Geoscience Reference
In-Depth Information
3
Aquatic Organic Matter Fluorescence
Paula G. Coble, Robert G. M. Spencer, Andy Baker,
and Darren M. Reynolds
3.1 Introduction
The earliest reference to the fluorescence of natural waters is attributed to Dienert (
1910
),
according to Smart et al. (
1976
). Almost three decades later, Kurt Kalle (Kalle
1938
,
1939) made observations of seawater fluorescence using direct observation of samples
under a microscope (Duursma,
1974
). Kalle recognized that the source of this material,
which he called “gelbstoff” (“yellow stuff”), was primarily from terrestrial inputs in coastal
regions. He described it as being “humic-like” and having a yellow color and a blue fluo-
rescence. An early list of substances found to have the properties of gelbstoff included rain,
natural source water, Bordeaux wine, light Italian vermouth, light export beer, dark malt
beer, melanin, bees' honey, house dust, air, rocks, filter paper, and brown lime-tree leaves
(Duursma,
1974
). Fluorescent organic matter has since been observed universally in natu-
ral waters, including in bottled drinking water and in the bluest open ocean regions.
Early studies lacked both the sensitivity and wavelength specificity required to fully
characterize aquatic organic matter (AOM) fluorescence. Broad-band excitation and emis-
sion provided increased sensitivity to measure fluorescence intensity at low concentrations,
but without wavelength resolution to determine peak positions. Smart et al. (
1976
) cited
several literature values for excitation and emission maxima, however, results of early stud-
ies must be examined carefully for inaccuracies due to instrument biases, including errors
in peak positions as well as in the number of peaks present in a sample. Many of these
errors were not recognized in the 1970s and 1980s, but are the subject of detailed discus-
sion in
Chapter 5
of this volume (see also Holbrook et al.,
2006
).
The development of the modern spectrofluorometers, equipped with grating monochro-
mators for wavelength resolution, xenon arc lamps for generating high-energy excitation
into the ultraviolet C (UVC, 100-289 nm) region, and photomultiplier tubes to boost sen-
sitivity, permitted high-resolution characterization of AOM fluorescence in the late 1980s.
The first study to show fluorescence spectral differences between marine and terrestrial
colored dissolved organic matter (CDOM) was that of Cabaniss and Shuman (
1987
) using
a synchronous scanning technique. Donard et al. (
1989
) were able to make the same dis-
crimination using high-resolution fluorescence spectroscopy of individual spectra. Coble
et al. (
1990
) introduced the use of excitation-emission matrix (EEM) spectroscopy for
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