Geoscience Reference
In-Depth Information
Table 3.2.
Fluorescence properties and PARAFAC analyses of moss leachate DOC
over time
Time
Sphagnum angustifolium
Feathermoss mix
24 hours
194 hours
3 months
24 hours
194 hours
3 months
FI
1.14
1.26
1.38
1.17
1.30
1.38
HIX
0.61
0.83
0.89
0.68
0.79
0.90
Tryptophan-like
fluorescence (%)
29
4
1
18
9
3
Tyrosine-like
fluorescence (%)
15
9
5
12
11
3
Source
: Modified from Wickland et al. (
2007
), Table 5, with kind permission from Springer
Science+Business Media.
other samples even showed a small increase, resulting in post-irradiation waters having an
increased contribution of protein-like relative to humic-like components in comparison to
initial waters (Cory et al.,
2007
). Whole water samples in freshwater systems also typically
show a decrease in FI with irradiation. The variation in FI has been shown to be related
to relative amounts of SQ1 and SQ2 in a sample and thus the decrease in FI with irradia-
tion time can be attributed to the greater loss of SQ2 in comparison to SQ1 in
Figure 3.10
(Cory et al.,
2007
). Fluorescence characterization of DOM can help understand how photo-
chemical processes influence DOM quantity and quality, and utilizing spectrophotometric
techniques in comparison with other DOM characterization techniques shows promise for
understanding how photochemical processes remove and modify DOM in aquatic systems
(Spencer et al.,
2009a
; Stubbins et al.,
2010
).
3.3.4 Rainwater DOM Fluorescence
Fluorescence characterization of rainwater samples has shown the presence of both humic-
like and protein-like materials in precipitation DOM (Kieber et al.,
2006
; Muller et al.,
2008
; Santos et al.,
2009
). Muller et al. (
2008
) highlighted that the highest humic-like fluo-
rescence intensities are observed during convective events and events of continental origin
reflecting the influence of terrestrial and anthropogenic sources. During well-mixed condi-
tions Muller et al. (
2008
) found that humic-like fluorescence intensity decreases, whereas
at low wind speeds stagnation of the atmosphere leads to higher fluorescence intensities
that the authors attributed to an increase of localized sources, especially anthropogenic-
ally derived sources. No significant trends were observed by Muller et al. (
2008
) between
protein-like fluorescence and meteorological variables and these fluorophores are likely
to have been derived from a number of sources and processes. Rainwater DOM has been
shown to be highly susceptible to photodegradation and variation in terms of photolabil-
ity between humic-like and protein-like components may lead to a lack of a relationship
with meteorological variables (Kieber et al.,
2007
). Finally, the integrated signal for entire
