What is eddy covariance?

Eddy Covariance (EC) is the micrometeorological technique for measuring the two-way vertical exchange (flux) of heat, mass and momentum between the Earth surface and the atmosphere above. EC systems are widely used to monitor flux densities of the greenhouse gases (GHGs) carbon dioxide (CO2) methane (CH4) and nitrous oxide N2O. They consist of a gas analyser and ultrasonic anemometer that record at high frequency (20 Hz), and are complemented by a suite of micrometeorological instruments, such as radiometers, temperature and humidity probes, and soil physics sensors to measure heat and moisture dynamics in the upper soil profile.

As turbulent eddies travel across the landscape, the concentration of gases within them changes due to interactions with the surface. Plant photosynthesis leads to a reduction in the amount of CO2 transported by eddies whereas plant and soil respiration increases the amount of CO2. Similarly, the evaporation of water from the surface increases humidity, and the soil surface releases and removes heat from the air above.

The EC method relies on several underlying assumptions, the key of which are that the measurements are made of fully developed turbulent (non-stationary) conditions, over a large homogenous surface of interest, or “flux footprint”. As such, EC is ideally suited for measuring at field scale. Several EC systems are deployed at Lowland Peatlands and other peatland areas in the UK, which in turn form part of the wider UK Land Flux Network.

How does the Skyline system work?

As with an EC system, robotic Skyline systems are used to measure the two-way GHG exchange between atmosphere and ecosystem, but for a much smaller footprint (typically less than 1 m2). This method is referred to as an automated chamber method, and allows scientists to perform manipulation studies, whereby conditions or ‘treatments’ (e.g. fertiliser, water supply, and shading) can be controlled and compared. In the Lowland Peat project, Skyline will be deployed across a transect, where drainage levels will be manipulated to three different depths. The Skyline chamber travels across the transect suspended on ropes and is lowered onto each plot in turn from which it pumps air to an analyser enabling GHG fluxes to be calculated in near real time  GHGs.