Improved carbon flux measurements in cold, snow-covered ecosystems
The Glacier Lakes Ecosystem Experiment Site (GLEES) in southeastern Wyoming.
Rocky Mountain Research Station researchers deployed infrared gas analyzers at the Glacier lakes Ecosystem Experiment Site (GLEES) AmeriFlux site to demonstrate improvements in eddy covariance measurements. Energy and trace gases fluxes between the atmosphere and land surface are fundamental for studies of ecosystem function, ecohydrology, carbon cycling, and climate change. The eddy covariance technique is a common methodology to study net ecosystem exchange of carbon. The premise of this technique is that the energy and mass that cross the hypothetical boundary dividing the atmosphere from the ecosystem can be measured at high frequency and then tallied over a longer period of time.
There are also non-biological effects that influence gas exchange - in particular, contraction and expansion of atmospheric gases. The eddy covariance technique typically includes adjustments to account for these non-biological processes, including a sensible heat flux adjustment. In cold ecosystems, the annual carbon balance can be dominated by winter respiration. However, the eddy covariance technique can be inaccurate in cold climates because the self-heating of warm sensors can interfere with the sensible heat flux adjustment. Often, this error can make an otherwise dormant ecosystem appear to be a carbon sink. RMRS researchers investigated and revised a common correction for this self-heating for open-path infrared gas analyzers.
In their findings, significant heating was observed at the US-GLE AmeriFlux at the Glacier Lakes Ecosystem Experiments site in southeastern Wyoming. They demonstrated that the commonly accepted self-heating correction had two errors, each off by an order of magnitude, that roughly cancel out at GLEES, though they would potentially be problematic at other cold-weather sites. Infrared gas analyzer errors on CO2 fluxes were considerable at GLEES, especially during the day and in winter. Two major errors in the Burba self-heating correction were both off by roughly an order of magnitude, though these tend to cancel each other at the GLEES site. These errors may not balance at other sites or with different sensor deployments, so there is a need for a revised gas analyzer self-heating correction.