Environmental Engineering Reference
In-Depth Information
dimensional plots in which excitation and emission wavelengths are plotted against
fluorescence intensity (Figure 2) 16 .
50
40
30
20
280
300
320
340
360
380
400
420
440
460
10
0
400
500
600
700
O emission (nm)
Figure 2. EEMS of Suwanne River fulvic acid (SRFA) (10 mg/L in MilliQ water). >O ex : 280-460 nm,
every 10 nm; O em : O ex +10 nm to700 nm]. [The emission spectra have not been corrected for the
instrument response].
Unfortunately, EEMS requires long time for collection, time that is not often
available in field studies. In this case, acquiring single excitation/emission spectra
becomes more advantageous, permitting large field mapping of CDOM over shorter
timescales 26-28 .
4. CDOM origin and fate
The origin and fate of CDOM is still a matter of discussion. The results from
field studies conducted at very different geographical locales are now available
(although comparisons among these different studies are often impossible because of
the different protocols employed to measure CDOM properties), but there remain many
unanswered questions about the factors controlling the seasonal and spatial distributions
of CDOM.
Salinity (a conservative tracer) can be employed to investigate sources and sinks
of CDOM. CDOM of terrestrially origin that is simply diluted in waters of increasing
salinity will follow an inverse linear relationship against salinity; in the presence of
sources or sinks this linear relationship will deviate upward or downward, respectively
(Figure 3).
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