HR: 0800h
AN: B51C-0604    [Abstracts]
TI: Linking photochemical transformation of an Antarctica Fulvic Acid to diminished bioavailability and oxidation of organic electron shuttles
AU: * Fimmen, R L
EM: fimmen.2@osu.edu
AF: School of Earth Sciences The Ohio State University, 275 Mendenhall Laboratory 125 S. Oval Mall, Columbus, OH 43210, United States
AU: Guerard, J J
EM: jenn.guerard@gmail.com
AF: School of Earth Sciences The Ohio State University, 275 Mendenhall Laboratory 125 S. Oval Mall, Columbus, OH 43210, United States
AU: Miller, P L
EM: penney.miller@rose-hulman.edu
AF: Department of Chemistry Rose-Hulman Institute of Technology, 5500 Wabash Ave. CM 109, Terre Haute, IN 47803, United States
AU: Cory, R M
EM: cory@chem.umn.edu
AF: Department of Chemistry University of Minnesota, 139 Smith Hall 207 Pleasant St. SE, Minneapolis, MN 55455, United States
AU: Chin, Y
EM: yo@geology.ohio-state.edu
AF: School of Earth Sciences The Ohio State University, 275 Mendenhall Laboratory 125 S. Oval Mall, Columbus, OH 43210, United States
AU: Foreman, C M
EM: cforeman@montana.edu
AF: Center for Biofilm Engineering Montana State University, P.O. Box 173980, Bozeman, MT 59717, United States
AU: McKnight, D M
EM: Diane.McKnight@colorado.edu
AF: INSTAAR University of Colorado at Boulder, 450 UCB, Boulder, CO 80309, United States
AB: Photolysis of fulvic acid isolated from Pony Lake, Antarctica, a hypereutrophic coastal pond located on Ross Island, was evaluated for transformation kinetics and photo-bleaching mechanisms by spectroscopy, as well as changes in bioavailability. The fulvic acid fraction of Pony Lake was isolated by sorption to non-ionic XAD-8 resin, and represents the fraction of the dissolved organic matter considered to be the most photo-reactive fraction. Spectroscopic and electrochemical analysis during Pony Lake fulvic acid photolysis reveals three fundamental alterations to the natural organic matter isolate: decreased molar absorptivity, decreased fluorescence, and a loss of reduced organic functional groups (potential electron shuttles). Surprisingly we observed no carbon loss to mineralization. Evaluation of the light absorbance decay kinetics in the presence/absence of oxygen indicate that approximately 70% of photo-bleaching occurs via direct pathways and 30% is due to reaction with photochemically generated reactive oxygen species (ROS). Of the ROS mediated pathways approximately 70% of the reactivity is attributable to hydroxyl-radical oxidation. Molecular level changes in fulvic acid showed a loss of electron-rich (reduced) components during photolysis, specifically redox active N/S functional groups. Reduced forms of organic nitrogen (amines) decrease in concentration, while sulfur moieties (thiols) are essentially eliminated during photolysis. Furthermore, as the suite of reduced fulvic acid components are photochemically oxidized, we observe a concomitant production of hydrogen peroxide, presumably due to the photo-reduction of dissolved oxygen coupled to organic matter oxidation. Decay kinetics of fluorescent components identified in the fulvic acid isolate were evaluated using parallel factor component analysis (PARAFAC) of excitation-emission matrices (EEMs), and further illustrate a loss of overall fluorescence and a decrease in the redox-active (electron- shuttling) components of the fulvic acid. These molecular-scale changes in photo-chemically altered fulvic acid illustrate a general trend towards broad-scale oxidation of chromophores, fluorophores, and reduced organic N/S functionalities. The loss of electron-donating capacity was correlated to decreases in relative concentrations of redox-active moieties in microbially-derived fulvic acid and suggests that photolysis attacks the electron shuttling properties of the fulvic acid. Photochemical oxidation of electron-rich functional groups and chemical degradation of organic electron shuttles may be related to the decreased bioavailability of photolyzed fulvic acid.
DE: 0400 BIOGEOSCIENCES
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0471 Oxidation/reduction reactions (4851)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting