Sediment samples were collected from three known sources contributing to a depositional basin of the Upper Mississippi River, USA. The heavy silt fraction (2-63 μm, density > 2.95) isolated from the sediments was analyzed for 42 elements by inductively coupled plasma-mass spectrophotometry (ICP-MS) to give signature profiles characteristic of each source catchment. Known proportions of heavy silt fractions from each source were mixed and the composite samples analyzed in the same way. The proportions of components in the composite samples were compared to their apportionments calculated statistically using the US Environmental Protection Agency (USEPA) chemical mass balance (CMB) air quality receptor model. This showed that the CMB technique can apportion sediments to their catchment sources reliably. The technique was then applied to dated sediments of Lake Pepin, in the Upper Mississippi basin, to apportion them to their contributing catchments. The results show that almost all the recent sediments deposited in the basin originated in the Minnesota River catchment, and that the sediment load increased over time as anthropogenic impacts increased. This technique could be used elsewhere to determine sediment provenance and identify changes in sediment sources over time.
Bibliographical noteFunding Information:
This study was funded in part by the Metropolitan Council Environmental Services, St. Paul, Minnesota. The authors thank D.R. Engstrom and J.E. Almendinger of the St. Croix Watershed Research Station, Science Museum of Minnesota, for their cooperation and the use of their unpublished data on sediment dating and accumulation in Lake Pepin.
- Clastic sediments
- Lake sediments
- Mass balance