Title: Fine sediment sources on conservation evaluation assessment watersheds Authors
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 2, 2014
Publication Date: N/A
Interpretive Summary: Sediment that is eroded from fields and channels in agricultural watersheds may destabilize channels which endangers bridges and other structures, degrades water quality and aquatic organisms, reduces soil fertility, decreases channel capacity and increase the likelihood of flooding. Knowledge of the sources of sediment in a watershed is necessary information needed by land use managers to effectively apply conservation practices to prevent on-site and off-site damages of eroded and deposited sediment. Through the use of naturally occurring isotopes of lead and beryllium, information on the relative sources of sediment delivered to channels in eight agricultural watersheds was determined. It was found that in six of the eight watersheds more than 50 percent of the sediment originated from channel sources. This information is important guidance for the effective design of conservation practices on these watersheds.
Technical Abstract: Two naturally occurring radionuclides, 7Be and 210Pbxs , were used as tracers to discriminate eroded surface soils from channel-derived sediments in the fine suspended sediment loads of eight Conservation Effects Assessment Project (CEAP) benchmark watersheds. Precipitation, source soils, and suspended sediment samples were collected in the watersheds from single storm events and analyzed for the radionuclide activities, which were then applied to a two end-member mixing model to determine the relative proportions from the two source areas. In larger watersheds where the transport length of the sediment was longer, the suspended sediment load contained lower proportions of eroded upland soils compared to smaller systems. The longer transport paths contained more depositional areas for fine sediment in which to settle and hence less eroded surface soils reached the stream channel resulting in higher proportions of sediment from the channels. This study showed that more than 50% of the fine sediment in six of the eight watersheds originated from channel sources that included stream banks, the riverine bed, and gullies. These results underscore the need to consider channel and gully processes when management practices are designed to reduce sediment yield in agricultural watersheds.