Colored and Chromophoric Dissolved Organic Matter in Natural Waters - Photobiogeochemistry of Organic Matter - page 402

correlate with river flow. Note that the remote sensing device generally detects
radiation that is reflected or backscattered from the target that initially absorbs
the radiation.
6.2 DOM Dynamics in Natural Waters
Good correlations between CDOM absorption and DOM (DOC concentration)
are usually characterized by a positive intercept on the DOC axis at 50-100 μ M,
because offshore waters contain only very small amounts of CDOM (Vodacek
et al. 1997 ; Rochelle-Newall and Fisher 2002 ; del Vecchio and Blough 2004 ;
Vodacek et al. 1995 ; Klinkhammer et al. 2000 ; Chen et al. 2002 ; Gueguen et al.
2011 ). The non-absorbing DOC fraction varies with the qualitative composition
of the CDOM (Kowalczuk et al. 2010 ). The CDOM/DOC dependence is typi-
cally changed in surface waters during the summer stratification period, when
the water samples show lower absorption to DOC ratios compared to waters
from below the mixed layer or collected in other seasons (Vodacek et al. 1997 ).
This might be the effect of high autochthonous production of non-absorbing
DOM in surface waters during the summer stratification period (Mitra et al.
2000 ; Ogawa and Tanoue 2003 ; Mostofa et al. 2005 ; Fu et al. 2010 ; Yoshioka
et al. 2002 ; Hayakawa et al. 2003 ; Hayakawa 2004 ; Ogawa and Ogura 1992 ),
and/or of photoinduced degradation of CDOM with production of non-absorbing
compounds (Coble 2007 ; Vodacek et al. 1997 ; Mostofa et al. 2005 ). Note that
a rough estimate shows that the increase in autochthonous DOC contents dur-
ing the summer stratification period is 0-88 in lakes and 0-194 % in oceans,
determined by comparing the epilimnionetic DOM with that of the hypolimnion
(Mostofa et al. 2009 ).
The predominant presence of colored DOM such as allochthonous fulvic
and humic acids is responsible for the good correlation that is usually observed
between CDOM absorbance and DOM contents in a variety of waters (Vione
et al. 2010 ). The contributions of allochthonous humic substances (fulvic and
humic acids) in rivers are 30-85 % (the ratio of fulvic acid to humic acid is 9:1
for lower stream DOC and it decreases to 4:1 or less for higher DOC stream),
15-60 % in lakes (30-60 % during winter and 15-40 % during the summer
period), 1-75 % in shelf seawater (38 % of marsh origin and or 62 % of river
origin), and 2-38 % in ocean (see chapter “ Dissolved Organic Matter in Natural
Waters ” for detailed description) (Mostofa et al. 2009 ; Moran et al. 1991 ; Moran
and Hodson 1994 ). The seasonal and spatial-temporal variations of the CDOM
absorbance to DOC ratios are dependent on the presence of colored DOM com-
pounds in natural waters.
A recent study demonstrates that DOC transport can be determined using
ocean color remote sensing if the empirical relationships between DOC and
CDOM, CDOM and salinity, and salinity and river flow are known (del Castillo
and Miller 2008 ). It has been shown that remote sensing estimates of river flow