Environmental Engineering Reference
In-Depth Information
2007
; Mostofa et al.
2007
; Patsayeva et al.
1991
; Kouassi and Zika
1990
; Kouassi
et al.
1990
). (vi) CDOM absorbs light of both ultraviolet and visible wavelengths,
which reduces the amount of PAR for photosynthesis (Bricaud et al.
1981
; Arrigo
and Brown
1996
; Kirk
1994
; Kalle
1966
) and influences ocean color as determined
by remote sensing (del Castillo and Miller
2008
; Carder et al.
1991
; Carder et al.
1999
; Hoge et al.
1995
; Hoge et al.
2001
). (vii) Phytoplankton usually absorbs
strongly in the blue and weakly in the green part of the spectrum. This is applied
for the estimation of the chlorophyll
a
concentration within the upper layer of the
water column, followed by empirical algorithms of ocean color based on blue-to-
green ratios (McClain et al.
2004
; Coble et al.
1998
; O'Reilly et al.
1998
). (viii)
CDOM absorbance could be used for determining the chemical composition and
structure of CDOM (González-Vila et al.
2001
; Hedges et al.
2000
; Osburn et
al.
2001
; Stabenau et al.
2004
; Bracchini et al.
2010
). (ix) The spectral slope (
S
)
is often used as a proxy for CDOM composition, including the ratio of fulvic to
humic acids and molecular weight (Twardowski et al.
2004
). Salinity is negatively
related to the spectral slopes from 275 to 295 nm, which might be considered a
good proxy for DOM molecular weight (Ortega-Retuerta et al.
2010
). (x) Finally,
CDOM is responsible for the global carbon cycle and for biogeochemical processes
through production, distribution, transport and decomposition of organic com-
pounds in natural waters (Moran et al.
2000
; Ma and Green
2004
; Mostofa et al.
2007
; Hedges et al.
2000
; Hedges
1992
; Amon and Benner
1994
; Takahashi et al.
1995
; Vähätalo et al.
2000
; Ogawa and Tanoue
2003
; Medina-Sánchez et al.
2006
).
2 CDOM in Natural Waters
Colored and chromophoric dissolved organic matter (CDOM) is defined as a opti-
cally active component of bulk DOM of both allochthonous and autochthonous
origin that absorbs light over a broad range of ultra-violet (UV) and visible wave-
lengths (200-800 nm), exhibiting absorbance spectra that generally decrease with
increasing wavelength for freshwater and marine water (Fig.
1
) (Bricaud et al.
1981
; Arrigo and Brown
1996
; Nelson et al.
1998
; Warnock et al.
1999
; Nelson
and Siegel
2002
; Vähätalo and Wetzel
2004
; Coble
2007
; Zhang et al.
2009
). The
absorbance of CDOM is useful for the knowledge of the contents of the materials
present and for the identification of absorbance changes due to physical, photoin-
duced and biological processes in a variety of waters (Vähätalo and Wetzel
2004
;
Coble
2007
; Vodacek et al.
1997
; del Vecchio and Blough
2004
; del Vecchio and
Blough
2002
; Vähätalo et al.
2000
). It has been reported that there are differences
in levels and optical properties between freshwater and marine water CDOM.
Extreme enrichment in CDOM is usually observed in freshwater environments
(Fig.
1
) (Vähätalo and Wetzel
2004
; del Vecchio and Blough
2004
; del Vecchio
and Blough
2002
; Conmy et al.
2004
; Kowalczuk et al.
2003
). CDOM shows
absorption at wavelengths 450-800 nm in freshwater (Kowalczuk et al.
2003
), but
usually not in marine waters. Carbon-specific absorption coefficients for riverine
