FOREST FIRE IMPACTS ON SOIL CHEMISTRY IN AN APPALACHIAN FOREST: FACTORS OF TEMPERATURE, MOISTURE, AND ORGANIC MATTER

Climatic changes may increase the frequency of forest fires in temperate forests of the Eastern United States. An understanding of the impact of forest fires on biogeochemical cycles will give better insight into a post-fire biome and hydrology. Our previous studies investigated the major, minor, and trace element composition of soils following fires (including prescribed and wildfire) in the mixed oak hardwood forest of the Pocono Mountains (Appalachians) of Northeast Pennsylvania, USA. An additional field experiment ascertained the composition of the contributing ash component from burned wood of different tree species. These studies identified post-fire soil enrichment in Fe, Mn, and Ca (as expected) as well as trace elements Cu and Ba. In addition, there was a post-fire soil depletion of almost all rare earth elements (REEs) despite the potential enrichment of REEs found in wood ash. The study presented here attempts to address, by lab experimentation, previously uninvestigated factors that may impact the retention, or volatility, of these signature elements.

Samples of natural forest soil from the area were obtained, including O, A, incipient E, and B horizons. The soil samples were dried (and moisture content recorded), then carbon content estimated using the loss on ignition method. Element composition of major, minor, and trace elements, in mass percent or parts per million, was determined using ICP-MS, with the sample solutions prepared by the fusion method, and calibrated against USGS rock standards. Using separates of the same soil sample, an unburned control sample was compared to samples heated to 350℃ or 550℃ in an oven or furnace then cooled (simulating forest fire burn and smolder), as well as with soils devoid of organic carbon (after loss on ignition). The hypotheses are: 1) REEs may volatilize more with higher temperatures, and may change with varying cooling rates; 2) signature element sequestration may depend on the amount of clay or remaining carbon (a factor of colloids and surface area).