ИСТИНА

The study of GHG fluxes in terrestrial ecosystems is becoming increasingly important as the observed rise in global temperature and increased frequency of extreme weather events have been attributed to elevated atmospheric GHG concentrations. Adequate and comprehensive knowledge of surface fluxes is important for obtaining reliable information on CO2 and other GHG fluxes at regional and global scales, as well as for preparing reports on national GHG emissions and removals. Eddy covariance is the most commonly used method for ecosystem-scale flux observations. However, due to methodological limitations, the eddy covariance technique is not applicable to non-uniform underlying surfaces and cannot be widely used. The chamber method provides fairly accurate local fluxes even for landscapes with heterogeneous structure, but it is difficult to upscale the data to the ecosystem scale. Therefore, the development of mathematical models with different levels of complexity for estimating GHG fluxes is still of great importance. In our study, we proposed and tested a model for estimating GHG fluxes over an inhomogeneous underlying surface. The model is based on the RANS hydrodynamic model for the calculation of wind velocity and turbulence coefficient, as well as on the solution of the advection-diffusion equation to find a three-dimensional distribution of GHG concentrations, which, taking into account the turbulence coefficient, allows the calculation of fluxes at the specified height above the ground surface. The main objective of the study was to test the representativeness of the model for areas with different surface topography and mosaic vegetation cover. For this purpose, the simulation results were compared with the results of CO2 flux measurements using the eddy covariance method at rather homogeneous sites (forest and peatland areas of the "Mukhrino" carbon supersite in the Khanty-Mansiysk Autonomous Okrug, Russia, 60°53'20" N, 68°42'10" E), as well as at the mixed forest site (the "Lyali" experimental site, Republic of Komi, Russia, 62°16'28" N, 50°39'54" E). In addition to the comparison of model and experimental CO2 fluxes, the calculated vertical profile of CO2 distribution within the vegetation cover was also examined. The calculations were performed using soil fluxes measured by the chamber method, measurements of photosynthesis rate, satellite data for LAI, and information on the vertical structure of the vegetation. The model results showed a fairly good agreement with the measured data and could help to interpret the experimentally observed dependence of CO2 fluxes on wind direction in areas with an inhomogeneous underlying surface.