Geoscience Reference
In-Depth Information
50%
A/T
A/C
A/M
40%
30%
20%
10%
0%
-10%
-20%
0.8
14.1
33.1
Salinity
Figure 7.9. The change to EEM fluorescence peak ratios after Suwannee River humic acid (SRHA)
was exposed to sunlight in solutions of increasing salinity. The ratio of A/T decreased in general
without a consistent effect of salinity. Ratios of A/C and A/M after sunlight exposure increased with
salinity, indicating an enhanced loss of C and M peak fluorescence as salinity increased. (Osburn,
unpublished results.)
fluorescence and ultimately contribute to changes in DOM fluorescent properties seen in
coastal waters.
The results from DOM fluorescence photobleaching studies suggest substantial molecu-
lar changes to DOM after it is exposed to sunlight. Dissolved inorganic carbon (CO
2
) photo-
production, attributed to decarboxylation reactions, represents complete DOM degradation
(mineralization) and can be used to assess carbon cycling implications for photodegra-
dation (e.g., Miller and Zepp,
1995
). Carboxylic acid oxidation should enhance fluores-
cence emission if a metal-ligand bond is disrupted once the carboxyl group is oxidized.
Thus, models of DOM fluorescence changes coupled with DOM molecular changes will
improve the predictability of carbon cycling in surface waters by means of fluorescence
measurements.
7.10 Summary and Future Directions
Changing environmental conditions in terrestrial and aquatic ecosystems can likely impact
the fluorescence signatures of DOM generated, transported, and transformed within and
between these systems. A first-order control on the source of DOM fluorescence in natural
waters will be the relative distribution of DOM molecular size and weight. The coupling of
fluorescence with size fraction technologies and other means of colloid investigation have
