Date of Award

Fall 12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

Program/Concentration

Chemistry

Committee Director

Patrick G. Hatcher

Committee Member

Andrew S. Wozniak

Committee Member

James W. Lee

Committee Member

Balasubramanian Ramjee

Committee Member

Sandeep Kumar

Abstract

With higher occurrences of forest fires worldwide, there has been an increase in scientific interest surrounding the chemistry of pyrogenic organic matter (pyOM). The main structural components of pyOM, the condensed aromatic compounds (ConAC), exhibit intriguing physico-chemical properties and have been one of the main focuses of biogeochemical research. The overwhelmingly large number of scientific articles regarding pyOM and ConAC are guided by the assumption that ConAC in the environment are exclusively of pyrogenic origin, even though some recent studies have suggested that some of these ConAC could also be derived from non-pyrogenic radical-driven processes. To evaluate this controversial proposition, two wood samples exposed to Fenton chemistry through iron nails are evaluated using several qualitative and quantitative techniques. Presented is quantitative evidence that ConAC can be produced non-pyrogenically from terrestrial biomass upon exposure to reactive oxygen species. Evidence from this study directly challenges the dogmatic assumption that ConAC are solely pyrogenic and implores that the global estimates of the contributions of fire-derived organic matter to both terrestrial and aquatic ecosystems must be re-evaluated.

During rain events, significant amounts of pyOM enter the aquatic environment by dissolution and become known as dissolved pyOM (pyDOM). Then, degradative processes driven by sunlight and microbes can alter its composition. Using advanced analytical techniques, the structural and molecular changes that occur to pyDOM after photo-irradiation and microbial incubation were evaluated. Multiple new insights into the photochemical degradation of pyDOM were uncovered, including the evolution of new structural entities, the development of a photo-transformation pathway, and the attribution of photo-reactivity to fire temperature and pyrolyzed biomass type. The bio-incubation of pyDOM with soil microbes indicated that a portion of pyDOM has been incorporated into microbial biomass which vastly differed for each different incubation. The lability and observed diversity in composition of the microbially produced compounds indicate that pyDOM contributes to the large complexity and diversity of natural organic matter in the environment.

Results from this Dissertation advance our understanding of pyOM, pyDOM, and ConAC in the environment, and reveal that the sourcing and degradation (fate) of ConAC (and, therefore, of pyOM/pyDOM) are much more complex than originally perceived.

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DOI

10.25777/fpsv-4e28

ISBN

9798557052610

ORCID

0000-0002-5103-0838

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