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Analytical distinctions of carbonates in desert soils

Kraimer, Rebecca Ann

Titre : Analytical distinctions of carbonates in desert soils

Auteur : Kraimer, Rebecca Ann

Université de Soutenance : NEW MEXICO STATE UNIVERSITY

Grade : Doctor of Philosophy (PhD) 2003

The steady rise in atmospheric carbon dioxide (CO2) has evoked much interest in the reservoirs and fluxes within the global carbon (C) cycle. The reservoir of soil carbonate (a.k.a. soil inorganic carbon, SIC) may serve as a sink for atmospheric CO2, especially in and and semi-arid environments where soil carbonate generally persists in the soil profile. However, not all SIC has the potential to remediatively sequester atmospheric CO2. In order to quantify desert soils as a remediative sink for atmospheric CO2 it is, therefore, necessary to identify and understand soil carbonate types.
The objective of this research project was to examine the efficacy of three analytical techniques for the purpose of classifying carbonates in desert soils with respect to atmospheric CO2 sequestration. Qualitative analysis with scanning electron microscopy (SEM) examined the biogenic morphology of calcified root hairs, fungal hyphae, needle-fibers, and peloids. No distinctions were apparent between the carbonate types under study. Evidence for the morphological evolution of needle-fibers and the biogenic formation of peloids was introduced.
Semi-quantitative analysis with x-ray diffractometry (XRD) revealed no mineralogical distinctions among the types of soil carbonate. All soil carbonate in this study was calcite. However, statistical scrutiny of d-spacings revealed several significant distinctions which need confirmation by a state-of-the-art XRD. Quantitative analysis with mass spectrometry (MS) revealed significant differences in δ13C values between some types of soil carbonate. In addition, a distinct positive relationship between δ 13C and particle size was apparent ; δ13C decreased with progressively decreasing particle size.
Of the three techniques investigated, microscopic analysis of biogenic carbonate morphologies offered the least promise. Both XRD and MS proved to be promising techniques for classifying the components of soil carbonate. However, each technique had its limitations. For the purpose of assessing atmospheric CO2 sequestration by SIC, optimal classification of the soil carbonate components may benefit from a combination of both XRD and MS.


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Page publiée le 13 février 2004, mise à jour le 11 novembre 2018