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Chemical and Spectroscopic Methods for Assessing Subsidence in Florida Histosols¹

ABSTRACT

The extent of subsidence of cultivated histosols in the Everglades of southern Florida can be assessed by chemical and spectroscopic methods. Higher subsidence rates tend to be associated with the following changes in the chemistry of humic acids, the principal constituent of histosols: (i) increases in CO₂H, phenolic OH, quinone, and ketonic C=O groups; (ii) decreases in aliphatic structures as shown by IR spectra and alcoholic OH groups; and (iii) decreases in molecular complexity as indicated by E₄/E₆ ratios and possibly by free radical measurements.

The chemical reactions involved appear to be mainly oxidative, leading at first to the degradation of aliphatic structures to C=O and CO₂H groups, and finally to attacking the more stable aromatic structures with degradation to CO₂ and H₂O.

Functional group analysis and measurements of E₄/E₆ ratios are useful and experimentally simple methods for estimating the degree of degradation of Florida histosols.

¹ Contribution from the Agricultural Research and Education Center, Inst. of Food and Agr. Sci., Univ. of Florida, Belle Glade (Florida Agr. Exp. Sta. Journal Series no. 4706) and Soil Research Institute, Canada Dep. of Agriculture, Ottawa, Ontario (no. 430).

² Assistant Professor of Soil Science at the Agricultural Research and Education Center, Belle Glade and Principal Research Scientist at the Soil Research Institute, Canada Dep. of Agriculture, Ottawa, Ontario, Canada, respectively.

Received for publication February 23, 1973. Accepted for publication July 16, 1973.