Use of Magnetic Fly Ash to Assess Upper Sangamon Basin Post-Settlement Sedimentation Rates

Sedimentation rates have been one of the most important factors that impact the landscapes and livelihoods of residents in Midwestern states. The occupation of the landscape by Europeans started in the mid- l800s, when the use of coal for heating houses and then later for railroads and power plants liberated humans' ability of production. This study focuses on the measurement of magnetic spherules, a byproduct of coal combustion call fly ash, as the marker of the beginning of coal burning in the upper Sangamon basin valley alluvium. Alluvium are river deposits left behind by the flowing of water. Samples were collected and analyzed from seven sites in 10 cm intervals up to 1.5 m beneath the ground throughout different parts of the Sangamon River valley and its tributary valleys. Fly ash were extracted and purified from the samples and examined under the microscope to try to provide a basis for identifying post-settlement alluvium from pre-settlement alluvium. The extracted magnetic fraction was also examined under a scanning electron microscope to confirm fly ash in alluvium. The data were combined with previous data collected from soil samples in the other locations in the area and analysis showing interesting relationships between fly ash percentage and depth beneath the surface. Alluvium from the tributaries shows that the highest fly ash percentage, about 15-20 percent, is at the 10-20 cm interval, while the main valleys in Allerton Park, Champaign County peaks around 35-40 cm beneath the surface with a 40-45 percent fly ash content. The data shows an increasing trend from the bottom of the soil core that peaks and then decreases. This result can suggest a correlation with the effects of the Clean Air Act implemented in the 1970s. Particle size analysis shows increases and decrease throughout the soil sample core. Sedimentation rate can be further examined through the data collected and analyzed to find any observable trends post European settlement. This study can provide valuable insight for scientists to understand the effects of modem agriculture and the impact to soils that industrialization and urbanization has brought upon this landscape. This project was originally part of the Critical Zone Observatory project, funded by NSF and later by the National Great Rivers Research and Education Center, to better understand human impacts on landscapes.