Identifying CO₂ advection on a hill slope using information flow

In hilly terrain affected by drainage flow, the horizontal advection of CO₂ makes it difficult to accurately observe the net ecosystem exchange of CO₂ by the eddy covariance technique. Downslope drainage can result in an overestimation of respiration at the bottom of a hill slope and an underestimation at the top, resulting in discrepancies among different flux corrections using filters based on the friction velocity, light response curve, and timing of advection. Vertical profiles of the CO₂ concentration from the ground to above the canopy were measured along with above-canopy EC flux measurements at the top and bottom of a hill slope at the Gwangneung KoFlux sites from 2008 to 2010. To infer the timing, direction, temporal scale, and structure of CO₂ advection from uphill to downhill, we constructed an information flow dynamical process network (DPN) based on the observed multi-level CO₂ concentrations. A site-specific quality control filter was developed to eliminate data strongly affected by CO₂ advection, which identifies the observations when strong downslope information flow exists in the DPN. This site-specific filter considerably reduced the discrepancies among different traditional flux corrections. This research provides a method for the general characterization of advection using information flow, and application of the method as a site-specific filter for eddy covariance observations in hilly and complex terrain.