Quantifying relative contributions from sediment sources in Conservation Effects Assessment Project watersheds

A technique using the relationship between the naturally occurring radionuclide tracers, Be-7 and Pb-210(xs), was used to differentiate eroded surface soils and channel-derived sediments in the fine suspended sediment loads of runoff events in five Conservation Effects Assessment Project watersheds. A simple two end-member mixing model was used to determine the relative contribution from each Source. Results Suggest that eroded surface soils were more prevalent in the Suspended load early in a runoff event, but channel contributions dominated the suspended load at later stages. The method proved useful for multiple sites due to a constant proportion of the atmospheric deliveries of the two radionuclides globally. Use of only two radionuclide tracers simplifies the differentiation of sediment sources within a watershed but limits precision.