A novel correction for biases in forest eddy covariance carbon balance

Matthew N. Hayek, Richard Wehr, Marcos Longo, Lucy R. Hutyra, Kenia Wiedemann, J. William Munger, Damien Bonal, Scott R. Saleska, David R. Fitzjarrald, Steven C. Wofsy

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Systematic biases in eddy covariance measurements of net ecosystem-atmosphere carbon dioxide exchange (NEE) are ubiquitous in forests when turbulence is low at night. We propose an alternative to the conventional bias correction, the friction velocity (u*) filter, by hypothesizing that these biases have two separate, concurrent causes: (1) a subcanopy CO2 storage pool that eludes typical storage measurements, creating a turbulence-dependent bias, and (2) advective divergence loss of CO2, creating a turbulence-independent bias. We correct for (1) using a simple parametric model of missing storage (MS). Prior experiments have inferred (2) directly from atmospheric measurements (DRAINO). For sites at which DRAINO experiments have not been performed or are infeasible, we estimate (2) empirically using a PAR-extrapolated advective respiration loss (PEARL) approach. We compare u* filter estimates of advection and NEE to MS-PEARL estimates at one temperate forest and two tropical forest sites. We find that for tropical forests, u* filters can produce a range of extreme NEE estimates, from long-term forest carbon emission to sequestration, that diverge from independent assessments and are not physically sustainable. Our MS model eliminates the dependence of nighttime NEE on u*, consistent with findings from DRAINO studies that nighttime advective losses of CO2 are often not dependent on the strength of turbulence. Our PEARL estimates of mean advective loss agree with available DRAINO measurements. The MS-PEARL correction to long-term NEE produces better agreement with forest inventories at all three sites. Moreover, the correction retains all nighttime eddy covariance data and is therefore more widely applicable than the u* filter approach, which rejects substantial nighttime data—up to 93% at one of the tropical sites. The full MS-PEARL NEE correction is therefore an equally defensible and more practical alternative to the u* filter, but leads to different conclusions about the resulting carbon balance. Our results therefore highlight the need to investigate which approach's underlying hypotheses are more physically realistic.

Original languageEnglish (US)
Pages (from-to)90-101
Number of pages12
JournalAgricultural and Forest Meteorology
Volume250-251
DOIs
StatePublished - Mar 15 2018

Keywords

  • Amazon
  • Carbon dioxide
  • Eddy covariance
  • Forest carbon flux
  • Friction velocity
  • Respiration

ASJC Scopus subject areas

  • Forestry
  • Global and Planetary Change
  • Agronomy and Crop Science
  • Atmospheric Science

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  • Cite this

    Hayek, M. N., Wehr, R., Longo, M., Hutyra, L. R., Wiedemann, K., Munger, J. W., Bonal, D., Saleska, S. R., Fitzjarrald, D. R., & Wofsy, S. C. (2018). A novel correction for biases in forest eddy covariance carbon balance. Agricultural and Forest Meteorology, 250-251, 90-101. https://doi.org/10.1016/j.agrformet.2017.12.186