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INTERACTIONS BETWEEN PHOTOCHEMICAL AND MICROBIAL DECOMPOSITION IN MODIFYING THE BIOLOGICAL AVAILABILITY AND OPTICAL PROPERTIES OF ESTUARINE DISSOLVED ORGANIC MATTER
Citation:
Zepp, R G., M. A. Moran, AND W. Sheldon. INTERACTIONS BETWEEN PHOTOCHEMICAL AND MICROBIAL DECOMPOSITION IN MODIFYING THE BIOLOGICAL AVAILABILITY AND OPTICAL PROPERTIES OF ESTUARINE DISSOLVED ORGANIC MATTER. Presented at American Geophysical Union Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000.
Description:
Direct photodecomposition and photochemically-mediated bacterial degradation (via photochemical modification of otherwise refractory DOM into biologically labile forms) provide
important pathways for the loss of dissolved organic matter in coastal waters. Here we report
laboratory studies of the effects of sunlight exposure on the decomposition of DOM from a
coastal estuary in the Southeastern U.S. Results of these studies showed that direct
photodecomposition resulted in significant loss of carbon, absorptivity, and fluorescence, that
was accompanied by consistently positive net effects on biological degradation of the residual
DOM. The efficiency of DOC loss decreased with increasing light exposure, suggesting that a
significant fraction of the DOC may not be readily susceptible to decomposition by solar
radiation. In contrast, the loss efficiency of the UV absorbing component of the DOM(350 nm)
did not detectably decrease with increased light exposure. Direct photodecomposition also
resulted in a general decrease in fluorescence quantum yields and significant changes in the
excitation-emission matrix spectra of the DOM with decreases in the emission and excitation
maxima of the humic component. Biological decomposition following photobleaching at least
partially reversed changes in optical properties caused by direct photodecomposition.