COMPARISON OF MOJAVE DESERT VARNISH AND SOIL USING FATTY ACID ANALYSIS

Desert (or rock) varnish is a dark coating predominantly composed of clays, and Mn- and Fe-oxides, which is commonly found in arid environments. It is a prominent feature of the Mojave desert of southern California, as well as in many deserts around the world. The mechanism of formation of these surficial deposits has been speculated to be biological, geochemical, or a combination of both processes (Taylor-George et al., 1983; Potter and Rossman, 1979). Wind-blown dust accumulating on rocks in desert environments has been proposed as a source for desert varnish material (Allen, 1978). The purpose of this study is to analyze the fatty acid content of rock varnish and adjacent soil samples from the Mojave desert to constrain the maximum amount of biomass, and to assess whether a unique biota inhabits varnished rocks. Lipids were extracted with methylene chloride/methanol, converted to fatty acid methyl esters, and analyzed by GCMS. Preliminary data from soil samples indicate fatty acids commonly associated with fungi and bacteria. These include 18:2D9,12 and 18:1D9, which are often associated with fungi (Bååth, 2003). Bacterial cell density, estimated using fatty acid analysis of Mojave desert soils was generally less than about 10⁸ cells/gram. No trends were observed from soil samples collected from different sites, and no correlation was found between varnished rocks and adjacent soil samples.

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