EROSION PATTERNS ON CULTIVATED AND UNCULTIVATED HILLSLOPES DETERMINED BY SOIL FLY ASH CONTENTS

Abstract

The severity of accelerated erosion is affected by slope gradient, slope shape, slope length, and tillage practices. Fly ash, the product of high temperature coal combustion, has been used previously as a sedimentation marker, but it has never been used on the upland as an indicator of soil loss from erosion. The objective of this study was to determine the extent of soil removal from a hillslope as a result of accelerated erosion and its subsequent deposition on a lower landscape position using the presence, depth distribution, and concentration of fly ash, organic carbon, and magnetic susceptibility to identify the remaining original soil as well as a sediment marker. The study was carried out by comparing the amount of fly ash contained in the soil profile at different landscape positions of a cultivated site with that in an uncultivated woodland site. Fly ash deposition began in 1855 with traffic on the Illinois Central railroad between Chicago and Cairo, Illinois. In 1889 and 1928, additional rail lines were located closer to both sites. Organic C, magnetic-mineral content, and magnetic susceptibility decreased regularly with depth at both sites. Magnetic susceptibility was generally higher on the uncultivated site compared with the cultivated site for all landscape positions except the lower footslope. Compared with the uncultivated site, there was 50% less fly ash on interfluve and shoulder landscape segments of the cultivated site, 35% less on the backslope, and 67% less on the depositional lower footslope position. When the entire transect site is considered, the cultivated site had 47% less fly ash in the upper 22.5-cm soil profile compared with the uncultivated site. These results indicated that 10.6 cm, or 47%, of the upper soil layer has been eroded from the hillslope since 1855 (142 years) as a result of accelerated erosion induced by cultivation. For the backslope, the presence of 65%, or 15 cm, of the original surface soil layers and 67% of the fly ash at the cultivated site places the soil in the moderately eroded phase of the Grantsburg soil.