Environmental Engineering Reference
In-Depth Information
substances of 19-67 % during 72 h to 70 days irradiation (Table
4
) (Moran et al.
2000
; Osburn et al.
2009
). In unfiltered seawater samples from the Baltic Sea irra-
diated for 4-5 days, the corresponding fluorescence intensity decrease has been of
44-52 % at the surface (0-50 m) and 56-65 % in the deeper layers (100-240 m).
In some cases the decrease has been more marked, i.e. 61-70 % at the surface
(0-50 m) and 73-75 % in the deeper layer (100-190 m). Interestingly the addi-
tion of chloroform significantly enhanced photodegradation, yielding a fulvic
acid-like fluorescence decrease of 59-81 % in surface samples (0-50 m) and of
83-84 % in deep-water ones (Table
4
) (Skoog et al.
1996
). The mechanism behind
the increased FDOM photodegradation upon addition of chloroform may be the
production of phosgene in the presence of O
2
(CHCl
3
+
O
2
+
h
υ
→
COCl
2
+
H
Cl). Phosgene is highly reactive toward the degradation of the fluorophores, such
as the amino groups (RNH
2
+
COCl
2
→
RN
=
CO
+
2HCl) or carboxylic acids
(RCO
2
H
+
COCl
2
→
RC(O)Cl
+
HCl
+
CO
2
) (Mostofa et al.
2011
; Shriner et al.
1943
). Such processes would contribute to the decrease of DOM fluorescence in
natural waters (Mostofa et al.
2009a
,
2011
).
Photoinduced degradation of Mediterranean Sea samples (8 h sunlight expo-
sure) showed a decrease in the fluorescence of fulvic acid-like or humic-like
fluorophores (peak C), in the range of 9-22 % for lagoon water and approaching
34 % for coastal water (Table
4
) (Abboudi et al.
2008
). Similarly, photoinduced
degradation of waters collected from Mackenzie River and Beaufort Sea (Estuary,
Shelf and Gulf) demonstrates that the degradation of fulvic acid-like fluorophores
(peak C) is usually higher during summer irradiation than in spring, autumn and
winter (Table
4
). The photodegradation of fulvic acid-like fluorophore (peak C)
is relatively higher in Beaufort Sea samples (47-60 % in Estuary during summer;
67-75 % in Shelf during summer; 66 % in Gulf during spring; 72 h irradiation)
than in Satilla Estuary (61-67 %, 70 days), Baltic Sea (44-52 % in surface waters,
4-5 days), and Gotland Deep seawater (32 %, 13 days) (Table
4
) (Stedmon et al.
2007a
; Skoog et al.
1996
; Moran et al.
2000
; Osburn et al.
2009
; Lepane et al.
2003
). The high photodegradation of fulvic acid-like substances in Beaufort Sea
samples has been explained by the occurrence of two phenomena. Firstly, in many
cases a significant fraction of the fulvic acid-like substances are of autochtho-
nous origin, which makes them highly susceptible to photodegradation (Mostofa
KMG et al., unpublished data; Johannessen et al.
2007
). Secondly, in the case of
the Beaufort Sea the fulvic acid-like substances have allochthonous origin as they
mainly derive from riverine input. Photoinduced degradation of these compounds
is poorly effective due to low water temperature in the Beaufort Sea (
−
0.54 to
21.81 °C in Estuary,
−
1.36 to 9.23 °C in Shelf, and
−
1.68 to 0.12 °C in Gulf
samples) (Osburn et al.
2009
). Therefore, unaffected allochthonous fulvic acid-like
substances are highly susceptible to degradation upon laboratory irradiation. The
case of the Beaufort Sea may be a particular one, however, because it has been
reported that DOM (or FDOM) components are produced from microbial assimi-
lation of phytoplankton biomass or organic matter in natural waters (Mostofa
et al.
2009a
; Parlanti et al.
2000
; Stedmon et al.
2007a
,
2007b
; Fu et al.
2010
;
Rochelle-Newall and Fisher
2002
; Yamashita and Tanoue
2004
; Rochelle-Newall
