406
K. M. G. Mostofa et al.
which may typically be produced by degradation of dissolved organic nitrogen
(DON) and dissolved organic phosphorus (DOP) in the epilimnion of natural
waters (Mostofa et al. 2011; Zagarese et al. 2001; Kim et al. 2006; Vähätalo
and Järvinen 2007; Li et al. 2008; Zhang et al. 2004). These nutrients are used
by algae and bacteria. (viii) Finally, releases of energy to the water ecosystem
(Wetzel 1992; Hedges et al. 2000; Tranvik 1992).
The decrease of CDOM absorption over the entire spectrum, induced by photoinduced processes is accompanied by the decrease of total fluorescence intensity at peak C-, A-, T- and T UV -regions of various fluorescent substances (Zhang
et al. 2009; Coble 1996; Moran et al. 2000; Mostofa et al. 2007; Mostofa et al.
2010). Photoinduced DOC mineralization (decrease of DOC concentration) is
also observed (Moran et al. 2000; del Vecchio and Blough 2002; Mostofa et al.
2007; Mostofa et al. 2005; Frimmel and Bauer 1987; Vione et al. 2009; de Haan
1993). As a matter of fact, the impacts of photoinduced degradation on CDOM
absorption are similar to those on DOC degradation that have been explained in
details in earlier chapter (see chapter “Photoinduced and Microbial Degradation of
Dissolved Organic Matter in Natural Waters”).
6.4 Protection of Microorganisms from UV Radiation
by CDOM
Natural UV radiation (280–400 nm) is a selective and strong environmental factor that damages the cell structures including proteins, lipids, membranes, pigments and DNA. It affects the productivity of freshwater and marine organisms
(Marchant et al. 1991; Vincent and Roy 1993; Bothwell et al. 1994; Banaszak and
Trench 1995; Leavitt et al. 1997; Poli et al. 2004; Lesser 2006; Valko et al. 2006;
Xiong et al. 1997; Teai et al. 1998). Such impacts are caused by the UV-radiation
induced production of strong reactive oxygen species such as superoxide radicals,
singlet oxygen, hydrogen peroxide and hydroxyl radicals. The main processes
involved are the photo-Fenton reaction and the photolysis of NO 2
− , NO 3
− and
DOM (see chapter “Photoinduced Generation of Hydroxyl Radical in Natural
Waters”). UV attenuation by CDOM is important in minimizing the deleterious
consequences of UV radiation on phytoplankton and other organisms in natural waters (Wetzel 1992; Morris et al. 1995; Schindler et al. 1996; Williamson
et al. 1996; Yan et al. 1996; Smith and Baker 1979). It is shown that postbloom
increases in DOM concentration induced by grazing and decomposition of
phytoplankton biomass cause an increase of DOM absorption and a related
decrease of UV transmission through the water column (Whitehead and Vernet
2000). The partial UV protection by autochthonous DOM has the consequence
that shallow blooming phytoplankton may assist the development of a subsequent bloom in deep waters (Whitehead and Vernet 2000). On the other hand,
any changes in hydrology (e.g., high temperature, drier climate) or geochemistry
(e.g., increased atmospheric deposition of strong acids) due to global warming
K. M. G. Mostofa et al.
which may typically be produced by degradation of dissolved organic nitrogen
(DON) and dissolved organic phosphorus (DOP) in the epilimnion of natural
waters (Mostofa et al. 2011; Zagarese et al. 2001; Kim et al. 2006; Vähätalo
and Järvinen 2007; Li et al. 2008; Zhang et al. 2004). These nutrients are used
by algae and bacteria. (viii) Finally, releases of energy to the water ecosystem
(Wetzel 1992; Hedges et al. 2000; Tranvik 1992).
The decrease of CDOM absorption over the entire spectrum, induced by photoinduced processes is accompanied by the decrease of total fluorescence intensity at peak C-, A-, T- and T UV -regions of various fluorescent substances (Zhang
et al. 2009; Coble 1996; Moran et al. 2000; Mostofa et al. 2007; Mostofa et al.
2010). Photoinduced DOC mineralization (decrease of DOC concentration) is
also observed (Moran et al. 2000; del Vecchio and Blough 2002; Mostofa et al.
2007; Mostofa et al. 2005; Frimmel and Bauer 1987; Vione et al. 2009; de Haan
1993). As a matter of fact, the impacts of photoinduced degradation on CDOM
absorption are similar to those on DOC degradation that have been explained in
details in earlier chapter (see chapter “Photoinduced and Microbial Degradation of
Dissolved Organic Matter in Natural Waters”).
6.4 Protection of Microorganisms from UV Radiation
by CDOM
Natural UV radiation (280–400 nm) is a selective and strong environmental factor that damages the cell structures including proteins, lipids, membranes, pigments and DNA. It affects the productivity of freshwater and marine organisms
(Marchant et al. 1991; Vincent and Roy 1993; Bothwell et al. 1994; Banaszak and
Trench 1995; Leavitt et al. 1997; Poli et al. 2004; Lesser 2006; Valko et al. 2006;
Xiong et al. 1997; Teai et al. 1998). Such impacts are caused by the UV-radiation
induced production of strong reactive oxygen species such as superoxide radicals,
singlet oxygen, hydrogen peroxide and hydroxyl radicals. The main processes
involved are the photo-Fenton reaction and the photolysis of NO 2
− , NO 3
− and
DOM (see chapter “Photoinduced Generation of Hydroxyl Radical in Natural
Waters”). UV attenuation by CDOM is important in minimizing the deleterious
consequences of UV radiation on phytoplankton and other organisms in natural waters (Wetzel 1992; Morris et al. 1995; Schindler et al. 1996; Williamson
et al. 1996; Yan et al. 1996; Smith and Baker 1979). It is shown that postbloom
increases in DOM concentration induced by grazing and decomposition of
phytoplankton biomass cause an increase of DOM absorption and a related
decrease of UV transmission through the water column (Whitehead and Vernet
2000). The partial UV protection by autochthonous DOM has the consequence
that shallow blooming phytoplankton may assist the development of a subsequent bloom in deep waters (Whitehead and Vernet 2000). On the other hand,
any changes in hydrology (e.g., high temperature, drier climate) or geochemistry
(e.g., increased atmospheric deposition of strong acids) due to global warming