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A new sampling technique to monitor concentrations of CH 4 , N 2 O and CO 2 in air at well‐defined depths in soils with varied water potential
Author(s) -
Kammann C.,
Grünhage L.,
Jäger H. J.
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.1365-2389.2001.00380.x
Subject(s) - atmosphere (unit) , soil water , trace gas , silicone , diffusion , chemistry , sampling (signal processing) , analytical chemistry (journal) , characterisation of pore space in soil , mineralogy , porosity , soil science , environmental chemistry , environmental science , physics , meteorology , optics , thermodynamics , organic chemistry , detector
Summary A new sampling technique for measuring the concentrations of trace gases (CH 4 , CO 2 and N 2 O) in the soil atmosphere from well‐defined depths is described. Probes are constructed from silicone tubing closed with silicone septa on both ends, thereby dividing an inner air space from the outer soil atmosphere without a direct contact. The gas exchanges between the inner and outer atmosphere only by diffusion through the walls of the silicone tube. Tests revealed that the gases N 2 O, CO 2 and CH 4 in the enclosed space reached 95% equilibrium with the surrounding atmosphere at 20°C within 7 h or faster. The probe measurements are reproducible: the standard deviation of samples taken from 26 probes stored in the laboratory atmosphere equalled that of a standard gas. The probes can easily be constructed and installed at specified depths in the soil. The method has the following advantages compared with other methods that use spaces with holes in them for gas exchange: (i) the silicone probe enables trace gases to be sampled in wet soils, including ones that are waterlogged or temporarily saturated; (ii) the sampling itself does not create low pressure and hence does not create mass flow in the soil matrix from undefined depths; and (iii) the probe can be made to take samples of gas of any required size. The silicone probes did not show ageing effects during 18 months of use in the field in a mineral soil under grass. The probes yielded comparable results: three probes inserted at 5 cm depth in a uniformly treated 100‐m 2 plot provided nearly identical average trace gas concentrations within the measurement period.