Adsorption Capacity of Wildfire-Derived Charcoal in Pacific Northwest Forest Soils.

Wildfire generated charcoal has the potential to adsorb non- and less-polar organic compounds in soil solution introduced from throughfall, which can directly influence biotic activity and nutrient cycling, but to date, there has been few serious attempts to study these processes. This research evaluates the ability of field-collected charcoal to adsorb organic compounds in forest soils along a fire chronosequence in a mixed-severity fire ecosystem of the Olympic Peninsula, Washington. Adsorption capacity and physical structure of charcoal collected from natural wildfire sites were compared to laboratory charcoal (created at 300C, 500C, and 800C) using adsorption batch experiments with phenol as a sorbate. Thermogravimetric analysis (TGA) was used to quantify the percent mass of volatile organic material and black carbon content of reference and field-collected charcoal along the fire chronosequence. Results show that increased formation temperature of charcoal also increases the ability to adsorb phenol. Field-collected charcoal does not follow a hypothesized trend of decreased adsorption capacity with time-since-fire. The TGA measurements, however, show significant trends in thermal removal of C for both laboratory (p < 0.01) and field-collected charcoal (p < 0.05). The inherent signature of formation temperature is evident in laboratory charcoals and these same trends are evident in the field-collected charcoal. The effect of time-since-fire in field-collected charcoal is less significant than variation of subplot-level charcoal characteristics. Preliminary results from this study do not support the generalization of decreased adsorption capacity with time since fire, perhaps because the spatial and temporal differences in fire severity and environmental subsequent increases the complexity of field-collected charcoal adsorption capacity.