Environmental Engineering Reference
In-Depth Information
and DOC transport are correlated well (r
2
=
~ 0.70) with field observation
data, showing low variability in DOC concentrations in the river end-member
(7-11 %), and high seasonal variability in river flow (~50 %) in the Mississippi
River Plume (del Castillo and Miller
2008
). This result can be influenced by
several biogeochemical processes such as high DOM photodegradation, biodeg-
radation, production and flocculation, as well as extreme precipitation caused
by natural disaster (del Castillo and Miller
2008
; Wright
2005
). These biogeo-
chemical processes have little or negligible effects in low salinity waters of river
plumes due to the predominance of riverine CDOM (Blough and del Vecchio
2002
; del Castillo and Miller
2008
; del Vecchio and Blough
2002
; del Castillo
et al.
1999
; del Castillo et al.
2000
; del Castillo et al.
2001
; Mantoura and
Woodward
1983
).
6.3 Photoinduced Degradation of CDOM and Its Impact
in Natural Waters
Photoinduced degradation of CDOM by sunlight can affect its optical and
chemical properties, by inducing decomposition of the CDOM chromophores
and thus reducing CDOM absorptivity of UV and visible radiation (Kieber
et al.
1990
; Moran et al.
2000
; Skoog et al.
1996
; Reche et al.
1999
; Whitehead
and Vernet
2000
; Twardowski and Donaghay
2001
; del Vecchio and Blough
2002
; Mostofa et al.
2007
; Patsayeva et al.
1991
; Kouassi and Zika
1990
;
Kouassi et al.
1990
; Morris and Hargreaves
1997
; Allard et al.
1994
; Fichot
and Miller
2010
). The effect of the photoinduced degradation of CDOM is an
increase of UV transparency in surface waters (Nelson et al.
1998
; Vodacek
et al.
1997
; Kieber et al.
1990
; Morris and Hargreaves
1997
; Zepp et al.
1995
).
However, CDOM absorption losses by photoinduced degradation can also result
in a variety of changes in CDOM composition, which can be listed as follows:
(i) Formation of strong oxidants such as singlet oxygen, superoxide, hydroxyl
radical, hydrogen peroxide, organic peroxides during the photodegradation
of CDOM may have severe and chronic toxic effects on aquatic organisms
and important ecological consequences in aquatic environments (Williamson
et al.
1996
; Thomas-Smith and Blough
2001
; Mostofa and Sakugawa
2009
;
Moore et al.
1993
; Zepp et al.
1998
; Vaughan and Blough
1998
; Zafiriou
et al.
1998
; Xenopoulos and Bird
1997
; Palenik et al.
1991
); (iii) Formation of
low molecular weight organic substances, which is generally more important
in lakes and oceans than in rivers (Moran and Zepp
1997
; Corin et al.
1996
;
Biddanda and Benner
1997
; Yoshioka et al.
2007
); (iii) Formation of biologi-
cally labile compounds that enhance biodegradation (Wetzel et al.
1995
; Moran
and Zepp
1997
); (iv) Photo formation of carbon-gas end photoproducts (CO
2
,
CO), DIC, COS and so on in natural waters (Ma and Green
2004
; Bertilsson
and Tranvik
2000
; Miller and Moran
1997
; Fichot and Miller
2010
; Weiss
et al.
1995
); (v) Release of nitrogen compounds (e.g. NH
4
+
) and phosphate,
