Colored and Chromophoric Dissolved Organic Matter in Natural Waters - Photobiogeochemistry of Organic Matter - page 365

2009 ; Du et al. 2010 ). The humic substances (fulvic and humic acids) of alloch-
thonous origin and autochthonous fulvic acids of algal origin are colored as they
absorb visible light. They can thus be denoted both as colored and as chromo-
phoric DOM (CDOM). Other terminology includes yellow substances or Gelbstoff
in natural waters. On the other hand, low molecular weight CDOM also shows
absorption at shorter wavelengths, such as formaldehyde at 207-250 nm, acetal-
dehyde at 208-224 nm, acetate at 204-270 nm, glyoxal at <240 nm, malonate at
225-240 nm, and pyruvate at 200-227 nm (Strome and Miller 1978 ; Mopper and
Stahovec 1986 ; Kieber et al. 1990 ; Mopper et al. 1991 ; Wetzel et al. 1995 ; Dahlén
et al. 1996 ). These LMW organic substances do not show any color as they do not
absorb in the visible, and they can thus be denoted as CDOM but not as colored
DOM.
Different variables such as the occurrence of allochthonous fulvic and humic
acids and/or autochthonous fulvic acids, particulate materials (e.g. algae), chloro-
phyll a or phytoplankton, as well as incident light wavelengths and solar zenith
angle, snow, ice, and water itself are responsible for the absorption and scattering
of UV and PAR radiation, which may affect deeper waters in lakes and oceans
(Smith and Baker 1981 ; Kirk 1984 , 1991 , 1994 ; Carder et al. 1989 ; McKnight et
al. 1994 ; Scully and Lean 1994 ; Morris et al. 1995 ; Vernet and Whitehead 1996 ;
Laurion et al. 1997 ; Sommaruga and Psenner 1997 ; Kahru and Mitchell 1998 ;
Laurion et al. 2000 ; Markager and Vincent 2000 ; Belzile et al. 2000 ; Shank et al.
2005 ; Warren et al. 2006 ; Green et al. 2008 ; Hayakawa and Sugiyama 2008 ; Zhao
et al. 2009 ; Shank et al. 2010 ).
CDOM absorption properties are significantly affected by several factors:
DOM content and its chemical nature (Ishiwatari 1973 ; Lawrence 1980 ; Zepp and
Schlotzhauer 1981 ; Hayase and Tsubota 1985 ; McKnight et al. 1994 ; Dubach et al.
1964 ; Zanardi-Lamardo et al. 2004 ; Singh et al. 2010 ; Singh et al. 2010 ; Minero
et al. 2007 ; Minero et al. 2007 ; Vione et al. 2010 ), occurrence and types of sus-
pended particulate matter (Zhang et al. 2009 ; Dupouy et al. 2010 ; Uusikivi et al.
2010 ; Gregg and Casey 2009 ; O'Donnell et al. 2010 ), photoinduced and microbial
processes in freshwater and marine environments (Shank et al. 2010 ; Boehme and
Coble 2000 ; Moran et al. 2000 ; Winch et al. 2002 ; Hernes and Benner 2003 ; Pullin
et al. 2004 ; Scully et al. 2004 ; Winter et al. 2007 ; Zhang et al. 2007 ; Zhang and
Qin 2007 ; Ma and Green 2004 ), and salinity (Singh et al. 2010 ; Singh et al. 2010 ;
Hernes and Benner 2003 ; del Vecchio and Blough 2004 ; Blough and del Vecchio
2002 ; Fournier 2007 ). The CDOM plays several key roles in biogeochemical
processes such as photoinduced reactions and biological processes, and it mini-
mizes the deleterious consequences of UV radiation exposure for phytoplankton
and other organisms in natural waters (Wetzel et al. 1995 ; Schindler et al. 1996 ;
Williamson et al. 1996 ; Yan et al. 1996 ; Moran and Zepp 1997 ; Thomas-Smith and
Blough 2001 ; Mostofa and Sakugawa 2009 ). Several reviews have been carried
out on CDOM including its optical and chemical properties, sinks and distribution,
relationship of CDOM with salinity, DOC and fluorescence, photochemistry, ocean
color, and finally remote sensing applications in natural waters (Coble 2007 ; del
Vecchio and Blough 2004 ; Blough and del Vecchio 2002 ; del Castillo 2005 ).