Using Sediment Fingerprinting Techniques to Elucidate Sediment and Phosphorus Transport Dynamics in an Agricultural Watershed.

A study was conducted in the Pleasant Valley Watershed (50 km ²) in South Central Wisconsin to better understand sediment transport processes using sediment fingerprinting techniques.  The results of event-based sampling using ²¹⁰Pb_xs, ⁷Be, and P as tracers indicate that agriculture is the dominant source of suspended sediment in the predominantly agricultural subwatershed, while both stream banks and agriculture are important sources of suspended sediment in the mixed land-use subwatershed. Fine sediment deposition on the stream bed was the dominant process during the smaller storm event; however, resuspension of bed sediment was important during the larger storm event.  The use of inorganic tracers to identify sources of fine sediment deposited on the stream bed showed that both stream bank and agriculture are important sources of sediment depending on the location within the watershed. Land use distribution within each subwatershed significantly affected the relative contribution from different sources to fine sediment deposited on the stream bed. Sources of suspended sediment varied temporally and spatially within this watershed. Generally, relative contributions from agriculture were greater during periods of high sediment loading at the watershed outlet, with the exception of snowmelt runoff, during which stream banks were important sources of suspended sediment.  To target best management practices effectively, identification of both suspended and bed sediment is needed.  The spatial and temporal variability in sediment transport dynamics within this watershed highlights the complexities involved in linking upland and in-stream sediment transport processes.