Colorado mountains
 

Comparison of chamber and eddy covariance CH4 fluxes using a new “open path” gas analyzer

Poster Number: 
109
Presenter/Primary Author: 
Terenzio Zenone
Co-Authors: 
Gerardo Fratini
Co-Authors: 
Kevin Kahmark
Co-Authors: 
Jiquan chen
Co-Authors: 
G. Philip Robertson

Traditional measurements of CH4 fluxes are made with static chamber techniques and/or with closed-path eddy covariance (EC) systems. Although each approach has its advantages, they also pose some critical limitations: measurements based on static chamber are time consuming, do not capture the dynamics of CH4 fluxes on continuous temporal scales due to the discontinuity of the sample collection, and can cover only a small soil surface. The development of a new “open-path” CH4 analyzer (LI-7700 LI-COR Biosciences, Lincoln, NE USA) provides the frequency response required by the EC measures and overcomes the pre-mentioned problems. Our objective was to test the application of LI-7700 and compare the results with the fluxes based on static chamber for justifying our future long term measurements of CH4. We measured the CH4 fluxes using a LI-7700 “open-path” gas analyzer in conjunction with a CSAT3 3-D sonic anemometer (Campbell Scientific Inc. CSI, UT, USA) and a LI-7550 (LI-COR Biosciences, Lincoln, NE) analyzer interface unit. Measurements from the chambers were performed using in situ closed-cover flux chambers following the methodology and fluxes calculation reported in: http://lter.kbs.msu.edu/protocols/23. We found a good agreement between the two techniques. EC CH4 fluxes showed no consistent daily pattern with the values that ranged from 0.001 to -0.009 mg CH4 m-2. Daily mean CH4 density showed considerable day-to-day variation varied  from 15 to 1.7 ppm, with particular high variation during the summer period when there are more rainy days than the autumn/winter season.  We did not found any significant correlation between CH4 fluxes with soil water content or temperature. The new open-path CH4 analyzer appeared to be reliable in locations that are not equipped with grid power. However, a necessity to conduct such comparison in sites characterized by higher level of CH4 emission is a critical step.

 
 
Background Photo by: Nicole Hansen - Jornada (JRN) LTER