Submitted to: Federal Interagency Sedimentation Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2005
Publication Date: 4/2/2006
Citation: Wilson, C.G., Kuhnle, R.A. 2006. Determining relative contributions of eroded landscape sediment and bank sediment to the suspended load of Goodwin Creek using radionuclides. In: Proceedings of the 8th Federal Interagency Sedimentation Conference, April 2-6, 2006, Reno, Nevada. CD-ROM. Interpretive Summary: Sediment has been identified by the US Environmental Protection Agency as the most common constituent degrading the quality of the water of the nation’s streams and rivers. Physical, chemical, and biological sediment damage has been estimated to be 16 billion dollars annually in North America. Knowledge of the rate of sediment at a location is necessary to gauge the level of impairment while knowledge of the source of the sediment is critical for designing environmentally aware management plans to rectify the sediment problem in agricultural watersheds. Currently the source and rate of sediment to the channels of an agricultural watershed may be predicted using one of the available watershed erosion models. While measured data on the total sediment rate at a location in a watershed are available, measured information on the source of the sediment is very rare. In this study, results are presented from the Goodwin Creek Experimental Watershed using a technique which uses naturally occurring substances to provide information on the sources of the sediment measured at a location of a watershed. The fraction of sediment that originated from channel boundaries and the land surface has been determined from two thunderstorm caused events on Goodwin Creek. This information provides a powerful tool to evaluate the accuracy of watershed erosion models. This information will be used to evaluate and improve sediment source prediction routines on watershed erosion models.
Technical Abstract: Identifying the major contributors to the fine suspended sediment load of a stream allows for better focus of Best Management Practices. This study was designed to quantify the relative proportion of landscape- and bank-derived sediment in the fine suspended sediment load of multiple runoff events in Goodwin Creek, MS using activities of 7Be and 210Pbxs. Each source material must have a unique radionuclide signature relative to the other to quantify the contributions from the different source areas to the suspended sediment load. Due to different erosion processes controlling the sediment delivery to streams, namely sheet erosion and bank collapse, landscape-derived sediment will have higher activities of the 7Be and 210Pbxs than contributed bank sediments. The fine suspended sediment, which is a mixture of landscape-derived sediment and collapsed bank sediment, will have an intermediate radionuclide signature that is quantified in terms of the relative contribution from both source materials. A simple two-end member mixing model would determine the relative contribution from each source area to the total fine sediment load. The radionuclide signature of suspended sediments would lie roughly along the mixing line between the signatures of the two end-member sources of sediment. Data presented here focus on one runoff event and suggest that eroded surface soils are more abundant in suspended sediment early in the runoff event; however, collapsed bank sediment dominates the suspended load later in the runoff event.