Black carbon formation by savanna fires: Measurements and implications for the global carbon cycle

Abstract

During a field study in southern Africa (Southern African Fire‐Atmosphere Research Initiative (SAFARI‐92)), black carbon formation was quantified in the residues of savanna fires. The volatilization ratios of C, H, N, and S were determined by measuring their contents in the fuel and residue loads on six experimental sites. The volatilization of sulfur (86 ± 8%) was significantly higher than previously reported. Volatilization of H, N, and S was significantly correlated with that of carbon, enabling us to estimate their volatilization during savanna fires by extrapolation from those of carbon. By partitioning the residues in various fractions (unburned, partially burned, and ash), a strong correlation between the H/C ratio in the residue and the formation of black carbon was obtained. The ratio of carbon contained in ash to carbon contained in the unburned and partially burned fraction is introduced as an indicator of the degree of charring. As nitrogen was enriched in the residue, especially in the ash fraction of >0.63 mm, this indicator may be useful for an assessment of nutrient cycling. We show that the formation of black carbon is dependent on the volatilization of carbon as well as the degree of charring. The ratio of black carbon produced to the carbon exposed to the fire in this field study (0.6–1.5%) was somewhat lower than in experimental fires under laboratory conditions (1.0–1.8%) which may be due to less complete combustion. The average ratio of black carbon in the residue to carbon emitted as CO2 ranged from 0.7 to 2.0%. Using these ratios together with various estimates of carbon exposed or emitted by savanna fires, the worldwide black carbon formation was estimated to be 10–26 Tg C yr−1 with more than 90% of the black carbon remaining on the ground. The formation of this black carbon is a net sink of biospheric carbon and thus of atmospheric CO2 as well as a source of O2.

Pedogenesis of Chernozems in Central Europe — A review

“…Despite methodological problems, there is evidence for black soils having been formed as a result of black carbon incorporation in soils through vegetation burning in Australia (Skjemstad et al, 1996(Skjemstad et al, , 1997 and Africa (Kuhlbusch et al, 1996) or through the accumulation of hear thashes in Amazonian Brazil (Terra Preta; Glaser et al, 2001). Although the processes of incorporation and colouring are not yet clearly understood, soil colour (lightness) and amount of aromatic carbon, typical for black carbon, correlate (Spielvogel et al, 2004).…”

A dynamic global vegetation model for studies of the coupled atmosphere‐biosphere system

“…Using this approach, calculated fire occurrence does exhibit a clear seasonality as a function of drought and litter, and simulated fire return times are reasonable. A parameterization of the transformation of biomass into black carbon, which can be regarded as totally inert at the timescales ORCHIDEE is designed for (a few thousand years at most), has been introduced into the fire subroutine following the work of Kuhlbusch et al [1996].…”

Black (pyrogenic) carbon: a synthesis of current knowledge and uncertainties with special consideration of boreal regions

“…Essentially two studies are available (Kuhlbusch and Crutzen, 1995;Kuhlbusch et al, 1996) that used a method based on resistance to thermal oxidation. For savanna fires in South Africa (Kuhlbusch et al, 1996), pre-fire vegetation and litter was approximately 2700 kg ha −1 from which 90% of C was volatilized.…”

“…Essentially two studies are available (Kuhlbusch and Crutzen, 1995;Kuhlbusch et al, 1996) that used a method based on resistance to thermal oxidation. For savanna fires in South Africa (Kuhlbusch et al, 1996), pre-fire vegetation and litter was approximately 2700 kg ha −1 from which 90% of C was volatilized. Conversion to BC was 0.5 to 2% (mean 1%) based on prefire C stocks (defined as the ratio BC/CE, where CE is carbon exposed to fire), or 1.3%, based on BC/CO 2 -C. From laboratory burns of 20 non-woody biomass substrates, Kuhlbusch and Crutzen (1995) found that BC/CE was 0.14-2.2%, or 0.15-2.9% as BC/CO 2 -C. For deciduous wood (mean for two substrates), the values were higher, with BC/CE 3.1%, and BC/CO 2 -C 4%.…”