Measuring Emissions Of Greenhouse Gases From The Soil - Text Version: Transcript
Measuring Emissions Of Greenhouse Gases From The Soil
Soils can both remove and release greenhouse gasses from the atmosphere and measurement of these processes in the field is important in order to understand how different management practices contribute to overall emissions.
Here we demonstrate how static chambers can be used to measure emissions of nitrous oxide and methane from soils.
We start by using a cutting frame to mark out a position for the chamber. The cutting frame is a heavy steel template with a circular cutting edge which is the same size as the chamber itself. It is hammered firmly into the ground.
Once the cut has been made, a polypropylene chamber is pushed into position to a depth of about 5cm. The chamber is level and the soil around the outside edge is pressed firmly against the chamber side to ensure a good seal.
Trapping The Gases
The chamber is closed using an aluminium lid. This is held in place with 4 clips and a gas-tight seal is maintained by a rubber gasket running around the top of the chamber.
A sampling valve is inserted into the chamber lid.
Whilst the gas measurements are being made, soil temperature is recorded with the use of a portable thermometer.
1 Hour Later
After about an hour it is time to sample the gases collected in the chamber. The exact time of closure is recorded and a sample is collected from the 3-way tap.
Sampling The Gases: Method 1- Large Sample
An evacuated sample phial is attached to one of the arms of the sample tube and the tube is flushed out several times before a sample is collected.
The vacuum within the sample container pulls part of the gas sample from the syringe. The syringe is then pushed further to over-pressurise the gas sample in the container. The container is sealed and removed from the side-arm.
Sampling the gases: Method 2- Small Sample
An alternative sampling method can be used in which a sample is collected using a syringe which is then transferred via a side-arm into sample phial using a hypodermic needle.
Measuring The Chamber Volume
Before completing the measurement, it is important to record the chamber height in order to allow the volume to be calculated.
Multiple chambers are often used in experiments in order to provide an estimate of spatial variability.
In this particular experiment we see a cluster of chambers that are being used to estimate emissions of nitrous oxide at SAC’s Dairy Research Centre in south-west Scotland.