820
K. M. G. Mostofa et al.
carbon (DOC) in natural waters (Brooks et al. 2007; Corin et al. 1996; Amador
et al. 1989; Allard et al. 1994; Moran et al. 2000; Mostofa et al. 2007; Backlund
1992; Kulovaara 1996; Bertilsson and Tranvik 1998; del Vecchio and Blough
2002; Vahatalo and Wetzel 2004; Lou and Xie 2006; Vione et al. 2009).
The most important functional groups or fluorophores in humic substances
(fulvic and humic acids), which are responsible for complex formation with trace
metals, are carboxylic and phenolic-type groups containing hydroquinone-like
moieties and non-quinoid phenols, as well as non-bonding O-, N- and S-atoms
contained in functional groups of DOM, such as thiols (Vidali et al. 2009; Mostofa
et al. 2011; Lu and Allen 2002; Schmeide and Bernhard 2009; Haitzer et al. 2003;
Benedetti et al. 1996; Kinniburgh et al. 1996; Pinheiro et al. 1999; Plaza et al.
2005; Zhang et al. 2004; Smith et al. 2002). High-affinity nitrogenous moieties
that make up 2–4 % of DOM can dominate complexation at low Cu concentrations
(McKnight et al. 1997; Croue et al. 2003), but model and natural organic nitrogen are readily decomposed by photoinduced processes (Langford 1973; Bushaw
et al. 1996). Photoinduced losses of amide carboxyls (15 %) are responsible for
a decrease of complexation between Cu and DOM in river water (Brooks et al.
2007). It is suggested that the photoinduced changes in the strong binding sites
of parent organic compounds are responsible for the decrease of the stability constants of M-DOM complexes in natural waters.
On the other hand, photoirradiation can increase the conditional stability constants between Cu and DOM in river water whilst it decreases the corresponding
values in wetland water (Table 1) (Brooks et al. 2007). Coherently, the ligand concentrations in DOM after photoinduced degradation are decreased by 41–45 %
in rivers whilst they are increased by 65–161 % in wetland waters (Brooks et al.
2007). Cu complexation is increased by approximately 150 % in wetland DOM
after photoinduced degradation, differently from riverine DOM at the same dissolved organic carbon concentrations (Brooks et al. 2007). It has similarly been
found that the conditional stability constants remained the same (log 10 K = 13.5)
after photoinduced degradation of estuarine DOM, but they increased a little in
lake DOM after hours to days of photoirradiation. In contrast, in both cases the
ligand concentrations were decreased photolytically by up to 95 and 24 %, respectively (Table 1) (Sander et al. 2005; Shank et al. 2006). DOM in wetland, lake and
estuarine water is mostly composed of algal-derived material that contains comparatively high proportions of lipids, autochthonous fulvic acids and allochthonous DOM (Parlanti et al. 2000; Mostofa and Sakugawa 2009; Zhang et al. 2009;
Brooks et al. 2007; Mostofa et al. 2009b; McCarthy et al. 1998; McCallister et al.
2006). Photolysis can decrease the binding affinity via scission of the allochthonous fraction of lignin-derived polyphenols in wetland DOM (Opsahl and Benner
1998; Sun et al. 1998). Simultaneously, it is hypothesized that photoirradiation
can double the binding-site density of wetland DOM by polymerizing and photooxidizing the polyunsaturated lipids produced by microbial communities. This
assumption is supported by the experimental observation that photooxidation of
polyunsaturated fatty acids and triacylglycerides can increase their content of
oxygen functional groups and produce aliphatic aldehydes (Kieber et al. 1997).
K. M. G. Mostofa et al.
carbon (DOC) in natural waters (Brooks et al. 2007; Corin et al. 1996; Amador
et al. 1989; Allard et al. 1994; Moran et al. 2000; Mostofa et al. 2007; Backlund
1992; Kulovaara 1996; Bertilsson and Tranvik 1998; del Vecchio and Blough
2002; Vahatalo and Wetzel 2004; Lou and Xie 2006; Vione et al. 2009).
The most important functional groups or fluorophores in humic substances
(fulvic and humic acids), which are responsible for complex formation with trace
metals, are carboxylic and phenolic-type groups containing hydroquinone-like
moieties and non-quinoid phenols, as well as non-bonding O-, N- and S-atoms
contained in functional groups of DOM, such as thiols (Vidali et al. 2009; Mostofa
et al. 2011; Lu and Allen 2002; Schmeide and Bernhard 2009; Haitzer et al. 2003;
Benedetti et al. 1996; Kinniburgh et al. 1996; Pinheiro et al. 1999; Plaza et al.
2005; Zhang et al. 2004; Smith et al. 2002). High-affinity nitrogenous moieties
that make up 2–4 % of DOM can dominate complexation at low Cu concentrations
(McKnight et al. 1997; Croue et al. 2003), but model and natural organic nitrogen are readily decomposed by photoinduced processes (Langford 1973; Bushaw
et al. 1996). Photoinduced losses of amide carboxyls (15 %) are responsible for
a decrease of complexation between Cu and DOM in river water (Brooks et al.
2007). It is suggested that the photoinduced changes in the strong binding sites
of parent organic compounds are responsible for the decrease of the stability constants of M-DOM complexes in natural waters.
On the other hand, photoirradiation can increase the conditional stability constants between Cu and DOM in river water whilst it decreases the corresponding
values in wetland water (Table 1) (Brooks et al. 2007). Coherently, the ligand concentrations in DOM after photoinduced degradation are decreased by 41–45 %
in rivers whilst they are increased by 65–161 % in wetland waters (Brooks et al.
2007). Cu complexation is increased by approximately 150 % in wetland DOM
after photoinduced degradation, differently from riverine DOM at the same dissolved organic carbon concentrations (Brooks et al. 2007). It has similarly been
found that the conditional stability constants remained the same (log 10 K = 13.5)
after photoinduced degradation of estuarine DOM, but they increased a little in
lake DOM after hours to days of photoirradiation. In contrast, in both cases the
ligand concentrations were decreased photolytically by up to 95 and 24 %, respectively (Table 1) (Sander et al. 2005; Shank et al. 2006). DOM in wetland, lake and
estuarine water is mostly composed of algal-derived material that contains comparatively high proportions of lipids, autochthonous fulvic acids and allochthonous DOM (Parlanti et al. 2000; Mostofa and Sakugawa 2009; Zhang et al. 2009;
Brooks et al. 2007; Mostofa et al. 2009b; McCarthy et al. 1998; McCallister et al.
2006). Photolysis can decrease the binding affinity via scission of the allochthonous fraction of lignin-derived polyphenols in wetland DOM (Opsahl and Benner
1998; Sun et al. 1998). Simultaneously, it is hypothesized that photoirradiation
can double the binding-site density of wetland DOM by polymerizing and photooxidizing the polyunsaturated lipids produced by microbial communities. This
assumption is supported by the experimental observation that photooxidation of
polyunsaturated fatty acids and triacylglycerides can increase their content of
oxygen functional groups and produce aliphatic aldehydes (Kieber et al. 1997).