Estimation of Pre-industrial Nitrous Oxide Emission from the Terrestrial Biosphere

Abstract:

Nitrous oxide (N₂O) is currently the third most important greenhouse gases (GHG) after methane (CH₄) and carbon dioxide (CO₂). Global N₂O emission increased substantially primarily due to reactive nitrogen (N) enrichment through fossil fuel combustion, fertilizer production, and legume crop cultivation etc. In order to understand how climate system is perturbed by anthropogenic N₂O emissions from the terrestrial biosphere, it is necessary to better estimate the pre-industrial N₂O emissions. Previous estimations of natural N₂O emissions from the terrestrial biosphere range from 3.3-9.0 Tg N₂O-N yr⁻¹. This large uncertainty in the estimation of pre-industrial N₂O emissions from the terrestrial biosphere may be caused by uncertainty associated with key parameters such as maximum nitrification and denitrification rates, half-saturation coefficients of soil ammonium and nitrate, N fixation rate, and maximum N uptake rate. In addition to the large estimation range, previous studies did not provide an estimate on preindustrial N₂O emissions at regional and biome levels. In this study, we applied a process-based coupled biogeochemical model to estimate the magnitude and spatial patterns of pre-industrial N₂O fluxes at biome and continental scales as driven by multiple input data, including pre-industrial climate data, atmospheric CO₂ concentration, N deposition, N fixation, and land cover types and distributions. Uncertainty associated with key parameters is also evaluated. Finally, we generate sector-based estimates of pre-industrial N₂O emission, which provides a reference for assessing the climate forcing of anthropogenic N₂O emission from the land biosphere.