Geoscience Reference
In-Depth Information
fluorescence of natural products to help increase understanding of DOM fluorescence and
to provide the foundation to improve data interpretation; and (2) to address the chemical
factors controlling fluorescence of organic molecules with an emphasis on their effects of
DOM fluorescence.
From a chemical perspective, fluorescence analysis of DOM is more complicated than
the ease of data collection and manipulation would suggest. Numerous types of compounds
containing different fluorophores exhibit similar fluorescence properties. In the absence
of additional, compound specific analyses, therefore, assignment of the fluorophores in a
given sample to particular classes of compounds is difficult. In general, the power of fluo-
rescence analyses in biogeochemical and ecological studies would be greater if accompa-
nied by specific compound analyses, such as those for amino acids and lignin phenols. A
further complication is that the fluorophores comprising DOM are well suited to engage
in chemical reactions that influence the molecular energetics involved with the absorption
of light and subsequent relaxation of excited molecules. In most studies reporting fluores-
cence data in the water sciences literature, these influences are largely ignored, even with
regard to obvious conditions (such as temperature) and chemical interferences (such as iron
and oxygen) influencing interpretation of data.
Finally, continued improvements in elucidating the roles of organic matter reactions on
both the absorption and fluorescence properties of DOM are necessary to improve data
interpretation, to develop new experiments designed to provide more organic matter struc-
tural information, and to develop new applications of fluorescence to address problems
in the aquatic sciences. As described in this chapter, reactions such as charge transfer
interactions and chemical bonding reactions can alter fluorescence spectra in nonconser-
vative ways. The influences of these interactions are often overlooked in interpreting data
obtained under various conditions or for samples with different distributions of reactive
constituents. In these cases, the tacit assumption is that fluorescence spectra are conser-
vative with regard to individual flourophores - an assumption that is not supported by
the large amount of research on the fluorescence properties of biomolecules and natural
products.
Acknowledgments
Thanks to Kenna Butler and Suzanne M. Bourret for providing fluorescence spectra, and
to Tamara Kraus for providing well characterized tannin samples. Thanks also to Laurel
Larsen, Robert Spencer, and two anonymous reviewers for providing critical feedback
during the writing of this chapter. Support was provided by the U.S. Geological Survey,
National Research Program.
References
Aiken, G.R. and Leenheer, L.A. (1993). Isolation and characterization of dissolved and
colloidal organic matter.
Chem. Ecol
.,
8
, 135-151.
