Title

The role of aluminum in regulating the retention of cations and dissolved organic carbon in organic forest soil horizons

Date of Award

2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Charles T. Driscoll

Keywords

Cation retention, Aluminum, Dissolved organic carbon, Forest, Soil horizons

Subject Categories

Biogeochemistry | Civil and Environmental Engineering | Earth Sciences | Engineering | Geochemistry | Physical Sciences and Mathematics

Abstract

Processes in organic forest soil horizons can play an important role in influencing surface water quality especially in watersheds where shallow flow paths through soil are important. Aluminum has an extremely high affinity for the acidic functional groups present in soil organic matter and binds nearly irreversibly with these groups. This reaction alters the response of organic forest soil horizons to atmospheric deposition as well as other environmental conditions such as calcite treatment. In this study, I evaluated the effect of organically bound aluminum on the retention of cations and dissolved organic carbon (DOC) in organic forest soil horizons.

Field and laboratory results were consistent with the reaction of aluminum with acidic functionality present in soil organic matter, and the resultant effect this reaction has on specific and nonspecific binding of protons and cations, and on DOC release. Under acidic conditions, increasing bound aluminum in organic forest soil horizons was shown to: (1) decrease acidity, and calcium concentrations in soil and solution; (2) decrease release of DOC from soil; and (3) increase aluminum concentration in soil solution. Bound aluminum had similar, but less influence under alkaline conditions, especially with respect to calcium concentrations in soil and solution. Results also showed that the heterogeneity of soil organic matter can diminish the strength of relationship observed between bound aluminum, and other solid and solution phase constituents present in organic forest soil horizons.

Field and laboratory results were reproducible with the Windermere Humic Aqueous Model (WHAM); a mechanistic model that describes proton and metal binding to humic and fulvic acids, and the effect of this binding on the solubility of organic matter. Simulations using WHAM showed that bound aluminum increased the response of organic forest soil horizons and associated solution to the environmental conditions evaluated in this study (i.e., calcite treatment of 9 Mg/hectare and a 50% reduction of individual and combined loading of basic cations and mineral acid anions). Simulations predicted that organic forest soil horizons with higher bound aluminum content would typically respond faster, and produce soil solutions with higher aluminum, and lower hydrogen ion, calcium and DOC concentrations than organic forest soil horizons with lower bound aluminum content.

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