James Hunt

Date of Award

2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Plant, Soil, and Environmental Sciences

Advisor

Tsutomu Ohno

Second Committee Member

Bryan Bail

Third Committee Member

Zhongqi He

Abstract

Dissolved organic matter (DOM) derived from a number of fresh and decomposed plant biomass and animal manure sources was chemically characterized using high performance size-exclusion chromatography (HPSEC), UV-vis spectroscopy, potentiometric titration, XAD fractionation, and fluorescence spectroscopy in both emission and excitation-emission matrix (EEM) modes. The EEM fluorescence data was modeled into spectral and concentration components using parallel factor analysis (PARAFAC). In most cases, source decomposition significantly increased the molar absorptivity, humification index (HIX), hydrophobicity, apparent molecular weight (MWAP) and humic-like fluorophore component concentrations of the DOM solutions. For a majority of the DOM extracts, the ratio of fluorescence intensity to molar absorptivity at 254 nm increased following decomposition, indicating that fluorescing DOM compounds were generally more resistant to biodegradation than non-fluorescing UV absorbing compounds. Correlation analysis showed a strong positive relationship between the EEM humic-like components and the MWAP, absorptivity, and HIX of the DOM solutions. In most cases, sorption of DOM onto the surfaces of goethite, gibbsite and kaolin was also strongly and positively related to these DOM parameters. Adsorptive fractionation following sorption corroborated the preference of the three mineral surfaces for DOM of higher MWAP, HIX and molar absorptivity. Sorption of DOM to goethite and gibbsite was significantly decreased in the presence of added orthophosphate (P), as were correlations between sorption and humification parameters. Thus, addition of P substantially lowered fractionation of DOM following sorption to goethite and gibbsite. In contrast, few significant P sorption-induced differences were observed in the kaolin system. According to one-point P sorption results, DOM in the form of Aldrich humic acid, oxalate, and decomposed clover and corn residue significantly inhibited P sorption to goethite at concentrations of 50 and 200 mg CTS L-1. Orthophosphate sorption to gibbsite was significantly inhibited by 50 mg CTSL-1 derived from decomposed corn residue, fresh dairy manure residue and oxalate solution. At 200 mg CTS L-1, all DOM solutions were found to inhibit P sorption to gibbsite. This research suggests that DOM inhibition of P sorption depends on the chemical properties of both the sorbent and the DOM itself. In general, DOM from decomposed organic materials inhibited P sorption to a greater extent than did DOM derived from fresh materials. This stronger inhibition highlights the importance of microbial processes in the release of soluble soil P, a key determinant of P availability to plants.

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