Moisture effects on carbon and nitrogen emission from burning of wildland biomass

Carbon (C) and nitrogen (N) released from biomass burning have multiple effects on the Earth's biogeochemical cycle, climate change, and ecosystem. These effects depend on the relative abundances of C and N species emitted, which vary with fuel type and combustion conditions. This study systematically investigates the emission characteristics of biomass burning under different fuel moisture contents, through controlled burning experiments with biomass and soil samples collected from a typical alpine forest in North America. Fuel moisture in general lowers combustion efficiency, shortens flaming phase, and introduces prolonged smoldering before ignition. It increases emission factors of incompletely oxidized C and N species, such as carbon monoxide (CO) and ammonia (NH<sub>3</sub>). Substantial particulate carbon and nitrogen (up to 4 times C in CO and 75% of N in NH<sub>3</sub>) were also generated from high-moisture fuels, maily associated with the pre-flame smoldering. This smoldering process emits particles that are larger and contain lower elemental carbon fractions than soot agglomerates commonly observed in flaming smoke. Hydrogen (H)/C ratio and optical properties of particulate matter from the high-moisture fuels show their resemblance to plant cellulous and brown carbon, respectively. These findings have implications for modeling biomass burning emissions and impacts

Lateral diffusion and atmospheric CO₂ mixing compromise estimates of rhizosphere respiration in a forest soil

Measurements of rhizosphere carbon efflux are critical to the determination of soil carbon balance by CO2 flux measurements. We attempted to measure rhizosphere respiration in a forest ecosystem by transplanting 13C-enriched soils from a tallgrass prairie into a mixed-conifer forest soil but found that atmospheric air mixing and lateral diffusion confounded delta13C-CO2 measurements. Surface CO2 efflux (delta13C [Formula: see text] –20‰) was enriched 6‰ relative to soil CO2 measured at depth because of the presence of atmospheric-derived CO2 (–8‰) near the soil surface. The delta13C-CO2 value of transplanted soil CO2 did not reflect its 13C-enriched carbon source but was within 1‰ of native soil CO2 because of lateral diffusion from the surrounding native soil. A two-component steady-state model of lateral diffusion supported our assertion that this soil was susceptible to atmospheric air mixing and lateral diffusion because of its high effective porosity and relatively low concentration of soil CO2. Percent rhizosphere respiration was estimated at 35 and 45% after applying corrections for atmospheric air mixing and (or) lateral diffusion. These confounding effects may be reduced or eliminated by utilizing a larger transplanted soil pit and by reducing soil CO2 diffusivity, for example, by increasing water content. </jats:p

Stormwater and fire as sources of black carbon nanoparticles to Lake Tahoe

Emitted to the atmosphere through fire and fossil fuel combustion, refractory black carbon nanoparticles (rBC) impact human health, climate, and the carbon cycle. Eventually these particles enter aquatic environments, where they may affect the fate of other pollutants. While ubiquitous, the particles are still poorly characterized in freshwater systems. Here we present the results of a study determining rBC in waters of the Lake Tahoe watershed in the western United States from 2007 to 2009. The study period spanned a large fire within the Tahoe basin, seasonal snowmelt, and a number of storm events, which resulted in pulses of urban runo# into the lake with rBCconcentrations up to 4 orders of magnitude higher than midlake concentrations. The results show that rBC pulses from both the fire and urban runoff were rapidly attenuated suggesting unexpectedaggregation or degradation of the particles. We find that those processes prevent rBC concentrations from building up in the clear and oligotrophic Lake Tahoe. This rapid removal of rBC soon after entry into the lake has implications for the transport of rBC in the global aquatic environment and the flux of rBC from continents to the global ocean

Moisture effects on carbon and nitrogen emission from burning of wildland biomass

Abstract. Carbon (C) and nitrogen (N) released from biomass burning have multiple effects on the Earth's biogeochemical cycle, climate change, and ecosystem. These effects depend on the relative abundances of C and N species emitted, which vary with fuel type and combustion conditions. This study systematically investigates the emission characteristics under different fuel moisture contents, through controlled burning experiments with biomass and soil collected from a typical alpine forest. Fuel moisture in general lowers combustion efficiency, shortens flaming phase, and introduces prolonged smoldering before ignition. It increases emission factors of incompletely oxidized C and N species, such as carbon monoxide (CO) and ammonia (NH3). Substantial particulate carbon and nitrogen (up to 4 times C in CO and 75% of N in NH3) were measured mainly from the pre-flame smoldering of fuels with high moisture contents; this process emits particles larger than soot agglomerates commonly observed in flaming smoke. Hydrogen (H)/C ratio and optical properties of particulate carbon from the high-moisture fuels show their resemblance to plant cellulous and brown carbon, respectively. These findings have implications for modeling biomass burning emission and impacts. </jats:p