Complexation of Dissolved Organic Matter with Trace Metal Ions in Natural Waters - Photobiogeochemistry of Organic Matter - page 767

and autochthonous origin. Allochthonous organic substances are generally derived
from terrestrial plant material in soil ecosystems (and may reach the aquatic envi-
ronmental because of soil leaching and runoff), while autochthonous organic sub-
stances are produced mostly from algae and phytoplankton within the water column.
The contribution of fulvic and humic acids (terrestrial humic substances) accounts
for the most of the dissolved organic carbon (DOC), approximately 20-85 % in riv-
ers and 14-90 % in lakes (Moran et al. 1991 ; Moran and Hodson 1994 ; Malcolm
1985 ; Hedges et al. 1997 ; Ma et al. 2001 ; Mostofa et al. 2009a ). In contrast, they
account for a relatively minor fraction in oceans, approximately 1-35 % except the
shelf (see also chapter “ Dissolved Organic Matter in Natural Waters ”) (Moran et al.
1991 ; Moran and Hodson 1994 ; Malcolm 1985 ; Hedges et al. 1997 ; Ma et al. 2001 ;
Mostofa et al. 2009a ). They play an important role on DOM physical, chemical and
biological characteristics in the aquatic environments.
On the other hand, autochthonous DOM of algal, phytoplankton or bacterial ori-
gin is generally composed of autochthonous fulvic acids, carbohydrates, amino acids,
proteins, lipids, organic acids and so on (Mostofa et al. 2009a ; Coble 1996 ; Parlanti
et al. 2000 ; Tanoue 2000 ; Jennings and Steinberg 1994 ; Yamashita and Tanoue 2003 ;
Wada et al. 2007 ; Hulatt et al. 2009 ; Mostofa and Sakugawa 2009 ; Zhang et al. 2009 ).
Phytoplankton is capable of releasing 10-60 % of the carbon and 15-50 % of the
nitrogen assimilated during photosynthesis in natural waters (Sundh 1992 ; Bronk
et al. 1994 ; Braven et al. 1995 ; MalinskyRushansky and Legrand 1996 ; Slawyk
et al. 1998 , 2000 ). The autochthonous DOM in the surface waters is significantly
high, by approximately 0-102 % in lakes and 0-194 % in oceans estimated com-
pared to the deeper waters during the summer stratification period (Mostofa et al.
2009a ; see also DOM chapter). Therefore, autochthonous DOM plays an impor-
tant role in M-DOM complexation, particularly in the surface layer of lakes, estuar-
ies, wetlands and oceans. Extracellular polymeric substances (EPS) are produced by
many microorganisms in natural waters and are mainly composed of polysaccharides,
proteins, uronic acids, lipids and so on (Beech and Sunner 2004 ; Quiroz et al. 2006 ;
Pal and Paul 2008 ; Merroun and Selenska-Pobell 2008 ; Zhang et al. 2008 , 2010 ).
Most of the DOM components, such as allochthonous fulvic and humic acids
of vascular plant origin, autochthonous fulvic acids of algal or phytoplank-
ton origin, proteins, aromatic amino acids (tryptophan, tyrosine and phenylala-
nine), extracellular polymeric substances (EPS) and so on, show fluorescence
properties and can simultaneously exhibit complexing properties (Saar and
Weber 1980 ; Ryan and Weber 1982a ; Cabaniss 1992 ; daSilva et al. 1996 , 1998a ;
Smith and Kramer 1998 , 1999 ; Mounier et al. 1999 ; Wu and Tanoue 2001a ;
Wu et al. 2004a ; Dudal et al. 2006 ; Manciulea et al. 2009 , 2011 ). DOM com-
ponents are composed of diverse functional groups (including fluorophores or
chromophores) in their molecular structures, which have strong binding capac-
ity with metals in water (Malcolm 1985 ; Mostofa et al. 2009a ; Saar and Weber
1980 ; Senesi 1990 ; Morel and Hering 1993 ; Morra et al. 1997 ; Xia et al. 1998 ;
Leenheer et al. 1998 ; Bloom et al. 2001 ; Steelink 2002 ; Leenheer and Croue
2003 ; Stenson et al. 2003 ; Schwartz et al. 2004 ; Klinck et al. 2005 ). Therefore, it
has been possible to assess the complexing properties of fluorescent DOM from