Adsorption capacity of wildfire-produced charcoal from Pacific Northwest forests

This research evaluated the adsorption capacity of charcoal collected from O-horizon soils of mixed-severity fire regime forests in the Olympic Peninsula, Washington, USA. This property is important to consider in the context of post-fire soil carbon (C) recovery and nutrient cycling as charcoal has a high affinity for dissolved organic C compounds released by throughfall and organic matter decomposition. Charcoal samples produced in the laboratory at 300°C, 500°C, and 800°C provided a baseline for chemical composition and adsorption capacity using phenol as the sorbate. These samples were used to compare charcoal collected at wildfire chronosequence sites (3 – 115 years) where formation temperature was unknown and adsorption capacity is likely modified through weathering and adsorption of organic compounds over time. Wildfire-produced charcoal displayed no trend with time since fire (TSF) (p > 0.1) yet measured an average capacity of 29.70 (± 6.23) μg phenol. mg charcoal-1 across all sites. Increased formation temperature of laboratory charcoal correlated with a higher adsorption affinity of simple phenol in solution. Thermogravimetric analysis (TGA) was used to provide information on the composition of samples and quantified as the percent of total mass released by pyrolysis and combustion using discrete regions of the thermal curve. The black carbon (BC) fraction, defined in this study as the mass combustible at 1000°C under O2 (gas), was positively correlated to temperature in laboratory charcoal (r2=0.82, p