Estimating sources and sinks for CO2, CH4 and N­2O from the CONUS soil during recent past decades

Abstract:

The terrestrial ecosystem, including natural (forest, grassland, shrubland, bare-land and wetland) and managed (cropland, pastureland and rangeland) lands are the major sources of three major Greenhouse Gases (GHGs) emissions, carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in the conterminous United States (CONUS). Here we apply a fully C-N coupled land surface model, Integrated Science and Assessment Model, ISAM, to quantify the GHGs fluxes from the CONUS terrestrial ecosystem soils from the. ISAM consistents of all major processes and feedbacks within carbon, CH₄ and nitrogen cycles. ISAM model has accounted for the vertical movement of SOC caused by bioturbation and cryoturbation, organo-mineral interaction and depth dependent environmental modifiers for better capturing SOC turnover time and CO₂ emission through soil respiration. Based on the vertically-resolved SOC model structure, CH₄ production and oxidation processes are added and calculated on each layer of the soil. Three transport pathways of CH₄ in soils (diffusion, ebullition and aerenchyma transport) module is accounted for estimating CH₄ source and sink. The N cycle in ISAM model has included all mineral and organic N processes in soils, including organic N mineralization and mineral N immobilization, plant uptake, nitrification, denitrification, leaching and volatilization. A detailed manure and N fertilizer application module is also applied to account for the GHG emissions from the managed lands. The coupled model captures the GHG emission dynamics, especially the interactions between different cycles. For example, the increase of the C:N ratio of the litter under the CO₂ fertilizer effect will increase litter C compared to litter N, resulting in increased amount of CO₂ emission and decreased amount of N2O emissions from the soils.

ISAM is evaluated and then applied to the CONUS to estimate the GHG fluxes over the recent past decades. The model results have been evaluated by comparing to previous regional observations and model estimations. This presentation will focus on the analysis of importance of the interactions of environmental conditions in estimating GHG sources and sinks.