| Much of the degradation of surface waters is linked to sediment and sediment-bound pollutants. Phosphorus, some pesticides, most metals, and many organic compounds are transported primarily in the particulate state attached to fine sediment. These pollutants are carried from the landscape by sediment eroded during runoff and are transported into surface waters attached to the suspended sediment. Evaluating the rate and magnitude of the various steps of this process is fundamental to developing measures to limit the harmful consequences of sediment and sediment-bound pollutants.; The fallout radionuclides 210Pb, 7Be, and 137CS vary in their physical properties (physical size, ionic strengths, charge, Kd, half-life, etc.) as well in their historical and continued delivery onto the landscape. Deposition, erosion, and cultivation add, remove and rearrange the radionuclides within the soils in such a way that their distributions become distinctive for each environment. These radionuclides are utilized to determine erosion rates, sediment source regions, sediment transport distances, and the magnitude of rill and sheet erosion in four separate studies. Analyses are conducted in the montane watershed of the Gold Fork River (GF), Idaho; the agricultural watersheds of Old Woman Creek (OWC), Ohio and Rock Creek (RC), Ohio; and an agricultural field in the National Soil Tilth Laboratory. Using several techniques, the GF, OWC, and RC studies establish sediment transport distances that are long relative to their respective stream lengths. All four studies determined soil erosion rates that are in good agreement with those of traditional methods, through mass balancing of radionuclides exiting the basin with their respective soil distributions. This mass balance approach is expanded to evaluate the magnitude of rill and sheet erosion resulting from storm runoff, and indicates the vast majority (95–97%) of sediment runoff is the result of rill erosion. The OWC and RC studies indicate that the 210Pb:7Be ratio of suspended sediments is uniquely associated with land use practices, thereby determining sediment source regions. The findings of these studies are significant to understanding the nature of erosion and sediment transport, and have specific implications for determining where and how erosion abatement measures should be implemented in each basin. |
