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Distinguishing black carbon from biogenic humic substances in soil clay fractions

Geoderma

By:
, , , , and
DOI: 10.1016/j.geoderma.2007.10.025

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Abstract

Most models of soil humic substances include a substantial component of aromatic C either as the backbone of humic heteropolymers or as a significant component of supramolecular aggregates of degraded biopolymers. We physically separated coarse (0.2-2.0????m e.s.d.), medium (0.02-0.2????m e.s.d.), and fine (> 0.02????m e.s.d.) clay subfractions from three Midwestern soils and characterized the organic material associated with these subfractions using 13C-CPMAS-NMR, DTG, SEM-EDX, incubations, and radiocarbon age. Most of the C in the coarse clay subfraction was present as discrete particles (0.2-5????m as seen in SEM images) of black carbon (BC) and consisted of approximately 60% aromatic C, with the remainder being a mixture of aliphatic, anomeric and carboxylic C. We hypothesize that BC particles were originally charcoal formed during prairie fires. As the BC particles aged in soil their surfaces were oxidized to form carboxylic groups and anomeric and aliphatic C accumulated in the BC particles either by adsorption of dissolved biogenic compounds from the soil solution or by direct deposition of biogenic materials from microbes living within the BC particles. The biogenic soil organic matter was physically separated with the medium and fine clay subfractions and was dominated by aliphatic, anomeric, and carboxylic C. The results indicate that the biogenic humic materials in our soils have little aromatic C, which is inconsistent with the traditional heteropolymer model of humic substances.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Distinguishing black carbon from biogenic humic substances in soil clay fractions
Series title:
Geoderma
DOI:
10.1016/j.geoderma.2007.10.025
Volume
143
Issue:
1-2
Year Published:
2008
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geoderma
First page:
115
Last page:
122
Number of Pages:
8