Rayleigh Distillation and the Depth Profile of ¹³C/¹²C Ratios of Soil Organic Carbon From Soils of Disparate Texture In Iron Range National Park, Far North Queensland, Australia

Authors

Jonathan G. Wynn, Australian National UniversityFollow
Michael I. Bird, Australian National University
Vanessa N.L. Wong, Australian National University

Document Type

Article

Publication Date

4-2005

Digital Object Identifier (DOI)

https://doi.org/10.1016/j.gca.2004.09.003

Abstract

A depth- and particle size-specific analysis of soil organic carbon (SOC) and its isotopic composition was undertaken to investigate the effects of soil texture (or particle size) on the depth profile of stable carbon isotopic composition of SOC (δ¹³C_SOC) in two tropical soils. Depth-specific samples from two soil profiles of markedly different texture (coarse grained and fine grained) were separated into particle size classes and analyzed for the (mass/mass) concentration of SOC (C) and δ¹³C_SOC. Within 1 m of the soil surface, δ¹³C_SOC in the coarse-textured soil increases by 1.3 to 1.6‰, while δ¹³C_SOC from the fine-textured soil increase by as much as 3.8 to 5.5‰. This increasing depth trend in the coarse-textured soil is approximately linear with respect to normalized C, while the increase in the fine-textured soil follows a logarithmic function with respect to normalized C. A model of Rayleigh distillation describing isotope fractionation during decomposition of soil organic matter (SOM) accounts for the depth profile of δ¹³C_SOC in the fine-textured soil, but does not account for the depth profile observed in the coarse-textured soil despite their similar climate, vegetation, and topographic position. These results suggest that kinetic fractionation during humification of SOM leads to preferential accumulation of ¹³C in association with fine mineral particles, or aggregates of fine mineral particles in fine-textured soils. In contrast, the coarse-textured soil shows very little applicability of the Rayleigh distillation model. Rather, the depth profile of δ¹³C_SOC in the coarse-textured soil can be accounted for by mixing of soil carbon with different isotopic ratios.

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Citation / Publisher Attribution

Geochimica et Cosmochimica Acta, v. 69, issue 8, p. 1961-1973

Scholar Commons Citation

Wynn, Jonathan G.; Bird, Michael I.; and Wong, Vanessa N.L., "Rayleigh Distillation and the Depth Profile of ¹³C/¹²C Ratios of Soil Organic Carbon From Soils of Disparate Texture In Iron Range National Park, Far North Queensland, Australia" (2005). School of Geosciences Faculty and Staff Publications. 231.
https://digitalcommons.usf.edu/geo_facpub/231