Dissolved Organic Carbon Adsorption By Charcoal in Fire-Impacted Watersheds of the Olympic Peninsula, Washington, USA.

Fire –an important natural disturbance in forest ecosystems – is often measured in terms of loss in above- and belowground productivity.  Charcoal represents a unique legacy of wildfires: it is highly resistant to degradation and possesses a high surface area, aromatic C structure. We evaluated the role of charcoal adsorption capacity in dissolved organic C flux on four forest stands in the Elwha River Valley of the Olympic Peninsula, Washington, USA. The stands were last exposed to wildfire in 1898, 1898, 1927, and 1977. At each site, we measured vegetation and soil attributes. Vegetation was characterized by a census of overstory and understory species composition and abundance. For soil measurements, a 250 m2 contiguous grid of 10 sub-plots was installed at each site. Within each sub-plot, mineral soil and forest floor were characterized by pH, total C, total N, texture, and soluble phenols. Additionally, one ionic and one non-ionic resin lysimeter was buried beneath the O-layer in each sub-plot. Three each of the ionic and non-ionic resin lysimeters at each site were spiked with 0.5 g of charcoal. Belowground environmental conditions were measured by buried ibutton temperature/humidity data loggers. Resin lysimeters and ibuttons were buried in November of 2013 and January of 2014 and were collected after eight months. Ionic resin lysimeters will be extracted for NH4+, NO3-, dissolved organic N, and PO4-3. Non-ionic resins will be extracted and analyzed for anthrone reactive C, total organic C, phenols, carbohydrates, and proteins. Preliminary charcoal quantification from visual separation in O-layer samples range from 0.1 – 0.5 kg charcoal/m2. Reference charcoals for three formation temperatures (300°C, 500°C, and 800°C) were created in the laboratory. Adsorption capacity and physical structure of charcoal collected from natural wildfire sites were compared to the reference charcoal using adsorption batch experiments with phenol and thermogravimetric analysis. Initial results indicate, first, an increasing adsorption affinity for phenol with increasing formation temperature, and second, a decreasing black carbon composition of natural charcoals with respect to time-since-fire. Additional sites and lysimeters will be installed in stands exposed to fire in 1985, 2006, 2009, and 2011 during the spring of 2014 for further investigation of the charcoal adsorption capacity in recently burned forests of the Olympic Peninsula.