Evaluation Of Density Corrections To Methane Fluxes Measured By Open-Path Eddy Covariance Over Contrasting Landscapes

  • Sites: US-Myb, US-Snd, US-Tw1, US-Tw3, US-Tw4, US-Twt
  • Chamberlain, S. D., Verfaillie, J., Eichelmann, E., Hemes, K. S., Baldocchi, D. D. (2017/06/22) Evaluation Of Density Corrections To Methane Fluxes Measured By Open-Path Eddy Covariance Over Contrasting Landscapes, Boundary-Layer Meteorology, (), . https://doi.org/10.1007/s10546-017-0275-9
  • Funding Agency: DOE/TES; DWR

  • Corrections accounting for air density fluctuations due to heat and water vapour fluxes must be applied to the measurement of eddy-covariance fluxes when using open-path sensors. Experimental tests and ecosystem observations have demonstrated the important role density corrections play in accurately quantifying carbon dioxide ( CO 2 ) fluxes, but less attention has been paid to evaluating these corrections for methane ( CH 4 ) fluxes. We measured CH 4 fluxes with open-path sensors over a suite of sites with contrasting  CH 4 emissions and energy partitioning, including a pavement airfield, two negligible-flux ecosystems (drained alfalfa and pasture), and two high-flux ecosystems (flooded wetland and rice). We found that density corrections successfully re-zeroed fluxes in negligible-flux sites; however, slight overcorrection was observed above pavement. The primary impact of density corrections varied over negligible- and high-flux ecosystems. For negligible-flux sites, corrections led to greater than 100% adjustment in daily budgets, while these adjustments were only 3–10% in high-flux ecosystems. The primary impact to high-flux ecosystems was a change in flux diel patterns, which may affect the evaluation of relationships between biophysical drivers and fluxes if correction bias exists. Additionally, accounting for density effects to high-frequency  CH 4 fluctuations led to large differences in observed CH 4 flux cospectra above negligible-flux sites, demonstrating that similar adjustments should be made before interpreting  CH 4 cospectra for comparable ecosystems. These results give us confidence in  CH 4 fluxes measured by open-path sensors, and demonstrate that density corrections play an important role in adjusting flux budgets and diel patterns across a range of ecosystems.

  • https://link.springer.com/article/10.1007%2Fs10546-017-0275-9