See more from this Session: General Soil Chemistry: II
Surface fire could induce heat-transferring into the soil, creating an environment in the subsoil similar to that of carbonization, and a temperature higher than 600oC had been reported for a fire-impacted surface soil. The chemical compositions of soil organic matters (SOM) could be altered upon carbonization of the soil accompanied with the release of soluble organic carbons (SOC). The labile C, i.e., SOC, in the heat-impacted soils may influence indirectly the transportations and transformations of pollutants due to its high mobility. In this study, two Taiwan peat soils from Yamingshan (YS) and Changhua (CHA) were carbonized in an oven up to 600oC under a limited air to simulate the soils heated under a surface fire. Influences of temperatures on the release of SOC were examined. Results showed that the concentrations of SOC derived from YS reached the highest at 200 oC (25.9 mg/L), but SOC concentrations decreased rapidly behind the specific temperatures. Unlike YS, SOC derived from CHA decreased continuously from 142.8 mg/L to nearly undetected with an increase of carbonized temperatures. Since the YS soil bear a significant amount of amorphous minerals, such as allophone and Fe/Al hydr(o)oxides, we speculated that the strong adsorption of SOC by these minerals may lead to a low SOC content in YS soils. With an increase of carbonized temperature up to 200 oC, these minerals may be converted to more crystalline structures, resulting in the release of adsorbed organic compounds. At higher carbonized temperatures of soils, conversions of the small organic fragments and SOM to CO2 and aromatic moieties, respectively, may further decrease SOC in these systems.