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Journal of Environmental Quality Abstract -

Relationship of the Nature of Suspended Clay Minerals to Hydrologic Conditions1


This article in JEQ

  1. Vol. 11 No. 3, p. 433-436

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  1. David Laird and
  2. M. E. Harward2



The clay mineralogy of sediments in suspended transport and their relationship to soils of a small agricultural watershed in western Oregon were evaluated. The clay fraction (<2 µm) was separated from suspended sediment and watershed surface soil samples by centrifugation in distilled water. Half of the clay fraction of each sample was Mg2+-saturated and the other half was K+-saturated. Slides of both the Mg2+- and K+-saturated fractions were prepared and subjected to a sequence of characterization treatments. After each treatment the samples were analyzed using copper k-alpha radiation on a Norelco x-ray diffractometer.

It was initially anticipated that the characteristics of sediments would change with progression of the rainfall season as downcutting began to erode material from the upper B horizon. However, no general seasonal trend in the nature of suspended clays was observed. Rather, the character of the entrained clay minerals was dependent on the type of hydrologic event. During high-energy hydrologic conditions, the clay mineralogy of suspended sediments was similar to that of the upper horizons of the watershed soils. In low-energy hydrologic conditions, the suspended sediments were enriched with well-organized kaolinite and smectite and depleted of chloritic intergrades. Selective dispersion combined with preferential settling of “nondispersed” materials are thought to be the mechanisms involved with this phenomenon.

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