INTEGRATED SET OF METHODS FOR EVALUATING SOIL EROSION AND TRANSPORT
A 9m by 4m plot was created in a no-till field near Treynor, Iowa. We compared pre- and post-event elevation data to produce a DEM showing the location and magnitude of erosion and deposition. These data were combined with measured soil bulk densities to estimate the masses of sediment eroded from and deposited within the plot and the sediment yield from the plot. We also measured sediment fluxes from the plot to compare with estimates derived from the laser scanning. We measured the distribution of Be-7, Cs-137, and Pb-210 in the soil profile, the radionuclide flux in rainfall, and the radionuclide flux out of the plot in runoff. Radionuclide activity profiles in the soil vary with depth in the soil and landuse history and by radionuclide which permits estimates of the relative contributions of surface and deeper soil to the flux from the plot. Finally, we applied rare-earth tagged soils in strips in the upper, middle, and lower part of the erosion plot and measured their concentrations in runoff and in soil.
The results indicate that 45% of the plot featured net erosion, 12% no net change, and 43% net deposition. Estimates of soil loss derived from the DEMs were within 20% of the measured sediment flux. The radionuclide concentrations in the soil combined with the depth distribution of erosion yielded radionuclide fluxes within 20% of measured values. The timing of radionuclide fluxes is interpreted to reflect initial dominance of surface erosion as evidenced by high Be-7 activities. Rare earth tagged soils indicate that the largest portion of sediment flux was derived from the lowest part of the plot and contributions to flux decreased progressively up slope. At most, only about 13% of the eroded material moved off the plot. The rest was re-deposited within the plot.