Publication Date

12-2012

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Hydrologic Sciences

Department

Geosciences

Supervisory Committee Chair

Shawn G. Benner, Ph.D.

Abstract

A geochemical investigation of upland soils in the Dry Creek Experimental Watershed (DCEW) near Boise, Idaho was conducted to assess the potential contributions of eolian dust. Major and trace element compositions of soils within the watershed, loess deposits in the adjacent Western Snake River Plain (WSRP), and underlying granodiorite bedrock were evaluated. Multiple lines of evidence suggest a significant contribution of dust in the soils. Plots of Co/Ti, V/Ti and Cr/Ti indicate that the loess and bedrock occupy distinctly different compositional spaces and that the soils are of intermediate composition, suggesting that the soils are a mixture of the loess and bedrock. In the same compositional space, isolates of the silt + clay size fraction exhibit compositions closer to the loess field than the associated bulk soils, also consistent with a dust contribution. A two-component mixing model, using the granodiorite and loess as end-members, indicates there is an average of 28% dust in the soils. This model also indicates that the dust contribution is greater in the upper portions of soil profiles, and that the dust contribution on north facing slopes is more than double that on south facing slopes (38% and 16%, respectively). Dust appears to be the dominant contributor of fine-grained material to these soils. Theoretical removal of estimated dust contributions from DCEW soils reduced soil water storage capacity by an average of 48% in the soils, suggesting that dust deposition is an important contributor to shallow water storage capacity and subsequent summertime availability in the upland soils of this watershed.

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