Soil, landscape, and erosion relationships in a northwest Illinois watershed

The study area consists of a first-order drainage basin about 10 ha in size. The hillslopes have mean gradients of 6 to 10% with overland flow the primary contributor to erosion. A detailed geomorphic map of the watershed was constructed on a 1-m topographic survey base map. Map units were delineated based on slope shape, gradient, and USDA erosion class. Erosion classes were determined for the transect pedons by comparison with two uneroded and uncultivated pedons in area cemeteries with similar slope gradient, slope shape, slope length, and landscape positions. The A horizon thickness and organic C content decreased and clay content increased as a consequence of cultivation and erosion. Transect data for all hillslope geomorphic units showed the erosion classes near the shoulder to be either slightly or moderately eroded. The lower backslopes and upper footslopes, just above the sediment basin, were either severely or very severely eroded, suggesting slope length to be the dominant factor affecting erosion. The geomorphic units with concave across-slope shapes were found to be less eroded than those with convex across-slope shapes. -Authors