Quantifying sediment transport across an undisturbed prairie landscape using cesium-137 and high resolution topography

Soil erosion is a global environmental problem, and anthropogenic fallout radionuclides offer a promising tool for describing and quantifying soil redistribution on decadal time scales. To date, applications of radioactive fallout to trace upland sediment transport have been developed primarily on lands disturbed by agriculture, grazing, and logging. Here we use Cs to characterize and quantify soil erosion at the Konza Prairie Long-Term Ecological Research (LTER) site, an undisturbed grassland in northeastern Kansas. We report on the small scale (b10 m) and landscape scale (10 to 1000 m) distribution of fallout Cs, and show significant variability in the concentrations and amounts of Cs in soils at our site. Cs soil concentrations and amounts typically vary by 10% to 30% on small scales, which most likely represents the spatial heterogeneity of the depositional processes. Landscape scale variability of soil Cs was significantly higher than small scale variability. Most notably, soils collected on convex (divergent) landforms had Cs inventories of 2500 to 3000 Bq m, which is consistent with the expected atmospheric inputs to the study area during the 1950s and 1960s. Concave landforms, however, had statistically lower inventories of 1800 to 2300 Bq m. The distribution of Cs on this undisturbed landscape contrasts significantly with distributions observed across disturbed sites, which generally have accumulations of radioactive fallout in valley bottoms. Because the upslope contributing area at each sampling point had a significant negative correlation with the soil inventory of Cs, we suggest that overland flow in convergent areas dominates soil erosion at Konza on time scales of decades. Very few points on our landscape had Cs inventories significantly above that which would be predicted from direct deposition of Cs on the soil surface; we conclude therefore that there is little net sediment storage on this undisturbed landscape. © 2005 Elsevier B.V. All rights reserved.