Factors in the Reversal of Hydrophobicity of Fire Affected Soils.

In a wild fire, organic volatile compounds from vegetation condense on soil particles forming a hydrophobic layer several centimeters below the soil surface. We are studying the mechanisms of degradation of the hydrophobic layer in soils from two fire sites.  One site is located in a montane woodland (Wood Camp, Logan Canyon, UT) that burned in 2006. The second site is located in an arid pinyon pine/juniper stand in Milford Flats, Beaver County, UT that burned in 2007. Both sites were sampled in 2008. In situ measurements of hydrophobicity demonstrated highly hydrophobic layers a few centimeters below the surface at both sites in contrast with unburned control sites, which were hydrophobicity was observed at the surface but fell off sharply with depth. Samples of surface and subsurface soil were collected from the burned and unburned areas at both sites. Samples of all the soils were placed in microlysimeters, treated with acid snowmelt, elevated temperatures, and UV light. Evolved CO₂ and DOC were monitored throughout the incubation period. After the treatments, the soils were air-dried and the surfaces characterized for evidence of change by FTIR.