Environmental Engineering Reference
In-Depth Information
2002
; Ortega-Retuerta et al.
2010
; Norman et al.
2011
; Kowalczuk
1999
; Kitidis
et al.
2006
). Absorption losses are likely different for a variety of natural waters
(Table
1
) (Zhang et al.
2009
; Moran et al.
2000
; Winter et al.
2007
; Mostofa
KMG et al., unpublished data; Norman et al.
2011
). They are of order 77-97 %
at 340-350 nm for upstream CDOM (Kago and Nishi-Mataya upstream, Japan)
and 58-59 % at 340-350 nm for downstream CDOM (Yasu River, Japan) after
13 days of irradiation (Table
1
) (Mostofa KMG et al. unpublished data). The
CDOM absorption is entirely quenched at 700-444 nm for Kago upstream and
700-366 nm for Nishi-Mataya upstream, but downstream CDOM is little decom-
posed (14-45 %) at 600-700 nm (Fig.
1
). Note that the upstream CDOM is mostly
made up of fulvic acids having low DOC concentrations (99 and 38
μ
M C for
NM upstream), whilst downstream CDOM has different origin such as autochtho-
nous (protein-like or tryptophan-like), allochthonous (fulvic acids), and agricul-
tural sources with relatively high levels of DOC (e.g., 194
μ
M C for Yasu River)
(Mostofa et al.
2007
; Mostofa et al.
2005
). This suggests that autochthonous
CDOM may originate in the river bed during the summer season and agricultural
CDOM may be released from nearby agricultural fields.
The differences in CDOM absorption losses between upstream and down-
stream river waters suggest three issues. First, absorption losses depend on CDOM
source and composition. Second, fulvic acids in upstream river waters are highly
decomposed, as demonstrated by the complete loss of absorption in the longer
wavelength region (from 366 to 700 nm). Such absorption losses are accompa-
nied by high losses (72-84 % at peak C-region) in the fluorescence intensity of
fulvic acids (Mostofa et al.
2007
). Third, CDOM absorption losses are relatively
limited in downstream river waters. A possible reason is that this CDOM may be
a mixture os compounds originating from several sources such as autochthonous,
allochthonous and agricultural. Because of the high decrease of the fluorescence
intensity of allochthonous fulvic acids (80 % in downstream waters) and tryp-
tophan (59 % in downstream waters) detected in earlier studies (Mostofa et al.
2007
), it is suggested that the remaining autochthonous and agricultural CDOM
might be recalcitrant or refractory to photoinduced degradation.
In addition, CDOM absorption losses are 55-76 % at 340 nm in the water of
various lakes and ponds after 13 days irradiation (Table
1
) (Winter et al.
2007
).
However, much lower absorption losses have been observed in the case of Lake
Taihu after 12 days irradiation: 30 % at 355 nm and 21 % at 280 nm (Table
1
)
(Zhang et al.
2009
). CDOM absorption losses are in the range of 50-64 % at
350 nm for estuarine CDOM after 70 days irradiation period (Table
1
) (Moran
et al.
2000
). It is estimated that approximately 70 % of terrestrial CDOM is lost
by photo-oxidation on the Middle Atlantic Bight shelf (Vodacek et al.
1997
). In
Antarctic surface waters, sea ice CDOM susceptibility to photo-bleaching in an
in situ 120 h exposure showed a loss in CDOM absorption of 53 % at 280 nm,
58 % at 330 nm, and 30 % at 375 nm (Norman et al.
2011
). This result sug-
gests that Antarctic CDOM is more photosensitive than average lake or seawa-
ter CDOM. Absorption losses for standard Aldrich humic acid are 42-47 % at
340 nm in deionized water after 13 days irradiation (Table
1
) (Winter et al.
2007
).
