Geoscience Reference
In-Depth Information
Table 2.1.
Commonly referenced peak and region locations for components
of excitation-emission matrices (EEMs) obtained for aquatic humic substances
and dissolved organic matter
Peak label
Excitation
maximum (nm)
Emission
maximum (nm)
Description of fluorophores
B
T
A
M
C
D
E
N
275
275
260
290-310
320-360
390
455
280
305
340
400-460
370-410
420-460
509
521
370
Tyrosine-like, protein-like
a
Tryptophan-like, protein-like
a
Humic-like
a
Marine humic-like
a
Humic-like
a
Soil fulvic acid
b
Soil fulvic acid
b
Plankton derived
b
a
Coble,
2007
;
b
Stedmon et al.,
2003
.
a spectrum. The components used in these analyses are not actual fluorophores, and care
is warranted in interpreting results. Further discussion of these approaches can be found in
this volume and in recent papers (e.g., Fellman et al.,
2010
; Larsen et al.,
2010
).
EEMs spectra can vary widely depending on the nature of DOM fluorophores and the
net effects of factors that influence fluorescence efficiency. The range of spectra for waters
containing vastly different DOM compositions is apparent in comparing spectra presented
in
Figure 2.2
for two extreme environments types - the open ocean sample dominated by
autochthonous DOM of microbial origin and a river sample with DOM predominantly
derived from higher plants are presented. The Pacific Ocean sample, which was collected
far from terrestrial sources, contains primarily proteinaceous fluorophores (Yamashita
and Tanoue,
2003
) and exhibits a relatively simple fluorescence spectrum. At the other
extreme is the Penobscot River sample, which is heavily influenced by higher plant and
soil sources of organic matter. This sample contains terrestrially derived DOM dominated
by more complicated aromatic molecules that are excited and fluoresce at much longer
wavelengths than the open ocean sample (e.g., Boyle et al.,
2009
). The sample from Maine
coastal waters (
Figure 2.2b
) exhibits aspects of both of the end-member samples. For most
waters, little is actually known about the chemistry of the different fluorophores in a sam-
ple, and, in general, interpreting spectra from all types of waters is complicated by the
lack of information related to their concentrations. A complementary approach to study-
ing whole water samples is to isolate functionally distinct DOM fractions from whole
water samples to determine the fundamental chemical properties of each fraction, ulti-
mately relating structural and chemical information to the biogenesis and environmental
roles of these materials. Fractionation is often accomplished using solid-phase extraction
on hydrophobic sorbents such as C
18
(Green and Blough,
1994
), styrene divinyl benzene
polymers such as PPL resin (Dittmar et al.,
2008
), and XAD resins (Aiken et al.,
1992
).
Using these approaches, the majority of chromophores and fluorophores present in the
