The Effects of Simulated Wildfire on Particle Size and Carbon Content in Piedmont Soils.

Abstract:

Soils are a known carbon sink, holding twice as much carbon as the atmosphere (Schlesinger, 1995). However, little is known about how much soil organic carbon (SOC) is released from the soil during fire events. Surface fires can heat mineral soils to up to 500°C at depths of several centimeters and maintain that temperature for hours (Werts and Jahren, 2007). This has been known to affect the size of particles in soils, carbon content in the soils, and the clay mineralogy (Hungerford et al, 1993). This study looks at relationships between soil clay content and clay chemistry in relation to carbon emissions during surface fires, to determine temperature effects on several piedmont soil types from South Carolina. Soil samples were taken from three different sites varying in clay content, clay type, parent material, and development. Temperature increases were applied in increments of 50°C, with a range from 100°C to 500°C, to determine fire effects on SOC, particle size, and clay mineralogy of the soils. We found a decrease in SOC (up to 98%) from the original amount in all soil horizons with temperature applications up to 500°C. At a temperature range between 100°C and 300°C, most soil horizons showed an increase in clay of a range between 0.1 and 34%. At temperatures ranging from 300°C to 500°C, there was a decrease in clay ranging from 2.5-42%. While previous research suggests that a positive correlation between the percentage of clay and SOC in soils is common (Feller and Beare, 1997), in this study, a negative correlation was found between the percentage of clay and SOC in all three soil types (R²=0.87, 0.76, and 0.59) at 100°C. There appears to be an increasingly positive relationship between clay and carbon as temperature increases, although a consistent high correlation was not present at all temperatures. This is counter to what was found initially in our soils prior to heating. While research into surface fires is important to the understanding of ecosystems and carbon cycling above ground, understanding SOC dynamics following a surface fire event can provide further insight on carbon cycling and erosion impacts of surface fires.