Source apportionment of lake bed sediments to watersheds in an Upper Mississippi basin using a chemical mass balance method

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.