The Piedmont region of the southeastern United States experienced a period of accelerated erosion in the 1800s. Clear-cutting of the forests coupled with soil tilling and inadequate erosion control practices led to substantial soil redistribution and loss. This redistribution exposed the subsoil clay (argillic) horizon in many locations and adversely altered the hydrologic processes across the landscape. Understanding current hydrologic and biogeochemical processes in this landscape requires an accurate assessment of this soil redistribution and the current depth to the argillic horizon. To achieve this mapping, the depth to the argillic horizon was measured in highly eroded (historically farmed) and undisturbed hillslopes (reference areas). In addition to directly measuring the depth to the argillic by soil auguring, and tile push probing we made geophysical measurements via electromagnetic induction (EMI) to assess our ability to predict the depth to the argillic horizon remotely. Combining these measurements with site topographic characteristics (i.e. landscape position, aspect, percent slope) we generated predictive models of the depth to the argillic horizon. Direct measures indicated that historically farmed watersheds, although reforested since the 1930s, had significant soil redistribution present (p-value = 0.0521) in the toe-slope position compared to reference landscapes which had fairly consistent depths. Our data suggests geophysical sensing is an efficient means of predicting depth-to-clay on previously farmed sites when combined with landscapes feature characteristics (R2 = 0.69); however, caution should be used when selecting these characteristics, as they may not represent all land use types.
Ryland, Rachel Carolan (2017): Depth to the Argillic Horizon on Historically Farmed Soil in the Southeastern USA Piedmont: Spatial Mapping and Hydrologic Influence. Master's Thesis, University of Georgia.