[M-IS11] Biogeochemistry

[MIS11-11] Evaluation of global riverine N₂ and N₂O emissions using biogeochemical model

*Kazuya Nishina¹, Akihiko Ito¹ (1.NIES National Institute of Environmental Studies)

Keywords:Global nitrogen cycling, Riverine N2O emission

A large amount of anthropogenic reactive nitrogen (Nr) is released to terrestrial ecosystems from chemical fertilizers by the Haber-Bosch process and fossil fuel combustion and the increase of wastewater due to urbanization. Anthropogenic Nr is absorbed and accumulated in terrestrial ecosystems and released to the atmosphere in gaseous forms via biotic and abiotic processes (i.e., nitrification and denitrification). In addition, with the movement of water, Nr is transported from the land to the ocean via rivers, causing eutrophication especially in coastal areas. During transport from land to ocean, some of the reactive nitrogen is released to the atmosphere as N₂ and N₂O through denitrification processes, but the flux is highly uncertain due to the limitations of difficult observation. For example, 190 Tg-N per year is denitrified from rivers according to the estimates presented in Gruber & Galloway (2009). This estimate was estimated using a global-scale distributed hydrological model by Seitzinger et al. (2005). In this study, spatial details are basin-based, and due to the lack of observations, there has not been sufficient validation of the observed data. In this study, we developed a global river denitrification model using a grid-based global river routing model. Using the observed data of inorganic nitrogen fluxes in the river mouths, the parameters related to denitrification were estimated by Bayesian inference with MCMC. In this study, we report the global inorganic nitrogen transport and river denitrification emissions (N₂, N₂O) from 1961 to 2010 using this model.