Dissolved Organic Matter in Natural Waters - Photobiogeochemistry of Organic Matter - page 30

et al. 1998 ; Fry and Sherr 1984 ; Currin et al. 1995 ; Sullivan and Moncreiff 1990 ).
Depending on the origin of DOM from these algae and plants, there can be found
variable carbon isotope ratios for DOM in natural waters.
The autochthonous DOM of algal or phytoplankton origin is usually very suit-
able for bacterial use, as suggested by the pattern of increased bacterial produc-
tion with increased primary production (Cole et al. 1988 ). Autochthonous DOM is
in fact relatively labile (Søndergaard and Middelboe 1995 ; Kirchman et al. 1991 ).
However, autochthonously derived DOC may become persistent over time (Ogawa
et al. 2001 ; Fry et al. 1996 ; Tranvik and Kokalj 1998 ). Laboratory studies have
shown that natural assemblages of marine bacteria become rapidly able (in <48 h)
to utilize labile compounds (glucose, glutamate) and produce refractory DOM that
can persist for more than a year (Ogawa et al. 2001 ). It has also been shown that
only 10-15 % of the bacterially derived DOM is identified as hydrolysable amino
acids and sugars, which is a characteristic nature of marine DOM (Ogawa et al.
2001 ). Moreover, the higher concentrations of DON observed in total DOM during
the summer period than in winter (Fellman et al. 2009 ; Vazquez et al. 2011 ) are
most likely accounted for by the produced autochthonous DOM in natural waters.
4.2 Molecular Size Distribution of DOM
The molecular size distribution of DOM is significantly variable in natural waters
(Table 1 ). One of the techniques for isolating DOM in natural waters is tangen-
tial flow ultrafiltration (also called cross-flow ultrafiltration). The results show that
the contributions of the various fractions to total DOC are 21-65 % for the frac-
tion <1 kDa, 44-68 % for <5 kDa, 57-65 % for <10-12 kDa. Moreover, they are
41 % for 1-30 kDa, 32-56 % for 1 kDa-0.1 μ m, 67-84 % for 1 kDa-0.45 μ m,
and 0.1-16 % for 0.1-0.45 or 0.1-GF/F μ m in rivers (Table 1 ) (Yoshioka et al.
2007 ; Guéguen et al. 2002 , 2006 ; Martin et al. 1995 ; Mannino and Harvey 2000 ;
de Zarruk et al. 2007 ; Wu and Tanoue 2001 ; Wu et al. 2003 ; Waiser and Robarts
2000 ; Huguet et al. 2010 ; Carlson et al. 1985 ). In lakes, the relative abundances of
various DOM fractions are 42-73 % for <1 kDa, 54-79 % for <5 kDa, 21-43 %
for 5 kDa-0.1 μ m, and 0-2 % for 0.1-0.45 μ m (Table 1 ) (Yoshioka et al. 2007 ;
Guéguen et al. 2002 ; Wu and Tanoue 2001 ; Wu et al. 2003 ; Waiser and Robarts
2000 ). In estuaries or lagoons, the contributions are 26-98 % for <1 kDa, 11-25 %
for 1-3 kDa, 63-75 % for <10 kDa, 25-31 % for 1-30 kDa, 2-45 % for 1 kDa-
0.2 μ m, 22-48 % for 3 kDa-0.2 μ m, 14-20 % for 30 kDa-0.2 μ m, and 1-2 %
for 30 kDa-0.2 μ m (Table 1 ) (Hagedorn et al. 2004 ; Mannino and Harvey 2000 ;
Guéguen et al. 2002 ; Waiser and Robarts 2000 ; Huguet et al. 2010 ). In coastal
and open oceans, the contributions of the relative DOM fractions are 30-85 % for
<1 kDa (30-70 % in coastal waters, 49-85 % in the open ocean), 23-53 % for
the fraction between 1 kDa and 10 kDa, 3-19 % for the fraction between 10 kDa
and 0.1-0.2 μ m, 15-70 % for the fraction between 1 kDa and 0.2 μ m, 85 % for
the fraction between 1.8 kDa and 0.2 μ m (Table 1 ) (Buesseler et al. 1996 ; Druon