Environmental Engineering Reference
In-Depth Information
Fig. 8
Changes in the
spectral slope values (
S
) in
the upstream (Kago, KG
and Nishi-Mataya, NM) and
downstream waters (Yasu
River) due to photochemical
and microbial degradation
of CDOM during the
13 days of irradiation and
dark incubation period.
Microbial degradation is
presented for 13 days using
the similar symbols for the
respective samples.
Data
source
Mostofa KMG et al.
(unpublished data)
295 -275 nm (KG upstream)
400 -350 nm (KG upstream)
295 -275 nm (NM upstream)
400 -350 nm (NM upstream)
295 -275 nm (YR downstream)
400 -350 nm (YR downstream)
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
012345678910
11
12
13
cases, CDOM photobleaching by solar radiation decreases
S
(Fig.
8
) (Helms
et al.
2008
; Stabenau et al.
2004
; Morris and Hargreaves
1997
; Gao and Zepp
1998
; Tzortziou et al.
2007
; Miller
1994
; Zepp et al.
1998
; del Castillo et al.
1999
). It is possible that
S
variation is caused by the different protocols employed
in its calculation (linear function, LF versus non-linear function, NLF) or by the
different spectral ranges adopted in the irradiation experiments (Zhang et al.
2009
;
del Vecchio and Blough
2002
). Spectral wavelength ranges used to calculate
S
are
most often 275-295 or 350-400 nm. Deviation of
S
for different spectral ranges
is mainly caused by the occurrence of different chromophores in CDOM, which
show variable reactivity toward photoinduced degradation.
However, variation in
S
is also observed when the same spectral range is con-
sidered and the same calculation method is adopted, in a variety of natural waters
and in their photobleached samples (Fig.
8
). Photoinduced degradation increases
S
at 275-295 nm (S
275-295
) for upstream (115 % for Kago, KG and 207 % for Nishi-
Mataya, NM) and downstream DOM (59 % for Yasu River, YR). In contrast,
S
at
350-400 nm (S
350-400
) is increased for upstream (92 % for KG) and downstream
DOM (6 % for YR), but is decreased for upstream DOM (41 % for NM) during
13 days irradiation (Fig.
8
). Earlier studies have shown that upstream DOM is
mainly composed of fulvic acids whist downstream DOM is contributed by several
sources including autochthonous, allochthonous and agricultural DOM (Mostofa
et al.
2007
; Mostofa et al.
2005
).
S
also increases at 290-500 nm in mangrove and
Sargassum CDOM after 48 h irradiation (Shank et al.
2010
). The highest increase
of
S
has been observed upon irradiation at shorter wavelengths, while irradiation
at
λ
> 400 nm produced small losses in absorption and little changes in
S
in Bay
waters (del Vecchio and Blough
2002
). Maxima of
S
290-350
and
S
250-650
and min-
ima of
a
300
have been attributed to CDOM photo-oxidation in the surface waters
of the Atlantic Ocean (Kitidis et al.
2006
).
