The Role of Dust on the Development of Granitic Soils in Southern Arizona.

Eolian dust deposition is a fundamental geomorphic process that contributes to soil formation and its associated geochemistry in landscapes spanning arid to alpine ecosystems. Fine-grained eolian inputs provide a critical medium for plant growth, in the form of nutrients and increased water holding capacities, in otherwise inhospitable or nutrient-limited terrain. Furthermore, fine-grained soil particles are incorporated into soils from in-situ production and external sources, such as dust inputs, both of which must be addressed when examining soil development. The objective of our research was to estimate dust fraction inputs to granitic soils in southern Arizona and to explore the geochemistry of the dust, soils, and rocks using immobile elemental ratios. Dust samples were collected from ridge top dust traps placed in the desert scrub and mixed conifer sites encompassed by the Catalina Critical Zone Observatory. The collected dust samples were examined using x-ray fluorescence and a geochemical method was employed to estimate dust fraction inputs to the soils. The desert scrub and mixed conifer soils exhibited unanticipated gains in biotite, Fe+Mg, and total feldspars, confirming that eolian deposition may have significant impacts on the development of regolith profiles. Dust fraction estimates ranged from 1 to 16% in desert scrub divergent soils and 1 to 21 % in convergent pedons. In the mixed conifer soils, dust fraction inputs spanned 1 to 19% in the divergent sites and 2 to 35% in the convergent landscapes. These findings suggest that eolian deposition may have significant impacts on soil development across the SCM and requires further consideration.