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Landscape position differentiates contrasting clay mineralogy in vernal pools


Vernal pools are shallow ponds during the rainy season, but are completely dry in the summer. They are noted for their unique flora and fauna. Soils are critical to the hydrologic function of the vernal pools, but little is known about the soil mineralogy, which contributes to both their hydrologic and biogeochemical behavior.

In a recently published article in the Soil Science Society of America Journal, researchers describe the soil mineral components of a vernal pool watershed on a basalt flow in southern California, and interpret the mineral origins and relationships to the soil hydrologic environment.

Kaolin, derived from feldspar weathering, is the predominant clay mineral in the loamy upper slope soils. Excess silica and other soluble cations from mineral weathering in upper slope soils are flushed with percolating water to the lower slope positions where they accumulate and precipitate as smectite, producing clayey Vertisols. Redox conditions favor iron oxides on upper slopes, imparting reddish hues to the soils, whereas lower slope soils accumulate manganese oxides which precipitate as the soils dry and impart dark colors.

Recognizing and interpreting soil mineralogical differences are key to understanding the chemistry and drainage patterns that support the unique organisms in this ecosystem.


Read the full article online in SSSAJ. Free preview April 21 - April 28