of error when using non‐steady‐state chambers. Finally, we discuss problems associated with computing the flux of a gas from the non‐linear increase in its concentration in the headspace of a non‐steady‐state chamber.