Changes in fire-derived soil black carbon storage in a subhumid woodland

Abstract

Fire-derived black carbon (BC) in soil, including charcoal, represents an important part in terrestrial carbon cycling due to its assumed long persistence in soil. Soil BC concentrations for a woodland in central Texas, USA, was found from study plots with a fire scar dendrochronology spanning 100 years. BC values were initially determined from 13 C nuclear magnetic resonance (NMR) spectroscopy. The NMR-based BC concentrations were used to calibrate midinfrared vibrational spectra (MIRS) for evaluation as a less expensive and expedient technique. However, unexpectedly high BC values from the MIRS method were found for sites without evidence of fire for the past 100 years. Estimation of BC from NMR technique showed mean BC concentration of 2.73 ± 3.06 g BC kg À1 (0.91 ± 0.51 kg BC m À2 ) for sites with fire occurrence within the last 40 years compared with BC values of 1.21 ± 1.70 g BC kg À1 soil (0.18 ± 0.14 kg BC m À2 ) for sites with fire 40-100 years ago. Sites with no tree ring evidence of fire during the last 100 years had the lowest mean soil BC concentration of 0.05 ± 0.11 g BC kg À1 (0.02 ± 0.03 kg BC m À2 ). Molecular proxies of stability (lignin/N) and decomposition (Alkyl C/O-Alkyl C) showed no differences across the sites, indicating low potential for BC mineralization. Modeled soil erosion and time since fire from fire scar data showed that soil BC concentrations were inversely correlated. These results suggest that the addition of BC may be limited by topography and timing of fire.

Post-wildfire Erosion in Mountainous Terrain Leads to Rapid and Major Redistribution of Soil Organic Carbon

“…These later erosion events generally transport more mineral material than the earlier erosion events, since pyrogenic material is typically preferentially transported in early erosion events after a fire (Rumpel et al, 2006(Rumpel et al, , 2009Yao et al, 2014). If the relatively SOCrich material that was originally deposited in the depositional landform position is buried with subsequent erosion, PyC and associated other soil C is likely to be physically stabilized in the soil profile of the depositional position.…”

“…The observed high enrichment ratios of PyC are partly due to its relatively lower density compared with other SOM constituents, along with its concentration in the upper soil horizons and hydrophobicity (DeBano, 2000;Rumpel et al, 2006Rumpel et al, , 2015Brewer et al, 2014). There is some evidence that erosion of PyC is controlled by different processes than non-pyrogenic C. Yao et al (2014) found that the proportion of PyC compared with total C decreases with increasing soil erosion, while total C erosion increases with bulk soil erosion due to mobilization of deep and mineral-associated C. Erosional loss of PyC from sloping landform positions and depositional input of PyC into lower-lying depositional landform positions post-fire can significantly decrease or increase its mean residence time, as is observed with bulk C in soils that are not fire impacted (Berhe et al, 2007. Furthermore, the previous research on non-pyrogenic C has indicated that the burial of eroded C in lower lying depositional landform positions can lead to stabilization of through physical and chemical mechanisms (Berhe et al, 2007).…”

“…So far, relatively few studies have focused specifically on the erosion of PyC. From the available data, it is becoming increasingly clear that PyC is highly susceptible to erosive forces, more so than non-pyrogenic C (Rumpel et al, 2006;Yao et al, 2014). After high severity wildfires, PyC has been documented to have enrichment ratios (concentration in eroded sediment divided by concentration in source soils) of up to 2.3 across the watershed scale (Rumpel et al, 2006).…”

Pyrogenic Carbon Erosion: Implications for Stock and Persistence of Pyrogenic Carbon in Soil

“…The role of erosion in controlling the fate of PyC is likely more important than for non-pyrogenic SOM, as fire can significantly increase the rate of soil erosion, and prior research has demonstrated that PyC is highly erodible (Rumpel et al, 2006;Yao et al, 2014). The increased rate of soil erosion post-fire results from a combination of environmental changes, including: loss of the protective litter layer, exposure of surface soil to erosive forces (precipitation, wind), increased hydrophobicity of the subsoil (DeBano et al, 1998;DeBano, 2000;BenavidesSolorio and MacDonald, 2001;MacDonald et al, 2001), and a reduction in water infiltration and water holding capacity of the surface soil (Robichaud, 1997;DeBano, 2000;Doerr and Thomas, 2000;Carroll et al, 2007).…”