Global phosphorus emission and deposition from wildfires

Wednesday, December 12, 2018 - 16:30
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Fire is an important mechanism for redistributing phosphorus (P) within and across biomes worldwide, influencing nutrient availability and net primary production. Here we synthesize observations of fire impacts on ecosystem and atmospheric P budgets in order to generate biome-level emission factors for use in global models. We then use these emission factors with a global fire inventory (the Global Fire Emissions Database version 4s or GFED4s) and a chemical transport model (GEOS-Chem) to assess fire contributions to patterns of global P deposition. From analysis of ecosystem studies that use a mass-balance approach to measure P loss during fire, we estimate that between 31 and 49% of P in combusted biomass is emitted into the atmosphere and transported downwind of the fire perimeter. The highest percentage of P loss occurs in savannas (49%), where near-complete combustion often occurs in a flaming stage, and is lower in shrub and forest ecosystems where contributions from smoldering combustion often are more pronounced. The mean P emission factor from the ecosystem mass-balance approach (~0.2 g kg-1) is about 20 times larger than that estimated from remote aerosol measurements, likely because of deposition of P in super-coarse particles near the fire source. Combining these observations with the GFED4s fire emissions and GEOS-Chem model, we create maps of the global distribution of P emission and atmospheric deposition fluxes from fires. Fires are a source of 0.91 Tg P yr-1 to the global atmosphere, with 64% of these emissions originating from savanna fires. About 5% of this flux (0.046 Tg P yr-1) is associated with long-range transport over spatial scales of hundreds to thousands of kilometers. Our analysis helps to resolve the significant discrepancy in estimates of the fire contribution to the global atmospheric P budget derived separately from ecosystem and aerosol measurements, and suggests that fire-emitted P could play more important role than previously thought in shaping the P cycle in ecosystems, particularly in the P-limited Amazon and tropical open ocean ecosystems. Using the newly derived global P emission map from the mass-balance approach and GFED4s coupled with the Energy Exascale Earth System Model (E3SM), the atmospheric fire-induced P budgets and its radiative effects are also evaluated and assessed.

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