COMPARISON OF FLY-ASH AND RADIO-CESIUM TRACER METHODS TO ASSESS SOIL EROSION AND DEPOSITION IN ILLINOIS LANDSCAPES (USA)

The radio-cesium (cesium-137 137Cs) and technogenic magnetic tracer (magnetic fly-ash spheroids) methods for the quantitative assessment of erosion-deposition processes were compared on Illinois landscapes with both cultivated and uncultivated sites located near Springfield, IL. The objectives of this study were to determine (1) the variability of the 137Cs and fly-ash contents within a stable landscape position, (2) the distribution and amount of fly ash and radio-cesium present in soil profiles on cultivated and uncultivated landscapes (summit, upper sideslope, lower sideslope, and alluvial fan/floodplain); and (3) the extent of soil erosion and deposition at four landscape positions on cultivated and uncultivated transect sites using both the radio-cesium and technogenic magnetic tracer methods. On a stable site, the fly-ash method had significantly greater natural variability (40% vs. 27%) than the 137Cs method as a result of bioturbation. The fly-ash and 137Cs methods did provide consistent results for six of eight cultivated and uncultivated landscape positions. At the other two sites where significant deposition or erosion did occur before the 1960s, the amount of erosion loss was different. The applicable time period for the fly-ash method assessment of the erosion and deposition situation was during the last 150 years, whereas the 137Cs method only assessed the last 50years. Land use, vegetation, erosion, and deposition may have differed during the first 100 years (1860s-1960s) of European settlement from those of the last 50 years (1960s to present) at the cultivated and uncultivated sites. Any such impact, either deposition or erosion before the 1960s, would not be reflected in the 137Cs data but would be reflected in the fly-ash data.