Geoscience Reference
In-Depth Information
x10
-2
x10
-2
x10
-2
440
440
440
20
A1
A2
A3
420
3
420
420
5
400
400
400
16
380
380
4
3
2
380
360
2
360
360
12
340
340
340
320
320
320
8
300
1
300
300
280
280
280
4
1
260
260
260
240
0
240
0
240
0
300
350
400
450
500
550
600
300
350
400
450
500
550
600
300
350
400
450
500
550
600
Emission Wavelength (nm)
Emission Wavelength (nm)
Emission Wavelength (nm)
x10
-2
x10
-2
x10
-2
440
440
440
B1
B2
B3
420
420
420
6
8
8
400
400
400
5
380
380
380
6
6
360
4
360
360
340
340
340
3
4
4
320
320
320
300
2
1
300
300
2
2
280
280
280
260
260
260
240
0
240
0
240
0
300
350
400
450
500
550
600
300
350
400
450
500
550
600
300
350
400
450
500
550
600
Emission Wavelength (nm)
Emission Wavelength (nm)
Emission Wavelength (nm)
Figure 3.9. Change in fluorescence of moss leachate DOM over time: (A1-A3)
Sphagnum angusti-
folium
at 24 hours (A1), 194 hours (A2), and 3 months (A3); Feathermoss mix at 24 hours (B1), 194
hours (B2), and 3 months (B3). The color bar to the right indicates fluorescence intensity, which has
been normalized to DOC concentration. (Reprinted from Wickland et al.,
2007
, With kind permission
from Springer Science+Business Media.) (See Plate 5.)
like fluorescence was removed at a faster rate than bulk concentrations of DOC and DON,
highlighting that certain DOM moieties were preferentially removed, which is consis-
tent with the idea that different DOM pools turn over at different rates (Brookshire et al.,
2005
; Fellman et al.,
2009c
). Therefore, future studies seeking to examine DOM uptake in
freshwater ecosystems could gain insight into the role of DOM pools with different reac-
tivities by combining instream tracer releases with fluorescence characterization of DOM
(Fellman et al.,
2010
). Changes in the composition of DOM during biodegradation experi-
ments can also be evaluated via fluorescence spectroscopy. For example, Wickland et al.
(
2007
) showed that in laboratory incubations of moss leachates, microbial degradation of
DOM resulted in an increase in the humification and fluorescence indices as well as a loss
of the protein-like fluorescence with time (
Figure 3.9
;
Table 3.2
).
The effect of photochemical degradation of DOM in freshwater systems can also be
examined with fluorescence measurements. A typical response for freshwater DOM was
observed in a study by Cory et al. (
2007
) with whole water samples from Alaskan (USA)
stream and lake water, which showed a decrease in total fluorescence by the end of the
short-term (12 hours) irradiation (
Figure 3.10
). On irradiation different fluorophores varied
with respect to their percent change of fluorescence but humic-like fluorophores (SQ1 and
SQ2;
Figure 3.9
) showed the greatest loss of fluorescence intensity. Overall the protein-
like fluorophores (Tyr and Trp;
Figure 3.10
) showed little change with irradiation and for
