GRASS FIRES - AN UNLIKELY PROCESS TO EXPLAIN THE MAGNETIC PROPERTIES OF PRAIRIE SOILS

It has been proposed that grass fires affect the magnetic properties of soils [e.g., Kletetschka and Banerjee, 1995] by combining generally reducing soil conditions with elevated temperatures. In this study we analyzed surface and subsurface samples from loessic soils and compared their differences in magnetic properties as a function of fire intensity. Fire intensity was established based on types of burnt vegetation, which ranged from low-intensity fires in short-grass areas to high-intensity fires in tall-grass and forested areas. We measured low-field magnetic susceptibility, a common proxy for the abundance of magnetic minerals, frequency-dependent susceptibility, a proxy for the presence of ultrafine-grained superparamagnetic minerals, and anhysteretic remanent magnetization, a magnetic proxy highly dependent on the presence of fine, single-domain magnetic particles. Although intense fires led to an increase in frequency-dependent susceptibility, no change occurred in the low-field susceptibility and ARM parameters. Magnetic changes are limited to sites that were very heavily burned in forest areas. These results agree with previous studies that found no increased magnetic enhancement in soils from burned short- and tall-grass prairies [Lopez et al., 2010].

Kletetschka, G., and S. K. Banerjee (1995), Magnetic stratigraphy of Chinese loess as a record of natural fires, Geophys. Res. Lett., 22(11), 1241-1343.

Lopez, G., W. C. Johnson, and C. E. Geiss (2010), The Effect of Prairie Fires on the Magnetic Properties of Modern Soils at Konza Prairie, Kansas, Abstract GP13B-0783 presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec.