Quantifying soil hydraulic property changes with fire severity by laboratory burning; data from Wieting et al. (2017)

Abstract

Infiltration processes are not well understood in fire-affected soils because soil hydraulic properties and soil-water content are altered by the heat. This study uses intact soil cores, which should maintain preferential flow paths, that were collected in the field to explore the impacts of fire on soil properties and infiltration processes during rainfall. Three soil scenarios are presented here: unburned control soils, and low- and high-severity burned soils. Fire severity was simulated in the laboratory using a heating gun, and established based on temperature and duration of heating. Soil properties pre- and post-burn were measured using laboratory techniques including: Mini Disk Infiltrometer tests, Water Drop Penetration Time (WDPT) Tests, and measurements of dry bulk density and total organic carbon (TOC). Soil moisture and temperature were recorded at approximately 2.5 cm and 7.5 cm in soil cores as was the cumulative volume of water exiting the core during rainfall simulations. Mini Disk infiltration experiments suggest a decrease in both cumulative infiltration and infiltration rates from unburned to low-severity burned soils. High-severity burned soils saw an increase in cumulative infiltration. We interpret these changes as a result of the burning off of organic materials, enabling water to infiltrate more instead of being stored in the organics. The field saturated hydraulic conductivity did not vary from unburned to low-severity burned soils, but increased in high-severity burned soils due to the lack of organics that help inhibit water movement. During rainfall simulations, soil-water storage decreased from when soils were burned, likely because of the inability to store water within organic materials since they were burned. Vulnerability to raindrop impact also increased with fire severity. Together, these results indicate that fire-induced changes from low-severity wildfires were not as drastic as high-severity wildfires, and that high-severity burned soils can infiltrate more water, but not necessarily store it. Quantifying soil properties affected by wildfire, which can be gained through controlled laboratory simulations like this study, will aid in predicting post-wildfire behavior on the watershed scale.