Modeling Tool for Estimating Carbon Dioxide Fluxes over a Non-Uniform Boreal Peatland

Abstract

We present a modeling tool capable of computing carbon dioxide (CO2) fluxes over a non-uniform boreal peatland. The three-dimensional (3D) hydrodynamic model is based on the “one-and-a-half” closure scheme of the system of the Reynolds-Averaged Navier–Stokes and continuity equations. Despite simplifications used in the turbulence description, the model allowed obtaining the spatial steady-state distribution of the averaged wind velocities and coefficients of turbulent exchange within the atmospheric surface layer, taking into account the surface heterogeneity. The spatial pattern of CO2 fluxes within and above a plant canopy is derived using the “diffusion–reaction–advection” equation. The model was applied to estimate the spatial heterogeneity of CO2 fluxes over a non-uniform boreal ombrotrophic peatland, Staroselsky Moch, in the Tver region of European Russia. The modeling results showed a significant effect of vegetation heterogeneity on the spatial pattern of vertical and horizontal wind components and on vertical and horizontal CO2 flux distributions. Maximal airflow disturbances were detected in the near-surface layer at the windward and leeward forest edges. The forest edges were also characterized by maximum rates of horizontal CO2 fluxes. Modeled turbulent CO2 fluxes were compared with the mid-day eddy covariance flux measurements in the southern part of the peatland. A very good agreement of modeled and measured fluxes (R2 = 0.86, p < 0.05) was found. Comparisons of the vertical profiles of CO2 fluxes over the entire peatland area and at the flux tower location showed significant differences between these fluxes, depending on the prevailing wind direction and the height above the ground.

Inverse problem for retrieving greenhouse gas fluxes at the non-uniform underlying surface from measurements of their concentrations at several levels

“…To describe the spatial distribution of GHG concentrations within the atmospheric boundary layer over a non-uniform surface, a 3D hydrodynamic model of turbulent GHG transfer in the atmospheric boundary layer has been implemented [15]. It is based on the E-ω closure scheme [16][17][18] of the averaged Navier-Stokes equation, the continuity equation and the 'diffusion-advection' equation for the transfer of GHGs [19][20][21][22].…”

“…It is based on the E-ω closure scheme [16][17][18] of the averaged Navier-Stokes equation, the continuity equation and the 'diffusion-advection' equation for the transfer of GHGs [19][20][21][22]. In this study we use a modified version of a previously developed 3D hydrodynamic model [15,23] to describe the airflow distribution over the area with complex topography and vegetation.…”

“…The main parameterisations of b F and ph F functions used to describe the sources and sinks of CO 2 within a plant canopy have been discussed in Mukhartova et al [15]. The 'instantaneous' distributions of the mean wind velocity components…”

“…and the turbulent coefficient were obtained using the relaxation algorithm for the averaged Navier-Stokes equation and the continuity equation using the "1.5-order closure" scheme (Eω model), analogous to the algorithm used in [15]:…”

“…, and the functions E and E ε ω = satisfy the equations of the "diffusion -reaction -advection" type [15][16][17][18], also taking into account the surface topography as an obstacle with a high drag coefficient.…”