Why Analyze for Trace Elements and Organic Compounds in Riverbed Sediments?
Sediments in rivers usually come from erodible materials in a watershed, primarily soils and weathering rocks. During storms these sediments wash into tributary channels and into the main channel of a river. As flow velocity and turbulence decrease following a storm, suspended particles settle, accumulating along the riverbed near the sediment sources in slow-moving waters. Reservoirs on a river system further decrease flow velocity and turbulence and accumulate the sediment transported by runoff from upstream watersheds. In the river channel where sediments accumulate, the top layer of sediment represents recent transport and deposition of erodible materials from tributary watersheds. Some transport of sediment will continue under base-flow conditions, but the transported sediment typically is finer grained; and less sediment is transported than under stormflow conditions. In a natural setting, the sources of trace elements in riverbed sediments are geologic materials and atmospheric
