Biomass burning and fossil fuel combustion have resulted in the global distribution and accumulation of black carbon in soils and sediments. Black carbon is currently produced at an estimated rate of 1014 g per year, but little is known about its environmental fate and reactivity. Most of this black carbon is charcoal formed by forest fires. The original research in this dissertation is divided among two overarching themes involving the organic geochemistry of the charcoal deposited to soils by biomass burning. The first theme is oriented toward understanding the importance of environmental charcoal as a geosorbent for hydrophobic contaminants (PAHs). The sorption capacity of environmental charcoal differs significantly from that of recently deposited or lab-generated chars. The competitive sorption of natural organic matter is implicated as the cause of diminished sorption capacity. New sorption models are proposed to address the prediction of PAH uptake by fire-impacted soils.
The second research theme deals with the environmental fate of charcoal black carbon. Advanced imaging and magnetic resonance techniques were used to compare and contrast the morphology and chemical composition of recently-formed forest fire charcoals to those aged in soil. The colonization of charcoal particles by filamentous microorganisms was an intriguing observation that motivated an investigation of the feasibility of enzymatic charcoal degradation. The lignolytic fungal enzyme, laccase, causes a modest but discernable oxidation and humification of soil charcoal. The spectroscopic analyses also extend to natural waters of a fire-impacted watershed as a potential conduit for the export of charcoal black carbon from soils. Condensed aromatic leachates from the soil charcoal are prevalent in the dissolved organic matter of the soil pore, river, and ground water.