Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 12/11/2006
Publication Date: 12/11/2006
Citation: Wilson, C.G., Kuhnle, R.A. 2006. Determining Relative Contributions of Eroded Landscape Sediment to the Suspended Load of Goodwin Creek Using 7Be and 210Pbxs. USDA-ARS National Sedimentation Laboratory Research Report. No. 53. 34 pp. Interpretive Summary: In Goodwin Creek, MS, the fine sediment carried downstream has two main sources: upland fields and the stream banks. This report presents a novel method of differentiating the sediment carried downstream into the eroded soils from agricultural fields and sediment from collapsed stream banks. The activities of two naturally produced radioactive elements (7Be and 210Pb) were used together to make this distinction. Identifying the main sources of sediment delivered to the stream will assist in focusing Best Management Practices to maximize their effectiveness. The two sources of sediment to Goodwin Creek, eroded surface soils and collapsed bank sediment, must have distinctly different activities to allow for identification in the suspended sediment. The suspended sediment carried downstream in Goodwin Creek is a mixture of these two types of sediment. It will have an activity that reflects this mixture by having a value that is between the activities of the two sources. A simple mixing model was used to determine the amount of sediment that came from the landscape surface and the stream banks following a rain event. Early in the rainfall event, most of the sediment came from upland fields. Later in the event most of the sediment came from the channel banks.
Technical Abstract: Identifying major contributors of fine sediment to the suspended load of a streams allows for better focus of Best Management Practices. This study utilized activities of 7Be and 210Pbxs to quantify the proportion of eroded surface soils in the fine suspended sediment load of runoff events in Goodwin Creek, MS, relative to other sources of sediment to the suspended load, predominantly collapsed bank sediment. Source materials must have unique radionuclide signatures relative to one another to quantify the contributions from the different source areas to the suspended sediment load. Due to the radionuclide profile in the soil column and the different erosion processes controlling the sediment delivery to streams, namely sheet erosion and bank collapse, eroded surface soils have higher activities of 7Be and 210Pbxs than collapsed bank sediment. The fine suspended sediment, which is a mixture of eroded surface soils and collapsed bank sediment, has an intermediate radionuclide signature that is quantified in terms of the relative contribution from both source materials. A simple two end-member mixing model determines the relative contribution from each source areas to the total fine sediment load. The radionuclide signatures of suspended sediment 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 in Goodwin Creek, MS, and suggest that eroded surface soils are more abundant in the suspended sediment early in the runoff event; however, collapsed bank sediment dominates the suspended load later in the runoff event.