Quantifying the magnitude of historical anthropogenic soil loss in the Midwestern United States

Abstract:

Anthropogenic soil erosion in agricultural landscapes is a major concern for crop production, social stability, and environmental quality. It has been recognized for a century that agricultural practices in the midwestern U.S. have degraded soils. Erosion rates have been measured experimentally over short timescales, but the total amount of soil that has been lost since the initiation of agriculture is poorly constrained. Although most of the midwestern U.S. has been converted to farmland, native prairie remnants, which record the pre-settlement topography, are scattered throughout the landscape. Accelerated rates of anthropogenic soil loss has created erosional escarpments between fields and adjacent prairies, causing the prairies to become perched above the surrounding farmland. We conducted high-precision surveys of the boundary between 20 native prairies and agricultural fields in the Midwest to quantify the elevation difference between the perched prairie remnants and row-crop fields. Assuming the initiation of erosion coincided with European settlement of the region, median erosion rates in the agricultural fields range from 0.2–4.3 mm yr^-1. The median erosion rates at 15 of the fields are greater than the soil loss tolerance value assigned to the soils by the U.S. Department of Agriculture. Most erosion has occurred on convex hilltops and hillslopes, where tillage erosion, which is a diffusion-like soil transport process, is predicted to be dominant. We combined our erosion rate measurements with topographic curvature derived from high-resolution LiDAR data to calculate a region-wide diffusion coefficient (D). We estimate D is equal to 0.19±0.03 m² yr^-1 in the Midwest, which is consistent with previous measurements of soil transport by tillage. The value of D we calculate is orders of magnitude higher than values measured in undisturbed landscapes, highlighting the role agriculture has played in increasing rates of soil transport and landscape evolution during the Anthropocene.