Photoinduced and Microbial Degradation of Dissolved Organic Matter in Natural Waters - Photobiogeochemistry of Organic Matter - page 333

populations and thus participate to the food chains for the growth of microbes
in natural waters. Moreover, the LMW organic compounds can be photolytically
mineralized into final end photoproducts such as CO or CO 2 , which can take part
to the global carbon cycle (Miller and Zepp 1995 ; Kieber et al. 2001 ).

5.3 Photoinduced Formation of Aromatic Mono- and Dibasic
Acids

Photoinduced degradation reactions can convert the high molecular weight DOM
into a variety of aromatic mono- and dibasic acids, phenolic compounds, aromatic
aldehydes and ketones in waters (Kramer et al. 1996 ; Wetzel et al. 1995 ; Chen
et al. 1978 ; Corin et al. 1996 ; Leenheer and Croue 2003 ; Peuravuori and Pihlaja
1997 ; Haan et al. 1979 ; Choudhry 1981 ; Langvik et al. 1994 ; Schmitt-Kopplin
et al. 1998 ). The aromatic compounds most commonly identified as photo prod-
ucts are 4-hydroxy- and 4-hydroxy-3-methoxybenzaldehyde, benzoic acid and its
derivatives such as 2-hydroxy-, 3-hydroxy-, 4-hydroxy-, 2,4-dihydroxy-, 3,4-dihy-
droxy-, 3-methoxy- and 4-hydroxy-3-methoxy-benzoic acid, 1,2-, 1,3- and
1,4-benzenedicarboxylic acid, benzene-di, -tri-, tetra-, penta-, and -hexa-carbox-
ylic acids, decanoic acid and its derivatives such as tetra-, hexa- and octa-decanoic
acid, acetophenone and its derivatives, methoxybenzene and its derivatives, meth-
oxytoluenes, methoxystyrene, phenols, methoxylated phenols and hydroxyfuran.
Most of the LMW aromatic acids are formed from humic and fulvic acids during
the first 2 h irradiation of the natural humic waters. Prolonged irradiation may lead
to a decrease of their concentrations due to further mineralization to end products
(Corin et al. 1996 ).

5.4 Photoinduced Formation of Carbon-Gas End
Photoproducts Including DIC

The photo mineralization of DOM leads to the formation of carbon-gas end pho-
toproducts, which include CO, CO 2 , dissolved inorganic carbon (DIC, usually
defined as the sum of an equilibrium mixture of dissolved CO 2 , H 2 CO 3 , HCO 3

−

,
and CO 3 2 − : (Eq. 5.1 ) and carbonyl sulfide (COS) in natural waters (Table 3 )
(Reche et al. 1999 ; Ma and Green 2004 ; Graneli et al. 1996 , 1998 ; Clark et al.
2004 ; Xie et al. 2004 ; Borges et al. 2008 ; Kujawinski et al. 2009 ; Tranvik et al.
2009 ; Omar et al. 2010 ; Ballaré et al. 2011 ; Zepp et al. 2011 ; Mopper et al. 1991 ;
Miller and Zepp 1995 ; Bertilsson and Tranvik 2000 ; Fujiwara et al. 1995 ; Bushaw
et al. 1996 ; Miller and Moran 1997 ; White et al. 2010 ; Cai 2011 ; Johannessen et
al. 2007 ; Valentine and Zepp 1993 ; Molot et al. 2005 ; Francko and Heath 1982 ;
Fang 2004 ; Chen et al. 2001 ; Karl and Tien 1997 ; Jones 1991 ; Jones and Amador
1993 ; Cai and Wang 1998 ; Zepp et al. 1998 ; Cai et al. 1998 , 1999 ; Fichot and