Applying a Lagrangian Dispersion Analysis to Infer Carbon Dioxide and Latent Heat Fluxes in a Corn Canopy.

Lagrangian dispersion methods have been used as an alternative to infer scalar source/sink distributions and fluxes inside plant canopies. The objective of this study was to apply a Lagrangian dispersion analysis (WT analysis) to infer source/sinks distributions of CO₂ and latent heat in a corn field and to compare the derived net flux from WT analysis with eddy covariance measurements taken at the top of the canopy. The WT analysis requires the specification of the turbulence statistics in advance, so parameterization proposed by Leuning (2000) (TSL) was used to estimate the Lagrangian time scale (T_L) and the standard deviation of vertical wind velocity (σ_w). The T_L and σ_w profiles were corrected for atmospheric stability.  The field experiment was carried out in a corn field during the field season in 2007 and 2008 at the Elora Research Station, Elora, ON. Profiles of water vapour were measured using a multiport sampling system connect to an infrared gas analyzer LI6262 (Li-Cor, Inc., Lincoln, NE, USA) at 6 heights inside and two heights above the canopy. ¹²CO₂ and ¹³CO₂ mixing ratios were measured at the same heights using tunable diode laser absorption spectroscopy.  The estimates of CO₂ and latent heat fluxes, provided by the sum of source strength profiles from WT analysis, were compared with the measurements taken using an eddy covariance system set up at the same site.  The measurements obtained by the eddy covariance method and WT analysis predictions showed good agreement (r²=0.83). However, the WT analysis tended to overestimate small fluxes and under stable conditions. The results show that WT analysis may be used to infer the net flux at the top of plant canopies.