We observed the micromorphology of artificial depositional crusts with a petro-graphic light microscope and a scanning electron microscope. The density and morphology of the crusts are strongly influenced by electrolyte concentration. Crusts formed from soil material (sandy loam texture, ESP 4.8) suspended in 0.002 M CI− solution had the highest bulk densities (1.95 Mg m−3); surface application of phos-phogypsum produced the lowest density crusts (1.41 Mg m−3). Crusts produced from suspension of soil material in distilled water and 0.005 M CI− had intermediate bulk densities. Suspensions of soil material in distilled water produced crusts with highly birefringent, oriented layers of clay; suspended material penetrated at least 5 mm into the bulk soil. The other treatments produced no birefringent, oriented layers. Suspended material penetrated the bulk soil, but to a lesser extent than with the distilled water treatment. Electrolyte concentration affects the degree of dispersion of clay-sized particles and the stability of the suspension produced. Clay particles are more dispersed and form more stable suspensions when salt concentration is low. Deposition and infiltration of the dispersed particles produce dense surficial crusts with oriented clay layers and very low permeability. At higher salt concentrations, clays are less dispersed and suspensions are less stable. Settling of flocculated particles forms a more porous crust due to more random orientation of particles. Depositional crust generally differs from structural crust in that most of the fine particles are concentrated at the upper surface of the crust, and a washed-in zone below the surface is not strongly developed, although penetration of dispersed material into the underlying soil increases as electrolyte concentration decreases.
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