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Title: Identification of Suspended Sediment Sources Using Soil Characteristics in a Semiarid Watershed

Author
item Rhoton, Fred
item Emmerich, William
item Dicarlo, David
item McChesney, Daniel
item Nearing, Mark
item Ritchie, Jerry

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2006
Publication Date: 7/7/2008
Citation: Rhoton, F.E., Emmerich, W.E., Dicarlo, D.A., Mcchesney, D.S., Nearing, M.A., Ritchie, J.C. 2008. Identification of Suspended Sediment Sources Using Soil Characteristics in a Semiarid Watershed. Soil Science Society of America Journal. 72(4): 1102-1112.

Interpretive Summary: The primary sources of sediment and chemical pollutants transported through stream systems are the upland soils in any given watershed. The implementation of stricter water quality standards by the USEPA require innovative approaches for reducing such stream loadings for compliance purposes. We developed a soil geomorphology-based approach to quantifying soil erodibility, in terms of a soil aggregation index, to improve the accuracy of basic soil data used as fingerprints for identifying specific areas in watersheds producing the greatest amounts of sediment. The results showed conclusively that the soils the lowest aggregation indices were producing the greatest amounts of sediment. Thus, these specific sites in watersheds can be targeted for those best management practices that will affect the greatest reduction in runoff and erosion for purposes of complying with water quality standards.

Technical Abstract: As water quality standards become more stringent, a knowledge of primary sediment source areas in watersheds becomes increasingly important from the standpoint of compliance through the design of efficient management practices that will reduce sediment and chemical loadings of receiving waters to acceptable levels. The objective of this research was to use a soil geomorphology-based approach to sediment sourcing to better define the effects of soil variability on erodibility and sediment transport at the watershed scale. Each major soil mapping unit in six subwatersheds (SW) was sampled along transects positioned to include the normal soil geomorphological features associated with a given mapping unit. At each sampling point, latitude-longitude, slope class, topographic position, and aspect were recorded. Soil samples collected from the surface 5.0 cm were characterized for a range of basic physical and chemical properties used for fingerprinting purposes. Additionally, 137Cs and stable C isotopes were evaluated as potential fingerprinting analyses. Suspended sediment samples collected from supercritical flumes at the mouth of each SW were analyzed identically. An aggregation index (AI), calculated for the soils in each SW as follows: 100 (1-water dispersible clay/total clay), served as a measure of soil erodibility. The physical and chemical signatures of the suspended sediment collected at the six flumes were used in a multivariate mixing model to identify the primary contributing source. The results suggested that the SWs with the lowest soil AI were contributing the greatest amounts of sediment, as confirmed by the delta 13C data.