Andrew Thomas Instrumentation |
Contact Us:
Department of Environmental and Geographical Sciences. Manchester Metropolitan University. Manchester. M1 5GD
Tel. +44 (0) 161 247 1600 (General Office)
A.D.Thomas@mmu.ac.uk
S.Hoon@mmu.ac.uk
Department of Environmental and Geographical Sciences. Manchester Metropolitan University. Manchester. M1 5GD
Tel. +44 (0) 161 247 1600 (General Office)
A.D.Thomas@mmu.ac.uk
S.Hoon@mmu.ac.uk
|
The Challenges of Quantifying Soil Gaseous Fluxes in Dryands
Understanding the magnitude of and controls on soil CO2 fluxes in all
environments is important, both in terms of predicting soil organic matter
turnover, atmospheric CO2 and ultimately the accuracy of climatic
models. In drylands, organic material is often concentrated at the soil
surface and associated with the microbial biomass and
exopolysaccharide exudates of a biological crust. Fluxes of CO2 through
crusts are, therefore, highly sensitive to changes in moisture,
temperature and disturbance.
Quantification of CO2 fluxes through dryland soils, however, presents
considerable technical difficulties associated with deriving data from
soils with a photosynthetic as well as a respiratory component in an
environment with a large diurnal temperature range. Consequently there
are very few data on in-situ dryland soil CO2 fluxes and our
understanding of the magnitude of CO2 fluxes through dryland soils and
their likely response to environmental change remains uncertain.
Understanding the magnitude of and controls on soil CO2 fluxes in all
environments is important, both in terms of predicting soil organic matter
turnover, atmospheric CO2 and ultimately the accuracy of climatic
models. In drylands, organic material is often concentrated at the soil
surface and associated with the microbial biomass and
exopolysaccharide exudates of a biological crust. Fluxes of CO2 through
crusts are, therefore, highly sensitive to changes in moisture,
temperature and disturbance.
Quantification of CO2 fluxes through dryland soils, however, presents
considerable technical difficulties associated with deriving data from
soils with a photosynthetic as well as a respiratory component in an
environment with a large diurnal temperature range. Consequently there
are very few data on in-situ dryland soil CO2 fluxes and our
understanding of the magnitude of CO2 fluxes through dryland soils and
their likely response to environmental change remains uncertain.
The ISCC, developed by Steve Hoon at MMU, is a member of the closed
or enrichment class of soil respiration chambers. It has been designed
to overcome some of the problems associated with quantifying gaseous
soil fluxes in drylands.
The ISCC, however, features an optical window possessing high
(>90%) transmission in the photosynthetic active region (PAR) of the
solar irradiance spectrum permitting observations of photosynthesis.
The ISCC possesses automatic venting and purging so that gaseous
concentrations inside the chamber do not change from ambient so
much as to significantly affect diffusion.
or enrichment class of soil respiration chambers. It has been designed
to overcome some of the problems associated with quantifying gaseous
soil fluxes in drylands.
The ISCC, however, features an optical window possessing high
(>90%) transmission in the photosynthetic active region (PAR) of the
solar irradiance spectrum permitting observations of photosynthesis.
The ISCC possesses automatic venting and purging so that gaseous
concentrations inside the chamber do not change from ambient so
much as to significantly affect diffusion.
| The Automated in-situ Closed Chamber (ISCC) and GC |
The ISCC features both active and passive cooling employing internal solid-state Peltier coolers and external
aluminised Mylar respectively. This avoids severe disturbance of the microclimate within the chamber due to admission
of high fluxes of PAR and permits in-situ operation under a wide range of ambient field temperatures (~ -5 to 40C).
Sensors internal to the chamber monitor temperature, relative humidity, irradiance and pressure. In this
implementation the ISCC is coupled to a portable gas chromatograph (Agilent GC-3000) to sample the chamber
atmosphere.
aluminised Mylar respectively. This avoids severe disturbance of the microclimate within the chamber due to admission
of high fluxes of PAR and permits in-situ operation under a wide range of ambient field temperatures (~ -5 to 40C).
Sensors internal to the chamber monitor temperature, relative humidity, irradiance and pressure. In this
implementation the ISCC is coupled to a portable gas chromatograph (Agilent GC-3000) to sample the chamber
atmosphere.