Fly-ash distribution to assess erosion and deposition in an Illinois landscape

Fly ash, the particulate matter resulting from high temperature combustion of coal, was historically dispersed into the atmosphere and settled as fly-ash spheres on the surface soil from a variety of boilers, including those of steam locomotives and steam-powered farm machinery. In Central Illinois, fly ash provides a time marker extending back to 1850s, coinciding with the development of railroads and cultivation. Two railroads, the primary sources of fly ash, were constructed just south of the Cahokia study site in 1852 and 1854. The objectives of this study were to determine: (1) the distribution, depth of occurrence and the total amount of fly ash present in soil profiles on stable, cultivated and uncultivated summit sites with little or no soil erosion; (2) the effects of elevation, aspect, slope gradient, landscape position, distance from source, past vegetation and time on the amount and depth of fly ash; (3) the effects of erosion on sloping sideslopes; and (4) the amount of deposition of fly-ash rich sediment on footslopes and toeslopes. Total fly-ash content of soil was similar for stable, cultivated and uncultivated summits. Two mound sideslopes maintained a high amount of fly ash because of a lack of cultivation and erosion for the past 80 or more years. Erosion reduced the depth of occurrence and the amount of fly ash present on cultivated sideslopes. It appeared that fly-ash content was initially deposited uniformly within the local landscape even though there were slight variations in the aspect, elevation, slope gradient, and distance from the source. The erosion phases of the soils on all landscape positions were determined based on the amount of fly ash remaining in soil surface layers. Accelerated erosion of cultivated sideslopes resulted in the deposition of fly-ash rich sediment on the adjacent footslopes or toeslopes. The proposed fly-ash method provides a tool to assess the extent of soil translocation from a cultivated landscape and subsequent deposition.